Information
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Patent Grant
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6484621
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Patent Number
6,484,621
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Date Filed
Wednesday, May 24, 200024 years ago
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Date Issued
Tuesday, November 26, 200221 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
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US Classifications
Field of Search
US
- 091 499
- 092 71
- 092 172
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International Classifications
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Abstract
Swash plate type compressor including a cylinder block having cylinder bores arranged along a circle, a drive shaft aligned with the circle, a swash plate rotated with the drive shaft, and single-headed pistons each including a head portion engaging the cylinder bore, and a neck portion engaging the swash plate, and wherein each piston is reciprocated by the swash plate rotated by the drive shaft, and the head portion includes a circular body portion, and an outer sliding portion and an inner sliding portion which are disposed between the body portion and the neck portion and which slidably engage respective circumferential portions of the cylinder bore which correspond to respective radially outer and inner portions of the cylinder block. Length from the end face of the body portion to the remote end of the inner sliding portion is larger than the corresponding length of the outer sliding portion. The inner sliding portion has a distal sliding part spaced from the end face by at least 40% of the entire piston length and having a central angle of not larger than 120° and a length of at least 5% of the entire piston length.
Description
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 limit. Accordingly, the durability of the distal sliding part (i.e., the durability of the piston) can be effectively increased while reducing the mass of the piston. Where the distal sliding part is coated with a coating film such as a film of PTFE, the local wear and removal of the coating film can be minimized.
The inner sliding portion may be formed so as to extend from the body portion in the axial direction (such that the outer circumferential surface of the inner sliding portion is continuous with that of the body portion). Alternatively, the inner sliding portion may be formed in spaced-apart relation with the body portion (such that the outer circumferential surface of the inner sliding portion is not continuous with that of the body portion). In the former case, the length or distance from the end face of the body portion to the end of the inner sliding portion on the side of the neck portion is equal to a sum of the axial length of the body portion and the axial length of the inner sliding portion (total axial length of the body portion and the inner sliding portion as measured on the radially inner side of the head portion). In the latter case, the above-indicated distance is larger than the above-indicated sum. The above description applies to the outer sliding portion. Namely, the outer sliding portion may either extend from the body portion, or be formed in spaced-apart relation with the body portion. Further, the relationship described above with respect to the inner sliding portion applies to the relationship between the distance from the end face of the body portion to the end of the outer sliding portion on the side of the neck portion and the sum of the axial lengths of the body portion and the outer sliding portion
The distance from the end face of the body portion to the end of the inner sliding portion on the side of the neck portion is made larger than the corresponding distance of the outer sliding portion, in view of a fact that the durability of the piston can be effectively improved by increasing the above-indicated distance of the inner sliding portion rather than the corresponding distance of the outer sliding portion. In this respect, it is noted that the sliding surface pressure at the end portion of the outer sliding portion on the side of the neck portion is maximized at a point of transition from the suction stroke to the compression stroke of the piston, and that the side force at this point of time is based primarily on the inertial force of the piston, and is smaller than the side force in the terminal portion of the compression stroke. Accordingly, it is more effective to increase the above-indicated distance of the inner sliding portion rather than the corresponding distance of the outer sliding surface.
The circumferential dimension (central angle) of the inner sliding portion may be constant over its entire axial length, or may be smaller or larger at its part nearer to the neck portion than at its part near to the body portion. In the latter case, the central angle of the distal sliding part of the inner sliding portion is made smaller or larger than that of the other part (referred to as “proximal sliding part” since it is adjacent or nearer to the body portion of the head portion) of the inner sliding portion. The distal sliding part may be configured such that its central angle is constant over its entire axial length or changes depending upon the axial position. For instance, the central angle of the distal sliding part may decrease continuously or in steps as it extends in the axial direction toward the neck portion. The distal sliding part may be formed integrally with the proximal sliding part, or in spaced-part relation with the proximal sliding part.
The proximal and distal sliding parts may have a suitable shape in transverse cross section, which may be generally defined by an arc and a chord, or by a part of an annulus, or may be crescent or generally rectangular. In other words, the surfaces of the proximal and distal sliding parts of the inner sliding portion which slidably engage the inner circumferential surface of the cylinder bore are required to have shapes which follow the corresponding parts of that inner circumferential surface. However, the surfaces of the proximal and distal sliding parts which are opposed to the outer sliding portion may have any shapes, for instance, may be flat surfaces or concave surfaces. Where these surfaces are concave, the mass of the piston is reduced owing to the concavity. The shapes in transverse cross section may be symmetrical or asymmetrical with respect to a plane which passes the centerline of the piston and the centerline of the cylinder block. As described before, a force of friction between the piston and the swash plate also acts on the piston, so that the direction in which a reaction force produced by the inner circumferential surface of the cylinder bore acts on the piston deviates from the plane passing the centerline of the piston and cylinder block, in a direction determined by the direction of rotation of the swash plate. Accordingly, where the swash plate (drive shaft) is rotated in a predetermined one direction, it is advantageous that the inner sliding portion has an asymmetric shape in transverse cross section such that the inner sliding portion has a larger sliding surface on one side of the above-indicated plane on which the above-indicated reaction force deviates from that plane, than on the other side.
The distal sliding part is spaced from the end face of the body portion by a distance which is at least 40% of the entire length of the piston. Preferably, this distance is at least 43% or 46% of the entire length of the piston. An effect of the distal sliding part to prevent the inclination of the piston relative to the centerline of the cylinder bore increases with an increase in the distance of the distal sliding part from the end face of the body. Where the distal sliding part is formed integrally with the proximal sliding part, the weight of the piston increases with the above-indicated distance. It is further noted that the maximum operating stroke of the piston is determined by the outside diameter and inclination angle of the swash plate. Therefore, the axial position of the distal sliding part is desirably determined by taking into account its effect to prevent the piston inclination, the amount of increase of the piston mass and the operating stroke.
(2) A swash plate type compressor according to the above mode (1) , wherein the central angle of the distal sliding part is not larger than 100°.
While the central angle of the distal sliding part is required to be not larger than 120° according to the above mode (1), this central angle is preferably not larger than 110° or 100°, for effectively reduce the mass of the piston. The mass of the piston can be more effectively reduced when the central angle is 95° or 90° or smaller.
A decrease in the central angle of the distal sliding part increases the sliding surf ace pressure of the distal sling part, but reduces the mass of the piston. Accordingly, the central angle of the distal sliding part is preferably determined by taking into account both the sliding surface pressure and the piston mass. Where the central angle of the distal sliding part is extremely small, for example 20°, the inner sliding portion having this distal sliding part provides some effect to prevent inclination of the piston relative to the centerline of the cylinder bore, as compared with the inner sliding portion which does not have the distal sliding part. In view of this, the central angle of the distal sliding part may be not larger than 85°, 80° or 70°.
(3) A swash plate type compressor according to the above mode (1) or (2), wherein the inner sliding portion includes a wide section disposed. on the side of the body portion, and a narrow section which is disposed on the side of the neck portion and which has a smaller circumferential dimension than the wide section.
The narrow section and the wide section may be respectively the distal sliding part and the proximal sliding part which have been described above.
(4) A swash plate type compressor according to the above mode (1) or (2), wherein the inner sliding portion includes a narrow section disposed on the side of the body portion, and a wide section which is disposed on the side of the neck portion and which has a larger circumferential dimension than the narrow section.
The narrow section and the wide section may be respectively the proximal sliding part and the distal sliding part which have been described above. This arrangement permits effective reduction of the sliding surface pressure while reducing the increase of the mass of the piston due to the provision of the inner sliding portion.
(5) A swash plate type compressor according to any one of the above modes (1)-(4), wherein the length of the distal sliding part is at least 8% of the entire length of the piston.
The axial length of the :distal sliding part is at least 5% of the entire length of the piston according to the principle of the above mode (1) of the present invention. In the above mode (5) wherein this axial length is at least 8% of the entire piston length, the sliding surface pressure of the piston can be further reduced. Where the length of the distal sliding part is at least 10%, 12% or 15% of the entire piston length, the piston can be further effectively prevented from being inclined.
Where the inner sliding portion extends continuously from the body portion in the axial direction, an increase in the axial length of the distal sliding part increases the entire axial length of the inner sliding portion and consequently the mass of the piston, if the axial length of the proximal sliding part is unchanged. Accordingly, the percentage of the axial length of the distal sliding part with respect to the entire piston length is desirably determined by taking account of the effect to reduce the sliding surface pressure of the piston, and the amount of increase in the mass of the piston due to the provision of the inner sliding portion.
(6) 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 protrusion and an inner protrusion which extend toward the neck portion from respective radially outer and inner portions of the cylinder block and which slidably engage respective circumferential portions of an inner circumferential surface of the corresponding cylinder bore,
and wherein a total length of the body portion and the inner protrusion in an axial direction of the piston is at least 45% of an entire length of the piston, the inner extension having a central angle of not larger than 120° in at least a distal end portion thereof which is remote from the body portion and whose axial length is at least 10% of the above-indicated total length, a distance of extension of the inner protrusion from the body portion being larger than that of the outer protrusion.
In the swash plate compressor constructed according to the above mode (6) of the present invention, the outer sliding portion and the inner sliding portion of the head portion are provided in the form of the outer protrusion and the inner protrusion, respectively which extend from the body portion of the head portion in the axial direction toward the neck portion. The head portion including these outer and inner protrusions has a larger strength than the head portion wherein the outer and inner sliding portions are formed in spaced-apart relation with the body portion.
The distal end portion of the inner protrusion whose central angle is not larger than 120° and whose axial length is at least 10% of the total length of the body portion and the inner protrusion corresponds to the distal sliding part described above with respect to the above mode (1). The distal sliding part may be referred to as a sliding distal end part.
(7) 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 inner sliding portion including (a) an inner protrusion which extends toward the neck portion from a radially inner portion of the cylinder block and which has a proximal inner sliding surface which slidably engages an inner circumferential surface of the corresponding cylinder bore, and (b) a spaced-apart distal sliding part which has a spaced-apart inner sliding surface spaced apart from the inner protrusion, the spaced-apart distal sliding part being spaced from an end face of the body portion remote from the neck portion, by a distance of at least 40% of an entire length of the piston, the spaced-apart distal sliding part having a central angle of not larger than 120° and an axial length which is at least 5% of the entire length of the piston.
In the swash plate type compressor constructed according to the above mode (7), the distal sliding part is the spaced-apart distal sliding part which is spaced from the inner protrusion. For instance, the spaced-apart distal sliding part may be formed on a connecting portion which connects the inner protrusion and the neck portion. The spaced-apart distal sliding part is located at an axial position between the inner protrusion and the neck portion, which axial position is spaced from the end face of the body portion by a distance of at least 40% of the entire piston length, as described above. This mode (7) of the invention provides an increased freedom of design in the position of the spaced-apart distal sliding part.
The above mode (7) may be modified such that the inner protrusion is a connecting portion which does not have the proximal inner sliding surface and which merely connects the spaced-apart distal sliding part and the body portion.
(8) A piston for a swash plate type compressor, said piston having a head portion slidably received in a cylinder bore formed in a cylinder block, and a neck portion engaging a swash plate, the head portion includes:
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 the piston. the each
There is also provided a piston for a swash plate type compressor, which is described with respect to any one of the above modes (2)-(7).
BRIEF DESCRIPTION OF THE DRAWINGS
The above and optional objects, features, advantages and technical and industrial significance of this invention will be better understood and appreciated by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which:
FIG. 1
is a front elevational view in cross section of a swash plate type compressor constructed according to one embodiment of this invention;
FIG. 2
is a perspective of a piston included in the swash type compressor of
FIG. 1
;
FIG. 3
is a cross sectional view of the piston of
FIG. 2
;
FIG. 4
is a bottom plate view of the piston of
FIG. 2
;
FIG. 5
is a graph indicating a relationship between the configuration of the piston and the peel-off surface area of the piston head coating;
FIG. 6
is a bottom plan view of a piston included in a swash plate type compressor according to another embodiment of this invention;
FIG. 7
is a bottom plan view of a piston included in a swash plate type compressor according to a further embodiment of this invention;
FIG. 8
is a bottom plan view of a piston included in a swash plate type compressor according to a still further embodiment of this invention;
FIG. 9
is a bottom plan view of a piston included in a swash plate type compressor according to a yet further embodiment of this invention; and
FIG. 10
is a fragmentary elevational view in cross section of a piston in an inclined state in a swash plate type compressor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the accompanying drawings, there will be described presently preferred embodiments of this invention in the form of a swash plate type compressor whose delivery capacity is variable.
In
FIG. 1
, reference numeral
10
denotes a cylinder block having a centerline M and a plurality of axially extending cylinder bores
12
formed therein such that the cylinder bores
12
are arranged along a circle whose center lies on the centerline M. In each of the cylinder bores
12
, there is received a piston
14
such that the piston
14
is axially reciprocable within the cylinder bore
12
. To one of axially opposed end faces of the cylinder block
10
(i.e., the left-hand side end face of the cylinder block
10
as viewed in
FIG. 1
, which will be referred to as “front end face”), there is attached a front housing
16
. To the other end face (i.e., the right-hand side end face as viewed in
FIG. 1
, which will be referred to as “rear end face”) of the cylinder block
10
, there is attached a rear housing
18
through a valve plate
20
. The front housing
16
, the rear housing
18
and the cylinder block
10
constitute a major part of a body portion of the swash plate type compressor.
Between the rear housing
18
and the valve plate
20
, there are formed a suction chamber
22
and a discharge chamber
24
, which are connected to a refrigerating circuit (not shown) through an inlet
26
and an outlet
28
, respectively. The valve plate is provided with suction ports
40
, suction valves
42
, discharge ports
46
and delivery valves
48
.
A rotary drive shaft
50
is disposed in alignment with the centerline M of the cylinder block
10
such that the drive shaft
50
is rotatable relative to the cylinder block
10
. The drive shaft
50
is supported at its opposite end portions by the front housing
16
and the cylinder block
10
through respective bearings. The cylinder block
10
has a central support hole
56
in a central portion thereof, so that the drive shaft
50
is supported at its rear end portion in the central support hole
56
.
To the rotary drive shaft
50
, there is attached a swash plate
50
such that the swash plate
60
is movable relative to the drive shaft
50
in the axial direction M of the drive shaft
50
and is tiltable relative to the axis of rotation of the drive shaft
50
. To the drive shaft
50
, there is also fixed a lug plate
62
such that the lug plate
62
is held in engagement with the swash plate
60
through a hinge mechanism
64
. The lug plate
62
is :also held in engagement with a thrust bearing
66
fixed to the front housing
16
. The hinge mechanism
64
enables the swash plate
60
to be rotated with the drive shaft
50
, and functions to guide the swash plate
60
for the axial movement of the swash plate
60
in the axial direction M and the inclination of the swash plate
60
relative to the drive shaft
50
.
The hinge mechanism
64
includes a pair of support arms
70
fixed to the lug plate
62
, and guide pins
72
extending from the swash plate
60
such that the guide pins
72
slidably engage guide holes
74
formed in the support arms
70
.
The piston
14
includes a neck portion
80
engaging
6
the swash plate
60
, a head portion
82
slidably engaging the corresponding cylinder bore
12
, and a connecting portion
83
which connects those neck and head portions
80
,
82
. The neck portion
80
has a groove
84
formed therein, and the swash plate
60
engages the groove
84
through a pair of hemispherical shoes
86
. Each shoe
86
has a hemisperical surface which slidably engages a hemispherical portion of the groove
84
, and a flat surface which slidably engages the corresponding one of the opposite surfaces of the swash plate
60
. The configuration of the piston
14
will be described in detail.
The head portion
82
cooperates with the cylinder block
10
and the valve plate
20
to define a pressurizing chamber
85
. A rotary motion of the swash plate
60
is converted into a linear reciprocating motion of the piston
14
through the pair of shoes
86
. When the piston
14
is in the suction stroke from the upper dead point to the lower dead point, a refrigerant gas in the suction chamber
22
is fed or admitted into the pressurizing chamber
85
through the suction port
40
, with the suction valve
42
being opened under a reduced pressure in the cylinder bore
12
. In the compression stroke of the piston
14
from the lower dead point to the upper dead point, the refrigerant gas in the pressurizing chamber
85
is compressed by the piston
14
, and the compressed gas is fed into the delivery chamber
46
through the delivery port
46
, with the delivery valve
48
being opened under an elevated pressure in the pressurizing chamber
85
. As a result of compression of the refrigerant gas in the pressurizing chamber
85
, a reaction force acts on the piston
14
in the axial direction. This reaction force is received by the front housing
16
through the piston
14
, swash plate
60
, lug plate
62
and thrust bearing
66
.
The neck portion
80
of the piston
14
has an integrally formed rotation preventing portion
88
, as shown in FIG.
2
. The rotation preventing portion
88
is held in contact with the inner circumferential surface of the front housing
16
, for preventing the piston
14
from being rotated about its centerline N.
The cylinder block
10
has a fluid passage
94
formed therethrough, for fluid communication between the delivery chamber
24
and a crank chamber
96
which is formed between the front housing
16
and the cylinder block
10
. A portion of the fluid passage
94
is provided by a solenoid-operated control valve
100
, which is provided to control the pressure in the crank chamber
96
. The solenoid-operated control valve
100
includes a solenoid coil
102
, and a shut-off valve
104
which is opened and closed depending upon whether the solenoid coil
102
is placed in an energized state or a de-energized state. The shut-off valve
104
is closed when the solenoid coil
102
is energized, and is opened when the solenoid coil
102
is de-energized.
The rotary drive shaft
50
has an exhaust passage
110
formed therethrough. The exhaust passage
110
is open at one of its opposite ends to the central support hole
56
indicated above, and at the other end to the crank chamber
96
through a communication passage
112
. The central support hole
56
is held in communication with the suction chamber
22
through an exhaust port
114
, which is formed through the bottom of the central support hole
56
and the valve plate
20
.
Upon energization of the solenoid coil
102
of the solenoid-operated control valve
100
, the fluid passage
94
is closed, whereby the pressurized refrigerant gas in the discharge chamber
24
is not fed into the crank chamber
96
. In this condition, the refrigerant gas in the crank chamber
96
is released into the suction chamber
22
through the exhaust passage
110
and the exhaust port
114
, whereby the pressure in the crank chamber
96
is lowered, so that the angle of inclination of the swash plate
60
is increased, resulting in an increase in the rate of change of the volume of the pressurizing chamber
85
and a consequent increase in the discharge capacity of the compressor.
While the fluid passage
94
is open with the solenoid coil
102
placed in the de-energized state, the pressurized refrigerant gas in the discharge chamber
24
is fed into the crank chamber
96
, whereby the pressure in the crank chamber
96
is raised, so that the angle of inclination of the swash plate
60
is reduced, resulting in a decrease in the discharge capacity of the compressor. Thus, the present swash plate type compressor is of a variable discharge-capacity type.
The maximum angle of inclination of the swash plate
60
is determined by abutting contact of a stop
120
provided on the swash plate
60
, with the lug plate
62
. The minimum angle of inclination of the swash plate
60
is determined by abutting contact of the swash plate
60
with a stop
122
in the form of a ring fixed to the drive shaft
50
.
It will be understood that the pressure in the crank chamber
96
is controlled by controlling the solenoid-operated control valve
100
so as to selectively connect and disconnect the crank shaft
96
to and from the discharge chamber
24
. With the pressure in the crank chamber
96
being changed, the angle of inclination of the swash plate
60
is changed, so that the discharge capacity of the compressor is changed. The operating state of the solenoid coil
102
of the solenoid-operated control valve
100
is controlled by a control device (not shown) principally constituted by a computer, depending upon appropriate input information such as a signal indicative of a load acting on the compressor.
The cylinder block
10
and the piston
14
are formed of suitable aluminum alloys, and the outer circumferential surface of the piston
14
is coated with a coating film of a fluoro resin. The fluoro resin coating prevents the piston
14
from directly contacting the cylinder block
10
whose material is similar to that of the piston
14
, making it possible to minimize the amount of gap between the outer circumferential surface of the piston
14
and the inner circumferential surface of the cylinder bore
12
. It is noted that the cylinder block
10
and the piston
14
may be formed of suitable hyper-eutectic crystal aluminum silicon alloys. The materials of the cylinder block
10
, the piston
14
and the coating of the piston
14
are not limited to those mentioned above by way of example.
Then, the configuration of the piston
14
will be explained.
As shown in
FIGS. 2-4
, the head portion
82
of the piston
14
includes a body portion
128
, an outer sliding portion
130
and an inner sliding portion or protrusion
132
disposed between the body portion
128
and the neck portion
80
. The body portion
128
has, a cylindrical shape in transverse cross section, and the outer and inner sliding portions
130
,
132
extend from respective circumferential portions of the body portion
128
in the radially outward and inward directions of the cylinder block
10
, respectively. The outer and inner sliding portions
130
,
132
are provided as outer and inner protrusions from the body portion
128
, for sliding contact or engagement with respective circumferential portions of the inner circumferential surface of the cylinder bore
12
which correspond to respective radially outer and inner portions of the cylinder block
10
. The inner sliding portion
132
is provided at a circumferential position of the head portion
82
at which the groove
84
of the neck portion
80
is open for engagement with the swash plate
60
. The outer sliding portion
130
is connected to the neck portion
80
by a rib
134
, while the inner sliding portion
132
is connected to the neck portion
80
by a rib
135
. The ribs
134
,
135
cooperate to constitute the connecting portion
83
indicated above.
In the present embodiment, a total length L
1
of the body portion
128
and the inner sliding portion
132
(referred to as “head inner length”, which is a length of the head portion
82
as measured at the inner sliding portion
132
) is made larger than a total length L
2
of the body portion
128
and the outer sliding portion
130
(referred to as “head outer length”, which is a length of the head portion
82
as measured at the outer sliding portion
130
). Namely, the length L
1
from an end face
136
of the body portion
128
(which is remote from the neck portion
80
) to the end of the inner sliding portion
132
which is remote from the end face
136
is made larger than the length L
2
from the end face
136
to the end of the outer sliding portion
130
remote from the end face
136
. By increasing the head inner length L
1
rather than the head outer length L
2
, an axial distance between axial positions at which the reaction forces Fc and Fd act on the piston
14
as indicated in
FIG. 10
can be made larger, so that the reaction force Fc can be reduced, provided the side force Fb is constant, whereby the durability of the piston
14
can be effectively improved. It is noted that the piston
14
may be formed by either joining together the head portion
82
, neck portion
80
and connecting portion
83
which have been formed as separate members, as shown in
FIG. 3
, or forming these portions
82
,
80
,
83
integrally with each other.
A percentage α(=100×L
1
/L) of the head inner length L
1
with respect to an entire length L of the piston
14
is determined to be 50%. By increasing the length of the inner sliding portion
132
, the inclination of the piston
14
relative to the rotation axis M of the drive shaft
50
can be restricted, and the durability of the compressor can be improved. As indicated in the graph of
FIG. 5
, the amount of wear and the peel-off surface area of the fluoro resin coating of the piston
14
can be significantly reduced, where the above-indicated percentage α is 45%. Although the percentage α is preferably at least 50%, and more preferably at least 55%, as is apparent from the graph, an increase in the head inner length L
1
will results in an increase in the weight of the piston
14
. It is also noted that the piston
14
has a given operating stroke. Therefore, the head inner length L
1
(percentage α) is desirably determined with those factors taken into account.
As shown in
FIGS. 3 and 4
, the configuration of the inner sliding portion
132
in transverse cross section is not uniform in the axial direction. That is, the circumferential dimension of the inner sliding portion
132
as represented by a central angle is smaller at a distal sliding part
140
nearer to the neck portion
80
than at a proximal sliding part
142
nearer to the body portion
128
, as indicated at Φ and θ. Were the central angle θ of the distal sliding part
140
is made smaller than the central angle Φ of the proximal sliding part
142
, the amount of increase in the weight of the piston
14
due to the provision of the inner sliding part
132
can be made smaller than where these distal and proximal sliding parts
140
,
142
have the same central angle (θ=Φ) or circumferential dimension. Although the sliding surface pressure of the distal sliding part
140
decreases with an increase in the central angle θ, the weight of the piston
14
increases with the central angle θ. Accordingly, it is desirable to determine the central angles θ and Φ with the above factors taken into account. However, the central angle θ of the front sliding part
140
must be 120° or smaller, and is preferably 110° or 100° or smaller. In the present embodiment, the central angle θ is 90°, while the central angle Φ of the proximal sliding part
142
is 120°.
The distal sliding part
140
has a length L
3
(referred to as “distal length”) whose percentage β(=100×L
3
/L
1
) with respect to the head inner length L
1
is determined to be 20%.
The percentage β must be at least 10%, and is preferably at least 15%, 20% or 25%. If the length of the proximal sliding part
142
is fixed, an increase in the percentage β increases an effect of preventing the inclination of the piston
14
, but increases the eight of the inner sliding portion
132
. Accordingly, it is desirable to determine the percentage β with these factors taken into account. The distal length L
3
may be determined based on a percentage γ of this length L
3
with respect to the entire length L of the piston
14
. In the present piston
14
, the percentage γ of the distal length L
3
with respect to the entire length L is determined to be 10%. The percentage γ must be at least 5%, and is preferably at least 8%, 10% or 12%. The axial position of the distal sliding part
140
is determined by the percentage α of the head inner length L
1
with respect to the entire length L of the piston
14
and the percentage β of the distal length L
3
with respect to the head inner length L
1
). In the present embodiment, the end of the distal sliding part
140
is spaced from the end face
136
of the piston
14
by a distance corresponding to the 40% of the entire length L.
In the present embodiment, the total length (L
1
−L
3
) of the body portion
128
and the proximal sliding part
142
is made equal to the head outer length L
2
(total length of the body portion
128
and the outer sliding portion
130
), as shown in FIG.
3
. In this sense, the distal sliding part
140
of the inner sliding portion
132
may be considered to be an extension of the proximal sliding part
142
. The total length (L
1
−L
3
) need not be equal to the head outer length L
2
, and may be different from the length L
2
.
In the present swash plate type compressor constructed as described above, the piston
14
has the distal sliding part
140
so that the distance between the axial positions at which the reaction forces Fc, Fd act on the head portion
82
of the piston
14
can be increased, whereby 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
14
due to the provision of the inner sliding portion
132
is reduced since the distal length L
3
of the distal sliding part
140
and its central angle θ are minimized to such an extent that assures a surface area of the distal sliding part
140
sufficient to limit its sliding surface pressure to a value not higher than a predetermined upper limit. Accordingly, the durability of the piston
14
can be effectively increased while reducing the mass of the piston
14
. Namely, the local wear and removal of the fluoro resin coating of the distal sliding part
140
can be minimized.
The configuration of the piston
14
is not limited to the details described above with respect to the first embodiment by reference to
FIGS. 2-4
. For instance, the connecting portion
83
need not include both of the ribs
134
,
135
, but may consist of only one of these two ribs
134
,
145
. Similarly, the configuration and size of the distal sliding part
140
are not limited to the details described above with respect to the first embodiment. The distal sliding part
140
may have any configuration and size provided the configuration and size assure an improvement in the durability of the piston
140
.
FIG. 6
shows a piston
148
according to a second embodiment of this invention, which has a modified distal sliding part as indicated at
150
. The distal sliding part
150
has a circumferential dimension and a central angle θ which continuously decrease as indicated by a curved line in
FIG. 6
as the part
150
extends in the axial direction of the piston
148
from the head portion toward the neck portion.
FIG. 7
shows a third embodiment wherein a piston
151
has a distal sliding part
152
which consists of a wide section
154
located on the side of the neck portion, and a narrow section
156
located on the side of the head portion. The wide section
154
has a comparatively large central angle and consequently a comparatively large pressure-receiving surface area, which further improves the durability of the piston
151
. On the other hand, the narrow section
156
contributes to a decrease in the amount of increase of the weight of the piston
151
due to the provision of the inner sliding part
152
, as compared with that of a piston whose inner sliding part consists of only the wide portion
154
. Only the wide portion
154
may be considered to be the distal sliding part
154
, and the narrow section
156
may be considered to be a part of the proximal sliding part.
Referring next to
FIG. 8
, there is shown a fourth embodiment of this invention wherein a piston
158
has a spaced-apart distal sliding part
159
on the rib
135
which connects the proximal part
142
and the neck portion
80
. The spaced-apart distal sliding part
159
is spaced from the proximal sliding part
142
. In this embodiment, the distal sliding part
159
is spaced from the end face
146
of the body portion
128
by a distance L
1
′ a percentage γ(=100×L
1
′/L) of which with respect to the entire length L of the piston
158
is determined to be 45%. A head inner length is a sum of the axial length L
1
of the proximal sliding part
152
and the axial length L
3
of the spaced-apart distal sliding part
159
, and a percentage {=100×(L
1
+L
3
)/L} of this head inner length with respect to the entire piston length L is determined to be 50%. The provision of the spaced-apart distal sliding part
159
eliminates a need of increasing the axial length of the proximal sliding part
142
, so that the weight increase of the piston
158
due to the provision of the inner sliding portion is accordingly reduced. The spaced-apart distal sliding part
159
may be configured such that its central angle continuously changes in the axial direction, along a straight or curved line.
In the preceding embodiments, the central angle (circumferential dimension) of the inner sliding portion
132
decrease in steps at the boundary between the proximal and distal sliding parts, in the direction from the head portion toward the neck portion
80
. However, this central angle of the inner sliding portion
132
may continuously decrease at the boundary between the proximal and distal sliding parts. The configuration of the inner sliding portion
132
may be either symmetrical or asymmetrical with respect to a plane which passes the centerline N of the piston
14
,
148
,
151
,
158
and the centerline M of the cylinder block
10
.
FIG. 9
shows a piston
160
according to a further embodiment of this invention, wherein the central angle θ of a distal sliding part
162
is larger than the central angle Φ of a proximal sliding part
164
, contrary to the arrangements in the preceding embodiments. The comparatively larger central angle (circumferential dimension) of the distal sliding part
162
provides a comparatively larger pressure-receiving surface area, which results in an effect of accordingly lowering the sliding surface pressure in the distal sliding part
162
. On the other hand, the proximal sliding part
164
does not receive a large reaction force from the inner surface of the cylinder bore, and need not have a pressure-receiving surface area as large as that of the distal sliding part
162
. Thus, the present arrangement permits an improved degree of durability of the piston
160
while assuring a reduced weight of the piston. It is noted that the provision of the proximal sliding part
164
is not essential, and that the distal sliding part
162
may be provided on the connecting portion which connects the body portion
128
of the head portion
82
and the neck portion
80
.
It is further noted that the various distal sliding parts described above may have suitable shapes in transverse cross section, and that the configuration of the body portion
128
is not limited to that of the illustrated embodiment. For instance, the body portion
128
may have an axially intermediate section which has a smaller diameter than the other axial sections. This arrangement also assures intended compression of the refrigerant gas by the piston, provided an air-tight sliding contact of the piston with the cylinder bore
12
is guaranteed at the opposite end portions of the piston.
The construction of the swash type compressor is not limited to the details of the illustrated embodiments, but may be modified as needed. For example, the solenoid-operated control valve
100
is not essential, and may be replaced by a shut-off valve which is opened and closed depending upon a difference between the pressures in the crank chamber
56
and the suction chamber
24
. In any arrangement for controlling the fluid communication between the crank chamber
56
and the suction chamber
24
, the angle of inclination of the swash plate
60
is increased to increase the discharge capacity of the compressor, by lowering the pressure in the crank chamber
56
.
Claims
- 1. A swash plate type compressor comprising:a cylinder block having a plurality of cylinder bores formed therein such that said cylinder bores are arranged along a circle; a rotary drive shaft having an axis of rotation aligned with a centerline of said circle; a swash plate rotated with said rotary drive shaft; and a plurality of single-headed pistons each including a head portion slidably engaging a corresponding one of said cylinder bores, and a neck portion engaging said swash plate, said each single-headed piston being reciprocated by said swash plate rotated by said rotary drive shaft, said head portion of said 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 said body portion and said neck portion, said outer and inner sliding portions slidably engaging respective circumferential portions of an inner circumferential surface of said corresponding cylinder bore which correspond to respective radially outer and inner portions of said cylinder block, wherein said inner sliding portion includes a narrow section disposed on the side of said body portion, and a wide section which is disposed on the side of said neck portion and which has a larger circumferential dimension than said narrow section, and wherein a distance from an end face of said body portion remote from said neck portion to an end of said inner sliding portion on the side of said neck portion is larger than a distance from said end face to an end of said outer sliding portion on the side of said neck portion, and said inner sliding portion has a distal sliding part which is spaced from said end face by a distance of at least 40% of an entire length of said piston in an axial direction of said piston and which has a length that is at least 5% of said entire length of said piston and a central angle of not larger than 120°, wherein said central angle is defined by two lines which connect a centerline of said body portion and circumferentially opposite ends of said inner sliding portion as seen in a circumferential direction of said body portion, said central angle of said distal sliding part being different from that of the other part of said inner sliding portion adjacent to said body portion.
- 2. A swash plate type compressor according to claim 1, wherein said central angle of said distal sliding part is not larger than 100°.
- 3. A swash plate type compressor according to claim 1, wherein said length of said sliding distal part is at least 8% of said entire length of said piston.
- 4. A swash plate type compressor comprising:a cylinder block having a plurality of cylinder bores formed therein such that said cylinder bores are arranged along a circle; a rotary drive having an axis of rotation aligned with a centerline of said circle; a swash plate rotated with said rotary drive shaft; and a plurality of single-headed pistons each including a head portion slidably engaging a corresponding one of said cylinder bores, and a neck portion engaging said swash plate, said each single-headed piston being reciprocated by said swash plate rotated by said rotary drive shaft, said head portion of said each single-headed piston including a body portion having a circular shape in transverse cross section, and an inner sliding portion including (a) an inner protrusion which extends toward said neck portion from a circumferential part of said body portion, which part corresponds to a radially inner portion of said cylinder block and which has a proximal inner sliding surface which slidably engages an inner circumferential surface of said corresponding cylinder bore, and (b) a spaced-apart distal sliding part which has a spaced-apart inner sliding surface spaced apart from said inner protrusion, said spaced-apart distal sliding part being spaced from an end face of said body portion remote from said neck portion, by a distance of at least 40% of an entire length of said piston, said spaced-apart distal sliding part having an axial length which is at least 5% of said entire length of said piston and a central angle of not larger than 120°, said central angle being defined by two lines which connect a ceniterline of said body portion and circumferentially opposite ends of said distal sliding part as seen in a circumferential direction of said body portion.
- 5. A swash plate type compressor comprising:a cylinder block having a plurality of cylinder bores formed therein such that said cylinder bores are arranged along a circle; a rotary drive shaft having an axis of rotation aligned with a centerline of said circle; a swash plate rotated with said rotary drive shaft; and a plurality of single-headed pistons each including a head portion slidably engaging a corresponding one of said cylinder bores, and a neck portion engaging said swash plate, said each single-headed piston being reciprocated by said swash plate rotated by said rotary drive shaft, said head portion of said each single-headed piston including a body portion having a circular shape in transverse cross section, and an outer sliding portion and inner sliding portion which are disposed between said body portion and said neck portion, said outer and an inner sliding portions slidably engaging respective circumferential portions of an inner circumferential surface of said corresponding cylinder bore which correspond to respective radially outer and inner portions of said cylinder block, wherein a distance from an end face of said body portion remote from said neck portion to an end of said inner sliding portion on the side of said neck portion is larger than a distance from said end face to an end of said outer sliding portion on the side of said neck portion, and said inner sliding portion has a distal sliding part which is spaced from said end face by a distance of at least 40% of an entire length of said piston in an axial direction of said piston and which has a length that is at least 5% of said entire length of said piston and a central angle of not larger than 120°, wherein said central angle is defined by two lines which connect a centerline of said body portion and circumferentially opposite ends of said distal sliding part as seen in a circumferential direction of said body portion, said central angle of said distal sliding part being abruptly or steppedly changed from that of the other part of said inner sliding portion adjacent to said body portion, and wherein said central angle of said distal sliding part continuously decreases as said distal sliding part extends in an axial direction of said piston from said head portion toward said neck portion.
- 6. A swash plate type compressor comprising:a cylinder block having a plurality of cylinder bores formed therein such that said cylinder bores are arranged along a circle; a rotary drive shaft having an axis of rotation aligned with a centerline of said circle; a swash plate rotated with said rotary drive shaft; and a plurality of single-headed pistons each including a head portion slidably engaging a corresponding one of said cylinder bores, and a neck portion engaging said swash plate, said each single-headed piston being reciprocated by said swash plate rotated by said rotary drive shaft, said head portion of said each single-headed piston including a body portion having a circular shape in transverse cross section, and an outer protrusion and an inner protrusion which extend toward said neck portion from respective circumferential parts of said body portion, which parts correspond to respective radially outer and inner portions of said cylinder block and which slidably engage respective circumferential portions of an inner circumferential surface of said corresponding cylinder bore, wherein said inner protrusion comprises a proximal sliding part which is adjacent said body portion, and a distal sliding part which is spaced apart from said body portion, said distal sliding part having a central angle which is different from that of said proximal sliding part, said central angle being defined by two lines which connect a centerline of said body portion and circumferentially opposite ends of said inner protrusion as seen in a circumferential direction of said body portion, and wherein a total length of said body portion and said inner protrusion in an axial direction of said piston is at least 45% of an entire length of said piston, said inner protrusion having said central angle of not larger than 120° in at least said distal sliding part whose axial length is at least 10% of said total length, a distance of extension of said inner protrusion from said body portion being larger than that of said outer protrusion by an amount of at least 5% of an entire length of said piston.
Priority Claims (1)
Number |
Date |
Country |
Kind |
11-150448 |
May 1999 |
JP |
|
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A |
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A |
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