Brakes – Internal-resistance motion retarder – Including means connecting thrust member to load
Reexamination Certificate
2001-08-31
2004-02-03
Rodriguez, Pam (Department: 3683)
Brakes
Internal-resistance motion retarder
Including means connecting thrust member to load
C188S313000, C188S322140, C188S322160, C267S064110, C280S124155
Reexamination Certificate
active
06684990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tube structure and a tube manufacturing method for a hydraulic damper.
2. Description of the Related Art
A. In a conventional tube structure for a hydraulic damper, as disclosed in Japanese Patent Application Laid-Open Publication No. 11-182610, by a drawing formation or extrusion formation such as of an aluminum alloy, an outer circumferential wall of an inner tube is integrally joined to an inner circumferential wall of an outer tube, via ribs. According to a tube structure with the integrated inner and outer tubes, because the outer tube is supported by the inner tube via ribs, the tubes' strengths are increased, and the inner and outer tube are centered by the ribs, with an enhanced assembly workability.
However, there are the following problems:
(1) The size of a reservoir formed by a gap between the outer tube and the inner tube is subject to restriction of durability of jigs used for the formation, with a difficulty to render the outer tube diameter narrow to have a compact tube size with a necessary reservoir volume secured.
(2) The outer tube and the inner tube are unable to be made of different materials (different kinds of material or metal).
(3) Because the outer tube and the inner tube are completely integrated, a fraction of axial length of the outer tube by which upper and lower end parts of the outer tube protrude relative to upper and lower end parts of the inner tube generates a small resilient thrust force, with a difficulty for a shaft sealing part or a bottom piece to be ensured to be held by the thrust force between the inner tube and the outer tube.
It is an object of the present invention to implement a hydraulic damper with an enhanced tube strength and with a necessary volume secured for a reservoir chamber between an outer tube and an inner tube, allowing for a tube size to be compact, for the outer tube and the inner tube to be made of different materials as well, and for incorporated components between the inner tube and the outer tube to receive a great thrust force, to be held with ease in an ensured manner.
B. In a conventional hydraulic damper, as disclosed in Japanese Patent Application Laid-Open Publication No. 11-182610, an outer circumferential wall of an inner tube is integrally joined by ribs to an inner circumferential wall of an outer tube. This hydraulic damper has a shaft sealing part provided for a piston rod and fixed between an upper end part of the inner tube and an upper end part of the outer tube, and a bottom piece fixed between a lower end part of the inner tube and a lower end part of the outer tube.
According to the hydraulic damper of a tube structure with the integrated inner and outer tubes, the outer tube is supported by the inner tube via the ribs, allowing for the rigidity of the outer tube to be increased, and for the inner and outer tubes to be centered by the ribs, with an enhanced assembly workability.
However, there are the following problems:
(1) The shaft sealing part interposed between the inner and outer tubes, which are integrated with each other, is fixed simply by an elastic thrust force generated by a short fraction of axial length of the outer tube by which the upper end part of the outer tube projects above the upper end part of the inner tube, and an elastic thrust force generated by a seal constituting the shaft sealing part. Therefore, the thrust forces are small so that they may be lost by the difference in amount of thermal expansion due to a difference between a material (such as an aluminum alloy) of the outer tube and a material (such as a steel) of a rod guide constituting the shaft sealing part, as well as by deterioration of a rubber member about a core metal constituting the seal, resulting in a play at the shaft sealing part.
(2) Also, the bottom piece interposed between the inner tube and the outer tube may, like the shaft sealing part, have thrust forces lost by the difference in amount of thermal expansion between the outer tube and the bottom piece, resulting in a play at the bottom piece.
It is an object of the present invention to provide a hydraulic damper of a tube structure with integrated inner and outer tubes, allowing for thrust forces to be maintained on a shaft sealing part.
It is another object of the present invention to provide a hydraulic damper of a tube structure with integrated inner and outer tubes, allowing for thrust forces to be maintained on a bottom piece.
C. In a hydraulic damper of a tube structure with integrated inner and outer tubes, it is impossible for a sub-assembly with a bottom piece fitted in advance such as by compression-joining into an end part of the inner tube to be placed in the outer tube to be assembled. In a conventional art, therefore, after a bottom piece is fitted in an inner tube, a cap for holding the bottom piece is welded to an end part of an outer tube.
Accordingly, there are the following problems:
(1) Because of a welding process accompanied after incorporation of the bottom piece, welding spatters may go inside the outer tube, contaminating valves of the bottom piece, degrading the quality of a resultant hydraulic damper.
(2) As the welding is performed generally within a processing line for the inner and outer tubes, dust and the like may enter the inner and outer tubes in a material handling stage up to a subsequent assembly line for the inner and outer tubes having the bottom piece as well as the cap incorporated. It is very difficult to remove dust by cleaning inside of the inner and outer tubes having the bottom piece as well as the cap incorporated.
It is an object of the present invention to provide a hydraulic damper of a tube structure with integrated inner and outer tubes, which does not need a welding after a bottom piece is incorporated in the inner tube, allowing for the bottom piece to be incorporated in the inner tube on an assembly line, and for the quality of a resultant hydraulic damper to be raised with ease.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a tube structure for a hydraulic damper of a double tube structure including an outer tube and an inner tube, wherein the outer tube and the inner tube are separately formed by extrusion, respectively, and ribs are integrally formed on an inside wall of the outer tube or an outside wall of the inner tube to be used. The inner tube is inserted inside the outer tube and the outer tube is forced to be reduced in diameter to have the outer tube compression-joined onto the inner tube, whereby the outer tube and the inner tube are integrally joined.
Furthermore, there is provided a tube manufacturing method for a hydraulic damper of a double tube structure including an outer tube and an inner tube, comprising the steps of:
separately forming the outer tube and the inner tube by extrusion, respectively, with ribs integrally formed on an inside wall of the outer tube or an outside wall of the inner tube; and
having the inner tube inserted inside the outer tube and a core bar inserted in the inner tube, diameter-reducing the outer tube to be compression-joined onto the inner tube to have the outer tube and the inner tube integrally joined.
Furthermore, there is provided a thrust force holding structure of a hydraulic damper in which an outer circumferential wall of an inner tube is integrally fastened by ribs to an inner circumferential wall of an outer tube, and a shaft sealing part for a piston rod to be inserted into the inner tube is fixed between an upper end part of the inner tube and an upper end part of the outer tube, wherein
a compression spring member is interposed within a range sandwiching the shaft sealing part between the upper end part of the inner tube and the upper end part of the outer tube.
Furthermore, there is provided a thrust force holding structure of a hydraulic damper in which an outer circumferential wall of an inner tube is integrally fastened by ribs to an inner circumferential wall of an outer tube, and a bottom
Orum & Roth
Rodriguez Pam
Showa Corporation
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