JP2001108314A - Refrigerating cycle controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly execute the control of a normal high pressure by eliminating a fault in case of bringing about an overheat in a refrigerant flowing out from an evaporator when a low load. SOLUTION: In the case of no degree of superheat, a target high pressure to become an optimum coefficient of performance is operated from a temperature of a refrigerant flowing to an expansion unit. Then, the expansion unit is controlled so that a refrigerant pressure of the high pressure side becomes the target high pressure. In case of generating the degree of the superheat, since the unit is controlled so that the degree of performance becomes a predetermined value or less, even in the case of a fault of closing the unit without raising the high pressure when a low load, when the degree of the superheat is raised, an expansion valve is opened so that the degree of the superheat becomes a predetermined value or less to supply the refrigerant to an evaporator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a refrigeration cycle in which carbon dioxide is used as a refrigerant and the refrigerant is compressed to a supercritical region at a high load.

[0002]

2. Description of the Related Art A refrigeration cycle disclosed in Japanese Patent Publication No. Hei 7-18602 discloses a compressor connected in series so as to form an integral closed circuit which is operated at a supercritical pressure on the high pressure side of a vapor compression cycle. A supercritical vapor compression cycle including a cooling device, a throttle means, an evaporator, and an accumulator, and further including an internal heat exchanger that exchanges heat between a high-pressure refrigerant and a low-pressure refrigerant.

In this refrigeration cycle, the gas-phase refrigerant sucked into the compressor is compressed to a supercritical region and discharged, cooled by the cooling device, and further heat-exchanged with the low-pressure refrigerant in an internal heat exchanger. Although cooled, the refrigerant is not condensed unlike the conventional CFC refrigeration cycle and is sent to the expansion means in a gaseous state. Then, the refrigerant pressure is reduced to the gas-liquid mixing region by the throttle means, and a liquid-phase component is generated.
It absorbs the heat of the air passing through the evaporator and evaporates.The liquid phase component is completely removed by the accumulator. Further, the internal heat exchanger exchanges heat with the high-pressure side refrigerant and is overheated and sucked into the compressor. Things.

In the above-described refrigeration cycle, the degree of opening of the throttle means is adjusted by the high pressure based on a high pressure at which an optimum coefficient of performance can be obtained with respect to the refrigerant temperature on the inlet side of the throttle means. Japanese Patent Application Laid-Open No. 9-2 discloses a method of controlling the throttle means so that the high-pressure pressure matches the pressure.
This is known from the publication No. 64622.

[0005]

However, in the conventional refrigeration cycle using carbon dioxide as described above, for example, when the outside air temperature is low and the load is reduced, the high pressure of the refrigeration cycle becomes lower than the critical pressure. A phenomenon occurs in which the refrigerant condenses in the heat exchanger for heat dissipation (gas cooler). The decrease in the specific volume of the refrigerant due to the liquefaction on the high pressure side cancels the pressure increase due to the discharge of the compressor, so that the high pressure is reduced, and the throttle means is fully closed, so that it is supplied to the evaporator. The refrigerant stops, and the amount of superheat of the refrigerant flowing out of the evaporator increases.

Accordingly, in the heat exchange between the high-pressure side refrigerant and the low-pressure side refrigerant performed in the internal heat exchanger, the amount of overheating of the low-pressure side refrigerant increases, so that the high-pressure side refrigerant is not cooled, and Because the temperature of the refrigerant does not decrease, the high-pressure pressure for obtaining the maximum coefficient of performance required from the refrigerant temperature does not decrease, so that the correct feedback is not provided to the restrictor and the restrictor does not open, so that the refrigerant supply to the evaporator is not performed. Since it is not performed correctly, there occurs a problem that the evaporator outlet temperature rises rapidly.

Therefore, the present invention is directed to a refrigeration cycle control device which can solve the problem when the refrigerant flowing out of the evaporator at a low load has a degree of superheat, and can correctly execute normal high pressure control. To provide.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a compressor using carbon dioxide as a refrigerant and having a discharge capacity variable mechanism, a heat-radiating heat exchanger for cooling the compressed refrigerant, and a control signal. In a refrigeration cycle control device for controlling a refrigeration cycle which is constituted by at least an expansion device capable of adjusting a valve opening and an evaporator for evaporating a refrigerant expanded by the expansion device, a refrigerant temperature on an inflow side of the expansion device From the refrigerant temperature detected by the refrigerant temperature detection means, the refrigerant pressure detection means for detecting the refrigerant pressure on the inflow side of the expansion device, and the refrigerant temperature detected by the refrigerant temperature detection means. Target high-pressure calculation means for calculating the target high-pressure pressure to be calculated, and the refrigerant pressure detected by the refrigerant pressure detection means are used to calculate the target high-pressure pressure. High pressure control means for controlling the expansion device so as to match the target high pressure calculated by the means; superheat degree detection means for detecting the degree of superheat of the refrigerant flowing out of the evaporator; and the superheat degree detection means A superheat degree control unit that outputs a control signal to the expansion device so that the superheat degree is equal to or less than a predetermined value based on the superheat degree detected by the superheat degree detection unit. A control switching means for executing superheat degree control means and executing high-pressure control means when the superheat degree is not detected by the superheat degree detection means.

Thus, when there is no degree of superheat, a target high pressure which gives an optimum coefficient of performance is calculated from the refrigerant temperature of the refrigerant flowing into the expansion device, and the high pressure side refrigerant pressure becomes the target high pressure. When the degree of superheating occurs, the expansion device can be controlled so that the degree of superheating becomes equal to or less than a predetermined value. Even if a problem occurs that the superheat is increased, the expansion valve is opened so that the superheat becomes a predetermined value or less, and the refrigerant can be supplied to the evaporator, so that the above-mentioned problem can be achieved.

[0010] It is preferable that the control switching means further executes a high pressure control means when the refrigerant pressure detected by the refrigerant pressure detecting means is higher than a critical pressure. This makes it possible to limit the execution of the superheat control to only when the superheat is increased due to the abnormality.

Further, in the high pressure control means and the superheat control means, it is preferable that the control signal outputted to the expansion device does not set the valve opening of the expansion device to zero. As a result, it is possible to prevent a state in which no refrigerant flows into the evaporator, and thus it is possible to prevent an abnormal increase in the degree of superheat.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a refrigeration cycle 1 uses carbon dioxide as a refrigerant, and includes a compressor 2, a heat-radiating heat exchanger 3, an internal heat exchanger 4, an expansion device 7, an evaporator 8, and an accumulator. 9 at least.

The compressor 2 includes an electromagnetic clutch 10
And is operated by being connected to a traveling engine (not shown), and has a known variable capacity mechanism 11. Thereby, the control signal output from the output circuit 19 of the control unit 18 described below is input to the variable capacity mechanism 11 controlled by the control signal, so that the refrigerant pressure on the evaporator outlet side is kept constant. The discharge amount of the compressor 2 is varied. In the variable displacement mechanism 11 having a built-in pressure control valve, the discharge amount is varied so as to keep the compressor suction pressure constant. Under normal load or high load, the gas-phase refrigerant sucked and compressed by the compressor 2 is compressed to a supercritical region as shown in the Mollier diagram ea shown in FIG.

The gas-phase refrigerant compressed by the compressor 2 is cooled by dissipating heat to the air passing through the heat exchanger 3 for heat dissipation in the heat exchanger 3 for heat dissipation. Under normal load or high load, as shown in the Mollier diagram ab of FIG.
It is cooled while maintaining the state of the gas-phase refrigerant. The gas-phase refrigerant cooled in the heat-radiating heat exchanger 3 further exchanges heat with the low-pressure side gas-phase refrigerant passing through the low-pressure section 6 when passing through the high-pressure section 5 of the internal heat exchanger 4. It is cooled and flows into the expansion device 7.

The expansion device 7 is a known device comprising an electromagnetic coil (not shown) to which a control signal is supplied and a valve (not shown) which opens and closes by an electromagnetic force generated by the electromagnetic coil. It is driven from to fully open. The throttle amount of the passing refrigerant is determined by the opening degree of the valve, and the amount and pressure of the refrigerant supplied to the evaporator 8 are determined. The pressure of the refrigerant flowing into the expansion device 4 is detected by the pressure sensor 12 and output to the input unit 17 as the refrigerant pressure Pexpin. The temperature of the refrigerant is detected by the temperature sensor 13 and the refrigerant temperature Tex
It is output to the input unit 17 as a pin. In the expansion device 7, the gaseous refrigerant in the supercritical region is decompressed to the gas-liquid two-phase region as shown by the Mollier diagram bc in FIG.

The evaporator 8 is disposed, for example, in an air-conditioning duct 21 disposed in the passenger compartment. The refrigerant decompressed to the gas-liquid two-phase region by the expansion device 7 flows into the evaporator 8 in FIG. As shown in the Mollier diagram cd, heat is absorbed from the passing air to evaporate. The temperature of the air passing through the evaporator 8 is detected by the temperature sensor 14 as the evaporator outlet temperature or the evaporator temperature Te, and is output to the input unit 17. The refrigerant pressure on the outlet side of the evaporator 8 is output to the input unit 17 as the low-pressure pressure Ps, and the refrigerant temperature is output as the low-pressure refrigerant temperature Ts.

The refrigerant evaporating after passing through the evaporator 8 is subjected to gas-liquid separation in an accumulator 9, containing a liquid phase component and supplying only a gas phase component to the low-pressure section 6. As shown by de, heat exchange occurs with the refrigerant passing through the high-pressure section 5 to increase the degree of superheat, and the refrigerant is sucked into the compressor 2.

Further, in the refrigeration cycle 1, when the load is low due to a low outside air temperature or the like, as shown by the Mollier diagram a'-b'-c'-d'-e 'in FIG. The compressed refrigerant is compressed only to a region below the critical pressure Pc, radiates heat in the heat radiating heat exchanger 3, and further passes through the high pressure
The enthalpy is reduced to the liquid phase by heat exchange with the low-pressure refrigerant passing through the evaporator. Then, the air passing through the evaporator 8 absorbs heat and evaporates, is vapor-liquid separated in the accumulator 9, passes through the low-pressure section 6, exchanges heat with the high-pressure refrigerant passing through the high-pressure section 5, and exchanges heat.
Is to be sucked.

A control unit 18 is provided to control the refrigeration cycle 1 having the above configuration. The control unit 18 is a known unit including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an input / output port (I / O), etc., which are not shown. The signal is an input unit (I /
U) 17 and further input through the operation panel (C /
P) The setting signal from 20 is input, converted into a control signal according to a predetermined program, and output to each control device via an output unit (O / U) 19 including a D / A converter, a drive circuit, and the like. Things. In this embodiment, the control devices are the expansion device 7, the variable capacity mechanism 11 of the compressor 2, and the electromagnetic clutch 10.

The control of the refrigeration cycle 1 executed by the control unit 18 will be described below with reference to FIGS.
This will be described according to the flowchart shown in FIG.

The flowchart shown in FIG. 2 shows the control of the refrigeration cycle according to the first embodiment, and includes a cooling operation switch (A / CS) provided on the operation panel 20.
When W) is input, the routine jumps to step 100 from the main control routine for performing normal air conditioning control and starts. First, in step 110, data necessary for the following control, for example, the refrigerant temperature Texpin and the refrigerant pressure Pexpin on the inflow side of the expansion device 7, the evaporator temperature Te, the evaporator outflow side refrigerant temperature Ts and the refrigerant pressure Pexp
s is input at least.

In step 120, the degree of superheat SH of the refrigerant flowing out of the evaporator 8 is calculated. The degree of superheat SH is equal to the difference (Ts-T) between the refrigerant temperature Ts and the saturated vapor temperature Ts' of the refrigerant obtained from the low pressure Ps.
s'). Alternatively, the refrigerant temperature Ts "on the inflow side of the evaporator may be detected, and the difference may be obtained from the difference (Ts-Ts") from the refrigerant temperature Ts. Basically, Ts' and Ts "coincide.

Then, in step 130, it is determined whether or not the degree of superheat SH is equal to or greater than a predetermined value ε. In this determination, when the degree of superheat is equal to or more than the predetermined value ε,
Proceeding to step 300 described below, the superheat control (SH control) is executed, and if the superheat is not equal to or greater than the predetermined value ε,
Proceeding to step 200 described below, high-pressure control is executed, and the routine returns from step 400 to a normal main control routine.

In this embodiment, ε is 0
It is. Therefore, when the superheat degree SH exists, the superheat degree control is executed, and when the superheat degree SH does not exist, the high pressure control is executed. However, in consideration of the stability of the control, a predetermined width may be provided for determining whether or not the superheat degree SH exists.
In this case, a value in the range of 2 ° C. to 5 ° C. is set for the ε.

The control of the refrigeration cycle according to the second embodiment shown in the flowchart of FIG.
After inputting various data at 0, it is determined at step 140 whether the actual refrigerant pressure Pexpin on the inflow side of the expansion device 7 is higher than the critical pressure Pc. If the actual refrigerant pressure Pexpin is greater than the critical pressure Pc in this determination, normal high-pressure control can be performed without delay, so the routine proceeds to step 200, where high-pressure pressure control is executed, and the actual refrigerant pressure is determined in the determination. If the pressure Pexpin is lower than the critical pressure Pc, the process proceeds to step 150 assuming that a problem may occur during low load, and it is determined whether the evaporator temperature Te is equal to or higher than a predetermined value λ. The determination in step 150 discloses one means for determining whether or not the degree of superheat SH has occurred.
The degree of superheat SH may be calculated in the same manner as in the first embodiment to determine whether or not the degree of superheat SH exists.

Thus, if the evaporator temperature Te is higher than the predetermined value λ, it is determined that the superheat degree SH has occurred, and the routine proceeds to step 300, where the superheat degree control described below is performed, and the evaporator temperature Te is set to the predetermined value. If it is equal to or smaller than λ, the process proceeds to step 200 to execute the high-pressure control described below.

In the high-pressure control started from step 200, as shown in FIG. 4, a target pressure Paim is calculated in step 210. This target pressure Paim is used to calculate an optimum high pressure (target pressure) Paim along the optimum control line ηmax shown in FIG. 9 from the inflow-side refrigerant temperature Texpin of the expansion device 7, and for example, a characteristic line shown in FIG. From the refrigerant temperature Texpin. And step 220
, A pressure difference ΔP between the calculated target pressure Paim and the actual refrigerant pressure Pexpin (ΔP = Paim-Pexpin) is obtained. In step 230, the expansion valve opening degree θ of the expansion device 7 is calculated from the pressure difference ΔP based on the characteristic line shown in FIG. 7, and in step 240, a control signal Sc is output to control the expansion device 7. Things.

If the target pressure Paim is higher than the actual refrigerant pressure Pexpin, step 230 sets the expansion valve opening θ to the minimum opening β.

In this embodiment, the minimum value β of the expansion valve opening θ is maintained in order to prevent the expansion device 7 from being fully closed. As a result, a minimum amount of refrigerant can be supplied to the evaporator 8, so that an increase in the evaporator temperature Te can be suppressed.

In superheat degree (SH) control started from step 300, first, in step 310, the superheat degree SH is calculated in the same manner as in step 120. In the SH control following the control of the refrigeration cycle according to the first embodiment, step 310 may be deleted, but in the case of the SH control following the control of the refrigeration cycle according to the second embodiment. This is because it is necessary to calculate the degree of superheat SH in step 310 because the determination of the presence or absence of the degree of superheat is made based on the evaporator temperature Te.

Then, in step 320, the expansion valve opening θ is calculated from the characteristic line shown in FIG. 8 so that the superheat degree SH is set to zero or constant, and in step 330, the expansion valve opening θ is corresponded to the expansion valve opening θ. The control signal Sc is output.

Thus, when the degree of superheat SH occurs at a low load or the like, the control of the expansion device 7 can be changed from the high pressure control to the superheat degree control, so that the control of the refrigeration cycle can be stably executed. is there.

Further, in the above-described embodiment, a method is employed in which the electric signal is maintained at a predetermined value so that the expansion valve opening of the expansion device does not become zero, but the valve body of the expansion device is seated on the valve seat. Also in this case, the refrigerant may be mechanically and structurally configured so that a predetermined amount of refrigerant leaks to the evaporator side.

[0035]

As described above, according to the present invention, in a case where the refrigerant is controlled to be compressed to the supercritical region under a high load or a normal load, it is necessary to obtain an optimum coefficient of performance. It is possible to execute a high-pressure control that matches the high-pressure pressure to the target high-pressure pressure, and to perform a control that keeps the superheat degree of the refrigerant constant at a low load,
It is possible to prevent problems such as a rapid rise in the blowout temperature of the evaporator that occur at a low load, and to achieve good air conditioning control.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a refrigeration cycle and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating control of a refrigeration cycle according to the first embodiment.

FIG. 3 is a flowchart illustrating control of a refrigeration cycle according to a second embodiment.

FIG. 4 is a flowchart illustrating an example of high-pressure control.

FIG. 5 is a flowchart illustrating an example of superheat control.

FIG. 6 shows the refrigerant temperature Texpin on the inflow side of the expansion device and the refrigerant pressure (target pressure) P at which the highest coefficient of performance can be obtained.
FIG. 4 is a characteristic diagram showing a relationship with aim.

FIG. 7 is a characteristic diagram showing a relationship between the pressure difference ΔP and the expansion valve opening θ.

FIG. 8 is a characteristic diagram showing a relationship between a degree of superheat SH and an opening degree θ of an expansion valve.

FIG. 9 is a Mollier diagram of the refrigeration cycle of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refrigeration cycle 2 Compressor 3 Radiation heat exchanger 4 Internal heat exchanger 7 Expansion device 8 Evaporator 9 Accumulator 10 Electromagnetic clutch 11 Capacity variable mechanism

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yuji Kawamura 39, Higashihara, Chiyo-ji, Odai-gun, Osato-gun, Saitama Prefecture Inside of Xexel Konan Plant (72) Inventor Shunji Muta 39, Higashihara, Chiyo-ji, Konan-cho, Osato-gun, Saitama Prefecture Address: Inside the Xexel Gangnam Plant (72) Inventor Kenji Iijima 39, Higashihara, Chiyo-ji, Odai-gun, Osato-gun, Saitama Prefecture Inside of the Zexxel Gangnam Plant (72) Inventor: Sakae Hayashi 39, Chiyo-ji, Higashihara, Konan-cho, Osato-gun, Saitama Prefecture Address: Inside the Xexel Gangnam Plant (72) Inventor Hiroshi Kanai 39, Higashihara, Chiyo-ji, Odai-gun, Osato-gun, Saitama 39 Inventor: Akihiko Takano 39, Higashihara, Chiyo-ji, Konan-cho, Osato-gun, Saitama Address Zexel Gangnam Plant

Claims (3)

[Claims] 1. A method using carbon dioxide as a refrigerant,
A compressor having a variable displacement capacity mechanism, a heat-radiating heat exchanger for cooling the compressed refrigerant, an expansion device capable of adjusting the valve opening degree by a control signal, and evaporating the refrigerant expanded by the expansion device A refrigeration cycle control device configured to control a refrigeration cycle constituted by at least a refrigerant unit. A refrigerant temperature detection unit that detects a refrigerant temperature on an inflow side of the expansion device; Detecting means, from the refrigerant temperature detected by the refrigerant temperature detecting means, target high pressure pressure calculating means for calculating a target high pressure from which the maximum coefficient of performance is obtained from the refrigerant temperature, detected by the refrigerant pressure detecting means The refrigerant pressure is
High-pressure control means for controlling the expansion device so as to coincide with the target high-pressure pressure calculated by the target high-pressure pressure calculation means; superheat degree detection means for detecting the degree of superheat of the refrigerant flowing out of the evaporator; Superheat control means for outputting a control signal to the expansion device based on the superheat detected by the superheat detection means so that the superheat is equal to or less than a predetermined value; and the superheat detection is detected by the superheat detection means. Refrigeration cycle control means for executing a superheat degree control means when the superheat degree is detected by the superheat degree detection means when the superheat degree is not detected by the superheat degree detection means. . 2. The control switching means according to claim 1, wherein said control switching means executes a high pressure control means when the refrigerant pressure detected by said refrigerant pressure detecting means is higher than a critical pressure. Refrigeration cycle control device. 3. The control signal output to the expansion device in the high-pressure control means and the superheat degree control means does not set the valve opening of the expansion device to zero. Refrigeration cycle control device.