JP4392711B2 - Heavy duty pneumatic radial tire - Google Patents

Description

【００３３】
この表１から判るように、従来例１，２のタイヤは、ビード部の耐久性は良好であるが、ビード部の補強に伴ってトレッド部の耐久性が低下しており、実用上、好ましい補強構造ではなかった。従来例３及び比較例のタイヤは、トレッド部の耐久性については問題ないものの、ビード部の耐久性の改善効果が不十分であった。これに対して、実施例のタイヤは、トレッド部の耐久性を損なうことなく、ビード部の耐久性を効果的に改善することができた。
【００３４】
【発明の効果】
以上説明したように本発明によれば、左右一対のビード部間にカーカス層を装架し、各ビード部に埋設されたビードコアの廻りに前記カーカス層を巻き上げた重荷重用空気入りラジアルタイヤにおいて、カーカス層の巻き上げ端部を独立気泡を有する発泡ゴム層で包み込み、更に該発泡ゴム層の外側全体を該発泡ゴム層よりもヤング率が高くかつ隣接する周辺ゴム層よりもヤング率が高いカバーゴム層で覆うようにしたから、カーカス層の巻き上げ端部を起点とするセパレーション故障を効果的に抑制し、ビード部の耐久性を向上することができる。
【図面の簡単な説明】
【図１】本発明の実施形態からなる重荷重用空気入りラジアルタイヤを示す子午線半断面図である。
【図２】本発明の実施形態からなる重荷重用空気入りラジアルタイヤのビード部を示す断面図である。
【図３】本発明の重荷重用空気入りラジアルタイヤにおけるビード部の変形例を示す断面図である。
【図４】本発明の重荷重用空気入りラジアルタイヤにおけるビード部の変形例を示す断面図である。
【図５】比較例のビード部を示す断面図である。
【図６】標準例のビード部を示す断面図である。
【図７】従来例１のビード部を示す断面図である。
【図８】従来例２のビード部を示す断面図である。
【図９】従来例３のビード部を示す断面図である。
【符号の説明】
１ トレッド部
２ サイドウォール部
３ ビード部
４ カーカス層
４ａ 巻き上げ端部
５ ビードコア
６ スチール補強層
７ ベルト層
８ 発泡ゴム層
９ カバーゴム層
１１ 下側ビードフィラー
１２ 上側ビードフィラー
１３ リムクッションゴム層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heavy-duty pneumatic radial tire suitable for a flatness ratio of 70% or less, and more particularly to a heavy-duty pneumatic radial tire in which durability of a bead portion is improved.
[0002]
[Prior art]
In a heavy-duty pneumatic radial tire, stress concentrates on the winding end of the carcass layer, and a separation failure may occur starting from the winding end. In order to prevent such a separation failure, conventionally, distortion of the bead portion is suppressed by increasing the thickness of the bead filler gauge or increasing the number of nylon reinforcing layers embedded in the bead portion. ing.
[0003]
However, in these methods, since the burden on the edge of the belt layer increases as the rigidity of the side portion increases, a separation failure is likely to occur in the tread portion. In particular, a tire with a small flatness ratio and a small side portion bending region is significantly affected by an increase in side portion rigidity. In addition, when the bead filler gauge is increased or the number of nylon reinforcing layers is increased, there is a problem in that it is necessary to change the carcass line or the tire mass is increased.
[0004]
On the other hand, in order to prevent a separation failure of the bead portion, it has been proposed to cover the rolled-up end portion of the carcass layer with a low modulus rubber layer and a high modulus rubber layer (see, for example, Patent Document 1). . By specifying the physical properties of the rubber layer covering the rolled-up end portion of the carcass layer in this way, it is possible to suppress separation failure starting from the rolled-up end portion of the carcass layer. However, even in this case, the effect of suppressing the separation failure is not always sufficient, and further improvement is required particularly for heavy-duty pneumatic radial tires having a small flatness ratio.
[0005]
[Patent Document 1]
JP-A-9-175122 [0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a heavy-duty pneumatic radial tire capable of effectively suppressing a separation failure starting from a winding end of a carcass layer and improving the durability of a bead portion. .
[0007]
[Means for Solving the Problems]
In order to achieve the above object, a heavy-duty pneumatic radial tire according to the present invention is a heavy load in which a carcass layer is mounted between a pair of left and right bead portions, and the carcass layer is wound around a bead core embedded in each bead portion. In a heavy duty pneumatic radial tire, the wound end of the carcass layer is wrapped with a foamed rubber layer having closed cells, and the entire outer periphery of the foamed rubber layer has a higher Young's modulus than the foamed rubber layer and is adjacent to the peripheral rubber layer It is characterized by being covered with a cover rubber layer having a higher Young's modulus.
[0008]
In this way, the rolled-up end of the carcass layer is wrapped with a foamed rubber layer, and the entire outside of the foamed rubber layer is covered with a cover rubber layer having a high Young's modulus, thereby effectively generating cracks at the rolled-up end of the carcass layer. And crack growth can be effectively prevented. Therefore, it is possible to effectively suppress a separation failure starting from the rolled-up end portion of the carcass layer and improve the durability of the bead portion.
[0009]
In the present invention, the foaming rate of the foamed rubber layer is preferably 3 to 50%, and the diameter of closed cells in the foamed rubber layer is preferably 20 to 1000 μm. The foamed rubber layer thus defined is effective in preventing a separation failure.
[0010]
The present invention is particularly suitable for a heavy-duty pneumatic radial tire with a flatness ratio of 70% or less in which side portion reinforcement is restricted. That is, when the present invention is applied to a heavy-duty pneumatic radial tire with a flatness ratio of 70% or less, it is not necessary to excessively increase the rigidity of the side portion, so the burden on the end portion of the belt layer is reduced and the tread portion is reduced. Occurrence of a separation failure in can be more reliably avoided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings.
[0012]
FIG. 1 shows a heavy-duty pneumatic radial tire according to an embodiment of the present invention. In FIG. 1, 1 is a tread portion, 2 is a sidewall portion, and 3 is a bead portion.
[0013]
As shown in FIG. 1, a carcass layer 4 in which a plurality of steel cords are arranged in the tire radial direction is mounted between a pair of left and right bead portions 3 and 3. The carcass layer 4 is wound up around the bead core 5 embedded in each bead portion 3 from the tire inner side to the outer side. In the bead portion 3, a steel reinforcing layer 6 formed by aligning a plurality of steel cords is embedded along the carcass layer 4. On the other hand, on the outer peripheral side of the carcass layer 4 in the tread portion 1, a plurality of belt layers 7 formed by aligning a plurality of reinforcing cords are embedded.
[0014]
FIG. 2 is an enlarged view of the bead portion of the heavy duty pneumatic radial tire. In FIG. 2, 11 is a lower bead filler, 12 is an upper bead filler, and 13 is a rim cushion rubber layer. In the heavy-duty pneumatic radial tire, the rolled-up end portion 4 a of the carcass layer 4 is wrapped with a foam rubber layer 8, and the outside of the foam rubber layer 8 is covered with a cover rubber layer 9.
[0015]
The foamed rubber layer 8 has a large number of closed cells. Therefore, even a rubber material that does not normally undergo compression deformation can be compressed and deformed by collapsing the closed cells. Thereby, the foamed rubber layer 8 exhibits excellent followability with respect to deformation, and effectively prevents the occurrence of cracks in the rolled-up end portion 4a of the carcass layer 4. Further, when a crack occurs in the foamed rubber layer 8 at the rolled-up end 4a of the carcass layer 4, the crack is temporarily stopped every time the growth of the crack reaches each closed cell. Therefore, the foamed rubber layer 8 effectively prevents crack growth.
[0016]
Here, the foaming rate of the foamed rubber layer 8 is preferably 3 to 50%. If the foaming ratio is less than 3%, the followability to deformation is lowered, and if it exceeds 50%, tire performance such as steering stability may be impaired. However, the foaming rate is the ratio of the total volume of closed cells to the apparent volume of the foamed rubber layer 8. The diameter of the closed cells in the foamed rubber layer 8 is preferably 20 to 1000 μm. If the diameter of the closed cells is less than 20 μm, the effect of stopping the growth of cracks is insufficient. Conversely, if the diameter exceeds 1000 μm, the tire performance such as steering stability may be impaired.
[0017]
The cover rubber layer 9 has a higher Young's modulus (100% modulus) than the foamed rubber layer 8 and a Young's modulus (100% modulus) than the adjacent peripheral rubber layers such as the upper bead filler 12 and the rim cushion rubber layer 13. high. Therefore, even if a crack generated in the foamed rubber layer 8 reaches the cover rubber layer 9, there is a difference in rigidity between the foamed rubber layer 8 and the cover rubber layer 9. Therefore, it progresses along the interface between the foamed rubber layer 8 and the cover rubber layer 9 rather than vertically. That is, the crack is processed inside the cover rubber layer 9 without diffusing outside the cover rubber layer 9. Therefore, the cover rubber layer 9 effectively prevents crack growth.
[0018]
The 100% modulus of the foamed rubber layer 8 is preferably 0.5 to 2.0 MPa, and the 100% modulus of the cover rubber layer 9 is preferably 4 to 20 MPa. However, the 100% modulus is measured according to JIS K6251. The thickness of the cover rubber layer 9 may be 0.5 to 3.0 mm.
[0019]
In the heavy-duty pneumatic radial tire, the rolled-up end 4a of the carcass layer 4 is wrapped with the foamed rubber layer 8, and the outside of the foamed rubber layer 8 is covered with the cover rubber layer 9 having a high Young's modulus. It is possible to effectively prevent generation of cracks at the rolled-up end portion 4a and effectively prevent growth of cracks. Therefore, the separation failure starting from the winding end 4a of the carcass layer 4 can be effectively suppressed, and the durability of the bead portion can be improved.
[0020]
3 to 4 each show a modification of the bead portion in the heavy duty pneumatic radial tire of the present invention. In FIG. 3, the foamed rubber layer 8 has an elliptical shape in the tire meridian cross section, and the major axis is arranged in the tire radial direction. In FIG. 4, the cover rubber layer 9 includes an inner layer 9a on the inner side in the tire width direction and an outer layer 9b on the outer side .
[0021]
【Example】
In the heavy-duty pneumatic radial tire of tire size 275 / 70R22.5, standard examples, conventional examples 1 to 3, examples and comparative examples in which the reinforcement structure of the bead portion was varied as described below were manufactured.
[0022]
Standard example:
As shown in FIG. 6 , the tire has a nylon reinforcing layer 21 inserted into the bead portion 3. However, the 100% modulus of the bead filler 12 was 2.8 MPa, and the 100% modulus of the rim cushion rubber layer 13 was 3.2 MPa.
[0023]
Conventional example 1:
As shown in FIG. 7 , the tire has the same structure as that of the standard example except that the gauge t of the bead filler 12 at the rolled-up end portion of the carcass layer is increased.
[0024]
Conventional example 2:
As shown in FIG. 8 , the tire has the same structure as the standard example except that the number of nylon reinforcing layers 21 is increased.
[0025]
Conventional example 3:
As shown in FIG. 9 , without providing a nylon reinforcing layer, the rolled-up end 4a of the carcass layer 4 is covered with a non-foamed rubber layer 22 (100% modulus: 1 MPa), and the outer side thereof is covered with a cover rubber layer 23 (100 % Modulus: 14 MPa), except that the tire has the same structure as the standard example.
[0026]
Example:
As shown in FIG. 2, without providing a nylon reinforcing layer, the rolled-up end 4a of the carcass layer 4 is covered with a foamed rubber layer 8 (100% modulus: 1 MPa), and the outer side thereof is covered with a cover rubber layer 9 (100% The tire has the same structure as the standard example except that it is coated with a modulus of 14 MPa.
[0027]
Comparative example:
As shown in FIG. 5 , a tire having the same structure as the standard example except that the rolled-up end 4a of the carcass layer 4 is covered with a foamed rubber layer 8 (100% modulus: 1 MPa) without providing a nylon reinforcing layer. It is.
[0028]
For these test tires, the crack generation rate and crack length at the rolled-up end of the carcass layer were measured by the following test method, the tread separation resistance was evaluated, the tire mass was further measured, and the results are shown in Table 1. It was.
[0029]
Crack generation rate and crack length:
After the test tire was mounted on a real vehicle and traveled 100,000 km, internal analysis of the bead portion was performed. As for the crack occurrence rate, the left and right bead portions were divided into eight on the circumference, and the crack occurrence status was confirmed, and the ratio (%) of the crack occurrence locations in the 16 confirmed locations was determined. Moreover, about the crack length, the total length of the crack measured in the 16 confirmation points was calculated | required, and it showed with the index | exponent which sets a standard example to 100. A larger index value means more cracks.
[0030]
Tread separation resistance:
The test tire was mounted on an actual vehicle, and after traveling 100,000 km, internal analysis of the belt edge portion was performed. Specifically, the left and right edge portions of the second and third belt layers counted from the carcass layer side are each divided into eight on the circumference to check the crack occurrence status, and the crack occurrence locations at the 32 check locations are confirmed. The ratio (%) was determined. The evaluation results are shown as an index using the reciprocal of the ratio as a standard example. A larger index value means better tread separation resistance.
[0031]
Tire mass:
The mass of the test tire was measured. The evaluation results are shown as an index with the standard example being 100. It means that mass is so large that this index value is large.
[0032]
[Table 1]

[0033]
As can be seen from Table 1, in the tires of Conventional Examples 1 and 2, the durability of the bead portion is good, but the durability of the tread portion is reduced with reinforcement of the bead portion, which is preferable in practice. It was not a reinforced structure. The tires of Conventional Example 3 and Comparative Example had no problem with respect to the durability of the tread portion, but the effect of improving the durability of the bead portion was insufficient. In contrast, the tires of the examples were able to effectively improve the durability of the bead part without impairing the durability of the tread part.
[0034]
【The invention's effect】
As described above, according to the present invention, in a heavy-duty pneumatic radial tire in which a carcass layer is mounted between a pair of left and right bead portions, and the carcass layer is wound around a bead core embedded in each bead portion, A cover rubber in which the rolled-up end of the carcass layer is wrapped with a foamed rubber layer having closed cells, and the entire outside of the foamed rubber layer has a higher Young's modulus than the foamed rubber layer and a higher Young's modulus than the adjacent peripheral rubber layer Since it is covered with the layer, the separation failure starting from the winding end of the carcass layer can be effectively suppressed, and the durability of the bead portion can be improved.
[Brief description of the drawings]
FIG. 1 is a meridian half sectional view showing a heavy duty pneumatic radial tire according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a bead portion of a heavy-duty pneumatic radial tire according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a modified example of the bead portion in the heavy duty pneumatic radial tire of the present invention.
FIG. 4 is a cross-sectional view showing a modified example of the bead portion in the heavy duty pneumatic radial tire of the present invention.
FIG. 5 is a cross-sectional view showing a bead portion of a comparative example.
FIG. 6 is a cross-sectional view showing a bead portion of a standard example.
7 is a cross-sectional view showing a bead portion of Conventional Example 1. FIG.
8 is a cross-sectional view showing a bead portion of Conventional Example 2. FIG.
9 is a cross-sectional view showing a bead portion of Conventional Example 3. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tread part 2 Side wall part 3 Bead part 4 Carcass layer 4a Roll-up end part 5 Bead core 6 Steel reinforcement layer 7 Belt layer 8 Foam rubber layer 9 Cover rubber layer 11 Lower bead filler 12 Upper bead filler 13 Rim cushion rubber layer

Claims (3)

In a heavy-duty pneumatic radial tire in which a carcass layer is mounted between a pair of left and right bead parts, and the carcass layer is wound around a bead core embedded in each bead part, foam wrapped with a rubber layer, more heavy duty pneumatic that the entire outside of the foamed rubber layer was covered with a high cover rubber layer Young's modulus than the surrounding rubber layer having a Young's modulus is high and the adjacent than the foam rubber layer having Radial tire. The pneumatic radial tire for heavy loads according to claim 1, wherein the foaming ratio of the foamed rubber layer is 3 to 50%. The heavy-duty pneumatic radial tire according to claim 1 or 2, wherein the foamed rubber layer has a closed cell diameter of 20 to 1000 µm.

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