JP2012056519A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic radial tire having both steering stability and market durability while restraining development in fatigue in use of highly rigid organic fiber for a carcass cord.SOLUTION: The pneumatic radial tire includes a pair of bead parts 11, side walls parts 12 and tread parts 13 continuing to the side wall parts, wherein the carcass 2 made of at least one or more carcass plies 2a, 2b, extending over a pair of bead cores 1 embedded respectively in the pair of bead parts in a toroidal manner serves as a framework. The carcass ply is made of organic fiber cords, tensile elasticity of which is 40 cN/dtex under stress load of 29.4 N per cord at a temperature of 180°C. All the carcass cords are folded from inside to outside in a tire radial direction around the bead core. A bead filler arranged outside the bead core in the tire radial direction has a triangular cross-section with height of 15 mm or below.

Description

  The present invention relates to a pneumatic radial tire (hereinafter, also simply referred to as “tire”), and more particularly, to a radial tire for a passenger car according to an improvement in a carcass cord and a bead portion structure.

  In general, the carcass cord used for the carcass that is a skeleton member of a tire has a small physical property difference between a high temperature during high-speed running or continuous running and a low temperature equivalent to the outside temperature, and a cord elastic modulus. It is said that the higher the value, the more stable the handling (maneuverability). An example of such a carcass cord is a rayon cord (for example, Patent Document 1).

  Polyethylene terephthalate (PET) cords that are generally used as carcass cords have very good fatigue properties and are suitable for use in carcass, but are stable because the cord elastic modulus is greatly reduced at high temperatures. There is a drawback that it is not possible to demonstrate the controllability. For this reason, rayon cords are generally used as carcass cords in high-performance tires having a wide tire width and a low aspect ratio that particularly require steering stability.

Japanese Patent Laid-Open No. 07-081331 (Claims etc.)

  By the way, there is lyocell as the same cellulosic fiber as rayon. Lyocell has the characteristic that the elastic modulus from low temperature to high temperature is equal to or higher than rayon and stable, and has higher elastic modulus than rayon, so when used in carcass cords, it has high cornering power as a single tire. Can be expressed. Therefore, lyocell is considered more suitable as a carcass cord for high performance tires.

  However, high-rigidity organic fibers such as lyocell have the disadvantage that they are poor in market durability although they are poor in fatigue as a characteristic of the cord itself and have good handling stability when applied to carcass cords. It was not widely used. That is, when a highly rigid carcass cord is used, an effect of suppressing deformation at the time of loading of the tire can be obtained, and although the input to the carcass cord is reduced, the durability performance is improved. Since the amount of deterioration is large, the durability as a whole deteriorates.

  On the other hand, there is a method to increase the twisting factor as a general method for ensuring fatigue resistance, but if the twisting factor is increased too much, the strength of the cord decreases or the characteristic of high rigidity is lost. Will occur. Accordingly, there has been a demand for the establishment of a technique that can improve the deterioration of fatigue properties when high-rigidity fibers are used in a carcass cord without causing such other problems.

  Accordingly, an object of the present invention is to provide a pneumatic system that solves the above-described problems and suppresses deterioration of fatigue when a high-rigidity organic fiber is used for a carcass cord, and achieves both handling stability and market durability. It is to provide a radial tire.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by combining the application of high-rigidity organic fibers to a carcass cord with a specific carcass arrangement and a bead filler structure, thereby completing the present invention. It came to.

That is, the pneumatic radial tire of the present invention has a pair of bead portions and sidewall portions, and a tread portion connected to the sidewall portions, and spans between a pair of bead cores embedded in the pair of bead portions. In a pneumatic radial tire having a skeleton of a carcass made of at least one carcass ply extending in a toroid shape,
The carcass ply is made of an organic fiber cord having a tensile elastic modulus of 40 cN / dtex or more at a stress load of 29.4 N per cord at a temperature of 180 ° C., and all the carcass cords are arranged inside the tire around the bead core. The bead filler that is folded back to the outside and disposed outside the bead core in the tire radial direction has a triangular cross section with a height of 15 mm or less.

  In the tire according to the present invention, it is preferable that the tensile modulus of the organic fiber cord at a stress load of 29.4 N per cord at a temperature of 180 ° C. is 100 cN / dtex or less. Moreover, as said organic fiber cord, what consists of a cellulosic fiber, especially a lyocell can be used conveniently.

Furthermore, in the present invention, the following formula:
Nt = tan θ = 0.001 × N × √ (0.125 × D / ρ)
Where N is the number of cord twists (times / 10 cm), D is half the total decitex (dtex) of the cord, and ρ is the specific gravity of the cord (g / cm ³ ) The twist coefficient Nt of the organic fiber cord is preferably 0.5 to 0.8. Furthermore, in the tire of the present invention, it is preferable that a side reinforcing rubber layer is disposed along the inner surface of the carcass over the entire region of the sidewall portion or substantially the entire region.

  According to the present invention, the above-described configuration suppresses deterioration of fatigue when a high-rigidity organic fiber is used for a carcass cord, and a pneumatic radial that achieves both steering stability and market durability. It became possible to realize tires.

1 is a cross-sectional view in the width direction showing an example of a pneumatic radial tire of the present invention. FIG. 6 is a cross-sectional view in the width direction showing another example of the pneumatic radial tire of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, the width direction one side sectional view which shows an example of the pneumatic radial tire of this invention is shown. The illustrated pneumatic radial tire 10 includes a pair of bead portions 11 and sidewall portions 12, and a tread portion 13 connected to the sidewall portions 12, and a pair of bead cores 1 embedded in the pair of bead portions 11. In the illustrated example, the carcass 2 including two carcass plies 2a and 2b is used as a skeleton. Further, on the outer side of the crown portion of the carcass 2 in the tire radial direction, one or more layers, in the illustrated example, a belt layer composed of two belts 3, a belt reinforcing layer 4 composed of a cap ply covering the entire width of the belt layer, and a tread 5 are sequentially arranged.

  FIG. 2 is a cross-sectional side view in the width direction showing another example of the pneumatic radial tire of the present invention. The pneumatic radial tire 20 shown in the figure has a crescent-shaped side reinforcing rubber layer 6 along the inner surface of the carcass 2 over the entire region of both side wall portions 12 or substantially the entire region. This is a run-flat tire having the same configuration as the pneumatic radial tire 10 shown in FIG.

  Here, in the illustrated example, only the cap ply that covers the entire width of the belt layer is disposed as the belt reinforcing layer 4. However, in the present invention, the belt reinforcing layer 4 is not necessarily disposed. 4, a layer ply that covers only both end portions of the belt layer may be disposed. Further, the belt reinforcing layer 4 may be composed of only layer plies, and the number of each ply is not particularly limited. Each of the cap ply and the layer ply is composed of a rubberized layer of a reinforcing cord disposed substantially in the tire circumferential direction. Further, the belt layer is usually composed of a rubber layer of a cord that extends at an inclination with respect to the tire equatorial plane, preferably a rubberized layer of at least one steel cord, and in the illustrated example, two belt layers are The belt 3 is configured by laminating the cords constituting the belt layer so as to cross each other.

  In the present invention, the carcass ply has a tensile elastic modulus of 40 cN / dtex or more, preferably 100 cN / dtex or less, particularly 50 to 75 cN / dtex when a stress load of 29.4 N per cord at a temperature of 180 ° C. is applied. It consists of an organic fiber cord. By using such a high-rigidity organic fiber cord as the carcass cord, it is possible to obtain an effect of improving steering stability. The tensile elastic modulus of the organic fiber cord needs to be 40 cN / dtex or more to improve the steering performance, and if it is less than that, the elastic modulus is equivalent to that of the current rayon. Cannot be obtained. In addition, the tensile modulus of the organic fiber cord is preferably set to 100 cN / dtex or less because if the modulus of elasticity is too large, depending on the tire size, the conventional molding method may induce a manufacturing defect such as cording. It is. Here, the problem of the tensile elastic modulus at a stress load of 29.4 N per cord at a temperature of 180 ° C. is that the carcass at a temperature assumed in a situation such as high speed running, low internal pressure running, or run flat running. This is because the generated tension at the (side portion) is about 29.4 N. In the present invention, when there are two or more carcass plies, it is necessary that all the carcass plies are made of the organic fiber cord.

  In the present invention, as shown in the figure, all the carcass cords are folded around the bead core 1 from the tire inner side to the outer side, and the bead filler 7 disposed on the outer side in the tire radial direction of the bead core 1 has a high height. It has a triangular cross section of 15 mm or less, preferably 10 mm or less. As described above, in the conventional tire with a high bead filler height, the carcass cord is repeatedly input to the folded portion by market input, thereby promoting the strength reduction of the folded portion of the carcass cord. Since there is a concern that the cord breaks down, it is required that the strength is not easily lowered by the compression input, that is, the fatigue property is good. In the present invention, since the bead filler 7 has a small shape, the turned-up portion of the carcass cord immediately follows the inner surface of the tire. When the bending input is applied, the carcass cord exists outside the bending deformation, and only the tensile input, not the compression input, is applied to the cord. As a result, it is possible to suppress the promotion of the strength reduction of the carcass cord at the folded portion caused by repeated bending deformation, and it is possible to suppress the occurrence of a failure due to the cord breakage. The tire performance can be controlled. As a result, even in a highly rigid carcass cord, it is possible to enjoy the merit of improving the maneuverability while securing the market durability.

  Here, the height of the bead filler 7 in the present invention means the height of the bead filler 7 in the tire radial direction in a no-load state in which a tire is assembled to an applicable rim and filled with a specified air pressure. The applicable rim means a rim defined in the following standard, and the prescribed air pressure means an air pressure defined in accordance with the maximum load capacity in the following standard. The standard is an industrial standard effective in an area where tires are produced or used. For example, in the United States, the Tire and Rim Association Inc. In Europe, it is Standards Manual of The European Tire and Rim Technical Organization, and in Japan it is JATMA Year book of Japan Automobile Tire Association.

  In the present invention, the height of the bead filler 7 is set to 15 mm or less because the shape and numerical value of the rim flange are standardized. This is because the code can be avoided. Further, when the height of the bead filler 7 is 15 mm or less, there is a possibility that the compression input is applied to the end of the ply depending on the bending rigidity around the bead, the internal pressure condition, input, and the like. By setting the thickness to 10 mm or less, compression input can be reliably avoided regardless of the type of tire. There is no restriction | limiting in particular in the lower limit of the height of the bead filler 7, For example, it can also be set to 0 mm (no bead filler rubber).

  In the present invention, it is only important to combine the application of high-rigidity organic fibers to the carcass cord with a specific carcass arrangement and a bead filler structure, and thereby the desired effect of the present invention can be obtained. It can be done. About another point, it can comprise suitably according to a conventional method as desired, and it does not restrict | limit in particular.

  The organic fiber cord used in the carcass ply of the present invention is not particularly limited as long as it satisfies the above-described conditions relating to the elastic modulus, and examples thereof include cellulosic fibers, aramids, polyketone fibers, and the like. Preferably, it shall consist of a cellulosic fiber. Examples of the cellulosic fibers include rayon and lyocell, as well as those made from a cellulose derivative obtained by chemically esterifying or etherifying cellulose, which is a natural polymer, as a raw material. In particular, in the present invention, a lyocell cord having a high elastic modulus compared with rayon and having a stable elastic modulus from a low temperature to a high temperature is preferably used as the organic fiber cord.

In the present invention, the following formula:
Nt = tan θ = 0.001 × N × √ (0.125 × D / ρ)
Where N is the number of cord twists (times / 10 cm), D is half the total decitex (dtex) of the cord, and ρ is the specific gravity of the cord (g / cm ³ ) The twist coefficient Nt of the organic fiber cord is preferably 0.5 to 0.8. If the twist coefficient Nt is too small, the tire uniformity is deteriorated because the fiber has almost no thermal shrinkage. On the other hand, if the twist coefficient Nt is too large, the direction of lower rigidity cannot be achieved and the desired cord elastic modulus range cannot be achieved. And the further improvement effect of steering performance is not acquired.

  Further, although not shown, in the tire of the present invention, an inner liner is usually disposed in the innermost layer of the tire, and a tread pattern is appropriately formed on the tread surface. Further, in the pneumatic radial tire of the present invention, the gas filled in the tire can be normal or air having a changed oxygen partial pressure, or an inert gas such as nitrogen.

Hereinafter, the present invention will be described in more detail with reference to examples.
As the carcass cord, an organic fiber cord satisfying the conditions shown in the table below is applied, and the height of the bead filler having a triangular cross section is changed as shown in the table below to obtain a tire size 215 / 45R17. Thus, pneumatic radial tires of Examples and Comparative Examples were produced. One carcass ply was used, and the carcass cord was folded around the bead core from the inside of the tire to the outside. Further, the belt layer was made of two layers, and was composed of a rubberized layer of a steel cord extending inclined at an angle of ± 30 ° with respect to the tire equatorial plane. Each of the obtained test tires was evaluated for durability and maneuverability according to the following.

<Durability>
Each test tire was run at 80 km / h on a drum tester under the conditions of a specified internal pressure and a specified load, and the time until failure occurred was measured. The results are shown as an index with the time until failure occurrence of Comparative Example 1 as 100. The larger the value, the better the durability.

<Maneuverability>
Each test tire was mounted on an actual vehicle, a driver's feeling test was conducted by a driver, and the maneuverability was scored with a perfect score of 100 points. The higher the score, the better the maneuverability.

＊１）Ｎｔ＝ｔａｎθ＝０．００１×Ｎ×√（０．１２５×Ｄ／ρ）
（式中、Ｎはコードの撚り数（回／１０ｃｍ）であり、Ｄはコードの総デシテックスの半分（ｄｔｅｘ）であり、ρはコードの比重（ｇ／ｃｍ^３）である）で定義される撚り係数Ｎｔである。
＊２）１８０℃でのコード１本あたり２９．４Ｎの応力負荷時における引張弾性率である。

* 1) Nt = tan θ = 0.001 × N × √ (0.125 × D / ρ)
Where N is the number of cord twists (times / 10 cm), D is half the total decitex (dtex) of the cord, and ρ is the specific gravity of the cord (g / cm ³ ) The twist coefficient Nt.
* 2) Tensile modulus at stress load of 29.4N per cord at 180 ° C.

  As shown in the above table, in the test tire of each example, a high-rigidity organic fiber cord that satisfies the conditions of the present invention is used as a carcass cord, and a specific carcass arrangement and a bead filler structure are satisfied. It is clear that good results are obtained in a balanced manner in terms of both durability and maneuverability as compared with the test tires of the comparative examples that do not satisfy such conditions.

DESCRIPTION OF SYMBOLS 1 Bead core 2 Carcass 2a, 2b Carcass ply 3 Belt 4 Belt reinforcement layer 5 Tread 6 Side reinforcement rubber layer 7 Bead filler 10, 20 Pneumatic radial tire 11 Bead part 12 Side wall part 13 Tread part

Claims (6)

At least one sheet having a pair of bead portions and sidewall portions, and a tread portion connected to the sidewall portions, and extending in a toroid shape across a pair of bead cores embedded in the pair of bead portions. In a pneumatic radial tire having a carcass made of the above carcass ply as a skeleton,
The carcass ply is made of an organic fiber cord having a tensile elastic modulus of 40 cN / dtex or more at a stress load of 29.4 N per cord at a temperature of 180 ° C., and all the carcass cords are arranged inside the tire around the bead core. A pneumatic radial tire characterized in that a bead filler that is folded outward from the tire and disposed outside the bead core in the tire radial direction has a triangular cross section with a height of 15 mm or less.   2. The pneumatic radial tire according to claim 1, wherein the organic fiber cord has a tensile elastic modulus of 100 cN / dtex or less at a stress load of 29.4 N per cord at a temperature of 180 ° C. 3.   The pneumatic radial tire according to claim 1 or 2, wherein the organic fiber cord is made of a cellulosic fiber.   The pneumatic radial tire according to claim 3, wherein the organic fiber cord is made of lyocell. The following formula,
Nt = tan θ = 0.001 × N × √ (0.125 × D / ρ)
Where N is the number of cord twists (times / 10 cm), D is half the total decitex (dtex) of the cord, and ρ is the specific gravity of the cord (g / cm ³ ) The pneumatic radial tire according to any one of claims 1 to 4, wherein a twist coefficient Nt of the organic fiber cord is 0.5 to 0.8.   The pneumatic radial tire according to any one of claims 1 to 5, wherein a side reinforcing rubber layer is disposed along the inner surface of the carcass over the entire or substantially entire region of the sidewall portion.

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