BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention generally relates to a positive-displacement-type refrigerant
compressor including a reciprocating type refrigerant compressor and a rotary type
refrigerant compressor and, more particularly, relates to an oil-separating and lubricating
system incorporated in the positive-displacement-type refrigerant compressor for the
lubrication of internal various portions and movable elements of the positive-displacement-type
refrigerant compressor by separating oil from a refrigerant at a high pressure and
by supplying the separated oil to the portions and elements to be lubricated.
2. Description of the Related Art
[0002] In a positive-displacement-type refrigerant compressor mainly incorporated in a vehicle
climate control system, lubrication of various internal portions and movable elements
of the compressor is achieved by an oil, i.e., by an oil mist suspended in a gas-phase
refrigerant which is compressed within the compressor. Therefore, when the compressed
refrigerant containing and suspending therein the oil is delivered from the compressor
to a refrigerating system in the climate control system, the oil is attached to an
internal wall of an evaporator of the refrigerating system to result in an reduction
in the heat exchanging efficiency of the evaporator. Thus, in the conventional refrigerating
system, an oil separating unit is arranged in a high pressure gas pipe extending from
the refrigerant outlet of the compressor to a condenser, and the separated oil is
returned from the oil separating unit into the interior of the refrigerant compressor
via a separate oil-return conduit. However, an arrangement of the oil separating unit
in the gas pipe and an addition of the oil-return conduit to the refrigerating system
make it cumbersome to assemble the refrigerating system of the vehicle climate control
in a rather narrow assembling space in a vehicle. Further, the oil-return conduit
is usually formed by a long pipe element having a small diameter, and accordingly,
clogging easily occurs during the operation of the compressor. Therefore, there has
been provided a refrigerant compressor provided with an oil-separating unit directly
incorporated therein.
[0003] The oil-separating unit incorporated in the conventional refrigerant compressor is
provided with an oil storing chamber formed in the compressor for storing an oil separated
from a refrigerant in a high pressure region in the compressor, and an oil-return
passage communicating the oil storing chamber with a low pressure region such as a
crank chamber in the compressor for supplying the oil from the oil storing chamber
to the low pressure region. The oil-return passage is provided with a valve unit arranged
therein to control an amount of oil to be supplied into the low-pressure region in
response to a change in the state of operation of the compressor.
[0004] For example, Japanese Unexamined Patent Publication (Kokai) No. 9-324758 (JP-A-9-324758)
discloses a valve unit which functions to interrupt the oil-return passage during
the running of the compressor, and to permit the oil to flow therethrough during the
stopping of operation of the compressor.
[0005] Japanese Unexamined Patent Publication (Kokai) No. 6-249146 (JP-A-6-249146) discloses
a valve unit used in a variable displacement type refrigerant compressor and operates
in such a manner that when an oil separating chamber is kept at a high pressure during
a large displacement operation of the compressor, a restricted amount of oil is permitted
to pass through an oil-return passage via the valve unit, and when the oil separating
chamber is kept at a low pressure during a small displacement operation of the compressor,
a large amount of oil is permitted to pass through the oil-return passage via the
valve unit.
[0006] Nevertheless, in the two conventional incorporated type oil separating systems of
JP-A-9-324758 and JP-A-6-249146, no positive means to completely prevent the oil from
being delivered from the interior of the compressor toward the associated refrigerating
system is provided. Namely, since lubrication of various internal portions and movable
elements of the refrigerant compressor must rely on mainly the oil suspended in the
refrigerant returned from an external refrigerating system, at least when the refrigerant
compressor is stopped, the amount of the oil supplied to the low pressure region in
the compressor must be increased to prevent lack of lubricant at the start of operation
of the refrigerant compressor. In this connection, even if the amount of oil delivered
from the refrigerant compressor is small, delivery of the oil from the compressor
into the external refrigerating system becomes a cause of preventing an increase in
the heat exchanging efficiency in the refrigerating system depending on the rate of
containment of an oil in the refrigerant. Moreover, when the compressor is stopped,
if a large amount of oil is supplied to the low pressure region in the compressor,
the oil remaining in the low pressure region is suddenly agitated due to re-starting
of the compressor and accordingly, the oil is splashed so that compression of the
oil, i.e., a liquid or oil compression occurs within the respective cylinder bores.
Thus, shock and noise are generated in the interior of the refrigerant compressor.
SUMMARY OF THE INVENTION
[0007] Therefore, an object of the present invention is to obviate all defects encountered
by the conventional oil separating and lubricating unit incorporated in a refrigerant
compressor.
[0008] Another object of the present invention is to provide a positive-displacement-type
refrigerant compressor internally provided with a novel oil-separating and lubricating
system able to lubricate the interior of the compressor and to enhance the heat exchanging
efficiency in a refrigerating system in which the compressor is incorporated.
[0009] A further object of the present invention is to provide a positive-displacement-type
refrigerant compressor internally provided with an oil-separating and lubricating
system having function to prevent occurrence of the oil compression even when the
compressor is started.
[0010] In accordance with a broad aspect of the present invention, there is provided a positive-displacement-type
refrigerant compressor including:
a suction system to receive a refrigerant, by suction, from an external refrigerating
system,
a compressing mechanism having a compression chamber in which the refrigerant introduced
from the suction system is compressed and discharged into a discharge chamber receiving
the compressed refrigerant at a discharge pressure, and
an oil-separating and lubricating system for lubricating the interior of the positive-displacement-type
refrigerant compressor by oil separated from the refrigerant,
wherein the oil-separating and lubricating system comprises:
an oil-separating unit accommodated in a high pressure region communicating with the
discharge chamber to cause separation of the oil from the compressed refrigerant;
an oil-storing chamber accommodated in the high pressure region to store the oil separated
by the oil-separating unit;
an oil-supply passage supplying the oil from the oil-storing chamber to the suction
system;
a valve assembly disposed in a portion of the oil-supply passage for regulating an
amount of flow of the oil from the oil-storing chamber to the suction system, the
valve assembly comprising:
a first valve chamber having a substantial volume therein;
a second valve chamber arranged adjacent to the first valve chamber via a partition
wall provided therebetween and fluidly communicating with an upstream side of the
oil-supply passage;
a movable valve actuating element accommodated in the first valve chamber to be moved
by an application of a pressure thereto against an elastic force, the movable valve
actuating element defining outer and inner separate regions, one of which fluidly
communicates with a downstream side of the oil-supply passage, and the other of which
fluidly communicates with the compression chamber;
a valve element extending from the movable valve actuating element and opening and
closing a valve port bored in the partition wall to provide a fluid communication
between the upstream and downstream of the oil-supply passage, the valve element moving
in response to a movement of the movable valve actuating element and closing the valve
port when the pressure introduced from the compression chamber and acting on the movable
valve actuating element is overcome by the elastic restoring force acting on the movable
valve actuating element; and
a restriction arranged in a portion of the oil-supply passage for applying a flow
restricting effect to the oil flowing through the oil-supply passage.
[0011] The movable valve actuating element may be either a bellows element accommodated
in the first valve chamber or a combination of a spool valve element and an o-ring
element.
[0012] In accordance with an embodiment, the valve assembly includes a first valve chamber
accommodating therein a bellows element to define separate outer and inner regions,
one of which fluidly communicates with a downstream side of the oil-supply passage,
a second valve chamber arranged adjacent to the first valve chamber via a partition
wall provided therebetween and fluidly communicating with an upstream side of the
oil-supply passage, a valve element arranged to extend from the bellows element and
being able to open and close a valve port bored in the partition wall in response
to a movement of the bellows element which can be moved by a pressure introduced from
the compression chamber, the valve element closing the valve port which, when opened,
can provide a fluid communication between the upstream and downstream of the oil-supply
passage when the pressure from the compression chamber acting on the bellows element
is overcome by an elastic restoring force of the bellows element.
[0013] The oil-storing chamber is formed to have a volume suitable for storing substantially
all of the oil filled in the interior of the compressor and circulated through the
interior of the refrigerant compressor for the purpose of lubrication, and arranged
to permit only the smallest possible amount of oil to flow out of the oil-storing
chamber into the refrigerating system. Thus, the amount of the oil contained in the
refrigerant is reduced to appreciably improve the heat exchanging efficiency of an
evaporator in the refrigerating system. Therefore, the interior of the compressor,
i.e., various internal portions and movable elements of the compressor can be lubricated
by the oil stored in the oil-storing chamber and circulated through the suction system
of the compressor and the oil-separating unit during the operation of the compressor.
When the operation of the compressor is stopped, the supply of the oil to the lubricated
portions and the movable elements of the compressor due to the circulation of the
oil is automatically stopped. Accordingly, the amount of oil remaining in the suction
system of the compressor, which includes a crank chamber, can be kept small to prevent
the occurrence of oil compression when the compressor is started. Further, when the
compressor is started, the oil stored in the oil-storing chamber can be quickly supplied
to the lubricated portions and the movable elements of the compressor due to an immediate
start of circulation of the oil through the suction system, and the oil-separating
and lubricating system.
[0014] Moreover, since the valve assembly includes the valve element which moves in association
with an expanding and contracting movement of the bellows element to open and close
the valve port providing a fluid communication between the upstream and downstream
of the oil-supplying passage extending through the first and second valve chambers,
and since the valve assembly requires no sealing means for fluidly sealing any of
the movable valve element and the bellows element, the opening and closing movement
of the valve element can be stable and accurate enough for guaranteeing the performance
of the valve assembly.
[0015] The restriction disposed in the oil-supplying passage can limit an amount of oil
flowing from the oil-storing chamber into the suction system.
[0016] The valve port may be provided so as to serve both as an aperture cooperating with
the valve element to adjustably change the amount of oil passing through the aperture
and a flow restriction to limit the amount of oil flowing through the oil-supplying
passage from the oil-storing chamber to the suction system of the compressor. Thus,
the construction of the valve assembly can be simplified.
[0017] Alternately, in accordance with another embodiment of the present invention, the
valve assembly may include a first valve chamber fluidly communicating with the downstream
side of the oil-supplying passage and having an inner wall, a spool valve element
disposed in the first valve chamber and having an outer face facing the inner wall
of the first valve chamber via a small gap, an o-ring element deformably disposed
in the small gap and fitted in a pair of annular recesses formed in the inner wall
of the first valve chamber and the outer face of the spool valve element to movably
support the spool valve element, a second valve chamber arranged adjacent to the first
valve chamber via a partition wall provided therebetween and fluidly communicating
with an upstream side of the oil-supply passage, a valve element arranged to extend
from the valve spool element and being able to open and close a valve port bored in
the partition wall in response to a movement of the valve spool element which can
be moved by a deformation of the o-ring which is caused by a pressure introduced from
the compression chamber, and a restriction arranged in a portion of the oil-supply
passage, the valve element closing the valve port which, when opened, can provide
a fluid communication between the upstream and downstream sides of the oil-supply
passage when the pressure from the compression chamber acting on the valve spool element
is overcome by an elastic restoring force of the o-ring.
[0018] The above-mentioned valve assembly employing the valve spool element and the o-ring
may be simpler in its construction than the afore-mentioned valve assembly employing
the bellows element and accordingly, can be less expensive.
[0019] Preferably, a pressure-introduction passage for introducing the pressure in the compression
chamber into a position acting on the valve element is provided with a flow restriction
function therein. Thus, when the positive-displacement-type refrigerant compressor
employs reciprocating pistons to compress the refrigerant, the pressure acting on
the valve element can be maintained substantially at an average pressure of the pressures
prevailing in the compression chamber and hardly changes.
[0020] On the other hand, when the positive-displacement-type refrigerant compressor is
a rotary type refrigerant compressor, the pressure acting on the valve element can
be an intermediate pressure of pressures prevailing in the compression chamber. Thus,
the movement of the valve element cooperating with the valve port can be very stable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other objects, features, and advantages of the present invention will
be made more apparent from the ensuing description of the preferred embodiments thereof
with reference to the accompanying drawings wherein:
Fig. 1 is a longitudinal cross-sectional view of a positive-displacement-type refrigerant
compressor, i.e., a swash plate operated double-headed piston type refrigerant compressor
with an oil-separating and lubricating system, according to an embodiment of the present
invention;
Fig. 2 is an enlarged cross-sectional view of a valve assembly adapted for use in
the oil-separating and lubricating system of the compressor of Fig. 1, illustrating
a state where a valve port is opened;
Fig. 3 is a similar view to Fig. 2, illustrating a state where the valve port is closed
by a valve element;
Fig. 4 is an enlarged cross-sectional view of a different valve assembly adapted for
use in the oil-separating and lubricating system of the compressor of Fig. 1, illustrating
a state where a valve port is opened by a valve element;
Fig. 5 is a similar view to Fig. 4, illustrating a state where the valve port is closed
by the valve element;
Fig. 6 is an enlarged cross-sectional view of a further different valve assembly adapted
for use in the oil-separating and lubricating system, illustrating a state where a
valve port is closed by the valve element;
Figs. 7A through 7C are schematic views illustrating opened and closed conditions
of the valve port of the valve assembly of Fig. 6, in relation to an elastic deformation
of an o-ring incorporated in the valve assembly of Fig. 6;
Figs. 8A and 8B are schematic views illustrating two modified constructions of the
valve assembly of Fig. 6; and,
Fig. 9 is a cross-sectional view of a scroll type refrigerant compressor, i.e., a
typical rotary type refrigerant compressor, provided with an oil-separating and lubricating
system therein, according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Referring to Fig. 1, a double-headed piston incorporated reciprocating type refrigerant
compressor is provided with a pair of axially combined cylinder blocks 1 and 2 having
later-described five cylinder bores on axially left and right sides of the combined
cylinder blocks. The combined cylinder blocks 1 and 2 have axially front and rear
ends closed by a front housing 5 and a rear housing 6, via a front valve plate 3 and
a rear valve plate 4, respectively. The front housing 5, the front cylinder block
1, the rear cylinder block 2 and the rear housing 6 are gas-tightly combined together
by several long screw bolts (not shown in Fig. 1). The connecting portion of the combined
front and rear cylinder blocks 1 and 2 is provided with a crank chamber 8 formed therein
to receive a swash plate (a cam plate) 10 fixedly mounted on a drive shaft 9 which
is rotatably supported by the combined cylinder blocks 1 and 2, and axially extends
through a central bores 1a and 2a of the combined cylinder blocks 1 and 2. The swash
plate 10 is thus rotated together with the drive shaft 9 about an axis of rotation
of the drive shaft 9.
[0023] The axially aligned five cylinder bores 11 on the left and right sides of the combined
cylinder blocks 1 and 2 are arranged in parallel with one another with respect to
and circumferentially spaced apart from one another around the axis of rotation of
the drive shaft 9.
[0024] Double-headed pistons 12 are slidably fitted in the cylinder bores 11 on the axially
left and right sides of the cylinder blocks 1 and 2, and each of the double-headed
pistons 12 is engaged with the swash plate 10 via a pair of semispherical shoes 13,
13.
[0025] The front and rear housings 5 and 6 are internally provided with suction chambers
14 and 15 formed in a radially outer region of the interior of the respective housings
5 and 6, and discharge chambers 16 and 17 formed in a radially inner region of the
interior of the front and rear housings 5 and 6. The front and rear valve plates 3
and 4 are provided with suction ports 18, 19 formed therein to permit the refrigerant
to be sucked from the respective suction chambers 14 and 15 into the respective cylinder
bores 11 on the left and right sides. The front and rear valve plates 3 and 4 are
also provided with discharge ports 20, 21 formed therein to permit the high pressure
refrigerant after compression to be discharged from the respective cylinder bores
11 on the left and right sides toward the discharge chambers 16 and 17. Suction valves
(not shown) are arranged in respective boundaries between the front and rear ends
of the combined cylinder blocks 1 and 2 and the front and rear valve plates 3 and
4 to openably close the suction ports 18, 19, and discharge valves (not shown) are
arranged in respective boundaries between the front and rear valve plates 3 and 4
and the front and rear housings 5 and 6 to openably close the discharge ports 20 and
21 and to be supported by valve retainers 22 and 23.
[0026] As best shown in Fig. 1, the discharge chambers 16 and 17 of the front and rear housings
1 and 2 are provided with partially radially extending portions therein, which are
fluidly connected to one another by discharge passages 30a and 30b formed in the combined
cylinder blocks 1 and 2, and are fluidly connected to a delivery passage 30c formed
in the rear housing 6, and the delivery passage 30c is fluidly connected to an outlet
port (not shown in Fig. 1) for delivering the compressed refrigerant into an external
refrigerating system via an oil-separating mechanism which is also formed in the rear
housing 6.
[0027] The above-mentioned oil-separating mechanism constitutes a part of an oil-separating
and lubricating system, and the oil-separating mechanism includes an oil-separating
chamber 41 formed as a cylindrical bore formed in the rear housing 6 to have an inner
bottom. The oil-separating chamber 41 fluidly communicates with the above-mentioned
delivery passage 30c and receiving therein a flanged oil-separating cylinder 43 which
is attached to an uppermost position of the oil-separating chamber 41 by means of
a snap ring 42. An oil-storing chamber 44 is arranged below the oil-separating chamber
41 for receiving an oil from the chamber 41. The oil-storing chamber 44 is formed
to have sufficient volume enough to store all of the oil which is preliminarily filled
into the interior of the compressor during the assembly of the compressor, and for
surely circulating all of the filled oil through various pressure regions in the interior
of the compressor for the purpose of lubricating many portions such as cylinder bores
11 and opposite faces of the swash plate 10, and movable elements of the compressor
such as double-headed pistons 12, shoes 13, and various radial and thrust bearings.
The fluid communication between the oil-separating chamber 41 and the oil-storing
chamber 44 is provided by an oil hole 45 formed in the bottom of the oil-separating
chamber 41.
[0028] The oil-separating and lubricating system is further provided with a valve assembly
50 formed as a differential pressure type valve assembly and seated in a bottomed
bore 51 formed in the rear housing 6. As shown in Figs. 2 and 3, the valve assembly
50 includes a framework 52 formed to be fitted in the bottomed bore 51 of the rear
housing 6. The framework 52 is formed by two separate frames 52a and 52b, and a plate
cap 52d which are fixedly seated in position within the bore 51 by means of a snap
ring 53. An opening of the bottomed bore 51 is closed by a plate-like lid 54. The
framework 52 of the valve assembly 50 is provided with a hollow first valve chamber
55a and a hollow second valve chamber 55b separated by a partition plate 52c, and
the first valve chamber 55a receives a bellows element 56 capable of expanding and
contracting therein and having one end fixed to the frame 52b and the other end sealingly
connected to a flange member. The bellows element 56 is provided as a movable valve
actuating element, and the interior of the bellows element 56 is formed as a pressure
sensing chamber communicating with a cylindrical pressure chamber 51a formed in the
bottomed bore 51 below the frame 52b. Namely, a small hole 72 is formed in the frame
52b to provide a fluid communication between the pressure sensing chamber of the bellows
element 56 and the cylindrical pressure chamber 51a. The cylindrical pressure chamber
51a also communicates with a compression chamber in a predetermined one of the cylinder
bores 11, via a pressure-introducing passage 57 which extends through the rear housing
6 from the above-mentioned cylindrical pressure chamber 51a to the predetermined cylinder
bore 11. The pressure-introducing passage 57 is formed as a passage having a small
diameter, so that it can function as a flow restriction to make a pressure flat when
it is introduced from the compression chamber of the cylinder bore 11 into the cylindrical
pressure chamber 51a.
[0029] The flange plate connected to the other end of the bellows element 56 is connected
at its central position to a valve element 59 extending in a direction corresponding
to a direction in which the bellows element 56 expands. An upper portion of the valve
element 59 extends through a through bore formed as a valve port 58 in the partition
plate 52c, and has a spherical valve 59a at an extreme end thereof positioned in the
second valve chamber 55b. The valve assembly 50 is mounted in the bottomed bore 51
so as to be hermetically sealed by suitable sealing members 70 such as o-rings fitted
in grooves recessed in the outer circumference of the framework 52.
[0030] The rear housing 6 is provided with a counter-bore 60 centrally formed therein, which
fluidly communicates with the crank chamber 8 via the central bore 2a of the combined
cylinder blocks 1 and 2. The rear housing 6 is further provided with an oil passage
61a extending between the oil-storing chamber 44 and the second valve chamber 55b
of the valve assembly 50 received in the bottomed bore 51, and an additional oil passage
61b extending between the first valve chamber 55a and the above-mentioned counter-bore
60. Thus, the counter-bore 60 is fluidly communicated with the oil-storing chamber
44 through the oil passages 61a and 61b and the valve assembly 50, so that the oil
stored in the oil-storing chamber 44 can be supplied to the counter-bore 60, and additionally
to the central bore 2a and the crank chamber 8. Namely, the oil passages 61a and 61b
are provided as upstream side and downstream side oil-supplying passages, respectively,
so that a circulating oil lubrication passageway is formed by which the oil to lubricate
the interior of the compressor is basically circulated through the oil-storing chamber
44, the upstream side oil passage 61a, the valve assembly 50, the downstream side
oil passage 61b, the counter-bore 60, the central bore 2a, the crank chamber 8, the
discharge chambers 16, 17, and the oil-separating chamber 41.
[0031] As best shown in Figs. 2 and 3, in a preferred embodiment, an oil restriction 62
is arranged in the oil passage 61a for restricting an amount of supply of the lubricating
oil from the oil-storing chamber 44 into the crank chamber 8 constituting a part of
the suction system of the compressor.
[0032] When the positive-displacement-type refrigerant compressor incorporating the oil-separating
and lubricating system of Figs. 2 and 3 is driven by an application of a drive power
from an external drive source, i.e., a vehicle engine to the drive shaft 9, the drive
shaft 9 is rotated together with the swash plate 10, and the double-headed pistons
12 engaged with the swash plate 10 are reciprocated in the corresponding cylinder
bores 11. Therefore, the refrigerant is sucked from the suction chambers 14, 15 into
the cylinder bores 11 and compressed by the pistons 12. The compressed refrigerant
is discharged by the pistons 12 from the compression chambers within the cylinder
bore 11 toward the discharge chambers 16, 17. When the compressed refrigerant is discharged
into the discharge chambers 16, 17, it is further introduced into the oil-separating
chamber 41 via the discharge passages 30a and 30b and the delivery passage 30c. When
the compressed refrigerant is introduced from the delivery passage 30c into the oil-separating
chamber 41, the compressed refrigerant is forcedly rotated around the oil-separating
cylinder 43 by the cylindrical inner wall of the oil-separating chamber 41, as shown
by arrows in Fig. 1, and is introduced into the interior of the flanged oil-separating
cylinder 43 via an opening thereof. The compressed refrigerant is further delivered
from the interior of the oil-separating cylinder 43 toward an external refrigerating
system via a delivery port (not shown in Fig. 1) of the compressor.
[0033] During the rotary movement of the compressed refrigerant in the oil-separating chamber
41, the oil component suspended in the compressed refrigerant is effectively separated
from the refrigerant due to a centrifugal force acting on the oil component, and the
separated oil flows down to the bottom of the oil-separating chamber 41, and further
into the oil-storing chamber 44 via the oil hole 45. At this stage, it should be understood
that due to the oil separation from the refrigerant in the oil-separating chamber
41, the refrigerant containing less oil component therein is delivered from the delivery
port of the compressor into the external refrigerating system. Namely, a rate of oil
contained in a unit weight of refrigerant is reduced within the oil-separating chamber
41 before the compressed refrigerant gas is delivered from the delivery port. Thus,
the compressed refrigerant containing less amount of oil component can be effectively
used as a heat-exchange-medium in the refrigerating system.
[0034] Further, when oil separation is conducted by the oil-separating mechanism within
the oil-separating chamber 41, pulsation in the pressure of the compressed refrigerant
can be physically suppressed. Thus, the compressed refrigerant under a relatively
stable pressure can be delivered from the compressor to the external refrigerating
system, so that any adverse affect, such as vibration and noise, is not provided by
the refrigerating system.
[0035] During the operation of the refrigerant compressor, a very high pressure prevails
in the cylindrical pressure chamber 51a and the interior of the bellows element 56
and through the pressure-introducing passage 57 which extends between the predetermined
one of the cylinder bores 11 and the cylindrical pressure chamber 51a. At this stage,
the cylindrical pressure chamber 51a and the interior of the bellows element 56 is
maintained at a relatively high and steady pressure intermediate between the peak
discharge pressure and the suction pressure within the cylinder bore 11, due to the
flow restriction effect of the narrow pressure-introducing passage 57.
[0036] When a high pressure prevails in the interior of the bellows element 56, the bellows
element 56 is extended by overcoming a force due to an addition of a pressure prevailing
in the first valve chamber 55a which communicates with the suction region of the compressor,
i.e., the counter-bore 60 via the downstream side oil passage 61b and the elastic
restoring force of the bellows element 56 (the contracting force of the element 56).
Therefore, the valve element 59 and the spherical valve 59a are moved together, by
the bellows element 56, to keep the valve port 58 at its opened state as shown in
Fig. 2. Accordingly, the upstream and downstream oil passages 61a and 61b are connected
to one another via the second valve chamber 55b, the opened valve port 58 and the
first valve chamber 55a, so that the oil stored in the oil-storing chamber 44 flows
through these oil passages into the counter-bore 60 in the rear housing 6, and the
amount of flow of the oil is restricted and kept constant by the flow restriction
62 in the upstream side oil passage 61a. The oil further flows from the counter-bore
60 into the crank chamber 8 via the central bore 2a of the rear cylinder block 2 to
lubricate many inner portions of the compressor such as the cylinder bores 11, and
the movable elements such as the double-headed pistons 12, various bearings, the swash
plate 10 and, the shoes 13 and is eventually mixed with the refrigerant within the
suction pressure region. Thus, during the operation of the compressor, a controlled
amount of oil component is constantly circulated through the oil-storing chamber 44,
the crank chamber 8, and the oil-separating chamber 41 while lubricating the interior
of the compressor.
[0037] It should be understood that at the initial stage of the starting of the operation
of the compressor, since the valve port 58 is not still opened by the valve element
59, a discharge pressure in the oil-separating chamber 41 acts in the second valve
chamber 55b of the valve assembly 50 via the oil stored in the oil-storing chamber
44 and the upstream side oil passage 61a so as to apply a resistance against the opening
movement of the valve element 59. Nevertheless, a pressure receiving area of the spherical
valve 59a of the valve element 59 is rather smaller than that of the bellows element
56 on which the pressure introduced from the compression chamber via the pressure-introducing
passage 57 acts to expand the bellows element 56. Thus, the opening of the valve port
58 of the valve assembly 50 can be easily and surely achieved immediately after the
starting of the operation of the refrigerant compressor.
[0038] When the operation of the refrigerant compressor is stopped, the pressure prevailing
in the cylindrical pressure chamber 51a and the interior of the bellows element 56
through the pressure-introducing passage 57 is reduced to a pressure level substantially
equal to the suction pressure of the compressor and, accordingly, the bellows element
56 of the valve assembly 50 contracts due to the elastic restoring force thereof to
move the valve element 59 and the spherical valve 59a to the closing position closing
the valve port 58, as shown in Fig. 3. Therefore, the circulation of the oil through
the oil-storing chamber 44, the crank chamber 8 and the oil-separating chamber 41
is stopped. Accordingly, the supply of oil to the crank chamber 8 is automatically
stopped to prevent an excessive amount of oil from remaining in the crank chamber
8. Thus, when the operation of the refrigerant compressor is again started, oil-compression
within the cylinder bores 11 does not occur. Moreover, as soon as the operation of
the refrigerant compressor is started, the circulation of the oil from the oil-storing
chamber 44 to the oil-separating chamber 4 through the crank chamber 8 is quickly
started to lubricate the interior of the compressor. It should be understood that
when the operation of the refrigerant compressor stops for a long continuous time,
the bellows element 56 of the valve assembly 50 is kept at its contracted condition
due to the elastic restoring force thereof while maintaining the valve element 59
at its closed position closing the valve port 58. Thus, a constant stoppage of supply
of the oil from the oil-storing chamber 44 to the crank chamber 8 can be prevented
by the valve assembly 50.
[0039] In a modified embodiment, it is possible to remove the flow restriction 62 arranged
in the upstream side oil passage 61a if the valve port 58 formed in the partition
plate 52c is provided with a flow restriction function by forming it as a narrow passage
having an increased length. Thus, the construction of the oil-separating and lubricating
system incorporated in the positive-displacement-type refrigerant compressor can be
simplified.
[0040] Figure 4 shows a different valve assembly 80 incorporated in an oil-separating and
lubricating system assembled in a refrigerant compressor according to the present
invention. The valve assembly 80 shown in Fig. 4 is kept at a condition where a valve
port 88 is opened. The valve assembly 80 is provided with a framework 82 formed by
a cylindrical frame 82a and a lid-like frame 82b. The framework 82 is provided with
hollow first and second valve chambers 85a and 85b separated by a partition plate
82c in which the valve port 88 in the form of a through-bore is formed. The first
valve chamber 85a receives therein a bellows element 86 expanding and contracting
in a longitudinal direction thereof. One end of the bellows element 86 is attached
to the partition plate 82c and the other end of the bellows element 86 is closed by
an end plate member. An outer region of the first valve chamber 85a surrounding the
bellows element 86 is fluidly connected to a compression chamber within a predetermined
one of the cylinder bores 11 via a cylindrical pressure chamber 51a and a pressure-introducing
passage 57 which are similar to those of the afore-mentioned embodiment of Figs. 2
and 3. A valve element 89 is arranged to extend from the end plate of the bellows
element 86 through the interior of the bellows element 86 and the valve port 88 into
the second valve chamber 85b in which the valve element 89 has a spherical valve 89a
at its extreme end to open and close the valve port 88. The second valve chamber 85b
is fluidly connected to an oil passage 61a, i.e., an upstream side passage connected
to the oil-storing chamber 44 (see Fig. 1), and the interior of the bellows element
86 is fluidly connected to a downstream side oil passage 61b extending toward the
counter-bore 60 (Fig. 1) of the rear housing 6 of the refrigerant compressor.
[0041] Thus, the operation principle of the valve assembly 80 of Fig. 4 is substantially
similar to that of the valve assembly 50 of the embodiment of Figs. 2 and 3 and is
different only in that the valve element 89 and the spherical valve 89a are moved
from its opened position to open the valve port 88 shown in Fig. 4 to its closed position
to close the valve port 88 when the bellows element 86 is expanded by an elastic restoring
force thereof in response to a reduction in a pressure prevailing in the cylindrical
pressure chamber 51a and the cylindrical region of the first valve chamber 85a surrounding
the bellows element 86 via the pressure-introducing passage 57. Therefore, the detailed
description of the operation of the valve assembly 80 is omitted for the sake of brevity.
[0042] Figures 5 and 6 illustrate a different embodiment of a valve assembly accommodated
in an oil-separating and lubricating system for a positive-displacement-type refrigerant
compressor.
[0043] The valve assembly 90 of the present embodiment is similarly provided with a framework
92 defining therein a first valve chamber 95a and a second valve chamber 95b separated
by a partition plate 92c. The first valve chamber 95a receives therein a valve spool
94 to be movable toward and away from the second valve chamber 95b. The valve spool
94 is provided as a movable valve actuating element to actuate a movement of a later-described
valve element. A small annular gap is provided between a cylindrical outer wall of
the valve spool 94 and a cylindrical inner wall of the first valve chamber 95a. The
valve spool 94 is provided with a circularly extending v-shape groove R1 formed in
the cylindrical outer wall, which is arranged to substantially confront a circularly
extending v-shape groove R2 formed in the cylindrical inner wall of the first valve
chamber 95a, and an o-ring 96 is arranged in the annular gap and received in the confronting
v-shape grooves R1 and R2. Thus, the o-ring 96 supports the valve spool 94 in position
within the first valve chamber 95a. The o-ring 96 further provides a fluid separation
in the first valve chamber 95a between a pressure chamber 97 facing one of the opposite
faces of the valve spool 94 and fluidly connected to the pressure-introducing passage
57 and an oil chamber region facing the other of the opposite faces of the valve spool
94. The valve spool 94 is provided with an integral valve element 99 which extends
longitudinally through the oil chamber region and a valve port 98 bored in the partition
plate 92c into the second valve chamber 95b. The valve element 99 has a spherical
valve 99a provided at an extreme end thereof within the second valve chamber 95b,
so that the spherical valve 99a of the valve element 99 opens and closes the valve
port 98 due to the longitudinal movement of the valve element 99 actuated by the valve
spool 94 movable in a direction parallel with the inner wall of the first valve chamber
95a.
[0044] In the embodiment of Figs. 5 and 6, when the spherical valve 99a is moved to its
opened position to open the valve port 98, the o-ring 96 is forcedly and elastically
deformed within the v-shape grooves R1 and R2. Thus, the elastic restoring force of
the o-ring 96 is used for moving the spherical valve 99a to its position to close
the valve port 98 via the valve spool 94 and the valve element 98. Thus, the construction
of the valve assembly 90 can be simpler than the previous embodiments of Figs. 2 and
3, and Fig. 4, employing a bellows element 56 and 86.
[0045] Further, in the embodiment of Fig. 5, the o-ring 96 received in the v-shape grooves
R1 and R2 does not come into contact with each of the cylindrical walls of the valve
spool 94 and the framework 92 during the movement of the valve spool 94 and, accordingly,
the movement of the valve spool 94 moving the spherical valve 99a of the valve element
99 can be free from any resistance due to a contacting movement. As a result, the
opening and closing movement of the spherical valve 99a can be always smooth.
[0046] Figures 7A through 7C illustrate a relationship between the opening and closing condition
of the port 98 and the deforming condition of the o-ring 96 in relation to the movement
of the valve spool 94 of the valve assembly 90.
[0047] In Figs. 7A through 7C, the three different levels of deformation of the o-ring 96
shown by level 0, level 1 and level 2, indicate a first condition in which no torsional
load is applied to the o-ring 96, a second condition in which a preliminarily torsional
load is applied to the o-ring to obtain an elastic restoring force to close the valve
port 98, and a third condition in which a maximum load is applied to the o-ring 96
to place the valve port 98 in a completely opened condition, respectively. Particularly,
Figs. 7B and 7C illustrate the spherical valve 99a attached to the extreme end of
the valve element 99 moved to its closing position to close the valve port 98 and
moved to its opened position to open the valve port 98. Nevertheless, Fig. 7A illustrates
an imaginary position of the spherical valve 98a if the torsional load is removed
from the o-ring 96. As can be understood from the illustrations of Figs. 7B and 7C,
the o-ring 96 is deformed to receive a torsional load even when the spherical valve
99a is moved to its closing position to close the valve port 98.
[0048] Figures 8A and 8B illustrate two modified constructions of the valve assembly.
[0049] In the valve assembly 90A of Fig. 8A, an elastic element, i.e., a spring 99b, and
a rest 99c are additionally arranged in the second valve chamber 95b to apply a spring
force urging the spherical valve 99a toward its closing position to close the valve
port 98. In this case, the o-ring 96 does not need to be preliminarily deformed to
exhibit a restoring force urging the spherical valve 99a to its closing position to
close the valve port 98. Namely, the o-ring 96 is received in the annular V-shape
grooves R1 and R2 of the valve spool 94 and the framework 92 in such a manner that
when the spherical valve 99a of the valve element 99 is in its closing position, the
two annular V-shape grooves R1 and R2 are substantially in registration with one another.
Thus, the o-ring 96 hermetically seals between the portion of the first valve chamber
95a connected to the oil passage 61b and the pressure chamber 97 of the first valve
chamber 97 but is not subjected to deformation during the closing of the valve port
98 by the spherical valve 99a of the valve element 99. More specifically, the o-ring
96 is deformed to receive a torsional load only when the valve spool 94 and the spherical
valve 99a of the valve element 99 are moved to the position to open the valve port
98 against the spring force of the spring 99b. Thus, the physical durability of the
o-ring 96 can be appreciably increased to ensure a long operation life of the o-ring
96.
[0050] In the valve assembly 90B of Fig. 8B, an elastically movable reed valve 100 is used
for opening and closing the valve port 98, and the valve element 99A integral with
the valve spool 94 is used for moving the reed valve 100 to its closed position to
close the valve port 98 to its opened position to open the valve port 98. The o-ring
96 is received in the annular V-shape grooves R1 and R2 of the valve spool 94 and
the framework 92 in such a manner that when the reed valve 100 is in its closing position,
the two annular V-shape grooves R1 and R2 are substantially in registration with one
another. Thus, the same advantage as that of the valve assembly 90A of Fig. 8A, i.e.,
a long operation life of the o-ring 96 can be obtained by the valve assembly 90B.
[0051] Figure 9 is a longitudinal cross-sectional view of a scroll type refrigerant compressor,
a typical rotary type refrigerant compressor, to which the present invention is applied.
[0052] The scroll type refrigerant compressor of Fig. 9 includes a fixed scroll element
101 formed to be integral with a shell element forming an outer framework of the compressor,
and front and rear housings 102 and 103 sealingly attached to opposite ends of the
fixed scroll element 101. The fixed scroll element 101 is provided with a fixed side
plate 101a and a fixed spiral member 101b integrally attached to the fixed side plate
101a. The front housing 102 supports therein a drive shaft 105 to be rotatable about
an axis of rotation thereof via a radial bearing 104. The drive shaft 105 has an outer
end connectable to an external drive source, and an inner end having a slide key member
106 arranged to be eccentric with the axis of rotation of the drive shaft 105 and
projecting axially. The slide key member 106 holds thereon a drive bush 107 so that
the drive bush 107 is permitted to radially slide with respect to the slide key member
106.
[0053] The scroll type refrigerant compressor further includes a movable scroll element
109, which is held on the drive bush 107 via a radial bearing 108. The movable scroll
element 109 is provided with a movable side plate 109a, and a movable spiral member
109b integrally attached to an inner face of the movable side plate 109a. The movable
scroll element 109 having the movable side plate 109a and the spiral member 109b is
engaged with the fixed scroll element 101 having the fixed side plate 101a and the
fixed spiral member 101b to define a plurality of compression chambers P therebetween.
[0054] The front housing 102 is further provided with a plurality of pins 111 fixed thereto.
Similarly, the movable side plate 109a of the movable scroll element 109 is provided
with a plurality of pins 112 fixed thereto. The pins 111 of the front housing 102
and the pins 112 of the movable scroll element 109 are engaged in a ring-like retainers
113, respective, which are slidably seated in a recess counter-bored in the inner
face of the front housing 102, to prevent the movable scroll element 109 from self-rotating.
[0055] The fixed side plate 101a of the fixed scroll element 101 is centrally provided with
a discharge passage 101c bored therein and having an outer open end closed by a reed
type discharge valve 114 which is permitted to open until it comes into contact with
a valve retainer 115.
[0056] A discharge chamber 106 is formed in both the fixed scroll element 101 and the rear
housing 103 for receiving a compressed refrigerant discharged from the compression
chambers P and the discharge passage 101c. The discharge chamber 116 communicates
with an oil separating chamber 119 via a short passage 118 formed in the rear housing
103.
[0057] An oil storing chamber 117 is formed in both the fixed scroll element 101 and the
rear housing 103 which is arranged to receive an oil separated from the compressed
refrigerant within the above-mentioned oil separating chamber 119 via an oil passage
120 formed in a bottom portion of the oil separating chamber 119.
[0058] A valve assembly 50A is assembled in a portion of the fixed side plate 101a of the
fixed scroll element 101 in a posture reverse to that of the valve assembly 50 of
the reciprocating type refrigerant compressor of Fig. 1. The function of the valve
assembly 50A is the same as that of the valve assembly 50. Thus, the valve assembly
50A is provided with a first valve chamber 55a in which a bellows element 56 is arranged
to have one end fixed to the bottom of the chamber 55a and to be able to expand and
contract within the first valve chamber 55a. The interior of the bellows element 56
communicates, via a pressure introducing passage 57, with one of the compression chambers
P in which an intermediate pressure smaller than a final pressure of the compressed
refrigerant prevails. An upstream side oil passage 61a extending from the oil storing
chamber 117 is fluidly connected to a second valve chamber 55b. A downstream side
oil passage 61b extends from the first valve chamber 55a to an opening formed in a
portion of a slidably engaging portion of the fixed spiral portion 101b and the movable
side plate 109a. Therefore, when the scroll type refrigerant compressor is driven
to move the movable scroll element 109 with respect to the fixed scroll element 101,
so that each of the compression chambers P is spirally displaced from an initial position
to a final position while compressing the refrigerant, the compressed refrigerant
is discharged from the compression chamber P to the discharge chamber 116 via the
discharge passage 101c and the discharge valve 114. The compressed refrigerant further
goes from the discharge chamber 116 into the oil separating chamber 119 via the short
passage 118, so that the compressed refrigerant is spirally rotated along the cylindrical
inner wall of the oil separating chamber 119 and around an oil-separating cylinder
121 fixed to an outer portion of the rear housing 103.
[0059] Thus, the compressed refrigerant is finally delivered from a delivery port formed
in the oil-separating cylinder 121 toward the external refrigerating system. During
the rotation of the compressed refrigerant around the oil-separating cylinder 121,
an oil component suspended in the refrigerant is separated therefrom due to centrifugal
force. Thus, the compressed refrigerant can be delivered into the external refrigerating
system after the amount of oil contained in a unit weight of compressed refrigerant
is sufficiently reduced to prevent heat exchanging units in the refrigerating system
such as a condenser and an evaporator from being adversely affected by the oil component
contained in the refrigerant from the viewpoint of thermal exchange.
[0060] During the operation of the scroll type refrigerant compressor, a pressure introduced
into the interior of the bellows element 56 of the valve assembly 50A from the compression
chamber P is very high and accordingly, the high pressure in the interior of the bellows
element 56 expands the bellows element 56 against a combined force of a pressure prevailing
in the first valve chamber 55a and the elastic restoring force of the bellows element
56 so as to keep the valve assembly 50A open. Therefore, the oil is supplied from
the oil storing chamber 117 to the above-mentioned slidably engaging portion of the
fixed spiral portion 101b and the movable side plate 109a which is a suction pressure
region of the compressor to lubricate there.
[0061] It should be understood that the intermediate pressure introduced from the compression
chamber P can be very stable due to a specific characteristic peculiar to the rotary
type refrigerant compressor.
[0062] When the scroll type compressor is stopped, the pressure introduced from the compression
chamber P and prevailing in the interior of the bellows element 56 is reduced to a
low pressure substantially equal to the suction pressure of the compressor. Thus,
the valve assembly 50A is quickly closed to fluidly disconnect the downstream side
oil passage 61b from the upstream side oil passage 61a. Therefore, no oil is supplied
from the oil storing chamber 117 to the slidably engaging portion of the movable and
fixed scroll elements 109 and 101. Accordingly, when the scroll type refrigerant compressor
is started, oil compression does not occur.
[0063] From the foregoing description of the several preferred embodiments of the present
invention, it will be understood that according to the present invention, a refrigerant
compressor is provided with an oil storing chamber having a sufficient volume for
storing substantially the entire amount of the oil which can be circulated within
the interior of the compressor and the oil suspended in the compressed refrigerant
is separated from the refrigerant before the compressed refrigerant is delivered from
the compressor to an external refrigerating system. Namely, the amount of oil contained
in a unit weight of compressed refrigerant delivered from the compressor to the external
refrigerating system is appreciably reduced and accordingly, the heat exchanging efficiency
in the external refrigerating system can be remarkably increased.
[0064] Further, the circulation of the oil component within the refrigerant compressor is
immediately started as soon as the compressing operation of the compressor is started,
and therefore, lubrication in the interior of the compressor can be ensured even at
the time of starting of the operation of the compressor. This fact means that, since
the crank chamber of the compressor is not required to hold a specific amount of oil
for the purpose of lubricating the interior in the crank chamber at the start of the
compressing operation of the compressor, oil compression can be surely prevented when
the compressing operation of the compressor is started.
[0065] Further, since the valve assembly incorporated in a refrigerant compressor employs
an elastic restoring force of either a bellows element or a o-ring to control the
opening and closing of a valve port located in a portion of an oil passage from an
oil storing chamber to a lubricated portion of the compressor, the valve port can
be surely and stably opened and closed by a movable valve element. Thus, an accurate
control of the circulation of the oil within the compressor can be ensured. In addition,
the valve assembly can be simple in its construction.
[0066] Finally, it should be understood that many and various changes and modifications
will occur to a person skilled in the art without departing from the scope and spirit
of the invention as claimed in the accompanying claims.
1. A positive-displacement-type refrigerant compressor including:
a suction system to receive a refrigerant at a suction pressure from an external refrigerating
system,
a compressing mechanism having a compression chamber in which the refrigerant introduced
from said suction system is compressed and discharged into a discharge chamber receiving
the compressed refrigerant at a discharge pressure, and
an oil-separating and lubricating system for lubricating an interior of said positive-displacement-type
refrigerant compressor by an oil separated from the refrigerant,
wherein said oil-separating and lubricating system comprises:
an oil-separating unit accommodated in a high pressure region communicating with said
discharge chamber to cause a separation of an oil from the compressed refrigerant;
an oil-storing chamber accommodated in said high pressure region to store the oil
separated by said oil-separating unit;
an oil-supply passage to supply the oil from said oil-storing chamber to said suction
system;
a valve assembly disposed in a portion of said oil-supply passage for regulating an
amount of flow of the oil from said oil-storing chamber to said suction system,
said valve assembly comprising:
a first valve chamber having a substantial volume therein;
a movable valve actuating element accommodated in said first valve chamber to be moved
by an application of a pressure thereto against an elastic force, said movable valve
actuating element defining outer and inner separate regions, one of which fluidly
communicates with a downstream side of said oil-supply passage, and the other of which
fluidly communicating with said compression chamber;
a second valve chamber arranged adjacent to said first valve chamber via a partition
wall provided therebetween and fluidly communicating with an upstream side of said
oil-supply passage;
a valve element extending from said movable valve actuating element and opening and
closing a valve port bored in said partition wall to provide a fluid communication
between said upstream and downstream of said oil-supply passage, said valve element
moving in response to a movement of said movable valve actuating element and closing
said valve port when the pressure introduced from said compression chamber and acting
on said movable valve actuating element is overcome by the elastic restoring force
acting on said movable valve actuating element; and
a restriction arranged in a portion of said oil-supply passage for applying a flow
restricting effect to the oil flowing through said oil-supply passage.
2. A positive-displacement-type refrigerant compressor according to claim 1, wherein
said movable valve actuating element comprises a bellows element having a fixed end
fixed to a portion of said first valve chamber, a movable end connected to said valve
element and expanding and contracting with respect to said fixed end, and an interior
chamber formed as said inner region between said fixed and movable ends, said bellows
element further having an exterior region therearound as said outer region of said
first valve chamber.
3. A positive-displacement-type refrigerant compressor according to claim 2, wherein
said interior chamber of said bellows element communicates with said compression chamber
of said compressing mechanism, and said exterior region around said bellows element
communicates with said downstream side of said oil-supply passage.
4. A positive-displacement-type refrigerant compressor according to claim 2, wherein
said interior chamber of said bellows element communicates with said downstream side
of said oil-supply passage and said exterior region around said bellows element communicates
with said compression chamber of said compressing mechanism.
5. A positive-displacement-type refrigerant compressor according to claim 1, wherein
said valve port bored in said partition wall is arranged to form a portion of said
oil-supply passage and cooperates with said valve element to define a narrow passage
portion functioning as said restriction.
6. A positive-displacement-type refrigerant compressor according to claim 1, wherein
said oil-storing chamber is formed to have a volume suitable for storing substantially
all of the oil component filled in said compressor and circulated through said suction
system and said oil-separating and lubricating system of said compressor.
7. A positive-displacement-type refrigerant compressor according to claim 1, wherein
said movable valve actuating element comprises:
a spool valve element disposed in said first valve chamber and having an outer face
facing an inner wall of said first valve chamber via a small gap; and
an o-ring element deformably disposed in said small gap and fitted in a pair of annular
recesses formed in said inner wall of said first valve chamber and said outer face
of said spool valve element to movably support said spool valve element, said valve
element being arranged to extend from said valve spool element and able to open and
close said valve port bored in said partition wall in response to a movement of said
valve spool element which can be moved by said pressure introduced from said compression
chamber against said elastic force caused by a deformation of said o-ring element.
8. A positive-displacement-type refrigerant compressor according to claim 7, wherein
said o-ring element received in said pair of annular recesses formed in said inner
wall of said first valve chamber and said outer face of said spool valve element is
preliminarily deformed to exhibit a predetermined amount of elastic force urging said
valve element toward its closing position to close said valve port, said o-ring being
further deformed when said valve element is moved to its opened position to open said
valve port.
9. A positive-displacement-type refrigerant compressor according to claim 7, wherein
said valve assembly further comprises an elastic element constantly applying a pressure
to said valve element to thereby urge said valve element toward its closed position
to close said valve port, said valve element being moved from its closed position
to its open position by said pressure introduced from said compression chamber against
a combination of said pressure of said elastic element and the elastic force of said
o-ring.
10. A positive-displacement-type refrigerant compressor according to claim 1, wherein
a pressure-introduction passage, for introducing said pressure from said compression
chamber into a position acting on said valve element, is provided and has a flow restriction
therein.
11. A positive-displacement-type refrigerant compressor according to claim 1, wherein,
when said positive-displacement-type refrigerant compressor employs reciprocating
pistons to compress the refrigerant, said pressure acting on said valve element can
be maintained substantially at an average of the pressures prevailing in the compression
chamber.
12. A positive-displacement-type refrigerant compressor according to claim 1, wherein,
when said positive-displacement-type refrigerant compressor is a rotary type refrigerant
compressor, said pressure acting on said valve element can be an intermediate value
of the pressures prevailing in the compression chamber.