U.S. patent application number 13/125386 was filed with the patent office on 2011-08-11 for refrigeration cycle system and automotive air-conditioning system including the refrigeration cycle system.
Invention is credited to Yuuichi Matsumoto.
Application Number | 20110192187 13/125386 |
Document ID | / |
Family ID | 42119449 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110192187 |
Kind Code |
A1 |
Matsumoto; Yuuichi |
August 11, 2011 |
Refrigeration Cycle System and Automotive Air-Conditioning System
Including the Refrigeration Cycle System
Abstract
There are provided a refrigeration cycle system which ensures
adequate lubrication in a compressor and operates at a satisfactory
coefficient of performance despite use of a working fluid
containing a lubricant and a refrigerant that separate from each
other in a condenser, and an automotive air-conditioning system
including the refrigeration cycle system. A refrigeration cycle
system (12) comprises a compressor (28), a condenser (24), an
expansion valve (26) and an evaporator (28) disposed in a
circulation path (14) along which a working fluid containing a
lubricant and a refrigerant that separates from each other at
temperatures higher than a two-layer separation temperature flows,
serially in a specified flow direction of the working fluid, and a
lubricant return means for preventing the lubricant from
accumulating in the condenser (24). The lubricant return means
reduces pressure of the refrigerant in the condenser (24) to a
saturation pressure of the refrigerant for the two-layer separation
temperature or below, when the working fluid is made to flow along
the circulation path in the specified flow direction and
temperature around the condenser (24) is lower than the two-layer
separation temperature.
Inventors: |
Matsumoto; Yuuichi; (Gumma,
JP) |
Family ID: |
42119449 |
Appl. No.: |
13/125386 |
Filed: |
October 23, 2009 |
PCT Filed: |
October 23, 2009 |
PCT NO: |
PCT/JP2009/068642 |
371 Date: |
April 21, 2011 |
Current U.S.
Class: |
62/470 |
Current CPC
Class: |
F25B 2700/195 20130101;
B60H 2001/327 20130101; F25B 2400/121 20130101; F25B 31/004
20130101; B60H 1/3214 20130101; F25B 9/002 20130101; B60H 2001/3251
20130101 |
Class at
Publication: |
62/470 |
International
Class: |
F25B 43/02 20060101
F25B043/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2008 |
JP |
2008-272955 |
Claims
1. A refrigeration cycle system comprising a compressor, a
condenser, an expansion valve and an evaporator disposed in a
circulation path along which a working fluid containing a
refrigerant and a lubricant that separate from each other at
temperatures higher than a two-layer separation temperature flows,
serially in a specified flow direction of the working fluid, and a
lubricant return means for preventing the lubricant from
accumulating in the condenser, wherein the lubricant return means
reduces pressure of the refrigerant in the condenser to a
saturation pressure of the refrigerant for said two-layer
separation temperature or below, when the working fluid is made to
flow along the circulation path in said specified flow direction
and temperature around the condenser is lower than said two-layer
separation temperature.
2. The refrigeration cycle system according to claim 1, wherein the
lubricant return means includes a displacement regulation means for
regulating displacement of the compressor to reduce the pressure of
the refrigerant by regulating the displacement of the compressor by
using the displacement regulation means.
3. The refrigeration cycle system according to claim 1, wherein the
lubricant return means further includes a flow reversing means for
causing the working fluid to flow along the circulation path in a
direction opposite to said specified flow direction.
4. The refrigeration cycle system according to claim 3, wherein the
flow reversing means includes a four-way switch valve disposed in
the circulation path and changed between a position to connect a
discharge port and a suction of the compressor to an inlet of the
condenser and an outlet of the evaporator, respectively, and a
position to connect the discharge port and the suction of the
compressor to the outlet of the evaporator and the inlet of the
condenser, respectively.
5. The refrigeration cycle system according to claim 1, wherein the
working fluid contains polyalkylene glycol as the lubricant and
R1234yf as the refrigerant.
6. An automotive air-conditioning system including a refrigeration
cycle system according to claim 1.
Description
TECHNICAL FIELD
[0001] This invention relates to a refrigeration cycle system and
an automotive air-conditioning system including the refrigeration
cycle system.
BACKGROUND ART
[0002] A system for performing a refrigeration cycle (refrigeration
cycle system) has a circulation path along which a working fluid
containing a refrigerant and a lubricant is forced to
circulate.
[0003] There are a variety of refrigerants and a variety of
lubricants (refrigerator oils), and some combinations of a
refrigerant and a lubricant show low compatibility. Patent document
1 points out that use of low-compatible refrigerant and
refrigerator oil in combination may lead to accumulation of the
refrigerator oil in piping, particularly in a heat pump
air-conditioner designed to also perform the refrigeration cycle
with the flow of the refrigerant reversed, and thus, oil deficiency
in the compressor. Patent document 1 also points out that the
refrigerator oil does not satisfactorily return to the compressor,
particularly at low revolving speeds of the compressor.
[0004] In view of this, patent document 1 discloses control of
compressor revolving speed or expansion valve position to make the
refrigerant flow upward in an ascending section of piping at a
velocity higher than the flow velocity that causes the oil adhering
to the inner surface of the piping to ascend (zero penetration
velocity). [0005] Patent document 1: Japanese Patent Application
Laid-open No. 2001-272117 Publication (Abstract, Par. Nos. 0019 to
0025, etc.)
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0006] To protect the global environment, research and development
of new refrigerants to substitute for R134a has been being
advanced. An example of such new refrigerant is R1234yf
(Tetrafluoropropene: F.sub.3C--CF.dbd.CH.sub.2). R1234yf has a GWP
(global warming potential) of 4, far lower than R134a's GWP of
1300.
[0007] However, a combination of R1234yf and PAG (polyalkylene
glycol) shows a low two-layer separation temperature, or
temperature at which the refrigerant and the lubricant separates
from each other, compared with the conventional combination of
R134a and PAG. Thus, if R1234yf and PAG are used in combination
under the conventional operating conditions, it follows that the
temperature of the working fluid in the condenser is higher than
the two-layer separation temperature so that the refrigerant and
the lubricant separate from each other in the condenser.
[0008] Thus, when R1234yf and PAG are used in combination, the
lubricant accumulates in the condenser, so that a reduced amount of
the lubricant returns to the compressor, resulting in inadequate
lubrication in the compressor. In addition, the lubricant
accumulating in the condenser hinders heat transfer in the
condenser, resulting in a decrease in COP (coefficient of
performance).
[0009] It is thought that if the refrigerant is made to flow at a
velocity higher than the zero penetration velocity by using the
technology disclosed in patent document 1, the separated lubricant
can be returned to the compressor to some extent.
[0010] PAG is however not always incompatible with R1234yf; PAG
separates from R1234yf solely in the condenser. Given this, in
order to prevent the lubricant from accumulating in the condenser,
it is more direct and effective to prevent separation of the
refrigerant and the lubricant in the condenser than to return the
lubricant separated from the refrigerant.
[0011] Further, under some operating conditions of the
refrigeration cycle, keeping the flow velocity of the refrigerant
higher than or equal to the zero penetration velocity results in
keeping the temperature of the working fluid in the condenser
higher than the two-layer separation temperature. It is therefore
likely to cause the separation of the lubricant in the
condenser.
[0012] The present invention has been made in consideration of the
above problems. An object of the present invention is to provide a
refrigeration cycle system which ensures adequate lubrication in
the compressor and operates at a satisfactory COP, despite the use
of a working fluid containing a refrigerant and a lubricant that
separate from each other in the condenser, and an automotive
air-conditioning system including the refrigeration cycle
system.
Means for Solving the Problem
[0013] In order to achieve the above object, the present invention
provides, as one embodiment, a refrigeration cycle system
comprising a compressor, a condenser, an expansion valve and an
evaporator disposed in a circulation path along which a working
fluid containing a refrigerant and a lubricant that separate from
each other at temperatures higher than a two-layer separation
temperature flows, serially in a specified flow direction of the
working fluid, and a lubricant return means for preventing the
lubricant from accumulating in the condenser, wherein the lubricant
return means reduces pressure of the refrigerant in the condenser
to a saturation pressure of the refrigerant for said two-layer
separation temperature or below, when the working fluid is made to
flow along the circulation path in said specified flow direction
and temperature around the condenser is lower than said two-layer
separation temperature (claim 1).
[0014] Desirably, the lubricant return means includes a
displacement regulation means for regulating displacement of the
compressor to reduce the pressure of the refrigerant in the
condenser by regulating the displacement of the compressor by using
the displacement regulation means (claim 2).
[0015] Desirably, the lubricant return means further includes a
flow reversing means for causing the working fluid to flow along
the circulation path in a direction opposite to said specified flow
direction (claim 3).
[0016] Desirably, the flow reversing means includes a four-way
switch valve disposed in the circulation path and changed between a
position to connect a discharge port and a suction of the
compressor to an inlet of the condenser and an outlet of the
evaporator, respectively, and a position to connect the discharge
port and the suction of the compressor to the outlet of the
evaporator and the inlet of the condenser, respectively (claim
4).
[0017] Desirably, the refrigerant and the lubricant contained in
the working fluid are R1234yf and polyalkylene glycol, respectively
(claim 5).
[0018] The present invention also provides, as an embodiment, an
automotive air-conditioning system including a refrigeration cycle
system as described above (claim 6).
Effect of the Invention
[0019] In the refrigeration cycle system according to the present
invention recited in claim 1, when the temperature around the
condenser is lower than the two-layer separation temperature, the
lubricant return means reduces the pressure of the refrigerant in
the condenser to the saturation pressure of the refrigerant for the
two-layer separation temperature or below. This not only prevents
the refrigerant and the lubricant from separating from each other
in the condenser, but also causes the lubricant having accumulated
in the condenser to mix with the refrigerant, and thus, ensures
that the lubricant returns to the compressor with the refrigerant.
As a result, adequate lubrication is maintained in the compressor
and a decrease in COP (coefficient of performance) is
prevented.
[0020] In the refrigeration cycle system recited in claim 2, the
pressure of the refrigerant in the condenser is reliably reduced to
the saturation pressure of the refrigerant for the two-layer
separation temperature or below by regulating the displacement of
the compressor.
[0021] In the refrigeration cycle system recited in claim 3, the
flow reversing means can cause the working fluid at relatively low
temperature to pass through the condenser, thereby causing the
lubricant having accumulated in the condenser to mix with the
refrigerant and return to the compressor. Thus, even when the
temperature around the condenser is higher than the two-layer
separation temperature, the lubricant having accumulated in the
condenser is returned to the compressor, so that adequate
lubrication is ensured in the compressor.
[0022] In the refrigeration cycle system recited in claim 4, the
use of the four-way switch valve enables reliable return of the
lubricant to the compressor with a simple structure.
[0023] The refrigeration cycle system recited in claim 5, which
uses low-GWP R1234yf as a refrigerant contained in the working
fluid, is global environment-friendly. The working fluid also
contains polyalkylene glycol as a lubricant, which ensures adequate
lubrication in the compressor.
[0024] In the automotive air-conditioning system recited in claim
6, the lubricant return means ensures that the lubricant having
accumulated in the condenser is returned to the compressor, even in
an environment in which the temperature of the working fluid
exceeds the two-layer separation temperature in the condenser, and
thus, the lubricant accumulates in the condenser. This automotive
air-conditioning system is therefore useful in every region of the
world.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a diagram schematically showing a configuration of
an automotive air-conditioning system according to a first
embodiment,
[0026] FIG. 2 is a diagram showing a part of the automotive
air-conditioning system near a four-way switch valve, inclusive of
the four-way switch valve, on an enlarged scale,
[0027] FIG. 3 is a graph representing relation between two-layer
separation temperature and oil circulation ratio for a combination
of R1234yf and PAG and a combination of R134a and PAG,
[0028] FIG. 4 is a graph showing relation between kinematic
viscosity and temperature for a combination of R1234yf and PAG,
together with isothermal lines, an incompatibility region and
refrigeration cycles, and
[0029] FIG. 5 is a graph representing relation between kinematic
viscosity and temperature for a combination of R134a and PAG,
together with isothermal lines, an incompatibility region and a
refrigeration cycle.
EXPLANATION OF THE REFERENCE CHARACTERS
[0030] 12 Refrigeration cycle system [0031] 14 Circulation path
[0032] 22 Compressor [0033] 24 Condenser [0034] 26 Expansion valve
[0035] 28 Evaporator
BEST MODE OF CARRYING OUT THE INVENTION
[0036] FIG. 1 schematically shows an automotive air-conditioning
system according to a first embodiment. The automotive air
conditioning system can cool a cabin 10 according to a temperature
setting set as desired. The automotive air-conditioning system
includes a refrigeration cycle system 12 for performing a
refrigeration cycle. The refrigeration cycle system 12 has a
circulation path 14 along which a working fluid is forced to
circulate.
[0037] The working fluid contains a refrigerant and a refrigerator
oil (lubricant), and the refrigerant and the refrigerator oil
separate from each other at temperatures higher than a two-layer
separation temperature. Preferably, the working fluid contains a
refrigerant R1234yf and a lubricant PAG (polyalkylene glycol).
[0038] The circulation path 14 runs from an engine room 16 to an
instrument space 18 through a partition 17. The instrument space 18
is defined by an instrument panel 20 in front of the cabin 10. A
compressor 22, a condenser and an expansion valve 25 are disposed
in the circulation path 14, in its section inside the engine room
16, serially in a direction in which the working fluid normally
flows (normal direction). An evaporator is disposed in the
circulation path 14, in its section inside the instrument space
18.
[0039] The compressor 22 is mechanically connected to an engine 29
by means of a belt and pulley system, for example, and driven by
power from the engine 29. Preferably, the compressor 22 is a
variable displacement compressor and includes a displacement
control valve.
[0040] The displacement control valve includes a solenoid 30
electrically connected to a control device 32. The control device
32 regulates the displacement, or volume discharged by the
compressor 22 per rotation, by regulating current supplied to the
solenoid 30. The control device 32 may be composed of electric
circuits, and for example, an ECU (electric control unit).
[0041] The displacement may be regulated, for example by Ps
control, i.e., controlling the pressure at which the working fluid
is sucked into the compressor 22 (suction pressure), or
differential pressure control, i.e., controlling the difference
(Pd-Ps differential pressure) between the pressure at which the
working fluid is discharged from the compressor 22 (discharge
pressure) and the suction pressure.
[0042] Near the condenser 24 is provided a condenser fan 33. The
working fluid passing through the condenser 24 in the normal
direction is cooled by airflow from before the vehicle, caused by
the vehicle travelling, and/or airflow from the condenser fan
33.
[0043] Preferably, the expansion valve 26 is an electronic
expansion valve. The control device 32 regulates the operating
position of the expansion valve 26. The expansion valve 26 causes
the working fluid flowing in the normal direction to expand.
[0044] The evaporator 28 is disposed inside an air-conditioning
unit housing 34. Also a blower fan 36 and a heater core (not shown)
are disposed inside the air-conditioning unit housing 34. An
inside/outside air switch damper 38 is arranged at an inlet of the
air-conditioning unit housing 34, and a vent switch damper (not
shown) is arranged at an outlet of the air-conditioning unit
housing 34.
[0045] The working fluid passing through the evaporator 28 in the
normal direction evaporates by taking heat from air from the blower
fan 36, so that the air from the blower fan 36 is cooled, or
becomes cold air and flows into the cabin 10 to cool the cabin
10.
[0046] The refrigeration cycle system 12 has a plurality of sensors
providing various information. One of those sensors is a pressure
sensor 40 for detecting pressure of the refrigerant in the
condenser 24 (high-pressure). The pressure sensor 40 may be
disposed in the circulation path 14, at any location between the
compressor 22 and the inlet of the expansion valve 26. Here, it is
disposed immediately downstream of the condenser 24 in
consideration of durability. The high-pressure detected by the
pressure sensor 40 is fed to the control device 32.
[0047] The sensors provided in the refrigeration cycle system 12
also include an outside air temperature sensor 42 for detecting
outside air temperature, or temperature around the condenser 24.
Also the outside air temperature detected by the outside air
temperature sensor 42 is fed to the control device 32. The control
device 32 holds, on its database, data concerning relation between
the outside air temperature and the refrigerant saturation
pressure, so that the control device 32 can retrieve a refrigerant
saturation pressure corresponding to an outside air temperature
detected.
[0048] The sensors provided in the refrigeration cycle system 12
also include an evaporator temperature sensor 44 for detecting
temperature of air cooled in the evaporator 28 (evaporator
temperature). The evaporator temperature detected by the evaporator
temperature sensor 44 is fed to the control device 32 and used in
determining a desired value of the suction pressure or of the Pd-Ps
differential pressure, for example.
[0049] Preferably, a four-way switch valve 46 is disposed in the
circulation path 14. As shown in FIG. 2 on an enlarged scale, the
four-way switch valve 46 is changed between two positions to
connect a discharge port and a suction port of the compressor 22 to
an inlet of the condenser 24 and an outlet of the evaporator 28 in
two alternative ways.
[0050] Specifically, in a normal position, the four-way switch
valve 46 connects the discharge port and the suction port of the
compressor 22 to the inlet of the condenser 24 and the outlet of
the evaporator 28, respectively. In a reverse position shown in
FIG. 2, the four-way switch valve 46 connects the discharge port
and the suction port of the compressor 22 to the outlet of the
evaporator 28 and the inlet of the condenser 24, respectively.
[0051] The control device 32 controls the four-way switch valve 46
to take the normal position or the reverse position. Next, how to
use the above-described automotive air-conditioning system, or in
other words, control performed by the control device 32 will be
explained.
[0052] The control device 32 can perform control in a mode selected
from a normal operation mode and a first lubricant return mode and
possibly also a second lubricant return mode, depending on the
varying situation. The second lubricant return mode is provided as
necessary.
[0053] In the normal operation mode, the control device 32 makes
the automotive air-conditioning system operate so that the
temperature in the cabin 10 will approach a temperature setting set
by a passenger in the vehicle, for example. In this case, the
displacement of the compressor 22 and the operating position of the
expansion valve 26 are controlled so that the temperature of the
air after passing across the evaporator 28 will approach a desired
value.
[0054] In the first and second lubricant return modes, the control
device 32 makes the automotive air-conditioning system operate so
that accumulation of the lubricant in the condenser 24 will be
prevented. Here, the accumulation of the lubricant in the condenser
24 not only means that the lubricant accumulates in the condenser
24 but also that the lubricant adheres to the inner surface of the
condenser 24 to some extent.
[0055] The first and second lubricant return modes are provided in
consideration of the fact that R1234yf and PAG experience two-layer
separation at low temperature compared with, for example R134a and
PAG, as shown in FIG. 3. In FIG. 3, the horizontal axis indicates
the ratio of the lubricant to the circulating working fluid.
[0056] FIG. 4 shows a kinematic viscosity versus temperature chart,
where how the kinematic viscosity of the working fluid containing a
refrigerant R1234yf and a lubricant PAG at different lubricant
concentrations 0, 10, 20 and 30% varies with temperature is plotted
(chain lines). In FIG. 4, also isobaric lines are plotted (broken
lines), the refrigeration cycle in the normal operation mode is
indicated by A (compressor inlet port)-B (compressor outlet port)-C
(expansion valve inlet)-D (expansion valve outlet) line, the
refrigeration cycle in the first lubricant return mode is indicated
by O (compressor inlet port)-P (compressor outlet port)-Q
(expansion valve inlet)-R (expansion valve outlet) line, and a
region in which R1234yf and PAG experience two-layer separation
(incompatibility region) is indicated by hatching.
[0057] FIG. 4 shows that the refrigeration cycle in the normal
operation mode A-B-C-D, specifically process B-C traverses the
incompatibility region, which means the lubricant separates from
the refrigerant in the condenser 24.
[0058] By contrast, the refrigeration cycle in the first lubricant
return mode O-P-Q-R does not traverse the incompatibility region.
This is because the first lubricant return mode is provided to
return the lubricant having accumulated in the condenser 24 to the
compressor 22, when the two-layer separation temperature for the
refrigerant and lubricant is lower than the temperature around the
condenser 24 (outside air temperature).
[0059] To achieve this, in the first lubricant return mode, the
automotive air-conditioning system is made to operate to reduce the
pressure of the refrigerant in the condenser 24 to a saturation
pressure of the refrigerant for the outside temperature or below.
Preferably, the control device 32 reduces the pressure of the
refrigerant in the condenser 24 to the saturation pressure of the
refrigerant for the outside temperature or below by reducing the
displacement of the compressor 22.
[0060] The control in the first lubrication return mode causes the
lubricant having accumulated in the condenser 24 to mix with the
refrigerant, and thus, return to the compressor 22 by flowing with
the refrigerant along the circulation path 14 in the normal
direction.
[0061] The pressure of the refrigerant in the condenser 24
(high-pressure) may be reduced to the saturation pressure of the
refrigerant for the outside temperature or below by taking one or
more measures selected from increase of airflow from the condenser
fan 33, reduction of airflow from the blower fan 36 and change of
the inside/outside air switch damper 38 into an inside air
circulation position, in addition to reducing the displacement.
[0062] The second lubricant return mode is provided to return the
lubricant having accumulated in the condenser 24 to the compressor
22, when the two-layer separation temperature for the refrigerant
and lubricant is higher than or equal to the temperature around the
condenser 24 (outside air temperature). The second lubricant return
mode is therefore not necessarily required in cold weather
regions.
[0063] To achieve this, in the second lubricant return mode, the
control device 32 changes the four-way switch valve 46 from the
normal position to the reverse position. As a result, the
refrigerant discharged from the compressor 22 flows along the
circulation path 14 in the reverse direction, namely flows through
the evaporator 28, the expansion valve 26 and the condenser 24
serially, and is sucked into the compressor 22.
[0064] In the second lubricant return mode, the working fluid at
low temperature passing through the condenser 24 mixes with the
lubricant having accumulated in the condenser 24, and returns to
the compressor 22.
[0065] FIG. 5 is a kinematic viscosity versus temperature chart for
an comparative example, where how the kinematic viscosity of the
working fluid containing a refrigerant R134a and a lubricant PAG at
different lubricant concentrations 0, 10, 20 and 30% varies with
temperature is plotted (chain lines) with isobaric lines (broken
line), the refrigeration cycle in the normal operation mode is
indicated by X (compressor inlet port)-Y (compressor outlet port)-V
(expansion valve inlet)-W (expansion valve outlet) line, and an
incompatibility region for R134a and PAG is indicated (by
hatching).
[0066] FIG. 5 shows that the refrigeration cycle X-Y-V-W does not
traverses the incompatibility region, which means the R134a and PAG
does not experience two-layer separation. If the refrigeration
cycle in the normal operation mode does not traverses the
incompatibility region like this, the first and second lubrication
return modes are not required.
[0067] In the above-described embodiment of the refrigeration cycle
system 12 applied to the automotive air-conditioning system,
control in the normal operation mode allows the cabin 10 to be
cooled or dehumidified according to a passenger's instruction.
[0068] In the normal operation mode, the refrigeration cycle
A-B-C-D traverses the two-layer separation region, and thus, the
lubricant adheres to the inner surface of the condenser 24 and of a
section of the piping near the condenser 24, and thus,
accumulates.
[0069] When the lubricant accumulates in the condenser 24 to a
certain extent, the control device 32 performs control in the first
or second lubricant return mode to return the lubricant having
accumulated to the compressor 22 to the compressor 22.
[0070] Specifically, when the temperature around the condenser 24
is lower than the two-layer separation temperature, control in the
first lubricant return mode is performed to reduce the pressure of
the refrigerant in the condenser 24 to the saturation pressure of
the refrigerant for the two-layer separation temperature or below.
This allows the lubricant having accumulated in the condenser 24 to
mix with the refrigerant and return to the compressor 22 with the
refrigerant, and thus, keeps adequate lubrication in the compressor
22 and prevents reduction in COP.
[0071] In the described refrigeration cycle circuit 12, the
pressure of the refrigerant in the condenser 24 is reliably reduced
to the saturation pressure of the refrigerant for the two-layer
separation temperature or below by regulating the displacement of
the compressor 22.
[0072] In the described refrigeration cycle circuit 12, when the
temperature around the condenser 24 is higher than or equal to the
two-layer separation temperature, control in the second lubricant
return mode is performed to return the lubricant having accumulated
in the condenser 24 to the compressor 22 to ensure adequate
lubrication in the compressor 22.
[0073] In the described refrigeration cycle circuit 12, the use of
the four-way switch valve 46 enables reliable return of the
lubricant to the compressor 22 with a simple structure.
[0074] Further, the described refrigerant cycle circuit 12, which
uses a working fluid containing low-GWP R1234yf as a refrigerant,
is global environment-friendly. The working fluid also contains
polyalkylene glycol as a lubricant, which ensures adequate
lubrication in the compressor 22.
[0075] In the above-described automotive air-conditioning system,
the temperature of the refrigerant in the condenser 22 is kept
lower than or equal to the two-layer separation temperature, even
in an environment in which the control in the normal operation mode
results in its exceeding the two-layer separation temperature. This
automotive air-conditioning system is therefore useful in every
region of the world.
[0076] The present invention is not restricted to the
above-described embodiment but can be modified in various ways.
[0077] For example, in the described embodiment, the working fluid
contains a refrigerant R1234yf and a lubricant PAG. The refrigerant
and the lubricant are however not restricted to these. The
refrigeration cycle according to the present invention is
applicable to working fluids experiencing separation of a
refrigerant and a lubricant in the condenser 24.
[0078] In the described embodiment, the control device 32 performs
control in the first or second lubricant return mode when the
lubricant has accumulated in the condenser 24 to a certain extent.
The control device may however perform control in the first or
second lubricant return mode, on a regular or irregular basis.
[0079] Alternatively, it may be arranged such that the control
device performs control in the first or second lubricant return
mode after a long period of low-flow rate circulation of the
working fluid, as observed in long engine idling in the vehicle,
for example.
[0080] Further, it may be arranged such that the control device
performs control in the first or second lubricant return mode when
the heat-transfer effectiveness in the condenser 24 has reduced to
a certain level or when the amount of the lubricant inside the
compressor 22 has reduced to a certain level.
[0081] In the described embodiment, a four-way switch valve 46 is
provided as a means for making the working fluid flow along the
circulation path 14 in the reverse direction. The reversing means
may however be a plurality of solenoid valves, for example.
[0082] In the described embodiment, the expansion valve 26 may be a
temperature-sensitive expansion valve or the like if control in the
second lubricant return mode is not required.
[0083] In the described embodiment, the compressor 22 may be any
type of compressor; it may be a swash-plate or wobble-plate
reciprocating compressor, a scroll compressor or a vane compressor,
for example.
[0084] Last, it goes without saying that the refrigeration cycle
system according to the present invention is applicable to
refrigerator-freezers, room air-conditioners, etc.
INDUSTRIAL APPLICABILITY
[0085] The present invention is applicable to a refrigeration cycle
system using a working fluid containing a lubricant and a
refrigeration that separate from each other in a condenser and an
automotive air-conditioning system including such refrigeration
cycle system, in order to ensure adequate lubrication in the
compressor and satisfactory COP.
* * * * *