JP7480554B2 - Heavy duty pneumatic tires - Google Patents

Description

The present invention relates to a heavy-duty pneumatic tire.

In recent years, there has been a demand for improved durability in the bead portion of heavy-duty pneumatic tires. The following Patent Document 1 proposes a heavy-duty pneumatic tire in which a reinforcing layer is provided on the axially outer side of the folded-up portion of the carcass ply in order to improve the durability of the bead portion.

JP 2018-111433 A

In the above-mentioned heavy-duty pneumatic tire, the reinforcing layer was able to suppress damage at the radially outer end of the turned-up portion. However, in a configuration in which a reinforcing layer is provided on the outside of the carcass ply, as in Patent Document 1, it was found that strain during running is transferred between the turned-up portion of the carcass ply and the bead apex rubber, and this portion is likely to become the starting point of new damage.

The present invention was devised in light of the above-mentioned circumstances, and its main objective is to provide a heavy-duty pneumatic tire that can exhibit excellent bead durability.

The present invention is a heavy-duty pneumatic tire comprising a tread portion, a pair of sidewall portions, a pair of bead portions each having a bead core embedded therein, and a carcass that spans the pair of bead portions in a toroidal shape, the carcass including a carcass ply having a main body portion extending between the bead portions and a turn-up portion connected to the main body portion and turned around the bead core from the inside to the outside in the tire axial direction, each of the bead portions including a bead apex rubber that extends from the bead core radially outward between the main body portion and the turn-up portion, and a reinforcing cord layer arranged on the outside of the turn-up portion in the tire axial direction, and the bead apex The bead apex rubber includes a first rubber portion extending from the bead core, and a second rubber portion having a rubber hardness smaller than that of the first rubber portion and disposed axially outboard of the first rubber portion, the reinforcing cord layer is disposed so that the radially outer end of the turn-up portion is located between the radially outer end and the radially inner end of the reinforcing cord layer, and in the tire cross section, the first rubber portion and the second rubber portion of the bead apex rubber are disposed so as to intersect with a carcass normal line that passes through the outer end of the turn-up portion and is perpendicular to the main body portion, and on the carcass normal line, the thickness t2 of the second rubber portion is equal to or greater than the thickness t1 of the first rubber portion.

In the heavy-duty pneumatic tire of the present invention, it is desirable that the thickness t2 of the second rubber portion is 1.0 to 3.0 times the thickness t1 of the first rubber portion.

In the heavy-duty pneumatic tire of the present invention, it is desirable that the thickness t1 of the first rubber portion be 3.0 to 7.0 mm.

In the heavy-duty pneumatic tire of the present invention, it is desirable that the bead apex rubber includes an interface where the first rubber portion and the second rubber portion are joined, and that the interface is curved so as to have at least one inflection point in the tire cross section.

In the heavy-duty pneumatic tire of the present invention, it is preferable that the interface includes a first curved portion that is convex on one side in the tire axial direction and a second curved portion that is convex on the other side in the tire axial direction.

In the heavy-duty pneumatic tire of the present invention, it is preferable that the reinforcing cord layer includes an organic fiber cord ply.

In the heavy-duty pneumatic tire of the present invention, the reinforcing cord layer includes an inner layer disposed closest to the folded portion, and the inner end of the inner layer in the tire radial direction is preferably located radially inward of the outer surface of the bead core on the outer side in the tire radial direction.

In the heavy-duty pneumatic tire of the present invention, the reinforcing cord layer includes an inner layer disposed closest to the folded portion and an outer layer disposed axially outward of the inner layer, and it is preferable that the radially inner end of the outer layer is located radially inward of the radially inner end of the inner layer.

In the heavy-duty pneumatic tire of the present invention, the reinforcing cord layer includes an inner layer disposed closest to the folded portion and an outer layer disposed axially outward of the inner layer, and it is preferable that the radially outer end of the outer layer is located radially outward of the radially outer end of the inner layer.

In the heavy-duty pneumatic tire of the present invention, it is preferable that a recess is provided on the bead heel surface of the bead portion.

By adopting the above-mentioned configuration, the heavy-duty pneumatic tire of the present invention is able to exhibit excellent durability of the bead portion.

1 is a cross-sectional view of a heavy-duty pneumatic tire according to one embodiment of the present invention. FIG. 2 is an enlarged view of a bead portion of FIG. 1 . FIG. 3 is an enlarged cross-sectional view of the bead apex rubber of FIG. 2 . FIG. 4 is an enlarged cross-sectional view of a bead apex rubber according to another embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view of a bead apex rubber according to another embodiment of the present invention.

An embodiment of the present invention will be described below with reference to the drawings. It should be noted that publicly known techniques can be applied to technical matters not described in this specification. FIG. 1 shows a tire meridian cross section including the tire rotation axis of a heavy-duty pneumatic tire (hereinafter sometimes simply referred to as "tire") 1 of this embodiment in a normal state. Note that FIG. 1 shows a tire cross section on one side in the tire axial direction from the tire equator C when the tire 1 extending in an annular shape is cut by a virtual plane perpendicular to the tire circumferential direction. The tire 1 of this embodiment is used, for example, for large trucks, buses, etc.

In the case of tires for which various standards are established, the normal state refers to a state in which the tire is mounted on a normal rim, inflated to the normal internal pressure, and no load is applied. In the case of tires for which various standards are not established, the normal state refers to a standard use state according to the intended use of the tire, and a state in which no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are values measured in the normal state. In the case of components inside the tire, the dimensions refer to the dimensions in a state in which the shape of the tire cross section is substantially the same as the shape in the normal state. Note that each configuration described in this specification is assumed to allow for normal errors contained in rubber molded products.

A "genuine rim" is a rim that is specified for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "design rim," and in the case of ETRTO, it is called a "measuring rim."

"Normal internal pressure" is the air pressure set for each tire by each standard in the standard system on which the tire is based. For JATMA, it is the "maximum air pressure." For TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." For ETRTO, it is the "INFLATION PRESSURE."

As shown in FIG. 1, the tire 1 of this embodiment includes a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4 each having a bead core 5 embedded therein, and a carcass 6 that spans the pair of bead portions 4 in a toroidal shape. Note that half of the tread portion 2, one of the pair of sidewall portions 3, and one of the pair of bead portions 4 are omitted in FIG. 1.

The carcass 6 includes, for example, one carcass ply 6A. The carcass 6 may be composed of, for example, multiple carcass plies 6A. The carcass ply 6A is composed of, for example, steel carcass cords arranged at an angle of 70 to 90 degrees relative to the tire circumferential direction.

The carcass ply 6A has a main body portion 6a and a folded-up portion 6b. The main body portion 6a extends between a pair of bead portions 4. The folded-up portion 6b is connected to the main body portion 6a and is folded up around the bead core 5 from the inside to the outside in the tire axial direction.

In a preferred embodiment, a belt layer 7 is disposed radially outward of the carcass 6 and inside the tread portion 2. The belt layer 7 is formed, for example, from multiple belt plies using steel belt cords. The belt layer 7 in this embodiment has a four-ply structure formed, for example, from first to fourth belt plies.

Figure 2 shows an enlarged view of a bead portion 4. As shown in Figure 2, each bead portion 4 includes a bead apex rubber 8 and a reinforcing cord layer 9 arranged on the axially outer side of the folded portion 6b. The bead apex rubber 8 extends radially outward from the bead core 5 between the main body portion 6a and the folded portion 6b. The reinforcing cord layer 9 is arranged on the axially outer side of the folded portion 6b.

The bead apex rubber 8 is, for example, triangular in shape with a width that decreases toward the outside in the tire radial direction. The bead apex rubber 8 also includes a first rubber portion 11 and a second rubber portion 12. The first rubber portion 11 extends from the bead core 5. The second rubber portion 12 has a rubber hardness smaller than that of the first rubber portion 11, and is disposed axially outward of the first rubber portion 11.

In this specification, rubber hardness refers to durometer A hardness measured in an environment of 23°C using a durometer type A based on JIS-K6253. The rubber hardness of the first rubber portion 11 is, for example, 80 to 95°. The rubber hardness of the second rubber portion 12 is, for example, 50 to 70°. However, the present invention is not limited to these embodiments.

The reinforcing cord layer 9 is arranged so that the radially outer end 13 of the folded portion 6b is located between the radially outer and inner ends of the reinforcing cord layer 9.

Figure 3 shows an enlarged cross-sectional view of the bead apex rubber 8. As shown in Figure 3, in the tire cross section, the first rubber portion 11 and the second rubber portion 12 of the bead apex rubber 8 are arranged so as to intersect with the carcass normal line 15. The carcass normal line 15 is an imaginary line that passes through the outer end 13 of the folded portion 6b and is perpendicular to the main body portion 6a.

In the present invention, the thickness t2 of the second rubber portion 12 is equal to or greater than the thickness t1 of the first rubber portion 11 on the carcass normal line 15. By adopting the above-mentioned configuration, the tire of the present invention is able to exhibit excellent durability of the bead portion 4. The following mechanism is presumed to be the reason for this.

In the present invention, the reinforcing cord layer 9 (shown in FIG. 2) can suppress damage at the radially outer end 13 of the turned-up portion 6b. On the other hand, in a configuration in which the reinforcing cord layer 9 is provided on the outside of the turned-up portion 6b, strain during running is transferred between the turned-up portion 6b of the carcass ply 6A and the bead apex rubber 8, and this portion is likely to become the starting point of new damage. In the present invention, by ensuring the thickness of the second rubber portion 12, which has a relatively small rubber hardness, it is believed that it is possible to absorb strain around the outer end 13 of the turned-up portion 6b and suppress the occurrence of damage starting around the outer end 13. It is believed that this mechanism allows the tire of the present invention to exhibit excellent durability of the bead portion 4.

The following describes the configuration of this embodiment in more detail. Note that the configuration described below shows a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-mentioned effects even if it does not have the configuration described below. Furthermore, even if any one of the configurations described below is applied alone to a tire of the present invention having the above-mentioned characteristics, an improvement in performance corresponding to each configuration can be expected. Furthermore, when several of the configurations described below are applied in combination, a composite improvement in performance corresponding to each configuration can be expected.

As shown in FIG. 2, the tire radial height h2 from the bead baseline BL to the tire radial outer end of the bead apex rubber 8 (hereinafter sometimes referred to as "height h2 of the bead apex rubber 8") is 35% to 45% of the tire total height h1 (shown in FIG. 1). However, the present invention is not limited to this embodiment. The tire total height h1 corresponds to the tire radial distance from the bead baseline BL to the tire radial outer end of the tread portion 2 in the normal state. The bead baseline BL is also the tire axial line that passes through the rim diameter position determined by the standard to which the tire is based.

The height h3 of the folded portion 6b from the bead baseline BL to the outer end 13 of the folded portion 6b is, for example, 30% to 60% of the height h2 of the bead apex rubber 8. This ensures the rigidity of the bead portion 4 while preventing an excessive increase in tire weight.

The first rubber portion 11 in this embodiment has a triangular shape with a width that decreases from the bead core 5 toward the outside in the tire radial direction. The inner surface of the first rubber portion 11 on the inside in the tire radial direction is in contact with, for example, the entire outer surface of the bead core 5 on the outside in the tire radial direction. The entire side surface of the first rubber portion 11 on the tire cavity side is in contact with the main body portion 6a. A part of the side surface of the first rubber portion 11 on the tire outer surface side (the base portion of the first rubber portion 11) is in contact with the folded portion 6b, and is joined to the second rubber portion 12 on the outside in the tire radial direction.

The height h4 from the bead baseline BL to the radially outer end of the first rubber portion 11 (hereinafter sometimes referred to as "height h4 of the first rubber portion 11") is, for example, 55% to 75% of the height h2 of the bead apex rubber 8.

As shown in FIG. 3, the thickness t1 of the first rubber portion 11 on the carcass normal line 15 is preferably 3.0 to 7.0 mm. This effectively prevents the bead apex rubber 8 from collapsing.

The thickness t1 of the first rubber portion 11 on the carcass normal 15 is preferably smaller than, for example, the minimum width t3 (shown in FIG. 1) of the sidewall portion 3. The thickness t1 of the first rubber portion 11 on the carcass normal 15 is 20% to 50% of the minimum width t3. This suppresses local deformation in the sidewall portion 3 and the bead portion 4, improving the durability of these areas.

During running, it is desirable for the bead apex rubber 8 to deform so as to bend overall without localized deformation. To facilitate such deformation, it is desirable for the intermediate thickness t4 of the first rubber portion 11 to be 1.5 to 3.0 times the thickness t1 of the first rubber portion 11 on the carcass normal 15. The intermediate thickness t4 corresponds to the thickness of the first rubber portion 11 on the bead intermediate normal 16. The bead intermediate normal 16 is an imaginary line that extends parallel to the carcass normal 15 and is 20% of the height h4 (shown in FIG. 2) of the first rubber portion 11 inward in the tire radial direction from the carcass normal 15. This optimizes the shape of the first rubber portion 11, suppresses localized deformation of the bead apex rubber 8, and improves the durability of the bead portion 4.

As shown in FIG. 2, in this embodiment, the side surface of the second rubber portion 12 on the tire inner cavity side is in contact with the first rubber portion 11 and the main body portion 6a. Also, a part of the side surface of the second rubber portion 12 on the tire outer surface side is in contact with the folded-back portion 6b. Also, the width of the second rubber portion 12 decreases from its widest portion toward the inside and outside in the tire radial direction.

The tire radial height h5 from the inner end to the outer end of the second rubber portion 12 in the tire radial direction (hereinafter sometimes referred to as "height h5 of the second rubber portion 12") is, for example, 70% to 90% of the height h2 of the bead apex rubber 8.

As shown in FIG. 3, the thickness t2 of the second rubber portion 12 on the carcass normal line 15 is preferably 7.0 to 11.0 mm. This effectively prevents damage between the folded portion 6b and the bead apex rubber 8.

The thickness t2 of the second rubber portion 12 is preferably 1.0 to 3.0 times, and more preferably 1.5 to 2.5 times, the thickness t1 of the first rubber portion 11. This ensures the rigidity of the bead portion 4 and effectively suppresses the damage. Therefore, the durability of the bead portion 4 is further improved.

The tip thickness t5 of the second rubber portion 12 is preferably 100% to 150% of the thickness t2 of the second rubber portion 12 on the carcass normal 15. The tip thickness t5 corresponds to the thickness of the second rubber portion 12 on the bead tip normal 17. The bead tip normal 17 is an imaginary line that passes through the outer end of the reinforcing cord layer 9 (shown in FIG. 2) in the tire radial direction and extends parallel to the carcass normal 15. By specifying the tip thickness t2 as described above, local deformation of the bead apex rubber 8, particularly between the outer end 13 of the folded portion 6b and the outer end of the reinforcing cord layer 9, is suppressed. Therefore, the durability of the bead portion 4 is further improved.

The bead apex rubber 8 includes an interface 20 where the first rubber portion 11 and the second rubber portion 12 are joined. In the tire cross section, the interface 20 is curved. In this embodiment, the interface 20 is curved in a convex direction toward the inside of the tire axial direction. This suppresses separation between the first rubber portion 11 and the second rubber portion 12. However, the shape of the interface is not limited to this embodiment, and other embodiments are described below.

As shown in FIG. 2, the reinforcing cord layer 9 preferably includes an organic fiber cord ply in which a plurality of organic fiber cords are arranged at an angle. As the organic fiber cord, for example, nylon cord, polyester cord, aromatic polyamide cord, or high tensile vinylon cord, etc., are preferably used. Such a reinforcing cord layer 9 has appropriate flexibility and can effectively suppress damage around the outer end 13 of the folded portion 6b.

The reinforcement cord layer 9 includes an inner layer 21 arranged closest to the folded portion 6b and an outer layer 22 arranged axially outward of the inner layer 21. The reinforcement cord layer 9 in this embodiment is composed of two layers, the inner layer 21 and the outer layer 22. However, this is not limited to this embodiment, and the reinforcement cord layer 9 may be composed of only one layer, or three or more layers.

The inner end 21a of the inner layer 21 in the tire radial direction is located radially inward of the outer surface of the bead core 5 in the tire radial direction. In a more preferable embodiment, the inner end 21a of the inner layer 21 overlaps with an area of the bead core 5 extending parallel to the tire axial direction toward the tire cavity surface. This suppresses damage to the bead portion 4 originating from the periphery of the inner end 21a.

The radially outer end 21b of the inner layer 21 is located radially outward of the outer end 13 of the folded portion 6b.

The radially inner end 22a of the outer layer 22 is located radially inward of the radially inner end 21a of the inner layer 21. In a more preferable embodiment, the inner end 22a of the outer layer 22 overlaps with an area of the bead core 5 extending parallel to the radial direction of the tire toward the radially inner side of the tire. This suppresses damage to the bead portion 4 originating from the periphery of the inner end 22a.

It is desirable that the radially outer end 22b of the outer layer 22 be located radially outward of the radially outer end 21b of the inner layer 21. This prevents the inner layer 21 from peeling off, and further improves the durability of the bead portion 4.

The bead portion 4 of this embodiment includes a U-shaped reinforcing layer 25. The U-shaped reinforcing layer 25 is substantially U-shaped and extends along the main portion 6a and the folded-back portion 6b of the carcass ply 6A. The U-shaped reinforcing layer 25 is composed of, for example, a steel ply in which multiple steel cords are arranged. Such a U-shaped reinforcing layer 25 increases the bending rigidity of the bead portion 4, and thus helps to improve the durability of the bead portion 4.

The U-shaped reinforcement layer 25 includes a first outer end 25a in the tire radial direction of the portion extending along the main body portion 6a, and a second outer end 25b in the tire radial direction of the portion extending along the folded portion 6b. The first outer end 25a is located, for example, on the outer side in the tire radial direction than the outer end 13 of the folded portion 6b. The first outer end 25a is also located on the inner side in the tire radial direction than the outer end 22b of the outer layer 22 of the reinforcement cord layer 9. This provides an appropriate degree of reinforcement on the tire inner cavity side and tire outer surface side of the bead apex rubber 8, suppressing local deformation of the bead portion 4.

The second outer end 25b is located, for example, radially outward of the outer surface of the bead core 5. The second outer end 25b is also located radially inward of the outer end 21b of the inner layer 21 and the outer end 22b of the outer layer 22 of the reinforcement cord layer 9. The second outer end 25b is also located radially inward of the outer end 13 of the folded portion 6b. This provides an appropriate level of reinforcement to the bead portion 4.

In this embodiment, it is preferable that the bead heel surface 27 of the bead portion 4 is provided with a recess 28. The recess 28 is located radially inward of the outer end 13 of the turned-up portion 6b. Such a recess 28 serves to distance the turned-up portion 6b from the contact portion between the rim flange and the bead heel surface 27, thereby improving the durability of the bead portion 4.

The bead portion 4 of this embodiment includes an adhesive rubber layer 23 between the outer end 13 of the folded portion 6b and the reinforcing cord layer 9, and an inner cord layer 24 between the outer end 13 of the folded portion 6b and the second rubber portion 12. As a result, the outer end 13 of the folded portion 6b is sandwiched between the adhesive rubber layer 23 and the inner cord layer 24. This further suppresses damage originating from the outer end 13 of the folded portion 6b.

Other embodiments of the present invention are described below. In the figures showing the other embodiments, the elements already described are given the same reference numerals as those described above, and the configurations described above can be applied.

Figures 4 and 5 show enlarged cross-sectional views of the bead apex rubber 8 of another embodiment. In the embodiment shown in Figures 4 and 5, the interface 20 where the first rubber portion 11 and the second rubber portion 12 are joined is curved to have at least one inflection point 30. The inflection point 30 is a point that is a boundary between a first curved portion 31 that is convex on one side in the tire axial direction and a second curved portion 32 that is convex on the other side in the tire axial direction. This further suppresses peeling between the first rubber portion 11 and the second rubber portion 12.

The interface 20 of the bead apex rubber 8 shown in FIG. 4 includes a first curved portion 31 that is convex on the outside in the tire axial direction, and a second curved portion 32 that is convex on the inside in the tire axial direction, radially inward of the first curved portion 31. The bead apex rubber 8 having such an interface 20 ensures a large rubber volume of the second rubber portion 12, and can suppress damage originating from the outer end 13 of the folded portion 6b.

The interface 20 of the bead apex rubber 8 shown in FIG. 5 includes a first curved portion 31 that is convex on the inside in the tire axial direction, and a second curved portion 32 that is convex on the outside in the tire axial direction, inside the tire radial direction. The bead apex rubber 8 having such an interface 20 ensures a large rubber volume of the first rubber portion 11 on the bead core 5 side, improving the rigidity of the bead portion 4.

The heavy-duty pneumatic tire according to one embodiment of the present invention has been described in detail above, but the present invention is not limited to the specific embodiment described above and can be modified and implemented in various ways.

Heavy-duty pneumatic tires of size 11R22.5 having the basic structure of FIG. 1 were prototyped based on the specifications of Table 1. As a comparative example, a heavy-duty pneumatic tire was prototyped in which the thickness t2 of the second rubber portion was smaller than the thickness t1 of the first rubber portion on the carcass normal line. Each test tire had substantially the same configuration except for the above-mentioned points. The durability of the bead portion of each test tire was tested. The common specifications and test method of each test tire are as follows.
Rim: 22.5 x 9.00
Tire pressure: 1000kPa

<Durability of bead part>
The test tire was run on a drum test machine under the following conditions, and the running distance until damage occurred in the bead portion was measured. The results are expressed as an index with the comparative example being 100, and the larger the value, the better the durability of the bead portion.
The test results are shown in Table 1.

The test results confirmed that the tire of the embodiment exhibited excellent durability in the bead area.

2 tread portion 3 sidewall portion 5 bead core 4 bead portion 6 carcass 6A carcass ply 6a main body portion 6b turned-up portion 8 bead apex rubber 9 reinforcing cord layer 11 first rubber portion 12 second rubber portion 15 carcass normal t1 thickness of first rubber on carcass normal t2 thickness of second rubber on carcass normal

Claims (9)

A heavy-duty pneumatic tire,
A tread portion;
A pair of sidewall portions;
A pair of bead portions each having a bead core embedded therein;
a carcass extending in a toroidal shape between the pair of bead portions,
the carcass includes a carcass ply including a main body portion extending between the bead portions and a turn-up portion connected to the main body portion and turned up around the bead core from the inner side to the outer side in the tire axial direction,
Each of the bead portions includes a bead apex rubber extending from the bead core to an outer side in a radial direction of the tire between the main body portion and the folded-back portion;
a reinforcing cord layer having a portion disposed on the outer side of the turned-up portion in the tire axial direction and a portion disposed on the inner side of the bead core in the tire radial direction ,
the bead apex rubber includes a first rubber portion extending from the bead core, and a second rubber portion having a rubber hardness smaller than that of the first rubber portion and disposed axially outward of the first rubber portion,
the reinforcement cord layer is disposed such that an outer end of the turned-up portion in the tire radial direction is located between an outer end and an inner end of the reinforcement cord layer in the tire radial direction,
In a tire cross section, the first rubber portion and the second rubber portion of the bead apex rubber are disposed so as to intersect with a carcass normal line that passes through an outer end of the turned-up portion and is perpendicular to the main body portion,
On the carcass normal line, the thickness t2 of the second rubber portion is equal to or greater than the thickness t1 of the first rubber portion,
the reinforcement cord layer includes an inner layer disposed closest to the turn-up portion in an axially outer region of the turn-up portion, and an outer layer disposed axially outward of the inner layer,
The inner end of the inner layer in the tire radial direction overlaps with a region of the bead core extending parallel to the tire axial direction toward the tire cavity surface.
Heavy duty pneumatic tires. 2. The heavy-duty pneumatic tire according to claim 1 , wherein an inner end in the tire radial direction of the outer layer overlaps with a region of the bead core extending inward in the tire radial direction in parallel to the tire radial direction. The bead portion includes a U-shaped reinforcing layer extending in a substantially U-shape along the main body portion and the folded-back portion,
the U-shaped reinforcing layer includes a first outer end in a radial direction of the tire of a portion extending along the main body portion and a second outer end in a radial direction of the tire of a portion extending along the turned-up portion,
The heavy-duty pneumatic tire according to claim 1 , wherein the first outer end of the U-shaped reinforcing layer is located radially outward of the outer end of the turned-up portion. the bead apex rubber includes an interface at which the first rubber portion and the second rubber portion are joined,
4. The heavy-duty pneumatic tire according to claim 1, wherein the interface is curved so as to have at least one inflection point in a cross section of the tire. The heavy-duty pneumatic tire according to claim 4, wherein the interface includes a first curved portion that is convex on one side in the tire axial direction and a second curved portion that is convex on the other side in the tire axial direction. The heavy-duty pneumatic tire according to any one of claims 1 to 5, wherein the reinforcing cord layer includes an organic fiber cord ply. 7. The heavy-duty pneumatic tire according to claim 1, wherein an inner end of the outer layer in the tire radial direction is located radially inward of an inner end of the inner layer in the tire radial direction. 8. The heavy-duty pneumatic tire according to claim 1, wherein a radially outer end of the outer layer is positioned radially outward of a radially outer end of the inner layer. The heavy duty pneumatic tire according to claim 1 , wherein a recess is provided on a bead heel surface of the bead portion.

Images