JP2017138034A - Refrigerating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigerating device capable of improving operation reliability.SOLUTION: A refrigerating device includes: a compressor in which a refrigerant is sucked from a low stage suction port through an inlet of the refrigerating device and which discharges the refrigerant from a high stage discharge port by performing a multi-stage compression; an oil separator for separating an oil from the discharge refrigerant from the high stage discharge port; an oil cooler for cooling the oil separated by the oil separator; an oil return circuit for returning the oil cooled by the oil cooler to the compressor; and a control part for increasing a circulation amount of the oil flowing in the oil return circuit, when it determines that the oil circulation amount in the oil return circuit is small, based on predetermined temperature information.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a refrigeration apparatus including an oil return circuit that returns oil separated by an oil separator to the inside of at least one compressor.

  Conventionally, this kind of refrigeration apparatus is described in Patent Document 1, for example. This refrigeration system includes 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 cooler that cools oil captured by the oil separator, and an oil cooler. An oil return pipe for returning the cooled oil into the case, an electric valve provided in the oil return pipe, a valve opening degree adjusting means for adjusting the valve opening degree of the electric valve according to the operating frequency of the compressor, It has.

JP 2011-7351 A

  In the conventional refrigeration system, the amount of oil circulation returned from the oil separator to the compressor via the oil cooler decreases when the load is stable depending on the operating conditions. As a result, the temperature of the compressor and oil becomes too high, and there is a problem that the operation reliability of the refrigeration apparatus is lowered.

  Therefore, an object of the present invention is to provide a refrigeration apparatus capable of improving operation reliability.

  One aspect of the present invention is a refrigeration apparatus, in which a refrigerant is sucked from a low-stage suction port through an inlet of the refrigeration apparatus, performs a multi-stage compression, and discharges the refrigerant from a high-stage discharge port; An oil separator that separates oil from refrigerant discharged from the stage discharge port, an oil cooler that cools the oil separated by the oil separator, and an oil return circuit that returns the oil cooled by the oil cooler to the compressor; A control unit that increases the amount of oil circulation flowing in the oil return circuit when it is considered that the amount of oil circulation in the oil return circuit is small based on predetermined temperature information.

  In another aspect, the refrigeration apparatus includes a compressor that compresses the refrigerant sucked from the low-stage suction port through the inlet of the refrigeration apparatus and discharges the refrigerant from the low-stage discharge port. An intercooler that cools the discharged refrigerant, and the compressor compresses the sucked refrigerant and discharges it from the high stage discharge port when the refrigerant cooled by the intercooler is sucked from the high stage suction port. The refrigeration apparatus further includes an oil separator that separates oil from refrigerant discharged from the high-stage discharge port, an oil cooler that cools oil separated by the oil separator, and oil that is cooled by the oil cooler as the compressor And an oil return circuit for returning the oil to the oil return circuit when the temperature of the refrigerant discharged from the low-stage discharge port is equal to or higher than a predetermined temperature.

  According to each said aspect, the refrigerating device which can improve driving | operation reliability can be provided.

It is a figure which shows the structure of the freezing apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the principal part (1st example) of the freezing apparatus of FIG. It is a flowchart which shows the first half part of the 1st example of the flow control by the control part of FIG. It is a flowchart which shows the second half part of the 1st example of the flow control by the control part of FIG. It is a figure which shows the time change of the compressor temperature by the flow control of FIG. 3A and FIG. 3B. It is a block diagram which shows the principal part (2nd example) of the freezing apparatus of FIG. It is a flowchart which shows the first half part of the 2nd example of the flow control by the control part of FIG. It is a flowchart which shows the second half part of the 2nd example of the flow control by the control part of FIG. FIG. 2 is a ph diagram of the refrigeration apparatus in FIG. 1.

<< 1. Embodiment >>
Hereinafter, with reference to the said drawings, the refrigeration apparatus A which concerns on one Embodiment is explained in full detail.

<< 1-1. Schematic configuration of refrigeration apparatus A >>
In FIG. 1, the refrigeration apparatus A is installed outside a store (for example, a rooftop) such as a convenience store. In addition, the refrigeration apparatus A is connected to a showcase (not shown) installed in the store using the gas refrigerant pipe P1 and the liquid refrigerant pipe P8 to constitute a refrigeration cycle, and a product group displayed in the showcase Freeze and refrigerate. In this refrigeration cycle, CO ₂ is used as a refrigerant.

  The refrigeration apparatus A generally includes, for example, two compressors 1a and 1b, an intercooler 2, a fan 3, an oil separator 4, a gas cooler (heat radiator) 5, a tank 6, and a split heat exchanger. 7, an oil return circuit 8, an oil cooler 9, and motor-operated valves 10 a and 10 b.

The compressors 1a and 1b are arranged in parallel in the refrigeration cycle.
Low-stage compression elements 12a and 12b and high-stage compression elements 13a and 13b are provided inside the cases 11a and 11b of the compressors 1a and 1b. Each compression element 12a, 13a rotates synchronously with the rotation of a motor (not shown) arranged inside the case 11a. Similarly, the compression elements 12b and 13b also rotate in synchronization with a motor (not shown) in the case 11b. By this rotation, the low-stage compression elements 12a and 12b boost the low-pressure refrigerant sucked from the low-stage suction ports 14a and 14b of the compressors 1a and 1b from the inlet Pin of the refrigeration apparatus A through the gas refrigerant pipe P1 to the intermediate pressure. To do. The low-stage compression elements 12a and 12b discharge the intermediate-pressure refrigerant from the low-stage discharge ports 15a and 15b of the compressors 1a and 1b.

Further, the intermediate pressure refrigerant compressed by the low-stage compression elements 12a and 12b is sucked into the high-stage suction ports 16a and 16b of the high-stage compression elements 13a and 13b. The high-stage compression elements 13a and 13b boost the suction refrigerant to a higher pressure and discharge it from the high-stage discharge ports 17a and 17b.
As described above, in the present embodiment, the compressors 1a and 1b compress the refrigerant in two stages.

  The compressors 1a and 1b change the operating frequency of the motor under the control of the control unit 20 described later. By this control, the rotational speeds of the low-stage compression elements 12a and 12b and the high-stage compression elements 13a and 13b can be adjusted.

  Intermediate pressure discharge pipes P3 and P4 are connected to the low-stage discharge ports 15a and 15b. The intermediate pressure discharge pipes P3 and P4 are connected to the intercooler 2 after joining at the downstream side of the low stage discharge ports 15a and 15b. A fan 3 is disposed near the intercooler 2. The intercooler 2 cools the refrigerant discharged from the low-stage compression elements 12 a and 12 b by the air flow from the fan 3. The intercooler 2 discharges the cooled refrigerant from the discharge port. An intermediate pressure suction pipe P5 is connected to the output port. The intermediate pressure suction pipe P5 is bifurcated immediately upstream of the high stage suction ports 16a and 16b, and then connected to the high stage suction ports 16a and 16b. The high-stage compression elements 13a and 13b suck the intermediate-pressure refrigerant from the high-stage suction ports 16a and 16b, further increase the pressure to a high pressure, and discharge the refrigerant from the high-stage discharge ports 17a and 17b.

  Further, high-pressure discharge pipes P6 and P7 are connected to the high stage discharge ports 17a and 17b. The high pressure discharge pipes P6 and P7 are joined to the oil separator 4 after joining at the downstream side of the high stage discharge ports 17a and 17b, and connected to the liquid refrigerant pipe P8 through the gas cooler 5, the tank 6 and the split heat exchanger 7. Is done.

  The oil separator 4 separates and captures the oil contained in the refrigerant discharged from the high-stage discharge ports 17a and 17b from the refrigerant. The oil separator 4 is further connected to an oil return circuit 8 that returns the captured oil to the compressors 1a and 1b. In FIG. 1, the return circuit 8 is indicated by a thick dotted line. An oil cooler 9 is provided immediately downstream of the oil separator 4 in the oil return circuit 8. The oil cooler 9 cools the captured oil. In the present embodiment, the oil cooler 9 is realized by using a part of the intercooler 2, cools the oil sucked from the suction port using the air flow from the fan 3, and discharges the oil from the discharge port. The oil return circuit 8 is branched into two systems on the downstream side of the oil cooler 9, and is connected to the cases 11a and 11b of the compressors 1a and 1b through the electric valves 10a and 10b for flow rate adjustment.

  The discharge port of the oil separator 4 is also connected to the suction port of the gas cooler 5. The refrigerant from which the oil has been separated is discharged from the discharge port of the oil separator 4 toward the suction port of the gas cooler 5. The gas cooler 5 cools the refrigerant sucked from the suction port by the air flow from the fan 3 disposed close to the gas cooler 5 and discharges the cooled refrigerant toward the tank 6 from its discharge port.

  The tank 6 has a predetermined volume space. The refrigerant discharged from the gas cooler 5 is decompressed and cooled by the decompression electric valve 61 and is sucked into the internal space from the upper part of the tank 6. From the lower part of the tank 6, the liquid refrigerant is discharged toward the second flow path 72 of the split heat exchanger 7. A gas refrigerant is discharged from the upper part of the tank 6 toward the first flow path 71 of the split heat exchanger 7 through the gas return motor operated valve 62.

  In the split heat exchanger 7, the refrigerant discharged from the lower part of the tank 6 passes through the second flow path 72, and the refrigerant discharged from the upper part of the tank 6 and a part of the refrigerant discharged from the second flow path 72 are the first flow path. Pass through 71. As a result, the refrigerant passing through the second flow path 72 is supercooled. Most of the subcooled refrigerant is discharged from the outlet Pout of the refrigeration apparatus A toward the showcase (not shown) through the liquid refrigerant pipe P8. It is returned to the first flow path 71 via the valve 63. Moreover, the refrigerant | coolant which passed the 1st flow path 71 is suck | inhaled from the high stage suction inlets 16a and 16b of the high stage compression elements 13a and 13b via the intermediate pressure suction pipe P5.

<< 1-2. Various sensors in refrigeration equipment A >>
Next, although various temperature sensors and pressure sensors are provided in the refrigeration apparatus A, the following is important in the flow rate control of the return circuit 8 according to the present embodiment.

  A low-pressure sensor Se1 and a low-stage suction temperature sensor Se2 are provided in a section from the inlet Pin to the low-stage suction ports 14a and 14b in the gas refrigerant pipe P1. The low pressure sensor Se1 and the low stage suction temperature sensor Se2 detect the suction pressure and the suction temperature of the refrigerant flowing from the inlet Pin toward the low stage suction ports 14a and 14b.

  In addition, an outside air temperature sensor Se3 is provided on the outer peripheral surface of the casing 51 that houses the fan 3 and the gas cooler 5. The outside air temperature sensor Se3 is a thermistor, for example, and detects the ambient temperature of the refrigeration apparatus A as the outside air temperature.

  An intermediate pressure sensor Se4 is provided in the intermediate pressure suction pipe P5. The intermediate pressure sensor Se4 detects the intermediate pressure of the refrigerant flowing through the intermediate pressure suction pipe P5.

<< 1-3. Control unit of refrigeration apparatus A >>
The detection results of the sensors are output to the control unit 20 including a microcomputer. Based on the detection results of the various sensors, the control unit 20 operates the operating frequencies of the motors (not shown) of the compressors 1a and 1b, the opening degrees of the motor-operated valves 10a, 10b, and 61 to 63, the air volume of the fan 3, and the show. The opening degree of the electric expansion valve of the case (not shown) is controlled, and thereby the inside of the showcase is set to the target temperature. Since the temperature control of the showcase is sufficient with known technology, the description thereof is omitted.

<< 1-4. Details of technical issues >>
It was found that when a conventional refrigeration system was operated under certain conditions, the compressor temperature exceeded the reference value defined in the calorimeter test. Specifically, in the calorimeter test, for example, the discharge temperature of the low-stage discharge port 15a and others (hereinafter referred to as low-stage discharge temperature), the compressor case temperature (hereinafter referred to as case temperature), and the compressor motor A reference value is defined for the coil temperature and the like provided. However, if the compressor is operated continuously for a long time (provided that the load is stable) under the conditions that the outside air temperature is high, the evaporation temperature on the showcase side is low, and the refrigerant superheat degree at the inlet of the refrigeration system is large It was found that at least one of the stage discharge temperature etc. exceeded the reference value. The reason is considered as follows.

  Although the conventional refrigeration system is operating under the above-mentioned severe conditions, when the load is stable, the amount of oil taken out from the compressor is reduced. Further, in the refrigeration apparatus of Patent Document 1, when the load is stable, the opening degree of the electric valve for adjusting the flow rate provided in the return pipe becomes small. Due to the above factors, the amount of oil cooled by the oil cooler (that is, the amount of oil circulation) decreases, and as a result, the low-stage discharge temperature and the like are considered to be too high. Such a problem becomes more apparent in a compressor (so-called low oil discharge type compressor) that originally has a small amount of oil discharged during operation.

  In addition, when the opening / closing frequency of the showcase door is high, when the showcase door is opened for a long time, when the piping length from the freezer installed on the store roof to the showcase in the store is long, or Even when the equipment and showcase connection pipes are exposed, the compressor temperature (at least one of the low stage discharge temperature, case temperature, coil temperature, etc.) may become too high for the same reason as above. is there.

  In view of the above problems, the refrigeration apparatus A performs the flow rate control (first example) of the oil return circuit 8 as described below in parallel with the temperature control of the showcase during operation, and the compressor 1a , 1b is prevented from becoming too high.

<< 1-5. Flow control of oil return circuit 8 (first example) >>
As shown in FIG. 2, in this flow control (first example), the control unit 20 receives the detection results of the low-pressure sensor Se1, the low-stage suction temperature sensor Se2, and the outside air temperature sensor Se3, and based on the received detection results. The opening degree of the motor operated valves 10a and 10b of the oil return circuit 8 is controlled. Hereinafter, the flow rate control (first example) by the control unit 20 will be described in detail with reference to FIGS. 3A and 3B.

  In FIG. 3A, the control unit 20 acquires the detection results of the low-pressure sensor Se1, the low-stage suction temperature sensor Se2, and the outside air temperature sensor Se3, for example, periodically (steps S01, S02, and S03).

  Next, the control unit 20 determines whether or not the detection result of the outside air temperature sensor Se3 obtained in step S03 is equal to or higher than a predetermined temperature (step S04). The predetermined temperature is a threshold value indicating whether or not the outside air temperature is high, and is obtained by an experiment or the like at the design and development stage of the refrigeration apparatus A. If it is determined in step S04 that the temperature is equal to or higher than the predetermined temperature (that is, if YES is determined), the oil circulation amount in the oil return circuit 8 may be small (that is, the compressors 1a and 1b may be too hot). Therefore, the control unit 20 executes step S05.

  In step S05, the control unit 20 determines whether or not the detection result of the low pressure sensor Se1 obtained in step S01 is equal to or lower than a predetermined pressure. Here, the detection result of the low-pressure sensor Se1 substantially uniquely correlates the evaporation temperature on the showcase side. The predetermined pressure is a threshold value indicating whether or not the evaporation temperature is low, and is obtained by an experiment or the like at the design and development stage of the refrigeration apparatus A. If it is determined in step S05 that the pressure is equal to or lower than the predetermined pressure (that is, if YES is determined), the control unit 20 executes step S06 assuming that there is a possibility that the oil circulation amount may be small.

  In step S06, the control unit 20 converts the detection result of the low-pressure sensor Se1 obtained in step S01 into a saturation temperature by a known method. Next, the control unit 20 derives the difference value between the detection result obtained in step S02 and the saturation temperature obtained in step S06 as the degree of superheat at the inlet Pin of the refrigeration apparatus A (step S07). Next, the control unit 20 determines whether or not the degree of superheat obtained in step S07 is equal to or greater than a predetermined degree of superheat (step S08). The predetermined degree of superheat is a threshold value indicating whether or not the degree of superheat is high, and is obtained by experiments or the like at the design and development stage of the refrigeration apparatus A. If it is determined in step S08 that the degree of superheat is greater than or equal to (that is, determined as YES), it is considered that there is a possibility that the amount of oil circulation is small, and the control unit 20 executes step S09.

  In step S09, the control part 20 starts a built-in timer, and starts time measurement of the compressor 1a other continuous operation time. In the present embodiment, the compressor 1a and the like mean the compressors 1a and 1b. Next, the control unit 20 determines whether or not the first predetermined time has elapsed from the start of timing by the timer (that is, whether or not the compressor 1a and others have been continuously operated for the first predetermined time) (step S010). . The first predetermined time is a time during which the compressor 1a and the like can be regarded as continuously operating while satisfying the conditions of steps S04, S05, and S08 as the oil circulation amount in the oil return circuit 8 decreases. It can be obtained through experiments or the like at the design and development stage of the refrigeration apparatus A. If it is determined that the first predetermined time has elapsed (that is, if YES is determined), the controller 20 considers that the compressor 1a and others may become too hot, and executes step S011 of FIG. 3B.

  In step S011, the control unit 20 increases the opening degree of the motor operated valves 10a and 10b to increase the amount of oil circulation in the oil return circuit 8. The opening degree of the electric valves 10a and 10b is defined by the number of pulses, for example. In this case, a greater number of pulses than before execution of step S011 are given to the motor operated valves 10a and 10b. As a result, the amount of oil flowing from the high pressure oil separator 4 to the intermediate pressure compressor 1a and the like increases. In this process, the oil is cooled by the oil cooler 9, so that the other parts of the compressor 1a are cooled.

  After step S011, the control unit 20 starts a built-in timer and starts measuring time for adjusting the opening degree of the electric valves 10a and 10b (step S012). Next, the control unit 20 determines whether or not a second predetermined time has elapsed from the start of timing by the timer (step S013). The second predetermined time is a time during which the compressor 1a and the like can be considered to be sufficiently cooled, and is obtained by an experiment or the like at the design and development stage of the refrigeration apparatus A in consideration of a reference value such as a calorimeter test. If it is determined that the second predetermined time has not elapsed (that is, if NO is determined), the control unit 20 executes step S012. On the other hand, when it is determined that the second predetermined time has elapsed (that is, when YES is determined), the control unit 20 returns the opening degrees of the motor operated valves 10a and 10b to, for example, the state before the execution of step S011 (step S014).

  Refer to FIG. 3A again. In step S010, when it is determined that the first predetermined time has not elapsed (that is, when NO is determined), the control unit 20 determines whether or not a condition for stopping the counting of the continuous operation time is satisfied (step S015). . An example of the stop condition is that the compressor 1a and other operations stop due to thermo-off or defrosting operation. If it is determined in step S015 that the stop condition is not satisfied (that is, if NO is determined), the control unit 20 executes step S010 again. On the other hand, when it is determined that the stop condition is satisfied (that is, when YES is determined), the control unit 20 stops counting the continuous operation time and initializes the timer (step S016).

  In addition, when NO is determined in steps S04, S05, and S08 in FIG. 3A, when step S016 in FIG. 3A is executed, or when step S014 in FIG. 3B is executed, the control unit 20 performs step S01 in FIG. 3A. Run again.

<< 1-6. Main effects of flow control (first example) >>
The inventor of the present application mounted flow control (first example) on the prototype of the refrigeration apparatus A and confirmed the effect. The result is shown in FIG. In FIG. 4, the change with time of the opening degree of the motor-operated valves 10a, 10b is indicated by a broken line, and the change with time of the refrigerant temperature (that is, the low-stage discharge temperature) at the low-stage discharge port 15a is indicated by a solid line. The change with time in the coil temperature is indicated by a one-dot chain line, and the change with time in the other temperature of the case 11a (ie, the case temperature) is indicated by a two-dot chain line. The opening degree of the motor-operated valves 10a, 10b fluctuates greatly immediately after the start of the operation of the refrigeration apparatus A, but is small and generally constant after the load is stabilized. Therefore, although the frequency is low, the compressor 1a and others are continuously operated for a long time under the condition that the outside air temperature is high, the evaporation temperature on the showcase side is low, and the refrigerant superheat degree at the inlet Pin of the refrigeration apparatus A is large. May end up. At this time, if the oil circulation amount of the oil return circuit 8 is small, as shown in the times Ta, Tb, Tc, etc. in FIG. 4, the other temperatures of the compressor 1a (that is, the low stage discharge temperature, coil temperature, case temperature) Becomes too hot.

  In the flow rate control (first example) in the refrigeration apparatus A, when the control unit 20 considers that the amount of oil circulation in the oil return circuit 8 is small at the time Ta, Tb, Tc, the motor valves 10a, 10b The amount of oil circulation in the oil return circuit 8 is increased by increasing the opening. As a result, the amount of oil flowing from the high pressure oil separator 4 to the intermediate pressure compressor 1a and the like increases. In the process, the oil is cooled by the oil cooler 9, and the other parts of the compressor 1a are cooled, and the other temperatures of the compressor 1a (that is, the low-stage discharge temperature, the coil temperature, the case temperature) are reduced (see FIG. 4 time Td, Te, Tf). As a result, the compressor 1a and others can be prevented from becoming too hot, and the operation reliability of the refrigeration apparatus A can be improved.

<< 1-7. Other effects of flow control (first example) >>
Further, the control unit 20 defines that the amount of oil circulation is small from the detection results of the low pressure sensor Se1, the low stage suction temperature sensor Se2 and the outside air temperature sensor Se3 and the continuous operation time of the compressor 1a and the like. ing. Therefore, the refrigeration apparatus A does not have to be provided with a sensor for detecting the oil circulation amount for the flow rate control (first example) of the oil return circuit 8. Furthermore, the low-pressure sensor Se1, the low-stage suction temperature sensor Se2, and the outside air temperature sensor Se3 are provided for different purposes if they are general refrigeration devices. In other words, according to the present refrigeration apparatus A, it is possible to improve the operation reliability while suppressing the manufacturing cost using the existing sensor.

<< 1-8. Additional notes on flow control (first example) >>
Note that the number of compressors provided in the refrigeration apparatus A may be other than two, and the number of stages of each compressor may be two or more.

  Further, in the flow control (first example), instead of step S013, when the detection result of the outside air temperature sensor Se3 is not higher than the predetermined temperature, when the detection result of the low pressure sensor Se1 is not lower than the predetermined pressure, or When the superheat degree is no longer equal to or higher than the predetermined superheat degree, it may be modified to execute step S014.

  Further, in the flow control (first example), instead of step S015, when the detection result of the outside air temperature sensor Se3 is not higher than the predetermined temperature, when the detection result of the low pressure sensor Se1 is not lower than the predetermined pressure, or If the degree of superheat is no longer equal to or greater than the predetermined degree of superheat, it may be modified to execute step S016.

  Further, in the above, as a preferable mode, the continuous operation time of the compressor 1a and the like has been taken into consideration (see step S09 and the like in FIG. 3A). However, the present invention is not limited to this, and step S011 may be executed immediately after determining YES in step S08.

<< 1-9. Flow control of oil return circuit 8 (second example) >>
In addition to the flow rate control (first example), the control unit 20 receives the detection results of the low pressure sensor Se1, the low stage suction temperature sensor Se2, and the intermediate pressure sensor Se4 as shown in FIG. Based on the above, the same effect as the flow rate control (first example) can be obtained by controlling the opening degree of the motor operated valves 10a and 10b of the oil return circuit 8. Hereinafter, the flow rate control (second example) by the control unit 20 will be described in detail with reference to FIGS. 6A and 6B.

  In FIG. 6A, the control unit 20 acquires the detection results of the low pressure sensor Se1, the low stage suction temperature sensor Se2, and the intermediate pressure sensor Se4, for example, periodically (steps S11, S12, S13).

  By the way, when the refrigerant is adiabatically compressed as in the compressor 1a and others, the temperature and pressure at the low-stage suction port 14a and others are T1 and P1, and the temperature and pressure at the low-stage discharge port 15a and others are T2 and P2. When the adiabatic index is k (known value), the following equation (1) is established.

  In the above equation (1), the detection result of the low pressure sensor Se1 corresponds to P1, the detection result of the low stage suction temperature sensor Se2 corresponds to T1, and the detection result of the intermediate pressure sensor Se4 corresponds to P2. An unknown temperature at the low-stage discharge port 15a and the like (ie, low-stage discharge temperature) T2 is obtained by calculating the detection results of the low-pressure sensor Se1, the low-stage suction temperature sensor Se2, and the intermediate pressure sensor Se4 in the above equation (1). It can be derived by substitution.

  After step S13, the control unit 20 derives the low stage discharge temperature T2 by the above calculation (step S14). In addition, the control unit 20 can derive the low stage discharge temperature T2 by referring to the table. Specifically, in the nonvolatile memory of the control unit 20, for each combination of detection results of the low pressure sensor Se 1, the low stage suction temperature sensor Se 2, and the intermediate pressure sensor Se 4, an experiment or the like is performed at the design development stage of the refrigeration apparatus A. The table describing the low stage discharge temperature T2 obtained by the above is stored. The control unit 20 acquires the low stage discharge temperature T2 corresponding to the detection results obtained in steps S11, S12, and S13.

Next, the control unit 20 determines whether or not the low stage discharge temperature T2 obtained in step S14 is equal to or higher than a predetermined temperature (step S15). The predetermined temperature is a threshold value indicating whether or not the low stage discharge temperature T2 is high, and is obtained by an experiment or the like at the design and development stage of the refrigeration apparatus A. Since the above equation (1) is an estimation equation when it is assumed that the adiabatic compression of the ideal gas, the derived low-stage discharge temperature T2 includes the difference between the ideal gas and the refrigerant used (CO ₂ ) and the refrigerant used. Errors due to the effects of oil contamination are included. In consideration of such errors, it is desirable to set the predetermined temperature used in step S15. If it is determined in step S15 that the temperature is equal to or higher than the predetermined temperature (i.e., YES), it is considered that the amount of oil circulating in the oil return circuit 8 is small and the compressors 1a and 1b are too hot.

  Thereafter, the control unit 20 performs the processes of steps S09 to S016. About steps S09-S016, << 1-5. Since the flow rate control (first example) of the oil return circuit 8 has been described in detail, the description thereof is omitted here.

<< 1-10. Effect of flow control (second example) >>
The flow rate control (second example) in the refrigeration apparatus A is also << 1-6. The main effect of the flow rate control (first example) is the same as that described in the section >>.

  Further, the control unit 20 is in an overheated state of the compressor 1a and others from the detection results of the low pressure sensor Se1, the low stage suction temperature sensor Se2 and the intermediate pressure sensor Se4 and the continuous operation time of the compressor 1a and others. I guess that. Therefore, the refrigeration apparatus A does not need to be separately provided with a sensor for detecting the low stage discharge temperature in order to control the flow rate of the oil return circuit 8 (second example). Furthermore, the low-pressure sensor Se1, the low-stage suction temperature sensor Se2, and the intermediate pressure sensor Se4 are provided for different applications as long as they are general refrigeration apparatuses. In other words, according to the present refrigeration apparatus A, it is possible to improve the operation reliability while suppressing the manufacturing cost using the existing sensor.

<< 1-11. Additional notes on flow control (second example) >>
Further, in the above, as a preferable mode, the continuous operation time of the compressor 1a and the like has been taken into consideration (see step S09 and the like in FIG. 6A). However, the present invention is not limited to this, and step S011 may be executed immediately after determining YES in step S15.

  Further, the flow rate control (second example) is modified to execute steps S016 and S014 when the low stage discharge temperature is not equal to or higher than the predetermined temperature instead of steps S015 and S013 in FIGS. 6A and 6B. It doesn't matter.

  The refrigeration apparatus according to the present invention can improve the operation reliability and is suitable for a refrigerator system and the like.

DESCRIPTION OF SYMBOLS A ... Refrigeration apparatus 1a, 1b ... Compressor 4 ... Oil separator 8 ... Oil return circuit 9 ... Oil cooler 10a, 10b ... Electric valve 20 ... Control part Se1 ... Low pressure sensor Se2 ... Low stage suction temperature sensor Se3 ... Outside air temperature sensor Se4 ... Intermediate pressure sensor

Claims (9)

A refrigeration device,
A compressor that sucks refrigerant from a low-stage suction port through an inlet of the refrigeration apparatus, performs multi-stage compression, and discharges the refrigerant from a high-stage discharge port;
An oil separator that separates oil from refrigerant discharged from the high-stage discharge port;
An oil cooler for cooling the oil separated by the oil separator;
An oil return circuit for returning the oil cooled by the oil cooler to the compressor;
A refrigeration apparatus comprising: a control unit configured to increase the amount of oil circulation flowing in the oil return circuit when it is considered that the amount of oil circulation in the oil return circuit is small based on predetermined temperature information. An outside air temperature sensor for detecting outside air temperature,
A low pressure sensor and a temperature sensor for detecting the suction pressure and temperature of the refrigerant from the inlet toward the low stage suction port, and
2. The refrigeration apparatus according to claim 1, wherein the control unit considers that the oil circulation amount is in a small state based on detection results of the outside air temperature sensor, the low pressure sensor, and the temperature sensor. The controller is
Based on the detection result of the temperature sensor and the detection result of the low-pressure sensor, the degree of superheat of the refrigerant from the inlet toward the low-stage suction port is derived,
When the detection result of the outside air temperature sensor is equal to or higher than a predetermined temperature, the detection result of the low pressure sensor is equal to or lower than a predetermined pressure, and the derived degree of superheat is equal to or higher than a predetermined value, it is considered that the oil circulation amount is small. Item 3. The refrigeration apparatus according to Item 2.   When the compressor continuously operates for a predetermined time in a state where the detection result of the outside air temperature sensor is equal to or higher than a predetermined temperature, the detection result of the low pressure sensor is equal to or lower than a predetermined pressure, and the derived superheat degree is equal to or higher than a predetermined value. The refrigeration apparatus according to claim 3, wherein an amount of circulating oil flowing in the oil return circuit is increased. A refrigeration device,
A compressor that compresses the refrigerant sucked from the low-stage suction port through the inlet of the refrigeration apparatus and discharges the refrigerant from the low-stage discharge port;
An intercooler for cooling the refrigerant discharged from the low-stage discharge port,
When the refrigerant cooled by the intercooler is sucked from the high stage suction port, the compressor compresses the sucked refrigerant and discharges it from the high stage discharge port.
The refrigeration apparatus further includes
An oil separator that separates oil from the refrigerant discharged from the high-stage discharge port;
An oil cooler for cooling the oil separated by the oil separator;
An oil return circuit for returning the oil cooled by the oil cooler to the compressor;
A refrigeration apparatus comprising: a control unit that increases circulation of oil flowing in the oil return circuit when the temperature of refrigerant discharged from the low-stage discharge port is equal to or higher than a predetermined temperature. A low-pressure sensor and a temperature sensor for detecting the suction pressure and temperature of the refrigerant from the inlet toward the low-stage suction port;
An intermediate pressure sensor for detecting the suction pressure of the refrigerant toward the high stage suction port,
The refrigeration apparatus according to claim 5, wherein the control unit estimates a temperature of refrigerant discharged from the low-stage discharge port based on detection results of the low-pressure sensor, the temperature sensor, and the intermediate pressure sensor.   The refrigeration according to claim 5 or 6, wherein the control unit increases an amount of circulating oil flowing in the oil return circuit when the compressor continuously operates for a predetermined time in a state where the estimated discharged refrigerant temperature is equal to or higher than a predetermined temperature. apparatus. A motorized valve provided on the return circuit,
The refrigeration apparatus according to any one of claims 1 to 7, wherein the controller increases the amount of oil circulating through the oil return circuit by increasing an opening of the motor-operated valve. The refrigeration apparatus according to claim 1, wherein the refrigerant is carbon dioxide.

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