Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Patent
1997-03-13
1999-04-20
Johnstone, Adrienne
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
57200, 57902, 152451, 152531, B60C 918, B60C 920, B60C 922
Patent
active
058948759
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a pneumatic radial tire using steel cords in a belt layer thereof, more specifically it relates to a pneumatic radial tire suitable for use in a light truck (LT) or a recreational vehicle (RV).
BACKGROUND ART
In the past, for the belt material of a pneumatic radial tire for a light truck (LT) or a recreational vehicle (RV), steel cords having twisted structures of 2+7, 2+6, 3+6, etc. were widely used. These twisted steel cords, however, are high in cost since two twisting processes are necessary for the twisting and are low in corrosion resistance since there is insufficient penetration of rubber into the steel cord, and therefore, there was the problem of the tire having a lower durability.
To eliminate this defect of the steel cords requiring two twisting processes, a flattened (or ellipse or oval) open structure of a 1.times.4 or 1.times.5 twist structure has been developed. However, as a result of studies by the present inventors, it has been found that a flattened open 1.times.4 or 1.times.5 twist structure is insufficient in strength as the belt material of a pneumatic radial tire for a light truck or a recreational vehicle. Therefore, consideration has been given to making it a 1.times.6 twist structure or a larger 1.times.7 twist structure. However, the inventors found that there was the defect that the cord shape became unstable in the case of a 1.times.7 structure.
However, even when adopting a flattened open 1.times.6 twist structure, it was necessary to make the flatness ratio (short diameter D.sub.S /Long diameter D.sub.L) smaller in order to ensure that the rubber fully penetrated into the steel cord. Therefore, the long diameter D.sub.L becomes inevitably larger. As a result, when arranging the cord so that its long diameter direction was along the planar direction of the belt layer, when the count of the steel cord is made equivalent to the count of the belt layer used in the past, the interval between cords becomes smaller, and therefore, the problem occurs that the durability of the belt edges falls.
Further, in the case of a 1.times.6 twist structure, there is the problem that the twist structure becomes unstable compared with the 1.times.4 or 1.times.5 twist structure and tends to cause defects in the twisting.
DISCLOSURE OF INVENTION
Accordingly, the object of the present invention is to provide a pneumatic radial tire which, when adopting a cost effective 1.times.6 twist structure for the steel cord of the belt layer, is capable of minimizing the long diameter of the cord to such an extent that the rubber can stably penetrate into the cord, whereby the twist structure is stabilized, and the steering stability and durability of the belt edge portion are improved.
In accordance with the present invention, there is provided a pneumatic radial tire comprising a belt layer, comprised of steel cords having a lateral flat cross-section, arranged around an outer periphery of a tread portion of the carcass layer so that the diameter direction of the steel cords is made to follow the planar direction of the belt layer, wherein filaments having a diameter d of 0.20 to 0.40 mm, the long diameter D.sub.L and twist pitch P of the steel cord when taken out from the tire are, with respect to the filament diameter d, as follows: 0.25 kg to 5.0 kg is 0.25% or less.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be explained in further detail with reference to the drawings, wherein:
FIG. IA and FIG. IB are each a lateral cross-section view of a steel cord used in a belt layer of a pneumatic radial tire of the present invention;
FIG. 2 is a cross-sectional view taken along the meridian of an example of a pneumatic radial tire according to the present invention;
FIG. 3 is a graph illustrating the relationship between the long diameter D.sub.L and the filament diameter d of the cord; and
FIG. 4 is a cross-sectional view taken along the meridian of another example of a pneumatic radial tire according to the present invention.
BES
REFERENCES:
patent: 4938015 (1990-07-01), Kinoshita
Database WPI. Section Ch, Week 9414, Derwent Publications Ltd., London, GB; Class A95, AN 94-115661, XP002060666 & JP 06 065 877 (Kanai H), Mar. 8, 1994, Abstract.
Form PCT/ISA/210 for PCT/JP96/00118.
Igarashi Eiji
Kanehira Yoshiki
Kawai Tosio
Komatsu Ryuzou
Masaki Takeo
Johnstone Adrienne
The Yokohama Rubber Co. Ltd.
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