WO2015182413A1

WO2015182413A1 - Heavy-load tire

Info

Publication number: WO2015182413A1
Application number: PCT/JP2015/064134
Authority: WO
Inventors: 淳喜寅; 翔吾和田
Original assignee: 株式会社ブリヂストン
Priority date: 2014-05-26
Filing date: 2015-05-18
Publication date: 2015-12-03

Abstract

A heavy-load tire (1) is provided with: a pair of bead portions (10) to be assembled to a rim flange; and a carcass ply (20) straddling the pair of bead portions (10). Each of the pair of bead portions (10) is provided with a bead core (12) having a bottom surface. The bead core (12) is such that, in a cross section taken in a tire radial direction, a length (L1) from the center in the tire width direction of the bottom surface (12B) to an inner-most portion (12IE) positioned at the most inside in the tire width direction is smaller than a length (L2) from the center in the tire width direction of the bottom surface (12B) to an outer-most portion (12OE) positioned at the most outside in the tire width direction, wherein a ply inclined angle (θ) is not more than 50°.

Description

Heavy duty tire

The present invention relates to a heavy duty tire having a pair of bead portions assembled to a rim flange.

Conventionally, a tread having a pair of bead portions assembled to a rim flange, a carcass ply straddling between the pair of bead portions, a side portion continuous to the pair of bead portions on the outer side in the tire radial direction, and a tire tread surface A heavy duty tire having a portion is known. Each of the pair of bead portions has a bead core, and the carcass ply is folded back by the bead core. Generally, the bead core has a symmetrical shape (for example, a hexagonal shape) in the tire radial direction cross section. In the present specification, the “tire radial direction cross section” means a cross section by a plane passing through the center of the tire (rotation center of the tire) and parallel to the tire width direction. That is, the tire radial direction cross section is a cross section along the tire radial direction and the tire width direction.

JP 2003-205714 A

By the way, in heavy-duty tires, it is important to reduce the tire weight. In reducing the tire weight, it is preferable to suppress the gauge thickness of the rubber material adjacent to the bead core in the tire width direction.

On the other hand, as a cause of failure of the carcass ply of the heavy duty tire, the distortion caused by the pulling force acting on the carcass ply (hereinafter referred to as pull-out distortion), the distortion caused by the pushing pressure received by the bead portion from the rim flange ( Hereinafter, the distortion caused by the fall of the bead portion (hereinafter referred to as the collapse distortion), the distortion generated in the tire rubber near the folded end of the carcass ply (hereinafter referred to as the ply end distortion), and the like.

Here, pull-out distortion is caused by the movement of the bead core rotating in the tire radial cross section (hereinafter referred to as rotation of the bead core). Indentation distortion is caused by the movement of the bead core along the tire width direction (hereinafter, translation of the bead core). Further, the ply end distortion is caused by a pulling force acting on the carcass ply.

However, as described above, when the bead core has a symmetrical shape, if the bead core is reduced in weight, the bead core is rotated by the pulling force acting on the carcass ply, and the carcass ply is easily moved away from the bead core. . That is, it is difficult to suppress the rotation and translation of the bead core while reducing the weight of the tire.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a heavy-duty tire that can reduce the weight of the tire and suppress the rotation and translation of the bead core.

A heavy load tire according to the present invention is a heavy load tire including a pair of bead portions assembled to a rim flange and a carcass ply straddling between the pair of bead portions, and the pair of bead portions includes: Each includes a bead core having a bottom surface, and the bead core has a length L1 from the center in the tire width direction of the bottom surface to the innermost portion in the tire width direction in the tire radial direction cross section. The gist of the invention is that it is shorter than the length L2 from the center in the direction to the outermost part located on the outermost side in the tire width direction, and the ply swing angle θ is 50 ° or less.

FIG. 1 is a tire radial direction sectional view for explaining a bead portion of a heavy duty tire according to an embodiment of the present invention. FIG. 2 is a schematic tire radial direction cross-sectional view of a bead portion for explaining a ply swing angle. FIG. 3A is a schematic cross-sectional view in the tire radial direction illustrating the change of the shape of the carcass ply of the bead portion in the analysis calculation example 1, and FIG. 3B is a diagram of the vicinity of the bead core in the analysis calculation example 1. It is a typical tire radial direction sectional view explaining the force applied to a carcass ply. FIG. 4 is a graph showing a calculation result of the analysis calculation example 1. FIG. 5 is a graph showing the calculation result of the analysis calculation example 2. FIG. 6 is a graph showing the calculation result of the analysis calculation example 3. FIG. 7 is a schematic tire radial direction cross-sectional view illustrating a bead portion in Experimental Example 1 as compared with the conventional example. FIG. 8 is a graph showing the experimental results of Experimental Example 1 and the conventional example. FIG. 9 is a graph showing the experimental results of Experimental Example 2 and the conventional example.

Hereinafter, a heavy duty tire according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the following description, the same or similar parts are denoted by the same or similar reference numerals, and the description thereof is omitted as appropriate. The following embodiments are exemplifications for embodying the technical idea of the present invention, and the embodiments of the present invention are described below in terms of the material, shape, structure, arrangement, etc. of the components. It is not limited to. The embodiments of the present invention can be implemented with various modifications without departing from the scope of the invention.

FIG. 1 is a tire radial direction cross-sectional view illustrating a bead portion of a heavy duty tire according to an embodiment of the present invention (hereinafter referred to as the present embodiment). That is, FIG. 1 shows a cross section of the heavy-duty tire 1 by a surface passing along the tire width direction TD and the tire radial direction TR and passing through the tire center (tire rotation center).

The heavy load tire 1 of the present embodiment includes a pair of bead portions 10 assembled to a rim flange, a carcass ply 20 straddling between the pair of bead portions 10, and a rubber layer adjacent to the inside of the carcass ply 20 in the tire width direction. 14, a side portion continuous to the pair of bead portions 10 on the outer side of the tire radial direction TR, and a tread portion having a tire tread surface. In FIG. 1, the side portion and the tread portion are omitted, and only one bead portion of the pair of bead portions is illustrated. The carcass ply 20 has a toroidal shape.

Each of the pair of bead portions 10 includes a bead core 12 having a hexagonal cross section having a bottom surface 12B. The bead core 12 is provided to fix the heavy load tire 1 to a rim flange (not shown). The bead core 12 is configured by a bead wire (hereinafter referred to as a wire). The rubber layer 14 is disposed inside the bead core 12 (carcass ply 20) in the tire width direction TD.

The bottom surface 12B may be parallel to the tire width direction TD, and may have an inclination with respect to the tire width direction TD.

The bead core 12 has an innermost portion 12IE located on the innermost side in the tire width direction TD and an outermost portion 12OE located on the outermost side in the tire width direction TD in the tire radial direction cross section.

In the cross section in the tire radial direction, the bead core 12 has a length L1 from the center 12BC in the tire width direction of the bottom surface 12B to the innermost portion 12IE, and a length L2 from the center 12BC in the tire width direction of the bottom surface 12B to the outermost portion 12OE. Is shorter (asymmetrical). The ply swing angle θ is set to 50 ° or less.

Here, the ply swing angle θ is defined as follows. As shown in FIG. 1 and FIG. 2, in the tire radial direction cross section, parallel to the tire axial direction passing through the upper surface end forming the innermost corner 12 </ b> UE of the upper surface 12 </ b> U substantially parallel to the bottom surface 12 </ b> B of the bead core 12. An intersection point between the straight line SP and the carcass ply body 20M is defined as a P point. Further, an intersection of the straight line SQ parallel to the tire axial direction passing through the folded end (tire radial direction outer side end) 20E of the folded ply 20R constituting the carcass ply 20 and the carcass ply body 20M is defined as Q point. The angle formed between the straight line ST connecting the point P and the point Q and the straight line SP is the ply swing angle θ. 1 and 2, the straight line ST, the straight line SP, and the straight line SQ are indicated by a one-dot chain line.

Further, in the tire radial direction cross section of the bead core 12, the tire width direction length UW is longer than the tire radial direction length VW.

In addition, in FIG. 1, FIG. 3 (a), FIG.3 (b), the structure shown in a prior art example is shown with the dashed-two dotted line. Specifically, FIG. 1 shows a conventional carcass ply 120 and a conventional carcass ply body 120M. Similarly, in FIG. 3A, the carcass ply body 120M of the conventional example and the folded end 120E of the carcass ply 120 of the conventional example are shown by two-dot chain lines.

The heavy load tire 1 of the present embodiment acts on the carcass ply 20 because the tire core cross-sectional shape in the radial direction of the bead core 12 is asymmetrical and the ply swing angle θ is small as described above. A tension | tensile_strength becomes small compared with the past, and the force which acts on the bead core 12 from the carcass ply 20 also becomes small (refer FIG.3 (b)). Therefore, the gauge thickness of the bead part 10 (thickness in the direction orthogonal to the longitudinal direction of the bead part 10) can be reduced, and the weight of the heavy load tire 1 can be reduced.

In the heavy load tire 1 of the present embodiment, the tire width direction length UW is longer than the tire radial direction length VW, and the ply swing angle θ is smaller than that of the conventional example. Therefore, in the heavy load tire 1 of the present embodiment, the bead core 12 becomes difficult to rotate as the ply swing angle θ is decreased.

The reason why the bead core 12 becomes difficult to rotate as the ply swing angle θ decreases is explained as follows.

The bead core 12 is rotated by the pulling force of the carcass ply 20 when viewed in the tire radial cross section, the position of the wire constituting the bead core 12 in the tire radial direction, that is, the distance from the tire center (tire rotation center) of the wire. Means change. Since the variation of the radial position of the wire constituting the bead core 12 is relatively different depending on the wire, the rotational motion of the bead core 12 as a whole is observed when viewed in the tire radial cross section.

Thus, the rotation of the bead core 12 is related to the change in the radial position of the wire constituting the bead core 12.

Note that the “tire center (tire rotation center)” and the “rotation center” of the bead core 12 are different concepts. Further, when the indentation distortion is caused by the indentation pressure received by the bead portion 10 from the rim flange, the translational motion of the bead core 12 exists, so that the rotation axis that is the rotation center of the bead core 12 when viewed in the tire radial cross section. Is not fixed during rotation.

Among the wires constituting the bead core 12, the circumferential direction length of the wire greatly varies as the wire in which the position in the tire radial direction varies greatly due to the pulling force of the carcass ply 20 is removed.

When the external force acting on the wire works against the tension of the wire, the circumferential length of the wire varies, and at the same time, the strain energy of the wire is stored. That is, in order to greatly change the position of the wire in the tire radial direction, the force in the tire radial direction acting on the wire against the tension of the wire must be large. Because of this relationship, in order to rotate the bead core 12 through fluctuations in the circumferential length of the wire, a tire radial force acting on the wire against the wire tension is required. Become.

Note that the direction of the force acting on the bead core 12 changes depending on the ply swing angle θ. When the magnitude of the force acting on the bead core 12 from the carcass ply 20 is compared under the same condition, when the ply swing angle θ is small and close to 0 °, the tire radial force acting on the wire is It turns out that it becomes weak compared with the case where angle (theta) is large (when it is close to 90 degrees) (refer FIG.3 (b)).

Therefore, when the magnitude of the force acting on the bead core 12 from the carcass ply 20 is compared under the same condition, the smaller the ply swing angle θ, the more difficult it is to change the position of the wire in the tire radial direction. It becomes difficult to rotate.

As described above, there is a relationship in which the strain energy of the wire increases as the amount of fluctuation in the circumferential length of the wire increases. Therefore, the total strain energy of all the wires constituting the bead core 12 can be expressed as a function of the rotation amount (rotation angle amount) of the bead core 12. This function is determined based on the arrangement of the wires constituting the bead core 12.

That is, based on the arrangement of the wires constituting the bead core 12, the total increase amount of the strain energy of all the wires with respect to the rotation amount of the bead core 12 can be calculated. Therefore, based on the arrangement of the wires constituting the bead core 12, a rotational stiffness index that represents the difficulty in rotating the bead core 12 can be defined.

The amount of rotation of the bead core 12 can be reduced by optimizing the rotational stiffness index defined based on the arrangement of the wires constituting the bead core 12 and the ply swing angle θ. Here, optimizing the rotational rigidity index means selecting a wire arrangement such that the total increase in strain energy of all wires with respect to the rotation amount of the bead core 12 is large.

</ RTI> According to such a wire arrangement, the amount of rotation of the bead core 12 can be reduced compared to the conventional case. Further, the strain generated in the rubber layer of the folded end 20E of the folded ply 20R can be reduced.

The present inventor, when the wire width is longer than the tire radial length VW and the ply swing angle θ is 50 ° or less, the rotation stiffness index and the ply swing We have found that the angle θ is optimal. That is, the present inventor has found that the bead core 12 is difficult to rotate according to such a wire arrangement and the ply swing angle θ.

Furthermore, as will be described in an analysis calculation example and an experimental example described later, the inventor has a width of the maximum width portion of the bead core 12 (hereinafter also referred to as a core maximum width) of 10 mm or more and 30 mm or less, and It has been discovered that the wire arrangement in which the cross-sectional area of the bead core 12 (hereinafter also referred to as the core cross-sectional area) is 70 mm ² or more and 240 mm ² or less is the arrangement of the wires that optimizes the rotational stiffness index. That is, the present inventor has found that, according to such a wire arrangement, the total increase amount of strain energy of all wires with respect to the rotation amount of the bead core 12 becomes large, so that the bead core 12 becomes difficult to rotate.

In the cross section shown in FIG. 1, it is the direction width along the bottom surface 12B, and the maximum core width is 10 mm or more and 30 mm or less. According to this structure, the base pressure by which the bead part 10 is pressed against a rim flange can be ensured, and the translation of the bead core 12 can be suppressed. Note that the maximum core width according to this embodiment is approximately the same as the maximum core width according to the conventional example.

In the cross section shown in FIG. 1, the cross-sectional area of the bead core 12 (hereinafter also referred to as a core cross-sectional area) is 70 mm ² or more and 240 mm ² or less. According to this configuration, rotation and translation of the bead core 12 can be suppressed. The core cross-sectional area according to this embodiment is approximately the same as the core cross-sectional area according to the conventional example.

Further, in the present embodiment, the outermost portion 12OE is located on the outer side in the tire radial direction than the innermost portion 12IE. Accordingly, since the carcass ply 20 and the rubber layer 14 pass near the bead core 12, the gauge thickness of the bead portion 10 is reduced, and the weight of the heavy load tire 1 can be further reduced.

In the present embodiment, when the bead core 12 is divided into two parts by the normal N passing through the center 12BC of the bottom surface 12B and extending along the direction perpendicular to the bottom surface 12B in the cross section described above. The cross-sectional area of the portion 12K including the outermost portion 12OE is larger than the cross-sectional area of the portion 12J including the innermost portion 12IE. Also by this, since the carcass ply 20 and the rubber layer 14 pass near the bead core 12, the gauge thickness of the bead portion 10 is reduced, and the weight of the heavy load tire 1 can be further reduced.

In the present embodiment, in the tire radial direction cross section, the width in the direction along the bottom surface 12B, and the width of the bottom surface 12B (hereinafter also referred to as the core bottom surface width) is D. In the tire radial direction cross-section, a width in the direction along the bottom surface 12B, the width of the portion which passes through the outermost portion 12 Oe, a X _W, in a direction perpendicular to the bottom surface 12B, outermost portion from the bottom surface 12B height to 12OE is _{X H.} In the above-described cross-section, a width in the direction along the bottom surface 12B, the width of the portion which passes through the innermost portion 12IE is _{Y W,} in the direction perpendicular to the bottom surface 12B, innermost portion from the bottom surface 12B 12IE height to is _{Y H.}

The present inventor has found that it is preferable to satisfy the following relational expressions 1 to 4 in such a case.
[Relational Expression 1] 1 ≦ X _W /D≦2.2,
[Relational expression 2] Y _H / D <X _H /D≦2.5,
[Relational Expression 3] 1 ≦ Y _W /D≦2.2,
[Relational Expression 4] 0 <Y _H /D≦1.4

When the heavy load tire 1 is a truck or bus tire and is a tubeless tire, the rim attached to the heavy load tire 1 is preferably a 15 ° DC rim. The 15 ° DC rim (15 ° deep rim) is a rim defined by the Japanese Industrial Standard number JIS D6402.

(Function and effect)
As described above, in this embodiment, the bead core 12 has a length L1 from the center 12BC in the tire width direction of the bottom surface 12B to the innermost portion 12IE in the tire radial direction cross section, and the center in the tire width direction of the bottom surface 12B. It is shorter than the length L2 from 12BC to the outermost part 12OE (left-right asymmetric type). Accordingly, the gauge thickness of the bead portion 10 is reduced, and the heavy duty tire 1 can be made lighter.

In addition, the swing angle θ is 50 ° or less, and by determining the direction of the tension of the carcass ply 20 in this way, the amount of rotation of the bead core 12 is suppressed, and distortion generated in the rubber layer of the folded end 20E of the folded ply 20R is suppressed. Thus, the rotation of the bead core 12 can be effectively suppressed.

In addition, in the tire radial direction cross section of the bead core 12, the tire width direction length UW is longer than the tire radial direction length VW. Therefore, when the bead core 12 is rotated by the pulling force acting on the carcass ply 20, the displacement of the wire constituting the bead core 12 increases as the wire is farther from the rotation center of the bead core 12 (that is, the circumferential direction of the bead core 12). Distortion increases). As a result, the amount of rotation of the bead core 12 can be significantly reduced as compared with the prior art.

Therefore, in the present embodiment, it is possible to reduce the weight of the tire and to make the heavy load tire 1 capable of effectively suppressing the rotation of the bead core 12. In addition, distortion generated in the rubber layer of the folded end 20E of the folded ply 20R can be reduced.

The width of the widest part of the bead core 12 (core maximum width) is at 10mm or more and 30mm or less, the cross-sectional area of the bead core 12 (core area) is preferably 70 mm ² or more and 240 mm ² or less. By setting it as such a structure, rotation and translation of the bead core 12 can be suppressed effectively, reducing a tire weight.

<Analysis calculation example 1>
As shown in FIGS. 3 (a) and 3 (b), the present inventor compared the case where the pulling force F2 is applied to the carcass ply 120 (strictly, the carcass ply body 120M) in the conventional example, as compared with the conventional example. In the embodiment in which the ply swing angle θ is reduced, the force acting on the carcass plies 20 and 120 was examined when the pulling force F1 was applied to the carcass ply 20 (strictly, the carcass ply body 20M).

The component force F1u in the tire radial direction of the pulling force F1 (see FIG. 3B) is smaller than the component force F2u in the tire radial direction of the pulling force F2 in the conventional example (see FIG. 3B). Focused on becoming.

Therefore, the present inventor performed analysis calculation by FEM on the tire of 275 / 80R22.5 size as the heavy load tire 1 and calculated the relationship between the ply swing angle θ at the normal internal pressure and the ply end separation index. . As the ply end separation index, the value of the shear strain of the tire rubber near the folded end 20E was obtained. In this analysis calculation, calculation was performed for four examples and one conventional example. The calculation results are shown in FIG. In all of the examples in which the ply swing angle θ was 50 ° or less, the ply end separation index was better than in the conventional example in which the ply swing angle θ was 60 °.

<Analysis calculation example 2>
The inventor obtained the bead core rotation amount (hereinafter referred to as “core rotation amount”) by the above-described pulling force when the tire internal pressure was set to the normal internal pressure in the example and the conventional example, by analytical calculation using FEM. The calculation results are shown in FIG.

The core rotation amount was 9.5 ° in the conventional example, and 5.0 ° in the example. Therefore, compared to the conventional example, the result was that the core rotation amount was significantly reduced in the example.

<Analysis calculation example 3>
The inventor of the present invention, for the example and the conventional example, at the normal internal pressure and the normal load, the position in the tire circumferential direction and the folded end of the carcass ply (that is, the folded end 20E of the carcass ply 20 in the example, the conventional example) A relationship with the shear strain of the tire rubber near the folded end 120E of the carcass ply 120 (see FIG. 3A) was calculated by FEM analysis calculation. The calculation results are shown in FIG. In FIG. 6, with reference to a perpendicular passing through the center of rotation of the tire and perpendicular to the ground contact surface, in FIG. 6, the position in the tire circumferential direction, which is the horizontal axis, is 0 ° on this perpendicular, The direction position is shown as 0 to 180 °, and the tire circumferential position on the other side is shown as 0 to −180 °.

As can be seen from FIG. 6, the shear strain of the tire rubber near the folded end of the carcass ply is lower in the example than in the conventional example in the entire angle range, that is, in all positions in the tire circumferential direction.

<Experimental example 1>
Next, the present inventor used a tire having a size of 275 / 80R22.5 M880BZ as the heavy load tire, and obtained the core rotation amount at normal internal pressure by CT imaging in the example and the conventional example. FIG. 7 shows a schematic cross-sectional shape of the bead portion between the example and the conventional example. The actual measurement results are shown in FIG.

In this experimental example, both the example and the conventional example were performed over a plurality. In FIG. 8, both the example and the conventional example show the obtained data with a solid plot of the core rotation amount on one side of the bead core of the tire and a hollow plot of the core rotation amount on the other side. ing. As can be seen from FIG. 8, the amount of core rotation was clearly reduced in the example compared to the conventional example.

<Experimental example 2>
The present inventor used a tire of the same size as 275 / 80R22.5 M880BZ as the heavy load tire, and in the example and the conventional example, the heavy duty tire was mounted on the rotating drum and traveled, and according to the travel distance. An experiment was conducted in which the load was increased step by step and the rotating drum was rotated until the tire was damaged. The experimental results are shown in FIG.

As can be seen from FIG. 9, compared to the conventional example, the result is that the traveling distance of the example is about 1500 km longer. In this experimental example, an accelerated test is performed in which a load larger than the load applied when the tire is actually used is performed. Therefore, when converted to the travel distance in actual use, it becomes longer than 1500 km.

<Experimental example 3>
The present inventor prepared Examples 1 to 3 and Comparative Examples 1 to 4 as samples having different core maximum widths and core cross-sectional areas. For Examples 1 to 3 and Comparative Examples 1 to 4, tire weight and core rotation were prepared. The amount, core translation, and BF durability were measured. The measurement results are as shown in Table 1.

In Table 1, the tire weight, the core rotation amount, the core translation amount, and the BF durability are represented by indexes with the value in Example 2 as “100”. The BF durability is an index indicating the durability time and the durability distance of the tire in the drum straight running test.

As for BF durability, the index means that the larger the index value, the better results were obtained. On the other hand, for the tire weight, the core rotation amount, and the core translation amount, the index means that the smaller the index value, the better the result. In comparison between the results obtained in Examples 1 to 3 and the results obtained in Comparative Examples 1 to 4, the tire weight was evaluated by comparison with Example 3.

As shown in Table 1, in Examples 1 to 3, the maximum core width is 10 mm or more and 30 mm or less, and the bead core cross-sectional area is 70 mm ² or more and 240 mm ² or less. In Example 1 and Example 3, it turns out that the amount of core rotation and the amount of core translation are small compared with Example 2. FIG. Furthermore, it turns out that BF durability is improving.

In Example 1 and Example 3, the tire weight is increased as compared with Example 2, but the increase is less than 10% and is in an acceptable range.

In Comparative Example 1, although the bead core cross-sectional area is 70 mm ² or more and 240 mm ² or less, the core maximum width is smaller than 10 mm. As shown in Table 1, in Comparative Example 1, it can be confirmed that the core rotation amount is increased and the BF durability is deteriorated as compared with Examples 1 to 3. Therefore, it can be seen that when the core maximum width is made smaller than 10 mm, the core rotation amount and the BF durability deteriorate.

In Comparative Example 2, the bead core cross-sectional area is 70 mm ² or more and 240 mm ² or less, but the core maximum width is larger than 30 mm. As shown in Table 1, in Comparative Example 2, it can be confirmed that the tire weight is increased as compared with Examples 1 to 3. In particular, the tire weight is increased by 50% compared to Example 2, which exceeds the allowable range. Therefore, it can be seen that the tire weight deteriorates when the maximum core width is larger than 30 mm.

In Comparative Example 3, although the maximum core width is 10 mm or more and 30 mm or less, the bead core cross-sectional area is smaller than 70 mm ² . As shown in Table 1, it can be confirmed that in Comparative Example 3, the amount of core translation increases compared to Examples 1 to 3, and the BF durability deteriorates. Therefore, it can be seen that when the cross-sectional area of the bead core is smaller than 70 mm ² , the core translation amount and the BF durability are deteriorated.

In Comparative Example 4, the maximum core width is 10 mm or more and 30 mm or less, but the bead core cross-sectional area is larger than 240 mm ² . As shown in Table 1, in Comparative Example 4, it can be confirmed that the tire weight is increased and the core translation amount is increased as compared with Examples 1 to 3. Therefore, it can be seen that when the bead core cross-sectional area is larger than 240 mm ² , the tire weight and the core translation amount deteriorate.

As described above, in Examples 1 to 3, the maximum core width is 10 mm or more and 30 mm or less, and the bead core cross-sectional area is 70 mm ² or more and 240 mm ² or less. Therefore, according to Examples 1 to 3, it was confirmed that rotation and translation of the bead core 12 can be effectively suppressed at the same time while reducing the tire weight as compared with Comparative Examples 1 to 4. Furthermore, it was confirmed that BF durability can be improved.

<Experimental example 4>
As shown in Table 2, the present inventor prepared conventional examples, examples 4 and comparative examples 5 to 8 as samples having different core bottom surface width D, core drip A, core maximum width B, and core cross-sectional area. , BF durability, tire weight, core rotation amount, core translation amount and flange pressure were measured. The measurement results are as shown in Table 2.

The conventional example is a sample using a symmetrical bead core. Example 4 and Comparative Examples 5 to 8 are samples in which the core bottom surface width D, the core stretch A, the core maximum width B, and the core cross-sectional area are changed as shown in Table 2. In Table 2, the core bottom surface width D, the core pulling A, the core maximum width B, and the core cross-sectional area are represented by indices with the value in the conventional example being “100”, unlike Experimental Example 3 (Table 1). . As shown in FIG. 1, the core A has a section from the innermost end of the bottom surface 12B to the innermost portion 12IE in the direction along the bottom surface 12B in the cross section along the tire width direction TD and the tire radial direction TR. Distance.

The BF durability, the tire weight, the core rotation amount, the core translation amount, and the flange pressure are represented by indices with the conventional example being “100”. For the flange pressure, the smaller the index value, the better the result. The indices for BF durability, tire weight, core rotation amount, and core translation amount are the same as in Experimental Example 3 (Table 1).

As shown in Table 2, in Example 4, the BF durability, the core rotation amount, the core translation amount, and the flange pressure are secured at the same level as the conventional example, but the tire weight is improved as compared with the conventional example. It was confirmed.

On the other hand, in Comparative Example 5 in which the width of the bead core is reduced in the direction along the bottom surface 12B while maintaining the symmetrical shape, the tire weight is reduced, but the BF durability, the core rotation amount, and the core translation are reduced. It was confirmed that both the amount and the flange pressure deteriorated.

In Comparative Example 6 in which only the core bottom width D is reduced while maintaining a symmetrical shape, the tire weight is reduced, but the BF durability, the core rotation amount, the core translation amount, and the flange pressure are all deteriorated. Confirmed to do.

In Comparative Example 7 in which only the core maximum width B was reduced while maintaining a symmetrical shape, it was confirmed that the tire weight was increased and the tire weight could not be reduced sufficiently.

In Comparative Example 8, in which A is reduced by the core and the cross-sectional area of the core is reduced, the tire weight is reduced, but the BF durability, the core rotation amount, the core translation amount, and the flange pressure may all be deteriorated. confirmed.

As described above, the maximum width portion of the bead core 12 is set while the length L1 from the center 12BC of the bottom surface 12B to the innermost portion 12IE is set shorter than the length L2 from the center 12BC of the bottom surface 12B to the outermost portion 12OE. It is confirmed that the rotation and translation of the bead core 12 can be effectively suppressed at the same time while reducing the tire weight by maintaining the width (hereinafter referred to as the core maximum width) and the cross-sectional area of the bead core 12 in the same manner as the conventional example. It was.

The embodiment described above is merely an example described for facilitating the understanding of the present invention, and the present invention is not limited to the embodiment. The technical scope of the present invention is not limited to the specific technical matters disclosed in the above embodiment, but includes various modifications, changes, alternative techniques, and the like that can be easily derived therefrom.

This application is based on the priority based on Japanese Patent Application No. 2014-107986 filed on May 26, 2014 and on the basis of Japanese Patent Application No. 2015-0666250 filed on March 27, 2015. Priority, and the entire contents of these applications are incorporated herein by reference.

According to the present invention, it is possible to provide a heavy duty tire capable of reducing the weight of the tire and effectively suppressing the rotation and translation of the bead core.

1 Heavy load tire 10 Bead portion 12

Bead core

12J, 12K portion 20 Carcass ply 12B Bottom surface 12IE Innermost portion 12OE Outermost portion N Normal

Claims

A heavy-duty tire comprising a pair of bead portions assembled to a rim flange and a carcass ply straddling the pair of bead portions,
Each of the pair of bead portions includes a bead core having a bottom surface;
In the cross section in the tire radial direction, the bead core has a length L1 from the center in the tire width direction on the bottom surface to the innermost portion located on the innermost side in the tire width direction, which is the longest in the tire width direction from the center in the tire width direction on the bottom surface. It is shorter than the length L2 to the outermost part located outside, and the tire width direction length is longer than the tire radial direction length,
A heavy duty tire having a ply swing angle θ of 50 ° or less.
The heavy duty tire according to claim 1,
In the tire radial direction cross section, the width in the direction along the bottom surface, the width of the maximum width portion of the bead core is 10 mm or more and 30 mm or less,
In the tire radial direction cross section, the cross-sectional area of the bead core is 70 mm 2 or more and 240 mm 2 or less,
A heavy duty tire equipped with a 15 ° DC rim.
The heavy duty tire according to claim 1 or 2,
The outermost portion is located on the outer side in the tire radial direction with respect to the innermost portion.
The heavy duty tire according to any one of claims 1 to 3,
In the tire radial direction cross section, the outermost portion is included when the bead core is divided into two portions by a normal line that passes through the center of the bottom surface and extends along a direction perpendicular to the bottom surface. A heavy duty tire characterized in that a cross-sectional area of the portion is larger than a cross-sectional area of the portion including the innermost portion.