Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Reexamination Certificate
2000-06-13
2001-12-25
Ryznic, John E. (Department: 3745)
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
C092S159000, C092S172000
Reexamination Certificate
active
06332394
ABSTRACT:
This application is based on Japanese Patent Application Nos. 11-168591 and 11-185638 filed Jun. 15 and Jun. 30, 1999, respectively, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piston used for a swash plate type compressor.
2. Discussion of the Related Art
As a piston for a swash plate type compressor, there are known various types of pistons each of which has (a) a head portion which is slidably fitted in a cylinder bore formed in a cylinder block, (b) a neck portion which engages a swash plate, and (c) a connecting portion which connects the head portion and the neck portion. An example of such pistons is disclosed in JP-A-9-203378. In the swash plate type compressor piston disclosed in this publication, the head portion has a through-hole formed therethrough in a direction substantially parallel to the circumferential direction of the cylinder block, and the head portion and the neck portion are connected to each other at two circumferential portions of the cylinder bore which correspond to respective radially inner and outer portions of the cylinder block. The through-hole formed in the head portion contributes to a reduction in the weight of the piston.
SUMMARY OF THE INVENTION
It is an object of the present invention to minimize the weight of a piston used for a swash plate type compressor. This object may be achieved by a piston for a swash plate type compressor, which is constructed according to any one of the following forms or modes of the present invention, each of which is numbered like the appended claims and depends 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 piston for a swash plate type compressor, including a head portion slidably fitted in a cylinder bore formed in a cylinder block of the compressor, a neck portion slidably engaging a swash plate of the compressor, and a connecting portion connecting the head and neck portions, wherein the head portion comprises a body portion having a circular shape in cross section, and an inner sliding projection extending toward the neck portion from a radially inner circumferential part of the body portion which corresponds to a radially inner portion of the cylinder block, the inner sliding projection having a sliding surface for sliding contact with an inner circumferential surface of the cylinder bore, the sliding surface being symmetrical with respect to a plane including a centerline of the piston and a centerline of the cylinder block, the connecting portion connecting the inner sliding projection and the neck portion, at the radially inner circumferential part of the body portion, and not connecting the head portion and the neck portion at a radially outer circumferential part of the body portion which corresponds to a radially outer portion of the cylinder block.
In the piston for a swash plate type compressor, which is constructed according to the above form (1) of this invention, the connecting portion connects the head portion and the neck portion at the radially inner circumferential part of the body portion, but does not connect the head and neck portions at the radially outer circumferential part of the body portion. This arrangement permits a smaller weight of the piston than the arrangement wherein the head and neck portions are connected at both of the radially inner and outer circumferential parts of the body portion which correspond to the respective radially inner and outer portions of the cylinder block. From the standpoint of the strength of the piston, the connection of the head and neck portions at both of the radially inner and outer circumferential parts of the body portion of the head portion is not essential, and the head and neck portions are connected to each other by the connecting portion only at the radially inner circumferential part of the body portion. In the absence of a connecting portion at the radially outer circumferential portion of the body portion, it may be necessary to increase the weight of the connecting portion extending from the radially inner circumferential portion of the body portion, for increasing the strength of the connecting portion. However, the weight of the piston can be generally made smaller in the above form (1) of the invention than where the head and neck portions are connected at both of the radially inner and outer circumferential parts of the body portion (head portion). Where the piston is formed by casting or forging, the configuration and dimensions of the connecting portion are determined not only by the required strength of the piston, but also depending upon the casting or forging technique used. In this respect, the elimination of the connecting portion at the radially outer circumferential part of the head portion does not necessarily require an increase in the strength of the connecting portion at the radially inner circumferential part of the head portion, and provides a reduction in the weight of the piston in most cases.
Further, the sliding surface of the inner sliding projection is symmetrical with respect to the plane including the centerlines of the piston and cylinder block. This arrangement permits the inner sliding projection to receive a reaction force due to a side force generated by the swash plate from the inner circumferential surface of the cylinder bore, from the inner circumferential surface of the cylinder bore, over a sufficiently large area of the sliding surface, irrespective of the direction of rotation of the swash plate. Accordingly, the present arrangement is effective to minimize a local wear of the surface of the cylinder bore and the sliding surface of the inner sliding projection. It is known that the point of action of the reaction force received from the cylinder bore is located on the leading side of the plane including the centerlines of the piston and cylinder block, as seen in the direction of rotation of the swash plate. Accordingly, the weight of the piston could be reduced and its local wear could be minimized, if the weight of the inner sliding projection were made relatively large on the leading side of the plane, and relatively small on the trailing side. However, this arrangement permits the use of the piston for only the swash plate type compressor of the type in which the swash plate is always rotated in the predetermined one direction (clockwise or counterclockwise direction). The piston according to the present invention wherein the inner sliding projection is symmetrical with respect to the above-indicated plane can be used irrespective of whether the swash plate is rotated in the clockwise or counterclockwise direction.
(2) A piston according to the above form (1), wherein at least one of a first inner surface of the inner sliding projection which faces in a radially outward direction of the cylinder block and a second inner surface of the body portion which faces toward the neck portion has at least one recess formed therein.
In the piston according to the above form (2) of this invention, at least one recess is formed in at least one of the first and second surfaces indicated above, so that the weight of the piston is accordingly reduced. It is desirable that the at least one recess be formed symmetrically with respect to the plane including the centerlines of the piston and the cylinder block. The term “recess” used herein is interpreted to mean either or both of a through-hole formed through the inner sliding projection, and a recess or blind hole not formed through the inner sliding projection. Where
Enokijima Fuminobu
Fukushima Shigeo
Katayama Seiji
Kato Takayuki
Takamatsu Masato
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Morgan & Finnegan , LLP
Ryznic John E.
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