JP4587375B2 - Pneumatic radial tire - Google Patents

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more particularly, to a pneumatic radial tire suitable for a run-flat tire for a passenger car, which includes a side reinforcing rubber having a substantially crescent-shaped cross section in a sidewall portion. .

  Conventionally, a tire that can safely travel a certain distance even in a state where the internal pressure of the tire has decreased due to puncture or the like, a so-called run-flat tire, a substantially crescent-shaped cross section on the innermost side of the carcass in the sidewall portion of the tire Side reinforcement type run flat tires in which the side reinforcement rubber is arranged to improve the rigidity of the sidewall portions are known. In this type of run-flat tire, the side reinforcement rubber has a hardness of 80 or more, and its cross-sectional area is larger than the bead filler, and the cross-sectional area of the side reinforcement rubber is increased so that it is durable as a run-flat tire. Was ensured.

As a technique related to the improvement of such a side reinforcing rubber, for example, Patent Document 1 discloses a standard that ensures a necessary run-flat performance, enables good high-speed running even in a state of air deflation, and originates from a rubber reinforcing layer. In order to minimize the decrease in riding comfort and increase in tire weight under internal pressure, the rubber reinforcement layer passes through the inner side of the carcass ply body, and the inside of the bead apex rubber in the tire axial direction. From the inner end of the belt layer to the outer end arranged below the outer end of the belt layer in the axial direction of the belt, and the maximum thickness portion is radially outward from the 1/2 height of the tire base excluding the tread rubber. And a bead apex rubber that is surrounded between the carcass ply body and the folded end and ends in the vicinity of a 1/2 height position of the tire base. Hate is described.
JP 2000-190715 A (Claims, [0037], etc.)

  As described above, increasing the cross-sectional area of the side reinforcing rubber is effective for ensuring run-flat durability. Uniformity gets worse. Along with this, a peak of non-uniformity is likely to rise at the joint portion, which also affects the deterioration of riding comfort. For this reason, even if the longitudinal spring of the tire is lowered by lowering the hardness of the side reinforcing rubber, the effect of improving the uniformity and the riding comfort corresponding to that cannot be obtained. Further, when the hardness of the side reinforcing rubber is lowered, the case rigidity tends to be lowered and the steering stability tends to be deteriorated, and this tendency is particularly remarkable in the all-season tire having a low block rigidity.

  Therefore, the object of the present invention is to improve the uniformity without improving the run-flat durability by improving the side-reinforcing rubber, and to achieve a high degree of compatibility between run-flat durability, uniformity and ride comfort. Another object of the present invention is to provide a radial radial tire and a pneumatic radial tire excellent in handling stability.

  In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, in order to reduce the joint portion of the side reinforcing rubber while ensuring the run flat durability, the bead filler has run flat performance as well as the side reinforcing rubber. It is effective to secure, i.e., reduce the cross-sectional area of the side reinforcing rubber and bring it closer to the back side of the tread, while increasing the cross-sectional area of the bead filler so that the bead filler plays part of the role of the side reinforcing rubber. As a result, it has been found that it is possible to simultaneously ensure run-flat durability and improve uniformity, thereby completing the present invention.

That is, the pneumatic radial tire of the present invention has a toroidal shape between a pair of bead portions in which a bead core is embedded, a pair of sidewall portions extending outward from the bead portion in the tire radial direction, and both sidewall portions. A carcass comprising a continuous tread portion, and reinforcing each of these portions between the bead portions, a belt layer disposed outside the tread portion of the carcass, and a substantially crescent cross section disposed inside the sidewall portion of the carcass A pneumatic radial tire comprising a bead filler extending in a radial direction toward the tread portion along the outer periphery of the carcass on the outer side in the tire radial direction of the bead core.
The cross-sectional area of the bead filler and the cross-sectional area of the side reinforcing rubber in the tire radial direction cross section are substantially the same, and the lower end position H ₁ of the side reinforcing rubber is 30 to 40% of the tire section height SH. It is characterized by this.

In the present invention, the bead upper end position of H ₂ filler is preferably 45 to 55% of the tire section height SH. The bead filler rubber preferably has a Shore A hardness of 80 or more, and the side reinforcing rubber preferably has a Shore A hardness of 70-80.

  Here, in the present invention, the tire section height SH means 1/2 of the difference between the outer diameter of the unloaded tire and the rim diameter when the tire is mounted on the applicable rim and filled with the prescribed air pressure. And The applicable rim refers to the rim specified in the following standards, the specified air pressure refers to the air pressure defined in accordance with the maximum load capacity in the following standards, and the maximum load capacity refers to the tire in the following standards. The maximum mass allowed to be loaded on. The standard is defined by an industrial standard effective in the region where the tire is produced or used. For example, “The Tire and Rim Association Inc. Year Book” in the United States, and “The European Tire and Land” in Europe. It is “Standards Manual” of Rim Technical Organization, and “JATMA Year Book” of Japan Automobile Tire Association in Japan.

  According to the present invention, by reducing the cross-sectional area of the side reinforcing rubber, it is possible to eliminate the problem of uniformity deterioration due to the increase in the joint portion. By ensuring the performance, it has become possible to prevent a decrease in run-flat durability. As a result, it is possible to improve the uniformity without lowering the run-flat performance, and as a result, to achieve a pneumatic radial tire that achieves a high balance between run-flat durability, uniformity and ride comfort. I was able to. Further, when the hardness of the bead filler rubber is set to the predetermined value or more, it is possible to obtain an effect of improving the steering stability.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
FIG. 1 is a right half cross-sectional view of a pneumatic radial tire according to a preferred embodiment of the present invention. As shown in the figure, a pneumatic radial tire 10 according to the present invention includes a pair of bead portions 11 in which a bead core 1 is embedded, a pair of sidewall portions 12 extending outward from the bead portion 11 in the tire radial direction, and both sidewall portions. The carcass 2 includes a tread portion 13 that forms a toroid between the twelve portions 12, and reinforces each portion between the bead portions 11, a belt layer 3 disposed outside the tread portion of the carcass 2, A side reinforcing rubber 4 having a substantially crescent-shaped cross section disposed on the inner side of the side wall part, and further extending outwardly in the tire radial direction of the bead core 1 toward the tread part 13 along the outer periphery of the carcass 2 A filler 5 is provided.

In the present invention, the cross-sectional area of the bead filler 5 and the cross-sectional area of the side reinforcing rubber 4 in the tire radial direction cross section are substantially the same, and the lower end position H ₁ of the side reinforcing rubber 4 is the tire section height SH. It needs to be 30 to 40%, preferably 34 to 37%.

Conventionally, since the cross-sectional area of the side reinforcing rubber is formed larger than the cross-sectional area of the bead filler, the cross-sectional area of the side reinforcing rubber 4 is made substantially the same as the cross-sectional area of the bead filler 5. Becomes smaller than the conventional one. However, if the lower end position H ₁ of the side reinforcing rubber 4 is less than 30% of the tire section height SH, it is difficult to reduce the joint area of the side reinforcing rubber 4 as compared with the conventional case, and the effect of improving uniformity and ride comfort can be obtained. I can't get it. On the other hand, if the lower end position H ₁ of the side reinforcing rubber 4 exceeds 40% of the tire section height SH, the joint area of the side reinforcing rubber 4 becomes too small, and improvement of uniformity and ride comfort can be realized, but run flat There is concern about ensuring the durability of the tire.

Therefore, in the present invention, by satisfying the condition of the lower end position H ₁ of the side reinforcing rubber 4, the cross-sectional area of the side reinforcing rubber 4 is made substantially the same as the cross-sectional area of the bead filler 5. The joint area can be reduced, thereby improving the uniformity and, consequently, the riding comfort.

  Moreover, in this invention, it is preferable that the hardness of a bead filler rubber shall be 80 or more by Shore A hardness, especially 80-85. By setting the hardness of the bead filler rubber to 80 or more, the rigidity around the bead portion 11 can be increased, and the driving stability can be drastically improved. Therefore, according to the present invention, both snowiness and steering stability can be achieved even in an all-season tire having low block rigidity and fearing steering stability. In addition, the hardness of the bead filler rubber of the conventional run flat tire is around 85, and the bead filler rubber hardness of the normal tire is 70-100.

Further, the upper end position of H ₂ bead filler 5, 45% to 55% of the tire section height SH, and particularly preferably from 48 to 52%. When the upper end position H ₂ is smaller than 45%, there is little overlap with the side reinforcing rubber 4 and the run flat performance is deteriorated. On the other hand, if it is larger than 55%, the proportion of the bead filler 5 having high hardness in the sidewall portion 12 is increased, and the load on the sidewall portion 12 is increased in the vicinity of the shoulder.

  In the present invention, the desired effect can be obtained if the side reinforcing rubber 4 and the bead filler 5 satisfy the above conditions, and other tire structures and materials are appropriately selected from conventionally known ones. There is no particular limitation. For example, the hardness of the side reinforcing rubber 4 can be set to 70 to 80 in Shore A hardness, and the number of the carcass 2 and the belt layer 3 is not limited to the illustrated example, and is arranged as appropriate according to demand. It is possible. The tire of the present invention is a run-flat tire that can travel safely over a certain distance even when the internal pressure of the tire is reduced due to puncture or the like, and can be suitably used particularly for a passenger car.

Hereinafter, the present invention will be described in more detail with reference to examples.
Test tires having a cross-sectional structure shown in FIG. 1 and a tread pattern shown in FIG. 2 were prepared at a tire size PSR235 / 50R17. For each tire, the lower end position H _{1 of} the side reinforcing rubber 4 and the ratio of the cross-sectional area of the bead filler 5 to the cross-sectional area of the side reinforcing rubber 4 in the tire radial cross section are as shown in Table 1 below. Set.

  For each of the obtained test tires, the hardness of the bead filler rubber, uniformity (RFV primary: index representing uniformity), run-flat durability, riding comfort and handling stability were evaluated according to the following. The evaluation results were relative compared with the index of the conventional example (reference) as 100. These results are shown together in Table 1 below. The higher the index value, the better the result.

* Bead filler rubber hardness (Shore A): Measurement was performed based on JIS K 6253.
* Runflat actual vehicle durability: Evaluation was performed by running the vehicle on a prescribed test course. The results were evaluated based on the distance traveled by run flat travel.
* Ride comfort: Evaluation was performed by running the vehicle on a prescribed test course.
* Steering stability of actual vehicle: Evaluation was performed by running the vehicle on a predetermined test course.

  In general, the uniformity of the side reinforcing rubber is dominant on the uniformity of the entire tire, and the uniformity of the bead filler is small. Therefore, if the position of the side reinforcing rubber is shifted upward to reduce the cross-sectional area, the uniformity of the entire tire is further improved, but the run-flat performance is deteriorated (Comparative Example 2).

As shown in Table 1 above, in the tire of the example in which the cross-sectional area of the side reinforcing rubber is substantially equal to the bead filler, and the lower end position H ₁ of the side reinforcing rubber is 30 to 40% of the tire section height SH, It was confirmed that both the uniformity (RFV primary) and the actual ride comfort level could be improved while ensuring the run-flat durability level equivalent to the conventional level.

1 is a right half sectional view of a pneumatic radial tire according to a preferred embodiment of the present invention. It is a partial development view showing a tread pattern of a test tire in an example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead filler 2 Carcass 3 Belt layer 4 Side reinforcement rubber 5 Bead filler 11 Bead part 12 Side wall part 13 Tread part

Claims (4)

It consists of a pair of bead portions in which bead cores are embedded, a pair of sidewall portions extending outward in the tire radial direction from the bead portions, and a tread portion connected in a toroidal shape between the both sidewall portions. A carcass that reinforces between the parts, a belt layer disposed outside the tread portion of the carcass, and a side reinforcing rubber having a substantially crescent-shaped cross section disposed inside the sidewall portion of the carcass, In a pneumatic radial tire provided with a bead filler extending outwardly in the radial direction of the bead core along the outer periphery of the carcass toward the tread portion,
The cross-sectional area of the bead filler in the tire radial cross sectional area of the side reinforcing rubber is substantially the same, and the lower end position H ₁ of the side reinforcing rubber is 30 to 40% of the tire section height SH A pneumatic radial tire characterized by that. It said bead upper end position of H ₂ filler, pneumatic radial tire according to claim 1, wherein 45 to 55% of the tire section height SH.   The pneumatic radial tire according to claim 1 or 2, wherein the bead filler rubber has a Shore A hardness of 80 or more.   The pneumatic radial tire according to any one of claims 1 to 3, wherein the side reinforcing rubber has a Shore A hardness of 70 to 80.

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