Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Reexamination Certificate
2000-09-22
2003-06-10
Look, Edward K. (Department: 3745)
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
C092S172000
Reexamination Certificate
active
06575080
ABSTRACT:
This application is based on Japanese Patent Application No. 11-270355 filed Sep. 24, 1999, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of producing a body member for a piston for a awash plate type compressor, and more particularly to a method of producing, by die-casting, such a body member having a hollow cylindrical head portion.
2. Discussion of the Related Art
A swash plate type compressor is adapted to compress a gas by a plurality of pistons which are reciprocated by a rotary movement of a swash plate. In general, the piston includes a head portion slidably fitted in a cylinder bore formed in a cylinder block of the compressor, and an engaging portion which sidably engages the swash plate. For reducing the weight of the piston, it has been proposed to form the piston with a hollow cylindrical head section. As one example of the method of producing such a piston, the assignee of the present invention proposed in JP-A-11-152239 a method of producing a blank for the piston, comprising the steps of preparing a body member including a hollow head section which is closed at one of its opposite ends and is open at the other end, and an engaging section which is formed integrally with the head section; and fixing a closing member prepared separately from the body member, to the body member so as to close the open end of the head section. While the closing member may be produced by any method, the body member is preferably produced by die-casting.
SUMMARY OF THE INVENTION
The present invention was made in the light of the background art described above. It is an object of the present invention to provide a single-headed piston for a swash plate type compressor, which has a reduced operating noise.
The object indicated above may be achieved according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depend from the other form or forms, where appropriate, to indicate and clarify possible combinations of technical features of the present invention, for easier understanding of the invention. It is to be understood that the present invention is not limited to the technical features and their combinations described below. It is also to be understood that any technical feature described below in combination with other technical features may be a subject matter of the present invention, independently of those other technical features.
(1) A single-headed piston for a swash plate type compressor including a head portion having an outer circumferential surface for sliding contact with an inner circumferential surface of a cylinder bore formed in a cylinder block of the compressor, and an engaging portion engaging a swash plate of the compressor, characterized in that: the outer circumferential surface of the head portion includes a cylindrical surface and a curved surface which is formed adjacent to at least one of opposite axial ends of the cylindrical surface, so as to smoothly extend from at least one circumferential part of the cylindrical surface, the curved surface being formed such that a radial distance between a centerline of the cylindrical surface and the curved surface gradually decreases in an axial direction of the cylindrical surface from the corresponding axial end of the cylindrical surface toward the corresponding axial end of the piston, and such that a radius of curvature of a cross sectional shape of the curved surface taken in a plane which includes the centerline of the cylindrical surface is larger than a diameter of the inner circumferential surface of the cylinder bore.
The curved surface formed adjacent to at least one of axially opposite ends of the cylindrical surface of the head portion of the single-headed piston is effective to reduce the noise generated by the awash plate type compressor during its operation. The presence of the curved surface permits the head portion of the piston to smoothly slide on the inner circumferential surface of the cylinder bore.
(2) A single-headed piston according to the above mode (1), the curved surface is formed at at least one of an axial end of the cylindrical surface nearer to the engaging portion so as to extend from a first circumferential part of the cylindrical surface which is nearer to an axis of rotation of the swash plate, and an axial end of the cylindrical surface remote from the engaging portion so as to extend from a second circumferential part of the cylindrical surface which is more distant from the axis of rotation of the swash plate than the first circumferential part.
The above-indicated first and second circumferential parts of the cylindrical surface of the head portion of the piston generally suffer from a particularly large contacting surface pressure when the head portion of the piston contacts the inner circumferential surface of the cylinder bore during operation of the swash plate type compressor. By forming the curved surfaces in these circumferential parts, the piston can be smoothly reciprocated within the cylinder bore.
(3) A single-headed piston according to the above mode (2), wherein the curved surface is formed at the axial end of the cylindrical surface which is remote from the engaging portion and extends over an entire circumference of the cylindrical surface.
It is confirmed that the curved surface formed at the axial end of the head portion of the piston which is remote from the engaging portion is particularly advantageous. In general, the axial end face of the head portion remote from the engaging portion has a simple circular configuration. Since the cylindrical surface and the circular end face intersect each other so as to define a simple circle, it is easy to form the curved surface which extends over the entire circumference of the cylindrical surface of the head portion at the axial end which is remote from the engaging portion.
(4) A single-headed piston according to the above mode (2) or (3), wherein the curved surface is formed at one of opposite axial ends of the head portion which is nearer to the engaging portion and extends over an entire circumference of the axial end of the head portion.
Where the single-headed piston has a hollow cylindrical head portion, the axial end of the outer circumferential surface of the head portion which is nearer to the engaging portion has a simple circular shape. Accordingly, it is easy to form the curved surface which extends over the entire circumference of the outer circumferential surface at that axial end. However, the curved surface which extends over the entire circumference of the outer circumferential surface may be formed at that axial end portion whose configuration is not a simple circle.
(5) A single-headed piston according to any one of the above modes (1)-(4), wherein the cross sectional shape of the curved surface taken in the plane which includes the centerline of the cylindrical surface is an arc.
The cross sectional shape of the curved surface may be suitably determined, provided it has a smooth convex curve. For instance, the cross sectional shape of the curved surface may be a plurality of arcs having respective different radii of curvature, an ellipse, or a part of a hyperbola. If the cross sectional shape of the curved surface is a simple arc, the piston can be economically manufactured.
(6) A single-headed piston according to any one of the above modes (1)-(5), wherein a dimension r
1
between a surface of extension of the cylindrical surface and a straight line which is parallel to the surface of extension and which passes one of opposite ends of the curved surface which is remote from the cylindrical surface is not greater than 15 &mgr;m.
When the dimension r
1
is excessively large, the lubricant oil adhering to the inner circumferential surface of the cylinder bore is less likely to be introduced into a wedge-shaped gap which is formed between the inner circumferential surface of the cylinder bore and the outer
Enokijima Fuminobu
Hoshida Takahiro
Katayama Seiji
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Leslie Michael
Woodcock & Washburn LLP
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