JP5586880B2 - Refrigeration equipment - Google Patents

Description

  The present invention relates to a refrigeration apparatus including an oil return pipe that returns oil captured by an oil separator into a compressor.

In general, a multi-stage (for example, two-stage) compressor that compresses and discharges the sucked refrigerant in multiple stages, an oil separator provided in a high-pressure discharge pipe of the compressor, and oil captured by the oil separator There is known a refrigeration apparatus including an oil return pipe that returns the gas to the compressor (see, for example, Patent Document 1). In this type of refrigeration system, the compressor case is configured to have an intermediate or low pressure, and an electromagnetic return valve is provided in the oil return pipe so that when the amount of oil in the case decreases to the lower limit, this electromagnetic There is a configuration in which oil is returned into the case using a differential pressure between the discharged refrigerant (high pressure) and the inside of the case (intermediate pressure or low pressure) by opening and closing the on-off valve.
JP 2008-144463 A

By the way, the amount of oil discharged from the compressor together with the refrigerant fluctuates in accordance with the operating frequency of the compressor, whereas the amount of oil returning into the case depends on the discharged refrigerant (high pressure) and the inside of the case (intermediate pressure or low pressure). ) And the pressure difference. In particular, in the configuration using CO ₂ (carbon dioxide) refrigerant, the above differential pressure is remarkably larger than that using chlorofluorocarbon (including alternative chlorofluorocarbon). It is difficult to adjust the amount of oil returned to For this reason, it is difficult to balance the amount of oil discharged and the amount of oil returned, and it has been difficult to control the amount of oil in the case.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a refrigeration apparatus that can easily control the amount of oil in a case.

In order to solve the above-described problems, the present invention provides a multistage compressor in which the inside of the case has an intermediate pressure, an oil separator provided in a high-pressure discharge pipe of the compressor, and oil captured by the oil separator. An oil return pipe that returns to the inside of the case, an electric valve provided in the oil return pipe, and the valve opening of the electric valve is enlarged and adjusted when the operating frequency of the compressor increases, and the operation of the compressor A valve opening degree adjusting means for reducing the valve opening degree of the motor-operated valve when the frequency is reduced, and an oil level detecting means for detecting the oil level in the case, and is detected by the oil level detecting means. When the oil level exceeds the upper limit level, a correction coefficient for correcting the valve opening adjusted by the valve opening adjusting means is set to increase stepwise every predetermined time. Open It was corrected to stepwise reduced, when the oil level drops below the lower limit level, the set by stepwise decreasing the correction coefficient for each predetermined time, is adjusted in the valve opening control means It is characterized by comprising valve opening correction means for correcting the valve opening so as to increase stepwise .
According to this configuration, since the valve opening degree adjusting means for adjusting the valve opening degree of the electric valve according to the operating frequency of the compressor is provided, the amount of oil discharged from the compressor and the oil returned into the compressor case The amount can be balanced and the amount of oil in the case can be easily controlled. Further, according to this configuration, since the amount of oil returned into the case can be controlled according to the amount of oil discharged, stable oil return control is possible. Further, according to this configuration, the amount of oil in the case can be controlled without excess or deficiency in order to correct the valve opening of the electric valve adjusted by the valve opening adjustment means in accordance with the oil level in the case. it can.

  The valve opening adjusting means may be configured to adjust the valve opening of the motor-operated valve step by step for each predetermined frequency width. According to this configuration, the frequency of valve opening control of the electric valve can be suppressed, and the durability of the electric valve can be improved.

  The oil return pipe may have a fixed throttle provided in series with the motor-operated valve. According to this configuration, since the differential pressure between the upstream side (primary side) and the downstream side (secondary side) of the motor-operated valve can be reduced by the fixed throttle, even when a refrigerant having a large high and low pressure difference is used. A stable oil return can be realized.

  According to the present invention, since the valve opening degree adjusting means for adjusting the valve opening degree of the electric valve according to the operating frequency of the compressor is provided, the amount of oil discharged from the compressor and the oil returned into the compressor case The amount can be balanced and the amount of oil in the case can be easily controlled.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a circuit configuration diagram showing a refrigerant circuit of the refrigeration apparatus according to the present embodiment.
The refrigeration apparatus 1 includes a refrigeration unit 3 and a plurality of (for example, two) showcase units 5A and 5B. The refrigeration unit 3 and the showcase units 5A and 5B include a liquid refrigerant pipe 7 and a gas. The refrigerant pipes 9 are connected to form a refrigeration cycle. In this refrigeration cycle, a CO ₂ (carbon dioxide) refrigerant having a supercritical pressure on the high pressure side is used. Since the CO ₂ refrigerant has an ozone depletion coefficient of 0 and a global warming coefficient of 1, the load on the environment is small, and it is safe and inexpensive without toxicity and flammability.

The refrigerator unit 3 includes two compressors 11 and 11 arranged in parallel. The compressor 11 is an internal intermediate pressure type rotary two-stage compressor in which the inside of the case 12 has an intermediate pressure. An electric motor part (not shown) in the case 12 and a low-stage compression element driven by the electric motor part. 11A and the high stage compression element 11B are arranged. The low-stage compression element 11A boosts and discharges low-pressure refrigerant sucked into the compressor 11 through the gas refrigerant pipe 9 to an intermediate pressure, and the high-stage compression element 11B is an intermediate pressure compressed by the low-stage compression element 11A. The refrigerant is further pressurized to a high pressure and discharged. The compressor 11 is a variable frequency compressor, and the rotation speed of the low-stage compression element 11A and the high-stage compression element 11B can be adjusted by changing the operating frequency of the electric motor unit.
The case 12 of the compressor 11 includes a low-stage suction port 12A and a low-stage discharge port 12B communicating with the low-stage compression element 11A, and a high-stage suction port 12C and a high-stage side communicating with the high-stage compression element 11B. A discharge port 12D is formed. Low-pressure suction pipes 13 and 13 are connected to the low-stage suction ports 12A and 12A of the compressors 11 and 11, respectively, and these low-pressure suction pipes 13 and 13 merge on the upstream side of the low-stage compression elements 11A and 11A. The gas refrigerant pipe 9 is connected via an accumulator 14. Further, the low pressure suction pipe 13 is provided with a suction pressure sensor 15 and a suction temperature sensor 16 for detecting the suction pressure and the suction temperature of the refrigerant flowing through the low pressure suction pipe 13, respectively.

  Intermediate pressure discharge pipes 17 and 17 are connected to the low-stage discharge ports 12B and 12B, respectively, and the intermediate-pressure discharge pipes 17 and 17 merge at the downstream side of the low-stage compression elements 11A and 11A. 18 is connected to one end. This intermediate cooler 18 cools the intermediate-pressure refrigerant discharged from the low-stage compression element 11A, and an intermediate-pressure suction pipe 19 is connected to the other end of the intermediate cooler 18. The suction pipe 19 is branched into two and then connected to the high-stage suction ports 12C and 12C. Further, the intermediate pressure suction pipe 19 is provided with an intermediate pressure sensor 20 that detects the intermediate pressure of the refrigerant flowing through the intermediate pressure suction pipe 19. In this configuration, the high stage side suction port 12 </ b> C communicates with the high stage compression element 11 </ b> B through the space in the case 12, and the inside of the case 12 is maintained at an intermediate pressure during the operation of the compressor 11.

High-pressure discharge pipes 21 and 21 are connected to the high-stage discharge ports 12D and 12D, respectively, and the high-pressure discharge pipes 21 and 21 merge on the downstream side of the high-stage compression elements 11B and 11B. The liquid refrigerant pipe 7 is connected via a cooler (heat radiator) 23 and a supercooling heat exchanger 24. The high-stage discharge ports 12D and 12D are provided with a discharge pressure sensor 25 and a discharge temperature sensor 26 for detecting the discharge pressure and discharge temperature of the refrigerant discharged from the high-stage compression elements 11B and 11B, respectively. Yes.
The oil separator 22 separates and captures the oil contained in the high-pressure discharged refrigerant discharged from the compressor 11 from the refrigerant. The oil separator 22 is an oil that returns the captured oil to the compressor 11. A return pipe 28 is connected. The oil return pipe 28 is provided with an oil cooler 27 that cools the captured oil. On the downstream side of the oil cooler 27, the oil return pipe 28 is branched into two systems, such as a strainer 29 and a flow rate adjusting valve. It is connected to the case 12 of the compressor 11 via the motor-operated valve 30. Since the inside of the case 12 of the compressor 11 is maintained at the intermediate pressure as described above, the trapped oil is contained in the case 12 due to the differential pressure between the high pressure in the oil separator 22 and the intermediate pressure in the case 12. Returned. Further, the case 12 of the compressor 11 is provided with an oil level sensor (oil level detecting means) 31 for detecting the level of oil held in the case 12.

The oil level sensor 31 is a two-contact type level sensor that can detect an upper limit level and a lower limit level. Although not shown, the oil level sensor 31 includes a sensor case that communicates with the case 12, and the oil level in the sensor case is the compressor level. 11 according to the oil level in the case 12. Also, a float switch is arranged in the sensor case, which includes a float that floats up and down in response to changes in the oil level, and upper and lower contacts that are opened and closed as the height of the float changes. Yes. In this float switch, a magnet is disposed in the float, and upper and lower contacts disposed at different heights are opened and closed by the magnetic force of the magnet.
Specifically, the upper contact is turned on when the oil level in the case 12 exceeds the upper limit level, and the upper contact is turned off when the oil level falls below the upper limit level. The lower contact is turned off when the oil level in the case 12 exceeds the lower limit level, and the lower contact is turned on when the oil level falls below the lower limit level.

The gas cooler 23 cools the high-pressure discharged refrigerant discharged from the compressor 11. In this configuration, the gas cooler 23 is arranged in parallel with the intermediate cooler 18 and the oil cooler 27 described above. The gas cooler 23, the intermediate cooler 18, and the oil cooler 27 are provided adjacent to a cooling fan 32 that blows air toward the gas cooler 23, the intermediate cooler 18, and the oil cooler 27.
The supercooling heat exchanger 24 is cooled by the gas cooler 23 and passes through the high pressure discharge pipe 21 and the liquid refrigerant pipe 7 from the gas cooler 23, and the first expansion valves (first throttle means) 42A included in the showcase units 5A and 5B. The refrigerant heading for 42B is supercooled using the branched refrigerant branched on the outlet side of the gas cooler 23. In the supercooling heat exchanger 24, a branch pipe 33 branched from the high-pressure discharge pipe 21 on the outlet side of the gas cooler 23 is connected to the intermediate pressure suction on the outlet side of the intermediate cooler 18 via the second expansion valve 34. Connected to tube 19. The high-pressure discharge pipe 21 is provided with an inlet temperature sensor 35 and an outlet temperature sensor 36 that detect the temperature of the refrigerant flowing through the high-pressure discharge pipe 21 on the inlet side and the outlet side of the supercooling heat exchanger 24, respectively.

The refrigerator unit 3 includes a main controller 50 that controls the operation of the entire refrigeration apparatus 1. The main controller 50 adjusts the operating frequency of the compressors 11 and 11 according to the refrigeration loads of the showcase units 5A and 5B, and adjusts the refrigerant discharge temperature of the high-stage compression element 11B detected by the discharge temperature sensor 26. Based on this, the opening degree of the second expansion valve 34 is adjusted. The opening degree of the second expansion valve 34 may be adjusted based on the outlet temperature of the branch refrigerant, which is an intermediate pressure of the supercooling heat exchanger 24, the refrigerant inlet / outlet temperature difference of the supercooling heat exchanger 24, and the like. good.
Further, the main control device 50 executes oil return control from the oil separator 22 to each of the compressors 11, 11, and at the time of oil return control, each motor-operated valve 30 is based on the operating frequency of each compressor 11, 11. , 30 valve opening is adjusted. Further, when the oil return control is performed, the valve opening degree is corrected based on the oil level detected by each oil level sensor 31. In this embodiment, the main controller 50 functions as a valve opening adjusting means for adjusting the valve opening of the motor operated valves 30 and 30 according to the operating frequency of the compressors 11 and 11, and according to the oil level. It functions as a valve opening correction means for correcting the valve opening.

On the other hand, the showcase units 5A and 5B are each installed in a store or the like, and are connected in parallel to the liquid refrigerant pipe 7 and the gas refrigerant pipe 9, respectively. Each showcase unit 5A, 5B includes case refrigerant pipes 40A, 40B that connect the liquid refrigerant pipe 7 and the gas refrigerant pipe 9, and the case refrigerant pipes 40A, 40B include strainers 41A, 41B, respectively, Expansion valves (first throttle means) 42A and 42B and case heat exchangers 43A and 43B are provided. The case heat exchangers 43A and 43B are provided with case fans 44A and 44B adjacent to the case heat exchangers 43A and 43B.
The showcase units 5A and 5B include case control devices 45A and 45B that control the operation of each part of the showcase units 5A and 5B. The case control devices 45A and 45B can communicate with the main control device 50. Composed. Case controller 45A, 45B adjusts the opening degree of 1st expansion valve 42A, 42B based on the inlet-outlet temperature difference (superheat degree) of case heat exchanger 43A, 43B, respectively.

Next, the operation during the oil return control described above will be described. FIG. 2 is a flowchart showing the operation of oil return control.
When the cooling operation of the refrigeration apparatus 1 is started, the main controller 50 acquires the initial valve opening degrees of the motor operated valves 30 and 30 (step S1). This initial valve opening is a valve opening that is set when the refrigeration apparatus 1 (that is, the compressors 11 and 11) is started. In this embodiment, the valve opening is set so that the motor-operated valves 30 and 30 are substantially closed. Degree (for example, 30 pulses).
Subsequently, main controller 50 adjusts the valve openings of motor-operated valves 30 and 30 according to the operating frequencies of compressors 11 and 11, respectively (step S2). The valve opening is calculated from the operating frequency of the compressors 11 and 11 and a correction coefficient A that is appropriately changed according to the oil level. In this embodiment, in order to suppress the valve opening degree of the motor operated valves 30 and 30 from being linearly adjusted following the change in the operation frequency, a dead band having a predetermined frequency width (for example, 5 Hz) is provided, and the operation is performed. It is desirable to adjust the valve opening stepwise each time the frequency changes a predetermined frequency width.

Subsequently, main controller 50 determines whether or not a first predetermined time (for example, 2 minutes) has elapsed after refrigeration apparatus 1 is started (step S3). The first predetermined time is set to a time sufficient for the compressor 11 to be stably driven after the refrigeration apparatus 1 is started, for example. In this determination, when the first predetermined time has not elapsed after the refrigeration apparatus 1 is started (step S3; No), the main controller 50 sets the correction coefficient A to A = 1.5. (Step S4), and the valve opening is adjusted using this value. Thus, immediately after the start of the refrigeration apparatus 1, the valve opening degree of the motor-operated valves 30, 30 can be expanded, and a necessary amount of oil can be returned to the compressors 11, 11. Insufficiency can be prevented.
On the other hand, if the first predetermined time has elapsed after the refrigeration apparatus 1 is started (step S3; Yes), the main controller 50 sets the correction coefficient A to A = 1.0 (step S5). The valve opening is adjusted using this value. Thereby, after the refrigeration apparatus 1 has elapsed for a predetermined time from the start, the valve opening degree of the motor-operated valves 30 and 30 is adjusted in accordance with the operating frequency of the compressors 11 and 11, so that the discharge is performed from the compressors 11 and 11. Balance between the amount of oil and the amount of oil returned into the cases 12 and 12 of the compressors 11 and 11 can be achieved. For this reason, the oil amount in the cases 12 and 12 of the compressors 11 and 11 is controlled appropriately.

Subsequently, main controller 50 determines whether or not a second predetermined time (for example, 3 minutes) has elapsed since the previous step was completed (step S6), and this second predetermined time has elapsed. If not (step S6; No), it waits until the said time passes. For example, when the correction coefficient A is changed, the second predetermined time is set as a time necessary for the change to be reflected in the oil return amount. When the second predetermined time has elapsed (step S6; Yes), main controller 50 determines whether or not the lower contact of the float switch is off (step S7).
In this determination, if the lower contact of the float switch is not off (step S7; No), that is, if the oil level is below the lower limit level, it is determined that the amount of oil in the case is too low. Shifting to S12, the valve opening degree of the motor-operated valve 30 is corrected.
If the lower contact of the float switch is off (step S7; Yes), that is, if the oil level is above the lower limit level, the main controller 50 determines whether the upper contact of the float switch is off. It is determined whether or not (step S8).

In the determination of step S8, if the upper contact of the float switch is not off (step S8; No), that is, if the oil level exceeds the upper limit level, it is determined that the amount of oil in the case 12 is excessive. The process proceeds to step S15 to correct the valve opening of the electric valve 30.
When the upper contact of the float switch is off (step S8; Yes), that is, when the oil level is below the upper limit level, the main controller 50 determines whether the compressors 11 and 11 are stopped. It is determined whether or not (step S9). In this determination, when at least one of the compressors 11 is not stopped (step S9; No), the correction coefficient A regarding the valve opening degree of the motor-operated valve 30 of the compressor 11 is set to A = 1.0 ( In step S10), the process is returned to step S2, and these processes are repeatedly executed. Moreover, when all the compressors 11 and 11 have stopped (step S9; Yes), the valve opening degree of the motor operated valves 30 and 30 is set to an initial valve opening degree, and a process is complete | finished.

As described above, when the lower contact of the float switch is not off (step S7; No), it is determined that the amount of oil in the case 12 is too small, so that the valve opening of the electric valve 30 is corrected to be increased. To do. Specifically, main controller 50 sets correction coefficient A related to the valve opening degree of motor-operated valve 30 of compressor 11 by a predetermined amount (for example, 5%) (step S12). Thereby, the valve opening degree of the motor-operated valve 30 adjusted according to the operating frequency of the compressor 11 is corrected based on the oil amount in the case 12. For this reason, the amount of oil returned into the case 12 can be increased, and the state where the amount of oil in the case 12 is too small can be eliminated early.
Subsequently, main controller 50 determines whether or not correction coefficient A is larger than a predetermined upper threshold (for example, 2.0) (step S13). This upper limit threshold value defines an upper limit value for increasing the correction coefficient A. When the correction coefficient A is smaller than the upper limit threshold value (step S13; No), the process returns to step S6 to perform these processes. Run repeatedly.
On the other hand, when the correction coefficient A reaches or exceeds the upper limit threshold (step S13; Yes), the oil in the case 12 is increased even if the valve opening of the motor-operated valve 30 is increased until the correction coefficient A reaches the upper limit threshold. Since it is determined that the state where the amount is too small is not resolved, the main control device 50 indicates an oil control abnormality, for example, because the amount of oil circulating in the refrigeration cycle is small or the float switch is broken. An alarm is issued (step S14), and the process is terminated.

Further, as described above, when the upper contact of the float switch is not off (step S8; No), it is determined that the amount of oil in the case 12 is excessive, so that the valve opening degree of the electric valve 30 is reduced. To correct. Specifically, main controller 50 sets a correction coefficient A related to the valve opening degree of motor-operated valve 30 of compressor 11 by a predetermined amount (for example, 5%) that is reduced (step S15). Thereby, the valve opening degree of the motor-operated valve 30 adjusted according to the operating frequency of the compressor 11 is corrected so as to be reduced based on the amount of oil in the case 12. For this reason, the amount of oil returned into the case 12 can be reduced, and the state where the amount of oil in the case 12 is excessive can be eliminated at an early stage.
Subsequently, main controller 50 determines whether or not correction coefficient A is equal to or less than a predetermined lower threshold (for example, 0.3) (step S16). This lower limit threshold value defines a lower limit value for decreasing the correction coefficient A. When the correction coefficient A is larger than the lower limit threshold value (step S16; No), the process returns to step S6 to perform these processes. Run repeatedly.
On the other hand, when the correction coefficient A reaches the lower limit threshold value or less (step S16; Yes), the oil in the case 12 is reduced even if the valve opening degree of the electric valve 30 is reduced until the correction coefficient A becomes the lower limit threshold value. Since it is determined that the excessive amount is not resolved, the main controller 50 issues an alarm indicating an oil control abnormality, for example, assuming that the float switch has failed (step S14) and ends the process. To do.

  As described above, according to the present embodiment, the two-stage compressor 11 in which the inside of the case 12 has an intermediate pressure, the oil separator 22 provided in the high-pressure discharge pipe 21 of the compressor 11, and the oil An oil return pipe 28 that returns the oil captured by the separator 22 into the case 12, a motor-operated valve 30 provided in the oil return pipe 28, and the valve opening degree of the motor-operated valve 30 according to the operating frequency of the compressor 11. Since the main control device 50 as a valve opening adjusting means to adjust is provided, it is possible to balance the amount of oil discharged from the compressor 11 and the amount of oil returned into the case 12 of the compressor 11, The amount of oil in the case 12 can be easily controlled.

  Further, according to the present embodiment, the main controller 50 increases the valve opening degree of the motor-operated valve 30 when the operating frequency of the compressor 11 increases, and when the operating frequency of the compressor 11 decreases. Since the valve opening degree of the motor-operated valve 30 is reduced, the amount of oil returned into the case 12 can be controlled in accordance with the amount of oil discharged from the compressor 11, so that stable oil return control is possible. .

  Further, according to the present embodiment, the main controller 50 adjusts the valve opening of the motor-operated valve 30 step by step for each predetermined frequency width. It is possible to prevent linear adjustment following the change in the operating frequency, and to suppress the frequency of valve opening control of the motor-operated valve 30.

  Further, according to the present embodiment, the oil level sensor 31 that detects the oil level in the case 12 is provided, and the main control device 50, when the oil level detected by the oil level sensor 31 exceeds the upper limit level, Correction is made to reduce the valve opening degree of the motor-operated valve 30 adjusted according to the operating frequency of the compressor 11, and when the oil level falls below the lower limit level, correction is made to increase the valve opening degree. Therefore, the state where the amount of oil in the case 12 is too small or excessive can be quickly eliminated, and the amount of oil in the case 12 can be controlled without excess or deficiency.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to this, A various change implementation is possible. For example, as shown in FIG. 3, the oil return pipe 28 may have a configuration in which a capillary tube (fixed throttle) 38 is provided in series with the motor-operated valve 30. According to this configuration, since the pressure difference between the primary side (inlet side) and the secondary side (outlet side) of the motor-operated valve 30 can be reduced by reducing the pressure in the capillary tube 38, the CO ₂ (carbon dioxide) Even when such a refrigerant with a large difference in pressure is used, stable oil return can be realized.
In this case, in particular, it is more preferable to provide the capillary tube 38 on the primary side (inlet side) of the motor-operated valve 30 because the controllability of the motor-operated valve 30 is improved. Needless to say, the capillary tube 38 may be provided on the secondary side (outlet side) of the motor-operated valve 30.
In the present embodiment, a compressor that can change the operating frequency by an inverter or the like is employed. However, the present invention is not limited to this, and a fixed frequency compressor may be used.
In the present embodiment, the predetermined frequency band is set as a dead band, and the valve opening degree of the motor-operated valve 30 is controlled stepwise. However, the present invention is not limited to this, and the valve opening degree of the motor-operated valve 30 is compressed. It is good also as a structure controlled linearly according to the operating frequency of the machine 11.

It is a circuit block diagram which shows the refrigerant circuit of the freezing apparatus which concerns on this embodiment. It is a flowchart which shows the operation | movement of oil return control. It is a circuit block diagram which shows the refrigerant circuit of the freezing apparatus concerning a modification.

DESCRIPTION OF SYMBOLS 1 Refrigeration apparatus 3 Refrigerator unit 5A, 5B Showcase unit 11 Compressor 12 Case 21 High pressure discharge pipe 22 Oil separator 23 Gas cooler 27 Oil cooler 28 Oil return pipe 30 Motor operated valve 31 Oil level sensor (oil level detection means)
38 Capillary tube (fixed throttle)
50 Main controller (valve opening adjusting means, valve opening correcting means)
A Correction factor

Claims (3)

A multistage compressor in which the inside of the case has an intermediate pressure, an oil separator provided in a high-pressure discharge pipe of the compressor, an oil return pipe for returning the oil captured by the oil separator into the case, and the oil return A motor-operated valve provided on a pipe, and when the operating frequency of the compressor increases, the valve opening of the motor-operated valve is enlarged and adjusted when the operating frequency of the compressor decreases. A valve opening adjusting means for reducing the opening and an oil level detecting means for detecting the oil level in the case;
When the oil level detected by the oil level detecting means exceeds the upper limit level, a correction coefficient for correcting the valve opening adjusted by the valve opening adjusting means is increased stepwise every predetermined time. Is set, and the valve opening is corrected to be reduced stepwise, and when the oil level falls below the lower limit level , the correction coefficient is set to be reduced step by step every predetermined time, A refrigeration apparatus comprising valve opening correction means for correcting the valve opening adjusted by the valve opening adjustment means so as to increase stepwise .   The refrigeration apparatus according to claim 1, wherein the valve opening adjustment means adjusts the valve opening of the motor-operated valve step by step for each predetermined frequency width.   The refrigeration apparatus according to claim 1 or 2, wherein the oil return pipe is provided with a fixed throttle in series with the motor-operated valve.

Images