U.S. patent application number 13/262119 was filed with the patent office on 2012-01-26 for refrigeration cycle apparatus.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Hiroshi Hasegawa, Takumi Hikichi, Shingo Oyagi, Yu Shiotani, Masanobu Wada.
Application Number | 20120017636 13/262119 |
Document ID | / |
Family ID | 43222402 |
Filed Date | 2012-01-26 |
United States Patent
Application |
20120017636 |
Kind Code |
A1 |
Wada; Masanobu ; et
al. |
January 26, 2012 |
REFRIGERATION CYCLE APPARATUS
Abstract
A refrigeration cycle apparatus (100) includes a first
compressor (101), a second compressor (102), a radiator (4), an
evaporator (6), and a pipe branching portion (30). The first
compressor (101) has a first compression mechanism (1) and an
expansion mechanism (5). The second compressor (102) has a second
compression mechanism (2). The pipe branching portion (30) serves
as a flow passage for introducing a refrigerant from the evaporator
(6) to the first compression mechanism (1) and the second
compression mechanism (2), respectively. The pipe branching portion
(30) includes an inlet pipe (31) for receiving the refrigerant from
the evaporator (6), a first branch outlet pipe (32) for introducing
the refrigerant flowing into the inlet pipe (31) to the first
compression mechanism (1), and a second branch outlet pipe (33) for
introducing the refrigerant flowing into the inlet pipe (31) to the
second compression mechanism (2). The inlet pipe (31) and the first
branch outlet pipe (32) form an obtuse angle or an angle of
180.degree. therebetween, and the inlet pipe (31) and the second
branch outlet pipe (33) form an acute angle therebetween.
Inventors: |
Wada; Masanobu; (Osaka,
JP) ; Hasegawa; Hiroshi; (Osaka, JP) ;
Hikichi; Takumi; (Osaka, JP) ; Oyagi; Shingo;
(Kyoto, JP) ; Shiotani; Yu; (Osaka, JP) |
Assignee: |
PANASONIC CORPORATION
Kadoma-shi, Osaka
JP
|
Family ID: |
43222402 |
Appl. No.: |
13/262119 |
Filed: |
May 21, 2010 |
PCT Filed: |
May 21, 2010 |
PCT NO: |
PCT/JP2010/003452 |
371 Date: |
September 29, 2011 |
Current U.S.
Class: |
62/510 |
Current CPC
Class: |
F25B 31/002 20130101;
F25B 2400/075 20130101; F25B 2500/01 20130101 |
Class at
Publication: |
62/510 |
International
Class: |
F25B 1/10 20060101
F25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2009 |
JP |
2009-131277 |
Claims
1. A refrigeration cycle apparatus comprising: a first compressor
having a first compression mechanism, an expansion mechanism, a
shaft coupling the first compression mechanism and the expansion
mechanism to each other, and a first closed casing accommodating
the first compression mechanism, the expansion mechanism, and the
shaft; a second compressor having a second compression mechanism
disposed in parallel with the first compression mechanism, and a
second closed casing accommodating the second compression
mechanism; a radiator for cooling a refrigerant compressed by the
first compression mechanism and the refrigerant compressed by the
second compression mechanism; an evaporator for evaporating the
refrigerant expanded by the expansion mechanism; and a pipe
branching portion serving as a flow passage for introducing the
refrigerant from the evaporator to the first compression mechanism
and the second compression mechanism, respectively, the pipe
branching portion including an inlet pipe for receiving the
refrigerant from the evaporator, a first branch outlet pipe for
introducing the refrigerant flowing into the inlet pipe to the
first compression mechanism, and a second branch outlet pipe for
introducing the refrigerant flowing into the inlet pipe to the
second compression mechanism, wherein the inlet pipe and the first
branch outlet pipe form an obtuse angle or an angle of 180.degree.
therebetween, and the inlet pipe and the second branch outlet pipe
form an acute angle therebetween.
2. The refrigeration cycle apparatus according to claim 1, wherein
the angle formed between the inlet pipe and the first branch outlet
pipe is an obtuse angle.
3. The refrigeration cycle apparatus according to claim 1, wherein
the first branch outlet pipe and the second branch outlet pipe are
located on the same straight line.
4. The refrigeration cycle apparatus according to claim 1, wherein
the first branch outlet pipe extends downwardly and the second
branch outlet pipe extends upwardly in a vertical direction.
5. The refrigeration cycle apparatus according to claim 1, wherein
an inlet port of the first compression mechanism formed in the
first closed casing is located below a branch point of the pipe
branching portion in a vertical direction.
6. The refrigeration cycle apparatus according to claim 1, wherein
the first branch outlet pipe has a larger flow passage area than
that of the second branch outlet pipe.
7. The refrigeration cycle apparatus according to claim 1, further
comprising a valve provided in a suction passage communicating the
pipe branching portion with an inlet port of the first compression
mechanism, wherein an internal flow passage of the valve has a
constant area throughout the passage between an inlet and an outlet
of the valve when the valve is opened.
8. The refrigeration cycle apparatus according to claim 7, wherein
the suction passage includes a portion parallel to a vertical
direction, and the valve is provided in the portion.
Description
TECHNICAL FIELD
[0001] The present invention relates to refrigeration cycle
apparatuses.
BACKGROUND ART
[0002] There has been known a refrigeration cycle apparatus
including a plurality of compressors connected in parallel with
each other to increase its refrigeration capacity or to respond to
changes in refrigeration load. In such a refrigeration cycle
apparatus, differences in the volumetric capacity and operation
control among the compressors may result in an imbalance in the
amount of oil among the compressors with the passage of the
operation time. That is, a shortage of oil may occur in one
compressor, while an excess of oil may occur in another compressor.
Patent Literature 1 discloses a refrigeration cycle apparatus
having a pipe arrangement shown in FIG. 7, as a refrigeration cycle
apparatus in which measures are taken to prevent the imbalance in
the amount of oil.
[0003] As shown in FIG. 7, the refrigeration cycle apparatus of
Patent Literature 1 includes a first compressor 92, a second
compressor 93, and a third compressor 94. A refrigerant is supplied
to the compressors 92, 93, and 94, respectively, through a main
suction pipe 95. The main suction pipe 95 is provided with a main
curved portion 96 and a main branch portion 97. The main suction
pipe 95 branches at the main branch portion 97 into a first suction
branch pipe 98 for supplying the refrigerant to the first
compressor 92 and a suction connection pipe 99 for supplying the
refrigerant to the compressors 93 and 94.
[0004] The main curved portion 96 is an elbow pipe connecting an
upstream-side pipe with a downstream-side pipe at a right angle.
The main branch portion 97 includes a first branch passage 97a and
a second branch passage 97b. The first branch passage 97a is
located below and outside the second branch passage 97b in the
radial direction of the main curved portion 96. That is, the first
branch passage 97a is provided obliquely below the second branch
passage 97b at an angle of 45.degree.. The first suction branch
pipe 98 is connected to the first branch passage 97a, and the
suction connection pipe 99 is connected to the second branch
passage 97b.
[0005] During the operation of the refrigeration cycle apparatus,
the refrigerant and oil mixed therein flow through the main suction
pipe 95. Gravity and centrifugal force generated in the main curved
portion 96 act on the refrigerant and the oil. There is a density
difference between the refrigerant and the oil. Therefore, in the
downstream of the main curved portion 96, the refrigerant flows in
the upper and inner part in the radial direction of the main curved
portion 96, and the oil flows in the lower and outer part in the
radial direction of the main curved portion 96. That is, the oil
tends to flow into the first branch passage 97a, and a relatively
large amount of oil is returned to the first compressor 92. If
there is an excess of oil in the first compressor 92, the oil is
transferred from the first compressor 92 to the second compressor
93 and the third compressor 94 through an oil equalizing pipe.
CITATION LIST
Patent Literature
[0006] Patent Literature 1 JP 2007-333376 A
SUMMARY OF INVENTION
Technical Problem
[0007] With the pipe arrangement shown in FIG. 7, the size of the
suction pipes for the compressors 92, 93, and 94 is increased,
which may make it difficult to place the refrigeration cycle
apparatus in a housing (i.e., a housing for an outdoor unit).
Furthermore, if the posture of the main branch portion 97 is wrong
or the connection accuracy of the main branch portion 97 is low, a
sufficient effect may not be obtained.
[0008] It is an object of the present invention to provide a
technique for returning an appropriate amount of oil to each of a
plurality of compressors.
Solution to Problem
[0009] The present invention provides a refrigeration cycle
apparatus including: a first compressor having a first compression
mechanism, an expansion mechanism, a shaft coupling the first
compression mechanism and the expansion mechanism to each other,
and a first closed casing accommodating the first compression
mechanism, the expansion mechanism, and the shaft; a second
compressor having a second compression mechanism disposed in
parallel with the first compression mechanism, and a second closed
casing accommodating the second compression mechanism; a radiator
for cooling a refrigerant compressed by the first compression
mechanism and the refrigerant compressed by the second compression
mechanism; an evaporator for evaporating the refrigerant expanded
by the expansion mechanism; and a pipe branching portion serving as
a flow passage for introducing the refrigerant from the evaporator
to the first compression mechanism and the second compression
mechanism, respectively, the pipe branching portion including an
inlet pipe for receiving the refrigerant from the evaporator, a
first branch outlet pipe for introducing the refrigerant flowing
into the inlet pipe to the first compression mechanism, and a
second branch outlet pipe for introducing the refrigerant flowing
into the inlet pipe to the second compression mechanism, wherein
the inlet pipe and the first branch outlet pipe form an obtuse
angle or an angle of 180.degree. therebetween, and the inlet pipe
and the second branch outlet pipe form an acute angle
therebetween.
Advantageous Effects of Invention
[0010] In the present invention mentioned above, the first
compressor has the expansion mechanism for recovering power from
the refrigerant, in addition to the first compression mechanism for
compressing the refrigerant. Therefore, the amount of oil mixed
with the refrigerant in the first compressor and discharged to the
outside (refrigerant circuit) usually exceeds the amount of oil
mixed with the refrigerant in the second compressor and discharged
to the outside. In other words, the amount of oil used in the first
compressor is greater than the amount of oil used in the second
compressor. In such a case, the amount of oil in the first
compressor and the amount of oil in the second compressor can be
balanced by returning the oil preferentially to the first
compressor.
[0011] According to the present invention, the inlet pipe and the
first branch outlet pipe form an obtuse angle or an angle of
180.degree. therebetween, and the inlet pipe and the second branch
outlet pipe form an acute angle therebetween. With this structure,
the liquid phase oil tends to flow to the first branch outlet pipe.
That is, the amount of oil returned to the first compressor exceeds
the amount of oil returned to the second compressor. As a result,
an appropriate amount of oil is always held in each of the first
compressor and the second compressor. Particularly in the case
where the present invention is applied to a refrigeration cycle
apparatus including first and second compressors having different
structures, excellent effects are obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a configuration diagram of a refrigeration cycle
apparatus according to an embodiment of the present invention.
[0013] FIG. 2 is an enlarged cross-sectional view of a pipe
branching portion shown in FIG. 1.
[0014] FIG. 3 is a schematic diagram showing a suitable positional
relationship between the pipe branching portion and respective
compressors.
[0015] FIG. 4 is a schematic diagram showing another structure of
the pipe branching portion.
[0016] FIG. 5 is a configuration diagram of a refrigeration cycle
apparatus according to a modification.
[0017] FIG. 6A is a cross-sectional view of a valve in a closed
position, provided in a suction pipe.
[0018] FIG. 6B is a cross-sectional view of the valve in an open
position, provided in the suction pipe.
[0019] FIG. 7 is a perspective view of a pipe arrangement in a
conventional refrigeration cycle apparatus including a plurality of
compressors.
DESCRIPTION OF EMBODIMENTS
[0020] Hereinafter, an embodiment of the present invention will be
described with reference to the drawings. The present invention is
not limited to the following embodiment.
[0021] As shown in FIG. 1, a refrigeration cycle apparatus 100 of
the present embodiment includes a first compressor 101, a second
compressor 102, a radiator 4, and an evaporator 6. These devices
are connected by flow passages 3a to 3d so as to form a refrigerant
circuit 105. The flow passages 3a to 3d typically are refrigerant
pipes. The refrigerant circuit 105 is filled with a refrigerant,
such as carbon dioxide or hydrofluorocarbon, as a working
fluid.
[0022] The first compressor 101 includes a first closed casing 9, a
first compression mechanism 1, an expansion mechanism 5, a first
motor 11, a first oil pump 15, and a first shaft 23. The axial
direction of the first shaft 23 is parallel to the vertical
direction. The first compression mechanism 1 is disposed in the
upper part of the first closed casing 9. The expansion mechanism 5
is disposed in the lower part of the first closed casing 9. The
first motor 11 is disposed between the first compression mechanism
1 and the expansion mechanism 5. The first compression mechanism 1,
the expansion mechanism 5, and the first motor 11 are coupled
together by the first shaft 23. The power recovered from the
refrigerant in the expansion mechanism 5 is transferred to the
first compression mechanism 1 through the first shaft 23. Thereby,
the load on the first motor 11 is reduced, and thus the efficiency
of the refrigeration cycle apparatus 100 is improved. This type of
compressor is often called an expander-integrated compressor. The
detailed configuration of an expander-integrated compressor is
disclosed in, for example, WO 2008/087795 A1.
[0023] The first closed casing 9 has a cylindrical shape with its
upper and lower ends closed. A first oil reservoir 13 is formed in
the bottom portion of the first closed casing 9. Oil for
lubricating and sealing the first compression mechanism 1 and the
expansion mechanism 5 is held in the first oil reservoir 13. The
expansion mechanism 5 is immersed in the oil in the first oil
reservoir 13.
[0024] In the present embodiment, the first compression mechanism 1
and the expansion mechanism 5 are both positive displacement fluid
mechanisms. Specifically, the first compression mechanism 1 is a
scroll compression mechanism, and the expansion mechanism 5 is a
two-stage rotary expansion mechanism. The types of the first
compression mechanism 1 and the expansion mechanism 5 are not
limited. The types such as a rotary type (including a rolling
piston type, a swing type, and a sliding vane type) and a scroll
type can be used as appropriate.
[0025] In the first shaft 23, oil supply passages 28a and 28b
extending in the axial direction are formed. The oil is supplied to
the first compression mechanism 1 and the expansion mechanism 5
through the oil supply passages 28a and 28b, respectively. Since
the first compression mechanism 1 and the expansion mechanism 5 are
coupled together by the first shaft 23, the rotational speed of the
first compression mechanism 1 is always equal to that of the
expansion mechanism 5. The first shaft 23 may be composed of a
plurality of parts. In this case, a gear, a clutch, a torque
converter, or the like may be provided to make the rotational speed
of the first compression mechanism 1 different from that of the
expansion mechanism 5.
[0026] The first oil pump 15 is disposed between the first
compression mechanism 1 and the expansion mechanism 5 to supply the
oil in the first oil reservoir 13 to the first compression
mechanism 1. The first oil pump 15 is, for example, a positive
displacement oil pump. The first shaft 23 penetrates the first oil
pump 15 so that the first oil pump 15 is driven by the first shaft
23. The first oil pump 15 has a suction port 25 opening into the
first oil reservoir 13. That is, the oil level S1 in the first oil
reservoir 13 is higher than the suction port 25. The oil in the
first oil reservoir 13 is drawn into the first oil pump 15 through
the suction port 25, and introduced to the oil supply passage
28a.
[0027] The first motor 11 is mounted coaxially with the first shaft
23 between the first oil pump 15 and the first compression
mechanism 1 so as to drive the first compression mechanism 1.
[0028] A first bearing member 17 for supporting the first shaft 23
is provided between the first motor 11 and the first oil pump 15.
The first bearing member 17 is formed of a flat circular plate, for
example, and is fixed to the first closed casing 9. The first
bearing member 17 also has a function of preventing the oil in the
first oil reservoir 13 from being agitated by the swirl flow
generated by the first motor 11.
[0029] A flow suppressing plate 27 is provided between the first
oil pump 15 and the expansion mechanism 5. A gap is formed between
the flow suppressing plate 27 and the first closed casing 9 so that
the oil can flow through the gap. The role of the flow suppressing
plate 27 mainly is to prevent, as much as possible, the mixing of
the oil above the flow suppressing plate 27 and the oil below the
flow suppressing plate 27. As the flow suppressing plate 27, for
example, a single or a plurality of flat circular plates can be
used. The normal direction of the flow suppressing plate 27 is
parallel to the axial direction of the first shaft 23. A spacer 42
is provided below the flow suppressing plate 27 to keep a certain
distance between the expansion mechanism 5 and the flow suppressing
plate 27. The spacer 42 may be integrated with another component,
for example, with the flow suppressing plate 27.
[0030] A suction pipe 7 and a discharge pipe 19 further are
connected to the first closed casing 9. The suction pipe 7 and the
discharge pipe 19 constitute the branch portions of the flow
passage 3d and the flow passage 3a, respectively. The suction pipe
7 penetrates the wall (side wall) of the first closed casing 9 and
is connected to the first compression mechanism 1. The refrigerant
is drawn directly into the first compression mechanism 1 not
through the internal space of the first closed casing 9 but through
the suction pipe 7. The discharge pipe 19 penetrates the wall
(upper wall) of the first closed casing 9 and opens into the
internal space of the first closed casing 9. In the present
embodiment, the refrigerant compressed by the first compression
mechanism 1 is discharged into the internal space of the first
closed casing 9, flows through the internal space, and then is
introduced to the radiator 4 through the discharge pipe 19. That
is, the first compressor 101 belongs to a high pressure shell type
compressor in which the internal space of the first closed casing 9
is filled with compressed refrigerant.
[0031] Generally, a high pressure shell type compressor is
advantageous in reducing the amount of oil discharged from the
compressor because the oil mixed in the refrigerant can be
separated from the refrigerant by the gravity of the oil or the
centrifugal force generated by the motor. Furthermore, since the
heat of the motor can be transferred to the refrigerant, the
heating capacity is increased.
[0032] A suction pipe 21 and a discharge pipe 22 further are
connected to the first closed casing 9. The suction pipe 21 and the
discharge pipe 22 each penetrate the wall (side wall) of the first
closed casing 9 and are connected to the expansion mechanism 5. The
refrigerant is drawn directly into the expansion mechanism 5 not
through the internal space of the first closed casing 9 but through
the suction pipe 21. The expanded refrigerant is discharged
directly to the outside of the first closed casing 9 through the
discharge pipe 22, and introduced to the evaporator 6.
[0033] The second compressor 102 includes a second closed casing
10, a second compression mechanism 2, a second motor 12, a second
oil pump 16, and a second shaft 24. The axial direction of the
second shaft 24 is parallel to the vertical direction. The second
compression mechanism 2 is disposed in the upper part of the second
closed casing 10. The second compression mechanism 2, the second
motor 12, and the second oil pump 16 are placed in this order from
the top.
[0034] The second closed casing 10 has a cylindrical shape with its
upper and lower ends closed. The area of the horizontal cross
section of the second closed casing 10 is equal to, for example,
the area of the horizontal cross section of the first closed casing
9. A second oil reservoir 14 is formed in the bottom portion of the
second closed casing 10. Oil for lubricating and sealing the second
compression mechanism 2 is held in the second oil reservoir 14. The
height of the bottom surface of the second closed casing 10 is
equal to, for example, the height of the bottom surface of the
first closed casing 9 in the vertical direction. However, the
positional relationship between the closed casings 9 and 10 in the
vertical direction is not particularly limited. For example, the
positional relationship between the closed casings 9 and 10 may be
adjusted so that the position of the first compression mechanism 1
coincides with the position of the second compression mechanism 2
in the vertical direction.
[0035] In the present embodiment, the second compression mechanism
2 also is a positive displacement fluid mechanism. Specifically,
the second compression mechanism 2 is a scroll compression
mechanism. Like the first compression mechanism 1, the type of the
second compression mechanism 2 also is not limited. The volumetric
capacity of the second compression mechanism 2 may be equal to or
different from that of the first compression mechanism 1. However,
the second compression mechanism 2 of the same type and the same
volumetric capacity as those of the first compression mechanism 1
is very advantageous in terms of cost and controllability.
[0036] The second shaft 24 couples the second compression mechanism
2 coaxially with the second motor 12 for driving the second
compression mechanism 2. In the second shaft 24, an oil supply
passage 29 extending in the axial direction is formed. The second
oil pump 16 is disposed at the end (lower end) of the second shaft
24 to supply the oil in the second oil reservoir 14 to the second
compression mechanism 2. The second oil pump 16 is, for example, a
positive displacement or centrifugal oil pump. The second oil pump
16 has a suction port 26 opening into the second oil reservoir 14.
That is, the oil level S2 in the second oil reservoir 14 is higher
than the suction port 26. The oil in the second oil reservoir 14 is
drawn into the second oil pump 16 through the suction port 26, and
introduced to the oil supply passage 29. The oil is supplied to the
second compression mechanism 2 through the oil supply passage
29.
[0037] A second bearing member 18 for supporting the lower part of
the second shaft 24 is provided between the second motor 12 and the
second oil pump 16. The second bearing member 18 is formed of a
flat circular plate, for example, and is fixed to the second closed
casing 10. The second bearing member 18 also has a function of
preventing the oil in the second oil reservoir 14 from being
agitated by the swirl flow generated by the second motor 12.
[0038] A suction pipe 8 and a discharge pipe 20 further are
connected to the second closed casing 10. The suction pipe 8 and
the discharge pipe 20 constitute the branch portions of the flow
passage 3d and the flow passage 3a, respectively. The suction pipe
8 penetrates the wall (side wall) of the second closed casing 10
and is connected to the second compression mechanism 2. The
refrigerant is drawn directly into the second compression mechanism
2 not through the internal space of the second closed casing 10 but
through the suction pipe 8. The discharge pipe 20 penetrates the
wall (upper wall) of the second closed casing 10 and opens into the
internal space of the second closed casing 10. In the present
embodiment, the refrigerant compressed by the second compression
mechanism 2 is discharged into the internal space of the second
closed casing 10, flows through the internal space, and then is
introduced to the radiator 4 through the discharge pipe 20. That
is, the second compressor 102 belongs to a high pressure shell type
compressor in which the internal space of the second closed casing
10 is filled with compressed refrigerant.
[0039] In the refrigerant circuit 105, the second compression
mechanism 2 is disposed in parallel with the first compression
mechanism 1. The discharge pipe 19 serves as a discharge passage
for introducing the refrigerant compressed by the first compression
mechanism 1 from the internal space of the first closed casing 9 to
the radiator 4. Likewise, the discharge pipe 20 serves as a
discharge passage for introducing the refrigerant compressed by the
second compression mechanism 2 from the internal space of the
second closed casing 10 to the radiator 4. More specifically, the
discharge pipe 19 and the discharge pipe 20 constitute the branch
portions of the flow passage 3a for introducing the compressed
refrigerant to the radiator 4. The suction pipe 7 and the suction
pipe 8 constitute the branch portions of the flow passage 3d for
introducing the refrigerant to be compressed to the first
compression mechanism 1 and the second compression mechanism 2,
respectively. Therefore, the refrigerant is evaporated in the
evaporator 6 and then compressed by either the first compression
mechanism 1 or the second compression mechanism 2. The refrigerant
compressed by the first compression mechanism 1 and the refrigerant
compressed by the second compression mechanism 2 are merged
together and flow into the radiator 4. The internal space of the
first closed casing 9 and the internal space of the second closed
casing 10 are in communication with each other through the
discharge pipe 19 and the discharge pipe 20. That is, the discharge
pipe 19 and the discharge pipe 20 serve also as pressure equalizing
pipes.
[0040] Specifically, a pipe branching portion 30 is provided in the
flow passage 3d for introducing the refrigerant from the evaporator
6 to the first compression mechanism 1 and the second compression
mechanism 2, respectively. The pipe branching portion 30 is a pipe
called a "Y-junction tube" with one inlet and two outlets. In the
present embodiment, a Y-junction tube having an asymmetrical shape
is used as the pipe branching portion 30.
[0041] As shown in FIG. 1 and FIG. 2, the pipe branching portion 30
includes an inlet pipe 31, a first branch outlet pipe 32, and a
second branch outlet pipe 33. The inlet pipe 31 is a portion for
receiving the refrigerant from the evaporator 6. The first branch
outlet pipe 32 is a portion for introducing the refrigerant flowing
into the inlet pipe 31 to the first compression mechanism 1. The
second branch outlet pipe 33 is a portion for introducing the
refrigerant flowing into the inlet pipe 31 to the second
compression mechanism 2. The angle .alpha. (first branch angle)
between the inlet pipe 31 and the first branch outlet pipe 32 is an
obtuse angle. The angle .beta. (second branch angle) between the
inlet pipe 31 and the second branch outlet pipe 33 is an acute
angle.
[0042] During the operation of the refrigeration cycle apparatus
100, the refrigerant is compressed by the first compression
mechanism 1 or the second compression mechanism 2. The compressed
refrigerant is introduced to the radiator 4 through the flow
passage 3a. At this time, a part of the oil in the first oil
reservoir 13 is mixed into the compressed refrigerant and flows
outside the first closed casing 9. Likewise, a part of the oil in
the second oil reservoir 14 is mixed into the compressed
refrigerant and flows outside the second closed casing 10. The
refrigerant is cooled in the radiator 4, and then introduced into
the expansion mechanism 5 through the flow passage 3b.
[0043] The expansion mechanism 5 expands the refrigerant and
recovers power from the refrigerant. The expanded refrigerant is
introduced into the evaporator 6 through the flow passage 3c. At
this time, a part of the oil in the first oil reservoir 13 is mixed
into the expanded refrigerant and flows outside the first closed
casing 9. In the first compressor 101, the oil is mixed into the
refrigerant in both of the first compression mechanism 1 and the
expansion mechanism 5. In the second compressor 102, the oil is
mixed into the refrigerant only in the second compression mechanism
2. Therefore, the amount of oil taken out of the first oil
reservoir 13 is usually greater than the amount of oil taken out of
the second oil reservoir 14.
[0044] The refrigerant is evaporated in the evaporator 6, and then
introduced into the inlet pipe 31 of the pipe branching portion 30
through the flow passage 3d. In the pipe branching portion 30, the
refrigerant is in the gas phase, and the oil is in the liquid
phase. Since the angle .alpha. is greater than the angle .beta.,
the pressure drop gradient caused by the flow of the refrigerant
and oil from the inlet pipe 31 to the second branch outlet pipe 33
is larger than that caused by the flow of the refrigerant and oil
from the inlet pipe 31 to the first branch outlet pipe 32. As
stated herein, the "pressure drop gradient" means a pressure
gradient based on a pressure drop.
[0045] In general terms, when a gas-liquid two-phase flow
containing a gas phase fluid and a liquid phase fluid branches in
two directions having different pressure drop gradients, the gas
phase fluid tends to flow toward the greater pressure drop gradient
side. Assuming that the same amount of gas phase fluid and liquid
phase fluid flow in the same flow passage, the pressure drop of the
gas phase fluid is greater than that of the liquid phase fluid.
Therefore, in the case where the pressure drop gradients in the two
directions are different from each other, more gas phase fluid
flows toward the greater pressure drop gradient side while more
liquid phase fluid flows toward the smaller pressure drop gradient
side to maintain the balance of the pressure drop in the two
directions.
[0046] For example, Asano, et al. have conducted experiments for
the separation of an air-water two-phase flow using a plurality of
Y-junction tubes with different branch angles, and reported the
results of the experiments ("A Study of the Phase Separation
Characteristics in Gas-Liquid Two-Phase Flows by an Impacting
Y-Junction", 1st Report, Journal of the Japan Society of Mechanical
Engineers (Series B), Vol. 67, No. 654, pp. 350-355). As a result
of these experiments for the flow separation, Asano, et al. have
confirmed that the phase separation performance is enhanced as the
branch angle .theta. (corresponding to the second branch angle
.beta. in the present embodiment) decreases in the range of
30.degree. to 90.degree.. This result coincides with the fact that
the liquid phase to which a greater inertial force is applied is
more likely to go straight ahead as the branch angle .theta. of a
Y-junction tube decreases. This result also shows that more gas
phase fluid flows toward the greater pressure drop gradient side
and more liquid phase fluid flows toward the smaller pressure drop
gradient side.
[0047] In the present embodiment, the compression mechanisms 1 and
2 are located downstream of the pipe branching portion 30, and the
flow rates of the refrigerant in the branch outlet pipes 32 and 33
depend on the rotational speeds and volumetric capacities of the
compression mechanisms 1 and 2, respectively. Therefore, there is a
certain validity in the finding that the difference in the pressure
drop gradient affects the distribution of the oil in the pipe
branching portion 30, although the phenomenon in the pipe branching
portion 30 cannot always be explained just in general terms
above.
[0048] An inertial force acting on a liquid phase oil is greater
than that acting on a gas phase refrigerant. In the present
embodiment, since the angle .alpha. between the inlet pipe 31 and
the first branch outlet pipe 32 is greater than the angle .beta.
between the inlet pipe 31 and the second branch outlet pipe 33, the
oil tends to flow into the first branch outlet pipe 32.
[0049] Due to the influences of pressure drops and inertial forces,
as described above, the proportion of oil flowing from the inlet
pipe 31 into the first branch outlet pipe 32 is higher than that
flowing from the inlet pipe 31 into the second branch outlet pipe
33. This means that a relatively large amount of oil is returned to
the first compressor 101, and a relatively small amount of oil is
returned to the second compressor 102. The pipe branching portion
30 can be constructed so that the ratio between the amount of oil
flowing into the first branch outlet pipe 32 and the amount of oil
flowing into the second branch outlet pipe 33 (distribution ratio
of oil) falls within, for example, the range of 6:4 to 9:1 when the
first compression mechanism 1 and the second compression mechanism
2 have the same volumetric capacity and the same rotational speed,
although it depends on other various conditions.
[0050] As described above, during the operation of the
refrigeration cycle apparatus 100, the amount of oil taken out of
the first oil reservoir 13 is greater than the amount of oil taken
out of the second oil reservoir 14. However, the oil distribution
function of the pipe branching portion 30 makes it possible to
return more oil to the first compression mechanism 101 than to the
second compression mechanism 102. As a result, the difference in
the amount of oil taken can be balanced out, and the oil levels S1
and S2 in the compressors can be maintained approximately constant.
Even with the passage of the operation time, an imbalance does not
occur between the amount of oil in the first oil reservoir 13 and
that in the second oil reservoir 14, and an appropriate amount of
oil can always be held in each of the oil reservoirs 13 and 14.
Therefore, the reliability of the refrigeration cycle apparatus 100
also is enhanced.
[0051] Next, the structure of the pipe branching portion 30 is
described in further detail.
[0052] In the example shown in FIG. 1 and FIG. 2, the angle .alpha.
is set to an obtuse angle. When the angle .alpha. is an obtuse
angle, the angle .alpha. is, for example, in the range of
100.degree. to 170.degree., and preferably in the range of
120.degree. to 160.degree.. The angle .beta. is, for example, in
the range of 10.degree. to 60.degree., and preferably in the range
of 20.degree. to 40.degree.. When the angle .alpha. and the angle
.beta. are set in these ranges, it is certainly possible to allow
more oil to flow into the first branch outlet pipe 32 than into the
second branch outlet pipe 33. In the example shown in FIG. 2, the
angle .alpha. is 150.degree., and the angle .beta. is
30.degree..
[0053] Furthermore, when the first branch outlet pipe 32 and the
second branch outlet pipe 33 are located on the same straight line,
as in the present embodiment, the first branch outlet pipe 32 and
the second branch outlet pipe 33 can be formed of a single pipe. As
a result, the structure of the pipe branching portion 30 is
simplified, and therefore variations in the quality are reduced in
mass production and a desired effect is obtained stably.
[0054] The angle .alpha. can be defined as an angle between the
center line L.sub.1 of the inlet pipe 31 and the center line
L.sub.2 of the first branch outlet pipe 32. Likewise, the angle
.beta. can be defined as an angle between the center line L.sub.1
of the inlet pipe 31 and the center line L.sub.3 of the second
branch outlet pipe 32. More precisely, the angle between the center
line L.sub.1 and the center line L.sub.2 on a plane including the
center line L.sub.1 and the center line L.sub.2 is regarded as the
angle .alpha.. Likewise, the angle between the center line L.sub.1
and the center line L.sub.3 on a plane including the center line
L.sub.1 and the center line L.sub.3 is regarded as the angle
.beta..
[0055] In the present embodiment, since the first branch outlet
pipe 32 and the second branch outlet pipe 33 are located on the
same straight line, the center line L.sub.2 coincides with the
center line L.sub.3. That is, the center line L.sub.1 of the inlet
pipe 31 and the center line L.sub.2 of the first branch outlet pipe
32 are located on the same plane, and the center line L.sub.1 of
the inlet pipe 31 and the center line L.sub.3 of the second branch
outlet pipe 33 are located on the same plane. Therefore, the center
line L.sub.1, the center line L.sub.2, and the center line L.sub.3
are located on the same plane. The inlet pipe 31, the first branch
outlet pipe 32, and the second branch outlet pipe 33 each do not
necessarily be formed of a straight pipe. These pipes may each be
formed of a curved pipe.
[0056] In the present embodiment, the first branch outlet pipe 32
extends downwardly and the second branch outlet pipe 33 extends
upwardly in the vertical direction. When the pipe branching portion
30 is mounted in such a posture, oil is allowed to flow into the
first branch outlet pipe 32 more easily under the influence of
gravity. Even if the pipe branching portion 30 is disposed in any
posture, of course, the oil distribution function of the pipe
branching portion 30 is sufficiently fulfilled.
[0057] In the example shown in FIG. 1 and FIG. 2, the center line
L.sub.1 of the inlet pipe 31 is parallel to the vertical direction,
and the center lines L.sub.2 and L.sub.3 of the branch outlet pipes
32 and 33 are inclined at 60.degree. with respect to the horizontal
direction. The inlet port of the first compression mechanism 1
formed in the first closed casing 9 is located below the branch
point CP of the pipe branching portion 30 in the vertical
direction. This positional relationship eliminates the need for a
U-shaped portion between the pipe branching portion 30 and the
inlet port of the first compression mechanism 1, and therefore the
oil can be smoothly introduced into the first compression mechanism
1. Furthermore, there is no need to consider the stagnation of oil
in such a U-shaped portion.
[0058] FIG. 3 shows another example of the mounting of the pipe
branching portion 30. In this example, the center line L.sub.2 of
the first branch outlet pipe 32 is parallel to the vertical
direction, and the center line L.sub.1 of the inlet pipe 31 is
inclined at a predetermined angle (90.degree.-angle .beta.) with
respect to the horizontal direction. When the bottom surface of the
first closed casing 9 is a reference plane, the height h.sub.1 from
the reference plane to the branch point CP is greater than the
height h.sub.2 from the reference plane to a joint between the
suction pipe 7 and the first closed casing 9. The flow passage from
the pipe branching portion 30 to a joint between the suction pipe 8
and the second closed casing 10 includes a U-shaped portion 35.
Compared to the structure shown in FIG. 1 and FIG. 2, this
structure allows a higher proportion of oil to be returned to the
first compressor 101, and therefore it is effective if more oil is
expected to be returned to the first compressor 101.
[0059] The angle .alpha. may be 180.degree.. That is, in the pipe
branching portion 30a shown in FIG. 4, the inlet pipe 31 and the
first branch outlet pipe 32 are located on the same straight line.
The angle .beta. between the inlet pipe 31 and the second branch
outlet pipe 33 is an acute angle. This pipe branching portion 30a
also allows the oil distribution function to be fulfilled, and the
oil can be returned to the first compressor 101 preferentially.
[0060] The cross sectional shapes and dimensions of the pipes that
constitute the pipe branching portion 30 are not particularly
limited. In the present embodiment, the inlet pipe 31, the first
branch outlet pipe 32, and the second branch outlet pipe 33 each
have a circular cross section. The first branch outlet pipe 32 has
a larger flow passage area than that of the second branch outlet
pipe 33. Specifically, as shown in FIG. 2, the inner diameter
D.sub.2 of the first branch outlet pipe 32 is larger than the inner
diameter D.sub.3 of the second branch outlet pipe 33. With this
structure, the pressure drop gradient caused by the flow of the
refrigerant and oil to the second branch outlet pipe 33 becomes
much larger. Therefore, the oil tends to flow into the first branch
outlet pipe 32, compared with the case where the inner diameter
D.sub.2 is equal to the inner diameter D.sub.3.
[0061] The dimensional ratio between the inner diameter D.sub.2 and
the inner diameter D.sub.3 is not particularly limited. For
example, it can be set as appropriate within the range of
D.sub.2:D.sub.3=1.5:1 to 3:1. In the present embodiment, the inner
diameter D.sub.1 of the inlet pipe 31 is equal to the inner
diameter D.sub.2 of the first branch outlet pipe 32.
[0062] Examples of oils that can be used in the refrigeration cycle
apparatus 100 include ester oil (such as polyol ester oil),
carbonate oil, polyalkylene glycol (PAG) oil, and polyvinyl ether
(PVE) oil. Since these oils are significantly different in specific
gravity from the gas phase refrigerant, they can be used without
any problem.
[0063] As shown in FIG. 1, in the present embodiment, the first
closed casing 9 is connected to the second closed casing 10 by an
oil equalizing pipe 50. The opening 51 of the oil equalizing pipe
50 in the first closed casing 9 is located between the suction port
25 of the first oil pump 15 and the first motor 11 in the axial
direction of the first shaft 23. Specifically, the opening 51 is
located in the vicinity of the lower surface of the first bearing
member 17 between the suction port 25 and the first bearing member
17. On the other hand, the opening 52 of the oil equalizing pipe 50
in the second closed casing 10 is located between the suction port
26 of the second oil pump 16 and the second motor 12 in the axial
direction of the second shaft 24. Specifically, the opening 52 is
located in the vicinity of the upper surface of the second bearing
member 18 between the second bearing member 18 and the second motor
12.
[0064] With the oil equalizing pipe 50, when there is an excess of
oil in the first oil reservoir 13, the excess oil automatically
moves from the first oil reservoir 13 to the second oil reservoir
14. That is, the amounts of oil are automatically balanced.
Specifically, when the oil level S1 of the first oil reservoir 13
reaches the opening 51, the oil flows from the first oil reservoir
13 to the second oil reservoir 14. The oil level S1 of the first
oil reservoir 13 is always maintained at the lower end of the
opening 51. The oil level S2 of the second oil reservoir 14 is
always maintained slightly below the second bearing member 18. With
a combined use of this oil equalizing pipe 50 and the pipe
branching portion 30, there is no need to change the dimensions and
shape of the pipe branching portion 30 according to the
specifications of the first compressor 101 and the second
compressor 102. The oil equalizing pipe 50 can be eliminated, of
course.
[0065] Furthermore, the temperature of the oil flowing from the
first oil reservoir 13 to the second oil reservoir 14 through the
oil equalizing pipe 50 is relatively high. When high temperature
oil moves from the first oil reservoir 13 to the second oil
reservoir 14, it is easy to maintain the state in which relatively
low temperature oil is retained around the expansion mechanism 5.
That is, the heat transfer between the first compression mechanism
1 and the expansion mechanism 5 through the oil can be suppressed.
Thereby, an increase in the temperature of the expanded refrigerant
and a decrease in the temperature of the compressed refrigerant can
be prevented, and as a result, the efficiency of the refrigeration
cycle apparatus 100 also is enhanced.
[0066] (Modification 1)
[0067] As shown in FIG. 5, various valves may be provided on the
refrigerant circuit 105. Specifically, a valve 61, a valve 62, a
valve 63, and a valve 64 are provided in the suction pipe 7, the
suction pipe 8, the discharge pipe 19, and the discharge pipe 20,
respectively. A valve 65 and a valve 66 are provided in the suction
pipe 21 and the discharge pipe 22, respectively, on the expansion
mechanism 5 side. A valve 67 is provided in the oil equalizing pipe
50. These valves 61 to 67 can be used to prevent air and moisture
from entering the refrigerant circuit 105 when the first compressor
101 or the second compressor 102 is insulated (separated) from the
refrigerant circuit 105 for the maintenance, for example.
Furthermore, the valves 62 and 64 can be used to insulate
(separate) the second compressor 102 from the refrigerant circuit
105 when the refrigeration cycle apparatus 100 is operated using
only the first compressor 101.
[0068] The valve 61 is provided in the suction pipe 7, that is, in
the suction passage communicating the pipe branching portion 30 and
the inlet port of the first compression mechanism 1. As the valve
61, a valve including no pressure reducing portion, such as a
throttle, can be used. In this case, the internal flow passage of
the valve 61 has a constant area throughout the passage between the
inlet and the outlet of the valve 61 when it is fully opened. This
valve 61 can be a ball valve, for example. As shown in FIG. 6A, the
valve 61 includes a housing 76 having an in-valve flow passage 70
(internal flow passage), and a ball 74 disposed in the housing 76
so as to partition the in-valve flow passage 70 into an upstream
side and a downstream side. When the valve 61 is closed, the ball
74 closes the in-valve flow passage 70. On the other hand, as shown
in FIG. 6B, when the valve 61 is opened, the ball 74 is rotated
90.degree. and a through-hole 72 formed in the ball 74 faces the
in-valve flow passage 70. The through-hole 72 has the same cross
sectional area as the in-valve flow passage 70.
[0069] With this valve 61 in the suction pipe 7, the oil flowing
into the suction pipe 7 through the first branch outlet pipe 32 can
flow smoothly into the first compressor 101 (more specifically,
into the first compression mechanism 1) without stagnating in the
valve 61. This is significant in returning an appropriate amount of
oil to the first compressor 101, and contributes to the improvement
of the reliability of the refrigeration cycle apparatus 100. Valves
similar to the valve 61 can also be used for the other valves 62 to
67.
[0070] Furthermore, in the modification shown in FIG. 5, the
suction pipe 7 serving as a suction passage communicating the pipe
branching portion 30 with the inlet port of the first compression
mechanism 1 includes a portion 7a (referred to as a vertical
portion) parallel to the vertical direction. The valve 61 is
provided in this vertical portion 7a. One end of the vertical
portion 7a is connected to the first branch outlet pipe 32 of the
pipe branching portion 30. On the other hand, the other end of the
vertical portion 7a is inserted into the first closed casing 9 so
as to be connected to the first compression mechanism 1. The oil
flows into the suction pipe 7 through the pipe branching portion 30
and further flows downwardly through the vertical portion 7a.
Therefore, even if the valve 61 has a pressure reducing portion
such as a throttle and the oil can stagnate temporarily in the
valve 61, the oil can flow out of the valve 61 by its own gravity
so as to flow into the first compressor 101.
[0071] (Other Modifications)
[0072] The present invention can also be applied to a refrigeration
cycle apparatus in which the expansion mechanism 5 is eliminated
from the first compressor 101, that is, a refrigeration cycle
apparatus including a plurality of standard compressors.
INDUSTRIAL APPLICABILITY
[0073] The refrigeration cycle apparatus of the present invention
can be used for apparatuses such as a water heater, a hot water
heating apparatus, and an air conditioner.
* * * * *