JP2018111434A - Heavy duty pneumatic tire - Google Patents

Abstract

To improve the durability of a bead portion. SOLUTION: The carcass 6 includes a main body 6a extending from a tread portion 2 to a bead core 5 of a bead portion 4 through a sidewall portion 3, and a folded portion 6b connected to the main body portion 6a and turned around the bead core 5. It is a pneumatic tire 1 for heavy load. In the tire meridian cross section, at least a part of the bead portion 4 includes a first reinforcement ply 10 made of a steel cord layer extending substantially in a U-shape from the tire radial direction inside of the folded portion 6b toward the tire radial direction outside, At least a part of the second reinforcing ply 11 is provided at least partially comprising a layer of an organic fiber cord extending radially outward of the first reinforcing ply 10 in the tire axial direction. The second reinforcing ply 11 has an end, which is the number of cords per 50 mm of the ply width, of 30 to 50 (lines / 50 mm). [Selection diagram] Fig. 1

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 therefore are particularly susceptible to damage at the bead portion. Conventionally, in order to improve the durability of the bead part, various heavy-duty pneumatic tires in which a reinforcement layer is provided on the bead part have been proposed.

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

Japanese Patent Application Laid-Open No. 11-020421 Japanese Patent Laying-Open No. 2015-123942

  Incidentally, 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 has as its main object to provide a heavy duty pneumatic tire capable of improving the durability of the bead portion.

  The present invention provides a carcass cord including a main body portion that extends from a tread portion through a sidewall portion to a bead core of a bead portion, and a folded portion that is continuous with the main body portion and that turns around the bead core from the inner side to the outer side in the tire axial direction. A heavy-duty pneumatic tire having a carcass composed of layers, and in the tire meridian section, at least a part of the bead portion is substantially U-shaped from the inner side in the tire radial direction to the outer side 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 at least partially in the tire radial direction outside the first reinforcing ply in the tire axial direction. The second reinforcing ply has an end which is the number of cords driven per 50 mm ply width of 30 to 50 ( / 50mm) to have been.

  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, an end of the second reinforcing ply may be set larger than an end of the first reinforcing ply.

  In another aspect of the present invention, the second reinforcement ply includes an inner second reinforcement ply adjacent to the first reinforcement ply and an outer second reinforcement ply disposed on the outer side in the tire axial direction of the inner second reinforcement ply. 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, and the outer second reinforcing ply The organic fiber cord may be inclined with respect to the carcass cord in an opposite direction to the organic fiber cord of the inner second reinforcing ply at an angle (α2) of 40 to 80 degrees.

  In another aspect of the present invention, an intersection 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 in the tire radial direction of the inner second reinforcing ply may be located on the inner side in the tire radial direction of the outer end in the tire radial direction of the outer second reinforcing ply.

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

  In another aspect of the present invention, a 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.

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

  Moreover, since the second reinforcing ply has an end which is the number of cords driven per 50 mm of the ply width adjusted to 30-50 (lines / 50 mm), 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.

1 is a cross-sectional view of a heavy duty pneumatic tire according to an embodiment of the present invention. It is a side view of the bead part of FIG. It is a principal part enlarged view of the bead part of FIG. FIG. 3 is an enlarged view of a main part of FIG. 2.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a tire meridian cross-sectional view including a rotating shaft in a normal state of a heavy-duty pneumatic tire (hereinafter sometimes simply referred to as “tire”) 1 of the present embodiment.

  The “normal state” is a no-load state in which the tire is assembled on the normal rim R and filled with the normal internal pressure. Hereinafter, unless otherwise specified, the dimensions and the like of each part of the tire are values measured in this normal state.

  The “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 JATMA, “Design Rim” for TRA, For ETRTO, "Measuring Rim".

  “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. The maximum value described in “VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” for ETRTO.

  As shown in FIG. 1, the tire 1 of the present embodiment has a toroidal carcass 6 that extends 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 part 6 a reaches the bead core 5 of the bead part 4 through the sidewall part 3 from the tread part 2. The folded portion 6b is connected to the main body portion 6a, is folded around the bead core 5 from the inner side in the tire axial direction to the outer side, and has an outer end 9 on the outer side in the tire radial direction. The height H1 with respect to the bead base line BL of the main body 6a of the carcass ply 6A is the maximum near the tire equator C.

  FIG. 2 shows a side view of the bead portion 4 where the main rubber portion has been peeled away so that the internal structure can be understood. As shown in FIG. 2, in the carcass ply 6A, the carcass cord c1 is preferably inclined at an angle of 0 to 20 degrees with respect to the tire radial direction (radial direction). Are arranged in degrees. The “essential” means that the tire 1 is a rubber vulcanized molded product and that some errors occur in view of the fact that the steel cord is not a perfect straight line.

  Further, the carcass cord c1 is made of a steel cord in order to ensure tire strength. Further, in order to obtain the basic strength of the tire, in the carcass ply 6A, the arrangement density of the carcass cords c1, that is, the end that is the number of cords driven per 50 mm ply width is about 26 to 40 (pieces / 50 mm). Is desirable. The tire 1 having such a carcass ply 6A has a low rolling resistance and can contribute to a low fuel consumption of the vehicle.

  As shown in FIG. 1, a belt layer 7 is disposed outside the carcass 6 in the radial direction and inside the tread portion 2. The belt layer 7 is configured by stacking a plurality of belt plies using a steel cord, for example. The belt layer 7 of the present embodiment is formed by, for example, the first to fourth belt plies 7A to 7D, but is not limited to such an aspect.

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

  In a normal state and a standard load state in which a normal load is applied to the normal state and grounded at a camber angle of 0 degrees, an angle β formed 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 the angle is 0 ° ± 3 °. In the tire 1 having such a bead core 5, rotation of the bead core 5 during traveling is suppressed, and the tensile force of the carcass ply 6A at the bead portion 4 is reduced, and as a result, bead durability is improved.

  Here, the “regular load” is a load determined by each standard for each tire in a standard system including the standard on which the tire is based. “JATMA” is “maximum load capacity”, and “TRA”. The maximum value listed in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”. If ETRTO, “LOAD CAPACITY”.

  In the case of the tubeless type in which the tire 1 is mounted on the regular rim R (15-degree tapered rim), the tire 1 as described above can be manufactured by using a bead core having a specific shape, for example. As such a bead core, for example, in a state before being incorporated in a tire, the inner side surface 5b is inclined in a direction in which the inner diameter increases toward the outer side in the tire axial direction, and about 20 degrees with respect to the tire axial direction. Have an angle of The 15-degree taper rim is a rim in which the rim seat surface R1 is inclined at an angle of approximately 15 degrees outward in the tire radial direction from the inner side in the tire axial direction toward the outer side.

  The bead core 5 includes, for example, a core body 5A configured with a bead wire. For example, a wrapping layer 5B that covers the core body 5A is desirably 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 binds and fixes bead wires.

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

  The inner apex 8A has, for example, a substantially triangular cross-sectional shape extending from the bead core 5 to the outer side in the tire radial direction between the main body portion 6a and the folded portion 6b of the carcass ply 6A. The outer end 13 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 of the carcass ply 6A. For example, the outer end 13 of the inner apex 8A is preferably located on the outer side in the tire radial direction with respect to the outer end 9 of the folded portion 6b. 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 conditions of a temperature of 70 ° C., a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of 2%. is there.

  The outer apex 8B is connected to the inner apex 8A via, for example, a boundary surface 14 extending radially inward from the outer end 13 of the inner apex 8A toward the folded 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 3 to 5 MPa, for example.

  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. And damage such as separation can be effectively prevented.

  The first reinforcing ply 10 is formed of at least one sheet, in the present embodiment, one sheet. The 1st reinforcement ply 10 can raise the bending rigidity of the bead part 4, and can suppress effectively the big bending deformation to the tire axial direction outer side of the bead part 4 by using the bead core 5 as a fulcrum by extension. 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 inner side in the tire radial direction of the folded portion 6b toward the outer side in the tire radial direction. 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 enhancing the ride 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 aspect.

  The outer end 15 in the tire axial direction of the first reinforcing ply 10 is positioned, for example, on the inner side in the tire radial direction by the distance L1 from the outer end 9 of the folded portion 6b. As a result, the concentration of strain near the outer end 15 of the first reinforcing ply 10 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, for example. 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. When 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 in the tire axial direction of the first reinforcing ply 10 is positioned, for example, on the inner side in the tire radial direction with respect to the outer end 13 of the inner apex 8A. As a further desirable aspect, the inner end 16 of the first reinforcing ply 10 is located on the inner side in the tire radial direction than the outer end 15 of the first reinforcing ply 10. In such an aspect, the length measured along the shape of the first reinforcement ply 10 can be made relatively small, and both the weight reduction of the tire and the reinforcement effect of the bead portion 4 can be achieved.

  As shown in FIG. 2, in the first reinforcing ply 10, preferably, a plurality of steel cords c2 are arranged to be inclined with respect to the carcass cord c1. At the time of bending deformation of the bead portion 4 that occurs during tire traveling, the first reinforcing ply 10 is elastically deformed so that the angle γ of the steel cord c2 is increased, 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 inclined 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 cords c2 of the first reinforcing ply 10, that is, the end that is the number of cords driven per 50 mm ply width is 20 to 40 (lines / 50 mm). Particularly preferably, the end of the first reinforcing ply 10 is desirably smaller than the end of the carcass ply 6A. Note that the ply width when 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 first reinforcing ply 10 in the tire axial direction. The second reinforcement ply 11 of the present embodiment includes, for example, an inner second reinforcement ply 11A adjacent to the first reinforcement ply 10 and an outer second reinforcement ply 11B disposed on the outer side in the tire axial direction of the inner second reinforcement ply 11A. And two. The inner second reinforcing ply 11A and the outer second reinforcing ply 11B overlap each other. In another aspect of the present invention, the second reinforcing ply 11 may be composed of a single sheet.

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

  As a result of various experiments conducted 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 increased. It has been found to improve. That is, when the end is less than 30 (pieces / 50 mm), the restraining force of the bead portion 4 by the second reinforcing ply 11 is remarkably reduced, so that the distortion of the bead portion 4 during tire running can be sufficiently dispersed or reduced. It is difficult. On the other hand, when the end exceeds 50 (lines / 50 mm), the restraining force of the bead portion by the second reinforcing ply 11 is increased. However, when the end of the second reinforcing ply 11 is increased, the outer end of the second reinforcing ply 11 in the tire radial direction (that is, in this embodiment, the inner second reinforcing ply 11A and the outer 2) The strain tends to concentrate on the outer ends 17 and 19) of the reinforcing ply 11B, and the outer end 17 or 19 tends to be a starting point of new damage. In a particularly preferred embodiment, the end is 40-50 (lines / 50 mm).

  The organic fiber cords c3 and c4 of the second reinforcing ply 11 are not particularly limited. For example, a nylon fiber cord, a polyester fiber cord, an aromatic polyamide fiber cord, or a high-tensile vinylon fiber cord is preferable. Used. Such an organic fiber cord ply is more flexible than a steel cord ply and has excellent adhesion to a rubber member.

  In the present embodiment, nylon fiber cords are suitably used as the organic fiber cords c3 and c4 of the second reinforcing ply 11. In particular, when the second reinforcing ply 11 has an end of 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 other hand, if the nylon fiber cord is thicker than 1400/1 (dtex), a new starting point of damage may be generated near the outer end of the second reinforcing ply 11.

  The second reinforcing ply 11 according to 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. The durability of the part 4 is greatly improved. In order to further enhance such operational effects, the end of the second reinforcing ply 11 is desirably larger than the end 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 seat surface R1 is softened due to the influence of heat or the like. Helps to flow over the rim flange and then harden. For this reason, the bead part 4 can reduce the damage resulting from hardening of rubber | gum.

  The second reinforcement ply 11 covers the outer end 15 of the first reinforcement ply 10 from the outer side in the tire axial direction. As in the present embodiment, the two second reinforcing plies 11A and 11B are easier to extend than the first reinforcing ply 10 and have an excellent adhesive strength to rubber. Therefore, the stress at the outer end 15 of the first reinforcing ply 10 is relieved, and the separation there can be suppressed over a long period of time.

  In the present embodiment, the outer end 17 in the tire radial direction of the inner second reinforcing ply 11A is located on the outer side in the tire radial direction by a distance L2 from the outer end 9 of the turned-up portion 6b. Thereby, inner side 2nd reinforcement ply 11A has covered the outer end 9 of the folding | turning part 6b. Therefore, the second reinforcement ply 11 can relieve the shear stress acting on the folded portion 6b of the carcass ply 6A, and can reduce the strain accompanying the shear stress. Moreover, the 2nd reinforcement ply 11 can also suppress the separation which started from the outer end 9 of the folding | turning part 6b effectively.

  The distance L2 is preferably 8 to 18 mm, for example. 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 there is a possibility that damage such as separation starting from the outer end 9 may occur. If the distance L2 is greater than 18 mm, the inner second reinforcing ply 11A can easily move during tire travel, and 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 portion 6b is substantially equal to the distance L1 between the outer end 9 of the folded portion 6b and the outer end 15 of the first reinforcing ply 10. desirable. Thereby, as for the bead part 4, stress is disperse | distributed uniformly and durability improves further.

  The inner end 18 in the tire radial direction of the inner second reinforcing ply 11 </ b> A is located on the inner side in the tire radial direction from 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 on the inner side in the tire axial direction than the inner end 20 of the outer second reinforcing ply 11B described later. Thereby, it is suppressed that distortion concentrates near inner end 18 of inner side 2nd reinforcement 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 in the tire radial direction of the outer second reinforcing ply 11B is positioned, for example, on the outer side in the tire radial direction by a distance L3 from the outer end 17 of the inner second reinforcing ply 11A. Thus, the outer second reinforcement ply 11B covers the outer end 17 of the inner second reinforcement ply 11A that 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 8 to 18 mm, for example. When the distance L3 is smaller than 8 mm, the rigidity difference at the outer end 17 of the inner second reinforcing ply 11A increases, and there is a risk that damage such as separation starting from the outer end 17 of the inner second reinforcing ply 11A may occur. is there. When the distance L3 is larger than 18 mm, the outer second reinforcing ply 11B can easily move during tire running, and there is a risk of damage such as separation starting from the outer end 19 of the outer second reinforcing ply 11B.

  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 portion 6b. It is desirable that they are approximately equal. In such a bead portion 4, stress is uniformly dispersed, and durability is further improved.

  The height H2 in the tire radial direction from the bead base line 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 base line 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 and curing on the rim flange of the regular rim R is small. There is a risk. 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 the starting point. Damage such as separation may occur.

  The inner end 20 in the tire radial direction of the outer second reinforcing ply 11 </ b> B of the present embodiment is located in the inner region S <b> 1 on the inner side in the tire radial direction of the bead core 5. Such outer second reinforcing ply 11B can effectively suppress the tensile force of the carcass ply 6A without moving greatly even when a tensile force is generated in the carcass ply 6A. For this reason, in the tire 1, distortion due to the tensile force of the carcass ply 6 </ b> A is suppressed, and damage such as cracking due to the distortion 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 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 to be 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 as the outer second reinforcing ply 11B and the inner second reinforcing ply 11A. This helps to promote part sharing 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. 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 inclinedly arranged 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 preferable aspect, 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 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. Such inner second reinforcing ply 11A and outer second reinforcing ply 11B more effectively disperse the strain at the time of bending deformation of the bead portion 4 to improve the durability of the bead portion.

  In a particularly preferred mode, as shown in an enlarged view 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 remarkably reduced with respect to the carcass ply 6A, and as a result, distortion tends to concentrate on the outer end 9 of the folded portion 6b of the carcass ply 6A. , It becomes easy to cause damage such as ply turn up loose.

  The inner second reinforcing ply 11A and the outer second reinforcing ply 11B described above can be easily performed by, for example, reversing and using the same ply at the time of manufacture. As a result, the inner second reinforcing ply 11A and the outer second reinforcing ply 11B can share components, and the manufacturing cost of the tire 1 can be reduced.

  The chafer rubber 12 is positioned on the outer side in the tire axial direction of the second reinforcing ply 11 and is in contact with the rim seat surface R1 of the regular rim R on the inner side in the tire radial direction of the bead core 5. The outer end 21 in the tire radial direction of the chafer rubber 12 is located, for example, on the outer side in the tire radial direction with respect to the outer end 19 of the outer second reinforcing ply 11B.

  The minimum thickness t1 of the chafer rubber 12 at the outer position in the tire axial direction of the bead core 5 is preferably 2.5 to 6.0 mm. If the minimum thickness t1 is less than 2.5 mm, the chafer rubber 12 may be cured 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 and the tire surface may be distorted.

  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, and the tire surface may be distorted. If the complex elastic modulus E * 3 is greater than 14 MPa, the chafer rubber 12 may be cured and damage such as cracking may occur.

  As mentioned above, although the heavy duty pneumatic tire of one embodiment of the present invention was explained in detail, the present invention is not limited to the above-mentioned specific embodiment, and can be carried out by being changed to various aspects. Needless to say.

Heavy duty pneumatic tires 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 cord specifications: Steel cord Carcass cord angle: 0 degrees (relative to tire radial direction)
End of carcass cord: 20 (book / 50mm)
<First reinforcement ply>
Number of plies: 1
Specification of first reinforcing ply: Steel cord Angle of steel cord of first reinforcing ply: 65 degrees (with respect to carcass cord)
End of steel cord for first reinforcement ply: 28 (pieces / 50mm)
Distance L1: 13mm
<Second reinforcement ply>
Number of plies: 2
Specification of second reinforcement ply: Nylon fiber cord 1400/1 (dtex)
Distance L2: 13mm
Distance L3: 13mm
H2 / H1 = 30%

<Bead durability test>
The test tire is mounted on a rim of 22.5 × 9.00, and is run on a drum testing machine at a speed of 20 km / h under conditions of an internal pressure of 850 kPa and a standard load of 200%, and the bead portion is damaged. Travel time to was measured. A result is displayed by the index | exponent which sets the value of the comparative example 1 to 100, and shows that the durability of a bead part is excellent, so that a numerical value is large.
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 portion 3 Side wall portion 4 Bead portion 5 Bead core 6 Carcass 6A Carcass ply 6a Main body portion 6b Folded portion 10 First reinforcing ply 11 Second reinforcing ply 11A Inner second reinforcing ply 11B Outer second reinforcing ply c1 Carcass cord c2 Steel Cord c3, c4 Organic fiber cord

Claims (10)

A carcass comprising a carcass cord layer including a main body part extending from a tread part through a sidewall part to a bead core of the bead part, and a turn-back part connected to the main body part and turning back around the bead core from the inner side to the outer side in the tire axial direction. A heavy duty pneumatic tire having
In the tire meridian cross section, the bead portion includes:
A first reinforcing ply consisting of a layer of steel cord extending at least partially from the inside in the tire radial direction of the folded portion toward the outside in the tire radial direction in a substantially U shape;
A second reinforcement ply consisting of at least one organic fiber cord layer extending in the tire radial direction on the outer side in the tire axial direction of the first reinforcement ply,
The second reinforcing ply is a heavy-duty pneumatic tire having an end, which is the number of cords driven per ply width of 50 mm, of 30 to 50 (lines / 50 mm).   The heavy duty pneumatic tire according to claim 1, wherein the organic fiber cord of the second reinforcing ply is a nylon fiber cord of 940/1 to 1400/1 (dtex).   The heavy duty pneumatic tire according to claim 1 or 2, wherein an end of the second reinforcing ply is larger than an end of the first reinforcing ply.   The second reinforcing ply includes an inner second reinforcing ply adjacent to the first reinforcing ply and an outer second reinforcing ply disposed on the outer side in the tire axial direction of the inner second reinforcing ply. The heavy duty pneumatic tire according to any one of the above. 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,
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 40 to 80 degrees with respect to the carcass cord. The heavy duty pneumatic tire according to claim 4.   The heavy-duty pneumatic tire according to claim 5, wherein an intersection angle (θ) between the organic fiber cord of the inner second reinforcing ply and the organic fiber cord of the outer second reinforcing ply is 80 to 160 degrees.   7. The heavy load according to claim 4, wherein an outer end of the inner second reinforcing ply in the tire radial direction is located on an inner side in the tire radial direction of an outer end of the outer second reinforcing ply in the tire radial direction. Pneumatic tire.   The heavy-duty pneumatic tire according to claim 7, wherein a distance in a 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.   The heavy-duty pneumatic tire according to any one of claims 4 to 8, wherein an outer end in the tire radial direction of the inner second reinforcing ply is positioned on an outer side in the tire radial direction with respect to an outer end in the tire radial direction of the folded portion. .   The heavy-duty pneumatic tire according to claim 9, wherein a distance in a tire radial direction between the outer end of the inner second reinforcing ply and the outer end of the folded portion is 8 to 18 mm.

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