Expansible chamber devices – Relatively movable working members – Interconnected with common rotatable shaft
Reexamination Certificate
2000-05-24
2002-11-26
Lopez, F. Daniel (Department: 3745)
Expansible chamber devices
Relatively movable working members
Interconnected with common rotatable shaft
C092S172000
Reexamination Certificate
active
06484621
ABSTRACT:
This application is based on Japanese Patent Application No. 11-150448 filed May 28, 1999, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a swash plate type compressor, and more particularly to the configuration of a single-headed piston of such type of compressor.
2. Discussion of the Related Art
There has been used a swash plate type compressor equipped with a plurality of single-headed pistons. The compressor of this swash plate type includes (1) a cylinder block having a plurality of cylinder bores formed therein such that the cylinder bores are, arranged along a circle, (2) a rotary drive shaft having an axis of rotation aligned with a centerline of the above-indicated circle, (3) a swash plate rotated with the rotary drive shaft, and (4) a plurality of single-headed pistons each of which includes a head portion slidably engaging a corresponding one of said cylinder bores, and a neck portion engaging said swash plate. In this compressor, the pistons are reciprocated by the swash plate rotated with the rotary drive shaft. An example of this swash plate type compressor is disclosed in JP-A-9-203378. In the swash plate type compressor disclosed in this publication, the head portion of each piston is formed with a through-hole substantially parallel to the circumferential direction of the cylinder block, so as to reduce the mass of the piston. As described below, the head portion of the piston has a relatively high sliding surface pressure at two circumferential portions of its outer circumferential surface which correspond to respective circumferential portions of the cylinder bore at respective radially outermost and innermost portions of the cylinder block, and a relatively low sliding surface pressure at circumferential portions of its outer circumferential surface which are intermediate between the above-indicated two circumferential portions in the circumferential direction of the cylinder block. This fact permits the above-indicated through-hole to be formed through the head portion, for the purpose of reducing the mass of the head portion.
However, the swash plate type compressor described above suffers from a problem that the head portion is subject to a local wear and has an insufficient degree of durability due to a tendency of inclination of the pistons within the cylinder bores. Where the outer circumferential surface of the head portion of each piston is coated with a coating film such as a film of polytetrafluoroethylene (PTFE), this coating film is subject to a local wear, and is relatively likely to suffer from a peel-off problem. Reference is made to
FIG. 10
, wherein a resultant force Fo consisting of an inertial force of a piston
200
and a force based on a pressure of a refrigerant gas in the cylinder bore acts on a swash plate
202
through a hemispherical shoe
201
(one of a pair of hemispherical shoes). The resultant force Fo is balanced with an axial component Fo′ of a force Fa which acts on the surface of the swash plate
202
in a direction perpendicular to that surface. The axial component Fo′ acts on the piston
200
in a direction parallel to the centerline of the piston
200
. A radial component Fb of the force Fa which component Fb acts on the piston
200
in the radial direction of the swash plate
202
is called a side force acting in a direction perpendicular to the centerline of the piston
200
. This radial component Fb (more precisely, a resultant force consisting of the radial component Fb and a friction force between the swash plate
202
and the hemispherical shoe
201
) is balanced with reaction forces Fc, Fd which the piston
200
receives from the inner circumferential surface of a cylinder bore
204
. Since the resultant force Fo increases as the piston
200
is moved to its upper dead point in its compression stroke, the reaction forces Fc, Fd are the largest at a point near the upper dead point. In particular, the reaction force Fc is comparatively large near the upper dead point of the piston
200
. Accordingly, the coating film such as the PTFE film formed on the outer circumferential surface of the piston
200
is likely to be locally worn or removed.
SUMMARY OF THE INVENTION
The present invention was made in the light of the background prior art described above. It is therefore an object of the present invention to provide a swash plate type compressor which has an improved degree of durability while reducing the mass of the pistons. This object may be achieved according to any one of the following modes of the present invention, each of which is numbered like the appended claims and depends from the other mode or modes, 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, and 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 swash plate type compressor including:
a cylinder block having a plurality of cylinder bores formed therein such that the cylinder bores are arranged along a circle;
a rotary drive shaft having an axis of rotation aligned with a centerline of the circle;
a swash plate rotated with the rotary drive shaft; and
a plurality of single-headed pistons each including a head portion slidably engaging a corresponding one of the cylinder bores, and a neck portion engaging the swash plate, each single-headed piston being reciprocated by the swash plate rotated by the rotary drive shaft, the head portion of each single-headed piston including a body portion having a circular shape in transverse cross section, and an outer sliding portion and an inner sliding portion which are disposed between the body portion and the neck portion, the outer and inner sliding portions slidably engaging respective circumferential portions of an inner circumferential surface of the corresponding cylinder bore which correspond to respective radially outer and inner portions of the cylinder block,
and wherein a distance from an end face of the body portion remote from the neck portion to an end of the inner sliding portion on the side of the neck portion is larger than a distance from the end face to an end of the outer sliding portion on the side of the neck portion, and the inner sliding portion has a distal sliding part which is spaced from the end face by a distance of at least 40% of an entire length of the piston in an axial direction of the piston and which has a central angle of not larger than 120°, the distal sliding part having a length which is at least 5% of the entire length of said piston.
In the swash plate type compressor constructed according to the above mode (1) of the invention, the head portion of each piston includes the body portion, the inner sliding portion and the outer sliding portion. The inner sliding portion has the distal sliding part which is spaced from the end face of the body portion by a distance of at least 40% of the entire length of the piston and which has the central angle of not larger than 120° and the length which is at least 5% of the entire length of the piston. This arrangement assures a relatively large distance between the axial positions at which the above-indicated two reaction forces act on the piston. Accordingly, the reaction force Fc corresponding to the given side force Fb can be reduced. Further, the amount of increase of the mass of the piston due to the provision of the inner sliding portion is reduced since the distal length of the distal sliding part and its circumferential dimension (central angle) are minimized to such an extent that assures a surface area of the distal sliding part sufficient to limit its sliding surface pressure to a value not higher than a predetermined upper li
Fukushima Shigeo
Katayama Seiji
Kato Takayuki
Kabushiki Kaisha Toyoda Jidoshokki Seisakusho
Lopez F. Daniel
Woodcock & Washburn LLP
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