U.S. patent application number 15/744638 was filed with the patent office on 2018-07-19 for multi-stage compression refrigeration cycle device.
The applicant listed for this patent is DENSO CORPORATION. Invention is credited to Hisashi IEDA.
Application Number | 20180202689 15/744638 |
Document ID | / |
Family ID | 58288970 |
Filed Date | 2018-07-19 |
United States Patent
Application |
20180202689 |
Kind Code |
A1 |
IEDA; Hisashi |
July 19, 2018 |
MULTI-STAGE COMPRESSION REFRIGERATION CYCLE DEVICE
Abstract
A multi-stage compression refrigeration cycle device includes a
controller that controls rotational speeds of a low-stage side
compression mechanism and a high-stage side compression mechanism,
and a physical quantity sensor that detects a physical quantity
correlated with a pressure of a low-pressure refrigerant. The
controller is configured to increase a rotational speed ratio of
the rotational speed of the low-stage side compression mechanism to
the rotational speed of the high-stage side compression mechanism
as the pressure of the low-pressure refrigerant becomes higher,
based on the physical amount detected by the physical quantity
sensor.
Inventors: |
IEDA; Hisashi; (Kariya-city,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DENSO CORPORATION |
Kariya-city, Aichi-pref. |
|
JP |
|
|
Family ID: |
58288970 |
Appl. No.: |
15/744638 |
Filed: |
August 26, 2016 |
PCT Filed: |
August 26, 2016 |
PCT NO: |
PCT/JP2016/074962 |
371 Date: |
January 12, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 2700/2104 20130101;
F25B 49/022 20130101; F25B 2700/1931 20130101; F25B 2600/111
20130101; F25B 1/10 20130101; F25B 2700/21172 20130101; F25B
2400/13 20130101; F25B 2600/021 20130101; F25B 2700/2106 20130101;
F25B 2700/1933 20130101; F25B 2600/0253 20130101; F25B 2500/29
20130101; F25B 2500/26 20130101; Y02B 30/70 20130101; F25B 2600/022
20130101; F25B 2600/112 20130101 |
International
Class: |
F25B 1/10 20060101
F25B001/10; F25B 49/02 20060101 F25B049/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 15, 2015 |
JP |
2015-182172 |
Claims
1. A multi-stage compression refrigeration cycle device,
comprising: a low-stage side compression mechanism that compresses
a low-pressure refrigerant to an intermediate-pressure refrigerant
and discharges the compressed intermediate-pressure refrigerant; a
high-stage side compression mechanism that compresses the
intermediate-pressure refrigerant discharged from the low-stage
side compression mechanism to a high-pressure refrigerant and
discharges the compressed high-pressure refrigerant; a heat
radiator that exchanges heat between the high-pressure refrigerant
discharged from the high-stage side compression mechanism and
exterior air to dissipate heat from the high-pressure refrigerant;
an intermediate-pressure expansion valve that decompresses and
expands the high-pressure refrigerant flowing out of the heat
radiator to an intermediate-pressure refrigerant and then flows out
the intermediate-pressure refrigerant to a suction side of the
high-stage side compression mechanism; a low-pressure expansion
valve that decompresses and expands the high-pressure refrigerant
flowing out of the heat radiator to the low-pressure refrigerant;
an evaporator that exchanges heat between the low-pressure
refrigerant decompressed and expanded by the low-pressure expansion
valve and ventilation air to be blown into a space to be cooled,
causing the refrigerant to evaporate, and then to flow out the
refrigerant to a suction side of the low-stage side compression
mechanism; a high-pressure sensor that detects a pressure of the
high-pressure refrigerant; a controller that controls rotational
speeds of the low-stage side compression mechanism and the
high-stage side compression mechanism; and a physical quantity
sensor that detects a physical quantity correlated with a pressure
of the low-pressure refrigerant, wherein the controller is
configured to increase a rotational speed ratio of the rotational
speed of the low-stage side compression mechanism to the rotational
speed of the high-stage side compression mechanism as the pressure
of the low-pressure refrigerant becomes higher, based on the
physical amount detected by the physical quantity sensor, and the
controller is configured to increase the rotational speed ratio as
the pressure of the low-pressure refrigerant becomes higher, when
the pressure of the high-pressure refrigerant detected by the
high-pressure sensor is equal to or higher than a predetermined
reference value.
2. The multi-stage compression refrigeration cycle device according
to claim 1, wherein the physical quantity sensor is an
in-refrigerator temperature sensor that detects a temperature of
the space to be cooled, and the controller is configured to
increase the rotational speed ratio as the temperature of the space
to be cooled, detected by the in-refrigerator temperature sensor,
becomes higher.
3. The multi-stage compression refrigeration cycle device according
to claim 1, further comprising: a determination unit that
determines whether or not a cool-down operation is necessary to
quickly cool the space to be cooled, based on a temperature of the
space to be cooled, wherein, the controller is configured to
increase the rotational speed ratio of the rotational speed of the
low-stage side compression mechanism to the rotational speed of the
high-stage side compression mechanism as the pressure of the
low-pressure refrigerant becomes higher, when the determination
unit determines that the cool-down operation is to be
performed.
4. The multi-stage compression refrigeration cycle device according
to claim 3, wherein the determination unit determines that the
cool-down operation is necessary when the pressure of the
high-pressure refrigerant detected by the high-pressure sensor is
equal to or higher than a predetermined reference value.
5. The multi-stage compression refrigeration cycle device according
to claim 1, further comprising a middle-pressure expansion valve
that decompresses and expands the high-pressure refrigerant flowing
out of the heat radiator to an intermediate-pressure refrigerant,
and flows out the intermediate-pressure refrigerant to a suction
side of the high-stage side compression mechanism.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on Japanese Patent Application No.
2015-182172 filed on Sep. 15, 2015, the contents of which are
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present disclosure relates to a multi-stage compression
refrigeration cycle device that includes multi-stage compression
mechanisms.
BACKGROUND ART
[0003] Conventionally, for example, Patent Document 1 discloses a
multi-stage compression refrigeration cycle device that includes a
low-stage side compression mechanism and a high-stage side
compression mechanism. The low-stage side compression mechanism
compresses a low-pressure refrigerant to an intermediate-pressure
refrigerant and then discharges the compressed
intermediate-pressure refrigerant. The high-stage side compression
mechanism compresses the intermediate-pressure refrigerant,
discharged from the low-stage side compression mechanism, to a
high-pressure refrigerant and then discharges the compressed
high-pressure refrigerant. In this way, the multi-stage compression
refrigeration cycle device is designed to pressurize the
refrigerant in multiple stages.
[0004] In more detail, the multi-stage compression refrigeration
cycle device described in Patent Document 1 is configured as a
so-called economizer refrigeration cycle. The economizer
refrigeration cycle includes a heat radiator that dissipates heat
from the high-pressure refrigerant discharged from the high-stage
side compression mechanism and an intermediate-pressure expansion
valve that decompresses and expands part of the high-pressure
refrigerant flowing out of the heat radiator to the
intermediate-pressure refrigerant. The economizer refrigeration
cycle guides the intermediate-pressure refrigerant, decompressed by
the intermediate-pressure expansion valve, to a suction side of the
high-stage side compression mechanism.
[0005] In this type of economizer refrigeration cycle, a mixed
refrigerant composed of the intermediate-pressure refrigerant
decompressed by the intermediate-pressure expansion valve and the
intermediate-pressure refrigerant discharged from the low-stage
side compression mechanism can be drawn into the high-stage side
compression mechanism. Thus, the mixed refrigerant at a lower
temperature can be drawn into the high-stage side compression
mechanism, compared to a case where only the intermediate-pressure
refrigerant discharged from the low-stage side compression
mechanism is drawn to the high-stage side compression mechanism.
Consequently, the compression efficiency of the high-stage side
compression mechanism can be improved.
[0006] The two-stage compression refrigeration device, described in
Patent Document 1, starts its operation by setting the rotational
speed of each of a low-stage side compressor and a high-stage side
compressor lower than the maximum rotational speed that exhibits
the maximum capacity of the compressor, at start-up of the device.
Subsequently, the refrigeration device increases the rotational
speed in multiple stages. Thus, the spill of oil from the
compressor can be suppressed, thereby preventing the occurrence of
breakdown of the refrigeration device due to the shortage of
oil.
RELATED ART DOCUMENT
Patent Document
[0007] [Patent Document 1] Japanese Unexamined Patent Application
Publication No. 2012-247154
SUMMARY OF THE INVENTION
[0008] Such a two-stage compression refrigeration cycle device is
required to cool the inside of a refrigerator, which is a space to
be cooled, as quickly as possible at start-up of the device. In
particular, in summer when the outside air temperature is high, the
refrigeration cycle device is increasingly required to cool the
inside of the refrigerator more quickly to shorten a cool-down
time.
[0009] However, a conventional device is configured to control the
rotational speeds of the low-stage side compressor and the
high-stage side compressor such that the rotational speed ratio of
the rotational speed of the low-stage side compression mechanism to
that of the high-stage side compression mechanism is constant. In
such a device, when the temperature inside the refrigerator is
high, the rotational speed of the high-stage side compressor is
limited to less than a predetermined protection control value in
order to protect a motor provided in the high-stage side
compressor. For this reason, the rotational speeds of the low-stage
side compressor and the high-stage side compressor might be
difficult to increase sufficiently. Consequently, at start-up of
the device, it takes a longer time to cool the inside of the
refrigerator.
[0010] The device described in Patent Document 1, mentioned above,
is configured to start its operation by setting the rotational
speed of each of a low-stage side compressor and a high-stage side
compressor lower than the maximum rotational speed that exhibits
the maximum capacity of the compressor, at start-up of the device,
and then to increase the rotational speed in multiple stages.
However, this device controls only the rotational speed of each of
the low-stage side and high-stage side compressors merely to
suppress the spill of oil, but never considers any means to shorten
the cool-down time.
[0011] The cool-down time can be shortened by upsizing the
low-stage side compressor and the high-stage side compressor.
However, if each compressor is upsized, the cost of the
refrigeration cycle device would be increased, and additionally, a
mounting space for the refrigeration cycle device would become
larger.
[0012] Therefore, it is an object of the present disclosure to
shorten the cool-down time at start-up of the refrigeration cycle
device without upsizing each compressor.
[0013] According to an aspect of the present disclosure, a
multi-stage compression refrigeration cycle device, includes: a
low-stage side compression mechanism that compresses a low-pressure
refrigerant to an intermediate-pressure refrigerant and discharges
the compressed intermediate-pressure refrigerant; a high-stage side
compression mechanism that compresses the intermediate-pressure
refrigerant discharged from the low-stage side compression
mechanism to a high-pressure refrigerant and discharges the
compressed high-pressure refrigerant; a heat radiator that
exchanges heat between the high-pressure refrigerant discharged
from the high-stage side compression mechanism and exterior air to
dissipate heat from the high-pressure refrigerant; an
intermediate-pressure expansion valve that decompresses and expands
the high-pressure refrigerant flowing out of the heat radiator to
an intermediate-pressure refrigerant and then flows out the
intermediate-pressure refrigerant to a suction side of the
high-stage side compression mechanism; a low-pressure expansion
valve that decompresses and expands the high-pressure refrigerant
flowing out of the heat radiator to the low-pressure refrigerant;
an evaporator that exchanges heat between the low-pressure
refrigerant decompressed and expanded by the low-pressure expansion
valve and ventilation air to be blown into a space to be cooled,
causing the refrigerant to evaporate, and then to flow out the
refrigerant to a suction side of the low-stage side compression
mechanism; a controller that controls rotational speeds of the
low-stage side compression mechanism and the high-stage side
compression mechanism; and a physical quantity sensor that detects
a physical quantity correlated with a pressure of the low-pressure
refrigerant. The controller is configured to increase a rotational
speed ratio of the rotational speed of the low-stage side
compression mechanism to the rotational speed of the high-stage
side compression mechanism as the pressure of the low-pressure
refrigerant becomes higher, based on the physical amount detected
by the physical quantity sensor.
[0014] In this way, the controller is configured to increase the
rotational speed ratio of the rotational speed of the low-stage
side compression mechanism to the rotational speed of the
high-stage side compression mechanism as the pressure of the
low-pressure refrigerant becomes higher, based on a physical
quantity detected by the physical quantity sensor. Thus, the
refrigerating capacity of the evaporator can be improved by
increasing the rotational speed of the low-stage side compression
mechanism, even though the rotational speed of the high-stage side
compressor is limited. Therefore, the cool-down time at start-up of
the refrigeration cycle device can be shortened without upsizing
each compressor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is an entire configuration diagram of a multi-stage
compression refrigeration cycle device according to an
embodiment;
[0016] FIG. 2 is a flowchart of control processing performed by a
controller in the multi-stage compression refrigeration cycle
device according to the embodiment;
[0017] FIG. 3 is a diagram representing the relationship between an
optimal rotational speed ratio of the low-stage side compressor to
the high-stage side compressor and the pressure of a low-pressure
refrigerant;
[0018] FIG. 4 is a diagram showing the relationship regarding the
time characteristics of the rotational speed ratio of the low-stage
side compression mechanism to the high-stage side compression
mechanism after the start of a cool-down operation;
[0019] FIG. 5 is a diagram showing the relationship between the
temperature inside the refrigerator and the cool-down time; and
[0020] FIG. 6 is a diagram showing the theoretically determined
result of the relationship between the pressure of a low-pressure
refrigerant and an optimal intermediate pressure ratio.
DESCRIPTION OF EMBODIMENTS
First Embodiment
[0021] A first embodiment will be described below with reference to
FIGS. 1 to 3. FIG. 1 is an entire configuration diagram of a
multi-stage compression refrigeration cycle device in the present
embodiment. The multi-stage compression refrigeration cycle device
is applied to a refrigerator and serves to cool ventilation air to
be blown into the inside of the refrigerator as a space to be
cooled, to an ultralow temperature of approximately -30.degree. C.
to -10.degree. C.
[0022] As illustrated in FIG. 1, the multi-stage compression
refrigeration cycle device includes two compressors, namely, a
high-stage side compressor 11 and a low-stage side compressor 12.
The multi-stage compression refrigeration cycle device is
configured to pressurize the refrigerant circulating through the
cycle in multiple stages. As the refrigerant, a normal fluorocarbon
refrigerant (for example, R404A) can be adopted. The refrigerant
contains therein a refrigerant oil (i.e., oil) for lubricating
sliding parts of the low-stage side compressor 12 and the
high-stage side compressor 11, and at least part of the refrigerant
oil circulates through the cycle together with the refrigerant.
[0023] The low-stage side compressor 12 is an electric compressor
that includes a low-stage side compression mechanism 12a and a
low-stage side electric motor 12b. The low-stage side compression
mechanism 12a compresses a low-pressure refrigerant to an
intermediate-pressure refrigerant and discharges the
intermediate-pressure refrigerant. The low-stage side electric
motor 12b rotatably drives the low-stage side compression mechanism
12a.
[0024] The low-stage side electric motor 12b is an AC motor that
has its operation (i.e., the rotational speed) controlled by AC
current output from a low-stage side inverter 22. The low-stage
side inverter 22 outputs the AC current at a frequency in response
to a control signal, output from a refrigerator controller 20 to be
described later. The refrigerant discharge capacity of the
low-stage side compression mechanism 12a is changed by controlling
the frequency.
[0025] Thus, in the present embodiment, the low-stage side electric
motor 12b configures a discharge-capacity changing portion for the
low-stage side compressor 12. It is apparent that the low-stage
side electric motor 12b may adopt a DC motor, whereby the
rotational speed of the motor may be controlled by a control
voltage output from the refrigerator controller 20. A discharge
port of the low-stage side compression mechanism 12a is connected
to a side of a suction port of the high-stage side compressor
11.
[0026] The high-stage side compressor 11 has substantially the same
basic structure as the low-stage side compressor 12. Thus, the
high-stage side compressor 11 is an electric compressor that
includes a high-stage side compression mechanism 11a and a
high-stage side electric motor 11b. The high-stage side compression
mechanism 11a compresses the intermediate-pressure refrigerant
discharged from the low-stage side compressor 12 to a high-pressure
refrigerant and discharges the compressed high-pressure
refrigerant.
[0027] The high-stage side electric motor 11b has the rotational
speed thereof controlled by AC current output from a high-stage
side inverter 21. In the present embodiment, a compression ratio of
the high-stage side compression mechanism 11a is substantially the
same as a compression ratio of the low-stage side compression
mechanism 12a.
[0028] A discharge port of the high-stage side compression
mechanism 11a is connected to a refrigerant inlet side of a heat
radiator 13. The heat radiator 13 is a heat-dissipation heat
exchanger that exchanges heat between the high-pressure refrigerant
discharged from the high-stage side compressor 11 and air outside
the refrigerator (i.e., exterior air) blown by a cooling fan 13a,
thereby dissipating heat from the high-pressure refrigerant to cool
the refrigerant.
[0029] In the present embodiment, the refrigerator controller 20
configures a controller that controls the rotational speeds of the
low-stage side compression mechanism 12a and the high-stage side
compression mechanism 11a. In more detail, the refrigerator
controller 20 configures the controller that controls the
rotational speed of each of the low-stage side electric motor 12b
for rotating the low-stage side compression mechanism 12a and the
high-stage side electric motor 11b for rotating the high-stage side
compression mechanism 11a.
[0030] The cooling fan 13a is an electric blower that has its
rotational speed controlled by a control voltage output from the
refrigerator controller 20. The blowing air volume of the cooling
fan is determined according to its rotational speed. The
multi-stage compression refrigeration cycle device in the present
embodiment configures a subcritical refrigeration cycle in which a
high-pressure side refrigerant pressure does not exceed the
critical pressure of the refrigerant while using a fluorocarbon
refrigerant as the refrigerant, and thereby the heat radiator 13
functions as a condenser that condenses the refrigerant.
[0031] A refrigerant outlet of the heat radiator 13 is connected to
a branch portion 14 that branches the flow of the refrigerant
flowing out of the heat radiator 13. The branch portion 14 has a
three-way joint structure with three flow inlet/outlets. One of the
flow inlet/outlets is a refrigerant flow inlet, while the other two
are refrigerant flow outlets. Such a branch portion 14 may be
formed by joining pipes or by providing a plurality of refrigerant
passages in a metal block or a resin block.
[0032] One refrigerant outlet of the branch portion 14 is connected
to an inlet side of an intermediate-pressure expansion valve 15,
while the other refrigerant outlet of the branch portion 14 is
connected to an inlet side of a high-pressure refrigerant flow
passage 16a in an intermediate heat exchanger 16. The
intermediate-pressure expansion valve 15 is a thermal expansion
valve that decompresses and expands the high-pressure refrigerant,
flowing out of the heat radiator 13, to an intermediate-pressure
refrigerant and then flows out the intermediate-pressure
refrigerant to a suction side of the high-stage side compression
mechanism 11a.
[0033] More specifically, the intermediate-pressure expansion valve
15 has a thermo-sensitive portion disposed on an outlet side of an
intermediate-pressure refrigerant flow passage 16b in the
intermediate heat exchanger 16. The thermo-sensitive portion of the
intermediate-pressure expansion valve 15 senses a superheat degree
of the refrigerant on the outlet side of the intermediate-pressure
refrigerant flow passage 16b based on the temperature and pressure
of the refrigerant on the outlet side of the intermediate-pressure
refrigerant flow passage 16b. The intermediate-pressure expansion
valve 15 adjusts its valve opening by a mechanical mechanism such
that the sensed superheat degree of the refrigerant reaches a
predetermined value previously set. The flow rate of the
refrigerant from the intermediate-pressure expansion valve 15 is
determined according to its valve opening degree. The outlet side
of the intermediate-pressure expansion valve 15 is connected to the
inlet side of the intermediate-pressure refrigerant flow passage
16b.
[0034] The intermediate heat exchanger 16 exchanges heat between
the intermediate-pressure refrigerant decompressed and expanded by
the intermediate-pressure expansion valve 15 and then circulating
through the intermediate-pressure refrigerant flow passage 16b and
the other high-pressure refrigerant branched by the branch portion
14 and then circulating through the high-pressure refrigerant flow
passage 16a. The high-pressure refrigerant is decompressed, so that
its temperature decreases. Thus, in the intermediate heat exchanger
16, the intermediate-pressure refrigerant circulating through the
intermediate-pressure refrigerant flow passage 16b is heated, while
the high-pressure refrigerant circulating through the high-pressure
refrigerant flow passage 16a is cooled.
[0035] The specific structure of the intermediate heat exchanger 16
adopts a double pipe heat exchanger structure in which an inner
pipe forming the intermediate-pressure refrigerant flow passage 16b
is disposed inside an outer pipe forming the high-pressure
refrigerant flow passage 16a. It is apparent that the high-pressure
refrigerant flow passage 16a may be positioned as the inner pipe,
and the intermediate-pressure refrigerant flow passage 16b may be
positioned as the outer pipe. Alternatively, the intermediate heat
exchanger 16 may adopt a structure in which refrigerant pipes
forming the high-pressure refrigerant flow passage 16a and
intermediate-pressure refrigerant flow passage 16b are bonded to
each other to exchange heat therebetween.
[0036] The intermediate heat exchanger 16 shown in FIG. 1 adopts a
parallel flow type heat exchanger in which the flow direction of
the high-pressure refrigerant circulating through the high-pressure
refrigerant flow passage 16a is aligned with the flow direction of
the intermediate-pressure refrigerant circulating through the
intermediate-pressure refrigerant flow passage 16b. Obviously, a
counterflow type heat exchanger may be adopted in which the flow
direction of the high-pressure refrigerant circulating through the
high-pressure refrigerant flow passage 16a is opposite to the flow
direction of the intermediate-pressure refrigerant circulating
through the intermediate-pressure refrigerant flow passage 16b.
[0037] The outlet side of the intermediate-pressure refrigerant
flow passage 16b in the intermediate heat exchanger 16 is connected
to a side of the suction port of the high-stage side compression
mechanism 11a, mentioned above, via a check valve (not shown).
Thus, the high-stage side compression mechanism 11a in the present
embodiment draws a mixed refrigerant including the
intermediate-pressure refrigerant flowing out of the
intermediate-pressure refrigerant flow passage 16b and the
intermediate-pressure refrigerant discharged from the low-stage
side compressor 12.
[0038] The outlet side of the high-pressure refrigerant flow
passage 16a in the intermediate heat exchanger 16 is connected to
the inlet side of a low-pressure expansion valve 17. The
low-pressure expansion valve 17 is a thermal expansion valve that
decompresses and expands the high-pressure refrigerant, flowing out
of the heat radiator 13, to the low-pressure refrigerant. The
low-pressure expansion valve 17 has a substantially the same basic
structure as that of the intermediate-pressure expansion valve
15.
[0039] More specifically, the low-pressure expansion valve 17 has a
thermo-sensitive portion disposed on the side of a refrigerant
outflow port of an evaporator 18 to be described later. The
thermo-sensitive portion of the low-pressure expansion valve 17
senses a superheat degree of the refrigerant on the outlet side of
the evaporator 18 based on the temperature and pressure of the
refrigerant on the outlet side of the evaporator 18. The
low-pressure expansion valve 17 adjusts its valve opening of the
refrigerant by a mechanical mechanism such that the sensed
superheat degree of the refrigerant reaches a predetermined value
previously set. The flow rate of the refrigerant flowing through
the low-pressure expansion valve 17 is determined according to its
valve opening degree.
[0040] The outlet side of the low-pressure expansion valve 17 is
connected to the side of the refrigerant flow inlet of the
evaporator 18. The evaporator 18 is a heat-absorption heat
exchanger that exchanges heat between the low-pressure refrigerant
decompressed and expanded by the low-pressure expansion valve 17
and the ventilation air blown to and circulating through the inside
of the refrigerator by a blower fan 18a, thereby evaporating the
low-pressure refrigerant to exhibit the heat absorption effect. The
blower fan 18a is an electric blower that has its rotational speed
controlled by a control voltage output from the refrigerator
controller 20. The blowing air volume of the blower fan 18a is
determined according to its rotational speed.
[0041] Further, the refrigerant flow outlet of the evaporator 18 is
connected to the side of the suction port of the low-stage side
compression mechanism 12a.
[0042] Next, an electric control unit in the present embodiment
will be described. The refrigerator controller 20 includes a
well-known microcomputer including a CPU and storage circuits, an
output circuit for outputting a control signal or a control voltage
to various control target devices, an input circuit into which a
detection signal from each sensor is input, and a power source
circuit. The CPU conducts control processing and arithmetic
processing. The storage circuits include an ROM and an RAM, which
store programs, data, and the like. The storage circuit is a
non-transitory physical storage medium.
[0043] The output side of the refrigerator controller 20 is
connected to the low-stage side inverter 22, the high-stage side
inverter 21, the cooling fan 13a, the blower fan 18a, and the like,
mentioned above as the control target devices. The refrigerator
controller 20 controls the operations of these control target
devices.
[0044] The refrigerator controller 20 incorporates therein control
units for controlling the operations of these control target
devices. A component (i.e., hardware and software) of the
refrigerator controller 20 that controls the operation of each
control target device configures the control unit for each of the
control target devices.
[0045] In the present embodiment, a first discharge-capacity
control unit 20a is defined as a component (i.e., hardware and
software) that controls the operation of the low-stage side
inverter 22 to thereby control the refrigerant discharge capacity
of the low-stage side compression mechanism 12a. A second
discharge-capacity control unit 20b is defined as a component
(hardware and software) that controls the operation of the
high-stage side inverter 21 to thereby control the refrigerant
discharge capacity of the high-stage side compression mechanism
11a.
[0046] Thus, the rotational speed of the low-stage side electric
motor 12b and the rotational speed of the high-stage side electric
motor 11b can be independently controlled from each other by the
first discharge-capacity control unit 20a and the second
discharge-capacity control unit 20b, respectively. It is apparent
that the first and second discharge-capacity control units 20a and
20b may be configured as separate controllers with respect to the
refrigerator controller 20.
[0047] The input side of the refrigerator controller 20 is
connected to an outside-air temperature sensor 23, an
in-refrigerator temperature sensor 24, a low-pressure sensor 25, an
intermediate-pressure sensor 26, a high-pressure sensor 27, and the
like. Detection signals from these sensors are input to the
refrigerator controller 20. The outside-air temperature sensor 23
detects an outside air temperature Tam of the air outside the
refrigerator (i.e., exterior air) that exchanges heat with the
high-pressure refrigerant in the heat radiator 13. The
in-refrigerator temperature sensor 24 detects an air temperature
Tfr of the ventilation air that exchanges heat with the
low-pressure refrigerant in the evaporator 18. The low-pressure
sensor 25 detects the pressure of the low-pressure refrigerant
having flowed out of the evaporator 18 and drawn into the low-stage
side compressor 12. The intermediate-pressure sensor 26 detects the
pressure of the intermediate-pressure refrigerant discharged from
the low-stage side compressor 12. The high-pressure sensor 27
detects the pressure of the high-pressure refrigerant discharged
from the high-stage side compressor 11. The low-pressure sensor 25
is a physical quantity sensor that detects a physical quantity
correlated with the pressure of the low-pressure refrigerant.
[0048] An operation panel 30 is connected to the input side of the
refrigerator controller 20. The operation panel 30 is provided with
an actuation/stop switch, a temperature setting switch, and the
like. Operation signals of these switches are input to the
refrigerator controller 20. The actuation/stop switch is a request
signal outputting portion that outputs an actuation request signal
or a stop request signal of the refrigerator. The temperature
setting switch is a target temperature setting portion for setting
a target cooling temperature Tset inside the refrigerator.
[0049] Next, the operation of the multi-stage compression
refrigeration cycle device with the above-mentioned configuration
in the present embodiment will be described with reference to FIG.
2. FIG. 2 is a flowchart showing control processing executed by the
refrigerator controller 20.
[0050] The control processing is started when the actuation/stop
switch on the operation panel 30 is closed (i.e., turned ON) to
output the actuation request signal. Note that the respective
control steps in the flowchart shown in FIG. 2 configure various
function implementing portions included in the refrigerator
controller 20.
[0051] First, in step S100, the refrigerator controller 20 reads
the detection signals detected by the outside-air temperature
sensor 23, the in-refrigerator temperature sensor 24, the
low-pressure sensor 25, the intermediate-pressure sensor 26, the
high-pressure sensor 27, and the like, as well as the operation
signal of the temperature setting switch on the operation panel
30.
[0052] In next step S102, it is determined whether the
refrigeration cycle device is in a cool-down state. That is, it is
determined whether or not a cool-down operation is necessary to be
performed to quickly cool the inside of the refrigerator as the
space to be cooled. In the present embodiment, the refrigerator
controller 20 specifies the outside air temperature based on the
detection signal from the outside-air temperature sensor 23, while
specifying the target cooling temperature inside the refrigerator
based on the operation signal from the temperature setting switch.
The refrigerator controller 20 determines that the refrigeration
cycle device is to be in the cool-down state when a temperature
difference between the outside air temperature and the target
cooling temperature is equal to or more than a predetermined
temperature. Meanwhile, the refrigerator controller 20 determines
that the refrigeration cycle device is not to be in the cool-down
state when a temperature difference between the outside air
temperature and the target cooling temperature is less than the
predetermined temperature.
[0053] If it is determined that the refrigeration cycle device is
to be in the cool-down state as the temperature difference between
the outside air temperature and the target cooling temperature is
equal to or more than the predetermined temperature, the
refrigerator controller 20 specifies an optimal rotational speed
ratio in step S104.
[0054] The ROM of the refrigerator controller 20 stores a map, as
shown in FIG. 3, representing the relationship between an optimal
rotational speed ratio of the low-stage side compressor 12 to the
high-stage side compressor 11 and the pressure of a low-pressure
refrigerant. The rotational speed ratio is defined as the
rotational speed ratio of the rotational speed of the low-stage
side compression mechanism 12a to the rotational speed of the
high-stage side compression mechanism 11a. The optimal rotational
speed ratio is a rotational speed ratio at which the refrigerating
capacity of the evaporator 18 is maximized. As shown in the figure,
as the pressure of the low-pressure refrigerant becomes higher, the
optimal rotational speed ratio is specified to increase. In the
present embodiment, the relationship between the pressure of the
low-pressure refrigerant and the optimal rotational speed ratio is
determined experimentally and stored in the ROM of the refrigerator
controller 20.
[0055] The optimal rotational speed ratio is specified with
reference to the map shown in FIG. 3. Specifically, the pressure of
the low-pressure refrigerant is specified based on the detection
signal detected by the low-pressure sensor 25, and then the optimal
rotational speed ratio corresponding to the specified pressure of
the low-pressure refrigerant is specified with reference to the map
shown in FIG. 3.
[0056] In an initial state of the cool-down operation, the
temperature inside the refrigerator is high, and the pressure of
the low-pressure refrigerant is high. Thus, the optimal rotational
speed ratio becomes a relatively large value. When the temperature
inside the refrigerator is decreased and the pressure of the
low-pressure refrigerant is reduced as the time elapses, the
optimal rotational speed ratio gradually becomes smaller.
[0057] In next step S106, the refrigerator controller 20 specifies
the rotational speed of the low-stage side compressor 12 and the
rotational speed of the high-stage side compressor 11. When the
temperature inside the refrigerator is high, the rotational speed
of the high-stage side compressor 11 is limited to less than a
protection control value previously determined in order to protect
the motor provided in the high-stage side compressor. To this end,
first, the rotational speed of the high-stage side compressor 11 is
specified to be a value lower by a predetermined rotational speed
than the limited value. Then, the rotational speed of the low-stage
side compressor 12 is specified based on the rotational speed of
the high-stage side compressor 11 and the optimal rotational speed
ratio specified in step S104.
[0058] In next step S108, the rotational speeds of the low-stage
side compressor 12 and the high-stage side compressor 11 are
controlled to take the respective rotational speeds specified in
step S106. Specifically, the refrigerator controller 20 instructs
the low-stage side compressor 12 and the high-stage side compressor
11 to rotate at the respective rotational speeds specified in step
S106.
[0059] The low-stage side inverter 22 outputs the AC current at a
frequency in response to a control signal, output from the
refrigerator controller 20. The refrigerant discharge capacity of
the low-stage side compression mechanism 12a included in the
low-stage side compressor 12 is changed by controlling the
frequency.
[0060] The high-stage side inverter 21 outputs the AC current at a
frequency in response to a control signal, output from the
refrigerator controller 20. The refrigerant discharge capacity of
the high-stage side compression mechanism 11a included in the
high-stage side compressor 11 is changed by controlling the
frequency.
[0061] The rotational speeds of the high-stage side compression
mechanism 11a and the low-stage side compression mechanism 12a are
controlled to achieve the optimal rotational speed ratio.
Accordingly, the rotational speed of the low-stage side compressor
12 is specified to become large, as compared to a case where the
rotational speed ratio of the rotational speed of the low-stage
side compression mechanism 12a to the rotational speed of the
high-stage side compression mechanism 11a is constant.
Consequently, the refrigerating capacity of the evaporator 18 is
maximized.
[0062] In next step S110, the refrigerator controller 20 determines
whether or not the operation of a refrigeration cycle device 10 is
to be stopped. Specifically, whether or not the operation of the
refrigeration cycle device 10 is to be stopped is determined based
on whether or not a stop request signal is output from the
operation panel 30.
[0063] If the stop request signal is not output, the determination
in step S110 is NO, and then the processing returns to step S100.
Subsequently, if the determination in step S102 is YES, the
processing of steps S104 to S110 is performed again.
[0064] When a temperature difference between the outside air
temperature and the target cooling temperature is less than the
predetermined temperature, it is determined that the refrigeration
cycle device is not to be in the cool-down state, and then the
processing proceeds to step S200 to transfer to the normal control.
In the normal control, the rotational speeds of the low-stage side
compressor and the high-stage side compressor are controlled such
that the rotational speed ratio of the rotational speed of the
low-stage side compression mechanism 12a to that of the high-stage
side compression mechanism 11a is constant.
[0065] When the actuation/stop switch on the operation panel 30 is
open (i.e., turned OFF) to output the stop request signal, the
control processing is finished.
[0066] FIG. 4 shows the time characteristic of the rotational speed
ratio of the low-stage side compression mechanism 12a to the
high-stage side compression mechanism 11a after the start of the
cool-down operation. Referring to the figure, the rotational speed
ratio of the low-stage side compression mechanism 12a to the
high-stage side compression mechanism 11a in the multi-stage
compression refrigeration cycle device of the present embodiment is
indicated by the solid line. In a comparative example, the
rotational speed ratio of the low-stage side compression mechanism
12a to the high-stage side compression mechanism 11a, which is set
constant, is indicated by the dotted line.
[0067] In an initial state of the cool-down operation, the
temperature inside the refrigerator is high, and the pressure of
the low-pressure refrigerant is high. Thus, the rotational speed
ratio of the low-stage side compression mechanism 12a to the
high-stage side compression mechanism 11a is controlled to become a
relatively large value.
[0068] When the temperature inside the refrigerator is decreased
and the pressure of the low-pressure refrigerant is reduced as the
time elapses, the optimal rotational speed ratio gradually becomes
smaller. As the time further elapses, the rotational speed ratio of
the low-stage side compression mechanism 12a to the high-stage side
compression mechanism 11a becomes a constant value that is the same
as that in the comparative example.
[0069] FIG. 5 shows the time characteristic of the temperature
inside the refrigerator after the start of the cool-down operation.
Referring to the figure, the temperature inside the refrigerator in
the multi-stage compression refrigeration cycle device of the
present embodiment is indicated by the solid line. In the
comparative example where the rotational speed ratio of the
low-stage side compression mechanism 12a to the high-stage side
compression mechanism 11a is set constant, the temperature inside
the refrigerator is indicated by the dotted line.
[0070] In the multi-stage compression refrigeration cycle device of
the present embodiment, the temperature inside the refrigerator is
quickly decreased immediately after the start of the cool-down
operation, compared to in the comparative example. As a result, in
the multi-stage compression refrigeration cycle device of the
present embodiment, the cool-down time taken until the temperature
inside the refrigerator reaches the target cooling temperature is
shortened significantly, compared to in the comparative
example.
[0071] As mentioned above, the refrigerator controller 20 is
configured to increase the rotational speed ratio of the rotational
speed of the low-stage side compression mechanism 12a to the
rotational speed of the high-stage side compression mechanism 11a
as the pressure of the low-pressure refrigerant, specified based on
the pressure of the low-pressure refrigerant detected by the
low-pressure sensor 25, becomes higher. Thus, the refrigerating
capacity of the evaporator 18 can be improved by increasing the
rotational speed of the low-stage side compression mechanism, even
though the rotational speed of the high-stage side compressor is
limited. Therefore, the cool-down time at start-up of the
refrigeration cycle device can be shortened without upsizing each
compressor.
[0072] The refrigerator controller 20 may determine whether or not
a cool-down operation is to be performed to quickly cool the space
to be cooled based on the temperature of the space to be cooled.
The refrigerator controller 20 may increase the rotational speed
ratio of the rotational speed of the low-stage side compression
mechanism to the rotational speed of the high-stage side
compression mechanism as the pressure of the low-pressure
refrigerant becomes higher, when it is determined that the
cool-down operation is to be performed. In this way, the space to
be cooled can be quickly cooled by increasing the rotational speed
ratio of the rotational speed of the low-stage side compression
mechanism to the rotational speed of the high-stage side
compression mechanism as the pressure of the low-pressure
refrigerant becomes higher, when it is determined that the
cool-down operation is to be performed.
[0073] The refrigeration cycle device 10 includes the high-pressure
sensor 27 that detects the pressure of a high-pressure refrigerant.
The refrigerator controller 20 can determine that the cool-down
operation is performed when the pressure of the high-pressure
refrigerant detected by the high-pressure sensor 27 is equal to or
higher than a reference value previously determined.
Other Embodiments
[0074] (1) In the above-mentioned embodiments, the refrigerator
controller 20 specifies the optimal rotational speed ratio based on
the experimentally determined relationship between the pressure of
a low-pressure refrigerant and the optimal rotational speed ratio.
Alternatively, the relationship between the pressure of a
low-pressure refrigerant and the optimal rotational speed ratio can
also be specified theoretically. FIG. 6 is a diagram showing the
theoretically determined result of the relationship between the
pressure of a low-pressure refrigerant at which the refrigerating
capacity of the evaporator 18 is maximized and an optimal
intermediate pressure ratio. The intermediate pressure ratio is
represented as the pressure Pm of the intermediate-pressure
refrigerant/ (the pressure Pd of the high-pressure refrigerant x
the pressure Ps of the low-pressure refrigerant). The ratio of the
rotational speed of the low-stage side compression mechanism 12a to
the rotational speed of the high-stage side compression mechanism
11a can be specified to achieve the intermediate pressure ratio
shown in FIG. 6. [0075] (2) In the refrigerator controller 20
according to the above-mentioned embodiments, the rotational speed
ratio of the rotational speed of the low-stage side compression
mechanism to the rotational speed of the high-stage side
compression mechanism is increased as the pressure of the
low-pressure refrigerant becomes higher. Alternatively, the
refrigerator controller 20 may detect the temperature inside the
refrigerator, correlated with the pressure of the low-pressure
refrigerant, by using the in-refrigerator temperature sensor 24,
and may increase the rotational speed ratio as the temperature
inside the refrigerator detected by the in-refrigerator temperature
sensor 24 becomes higher. In this case, the in-refrigerator
temperature sensor 24 is a physical quantity sensor that detects a
physical quantity correlated with the pressure of the low-pressure
refrigerant.
[0076] The refrigerator controller 20 may specify the pressure of
the low-pressure refrigerant based on the physical quantity
detected by the in-refrigerator temperature sensor 24. The
refrigerator controller 20 may increase the rotational speed ratio
of the rotational speed of the low-stage side compression mechanism
12a to the rotational speed of the high-stage side compression
mechanism 11a as the specified pressure of the low-pressure
refrigerant becomes higher. [0077] (3) In the above-mentioned
embodiments, the refrigerator controller 20 specifies the
rotational speed ratio, which is the ratio of the rotational speed
of the low-stage side compression mechanism 12a to the rotational
speed of the high-stage side compression mechanism 11a, based on
the pressure of the low-pressure refrigerant. Alternatively, the
refrigerator controller 20 may specify the rotational speed ratio,
which is the ratio of the rotational speed of the low-stage side
compression mechanism 12a to the rotational speed of the high-stage
side compression mechanism 11a, for example, based on the pressure
of the low-pressure refrigerant and the pressure of the
intermediate-pressure refrigerant. The refrigerator controller 20
may specify the rotational speed ratio, which is the ratio of the
rotational speed of the low-stage side compression mechanism 12a to
the rotational speed of the high-stage side compression mechanism
11a, based on the pressure of the low-pressure refrigerant, the
pressure of the intermediate-pressure refrigerant, and the pressure
of the high-pressure refrigerant. In this way, not only the
pressure of the low-pressure refrigerant, but also the pressure of
the intermediate-pressure refrigerant or high-pressure refrigerant
can be used to specify the optimal rotational speed ratio with
higher accuracy. [0078] (4) In the above-mentioned embodiments, the
refrigerator controller 20 specifies the rotational speed ratio,
which is the ratio of the rotational speed of the low-stage side
compression mechanism 12a to the rotational speed of the high-stage
side compression mechanism 11a, based on the pressure of the
low-pressure refrigerant. Alternatively, the refrigerator
controller 20 may specify the rotational speed ratio, which is the
ratio of the rotational speed of the low-stage side compression
mechanism 12a to the rotational speed of the high-stage side
compression mechanism 11a, for example, based on the temperature of
the low-pressure refrigerant correlated with the pressure of the
low-pressure refrigerant. In this case, the refrigerator controller
20 may detect, for example, the temperature of a pipe through which
the low-pressure refrigerant flows with a temperature sensor
without directly detecting the temperature of the low-pressure
refrigerant. Alternatively, the refrigerator controller 20 may
specify the rotational speed ratio, which is the ratio of the
rotational speed of the low-stage side compression mechanism 12a to
the rotational speed of the high-stage side compression mechanism
11a, based on the temperature of the low-pressure refrigerant and
the temperature of the intermediate-pressure refrigerant.
Alternatively, the refrigerator controller 20 may specify the
rotational speed ratio, which is the ratio of the rotational speed
of the low-stage side compression mechanism 12a to the rotational
speed of the high-stage side compression mechanism 11a, based on
the temperature of the low-pressure refrigerant, the temperature of
the intermediate-pressure refrigerant, and the temperature of the
high-pressure refrigerant. [0079] (5) In the above-mentioned
embodiments, the refrigerator controller 20 specifies the
rotational speed ratio, which is the ratio of the rotational speed
of the low-stage side compression mechanism 12a to the rotational
speed of the high-stage side compression mechanism 11a, based on
the pressure of the low-pressure refrigerant. Alternatively, the
refrigerator controller 20 may specify the rotational speed ratio,
which is the ratio of the rotational speed of the low-stage side
compression mechanism 12a to the rotational speed of the high-stage
side compression mechanism 11a, for example, based on the outside
air temperature and the temperature inside the refrigerator. In
this case, when the ROM of the refrigerator controller 20 stores
the map that specifies an optimal rotational speed corresponding to
the outside air temperature and the temperature inside the
refrigerator, the refrigerator controller 20 can specify the
rotational speed ratio, which is the ratio of the rotational speed
of the low-stage side compression mechanism 12a to the rotational
speed of the high-stage side compression mechanism 11a by using the
map. [0080] (6) In the above-mentioned embodiments, the
refrigerator controller 20 determines that the refrigeration cycle
device is in the cool-down state when a temperature difference
between the outside air temperature and the target cooling
temperature is equal to or more than the predetermined temperature.
Alternatively, the refrigerator controller 20 may determine that
the refrigeration cycle device is to be in the cool-down state when
a pressure of the high-pressure refrigerant is equal to or higher
than a protection control value. The refrigerator controller 20 may
determine that the refrigeration cycle device is to be in the
cool-down state when a temperature difference between the outside
air temperature and the target cooling temperature is equal to or
more than the predetermined temperature, and when a pressure of the
high-pressure refrigerant is equal to or higher than the protection
control value. [0081] (7) In the above-mentioned embodiments, the
respective features of the present disclosure are applied to any
multi-stage compression refrigeration cycle that has two-stage
compression mechanisms on the high-stage side and the low-stage
side. However, the respective features of the present disclosure
can also be applied to a multi-stage compression refrigeration
cycle device that includes three or more stages of compression
mechanisms. [0082] (8) In the above-mentioned embodiments, the
refrigerator controller 20 may determine whether or not the
pressure of the high-pressure refrigerant exceeds a threshold
value. The refrigerator controller 20 may respectively decrease the
rotational speed of the high-stage side compression mechanism 11a
and the rotational speed of the low-stage side compression
mechanism 12a for protection of the refrigeration cycle device when
the pressure of the high-pressure refrigerant is determined to
exceed the threshold value. [0083] (9) In the above-mentioned
embodiments, a fluorocarbon refrigerant (for example, R404A) is
adopted as the refrigerant. However, the refrigerant in use is not
limited to the fluorocarbon refrigerant and may be, for example, a
refrigerant containing carbon dioxide as a main component.
[0084] The present disclosure is not limited to the above-mentioned
embodiments, and various modifications and changes can be made to
the embodiments as appropriate. It is obvious that in the
above-mentioned respective embodiments, the elements included in
the embodiments are not necessarily essential particularly unless
otherwise specified to be essential, except when clearly considered
to be essential in principle, and the like.
[0085] The refrigerator controller 20 executes the processing in
step S102, which corresponds to a determination unit.
* * * * *