U.S. patent application number 10/909547 was filed with the patent office on 2005-02-10 for vapor compression type refrigerating machine.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Ikemoto, Toru, Matsunaga, Hisatsugu, Nishijima, Haruyuki, Takeuchi, Hirotsugu.
Application Number | 20050028552 10/909547 |
Document ID | / |
Family ID | 34114023 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050028552 |
Kind Code |
A1 |
Nishijima, Haruyuki ; et
al. |
February 10, 2005 |
Vapor compression type refrigerating machine
Abstract
A bypass valve 81 is opened until a predetermined period of time
elapses after compressors 10a, 10b are stopped so as to equalize
the pressure of a refrigerant circuit on a condenser 20 side with
the pressure of a refrigerant circuit on an evaporator 30 side and,
after the bypass valve 81 is closed, at least either of a
refrigerant circuit 91 connecting to the compressor 10aand a
refrigerant circuit 92 connecting to the compressor 10b is opened
by opening a three-way valve 90 so that the refrigerant circuit on
the condenser 20 side is made to communicate with the refrigerant
circuit on the evaporator 30 side via the compressor 10 whereby, as
the pressure equalized state can be maintained, it is possible to
prevent the accumulation of a large amount of refrigerating machine
oil on suction sides of the compressors 10 while the compressors 10
are stopped, thereby making it possible to prevent damage to the
compressors 10 due to excessive compression when activated.
Inventors: |
Nishijima, Haruyuki;
(Obu-city, JP) ; Takeuchi, Hirotsugu;
(Nagoya-city, JP) ; Ikemoto, Toru; (Chiryu-city,
JP) ; Matsunaga, Hisatsugu; (Anjo-city, JP) |
Correspondence
Address: |
POSZ & BETHARDS, PLC
11250 ROGER BACON DRIVE
SUITE 10
RESTON
VA
20190
US
|
Assignee: |
DENSO CORPORATION
|
Family ID: |
34114023 |
Appl. No.: |
10/909547 |
Filed: |
August 3, 2004 |
Current U.S.
Class: |
62/500 ; 62/470;
62/527 |
Current CPC
Class: |
F25B 41/00 20130101;
F25B 2341/0012 20130101; F25B 31/004 20130101; F25B 2700/171
20130101; F25B 2600/2501 20130101; F25B 2500/26 20130101; F25B
2400/23 20130101; F25B 2400/0401 20130101; F25B 2500/27 20130101;
F25B 2700/21175 20130101; F25B 2400/075 20130101 |
Class at
Publication: |
062/500 ;
062/470; 062/527 |
International
Class: |
F25B 043/02; F25B
001/06; F25B 041/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2003 |
JP |
2003-287719 |
Claims
1. A vapor compression type refrigerating machine, for moving heat
on a low temperature side to a high temperature side, comprising: a
plurality of compressors arranged in parallel relative to the flow
of a refrigerant for sucking in and compressing a refrigerant; a
high-pressure side heat exchanger for removing heat from a highly
pressurized refrigerant discharged from the compressors; a
low-pressure side heat exchanger for absorbing heat by vaporizing a
low pressure refrigerant; an oil separator provided on a
refrigerant inlet side of the high-pressure heat exchanger for
separating and extracting a refrigerating machine oil mixed in the
refrigerant; an oil return circuit for returning the refrigerant so
separated and extracted by the oil separator to suction sides of
the compressors; a bypass circuit for establishing a communication
between a refrigerant circuit on a high-pressure side heat
exchanger side and a refrigerant circuit on a low-pressure side
heat exchanger side; a bypass valve for opening and closing the
bypass circuit; a compressor valve for opening and closing
refrigerant circuits which connect to the compressors,
respectively; and a control unit for controlling both the valves
such that the bypass valve is kept open until a predetermined
period of time elapses after the plurality of compressors are
stopped and that, after the predetermined period of time has
elapsed, the bypass valve is closed, while the compressor valve is
opened.
2. A vapor compression type refrigerating machine as set forth in
claim 1, wherein the compressor valve opens and closes the
refrigerant circuits which connect to discharge sides of the
compressors.
3. A vapor compression type refrigerating machine comprising: a
plurality of compressors (10) arranged in parallel relative to the
flow of a refrigerant for sucking in and compressing a refrigerant;
a high-pressure side heat exchanger for removing heat from a highly
pressurized refrigerant discharged from the compressors; a
low-pressure side heat exchanger for absorbing heat by vaporizing a
low pressure refrigerant; an ejector having a nozzle for converting
pressure energy of the highly pressurized refrigerant that flows
out from the high-pressure side heat exchanger into velocity energy
so as to reduce the pressure of the refrigerant for expansion
thereof and a pressure increasing portion for sucking in a
vapor-phase refrigerant vaporized by a high-speed flow of
refrigerant injected from the nozzle at the low-pressure side heat
exchanger and mixing the refrigerant injected from the nozzle with
the refrigerant sucked in from the low-pressure side heat exchanger
so as to convert the velocity energy into a pressure energy to
thereby increase the pressure of the refrigerant; a vapor-liquid
separator for separating the refrigerant that has flowed out from
the ejector into a vapor-phase refrigerant and a liquid-phase
refrigerant in which an outlet for the vapor-phase refrigerant is
connected to suction sides of the compressors and an outlet for the
liquid-phase refrigerant is connected to the low-pressure side heat
exchanger; an oil separator provided on a refrigerant inlet side of
the high-pressure heat exchanger for separating and extracting a
refrigerating machine oil mixed in the refrigerant; an oil return
circuit for returning the refrigerant so separated and extracted by
the oil separator to the suction sides of the compressors; a bypass
circuit for establishing communication between a refrigerant
circuit on a high-pressure side heat exchanger side and a
refrigerant circuit on a low-pressure side heat exchanger side; a
bypass valve for opening and closing the bypass circuit; a
compressor valve for opening and closing refrigerant circuits which
connect to the compressors, respectively; and a control unit for
controlling both the valves such that the bypass valve is kept open
until a predetermined period of time elapses after the plurality of
compressors are stopped and that after the predetermined period of
time has elapsed, the bypass valve is closed, while the compressor
valve is opened.
4. A vapor compression type refrigerating machine as set forth in
claim 3, wherein the compressor valve opens and closes the
refrigerant circuits which connect to discharge sides of the
compressors.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to, among refrigerating
machines in which heat on a low temperature side is moved to a high
temperature side, a vapor compression type refrigerating machine
having a plurality of compressors which is effective when applied,
in particular, to an ejector cycle.
[0003] 2. Description of the Related Art
[0004] The ejector cycle is a cycle used in a vapor compression
type refrigerating machine in which the pressure of a refrigerant
is reduced by an ejector so that the refrigerant is allowed to
expand, vapor-phase refrigerant that has been vaporized by an
evaporator is sucked into the ejector, and the suction pressure of
the compressor is increased by converting expansion energy into
pressure energy (for example, refer to the Japanese Unexamined
Patent Publication No. 6-11197).
[0005] Incidentally, in a vapor compression type refrigerating
machine in which the pressure of a refrigerant is reduced, in an
isenthalpic fashion, by a pressure reducing unit such as an
expansion valve (hereinafter, referred to as an expansion valve
cycle), the refrigerant flowing out from the expansion valve flows
into the evaporator, whereas in the ejector cycle, the refrigerant
flowing out from the ejector flows into a vapor-liquid separator,
and a liquid phase refrigerant resulting from separation by the
vapor-liquid separator is supplied into the evaporator while a
vapor phase refrigerant resulting from separation by the
vapor-liquid separator is sucked into the compressor.
[0006] Namely, the expansion valve cycle provides a flow of
refrigerant in which the refrigerant circulates from the compressor
back to the compressor via the condenser, the expansion valve, and
the evaporator sequentially in that order, whereas the ejector
cycle provides two flows of refrigerant; one is a flow of
refrigerant in which the refrigerant circulates from the compressor
back to the compressor via the condenser (a high pressure side heat
exchanger), the ejector, and the vapor-liquid separator
sequentially in that order, and the other is a flow of refrigerant
in which the refrigerant circulates from the vapor-liquid separator
back to the vapor-liquid separator via the evaporator and the
ejector sequentially in that order.
[0007] Then, in the ejector cycle, as the refrigerant in a
saturated state flows into a low pressure side heat exchanger, if a
low pressure side heat exchanger whose size is the same as that of
the low pressure side heat exchanger used in the expansion valve
cycle is used in the ejector cycle, the amount of liquid phase
refrigerant flowing through the low pressure side heat exchanger
becomes larger than that in the expansion valve cycle, and
therefore, the amount of refrigerant to be sealed in the cycle must
be increased, compared with the expansion valve cycle.
[0008] While the amount of a refrigerating machine oil that is
mixed in the refrigerant needs to be increased in association with
the increase in the amount of refrigerant, in the event that the
amount of refrigerating machine oil that is mixed in the
refrigerant is increased, the amount of refrigerating machine oil
mixed in the refrigerant discharged from the compressor is
inevitably increased.
[0009] Incidentally, the refrigerating machine oil is a lubricating
oil which lubricates sliding parts and bearings within the
compressor.
[0010] In addition, in the event that the refrigerant that contains
a large amount of refrigerating machine oil flows into the heat
exchanger such as the high pressure side heat exchanger and the low
pressure side heat exchanger, the refrigerating machine oil whose
kinematic viscosity is larger than the refrigerant adheres to an
internal wall of the heat exchanger to thereby decrease the heat
exchange efficiency of the heat exchanger. Thus, it is a normal
practice to provide an oil separator for separating the
refrigerating machine oil mixed in the refrigerant on a discharge
side of the compressor, that is, a refrigerant inlet side of the
high pressure side heat exchanger, so that refrigerating machine
oil separated by the oil separator is returned to a suction side of
the compressor via an oil return circuit which is constituted as a
restriction unit such as a capillary tube.
[0011] In addition, in a vapor compression type refrigerating
machine having a plurality of compressors, as the vapor compression
type refrigerating machine is operated while a high load operation
mode, in which all the compressors are in operation, and a low load
operation mode, in which any of the plurality of compressors is in
operation are changed over, in order to prevent a high pressure
refrigerant discharged from the compressor from flowing into the
compressors which are not in operation, check valves 10c, 10d are
provided, as shown in FIG. 2, along refrigerant circuits which
connect to discharge sides of the respective compressors 10a,
10b.
[0012] In the refrigerating machine shown in FIG. 2, that is, the
refrigerating machine including the plurality of compressors 10a,
10b arranged in parallel relative to the flow of refrigerant for
sucking in and compressing a refrigerant, a high pressure side heat
exchanger 20 for removing heat from a high pressure refrigerant
discharged from the compressors 10a, 10b, a low pressure side heat
exchanger 30 for vaporizing a low pressure refrigerant and
absorbing heat therefrom, an oil separator 70 provided on a
refrigerant inlet side of the high pressure side heat exchanger 20
for separating and extracting a refrigerating machine oil mixed in
the refrigerant, and an oil return circuit 71 for returning the
refrigerating machine oil so separated and extracted by the oil
separator 70 to the suction sides of the compressors 10a, 10b, a
difference in pressure between a pressure remaining on the high
pressure side heat exchanger 20 side and a pressure remaining on
the low pressure side heat exchanger 30 side is large immediately
after all the plurality of compressors 10a, 10b are stopped, and as
the check valves 10c, 10d are provided on the discharge sides of
the compressors 10a, 10b, the refrigerating machine oil separated
and extracted by the oil separator 70 returns to the suction sides
of the compressors 10a, 10b via the oil return circuit 71.
[0013] Due to this, as the refrigerating machine oil that has been
separated and extracted by the oil separator 70 continues to return
to the suction sides of the compressors 10a, 10b via the oil return
circuit 71 until the pressures on the high and low pressure sides
become equal, a large amount of refrigerating machine oil is
accumulated on the suction sides of the compressors 10a, 10b.
[0014] Then, when the compressors 10a, 10b are activated with the
large amount of refrigerating machine oil being accumulated on the
suction sides of the compressors 10a, 10b, as the compressors 10a,
10b pick up a large amount of refrigerating machine oil, which is
liquid, an excessively compressed state results from liquid
compression, and it is highly probable that the compressors 10a,
10b are damaged.
[0015] In contrast to this, as shown in FIG. 3, there are provided
a bypass circuit 80 for establishing a communication between the
refrigerant circuit on the high pressure side heat exchanger 20
side and the refrigerant circuit on the low pressure side heat
exchanger 30 side and a bypass valve 81 for opening and closing the
bypass circuit 80, whereby, when the plurality of compressors 10a,
10b are stopped, the bypass valve 81 is opened. This construction
provides, however, another problem as described below.
[0016] Namely, in addition to the difference in pressure, there
also exists a large difference in temperature between the
refrigerant circuit on the high pressure side heat exchanger 20
side and the refrigeration cycle on the low pressure side heat
exchanger 30 side.
[0017] As this occurs, while the difference in pressure between the
refrigerant circuit on the high pressure side heat exchanger 20
side and the refrigeration cycle on the low pressure side heat
exchanger 30 side can be eliminated to provide an equalized
pressure therebetween within a relatively short period of time (for
example, in the order of 30 seconds) by opening the bypass valve
81, as the high pressure side heat exchanger 20 and the low
pressure side heat exchanger 30 have a relatively large heat
capacity, even in the event that the pressures of the refrigerant
circuit on the high pressure side heat exchanger 20 side and the
refrigeration cycle on the low pressure side heat exchanger 30 side
become equal, the difference in temperature between the refrigerant
circuit on the high pressure side heat exchanger 20 side and the
refrigeration cycle on the low pressure side heat exchanger 30 side
cannot be reduced in the same way as the pressure difference is
reduced.
[0018] Consequently, when the bypass valve is closed after the
pressure of the refrigerant circuit on the high pressure side heat
exchanger 20 side and the pressure of the refrigerant circuit on
the low pressure side heat exchanger 30 side become equal by
opening the bypass valve 81, there is caused, as shown in FIG. 4, a
difference in pressure between the refrigerant circuit on the high
pressure side heat exchanger 20 side and the refrigerant circuit on
the low temperature side heat exchanger 30 side due to the
difference in temperature between the refrigerant circuit on the
high pressure side heat exchanger 20 side and the refrigerant
circuit on the low temperature side heat exchanger 30 side.
[0019] Due to this, in order to make sufficiently uniform the
pressure of the refrigerant circuit on the high pressure side heat
exchanger 20 side and the pressure of the refrigerant circuit on
the low temperature side heat exchanger 30 side, it is desirable to
keep the bypass valve 81 open until the compressors 10a, 10b, that
is, the vapor compression type refrigerating machine is
re-activated after the refrigerating machine has been stopped.
[0020] On the other hand, in order to prevent the occurrence of a
problem with operation of the vapor compression type refrigerating
machine even in the event that the bypass valve 81 fails, a
normally-closed type valve is desirably adopted for the bypass
valve 81.
[0021] Note that, in electromagnetic valves or the like, for
example, the normally-closed type valve means a valve which closes
when not energized and opens when energized.
[0022] When adopting a normally-opened valve as the bypass valve
81, however, as the bypass valve 81 needs to be energized until the
vapor compression type refrigerating machine is re-activated after
it has been stopped, the dark current, that is, the current
consumed while the vehicle is stopped increases.
SUMMARY OF THE INVENTION
[0023] The invention was made in view of the situations and a first
object thereof is to provide a novel vapor compression type
refrigerating machine which is different from conventional ones,
and a second object of the invention is to prevent damage to a
compressor due to excessive compression when the refrigerating
machine is activated.
[0024] With a view to attaining the objects, according to one
aspect of the invention, there is provided a vapor compression type
refrigerating machine for moving heat on a low temperature side to
a high temperature side comprising a plurality of compressors (10a,
10b) arranged in parallel relative to the flow of a refrigerant for
sucking in and compressing a refrigerant, a high-pressure side heat
exchanger (20) for removing heat from a highly pressurized
refrigerant discharged from the compressors (10a, 10b), a
low-pressure side heat exchanger (30) for absorbing heat by
vaporizing a low pressure refrigerant, an oil separator (70)
provided on a refrigerant inlet side of the high-pressure heat
exchanger (20) for separating and extracting a refrigerating
machine oil mixed in the refrigerant, an oil return circuit (71)
for returning the refrigerant so separated and extracted by the oil
separator (70) to suction sides of the compressors (10a, 10b), a
bypass circuit (80) for establishing a communication between a
refrigerant circuit on a high-pressure side heat exchanger (20)
side and a refrigerant circuit on a low-pressure side heat
exchanger (30) side, a bypass valve (81) for opening and closing
the bypass circuit (80), a compressor valve (90) for opening and
closing refrigerant circuits (91, 92) which connect to the
compressors (10a, 10b), respectively, and a control unit (100) for
controlling both the valves (81, 90) such that the bypass valve
(81) is kept open until a predetermined period of time has elapsed
after the plurality of compressors (10a, 10b) were stopped and
that, after the predetermined period of time has elapsed, the
bypass valve (81) is closed while the compressor valve (90) is
opened.
[0025] Then, according to the invention, the bypass valve (81) is
kept open until the predetermined period of time has elapsed after
the compressors (10a, 10b) were stopped, so that the pressure of
the refrigerant circuit on the high-pressure side heat exchanger
(20) side and the pressure of the refrigerant circuit on the
low-pressure side heat exchanger (30) side are made equal, and
after the bypass valve (81) is closed, the compressor valve (90) is
opened, so that the refrigerant circuit on the high-pressure side
heat exchanger (20) side is made to communicate with the
refrigerant circuit on the low-pressure side heat exchanger (30)
side via the compressors (10a, 10b). Thus, even in the event that
there is a big difference in temperature between the high-pressure
side heat exchanger (20) side and the low-pressure side heat
exchanger (30) side, it is possible to prevent the generation of a
difference in pressure to cause the refrigerating machine oil to
flow between the refrigerant circuit on the high-pressure side heat
exchanger (20) side and the refrigerant circuit on the low-pressure
side heat exchanger (30) side due to the difference in
temperature.
[0026] Consequently, as the accumulation of a large amount of
refrigerating machine oil on the suction sides of the compressors
(10a, 10b), while the compressors (10a, 10b) are stopped, can be
prevented, it is possible to prevent a risk that the compressors
(10a, 10b) are damaged due to excessive compression when the
refrigerating machine is activated.
[0027] According to another aspect of the invention, there is
provided a vapor compression type refrigerating machine comprising
a plurality of compressors (10) arranged in parallel relative to
the flow of a refrigerant for sucking in and compressing a
refrigerant, a high-pressure side heat exchanger (20) for removing
heat from a highly pressurized refrigerant discharged from the
compressors (10a, 10b), a low-pressure side heat exchanger (30) for
absorbing heat by vaporizing a low pressure refrigerant, an ejector
(40) having a nozzle (41) for converting a pressure energy of the
highly pressurized refrigerant that flows out from the
high-pressure side heat exchanger (20) into a velocity energy so as
to reduce the pressure of the refrigerant for expansion and
pressure increasing portions (42, 43) for sucking in a vapor-phase
refrigerant vaporized by a high-speed flow of refrigerant injected
from the nozzle (41) at the low-pressure side heat exchanger (30)
and mixing the refrigerant injected from the nozzle (41) with the
refrigerant sucked in from the low-pressure side heat exchanger
(30) so as to convert the velocity energy into a pressure energy to
thereby increase the pressure of the refrigerant, a vapor-liquid
separator (50) for separating the refrigerant that has flowed out
from the ejector (40) into a vapor-phase refrigerant and a
liquid-phase refrigerant in which an outlet for the vapor-phase
refrigerant is connected to suction sides of the compressors (10a,
10b) and an outlet for the liquid-phase refrigerant is connected to
the low-pressure side heat exchanger (30), an oil separator (70)
provided on a refrigerant inlet side of the high-pressure heat
exchanger (20) for separating and extracting a refrigerating
machine oil mixed in the refrigerant, an oil return circuit (71)
for returning the refrigerant so separated and extracted by the oil
separator (70) to the suction sides of the compressors (10a, 10b),
a bypass circuit (80) for establishing a communication between a
refrigerant circuit on a high-pressure side heat exchanger (20)
side and a refrigerant circuit on a low-pressure side heat
exchanger (30) side, a bypass valve (81) for opening and closing
the bypass circuit (80), a compressor valve (90) for opening and
closing refrigerant circuits (91, 92) which connect to the
compressors (10a, 10b), respectively, and a control unit (100) for
controlling both the valves (81, 90) such that the bypass valve
(81) is kept open until a predetermined period of time has elapsed
after the plurality of compressors (10a, 10b) were stopped and that
after the predetermined period of time has elapsed, the bypass
valve (81) is closed while the compressor valve (90) is opened.
[0028] Then, according to the invention, the bypass valve (81) is
kept open until the predetermined period of time has elapsed after
the compressors (10a, 10b) were stopped, so that the pressure of
the refrigerant circuit on the high-pressure side heat exchanger
(20) side and the pressure of the refrigerant circuit on the
low-pressure side heat exchanger (30) side are made equal, and
after the bypass valve (81) is closed, the compressor valve (90) is
opened, so that the refrigerant circuit on the high-pressure side
heat exchanger (20) side is made to communicate with the
refrigerant circuit on the low-pressure side heat exchanger (30)
side via the compressors (10a, 10b). Thus, even in the event that
there is a big difference in temperature between the high-pressure
side heat exchanger (20) side and the low-pressure side heat
exchanger (30) side, it is possible to prevent the generation of a
difference in pressure to cause the refrigerating machine oil to
flow between the refrigerant circuit on the high-pressure side heat
exchanger (20) side and the refrigerant circuit on the low-pressure
side heat exchanger (30) side due to the difference in
temperature.
[0029] Consequently, as the accumulation of a large amount of
refrigerating machine oil on the suction sides of the compressors
(10a, 10b) while the compressors (10a, 10b) are stopped can be
prevented, it is possible to prevent a risk that the compressors
(10a, 10b) are damaged due to excessive compression when the
refrigerating machine is activated.
[0030] According to the invention, the compressor valve (90) opens
and closes the refrigerant circuits (91, 92) which connect to
discharge sides of the compressors (10a, 10b).
[0031] Incidentally, parenthesized reference numerals imparted to
the respective units above correspond to specific examples of units
that are described in an embodiment of the invention that will be
described later on.
[0032] The present invention will be more fully understood with
reference to the accompanying drawings and a preferred embodiment
of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] In the drawings:
[0034] FIG. 1 is an exemplary diagram illustrating an ejector cycle
according to an embodiment of the invention; FIG. 2 is an exemplary
diagram illustrating an ejector cycle according to a related
art;
[0035] FIG. 3 is an exemplary diagram illustrating an ejector cycle
according another related art; and
[0036] FIG. 4 is a graph illustrating pressure behaviors of the
ejector cycles according to the related arts.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0037] In an embodiment of the invention, an ejector cycle
according to the invention is applied to a vapor compression type
refrigerating machine which needs to decrease the temperature in a
showcase for preserving foods and drinks in cooled and frozen
conditions or a refrigerator of a refrigerated vehicle for
transporting foods and drinks that are preserved in cooled and
frozen conditions lower than the temperature of an air
conditioner.
[0038] Compressors 10a, 10b suck in and compress a refrigerant by
obtaining power from an electric motor, and these two compressors
10a, 10b are arranged in parallel relative to the flow of a
refrigerant. Note that when the compressors 10a, 10b are referred
to collectively, they are described as the compressor 10, whereas
when the respective compressors need to be described individually,
they are described as the compressor 10a or the compressor 10b.
[0039] A condenser 20 is a high-pressure side heat exchanger
constituting a radiator for implementing a heat exchange between a
high-temperature, high-pressure refrigerant discharged from the
compressor 10 and outside air so as to cool and condense the
refrigerant, and an evaporator 30 is a low-pressure side heat
exchanger for implementing a heat exchange between air sent into a
refrigerator and a low-pressure refrigerant so as to vaporize a
liquid-phase refrigerant to thereby exhibit a refrigerating
capacity.
[0040] An ejector 40 is an ejector for sucking in a vapor-phase
refrigerant which is vaporized at the evaporator 30 by reducing the
pressure of the refrigerant that has flowed out from the condenser
20 for expansion and converting an expansion energy into a pressure
energy so as to increase the suction pressure of the compressor
10.
[0041] Then, the ejector 40 includes a nozzle 41 for converting the
pressure energy of the high-pressure refrigerant that flows
thereinto into a velocity energy so as to reduce the pressure of
the refrigerant, in an isenthalpic fashion, a fixing portion 42 for
sucking in the vapor-phase refrigerant that is vaporized at the
evaporator 30 through an entrainment action by a high-speed flow of
refrigerant injected from the nozzle 41 for mixing with the flow of
refrigerant injected from the nozzle 41 and a diffuser 43 for
mixing the refrigerant injected from the nozzle 41 with the
refrigerant sucked in from the evaporator 30 so as to convert the
velocity energy into a pressure energy to thereby increase the
pressure of the refrigerant.
[0042] As this occurs, at the mixing portion 42, as a drive flow
and a suction flow mix with each other so that a sum of the kinetic
momentum of the drive flow and the kinetic momentum of the suction
flow is preserved, the pressure (the static pressure) of the
refrigerant is also increased at the mixing portion 42.
[0043] On the other hand, at the diffuser 43, as the velocity
energy (the dynamic pressure) of the refrigerant is converted into
a pressure energy (a static pressure) by gradually expanding the
cross-sectional area of a passageway, the pressure of the
refrigerant is increased at both the mixing portion 42 and the
diffuser 43 in the ejector 40. Hence, hereinafter, the mixing
portion 42 and the diffuser 43 are generally referred to as a
pressure increasing portion.
[0044] Incidentally, in this embodiment, in order to accelerate the
velocity of the refrigerant injected from the nozzle 41 to a
velocity equal to or faster than the sonic velocity, while an Laval
nozzle (refer to Fluid Engineering (Tokyo University Publication
Association)) having a throat portion where the area of the passage
is reduced to the minimum at a position along the length of the
passageway is adopted, of course, it goes without saying that a
tapered nozzle may be adopted.
[0045] In addition, the vapor-liquid separator 50 is a vapor-liquid
separating unit into which the refrigerant that has flowed out from
the ejector 40 flows and which is adapted to store the refrigerant
that has so flowed in by separating the refrigerant into a
vapor-phase refrigerant and a liquid-phase refrigerant, and an
outlet for the vapor-phase refrigerant of the vapor-liquid
separator 50 is connected to a suction side of the compressor 10,
whereas an outlet for the liquid-phase refrigerant thereof is
connected to the evaporator 30 side.
[0046] A variable restriction unit 60 is an expansion valve which
is provided at a position along the refrigerant passageway between
the condenser 20 and the ejector 40, that is, upstream of the
nozzle 41 with respect to the flow of refrigerant for reducing the
pressure of the highly-pressurized refrigerant that has flowed out
from the condenser 20 to a vapor-liquid two-phase area for
expansion. This variable restriction unit 60 is such as to control
the opening of restriction so that the degree of superheating of
refrigerant on the refrigerant outlet side of the evaporator 30
resides within a predetermined range (for example, 0.1 deg to 10
deg) and has a similar construction to that of a known external
pressure equalizing type expansion valve.
[0047] To be specific, the variable restriction unit 60 is such as
to include a valve element 61 for varying the opening of the
restriction, a film-like diaphragm 63 constituting a back pressure
compartment 62 where an internal pressure varies by sensing the
refrigerant temperature on the refrigerant outlet side of the
evaporator 30, a connecting rod 64 which connects the valve element
61 to the diaphragm 63 so as to transfer the displacement of the
diaphragm 63, a spring 65 adapted to apply a spring pressure in a
direction in which the volume of the back pressure compartment 62
is reduced and an external equalizer pipe 67 for introducing the
pressure of the refrigerant on the refrigerant outlet side of the
evaporator 30 into a pressure compartment 66 which is situated
opposite to the back pressure compartment 62 across the diaphragm
63.
[0048] Note that the back pressure compartment 62 communicates with
a temperature sensing tube 62a for sensing the temperature of
refrigerant on the refrigerant outlet side of the evaporator 30,
whereby the temperature of refrigerant on the refrigerant outlet
side of the evaporator 30 is transmitted to the back pressure
compartment 62 via the temperature sensing tube 62a.
[0049] Due to this, the variable restriction unit 60 reduces the
opening of restriction thereof so as to increase the velocity of
the drive flow injected from the nozzle 41 to thereby increase the
suction flow or the amount of refrigerant circulating through the
evaporator 30 when the pressure in the evaporator 30, that is, the
heat load in the evaporator 30 increases, whereby the degree of
superheating of refrigerant on the outlet side of the evaporator 30
increases. On the contrary, when the pressure within the evaporator
30 decreases, whereby the degree of superheating of refrigerant on
the outlet side of the evaporator 30 decreases, the variable
restriction unit 60 increases the opening of restriction thereof so
as to decrease the velocity of the drive flow injected from the
nozzle 41 to thereby decrease the amount of refrigerant which
circulates through the evaporator 30.
[0050] An oil separator 70 is such as to separate and extract a
refrigerating machine oil mixed in the refrigerant, and this oil
separator 70 is provided on a refrigerant inlet side of the
condenser 20.
[0051] Note that, as oil separators, there are a centrifugal
separation method for separating a refrigerating machine oil from a
refrigerant by rotating, at high speed, the refrigerant in which
the refrigerating machine oil is mixed and a collision separation
method for separating a refrigerating machine oil from a
refrigerant by causing the refrigerant in which the refrigerating
machine oil is mixed to collide against a wall surface at high
speed. In this embodiment, the centrifugal separation system is
adopted.
[0052] An oil return circuit 71 is a circuit for returning the
refrigerating machine oil separated and extracted by the oil
separator 70 to the suction side of the compressor 10. This oil
return circuit 71 is made up of a fixed restriction such as a
capillary tube (a fine tube) or an orifice whose restriction
opening is fixed, and in this embodiment, a capillary tube is
adopted.
[0053] Note that the oil return circuit 71 is set such that a
pressure loss is generated which is substantially equal to a sum of
the pressure reduction amount of the nozzle 41 and the pressure
reduction amount of the variable restriction unit 60.
[0054] A bypass circuit 80 is a refrigerant circuit for
establishing a communication between a refrigerant circuit on the
condenser 20 side and a refrigerant circuit on the evaporator 30
side, and a bypass valve 81 is a normally-closed electromagnetic
valve for opening and closing the bypass circuit 80.
[0055] Note that, in this embodiment, a high-pressure side of the
bypass circuit 80 is connected to the refrigerant circuit on the
condenser 20 side at a position between the condenser 20 and the
oil separator 70, whereas a low-pressure side of the bypass circuit
80 is connected to the refrigerant circuit on the evaporator 30
side at a position between the vapor-liquid separator 50 and the
evaporator 30.
[0056] A three-way valve 90 is a compressor valve for opening and
closing refrigerant circuits 91, 92 which connect to the
compressors 10a, 10b, respectively. The three-way valve 90 is an
electric valve for switching the case where the refrigerant circuit
91 connecting to the compressor 10a is opened whereas the
refrigerant circuit 92 connecting to the compressor 10b is closed,
the case where the refrigerant circuit 91 connecting to the
compressor 10a is closed whereas the refrigerant circuit 92
connecting to the compressor 10b is opened, and the case where the
refrigerant circuits 91, 92 are both opened.
[0057] Note that, in this embodiment, while the three-way valve 90
is disposed on a merging side of the refrigerant circuits 91, 92,
that is, on discharge sides of the compressors 10a, 10b, the
three-way valve 90 may be disposed on a branching side of the
refrigerant circuits 91, 92, that is, the suction sides of the
compressors 10a, 10b.
[0058] Then, the operations of the bypass valve 81 and the
three-way valve 90 are controlled by an electronic control unit
100, and signals from rotational speed sensors 101, 102 for
detecting the rotational speed of the compressors 10a, 10b are
inputted into the electronic control unit 100.
[0059] Note that the electronic control unit 100 detects whether or
not the compressors 10a, 10b are stopped based on the rotational
speeds, of the compressors 10a, 10b, that are detected by the
rotational speed sensors 101, 102.
[0060] Next, the operation of an ejector cycle will be described
briefly.
[0061] 1. Basic Operation
[0062] This operation is an operation mode for generating a
refrigerating capacity at the compressor 30.
[0063] To be specific, the refrigerant discharged from the
compressor 10 is circulated to the condenser 20 side, whereby the
pressure of the highly pressurized refrigerant that is cooled at
the condenser 20 is reduced in an isenthalpic fashion down to the
vapor-liquid two-phase area by the variable restriction unit 60.
Thereafter, the pressure of the refrigerant so reduced in pressure
is reduced in an isenthalpic fashion by the nozzle 41 of the
ejector 40 so that the refrigerant expands, whereby the refrigerant
flows into the mixing portion 42 at faster speed than sonic
velocity.
[0064] As this occurs, in this embodiment, the refrigerant is once
boiled at the variable restriction unit 60, and the refrigerant is
expanded at an inlet portion of the nozzle 41 so as to restore the
pressure, whereby the refrigerant can be boiled at a second-stage
nozzle while continuing to generate boiling nucleus. Thus, the
boiling of refrigerant at the nozzle 41 can be promoted, thereby
making it possible to improve the ejector efficiency .eta.e by
making the drops of refrigerant become minute particles.
[0065] Incidentally, the ejector efficiency .eta.e is defined by
using, as a denominator, a product of the mass flow rate Gn of
refrigerant which flows through the condenser 20 and a difference
in enthalpy .DELTA.ie between the outlet and inlet of the nozzle 41
and putting, as a numerator, a sum of a refrigerant flow rate Gn
indicating to what extent the energy is recovered, as work done, by
the compressor 10 and the mass flow rate Ge of refrigerant which
flows through the evaporator 30 and a pressure recovery .DELTA.P at
the ejector 40.
[0066] Note that, in this embodiment, chlorofluorocarbon is used as
refrigerant, and the high-pressure side refrigerant pressure, that
is, the pressure of refrigerant that flows into the nozzle is made
to be equal to or less than the critical pressure of the
refrigerant.
[0067] On the other hand, as refrigerant vaporized within the
evaporator 30 is sucked into the mixing portion 42 by virtue of a
pumping action (refer to Japanese Industry Standard (JIS) Z8126,
No. 2. 1. 2. 3 and the like) generated in association with the
entrainment action of the high-speed refrigerant that has flowed
into the mixing portion 42, the refrigerant on the low-pressure
side circulates from the vapor-liquid separator 50 back to the
vapor-liquid separator 50 via the evaporator 30 and the ejector 40
(the pressure increasing portion) sequentially and in that
order.
[0068] Then, while the refrigerant (suction flow) sucked in from
the evaporator 30 and the refrigerant (drive flow) spouted from the
nozzle 41 are being mixed together at the mixing portion 42, the
dynamic pressure of the mixed refrigerants is converted into a
static pressure by the diffuser 43 and the refrigerant is then
returned to the vapor-liquid separator 50.
[0069] Note that when the refrigeration load is large as in a case
where a large refrigerating capacity is exhibited at the evaporator
30 or a case where the outside temperature is high, the two
compressors 10a, 10b are both operated, whereas when the
refrigeration load is small, only one (for example, the compressor
10a) of the two compressors 10a, 10b is operated.
[0070] 2. Refrigerating Machine Stop Mode
[0071] This operation mode is such as to be executed in a case
where the two compressors 10a, 10b are both stopped.
[0072] To be specific, the electronic control unit 100 continues to
energize the bypass valve 81 until a predetermined period of time
(for example, 30 sec) has elapsed since the compressors 10a, 10b
were stopped so as to open the bypass circuit 80, and when the
predetermined period of time has elapsed, the electronic control
unit 100 cuts off the energization of the bypass valve 81 so as to
close the bypass circuit 80 and opens the three-way valve 90,
whereby at least one (for example, the refrigerant circuit 91) of
the refrigerant circuit 91 connecting to the compressor 10a and the
refrigerant circuit 10b connecting to the refrigerant circuit 92 is
opened.
[0073] Next, the function and advantage of the embodiment will be
described below.
[0074] In this embodiment, the bypass valve 81 is opened until the
predetermined period of time has elapsed since the compressors 10a,
10b were stopped so that the pressure of the refrigerant circuit on
the condenser 20 side and the pressure of the refrigerant circuit
on the evaporator 30 side are equalized and, after the bypass valve
81 is closed, the three-way valve 90 is opened so as to open at
least either of the refrigerant circuit 91 connecting to the
compressor 10a and the refrigerant circuit 92 connecting to the
compressor 10b to thereby establish a communication between the
refrigerant circuit on the condenser 20 side and the refrigerant
circuit on the evaporator 30 side via the compressor 10. Thus, even
in the event that the difference in temperature between the
condenser 20 side and the evaporator 30 side is large, it is
possible to prevent the generation of a difference in pressure to
cause the refrigerating machine oil to flow between the refrigerant
circuit on the condenser 20 side and the refrigerant circuit on the
evaporator 30 side due to the difference in temperature.
[0075] Namely, the embodiment is such that when the compressors
10a, 10b are stopped, firstly, the bypass valve 81 is opened so as
to equalize the pressure of the refrigerant circuit on the
condenser 20 side with the pressure of the refrigerant circuit on
the evaporator 30 side, and thereafter, the refrigerant circuit on
the condenser 20 side and the refrigerant circuit on the evaporator
30 side are made to communicate with each other via the refrigerant
circuits 91, 92 connecting to compressor 10, whereby the equalized
pressure state is maintained.
[0076] Consequently, as it is possible to prevent the accumulation
of a large amount of refrigerating machine oil on the suction side
of the compressor 10 while the compressor is stopped, it is
possible to prevent the occurrence of a risk that the compressor 10
is damaged due to excessive compression when activated.
[0077] In the embodiment, while the compressors 10a, 10bsuck in and
compress refrigerant by obtaining power from the electric motor,
the invention is not limited thereto, and the compressors 10a, 10b
may suck in and compress refrigerant by obtaining power from an
engine such as an internal combustion engine.
[0078] In addition, while, in the embodiment, the invention is
applied to the showcase or the like for preserving foods and drinks
in cooled and frozen conditions, the application of the invention
is not limited thereto, and the invention may be applied to, for
example, a vapor compression type refrigerating machine for an air
conditioner.
[0079] Additionally, while, in the embodiment, the external
pressure equalizing type temperature expansion valve is adopted as
the variable restriction unit 60, an internal pressure equalizing
type temperature expansion valve may be adopted as the variable
restriction unit 60.
[0080] In addition, while, in the embodiment, the variable
restriction unit 60 and the nozzle 41 are provided separately, the
invention is not limited thereto, and for example, the variable
restriction unit 60 and the nozzle 41 may be integrated into a
single unit.
[0081] Additionally, in Description of the Related Art, while the
description is made by comparing the expansion valve cycle with the
ejector cycle, the aforesaid problems also occur, more or less, in
the expansion valve cycle, and therefore, the invention can be
applied to the expansion valve cycle.
[0082] In addition, while, in the embodiment, the compressor valve
is made up of the three-way valve 90, the invention is not limited
thereto, and the compressor valve may be made up by disposing an
electromagnetic switching valve along the length of, for example,
each of the refrigerant circuit 91 connecting to the compressor 10a
and the refrigerant circuit 92 connecting the compressor 10b.
[0083] While the invention has been described by reference to
specific embodiments chosen for purposes of illustration, it should
be apparent that numerous modifications could be made thereto by
those skilled in the art without departing from the basic concept
and scope of the invention.
* * * * *