JP2000320936A - Safety unit for refrigeration cycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a refrigeration cycle against leakage of refrigerant or high pressure by judging that the refrigerant is leaking if the value detected through a pressure sensor at the start of refrigeration cycle is lower by a specified value than a balance pressure during stoppage of the refrigeration cycle thereby interrupting operation of a compressor. SOLUTION: A decision is made whether an air conditioner is operating or not by inputting a detection value of a pressure sensor 17 to a control unit 21 for refrigeration cycle 1. If the air conditioner is operating, a decision is made whether it is starting operation or not. If it is starting operation, a decision is made whether the detection value of the pressure sensor 17 is lower than the saturation pressure at refrigeration temperature of 0 deg.C or not, and if it is lower than the saturation pressure, a compressor 2 is stopped (conduction of an electromagnetic clutch 3 is interrupted). If the detection value is higher than the saturation pressure but lower than a specified value which is lower than the balance pressure of a high pressure line 13 and a low pressure line 14 during stoppage of the refrigeration cycle 1, the compressor 2 is stopped because it suggests possibility of leakage of refrigerant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety device for securing a refrigeration cycle using carbon dioxide as a refrigerant.

[0002]

2. Description of the Related Art An air conditioner for a vehicle disclosed in Japanese Patent Application Laid-Open No. 5-50843 has a high-pressure switch for protecting an abnormally high pressure and a low-pressure switch for protecting an abnormally low pressure on the high pressure side of a refrigerant circuit. When these switches are actuated, the clutch is turned off to stop the compressor, and an intermediate pressure switch that operates at a pressure lower than the operation pressure of the high pressure switch is provided on the high pressure side of the refrigerant circuit. When the pressure switch is operated, the operation of the compressor is stopped for a predetermined time. Therefore, the intermediate pressure switch stops the operation of the compressor for a predetermined time before the high pressure switch is operated, thereby preventing the compressor from being stopped for a long time by the high pressure switch and preventing the air conditioning feeling from being deteriorated. Is what you do.

A pressure switch for a refrigeration cycle disclosed in Japanese Patent Application Laid-Open No. 61-213565 is a refrigeration cycle having a heat pump function for heating by reversing the flow of the refrigerant in the refrigeration cycle. Is calculated to derive the refrigerant pressure of the refrigeration cycle, and when the refrigerant pressure is smaller than the saturated vapor pressure and the difference is equal to or more than a predetermined value, the operation of the compressor is stopped. Therefore, the pressure switch determines that the refrigerant gas is insufficient when the refrigerant pressure of the refrigeration cycle is smaller than the saturated vapor pressure of the refrigerant that changes according to the outside temperature, and when the difference becomes a certain value or more. Then, the operation of the compressor is stopped.

[0004]

However, the intermediate pressure switch disclosed in Japanese Patent Application Laid-Open No. 5-50843 operates at a pressure lower than the operating pressure of the high pressure switch. There is a problem that the drop cannot be detected.

A pressure switch disclosed in Japanese Patent Application Laid-Open No. 61-213565 detects a shortage of refrigerant when the detected pressure is lower than a saturated vapor pressure by a predetermined value, and stops the operation of the compressor. Therefore, in a cycle using carbon dioxide as a refrigerant, it is effective when the outside air temperature is below the critical point of carbon dioxide (approximately 31.1 ° C.), but is meaningless in the region exceeding the critical point. Has the disadvantage of becoming

Further, in the present invention, since carbon dioxide is used as the refrigerant of the refrigeration cycle, the high pressure becomes extremely high, so that it becomes necessary to cope with abnormalities in the high pressure.

Accordingly, an object of the present invention is to provide a refrigeration cycle safety device that can protect the refrigeration cycle from refrigerant leakage and high pressure in a refrigeration cycle using carbon dioxide as a refrigerant.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a compressor that uses carbon dioxide as a refrigerant and compresses the refrigerant, a radiator that lowers the temperature of the compressed refrigerant, and a refrigerant that flows out of the radiator. An internal heat exchanger including a first heat exchanger passing therethrough and a second heat exchanger through which refrigerant sucked into the compressor passes; and an expansion valve for adiabatically expanding the refrigerant flowing out of the first heat exchanger And an evaporator for evaporating the refrigerant expanded by the expansion valve, and an accumulator connected to the second heat exchanger while accumulating the refrigerant flowing out of the evaporator and performing gas-liquid separation, A high pressure line from the discharge side of the compressor to the inflow side of the expansion valve, and a low pressure line from the outflow side of the expansion valve to the suction side of the compressor. In the freezing cycle, a pressure detection sensor provided in the high-pressure line and detecting a pressure of the refrigerant, and at the time of starting the refrigeration cycle, a detection value of the pressure detection sensor is estimated from a balance pressure at the time of stopping the refrigeration cycle. Starting pressure determining means for determining whether the pressure is equal to or less than a predetermined pressure value, and when the detected value is determined to be equal to or less than a predetermined pressure value by the starting pressure determining means, And a start-up safety control means for stopping the operation.

According to the present invention, when the refrigeration cycle is started, the detected value of the pressure detection sensor is a predetermined pressure value estimated from the balance pressure at the time of stopping the refrigerant cycle, for example, a value lower than the balance pressure by a predetermined value. In the following cases, it is determined that the refrigerant is leaking, and the operation of the compressor is stopped.Therefore, it is necessary to prevent problems such as idle operation of the compressor, promotion of refrigerant leakage, and problems caused by these. Can be done.

Further, the present invention provides a pressure fluctuation value calculating means for calculating a pressure fluctuation value from a value of the pressure detection sensor during operation of the refrigeration cycle, and a fluctuation value calculated by the pressure fluctuation value calculating means. Pressure change determining means for determining whether or not the pressure has dropped sharply, and operating safety control means for stopping the operation of the compressor when the pressure change determining means determines that the pressure has dropped sharply. And that

[0011] Thus, when it is determined that the high pressure is rapidly reduced during the normal operation of the refrigeration cycle, it is determined that a refrigerant leak has occurred, and the operation of the compressor can be stopped. The refrigeration cycle can be protected from refrigerant leakage.

Further, the present invention provides an elapsed time determining means for determining whether a predetermined time has elapsed after the compressor is stopped by the operating safety control means, and a predetermined time elapsed by the elapsed time determining means. When it is determined that the detected value is greater than or equal to a predetermined threshold, the pressure determination unit determines whether the detection value of the pressure detection sensor is greater than or equal to a predetermined threshold. A stop continuation control unit that restarts the operation of the compressor when it is determined to be present, and continues the stop of the compressor when it is determined that the detection value is smaller than a predetermined threshold. It is in.

Thus, even if a predetermined time has elapsed after the compressor was stopped by the above-mentioned safety control means during operation,
If the detected pressure does not become equal to or higher than the predetermined threshold value, it is determined that the refrigerant leakage is reliable, and the operation of the compressor is stopped. When the detected pressure returns to or above the predetermined threshold, it is determined that the pressure has become below the predetermined threshold due to short-term pressure fluctuation due to some factor, and the operation of the compressor is restarted.

Further, the present invention provides an outside air temperature detecting means for detecting an outside air temperature, an outside air temperature judging means for judging whether or not the outside air temperature is equal to or higher than a critical point of the refrigerant.
When the outside air temperature determining means determines that the outside air temperature is lower than the critical point of the refrigerant, a first operation is performed to calculate a saturation pressure of the refrigerant from the outside air temperature, and the calculated saturation pressure is used as the predetermined threshold. Threshold setting means, and second threshold setting means for calculating and setting the predetermined threshold based on the outside air temperature when the outside air temperature is judged to be equal to or higher than the critical point of the refrigerant by the outside air temperature judgment means. And that

According to the present invention, when the outside air temperature is lower than the critical point of the refrigerant and carbon dioxide (about 31.1 ° C.), the saturation pressure of the refrigerant is calculated from the outside air temperature and this saturation pressure is calculated. When the outside air temperature is equal to or higher than the critical point of carbon dioxide, the predetermined pressure calculated from the outside air temperature is used as the predetermined threshold. The set threshold can be set. As a result, useless stoppage of the compressor can be suppressed, and a smooth operation of the refrigeration cycle can be obtained.

Further, the present invention is characterized in that the high-pressure line is provided with a high-pressure control valve for communicating the high-pressure line and the low-pressure line at a first high pressure.

Further, according to the present invention, the high-pressure line
A high pressure side leaking means is provided for communicating the high pressure line with the atmosphere at a second high pressure higher than the first high pressure. It is desirable that the high-pressure side leak means is a rupture disk mechanism that ruptures at the second high pressure.

Still further, the present invention is characterized in that the low-pressure line is provided with a low-pressure side leak means for communicating the low-pressure line with the atmosphere at a pressure higher than a balance pressure when the refrigeration cycle is stopped by a predetermined value. . Preferably, the low pressure side leak means is a rupture disk mechanism that ruptures at a pressure higher than the balance pressure by a predetermined value.

[0019]

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

A refrigeration cycle 1 shown in FIG. 1 uses carbon dioxide as a refrigerant and is mounted on an air conditioner for a vehicle. The compressor 2 is driven by an engine 4 as a drive source via an electromagnetic clutch 3. A radiator 5 connected to the discharge side of the compressor 2, a first heat exchanger 6 connected to the outlet side of the radiator 5, and a second heat connected to the suction side of the compressor 2. An internal heat exchanger 8 comprising an exchanger 7, an expansion valve 9 connected to the outlet side of the first heat exchanger 6, an evaporator 11 connected to the outlet side of the expansion valve 9, and an evaporator 11 And an accumulator 12 connected between the second heat exchanger 7. The high pressure line 13 extends from the discharge side of the compressor 2 to the inflow side of the expansion valve 9, and the low pressure line 14 extends from the outflow side of the expansion valve 9 to the suction side of the compressor 2.

The high-pressure line 13 of the refrigeration cycle 1 is provided in parallel with the expansion valve 9 and communicates with the high-pressure line 13 and the low-pressure line 14 at a predetermined pressure (for example, about 11 MPa to 12 MPa). 10, a high-pressure side rupture disk mechanism 15 having a rupture disk that ruptures at a pressure greater than the predetermined pressure (for example, 14 MPa), and a pressure detection sensor 17 for detecting the pressure of the high-pressure line. The low pressure line 14 has a pressure (for example, a predetermined value larger than the balance pressure (about 5 to 6 MPa) of the high pressure line 13 and the low pressure line 14 when the compressor 2 is stopped).
A low pressure side rupture disk mechanism 16 having a rupture disk that ruptures at 8 MPa) is provided. The high-pressure side rupturable disc mechanism 15 and the low-pressure side rupture disc mechanism 16 are configured to release the refrigerant into the atmosphere when the rupture disc ruptures.

In the refrigeration cycle 1 having the above-described structure, the compressor 2
Operates, and the gas-phase refrigerant is compressed to the supercritical region. The high-pressure and high-temperature gas-phase refrigerant is radiated and cooled by the radiator 5, and further cooled by the internal heat exchanger 8.
The refrigerant is cooled by exchanging heat with the low-pressure low-temperature gas-phase refrigerant sucked into the chamber, and the pressure is reduced to the gas-liquid mixing region by the expansion valve 9.
The refrigerant in the gas-liquid mixed state is supplied to the evaporator 11
At this time, the air passing through the evaporator 11 is deprived of heat and evaporates to become a gas-phase refrigerant. The accumulator 12 adjusts the amount of the refrigerant circulating in the refrigeration cycle 1 and separates and stores the liquid-phase refrigerant that could not be evaporated by the evaporator 11 from the gas-phase refrigerant. The gas-phase refrigerant separated by gas and liquid in the accumulator 12 exchanges heat with a high-temperature and high-pressure refrigerant in the internal heat exchanger 8, is superheated, and is sucked into the compressor 2. Thereby, the refrigeration cycle 1 in which heat is sucked by the evaporator 11 and radiated by the radiator 5 is configured.

A control unit (C / U) 21 is provided for controlling the refrigeration cycle 1. The control unit 21 is a device known per se including at least a central processing unit (CPU) (not shown), a read-only memory (ROM), a random access memory (RAM), an input / output port (I / O), and the like. A detection signal from the pressure detection sensor 17 and a detection signal from the outside air temperature detection sensor 18 are input via a multiplexer (MPX) 19 and an A / D converter 20, and these detection signals are processed according to a predetermined program. After that, it is output as a control signal for controlling the electromagnetic clutch 3.

Hereinafter, an example of the safety control executed by the control unit 21 will be described with reference to flowcharts shown in FIGS. The safety control started from step 100 is periodically started from, for example, a main control routine that is the basis of control of the vehicle air conditioner (air conditioner). In step 110, the detected value Psp from the pressure detection sensor 17 is determined. After the input, in step 120, it is determined whether or not an A / C (air conditioner) operation is being performed. During the A / C operation, it indicates whether the air conditioner is operating or not, and determines whether the compressor 2 is operating. If the air conditioner is operating, the routine proceeds to step 130, where it is determined whether the A / C (air conditioner) is started. In this determination, if it is determined that the air conditioner is to be started, the initial safety control in step 140 and subsequent steps is performed. If not, the safety control during normal operation of the air conditioner is performed via the A connector 18. Move to Note that, in the determination in step 120,
If the air conditioner is not operating, the process returns to the main control routine via step 170.

If it is determined in step 130 that the air conditioner has been started, step 140
Then, it is determined whether or not the detection value Psp of the pressure detection sensor 17 is equal to or lower than the saturation pressure Psao (about 3.7 MPa) at the refrigerant temperature of 0 ° C. In this determination, if the pressure is equal to or lower than the saturation pressure Psao, the routine proceeds to step 160, where the compressor 2 is stopped (the power supply to the electromagnetic clutch 3 is cut off).
To prevent the liquid from returning to the compressor 2.

If it is determined in step 140 that the detected value Psp is larger than the saturation pressure Psao, the flow advances to step 150 to determine whether or not the detected value Psp is equal to or more than a predetermined value α. The predetermined value α is a value α (3 to 4 MPa) lower than the balance pressure (5 to 6 MPa) of the high-pressure line 13 and the low-pressure line 14 when the refrigeration cycle 1 is stopped.
a) is set, and if it is lower than this value α, it is assumed that refrigerant leakage is assumed, and the routine proceeds to step 160, the compressor 2 is stopped, and the routine returns from step 170 to the main control routine. . If the detection value Psp is higher than the value α in the determination in step 160, the process returns from step 170 to the main control routine, and the operation of the compressor 2 is continued.

Then, after the end of the initial safety control, since it is not the time of the initial start of the air conditioner, the process proceeds from the step 130 to the safety control in the normal operation shown in FIG. In the safety control during the normal operation, first, at step 190, a fluctuation value ΔPsp of the detection value Psp at a predetermined time is calculated by the following equation (1).

ΔPsp = Psp (n) −Psp (n−1) (1)

Then, in step 200, the cut pressure Pth, which is the specification value of the low pressure cut, is calculated based on the outside air temperature Ta according to the flowchart shown in FIG.

The outside air temperature Ta input in step 210 is compared with the critical point Tcp of carbon dioxide (about 31.1 ° C.) in step 220, and when it is determined that the temperature is lower than the critical point Tcp, step 230 is performed. Proceed to
The saturation pressure Psa is calculated. This saturation pressure Psa can be obtained from a Mollier diagram of carbon dioxide. And
This saturation pressure Psa is set as the cut pressure Pth in step 240, and the process returns from step 260 to the safety control during normal operation shown in FIG. If it is determined in step 220 that the outside air temperature Ta is equal to or higher than the critical point Tcp, the process proceeds to step 250, where the cut pressure Pth is calculated and set from the outside air temperature Ta based on the function F (Ta). Then, the process returns from step 260 to the safety control during normal operation shown in FIG.

Then, in step 270, it is determined whether or not "1" is set in the timer flag (TIMERFLAG) in step 310 described below. If the process first passes through step 270, "1" is not set, so the process proceeds to step 280 to determine whether or not the fluctuation value ΔPsp calculated in step 190 has largely changed in the direction of decreasing the pressure ( ΔPth ≦ −β?) Is determined.
Thereby, when the variation value ΔPth is smaller than −β,
If it fluctuates greatly in the so-called minus direction, it is determined that there is a risk of refrigerant leakage, and the process proceeds to step 290 to stop the compressor 2, the timer t is started in step 300, and the timer flag (TIMERFLAG) is set to “1”. Set to indicate that the compressor 2 has stopped and the timer t has started.

Then, at step 320, it is determined whether or not the timer t has exceeded a predetermined time Tset. If less than the predetermined time, the process returns from step 350 to the main control routine. Then, the safety control proceeds to step 320 by setting the timer flag to “1”.
Until the timer t becomes equal to or longer than the predetermined time Tset, a route detouring from step 270 to step 320 is followed. If it is determined in step 320 that the predetermined time Tset is equal to or longer than the predetermined time Tset and the predetermined time has elapsed,
Proceeding to step 330, the detected value Psp is set to the cut pressure Pth.
It is determined whether or not the above has been achieved.

In this determination, when the detection value Psp of the pressure detection sensor 17 returns to the cut pressure Pth or more, it is determined that the above-mentioned pressure fluctuation is not a refrigerant leak but a temporary pressure fluctuation, and Proceeding to 340, the operation of the compressor 2 is started, and the routine returns from step 350 to the main control routine. If the cut pressure does not exceed the cut pressure Pth in the determination of step 330,
It is assumed that the refrigerant leak is certain and the stop of the compressor 2 is continued, and the process returns from step 350 to the main control routine.

Thus, it is possible to reliably detect the refrigerant leakage at the time of stoppage and the refrigerant leakage at the time of operation and stop the operation of the refrigeration cycle.

[0035]

As described above, according to the present invention, when the pressure at the time of starting is equal to or lower than the predetermined value, the compressor is stopped, so that the refrigeration cycle is not driven when the refrigerant is insufficient. Therefore, it is possible to prevent spurs of idling of the compressor and leakage of the refrigerant.

During operation of the refrigeration cycle, a fluctuation value of the pressure is calculated. If the fluctuation value is large in the negative direction, it is determined that the refrigerant is leaking, and the compressor is stopped. Can be prevented. Furthermore, it is determined whether or not the fluctuation of the fluctuation value is temporary, and if the fluctuation is temporary, the compressor is restarted, so that a decrease in the air conditioning feeling can be suppressed. Things.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a refrigeration cycle according to the present invention.

FIG. 2 is a flowchart of the safety control according to the present invention, in particular, a flowchart showing an initial safety control.

FIG. 3 is a flowchart of safety control during normal operation according to the present invention.

FIG. 4 is a flowchart illustrating a cut pressure calculation according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refrigeration cycle 2 Compressor 3 Electromagnetic clutch 4 Running engine 5 Radiator 6 First heat exchanger 7 Second heat exchanger 8 Internal heat exchanger 9 Expansion valve 10 Pressure control valve 11 Evaporator 12 Accumulator 13 High pressure line 14 Low pressure Line 15 High pressure side rupture disk mechanism 16 Low pressure side rupture disk mechanism 17 Pressure detection sensor 18 Outside air temperature detection sensor

Claims (8)

[Claims] 1. A compressor that uses carbon dioxide as a refrigerant and compresses the refrigerant, a radiator that lowers the temperature of the compressed refrigerant, a first heat exchanger through which the refrigerant flowing out of the radiator passes, and An internal heat exchanger including a second heat exchanger through which the refrigerant drawn into the compressor passes; an expansion valve that adiabatically expands the refrigerant flowing out of the first heat exchanger; and a refrigerant expanded by the expansion valve. The evaporator is constituted by at least an evaporator to be evaporated and an accumulator connected to the second heat exchanger while accumulating the refrigerant flowing out of the evaporator and performing gas-liquid separation. The inflow of the expansion valve from the discharge side of the compressor A high pressure line from the outlet of the expansion valve to the suction side of the compressor. A pressure detection sensor that detects the pressure of the refrigerant, and at the time of starting the refrigeration cycle, the detection value of the pressure detection sensor is equal to or less than a predetermined pressure value estimated from the balance pressure when the refrigeration cycle is stopped. Start-up pressure determining means for determining whether or not the start-up pressure determining means determines that the detected value is equal to or less than a predetermined pressure value. A safety device for a refrigeration cycle, comprising: a control unit. 2. A pressure fluctuation value calculating means for calculating a pressure fluctuation value from a value of the pressure detection sensor during operation of the refrigeration cycle, and a pressure abruptly increased by the fluctuation value calculated by the pressure fluctuation value calculating means. Pressure change determining means for determining whether or not the pressure has decreased, and operating safety control means for stopping the operation of the compressor when the pressure change determining means determines that the pressure has rapidly decreased. The refrigeration cycle safety device according to claim 1, wherein: 3. A compressor that uses carbon dioxide as a refrigerant and compresses the refrigerant, a radiator that lowers the temperature of the compressed refrigerant, a first heat exchanger through which the refrigerant flowing out of the radiator passes, and An internal heat exchanger including a second heat exchanger through which the refrigerant drawn into the compressor passes; an expansion valve that adiabatically expands the refrigerant flowing out of the first heat exchanger; and a refrigerant expanded by the expansion valve. The evaporator is constituted by at least an evaporator to be evaporated and an accumulator connected to the second heat exchanger while accumulating the refrigerant flowing out of the evaporator and performing gas-liquid separation. The inflow of the expansion valve from the discharge side of the compressor A high pressure line from the outlet of the expansion valve to the suction side of the compressor. A pressure detection sensor that detects a pressure of the refrigerant, a pressure fluctuation value calculation unit that calculates a pressure fluctuation value from a detection value of the pressure detection sensor during operation of the refrigeration cycle, and a pressure fluctuation value calculation. Pressure change determining means for determining whether or not the pressure has rapidly decreased based on the fluctuation value calculated by the means; and when the pressure change determining means determines that the pressure has rapidly decreased, the operation of the compressor is stopped. A safety device for a refrigeration cycle, comprising: an operation safety control means for stopping the operation. 4. An elapsed time determining means for determining whether or not a predetermined time has elapsed after the compressor is stopped by the operating safety control means, and determining that the predetermined time has elapsed by the elapsed time determining means. If the pressure detection sensor determines that the detection value of the pressure sensor is equal to or greater than a predetermined threshold, the pressure determination unit determines that the detection value of the pressure sensor is equal to or greater than a predetermined threshold. And a stop continuation control unit for continuing the stop of the compressor when it is determined that the detected value is smaller than a predetermined threshold value. The refrigeration cycle safety device according to claim 2 or 3. 5. An outside air temperature detecting means for detecting an outside air temperature; an outside air temperature judging means for judging whether said outside air temperature is equal to or higher than a critical point of said refrigerant; When it is determined that the temperature is lower than the critical point of the refrigerant, a saturation pressure of the refrigerant is calculated from the outside air temperature, a first threshold value setting unit that sets the calculated saturation pressure as the predetermined threshold, and the outside air temperature determination unit. And a second threshold value setting unit that calculates and sets the predetermined threshold value based on the outside air temperature when the outside air temperature is determined to be equal to or higher than the critical point of the refrigerant. Item 4. The safety device for a refrigeration cycle according to Item 4. 6. The high pressure line is provided with a high pressure control valve for communicating the high pressure line and the low pressure line at a first high pressure. The refrigeration cycle safety device according to any one of the first to third aspects. 7. The high-pressure line further includes high-pressure side leaking means for communicating the high-pressure line with the atmosphere at a second high pressure higher than the first high pressure. The safety device for a refrigeration cycle according to any one of claims 1 to 6. 8. The low-pressure line includes low-pressure side leaking means for communicating the low-pressure line with the atmosphere at a pressure higher than a balance pressure when the refrigeration cycle is stopped by a predetermined value. The refrigeration cycle safety device according to any one of 1 to 7.