JP2011143823A - Pneumatic radial tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire enhanced in bead part durability more than before by effectively preventing separation from a winding end of a carcass ply cord. <P>SOLUTION: This pneumatic radial tire 10 has a carcass layer 2 extending toroidally to stretch over a pair of bead cores 1 as a frame, and an end part of the carcass layer 2 is wound around the bead cores 1 from the inside of the tire 10 to the outside. The product A of cord bending rigidity (kg/mm) defined by inclination at 2-6 mm pushing-in deformation of stress-bending displacement curve obtained by a cord 3-point bending test of a steel cord constituting the carcass layer 2 and the number of hitting (number/50 mm) in a bead winding part is ≤0.175. The product B of cord tensile rigidity (kg) defined by load at 1.0% tension of the steel cord constituting the carcass layer 2 and the number of hitting (number/50 mm) in the bead winding part is ≥1,600. <P>COPYRIGHT: (C)2011,JPO&INPIT

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 that prevents separation from a carcass ply cord winding end and has improved bead portion durability.

  Conventionally, in a pneumatic radial tire, in order to prevent a separation failure from the end portion of the carcass ply, various improvements have been made regarding the position of the end portion, the bead core structure, the reinforcing method, the shape of the bead portion, and the like. In order to prevent separation from the winding end of the carcass ply cord wound around the bead core, the shape and material of the reinforcing layer (chafer) arranged outside the winding portion of the carcass ply cord can be devised. A method for reducing the distortion at the end of the carcass ply and a method for reducing the distortion at the end by devising the height and shape of the carcass ply winding portion itself are generally used as conventional improvements.

  For example, in Patent Document 1, by providing a bent portion at the ply end winding portion under a predetermined condition, failure from the end portion of the carcass ply can be prevented and durability of the bead portion can be improved. Is disclosed.

JP 2000-225816 A (Claims etc.)

  Conventionally, the reinforcing layer disposed outside the carcass ply winding end in order to increase the durability of the bead portion is effective in preventing the deformation of the entire bead portion. Was not necessarily effective. Further, with respect to the height of the carcass ply winding portion itself, the distortion at the end can be reduced by increasing the height, but there is a problem in that separation occurs in the portion near the bead core.

  Accordingly, an object of the present invention is to provide a pneumatic radial tire that solves such problems, effectively prevents separation from the winding end of the carcass ply cord, and has improved the bead portion durability more than ever. There is to do.

  In order to solve the above-mentioned problems, the present inventor has conducted various experimental studies. As a result, the generation of local strain at the ply end is controlled in the bead portion (bead core and carcass layer) at the time of air filling, load application, or change with time. It was found that the following two deformations occurred.

1) Due to the tension applied to the carcass layer, a deformation in which the carcass layer is pulled out from the bead core occurs in the cross section in the tire width direction, and this deformation causes a ply end local strain. Hereinafter, this deformation is referred to as “draw-out deformation”.
2) Due to the tension applied to the carcass layer, a deformation in which the bead core expands in the tire radial direction occurs, and this deformation reduces the ply end local strain due to the pull-out deformation. Hereinafter, this deformation is referred to as “bead expansion deformation”.

  In other words, in order to suppress the ply end local strain, it is necessary to reduce the pull-out deformation and increase the bead expansion deformation. Therefore, important characteristics necessary for the steel cord constituting the carcass layer. For the following two reasons, the bending rigidity of the cord is low and the tensile rigidity in the cord direction is high.

1) When the steel cord of the carcass layer is tightly wound around the bead core, the above-mentioned pull-out deformation is less likely to occur, and the lower the bending rigidity of the cord, the tighter the carcass ply can be wound around the bead core during tire manufacture. This is possible, and the ply end local strain can be reduced. If the bending rigidity of the cord is high, the force to return to the original straight state after bending is strong. For this reason, the wire reinforcement layer adhered along the bead core may float so as to float from the carcass ply to return to the original flat state, and the winding property may be reduced.
2) As the tensile rigidity of the cord is higher, the tension of the carcass layer is firmly transmitted to the bead core, so that the deformation for expanding the bead core can be increased, and the ply end local strain can be reduced.

  From this point of view, the present inventors have further studied and found that the effect of improving the ply end local strain can be obtained by using a cord satisfying specific physical properties as the steel cord of the carcass layer. It came to complete.

That is, the present invention provides a pneumatic radial tire in which a carcass layer extending in a toroid shape between a pair of bead cores is used as a skeleton, and ends of the carcass layers are wound around the bead cores from the inside to the outside of the tire. In
The cord bending stiffness (kg / mm) defined by the inclination of 2-6 mm indentation deformation of the stress-bending displacement curve obtained by the three-point bending test of the steel cord constituting the carcass layer, and the bead winding portion The product A with the number of driven wires (pieces / 50 mm) is 0.175 or less, and
The product B of the cord tensile rigidity (kg) defined by the load at 1.0% tension of the steel cord constituting the carcass layer and the number of driven portions (pieces / 50 mm) at the bead-wrapped portion is 1600. It is the above, It is characterized by the above.

  The present invention is particularly effective when applied to a heavy-duty pneumatic radial tire having a ply rating of 16 or more.

  According to the present invention, by adopting the above-described configuration, it is possible to effectively prevent separation from the winding end of the carcass ply cord and to realize a pneumatic radial tire with improved bead portion durability. It was.

1 is a one-side cross-sectional view in a width direction showing a pneumatic radial tire according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail.
FIG. 1 shows a cross-sectional side view in the width direction of an example of the pneumatic radial tire of the present invention. As shown in the figure, the pneumatic radial tire 10 of the present invention has a carcass layer 2 extending in a toroidal shape across a pair of bead cores 1, and the end of the carcass layer 2 is formed around the bead core 1. It is wound from the inside to the outside. In the present invention, it is important that the carcass layer 2 satisfies the following conditions with respect to the steel cord rigidity per unit width.

  In the present invention, first, the cord bending stiffness (kg / mm) defined by the inclination at the time of 2-6 mm indentation deformation of the stress-bending displacement curve of the steel cord constituting the carcass layer 2 obtained by the cord three-point bending test. ) And the number of driven-in portions (pieces / 50 mm) at the bead-wrapped portion is required to be 0.175 or less. The reason why A is set to 0.175 or less is that when A is 0.175 or less, the inner surface floating during the production is clearly improved, and the bead winding property of the carcass ply is improved. In terms of performance, the smaller the value, the better. However, if the value is less than 0.010, a problem occurs in productivity and a problem of manufacturing defect rate deterioration occurs. In particular, it is 0.010 or more and 0.160 or less.

  Further, in the present invention, the cord tensile rigidity (kg) defined by the load at the time of 1.0% tension of the steel cord constituting the carcass layer 2 and the number of driven in the bead-wrapped portion (pieces / 50 mm) Product B must be 1600 or more. By setting this value to 1600 or more, the bead expansion deformation can be increased, and the effect of reducing the ply end local strain can be obtained. B is preferably 1750 or more and 6000 or less.

  In the present invention, the bending rigidity (bending resistance) and tensile rigidity of the steel cord used for the carcass layer 2 satisfy the above, thereby suppressing pull-out deformation and increasing bead expansion deformation, The ply end local strain can be clearly suppressed. The carcass cord used in the present invention may have any twisted structure and filament diameter (elementary wire diameter) as long as the steel cord satisfies the above relationship. Can be improved. For example, the twisted structure may be any structure such as single twist, layer twist, double twist, no twist, and flat cross section. In the present invention, the number of driving in the bead-wrapped portion is a problem because the number of ply driving in the product tire is greatly different for each part in the production method of the tire. In this case, the bead-wrapped portion, which has substantially the same number of plies in the molded product tire, is used as a reference.

  Further, in the present invention, the effect of the present invention can be used more advantageously as the number of driven cords having a smaller wire diameter is used, but the distance between adjacent steel cords in the layer is preferably 0.15 mm or more. If the distance between adjacent steel cords in the layer is less than 0.15 mm, a fine crack generated at the end of the steel cord grows between adjacent steel cords, and then leads to ply end separation. The speed of progress will be much faster. The distance between adjacent steel cords in the layer is more preferably 0.25 mm or more, for example, in the range of 0.25 to 1.5 mm.

  In the present invention, the steel cord used for the carcass layer 2 only needs to satisfy the above conditions, and other details of the tire structure and the material of each member are not particularly limited, and are conventionally known. It can be configured by appropriately selecting from the above. For example, the number of carcass plies constituting the carcass layer 2 can be one, and at least two, preferably 1 to 5 crossing belt layers 3 on the outer side of the carcass layer 2 in the tire radial direction. The angle with respect to the tire circumferential direction can be set to, for example, 0 to 70 °.

  A tread portion 4 is disposed on the outer periphery of the crown portion of the crossing belt layer 3, and a tread pattern is appropriately formed on the surface of the tread portion 4. Further, a bead filler (not shown) is disposed outside the bead core 1 in the tire radial direction, and an inner liner is disposed in the innermost layer of the tire. Furthermore, in the tire of the present invention, as the gas filled in the tire, it is possible to use normal or air having a changed oxygen partial pressure, or an inert gas such as nitrogen.

  The present invention is particularly effective when applied to a heavy-duty pneumatic radial tire having a ply rating of 16 or more.

Hereinafter, the present invention will be described more specifically with reference to examples.
In order to confirm the effect of the present invention, only the steel cord used for the carcass ply of the tire of the example to which the present invention is applied and the tire of the comparative example at a tire size of 11R22.5 is shown in the following table. It was made by changing to One carcass ply and a ply rating of 16 were used. Further, on the outer side in the tire radial direction of the carcass layer, four crossing belt layers are arranged in order from the first layer so that the angles with respect to the tire circumferential direction are + 50 °, + 20 °, −20 °, and −20 °. .

  Each of the obtained test tires was subjected to a tire durability test using a drum testing machine. The drum test consists of normal internal pressure (air pressure corresponding to the maximum load capacity in the applicable size / ply rating for JATMA YEAR BOOK), standard rim (described in JATMA YEAR BOOK), speed 60 km / h, maximum load (JATMA YEAR BOOK at It was carried out under the condition of 150% load application (maximum load capacity in application size and ply rating). The evaluation was performed by measuring the time until ply end separation occurred in the bead portion of each test tire. The results were expressed as an index with the time taken for the tire of Comparative Example 1 to generate ply end separation as 100. The higher this number, the better the result. The results are also shown in the following table.

＊１）Ａ：カーカスプライコードの、コード３点曲げ試験で得られる応力−曲げ変位曲線の２〜６ｍｍ押し込み変形時の傾きで定義されるコード曲げ剛性（ｋｇ／ｍｍ）×ビード巻付き部での打込み本数（本／５０ｍｍ）の値である。なお、曲げ剛性の測定は、サンプル長さ２３５ｍｍ、曲げＲ１０ｍｍ、曲げ間隔６０ｍｍにて実施した。
＊２）Ｂ：カーカスプライコードの、１．０％引張時の荷重で定義されるコード引張剛性（ｋｇ）×ビード巻付き部での打込み本数（本／５０ｍｍ）の値である。なお、引張剛性の測定は、サンプル長さ４００ｍｍにて実施した。

* 1) A: Cord bending stiffness (kg / mm) defined by the inclination of 2-6mm indentation deformation of the stress-bending displacement curve of the carcass ply cord obtained by the three-point bending test of the cord. This is the value of the number of implantations (number / 50 mm). The bending stiffness was measured with a sample length of 235 mm, a bending R of 10 mm, and a bending interval of 60 mm.
* 2) B: Cord tensile stiffness (kg) defined by the load at 1.0% tension of the carcass ply cord × value of the number of driven portions (pieces / 50 mm) at the bead-wound portion. The tensile rigidity was measured at a sample length of 400 mm.

  As can be seen from the results in the above table, according to the present invention, it is clear that the separation from the winding end of the carcass ply cord can be effectively prevented and the durability of the bead portion can be further enhanced.

1 Bead core 2 Carcass layer 3 Cross belt layer 4 Tread part 10 Pneumatic radial tire

Claims (2)

In a pneumatic radial tire in which a carcass layer extending in a toroid shape between a pair of bead cores is used as a skeleton, and an end portion of the carcass layer is wound around the bead core from the inside to the outside of the tire.
The cord bending stiffness (kg / mm) defined by the inclination of 2-6 mm indentation deformation of the stress-bending displacement curve obtained by the three-point bending test of the steel cord constituting the carcass layer, and the bead winding portion The product A with the number of driven wires (pieces / 50 mm) is 0.175 or less, and
The product B of the cord tensile rigidity (kg) defined by the load at 1.0% tension of the steel cord constituting the carcass layer and the number of driven portions (pieces / 50 mm) at the bead-wrapped portion is 1600. A pneumatic radial tire characterized by the above.   The pneumatic radial tire according to claim 1, wherein the pneumatic tire is a heavy-duty pneumatic radial tire having a ply rating of 16 or more.

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