Resilient tires and wheels – Tires – resilient – Pneumatic tire or inner tube
Reexamination Certificate
2000-03-24
2002-07-30
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Pneumatic tire or inner tube
C057S212000, C057S311000, C057S902000, C152S451000
Reexamination Certificate
active
06425428
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a steel cord used to reinforce rubber articles, and a method of manufacturing the steel cord, and particularly to a steel cord used as a reinforcing material for a belt layer in a pneumatic tire, and a method of manufacturing the steel cord.
Further, the present invention also relates to a pneumatic radial tire in which a steel cord is used as a reinforcing material for a belt layer.
BACKGROUND ART
As a reinforcing material of a pneumatic radial tire, conventionally, a steel cord formed by twisting a plurality of steel filaments subjected to brass plating has been widely used.
Regions in which the steel cords are used as reinforcing materials of a radial tire are principally a carcass and a belt layer between the carcass and a tread rubber. The belt layer usually includes two or more layers of reinforcement plies. Each of the reinforcement plies is comprised of a large number of steel cords arranged in a transverse direction of the tire and embedded in rubber. Further, steel cords for each reinforcement ply are disposed at a predetermined angle of inclination to the equatorial plane of the tire and respective steel cords of adjacent reinforcement plies are disposed so as to cross each other, that is, so that angles of inclination thereof are formed in opposite directions with respect to the equatorial plane of the tire.
Usually, the steel cord is manufactured by twisting steel filaments in a helical manner by using a buncher-type or tubular-type wire twisting machine. Accordingly, the most common shape of a cross section of the steel cord is substantially circular. On the other hand, in order to improve penetration of rubber, improve tensile rigidity, and reduce the thickness of a belt layer, and the like, a steel cord having a flat cross section has been proposed. For example, an example of a steel cord having a layer twisted structure is given below.
Japanese Patent Application Laid-Open (JP-A) No. 9-156314 discloses a steel cord having a substantially elliptical cross section, which comprises a core having two filaments disposed in parallel and a sheath formed by twisting five to eight filaments around and close to the core. Further, JP-A No. 9-158965 discloses a steel cord having an elliptical cross section or having an elliptical or a substantially circular cross section depending on portions in a longitudinal direction of the steel cord, which steel cord is comprised of a core having a plurality of filaments transversely arranged in parallel without being twisted, and a sheath formed by twisting a plurality of filaments around and in externally contact with the core. Moreover, JP-A No. 9-158066 discloses a steel cord having a 2+6 structure, comprising a core having two filaments twisted at a twist pitch of 30 mm or more, in which the ratio of a minor axis to a major axis in any cross section of the cord is in the range from 100% to 68.4%.
On the other hand, there has recently been demanded for reduction in weight of steel cord required for each tire in order to achieve lightening of a tire from the standpoint of resources/energy saving or environmental protection.
However, when a weight of steel cord used in a belt layer of a tire is reduced, tensile rigidity in a tire circumferential direction of a belt layer which is a composite body of steel cord and rubber deteriorates. Accordingly, an amount of deformation of the belt layer during rolling of tires increases and a tread is apt to be worn down. In addition, rolling resistance increases and fuel consumption cannot be reduced. Further, it is not possible to achieve improvement in controlling stability, which has been demanded in association with the advance of vehicle performance. In order to reduce the weight of steel cord with the tensile strength of the steel cord being maintained at a sufficient level, it is necessary to use filaments having high tensile strength. For this reason, there have also been used, as a filament, a high-strength steel wire in which tensile strength T (N/mm
2
) and filament diameter d (mm) are set so as to satisfy the relation T≧2250−1450 logd, and an ultra high-strength steel wire which satisfies the relation T≧2750−1450 logd.
On the other hand, when a steel cord having a high strength per unit weight is used as a reinforcing material of a tire so as to only reduce the weight of the steel cord used, the above-described object cannot sufficiently be achieved.
Accordingly, in order that tensile rigidity of a belt layer which is a composite body of steel cord and rubber be improved, an angle of inclination of the steel cord in a belt layer, a distance between reinforcement plies, and the like have been designed in consideration of not only the tensile rigidity of steel cord, but also shear deformation resistance of rubber between steel cords. However, when a conventional layer twisted steel cord having a compressed cross section is used, the shear deformation resistance of rubber between steel cords cannot sufficiently be utilized. Therefore, it was difficult to obtain a belt layer whose weight is light and whose tensile rigidity is high.
In view of the above-described circumstances, it is a first object of the present invention to provide a steel cord in which tensile rigidity of the steel cord itself is high, and when the steel cord is used as a reinforcing material for a belt layer, shear deformation resistance of rubber between steel cords is effectively utilized, thereby allowing improvement in tensile rigidity of the belt layer per unit weight of steel cord used.
A second object of the present invention is to provide a method of manufacturing the steel cord adapted to achieve the first object of the present invention.
Further, a third object of the present invention is to provide a pneumatic radial tire in which the steel cord adapted to achieve the first aspect of the present invention is used as a reinforcing material for a belt layer, thereby allowing lightening of the tire, reduction in fuel consumption, and improvement in controlling stability.
DISCLOSURE OF THE INVENTION
In order to achieve the first object of the present invention, a steel cord comprising: a core; and an outer layer sheath including plural filaments, each filament having a diameter, all the diameters being substantially equal and said plural filaments being twisted around the core at substantially the same pitches, wherein said steel cord has a flat side surface portion on which at least two of said plural filaments forming the outer layer sheath are substantially arranged.
A conventional compressed layer twisted structure has a substantially elliptical cross section and has no flat side surface portion. On the other hand, the steel cord of the present invention has the above-described feature, and therefore, shear deformation resistance of rubber interposed between steel cords is effectively utilized. The reasons will be hereinafter explained.
Here, there is supposed a belt layer in which reinforcement plies formed by a large number of steel cords arranged in a transverse direction of a tire and embedded in rubber are laminated in a radial direction of the tire so that steel cords in adjacent reinforcement plies cross each other with rubber interposed therebetween. When a conventional steel cord having a substantially elliptical cross section is used as a reinforcing material, even if the steel cord is disposed so that the direction of a major axis thereof is placed parallel with a transverse direction of the reinforcement plies, respective bent side surfaces of adjacent steel cords in the direction in which the reinforcement plies are laminated face each other with rubber interposed therebetween. Accordingly, the thickness of rubber (hereinafter referred to as layer-to-layer rubber) interposed between the adjacent steel cords in the direction in which the reinforcement plies are laminated is not uniform. On the other hand, when the steel cord of the present invention is used as a reinforcing material and respective flat side surface
Kusaba Noboru
Obana Naohiko
Onuma Shuichi
Bridgestone Corporation
Johnstone Adrienne C.
Sughrue & Mion, PLLC
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