U.S. patent application number 11/882161 was filed with the patent office on 2008-01-31 for two-stage expansion refrigerating device.
This patent application is currently assigned to SANYO ELECTRIC CO. LTD.. Invention is credited to Satoshi Imai, Hiroyuki Itsuki, Satoshi Sakimichi, Ryosuke Tsuihiji.
Application Number | 20080022706 11/882161 |
Document ID | / |
Family ID | 38694120 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080022706 |
Kind Code |
A1 |
Sakimichi; Satoshi ; et
al. |
January 31, 2008 |
Two-stage expansion refrigerating device
Abstract
An object is to provide a two-stage expansion refrigerating
device capable of performing control with low cost so that a
pressure of a refrigerant which has flowed through a
high-pressure-side expansion unit is an optimum pressure, the
device comprises a control unit (a controller) which controls a
compressor (a low-stage-side compression element and a
high-stage-side compression element) and each expansion unit (a
high-pressure-side expansion valve as a high-pressure-side
expansion unit and a low-pressure-side expansion valve as a
low-pressure-side expansion unit), and a temperature sensor (a
temperature detection unit) which detects a temperature of the
refrigerant which has flowed through the high-pressure-side
expansion valve, and the controller estimates a pressure of the
refrigerant which has flowed through the high-pressure-side
expansion valve based on a temperature detected by the temperature
sensor, and controls one of the high-pressure-side expansion valve
and the low-pressure-side expansion valve based on the estimated
pressure.
Inventors: |
Sakimichi; Satoshi;
(Ora-gun, JP) ; Tsuihiji; Ryosuke; (Ota-shi,
JP) ; Imai; Satoshi; (Ota-shi, JP) ; Itsuki;
Hiroyuki; (Ora-gun, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SANYO ELECTRIC CO. LTD.
|
Family ID: |
38694120 |
Appl. No.: |
11/882161 |
Filed: |
July 31, 2007 |
Current U.S.
Class: |
62/190 |
Current CPC
Class: |
Y02B 30/70 20130101;
F25B 2600/0253 20130101; F25B 2700/2109 20130101; F25B 2700/21175
20130101; F25B 41/39 20210101; F25B 2700/2106 20130101; F25B
2400/23 20130101; F25B 2700/21 20130101; F25B 2400/13 20130101;
F25B 1/10 20130101; F25B 2700/2102 20130101; F25B 2600/2513
20130101; F25B 2600/2509 20130101; F25B 2700/21174 20130101 |
Class at
Publication: |
62/190 |
International
Class: |
F25B 1/00 20060101
F25B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 31, 2006 |
JP |
JP 2006-207815 |
Claims
1. A two-stage expansion refrigerating device which is provided
with a refrigerant circuit including a compressor, a gas cooler,
high-pressure-side expansion means, gas-liquid separation means,
low-pressure-side expansion means and an evaporator and which
returns a gas-phase refrigerant separated by the gas-liquid
separation means to an intermediate-pressure section of the
compressor and which allows a liquid-phase refrigerant to flow into
the evaporator via the low-pressure-side expansion means, the
device comprising: control means for controlling the compressor and
each expansion means; and temperature detection means for detecting
a temperature of the refrigerant which has flowed through the
high-pressure-side expansion means, wherein the control means
estimates a pressure P2 of the refrigerant which has flowed through
the high-pressure-side expansion means based on a temperature
detected by the temperature detection means, and controls one of
the high-pressure-side expansion means and the low-pressure-side
expansion means based on the estimated pressure P2.
2. The two-stage expansion refrigerating device according to claim
1, wherein the temperature detection means detects the temperature
of the liquid-phase refrigerant separated by the gas-liquid
separation means.
3. The two-stage expansion refrigerating device according to claim
1 or 2, wherein the control means controls one of the
high-pressure-side expansion means and the low-pressure-side
expansion means based on the pressure P2 and a pressure P1 of the
intermediate-pressure section of the compressor.
4. The two-stage expansion refrigerating device according to claim
1, 2 or 3, wherein the control means controls one of the
high-pressure-side expansion means and the low-pressure-side
expansion means so that the pressure P2 is lager than the pressure
P1.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a two-stage expansion
refrigerating device in which expansion means includes
high-pressure-side expansion means and low-pressure-side expansion
means and in which a pressure of a refrigerant having the pressure
reduced by the high-pressure-side expansion means is further
reduced by the low-pressure-side expansion means.
[0002] Heretofore, in this type of two-stage expansion
refrigerating device, a compressor including a low-stage-side
compression element and a high-stage-side compression element, a
gas cooler (or condenser), high-pressure-side expansion means,
gas-liquid separation means, low-pressure-side expansion means and
an evaporator constitute a refrigerant circuit. Moreover, a gas
refrigerant discharged from the high-stage-side compression element
of the compressor flows into the gas cooler to radiate heat. After
the pressure of the refrigerant condensed by the gas cooler is
reduced to an intermediate pressure by the high-pressure-side
expansion means, the refrigerant flows into the gas-liquid
separation means. The intermediate-pressure refrigerant in the
gas-liquid separation means is separated into a gas-phase
refrigerant (a saturated gas refrigerant) and a liquid-phase
refrigerant (a saturated liquid refrigerant). Moreover, the
intermediate-pressure gas-phase refrigerant separated by the
gas-liquid separation means is combined with the refrigerant gas
discharged from the low-stage-side compression element of the
compressor, flows into the high-stage-side compression element, and
compressed.
[0003] On the other hand, the intermediate-pressure liquid-phase
refrigerant in the gas-liquid separation means has the pressure
reduced by the low-pressure-side expansion means before reaching
the evaporator. Moreover, after the refrigerant absorbs heat in the
evaporator to evaporate, the refrigerant flows into the
low-stage-side compression element of the compressor. This cycle is
repeated. As described above, the refrigerant (the gas-phase
refrigerant) having the pressure thereof reduced by the
high-pressure-side expansion means to evaporate does not evaporate
in the evaporator. Therefore, since the refrigerant does not
contribute to refrigeration, the refrigerant is separated into the
liquid-phase refrigerant and the gas-phase refrigerant by the
gas-liquid separation means, and returned to a suction side of the
high-stage-side compression element of the compressor. In
consequence, the pressure of the only liquid-phase refrigerant is
reduced by the low-pressure-side expansion means, the refrigerant
is evaporated by the evaporator, and a refrigeration effect at the
evaporator can be improved. Furthermore, the gas-phase refrigerant
which does not contribute to the refrigeration is returned to the
suction side of the high-stage-side compression element of the
compressor. In consequence, since the gas-phase refrigerant passes
by the low-stage-side compression element of the compressor, an
amount of the refrigerant to be compressed by the low-stage-side
compression element of the compressor, and the input can be
reduced. Therefore, as compared with a conventional single-stage
expansion refrigerating device, a coefficient of performance can be
improved (e.g., see Japanese Patent Application Laid-Open No.
11-142007).
[0004] In addition, in such a two-stage expansion refrigerating
device, in a case where the pressure of the refrigerant which has
flowed through the high-pressure-side expansion means is higher
than the pressure of the intermediate-pressure section on a suction
side of high-stage-side compression means, the gas-phase
refrigerant separated by the gas-liquid separation means can
smoothly flow through the intermediate-pressure section by use of a
pressure difference. However, the pressure difference between the
pressure of the refrigerant which has flowed through the
high-pressure-side expansion means (a region on a downstream side
of the high-pressure-side expansion means and on an upstream side
of the low-pressure-side expansion means) and the pressure of the
intermediate-pressure section on the suction side of the
high-stage-side compression means is excessively small.
Alternatively, when the pressure of the intermediate-pressure
section on the suction side of the high-stage-side compression
means is higher, the gas-phase refrigerant separated by the
gas-liquid separator does not easily flow through the
intermediate-pressure section. In consequence, the gas-phase
refrigerant separated by the gas-liquid separation means flows into
the low-pressure-side expansion means together with the
liquid-phase refrigerant, and reaches the evaporator. Therefore,
since the refrigerant evaporates early at the evaporator, the
gas-phase refrigerant which does not produce any refrigeration
effect flows. The refrigeration effect deteriorates, and
characteristics of the two-stage expansion refrigerating device
cannot be utilized. To solve the problem, the pressure of the
refrigerant which has flowed through the high-pressure-side
expansion means needs to be detected to control this pressure into
an optimum pressure. However, when a pressure sensor to detect such
a pressure is attached, a disadvantage that costs of the
refrigerating device remarkably increase has been caused.
SUMMARY OF THE INVENTION
[0005] The present invention has been developed to solve such a
problem of the conventional technology, and an object is to provide
a two-stage expansion refrigerating device capable of controlling a
pressure of a refrigerant which has flowed through
high-pressure-side expansion means into an optimum pressure with
low cost.
[0006] A two-stage expansion refrigerating device of a first
invention is provided with a refrigerant circuit including a
compressor, a gas cooler, high-pressure-side expansion means,
gas-liquid separation means, low-pressure-side expansion means and
an evaporator, returns a gas-phase refrigerant separated by the
gas-liquid separation means to an intermediate-pressure section of
the compressor, and allows a liquid-phase refrigerant to flow into
the evaporator via the low-pressure-side expansion means, the
device comprising: control means for controlling the compressor and
each expansion means; and temperature detection means for detecting
a temperature of the refrigerant which has flowed through the
high-pressure-side expansion mean, the device being characterized
in that the control means estimates a pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion means based on a temperature detected by the temperature
detection means, and controls one of the high-pressure-side
expansion means and the low-pressure-side expansion means based on
the estimated pressure P2.
[0007] The two-stage expansion refrigerating device of a second
invention is characterized in that, in the above first invention,
the temperature detection means detects the temperature of the
liquid-phase refrigerant separated by the gas-liquid separation
means.
[0008] The two-stage expansion refrigerating device of a third
invention is characterized in that, in the above inventions, the
control means controls one of the high-pressure-side expansion
means and the low-pressure-side expansion means based on the
pressure P2 and a pressure P1 of the intermediate-pressure section
of the compressor.
[0009] The two-stage expansion refrigerating device of a fourth
invention is characterized in that, in the above inventions, the
control means controls one of the high-pressure-side expansion
means and the low-pressure-side expansion means so that the
pressure P2 is lager than the pressure P1.
[0010] According to the first invention, the device is provided
with the refrigerant circuit including the compressor, the gas
cooler, the high-pressure-side expansion means, the gas-liquid
separation means, the low-pressure-side expansion means and the
evaporator, returns the gas-phase refrigerant separated by the
gas-liquid separation means to the intermediate-pressure section of
the compressor, and allows the liquid-phase refrigerant to flow
into the evaporator via the low-pressure-side expansion means. The
device comprises the control means for controlling the compressor
and each expansion means, and the temperature detection means for
detecting the temperature of the refrigerant which has flowed
through the high-pressure-side expansion means. The control means
estimates the pressure P2 of the refrigerant which has flowed
through the high-pressure-side expansion means based on the
temperature detected by the temperature detection means, and
controls the high-pressure-side expansion means based on the
estimated pressure P2. Therefore, without using any pressure
sensor, the pressure P2 of the refrigerant which has flowed through
a high-pressure-side expansion valve is estimated in accordance
with the temperature detected by the temperature detection means,
and the high-pressure-side expansion means or the low-pressure-side
expansion means can correctly be controlled. In consequence, costs
can be reduced.
[0011] Especially, as in the second invention, the temperature
detection means detects the temperature of the liquid-phase
refrigerant separated by the gas-liquid separation means.
Therefore, the refrigerant temperature can more correctly be
detected. In consequence, the high-pressure-side expansion means or
the low-pressure-side expansion means can more correctly be
controlled.
[0012] Furthermore, as in the third invention, the control means
controls one of the high-pressure-side expansion means and the
low-pressure-side expansion means based on the pressure P2 and the
pressure P1 of the intermediate-pressure section of the compressor.
Therefore, for example, in a case where the control means controls
one of the high-pressure-side expansion means and the
low-pressure-side expansion means so that the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion means is larger than the pressure P1 of the
intermediate-pressure section of the compressor as in the fourth
invention, the gas-phase refrigerant separated by the gas-liquid
separation means smoothly flows into the intermediate-pressure
section of the compressor. In consequence, correct gas-liquid
separation can be performed.
[0013] In general, according to the present invention, the
refrigerant which has flowed through the high-pressure-side
expansion means is controlled into an optimum pressure, and a
refrigeration effect can be obtained by utilizing characteristics
of the two-stage expansion refrigerating device at the maximum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a refrigerant circuit diagram of a two-stage
expansion refrigerating device according to one embodiment of the
present invention;
[0015] FIG. 2 is a functional block diagram of the two-stage
expansion refrigerating device of FIG. 1;
[0016] FIG. 3 is a p-h graph (a Mollier diagram) of the two-stage
expansion refrigerating device of FIG. 1;
[0017] FIG. 4 is a flow chart showing control of a
high-pressure-side expansion valve of the two-stage expansion
refrigerating device of Embodiment 1;
[0018] FIG. 5 is a flow chart showing control of a
low-pressure-side expansion valve of the two-stage expansion
refrigerating device of FIG. 1;
[0019] FIG. 6 is a flow chart showing control of a
high-pressure-side expansion valve of another two-stage expansion
refrigerating;
[0020] FIG. 7 is a flow chart showing control of a
low-pressure-side expansion valve of a two-stage expansion
refrigerating device of Embodiment 2; and
[0021] FIG. 8 is a flow chart showing control of a
high-pressure-side expansion valve of a two-stage expansion
refrigerating device of Embodiment 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Embodiments of a two-stage expansion refrigerating device of
the present invention will hereinafter be described in detail with
reference to the drawings.
Embodiment 1
[0023] FIG. 1 shows a refrigerant circuit diagram of a two-stage
expansion refrigerating device according to one embodiment of the
present invention. In the two-stage expansion refrigerating device,
a compressor 1, a gas cooler 2, a high-pressure-side expansion
valve (high-pressure-side expansion means) 3, a gas-liquid
separator 4, a low-pressure-side expansion valve (low-pressure-side
expansion means) 5 and an evaporator 6 constitute a refrigerant
circuit. The compressor 1 includes a low-stage-side compression
element 1A and a high-stage-side compression element 1B, and both
of the compression elements 1A, 1B are integrally combined with a
single motor (not shown). Moreover, the low-stage-side compression
element 1A compresses a low-pressure refrigerant to obtain an
intermediate pressure. After discharging this refrigerant to a
intermediate-pressure section between the low-stage-side
compression element 1A and the high-stage-side compression element
1B, the refrigerant is compressed at a high pressure by the
high-stage-side compression element 1B.
[0024] The low-stage-side compression element 1A on a suction side
is connected to one end of a refrigerant suction tube 30, and a
low-temperature low-pressure refrigerant gas is introduced into the
low-stage-side compression element 1A from this end. The other end
of the refrigerant suction tube 30 is connected to an outlet of the
evaporator 6. The low-stage-side compression element 1A on a
discharge side is connected to one end of a refrigerant suction
tube 32, this refrigerant suction tube 32 is connected to the
high-stage-side compression element 1B on the suction side, and an
intermediate-pressure refrigerant gas is introduced into the
high-stage-side compression element 1B from this end. A middle
portion of the refrigerant suction tube 32 is connected to one end
of a refrigerant pipe 40.
[0025] The high-stage-side compression element 1B on the discharge
side is connected to one end of a refrigerant discharge tube 34,
and a high-temperature high-pressure refrigerant gas compressed by
the high-stage-side compression element 1B is discharged from the
compressor 1 via the refrigerant discharge tube 34. The other end
of the refrigerant discharge tube 34 is connected to an inlet of
the gas cooler 2. That is, the compressor 1 sucks the refrigerant
flowed out from the evaporator 6 via the low-stage-side compression
element 1A to compress the refrigerant. The refrigerant is
discharged from the low-stage-side compression element 1A via the
refrigerant suction tube 32, and combined with the refrigerant
flowed out from the gas-liquid separator 4 described later.
Subsequently, the refrigerant is allowed to flow into the
high-stage-side compression element 1B, and the
intermediate-pressure refrigerant is compressed by the
high-stage-side compression element 1B, and discharged to the gas
cooler 2.
[0026] The gas cooler 2 is a heat exchanger which performs heat
exchange between the high-temperature high-pressure refrigerant gas
discharged from the high-stage-side compression element 1B and a
heat medium such as a water or air to radiate heat of the
refrigerant. An outlet of the gas cooler 2 is connected to a
refrigerant pipe 36, and this refrigerant pipe 36 is connected to
an inlet of the high-pressure-side expansion valve 3. The
high-pressure-side expansion valve 3 is throttle means for reducing
the pressure of the refrigerant flowed out from the gas cooler 2.
Moreover, a refrigerant pipe 38 connected to an outlet of the
high-pressure-side expansion valve 3 is connected to the gas-liquid
separator 4.
[0027] The gas-liquid separator 4 is separation means for
separating the refrigerant brought into a gas/liquid two-phase
region by reducing the pressure of the refrigerant by the
high-pressure-side expansion valve 3 into a gas-phase refrigerant
(a saturated gas refrigerant) and a liquid-phase refrigerant (a
saturated liquid refrigerant). This separator includes a vertically
long cylindrical main body. Moreover, an inlet which communicates
with the inside of the main body is formed at one side surface of
the main body of the gas-liquid separator, and this inlet is
connected to the refrigerant pipe 38. Moreover, a refrigerant
outlet is formed at an upper surface of the main body. The
refrigerant outlet is a take-out port via which the gas-phase
refrigerant separated from the liquid-phase refrigerant by the
gas-liquid separator 4 is taken from an inner space of the
separator via an upper portion. The refrigerant outlet is connected
to the refrigerant pipe 40, and the other end of this refrigerant
pipe 40 opens above the gas-liquid separator 4. One end of this
refrigerant pipe 40 is connected to a middle portion of the
refrigerant suction tube 32. A check valve 7 is connected to the
refrigerant pipe 40, and one end of the valve connected to a middle
portion of the refrigerant suction tube 32 is regarded as a forward
direction. When the refrigerant is compressed by the low-stage-side
compression element 1A, the refrigerant has an intermediate
pressure, and is discharged to the refrigerant suction tube 32. The
check valve 7 is disposed so as to avoid a counter flow of such a
refrigerant into the refrigerant pipe 40 connected to the middle
portion of the refrigerant suction tube 32.
[0028] On the other hand, a lower surface (a bottom surface) of the
main body of the gas-liquid separator 4 is provided with another
refrigerant outlet. This refrigerant outlet is a takeout port via
which the liquid-phase refrigerant separated from the gas-phase
refrigerant by the gas-liquid separator 4 is taken, and is
connected to one end of a refrigerant pipe 42. One end of the
refrigerant pipe 42 opens at a lower portion of the gas-liquid
separator 4, and the other end of the pipe is connected to an inlet
of the low-pressure-side expansion valve 5. This low-pressure-side
expansion valve 5 is a throttle means for reducing the pressure of
the liquid-phase refrigerant separated by the gas-liquid separator
4, and an outlet of the low-pressure-side expansion valve 5 is
connected to an inlet of the evaporator 6 via a refrigerant pipe
44.
[0029] Moreover, the refrigerant pipe 42 connected to the takeout
port of the gas-liquid separator 4 via which the liquid-phase
refrigerant is taken is provided with a temperature sensor 52 via
the high-pressure-side expansion valve 3. The sensor detects a
temperature of the liquid-phase refrigerant separated by the
gas-liquid separator 4. The refrigerant pipe 44 connected to the
inlet of the evaporator 6 is provided with an evaporator inlet
temperature sensor 53 which detects a refrigerant temperature Tin
at the inlet of the evaporator 6. The refrigerant pipe 30 connected
to an outlet of the evaporator 6 is provided with an evaporator
outlet temperature sensor 54 which detects a temperature (a
refrigerant temperature at the outlet of the evaporator 6) Tout of
the refrigerant evaporated at the evaporator 6 and flows into the
low-stage-side compression element 1A. These temperature sensors
52, 53 and 54 are connected as control means described later to a
controller 50.
[0030] In addition, the compressor 1, the high-pressure-side
expansion valve 3 and the low-pressure-side expansion valve 5 of
the two-stage expansion refrigerating device of the present
embodiment are connected to the controller 50, and the controller
50 controls operations and valve open degrees of the compressor and
the valves. This controller 50 is control means for controlling the
two-stage expansion refrigerating device. As shown in FIG. 2, the
controller on an input side is connected to the refrigerant
temperature sensor 52, the evaporator inlet temperature sensor 53,
the evaporator outlet temperature sensor 54 and an outside air
temperature sensor 55. The outside air temperature sensor 55 is a
temperature sensor which detects a temperature of the outside
(outside air) of the two-stage expansion refrigerating device.
[0031] On the other hand, the controller 50 on an output side is
connected to the compressor 1, the high-pressure-side expansion
valve 3 and the low-pressure-side expansion valve 5. Moreover, the
controller 50 controls an operation frequency (Hz) of the
compressor 1 based on the outside air temperature detected by the
outside air temperature sensor 55 and a temperature of a space
(i.e., a space to be refrigerated) to be frozen by the evaporator
6. Specifically, the compressor 1 is controlled to turn ON/OFF in
accordance with the temperature of the space to be refrigerated.
Moreover, the operation frequency of the compressor 1 is controlled
in accordance with the outside air temperature. For example, when
the two-stage expansion refrigerating device of the present
embodiment is used in a refrigerator, the frequency of the
compressor 1 is controlled at three-stage frequency bands in
accordance with the outside air temperature. That is, when the
outside air temperature is low, the controller 50 controls the
frequency of the compressor 1 into the lowest frequency. When the
outside air temperature is high, the controller controls the
frequency of the compressor 1 into the highest frequency. At a
usual outside air temperature, the controller controls the
compressor 1 so as to obtain a frequency between the
above-mentioned operation frequencies. It is to be noted that, in
the present embodiment, the controller 50 controls the operation
frequency of the compressor 1 based on an output of the outside air
temperature sensor 55, but the present invention is not limited to
the outside air temperature sensor 55. For example, as shown by a
broken line of FIG. 2, a temperature sensor 56 is installed at the
gas cooler 2, and the controller 50 may control the operation
frequency of the compressor 1 by the gas cooler temperature sensor
56.
[0032] Furthermore, the controller 50 controls the
high-pressure-side expansion valve 3 based on the pressure of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3. In the present embodiment, the controller 50
estimates the pressure of the refrigerant which has flowed through
this high-pressure-side expansion valve 3 based on the refrigerant
temperature detected by the refrigerant temperature sensor 52
installed at the refrigerant pipe 38. The controller controls the
high-pressure-side expansion valve 3 based on this estimated
pressure P2.
[0033] That is, the controller 50 detects the temperature of the
liquid-phase refrigerant flowed out from the gas-liquid separator 4
with the temperature sensor 52, and estimates the pressure P2 of
the refrigerant passed trough the high-pressure-side expansion
valve 3 based on this temperature. That is, the refrigerant which
has flowed through the high-pressure-side expansion valve 3 has a
gas/liquid two-phase region mixed with the liquid-phase
refrigerant, and the refrigerant including the liquid phase has a
correlation between the temperature and the pressure. Therefore, in
a case where the temperature of the refrigerant which has flowed
through the high-pressure-side expansion valve 3 is detected, the
pressure can be estimated from the temperature of the
refrigerant.
[0034] Specific control will be described later in detail in the
following operation description. The controller 50 controls the
high-pressure-side expansion valve 3 so that the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 is a target pressure Ptg set beforehand. It is to
be noted that the target pressure Ptg has a positive value set
beforehand.
[0035] Furthermore, the controller 50 controls the valve open
degree of the low-pressure-side expansion valve 5 based on a
difference between the outlet temperature Tout of the evaporator 6
detected by the evaporator outlet temperature sensor 54 and the
inlet temperature Tin of the evaporator 6 detected by the
evaporator inlet temperature sensor 53, so that the refrigerant
flowed out from the evaporator 6 and flows into the compressor 1
indicates a predetermined superheat degree. In a case where the
valve open degree of the low-pressure-side expansion valve 5 is
controlled in this manner so that the refrigerant evaporated by the
evaporator 6 and flows into the low-stage-side compression element
1A of the compressor 1 has the predetermined superheat degree, the
refrigerant flows into the low-stage-side compression element 1A
can be brought into a gas-phase state. In consequence, without
disposing any liquid refrigerant storage means such as a receiver
tank on the suction side of the compressor 1, it is possible to
avoid in advance a disadvantage that the liquid refrigerant flows
into the compressor 1 to compress the liquid.
[0036] It is to be noted that, in the present embodiment, a
fluorine-based refrigerant such as 134a or 410A is used as the
refrigerant.
[0037] Next, an operation of the device constituted as described
above will be described with reference to a p-h graph (a Mollier
diagram) of FIG. 3. When the compressor 1 is started by the
controller 50, the low-temperature low-pressure refrigerant gas
flowed out from the evaporator 6 is sucked from the refrigerant
suction tube 30 to the low-stage-side compression element 1A on the
suction side (state A of FIG. 3). The refrigerant flows into the
low-stage-side compression element 1A is compressed at the element
to form the intermediate-pressure refrigerant gas, and the gas is
discharged from the low-stage-side compression element 1A on the
discharge side to pass through the refrigerant suction tube 32
(state B of FIG. 3). The intermediate-pressure refrigerant gas
which has flowed through the refrigerant suction tube 32 is
combined with the gas-phase refrigerant from the refrigerant pipe
40 connected to the middle portion of the refrigerant suction tube
32 (state C of FIG. 3). Subsequently, the refrigerant flows into
the high-stage-side compression element 1B and compressed at the
element to form the high-temperature high-pressure refrigerant gas,
and the gas is discharged from the high-stage-side compression
element 1B (state D of FIG. 3).
[0038] The high-temperature high-pressure refrigerant gas
discharged from the high-stage-side compression element 1B flows
into the gas cooler 2 through the refrigerant discharge tube 34,
and radiates heat by an air-cooling or water-cooling system in the
gas cooler 2 (state E of FIG. 3). The refrigerant which has
radiated the heat in the gas cooler 2 flows through the refrigerant
pipe 36 to reach the high-pressure-side expansion valve 3.
Moreover, the pressure of the refrigerant is reduced by the
high-pressure-side expansion valve 3. In consequence, a part of the
refrigerant evaporates, and is brought into the two-phase region in
which the gas and the liquid are mixed (state F of FIG. 3).
Moreover, the remaining refrigerant (the liquid-phase refrigerant)
is cooled by such evaporation (state G of FIG. 3).
[0039] Moreover, the refrigerant which has flowed through the
high-pressure-side expansion valve 3 and which has the two-phase
region flows into the gas-liquid separator 4 via the refrigerant
pipe 38, and is separated into the gas-phase refrigerant and the
liquid-phase refrigerant by the gas-liquid separator 4. Moreover,
the gas-phase refrigerant separated by this gas-liquid separator 4
flows through the refrigerant pipe 40 connected to one outlet of
the gas-liquid separator 4, and is combined with the
intermediate-pressure refrigerant which flows through the
refrigerant suction tube 32 (the state C of FIG. 3 described
above). Here, in the refrigerant brought into the gas/liquid
two-phase region by reducing the pressure of the refrigerant by the
high-pressure-side expansion valve 3, the gas-phase refrigerant
does not have any evaporation latent heat. That is, the refrigerant
has already evaporated at the high-pressure-side expansion valve 3.
Therefore, even when the refrigerant flows into the evaporator 6,
the refrigerant does not evaporate. Therefore, the refrigerant does
not contribute to the refrigeration. To solve the problem, the
gas-phase refrigerant is separated from the liquid-phase
refrigerant by the gas-liquid separator 4. The only gas-phase
refrigerant is returned from the refrigerant pipe 40 to an
intermediate-pressure section on the discharge side of the
low-stage-side compression element 1A. In consequence, a
refrigeration effect of the evaporator 6 can be improved.
Furthermore, the gas-phase refrigerant which does not contribute to
the refrigeration is returned to the suction side of the
high-stage-side compression element 1B of the compressor 1. In
consequence, the gas-phase refrigerant passes by the low-stage-side
compression element 1A of the compressor 1.
[0040] In consequence, an amount of the refrigerant to be
compressed by the low-stage-side compression element 1A decreases,
and an input is reduced. Therefore, as compared with a conventional
single-stage expansion refrigerating device, a coefficient of
performance can be improved.
[0041] On the other hand, the liquid-phase refrigerant (the state G
of FIG. 3) separated by the gas-liquid separator 4 flows through
the refrigerant pipe 42 connected to the other outlet of the
gas-liquid separator 4 to reach the low-pressure-side expansion
valve 5. At the valve, the pressure of the refrigerant is further
reduced (state H of FIG. 3). Moreover, since the pressure of the
refrigerant is reduced by the low-pressure-side expansion valve 5,
the refrigerant is brought into the gas/liquid two-phase region
again. However, in the refrigerant brought into the gas/liquid
two-phase region by the high-pressure-side expansion valve 3 as
described above, the gas-phase refrigerant is separated by the
gas-liquid separator 4, and the pressure of the only liquid-phase
refrigerant is reduced at the low-pressure-side expansion valve 5.
In consequence, an amount of the gas-phase refrigerant which flows
into the evaporator 6 can be reduced.
[0042] The refrigerant having the pressure reduced by the
low-pressure-side expansion valve 5 and brought into the gas/liquid
two-phase region flows into the evaporator 6 in this state, heat
exchange between the refrigerant and surrounding air is performed,
and the refrigerant evaporates. At this time, the surrounding air
is cooled by a heat absorption effect. The refrigerant which has
evaporated at the evaporator 6 (the state A of FIG. 3) is sucked
from the refrigerant suction tube 30 into the low-stage-side
compression element 1A of the compressor 1 to repeat a cycle.
[0043] In addition, as described above, the controller 50 estimates
the pressure of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 from the refrigerant
temperature detected by the temperature sensor 52 at the
high-pressure-side expansion valve 3, and controls the
high-pressure-side expansion valve 3 based on this estimated
refrigerant pressure P2. Here, the control of the
high-pressure-side expansion valve 3 of the two-stage expansion
refrigerating device according to the present embodiment will be
described with reference to a flow chart of FIG. 4.
[0044] First, when the controller 50 is started in step S1 of FIG.
4 (Start), the controller 50 detects a temperature T of the
liquid-phase refrigerant flowed out from the gas-liquid separator 4
with the temperature sensor 52 (step S2 of FIG. 4), and estimates
the pressure P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 from the temperature T (step
S3 of FIG. 4).
[0045] Subsequently, the controller 50 shifts to step S4 of FIG. 4,
and judges whether or not the refrigerant pressure P2 estimated in
the step S3 is the target pressure Ptg. In this case, when the
refrigerant pressure P2 estimated in the step S3 is equal to the
target pressure Ptg, the controller 50 shifts to step S6, allows
the high-pressure-side expansion valve 3 to stay at the current
valve open degree as it is (Stay), advances to step S9, and returns
to the step S1 (Return), thereby repeating the control
(Return).
[0046] On the other hand, in a case where it is judged in the step
S4 that the refrigerant pressure P2 estimated in the step S3 has a
value different from that of the target pressure Ptg, the
controller 50 shifts to step S5 to judge whether or not the
estimated refrigerant pressure P2 is larger than the target
pressure Ptg. Moreover, when the refrigerant pressure P2 is larger
than the target pressure Ptg, the controller shifts to step S8 of
FIG. 4. When the refrigerant pressure P2 is larger than the target
pressure Ptg in this manner, the valve open degree of the
high-pressure-side expansion valve 3 is decreased as much as one
step. The controller advances to the step S9 to return to the step
S1 (Return).
[0047] As described above, in a case where it is judged in the step
S5 that the refrigerant pressure P2 is larger than the target
pressure Ptg, the controller 50 closes the high-pressure-side
expansion valve 3 as much as one step (Close). Therefore, an effect
of reducing the pressure of the refrigerant improves at the
high-pressure-side expansion valve 3, and the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 drops.
[0048] On the other hand, in a case where it is judged in the step
S5 that the estimated refrigerant pressure P2 is smaller than the
target pressure Ptg, the controller 50 shifts to step S7. When the
estimated refrigerant pressure P2 is smaller than the target
pressure Ptg in this manner, the pressure P2 of the refrigerant
which has flowed through the high-pressure-side expansion valve 3
is excessively small. The gas-phase refrigerant separated by the
gas-liquid separator 4 might not easily flow into the
intermediate-pressure section of the compressor 1 or might not
flow. In consequence, the gas-phase refrigerant reaches the
low-pressure-side expansion valve 5 together with the liquid-phase
refrigerant, flows through the evaporator 6, and flows into the
low-stage-side compression element 1A. In consequence, since the
refrigerant evaporates early at the evaporator 6, a large amount of
the gas-phase refrigerant which does not produce any refrigeration
effect flows. A disadvantage that the refrigeration effect is
remarkably deteriorated occurs. Furthermore, any input at the
low-stage-side compression element 1A is not reduced. In
consequence, the coefficient of performance remarkably drops, and
characteristics of the two-stage expansion refrigerating device
cannot be utilized sufficiently.
[0049] To solve the problem, in a case where it is judged in the
step S5 of FIG. 4 that the estimated refrigerant pressure P2 is
smaller than the target pressure Ptg, the controller 50 shifts to
the step S7, increases the valve open degree of the
high-pressure-side expansion valve 3 as much as one step, and
advances to the step S9 to return to the step S1 (Return).
[0050] As described above, in a case where it is judged in the step
S5 that the estimated refrigerant pressure P2 is smaller than the
target pressure Ptg, the controller 50 increases the valve open
degree of the high-pressure-side expansion valve 3 as much as one
step (Open). Therefore, the effect of reducing the pressure of the
refrigerant is reduced at the high-pressure-side expansion valve 3,
and the pressure P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 increases. In consequence, the
pressure P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 increases. Owing to such a
refrigerant pressure P2, the gas-phase refrigerant separated by the
gas-liquid separator 4 can smoothly be returned to the discharge
side of the low-stage-side compression element 1A of the compressor
1 (the suction side of the high-stage-side compression element 1B)
via the refrigerant pipe 40.
[0051] Furthermore, as described above, the controller 50 controls
the low-pressure-side expansion valve 5 in accordance with the
refrigerant temperature Tin at the inlet of the evaporator 6
detected by the evaporator inlet temperature sensor 53 and the
refrigerant temperature Tout at the outlet of the evaporator 6
detected by the evaporator outlet temperature sensor 54. Next, the
control of the low-pressure-side expansion valve 5 of the two-stage
expansion refrigerating device according to the present embodiment
will be described with reference to a flow chart of FIG. 5.
[0052] First, when the controller 50 is started in step S1 of FIG.
5 (Start), the controller 50 detects the refrigerant temperature
Tin at the inlet of the evaporator 6 with the evaporator inlet
temperature sensor 53 in step S2. Subsequently, after detecting the
refrigerant temperature Tout at the outlet of the evaporator 6 with
the evaporator outlet temperature sensor 54 in step S3 of FIG. 5,
the controller shifts to step S4 of FIG. 5.
[0053] Moreover, in the step S4 of FIG. 5, the controller 50
compares, with a predetermined lower limit value .DELTA.Tmin (a
positive value set beforehand), a difference (Tout-Tin) between the
refrigerant temperature Tout at the outlet of the evaporator 6
detected in the step S3 of FIG. 5 and the refrigerant temperature
Tin at the inlet of the evaporator 6 detected in the step S2 of
FIG. 5. When a value of Tout-Tin is larger than the predetermined
lower limit value .DELTA.Tmin, the controller shifts to step S5 of
FIG. 5.
[0054] On the other hand, when the value of Tout-Tin is the lower
limit value .DELTA.Tmin or less, the controller shifts to step S6
of FIG. 5. When the value of Tout-Tin is the predetermined lower
limit value .DELTA.Tmin or less in this manner, a temperature
difference between the temperatures Tout and Tin is excessively
small, and the superheat degree of the refrigerant flowed out from
the evaporator 6 is not sufficiently secured. That is, the
refrigerant having the liquid-phase state might remain in the
refrigerant flowed out from the evaporator 6. In consequence, the
liquid-phase refrigerant flows into the low-stage-side compression
element 1A of the compressor 1, and the liquid might be
compressed.
[0055] To solve the problem, in a case where it is judged in the
step S4 of FIG. 5 that the value of Tout-Tin is the predetermined
lower limit value .DELTA.Tmin or less, the controller 50 shifts to
the step S6 to reduce the valve open degree of the
low-pressure-side expansion valve 5 (Close). The controller then
advances to step S9 to return to the step S1 (Return), thereby
repeating the control.
[0056] As described above, in a case where it is judged in the step
S4 that the value of Tout-Tin is the predetermined lower limit
value .DELTA.Tmin or less, the controller 50 reduces the valve open
degree of the low-pressure-side expansion valve 5. Therefore, the
amount of the refrigerant which flows through the evaporator 6
decreases, and the refrigerant can sufficiently be evaporated in
the evaporator 6. In consequence, such liquid compression can be
released.
[0057] On the other hand, when the value of Tout-Tin is higher than
the predetermined lower limit value .DELTA.Tmin, the controller 50
shifts to the step S5 to compare the value of Tout-Tin with a
predetermined upper limit value .DELTA.Tmax (a positive value set
beforehand) set beforehand. Moreover, when the value of Tout-Tin is
smaller than the predetermined upper limit value .DELTA.Tmax, the
controller shifts to step S7, and allows the low-pressure-side
expansion valve 5 to stay at the current valve open degree as it is
(Stay). The controller then advances to the step S9 to return to
the step S1 (Return), thereby repeating the control.
[0058] On the other hand, when the value of Tout-Tin is the
predetermined upper limit value .DELTA.Tmax or more, the controller
shifts to step S8. When the value of Tout-Tin is the predetermined
upper limit value .DELTA.Tmax or more, the refrigerant temperature
Tout at the outlet of the evaporator 6, that is, the temperature of
the refrigerant flows into the low-stage-side compression element
1A of the compressor 1 is excessively high. A disadvantage that the
temperature and the pressure of the refrigerant flowing through the
circuit abnormally increase might be caused.
[0059] To solve the problem, when the value of Tout-Tin is the
predetermined upper limit value .DELTA.Tmax or more, the controller
50 shifts to the step S8 of FIG. 5 to loosen throttle of the
low-pressure-side expansion valve 5 (open the low-pressure-side
expansion valve 5 from the current valve open degree (Open)). In
consequence, the amount of the refrigerant flowing through the
evaporator 6 increases, the temperature of the refrigerant at the
outlet of the evaporator 6 drops, and such abnormal increases of
the temperature and the pressure of the refrigerant flowing through
the circuit can be eliminated.
[0060] In addition, as described above, when the controller 50
closes the low-pressure-side expansion valve 5 in the step S6 of
FIG. 5 (Close), the amount of the refrigerant flowing from the
low-pressure-side expansion valve 5 to the evaporator 6 decreases,
and the refrigerant is dammed by the low-pressure-side expansion
valve 5. Therefore, the refrigerant pressure on an upstream side
and the refrigerant temperature having a correlation with respect
to the refrigerant pressure increase. That is, the temperature of
the refrigerant which has flowed through the high-pressure-side
expansion valve 3, detected by the temperature sensor 52, rises,
and the refrigerant pressure P2 estimated from the refrigerant
temperature also rises. Even in such a case, as described in the
control of the high-pressure-side expansion valve 3 with reference
to FIG. 4, in a case where the pressure P2 of the refrigerant which
has flowed through the high-pressure-side expansion valve 3 is
higher than the target pressure Ptg set beforehand, as shown in the
step S8 of FIG. 4, since the controller 50 reduces the valve open
degree of the high-pressure-side expansion valve 3 as much as one
step. (Close), the refrigerant flows without any problem.
[0061] As described above in detail, according to the two-stage
expansion refrigerating device of the present embodiment, the
controller 50 estimates the pressure P2 of the refrigerant which
has flowed through the high-pressure-side expansion valve 3 based
on the refrigerant temperature detected by the temperature sensor
52, and controls the high-pressure-side expansion valve 3 based on
the estimated pressure P2. In consequence, without using any
expensive pressure sensor, the pressure P2 of the refrigerant which
has flowed through the high-pressure-side expansion valve 3 is
estimated using the inexpensive temperature sensor 52, and the
high-pressure-side expansion valve 3 can correctly be controlled.
Therefore, costs can be reduced.
[0062] Furthermore, in the present embodiment, the temperature
sensor 52 is installed at the refrigerant pipe 42 connected to the
refrigerant outlet formed at the main body lower portion of the
gas-liquid separator 4. The refrigerant temperature sensor 52
detects the temperature of the liquid-phase refrigerant separated
by the gas-liquid separator 4. Therefore, it is possible to more
correctly detect the refrigerant temperature with the temperature
sensor 52.
[0063] That is, as described above, the refrigerant which has
flowed through the high-pressure-side expansion valve 3 has the
gas/liquid two-phase region in which the refrigerant having the
liquid-phase state is mixed. The refrigerant including such a
liquid phase has a correlation between the temperature and the
pressure. Therefore, in a case where the temperature of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 is detected, the pressure can be estimated.
[0064] In this case, the temperature sensor is installed at the
refrigerant pipe 38 connected to the outlet of the
high-pressure-side expansion valve 3, the refrigerant pipe 40
connected to the gas-liquid separator 4 or the refrigerant pipe 42
to detect the temperature of the refrigerant. In consequence, the
pressure can be estimated. However, especially the temperature of
the liquid-phase refrigerant passed through the refrigerant pipe 42
and separated by the gas-liquid separator 4 as in the present
embodiment does not easily rise or does not rise, even if the heat
enters the device from the outside as described above. Therefore,
the temperature sensor 52 is installed at the refrigerant pipe 42
to detect the temperature of the liquid-phase refrigerant separated
by the gas-liquid separator 4. In consequence, the refrigerant
temperature can more correctly be detected by the temperature
sensor 52. Therefore, the high-pressure-side expansion valve 3 can
more correctly be controlled.
[0065] It is to be noted that, in the present embodiment, the
controller 50 controls the high-pressure-side expansion valve 3 so
that the pressure P2 of the refrigerant which has flowed through
the high-pressure-side expansion valve 3 is the target pressure Ptg
set beforehand. However, the target pressure Ptg may be determined
by the controller 50 in accordance with the outside air temperature
detected by the outside air temperature sensor 55 or the frequency
of the compressor 1. The controller may control the
high-pressure-side expansion valve 3 so that the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 is set in a range of an upper limit pressure
(Ptg+p) to a lower limit pressure (Ptg-p). The range has a
predetermined pressure width .+-.p above and below the target
pressure Ptg.
[0066] The control in this case will be described with reference to
a flow chart of FIG. 6. When the controller 50 is started in step
S1 of FIG. 6 (Start), the controller 50 detects the temperature T
of the liquid-phase refrigerant flowed out from the gas-liquid
separator 4 with the temperature sensor 52 (step S2 of FIG. 6), and
estimates the pressure P2 of the refrigerant which has flowed
through the high-pressure-side expansion valve 3 from the
temperature T (step S3 of FIG. 6).
[0067] Subsequently, the controller 50 shifts to step S4 of FIG. 6,
and judges whether or not the refrigerant pressure P2 estimated in
the step S3 is higher than the upper limit (Ptg+p) of the target
pressure Ptg. In this case, when the refrigerant pressure P2
estimated in the step S3 is higher than the upper limit pressure
(Ptg+p), the controller shifts to step S6, closes the
high-pressure-side expansion valve 3 as much as one step, advances
to step S9, and returns to the step S1 (Return).
[0068] On the other hand, in a case where it is judged in the step
S4 that the estimated refrigerant pressure P2 is the upper limit
value (Ptg+p) of the target pressure Ptg or less, the controller 50
shifts to step S5 to judge whether or not the estimated refrigerant
pressure P2 is lower than the lower limit pressure (Ptg-p).
Moreover, when the estimated refrigerant pressure P2 is smaller
than the lower limit pressure (Ptg-p), the flow shifts to step S8
of FIG. 6. When the estimated refrigerant pressure P2 is smaller
than the lower limit pressure (Ptg-p) in this manner, the pressure
P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 is excessively small.
Therefore, the gas-phase refrigerant separated by the gas-liquid
separator 4 might not easily flow through the intermediate-pressure
section of the compressor 1 or might not flow. In consequence, the
gas-phase refrigerant reaches the low-pressure-side expansion valve
5 together with the liquid-phase refrigerant, flows through the
evaporator 6, and flows into the low-stage-side compression element
1A. In consequence, since the refrigerant evaporates early at the
evaporator 6, a large amount of the gas-phase refrigerant which
does not produce any refrigeration effect flows. A disadvantage
that the refrigeration effect is remarkably deteriorated occurs.
Furthermore, any input at the low-stage-side compression element 1A
is not reduced. In consequence, the coefficient of performance
remarkably drops, and the characteristics of the two-stage
expansion refrigerating device cannot be utilized sufficiently.
[0069] To solve the problem, in a case where it is judged in the
step S5 of FIG. 6 that the estimated refrigerant pressure P2 is
smaller than the lower limit pressure (Ptg-p), the controller 50
shifts to the step S8, increases the valve open degree of the
high-pressure-side expansion valve 3 as much as one step, and
advances to the step S9 to return to the step S1 (Return).
[0070] As described above, in a case where it is judged in the step
S5 that the estimated refrigerant pressure P2 is smaller than the
lower limit pressure (Ptg-p), the controller 50 increases the valve
open degree of the high-pressure-side expansion valve 3 (Open) as
much as one step. Therefore, the effect of reducing the pressure of
the refrigerant is reduced at the high-pressure-side expansion
valve 3, and the pressure P2 of the refrigerant which has flowed
through the high-pressure-side expansion valve 3 increases. In
consequence, the pressure P2 of the refrigerant which has flowed
through the high-pressure-side expansion valve 3 increases. Owing
to such a refrigerant pressure P2, the gas-phase refrigerant
separated by the gas-liquid separator 4 can smoothly be returned to
the discharge side of the low-stage-side compression element 1A of
the compressor 1 (the suction side of the high-stage-side
compression element 1B) via the refrigerant pipe 40.
[0071] On the other hand, in a case where it is judged in the step
S5 of FIG. 6 that the estimated refrigerant pressure P2 is the
lower limit pressure (Ptg-p) or more, the controller 50 shifts to
step S6, allows the high-pressure-side expansion valve 3 to stay at
the current valve open degree as it is (Stay), and advances to the
step S9 to return to the step S1 (Return), thereby repeating the
control.
Embodiment 2
[0072] It is to be noted that, in Embodiment 1 described above, a
controller 50 estimates a pressure P2 of a refrigerant which has
flowed through a high-pressure-side expansion valve 3 from a
temperature of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 detected with a temperature
sensor 52, and controls the high-pressure-side expansion valve 3
based on the estimated pressure P2, so that the pressure of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 is optimized. However, the present invention is
not limited to this embodiment, and the present invention is
effective as long as at least control means (the controller 50 in
the embodiment) estimates the pressure P2 of the refrigerant which
has flowed through high-pressure-side expansion means (the
high-pressure-side expansion valve 3) based on the temperature
detected by temperature detection means (the temperature sensor 52
in the embodiment), and controls one of the high-pressure-side
expansion means (the high-pressure-side expansion valve 3) and
low-pressure-side expansion means (a low-pressure-side expansion
valve 5) based on the estimated pressure P2.
[0073] Here, one example of a case where the controller 50 controls
the low-pressure-side expansion valve 5 based on the estimated
pressure P2 will be described. It is to be noted that, in the
present embodiment, a refrigerant circuit similar to that of
Embodiment 1 shown in FIG. 1 is used. Therefore, description
thereof is omitted, and only control will be described.
[0074] The controller 50 controls the low-pressure-side expansion
valve 5 so that the pressure P2 of the refrigerant which has flowed
through the high-pressure-side expansion valve 3 is a target
pressure Ptg set beforehand. It is to be noted that the target
pressure Ptg is a positive value set beforehand. The control of the
low-pressure-side expansion valve 5 of a two-stage expansion
refrigerating device according to the present embodiment will be
described with reference to a flow chart of FIG. 7.
[0075] First, when the controller 50 is started in step S1 of FIG.
7 (Start), the controller 50 detects a temperature T of a
liquid-phase refrigerant flowed out from a gas-liquid separator 4
with the temperature sensor 52 (step S2 of FIG. 7), and estimates
the pressure P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 from the temperature T (step
S3 of FIG. 7).
[0076] Subsequently, the controller 50 shifts to step S4 of FIG. 7
to judge whether or not the refrigerant pressure P2 estimated in
the step S3 is the target pressure Ptg. In this case, when the
refrigerant pressure P2 estimated in the step S3 is equal to the
target pressure Ptg, the controller 50 shifts to step S6, allows
the low-pressure-side expansion valve 5 to stay at the current
valve open degree as it is (Stay), advances to step S9, and returns
to the step S1 (Return), thereby repeating the control.
[0077] On the other hand, in a case where it is judged in the step
S4 that the refrigerant pressure P2 estimated in the step S3 has a
value different from that of the target pressure Ptg, the
controller 50 shifts to step S5 to judge whether or not the
estimated refrigerant pressure P2 is larger than the target
pressure Ptg. Moreover, when the refrigerant pressure P2 is larger
than the target pressure Ptg, the controller shifts to step S8 of
FIG. 7. When the refrigerant pressure P2 is larger than the target
pressure Ptg in this manner, the valve open degree of the
low-pressure-side expansion valve 5 is increased as much as one
step. The controller advances to the step S9 to return to the step
S1 (Return).
[0078] As described above, in a case where it is judged in the step
S5 that the refrigerant pressure P2 is larger than the target
pressure Ptg, the controller 50 increases the low-pressure-side
expansion valve 5 (Open) as much as one step. Therefore, the
refrigerant easily flows through the low-pressure-side expansion
valve 5, and the pressure P2 of the refrigerant which has flowed
through the high-pressure-side expansion valve 3 drops.
[0079] On the other hand, in a case where it is judged in the step
S5 that the estimated refrigerant pressure P2 is smaller than the
target pressure Ptg, the controller 50 shifts to step S7. When the
estimated refrigerant pressure P2 is smaller than the target
pressure Ptg in this manner, the pressure P2 of the refrigerant
which has flowed through the high-pressure-side expansion valve 3
is excessively low. The gas-phase refrigerant separated by the
gas-liquid separator 4 might not easily flow into an
intermediate-pressure section of a compressor 1 or might not flow.
In consequence, the gas-phase refrigerant reaches the
low-pressure-side expansion valve 5 together with the liquid-phase
refrigerant, flows through an evaporator 6, and flows into-a
low-stage-side compression element 1A. In consequence, since the
refrigerant evaporates early at the evaporator 6, a large amount of
the gas-phase refrigerant which does not produce any refrigeration
effect flows. A disadvantage that the refrigeration effect is
remarkably deteriorated occurs. Furthermore, any input at the
low-stage-side compression element 1A is not reduced. In
consequence, the coefficient of performance remarkably drops, and
characteristics of the two-stage expansion refrigerating device
cannot be utilized sufficiently.
[0080] To solve the problem, in a case where it is judged in the
step S5 of FIG. 7 that the estimated refrigerant pressure P2 is
smaller than the target pressure Ptg, the controller 50 shifts to
the step S7, reduces the valve open degree of the low-pressure-side
expansion valve 5 as much as one step, and advances to the step S9
to return to the step S1 (Return).
[0081] As described above, in a case where it is judged in the step
S5 that the estimated refrigerant pressure P2 is smaller than the
target pressure Ptg, the controller 50 reduces the valve open
degree of the low-pressure-side expansion valve 5 (Close) as much
as one step. Therefore, the effect of reducing the pressure of the
refrigerant is reduced at the low-pressure-side expansion valve 5.
That is, the effect of reducing the pressure of the
low-pressure-side expansion valve 5 increases, and the refrigerant
does not easily flow. Therefore, the pressure P2 of the refrigerant
which has flowed through the high-pressure-side expansion valve 3
increases. In consequence, the pressure P2 of the refrigerant which
has flowed through the high-pressure-side expansion valve 3
increases. Owing to such a refrigerant pressure P2, the gas-phase
refrigerant separated by the gas-liquid separator 4 can smoothly be
returned to the discharge side of the low-stage-side compression
element 1A of the compressor 1 (a suction side of a high-stage-side
compression element 1B) via a refrigerant pipe 40.
[0082] As described above in detail, as in the present embodiment,
the controller 50 estimates the pressure P2 of the refrigerant
which has flowed through the high-pressure-side expansion valve 3
based on the refrigerant temperature detected by the temperature
sensor 52, and controls the low-pressure-side expansion valve 5
based on the estimated pressure P2. In consequence, without using
any expensive pressure sensor, the pressure P2 of the refrigerant
which has flowed through the high-pressure-side expansion valve 3
is estimated using the inexpensive temperature sensor 52, and the
low-pressure-side expansion valve 5 can correctly be controlled.
Therefore, an effect similar to that of the above embodiment can be
obtained.
Embodiment 3
[0083] Moreover, in the above embodiments, a pressure P2 of a
refrigerant which has flowed through a high-pressure-side expansion
valve 3 is estimated based on an only temperature detected by a
temperature sensor 52, and an high-pressure-side expansion valve 3
or a low-pressure-side expansion valve 5 is controlled based on the
estimated pressure P2. However, the high-pressure-side expansion
valve 3 or the low-pressure-side expansion valve 5 may be
controlled based on a pressure P1 of an intermediate-pressure
section of a compressor 1 in addition to the pressure of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3. One example of this case will hereinafter be
described in detail. It is to be noted that, in the present
embodiment, a refrigerant circuit similar to that of Embodiment 1
shown in FIG. 1 is used.
[0084] In the present embodiment, the controller 50 controls the
high-pressure-side expansion valve 3 based on the pressure P2 of
the refrigerant which has flowed through the high-pressure-side
expansion valve 3 and the pressure P1 of the intermediate-pressure
section of the compressor. Specifically, the controller 50 controls
the high-pressure-side expansion valve 3 so that the pressure P2 of
the refrigerant which has flowed through the high-pressure-side
expansion valve 3 is lager than the pressure P1 of the
intermediate-pressure section of the compressor 1. Here, the
intermediate-pressure section of the compressor 1 is in a range
from a time when the refrigerant compressed by a low-stage-side
compression element 1A of the compressor 1 has an intermediate
pressure until the refrigerant flows into a high-stage-side
compression element 1B and compressed. The pressure P1 of the
intermediate-pressure section of the compressor 1 is a pressure of
the refrigerant compressed by the low-stage-side compression
element 1A. This pressure P1 of the intermediate-pressure section
of the compressor 1 is shown in a table based on an outside air
temperature sensor 55 and an operation frequency. That is, the
controller 50 contains information of the table based on the
outside air temperature sensor 55 and the operation frequency, and
the pressure P1 of the intermediate-pressure section of the
compressor 1 is calculated from the operation frequency at that
time in accordance with an outside air temperature input by the
outside air temperature sensor 55.
[0085] Moreover, in the present embodiment, a controller 50 detects
a temperature of a liquid-phase refrigerant flowed out from a
gas-liquid separator 4 with the temperature sensor 52, and
estimates the pressure P2 of the refrigerant which has flowed
through the high-pressure-side expansion valve 3 based on this
temperature. That is, the refrigerant which has flowed through the
high-pressure-side expansion valve 3 has a gas/liquid two-phase
region in which a liquid-phase refrigerant is mixed, and the
refrigerant including such a liquid phase has a correlation between
a temperature and a pressure. Therefore, the temperature or the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 can be detected to estimate the pressure from the
temperature of the refrigerant.
[0086] Furthermore, the controller 50 controls the
high-pressure-side expansion valve 3 so that the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 estimated as described above is higher than the
pressure P1 of the intermediate-pressure section of the compressor
1. Specifically, as described later in detail in description of an
operation, the controller 50 controls a valve open degree of the
high-pressure-side expansion-valve 3 in a stepwise manner so that a
difference (P2-P1) between the pressure P2 of the refrigerant which
has flowed through the high-pressure-side expansion valve 3 and the
pressure P1 of the intermediate-pressure section of the compressor
1 is between an upper limit value .DELTA.Pmax and a lower limit
value .DELTA.Pmin. In the present embodiment, when the value of
P2-P1 is a predetermined lower limit value .DELTA.Pmin or less, the
controller 50 increases the valve open degree of the
high-pressure-side expansion valve 3 as much as one step. When the
value is a predetermined upper limit value .DELTA.Pmax or more, the
controller controls the high-pressure-side expansion valve 3 so as
to reduce the valve open degree as much as one step. It is to be
noted that the lower limit value .DELTA.Pmin and the upper limit
value .DELTA.Pmax are both positive values set beforehand.
[0087] In addition, as described above, the controller 50 controls
the high-pressure-side expansion valve 3 so that the pressure P2 of
the refrigerant which has flowed through the high-pressure-side
expansion valve 3, estimated from the refrigerant temperature
detected by the temperature sensor 52, is higher than the pressure
P1 of the intermediate-pressure section of the compressor 1
estimated from an outside air temperature detected by the outside
air temperature sensor 55. Here, control of the high-pressure-side
expansion valve 3 of the two-stage expansion refrigerating device
according to the present embodiment will be described with
reference to a flow chart of FIG. 8.
[0088] First, when the controller 50 is started in step S1 of FIG.
8 (Start), the controller 50 detects a temperature of the
liquid-phase refrigerant flowed out from the gas-liquid separator 4
with the temperature sensor 52 to estimate the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 from the temperature (step S2 of FIG. 8). The
controller 50 calculates the pressure P1 of the
intermediate-pressure section of the compressor 1 from the table
stored in the controller 50 based on the outside air temperature
detected by the outside air temperature sensor 55 and an operation
frequency of the compressor 1 (step S3 of FIG. 8).
[0089] Subsequently, the controller 50 shifts to step S4 of FIG. 8
to compare the difference (P2-P1) between the pressure P2 estimated
in the step S2 and the pressure P1 calculated in the step S3 with a
predetermined lower limit value .DELTA.Pmin set beforehand.
Moreover, when the value of the P2-P1 is larger than the lower
limit value .DELTA.Pmin, the controller shifts to step S5.
[0090] On the other hand, when the value of P2-P1 is smaller than
the predetermined lower limit value .DELTA.Pmin or less, the
controller shifts to step S6 of FIG. 8. When the value of P2-P1 is
the predetermined lower limit value .DELTA.Pmin or less, a pressure
difference between P2 and P1 is excessively small, and the
gas-phase refrigerant separated by the gas-liquid separator 4 might
not easily flow into the intermediate-pressure section of the
compressor 1 or might not flow. In consequence, the gas-phase
refrigerant reaches the low-pressure-side expansion valve 5
together with the liquid-phase refrigerant, flows through an
evaporator 6, and flows into the low-stage-side compression element
1A. In consequence, since the refrigerant evaporates early at the
evaporator 6, a large amount of the gas-phase refrigerant which
does not produce any refrigeration effect flows. A disadvantage
that the refrigeration effect is remarkably deteriorated occurs.
Furthermore, any input at the low-stage-side compression element 1A
is not reduced. In consequence, a coefficient of performance
remarkably drops, and characteristics of the two-stage expansion
refrigerating device cannot be utilized sufficiently.
[0091] To solve the problem, when the value of P2-P1 is the
predetermined lower limit value .DELTA.Pmin or less in the step S4
of FIG. 8, the controller 50 shifts to the step S6 to increases the
valve open degree of the high-pressure-side expansion valve 3 as
much as one step, and advances to step S9 to return to the step S1
(Return).
[0092] In a case where it is judged in the step S4 that the value
of P2-P1 is the predetermined lower limit value .DELTA.Pmin or less
in this manner, the controller 50 increases the valve open degree
of the high-pressure-side expansion valve 3 as much as one step
(Open). Therefore, an effect of reducing the pressure of the
refrigerant is reduced at the high-pressure-side expansion valve 3,
and the pressure P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 increases. In consequence, a
predetermined pressure difference can be secured between the
pressure P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 and the pressure P1 of the
intermediate-pressure section. Therefore, owing to such a pressure
difference, the gas-phase refrigerant separated by the gas-liquid
separator 4 can smoothly be returned to the discharge side of the
low-stage-side compression element 1A of the compressor 1 (the
suction side of the high-stage-side compression element 1B) via a
refrigerant pipe 40.
[0093] On the other hand, when the value of P2-P1 is higher than
the predetermined lower limit value .DELTA.Pmin, the controller 50
shifts to the step S5 to compare the difference (P2-P1) between the
pressures P1 and P2 with the predetermined upper limit value
.DELTA.Pmax set beforehand. Moreover, when the value P2-P1 is
smaller than the predetermined upper limit value .DELTA.Pmax, the
controller shifts to step S7, allows the high-pressure-side
expansion valve 3 to stay at the current valve open degree as it is
(Stay), advances to the step S9, and returns to the step S1,
thereby repeating the control.
[0094] On the other hand, when the value of P2-P1 is the
predetermined upper limit value .DELTA.Pmax or more, the controller
shifts to step S8. When the value of P2-P1 is the predetermined
upper limit value .DELTA.Pmax or more in this manner, the
controller reduces the valve open degree of the high-pressure-side
expansion valve 3 as much as one step, advances to the step S9, and
returns to the step S1 (Return).
[0095] When the value of P2-P1 is the predetermined upper limit
value .DELTA.Pmax or more in the step S7, the controller 50 reduces
the valve open degree of the high-pressure-side expansion valve 3
as much as one step (Close), the effect of reducing the pressure of
the refrigerant increases at the high-pressure-side expansion valve
3, and the pressure P2 of the refrigerant which has flowed through
the high-pressure-side expansion valve 3 drops.
[0096] Furthermore, as described above, the controller 50 controls
the low-pressure-side expansion valve 5 in accordance with a
refrigerant temperature Tin at an inlet of the evaporator 6
detected by an evaporator inlet temperature sensor 53 and a
refrigerant temperature Tout at an outlet of the evaporator 6
detected by an evaporator outlet temperature sensor 54. Next, the
control of the low-pressure-side expansion valve 5 of the two-stage
expansion refrigerating device according to the present embodiment
will be described with reference to a flow chart of FIG. 5.
[0097] First, when the controller 50 is started in step Si of FIG.
5 (Start), the controller 50 detects the refrigerant temperature
Tin at the inlet of the evaporator 6 with the evaporator inlet
temperature sensor 53 in step S2 of FIG. 5. Subsequently, after
detecting the refrigerant temperature Tout at the outlet of the
evaporator 6 with the evaporator outlet temperature sensor 54 in
step S3 of FIG. 5, the controller shifts to step S4 of FIG. 5.
[0098] Moreover, in the step S4 of FIG. 5, the controller 50
compares, with a predetermined lower limit value .DELTA.Tmin (a
positive value set beforehand), a difference (Tout-Tin) between the
refrigerant temperature Tout at the outlet of the evaporator 6
detected in the step S3 of FIG. 5 and the refrigerant temperature
Tin at the inlet of the evaporator 6 detected in the step S2 of
FIG. 5. When a value of Tout-Tin is larger than the predetermined
lower limit value .DELTA.Tmin, the controller shifts to step S5 of
FIG. 5.
[0099] On the other hand, when the value of Tout-Tin is the
predetermined lower limit value .DELTA.Tmin or less, the controller
shifts to step S6 of FIG. 5. When the value of Tout-Tin is the
predetermined lower limit value .DELTA.Tmin or less in this manner,
a temperature difference between the temperatures Tout and Tin is
excessively small, and a superheat degree of the refrigerant flowed
out from the evaporator 6 is not sufficiently secured. That is, the
refrigerant having the liquid-phase state might remain in the
refrigerant flowed out from the evaporator 6. In consequence, the
liquid-phase refrigerant may flow into the low-stage-side
compression element 1A of the compressor 1, and the liquid might be
compressed.
[0100] To solve the problem, in a case where it is judged in the
step S4 of FIG. 5 that the value of Tout-Tin is the predetermined
lower limit value .DELTA.Tmin or less, the controller 50 shifts to
the step S6 to reduce the valve open degree of the
low-pressure-side expansion valve 5 (Close). The controller then
advances to step S9 to return to the step S1, thereby repeating the
control (Return).
[0101] As described above, in a case where it is judged in the step
S4 that the value of Tout-Tin is the predetermined lower limit
value .DELTA.Tmin or less, the controller 50 reduces the valve open
degree of the low-pressure-side expansion valve 5. Therefore, the
amount of the refrigerant which flows through the evaporator 6
decreases, and the refrigerant can sufficiently be evaporated in
the evaporator 6. In consequence, such liquid compression can be
released.
[0102] On the other hand, when the value of Tout-Tin is higher than
the predetermined lower limit value .DELTA.Tmin, the controller 50
shifts to the step S5 to compare the value of Tout-Tin with a
predetermined upper limit value .DELTA.Tmax (a positive value set
beforehand) set beforehand. Moreover, when the value of Tout-Tin is
smaller than the predetermined upper limit value .DELTA.Tmax, the
controller shifts to step S7, and allows the low-pressure-side
expansion valve 5 to stay at the current valve open degree as it is
(Stay). The controller then advances to the step S9 to return to
the step S1, thereby repeating the control (Return).
[0103] On the other hand, when the value of Tout-Tin is the
predetermined upper limit value .DELTA.Tmax or more, the controller
shifts to step S8. When the value of Tout-Tin is the predetermined
upper limit value .DELTA.Tmax or more, the refrigerant temperature
Tout at the outlet of the evaporator 6, that is, the temperature of
the refrigerant flows into the low-stage-side compression element
1A of the compressor 1 is excessively high. A disadvantage that the
temperature and the pressure of the refrigerant flowing through the
circuit abnormally increase might be caused.
[0104] To solve the problem, when the value of Tout-Tin is the
predetermined upper limit value .DELTA.Tmax or more, the controller
50 shifts to the step S8 of FIG. 5 to loosen throttle of the
low-pressure-side expansion valve 5 (open the low-pressure-side
expansion valve 5 from the current valve open degree (Open)). In
consequence, the amount of the refrigerant flowing through the
evaporator 6 increases, the temperature of the refrigerant at the
outlet of the evaporator 6 drops, and such abnormal increases of
the temperature and the pressure of the refrigerant flowing through
the circuit can be eliminated.
[0105] In addition, as described above, when the controller 50
closes the low-pressure-side expansion valve 5 in the step S6 of
FIG. 5 (Close), the amount of the refrigerant flowing from the
low-pressure-side expansion valve 5 to the evaporator 6 decreases,
and the refrigerant is dammed by the low-pressure-side expansion
valve 5. Therefore, the refrigerant pressure on an upstream side of
the low-pressure-side expansion valve and the refrigerant
temperature having a correlation with respect to the refrigerant
pressure increase. That is, the temperature of the refrigerant
which has flowed through the high-pressure-side expansion valve 3,
detected by the temperature sensor 52, rises, and the refrigerant
pressure P2 estimated from the refrigerant temperature also rises.
Even in such a case, as described in the control of the
high-pressure-side expansion valve 3 with reference to FIG. 8, in a
case where the difference P2-P1 between the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 and the pressure P1 of the intermediate-pressure
section of the compressor 1 is the predetermined upper limit value
.DELTA.Pmax set beforehand or more, as shown in the step S8 of FIG.
8, since the controller 50 reduces the valve open degree of the
high-pressure-side expansion valve 3 as much as one step (Close),
the refrigerant flows without any problem.
[0106] As described above in detail, according to the two-stage
expansion refrigerating device of the present embodiment, the
controller 50 estimates the pressure P2 of the refrigerant which
has flowed through the high-pressure-side expansion valve 3 based
on the refrigerant temperature detected by the temperature sensor
52, and controls the high-pressure-side expansion valve 3 based on
the estimated pressure P2 and the pressure P1 of the
intermediate-pressure section of the compressor 1. In consequence,
the pressure,P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 can easily be controlled.
[0107] Especially, the pressure P2 of the refrigerant which has
flowed through the high-pressure-side expansion valve 3 is
estimated based on the refrigerant temperature detected 5 by the
temperature sensor 52. Therefore, in the same manner as in the
above embodiments, without using any expensive pressure sensor, the
pressure P2 of the refrigerant which has flowed through the
high-pressure-side expansion valve 3 is estimated using the
inexpensive temperature sensor 52, and the high-pressure-side
expansion valve 3 can correctly be controlled. Therefore, costs can
be reduced.
[0108] Furthermore, the temperature sensor 52 is installed at a
refrigerant pipe 42 connected to a refrigerant outlet formed at a
main body lower portion of the gas-liquid separator 4. The
temperature sensor 52 detects the temperature of the liquid-phase
refrigerant separated by the gas-liquid separator 4. Therefore, it
is possible to more correctly detect the refrigerant temperature
with the temperature sensor 52.
[0109] In addition, the controller 50 controls the
high-pressure-side expansion valve 3 so that the pressure P2 of the
refrigerant which has flowed through the high-pressure-side
expansion valve 3 is higher than the pressure P1 of the
intermediate-pressure section of the compressor. Therefore, the
gas-phase refrigerant separated by the gas-liquid separator 4
smoothly flows into the intermediate-pressure section of the
compressor 1. In consequence, the gas-phase refrigerant which does
not contribute to the refrigeration of an object to be refrigerated
in the evaporator 6 is separated from the liquid-phase refrigerant
by the gas-liquid separator 4, and can smoothly be returned to the
intermediate-pressure section of the compressor 1. Therefore, the
amount of the refrigerant to be compressed by the low-stage-side
compression element 1A can be reduced.
[0110] In consequence, a refrigeration effect of the evaporator 6
can be improved, and the input at the low-stage-side compression
element 1A can be reduced. Therefore, according to the present
invention, the refrigerant which has flowed through the
low-pressure-side expansion valve 5 can be controlled into an
optimum pressure, and a refrigeration effect can be obtained
utilizing characteristics of the two-stage expansion refrigerating
device at the maximum.
[0111] It is to be noted that, in the above embodiments, as the
compressor, the compressor 1 including two compression means of the
low-stage-side compression element 1A and the high-stage-side
compression element 1B is used, but the compressor applicable to
the two-stage expansion refrigerating device of the present
invention is not limited to the compressor 1 of the present
embodiment. That is, any compressor may be used as long as the
gas-phase refrigerant separated by the gas-liquid separation means
can be returned to the intermediate-pressure section of the
compressor. For example, the compression elements 1A, 1B may
include two compression means including motors, respectively, and
include one compression element provided with an intermediate
suction port.
* * * * *