JP2015148383A - Refrigerating circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure that a deterioration in performance of a refrigerating circuit can be prevented by preventing oil foaming from occurring.SOLUTION: A refrigerating circuit comprises: a compressor 4 in which a cylinder 18 is hermetically sealed in a case 22; a return circuit 16 that connects an oil separator 5 to a discharge port 4a of the compressor 4 and returns oil accumulated in the oil separator 5 to a suction port 4b of the compressor 4; and a connecting pipe 15 that allows the case 22 to communicate with the oil separator 5. The connecting pipe 15 is connected to the case 22 at a position below a cylinder outlet 19 of the compressor 4.

Description

  The present invention relates to a refrigeration circuit.

Conventionally, in order to detect the oil level of the compressor, a proposal has been made to detect the position of the oil level in the compressor casing based on the temperature of the temperature detecting means, and to detect the oil level drop to protect the compressor. (For example, refer to Patent Document 1).
In addition, a resistor is provided in each of the oil reflux pipes connected to different height positions of the oil separator, the temperature of the oil after passing through the resistor is detected, and the temperature inside the oil separator is compared by comparing these temperatures. A technique for detecting the oil level and adjusting the amount of reflux to the compressor is known (see, for example, Patent Document 2).
In both Patent Documents 1 and 2, the temperature at two measurement points is detected. If there is a temperature difference, it is determined that an oil level exists between the two measurement points. It is determined that there is no oil level between them.

JP 2005-325733 A Japanese Patent Laid-Open No. 08-5167

By the way, in the conventional refrigeration circuit, although it is possible to determine whether the oil in the compressor or the oil separator is sufficient or insufficient, it is not possible to determine when the oil is present more than expected. Here, if more oil is present in the compressor than expected, that is, if there is more oil than the discharge port of the cylinder in the compressor, the gas refrigerant compressed in the cylinder is transferred from the discharge port of the cylinder into the oil liquid. It will be discharged. In that case, the compressed gas refrigerant diffuses into the oil liquid, resulting in a so-called oil forming state in which a large number of bubbles are generated. When oil forming occurs in the compressor, the amount of oil discharged from the compressor increases, and more oil than expected flows into the oil separator, exceeding the predetermined separation capacity of the oil separator, and the separation capacity is reduced. Furthermore, the oil that has flowed into the oil separator whose separation efficiency has decreased flows directly into the refrigeration circuit, stays in the connection piping and heat exchanger, and narrows the flow path to increase refrigerant pressure loss and heat. In the exchanger, the heat exchange between the refrigerant and the air is hindered and the performance is lowered.
The present invention has been made in view of the above-described circumstances, and an object thereof is to prevent the occurrence of oil forming and prevent the performance of the refrigeration circuit from being deteriorated.

In order to achieve the above object, the present invention includes a hermetic compressor in which a compression portion is hermetically sealed in a case, an oil separator is connected to a discharge port of the hermetic compressor, and oil accumulated in the oil separator is hermetically sealed. A return circuit for returning to the suction port of the compressor, and a connecting pipe that communicates the case with the oil separator. The connecting pipe is located at a position below the outlet of the compression section of the hermetic compressor. Provided is a refrigeration circuit connected to the case.
Further, in the above configuration, the connection pipe is located at a position below a discharge pipe connecting the discharge port to the oil separator, and at a position above a connection portion between the return circuit and the oil separator. It is good also as a structure connected to an oil separator.

In addition, a first temperature sensor provided in the discharge pipe and a second temperature sensor provided in the connection pipe are provided, and the difference between the temperatures detected by the first temperature sensor and the second temperature sensor is determined. On the basis of this, it may be configured to include a control unit that detects the oil level in the case.
Further, the return circuit includes an opening / closing valve that opens at one end in the oil separator and communicates with the suction port of the hermetic compressor at the other end and opens and closes the flow path of the return circuit. When the oil level is detected to be higher than the connection position of the connection pipe, the section performs a closing control to close the on-off valve, and the oil level is lower than the connection position of the connection pipe. When it is detected that the valve is in the position, the opening / closing valve may be controlled to open.

  According to the present invention, it is possible to prevent the occurrence of oil forming and prevent the performance of the refrigeration circuit from degrading.

It is a mimetic diagram of an air harmony device concerning an embodiment of the invention. It is a figure which shows schematic structure of a compressor. It is a figure which shows the structure of the periphery of a compressor and an oil separator. It is sectional drawing of an oil separator. It is a figure which shows the compressor in the state which has an oil level below the opening position of a connection pipe. It is a flowchart which shows the opening degree control of the electronic expansion valve by a control part.

Hereinafter, an air conditioner according to an embodiment of the present invention will be described with reference to the drawings. Here, as an example, an air conditioner in which one outdoor unit and one indoor unit are connected to each other by a refrigerant pipe will be described as an example, but the number of outdoor units and outdoor units is respectively A plurality of units may be provided.
FIG. 1 is a schematic diagram of an air conditioner according to an embodiment of the present invention.
As shown in FIG. 1, the air conditioner 1 includes one outdoor unit 2 and one indoor unit 3, and the outdoor unit 2 and the indoor unit 3 are connected by a refrigerant pipe. The refrigerant pipe includes a gas refrigerant pipe 10 connected to one end of the indoor heat exchanger 12 of the indoor unit 3 and a refrigerant liquid pipe 11 connected to the other end of the indoor heat exchanger 12.

The outdoor unit 2 includes a compressor 4 (sealed compressor), an oil separator 5, a four-way valve 6, an outdoor heat exchanger 7, an outdoor expansion mechanism 8, an accumulator 9, and the gas refrigerant pipe that connects these components. 10 and the refrigerant liquid pipe 11.
The indoor unit 3 includes the indoor heat exchanger 12, the indoor expansion mechanism 13, and the gas refrigerant pipe 10 and the refrigerant liquid pipe 11 that connect these components.
That is, the compressor 4, the oil separator 5, the four-way valve 6, the outdoor heat exchanger 7, the outdoor expansion mechanism 8, the accumulator 9, the indoor heat exchanger 12, and the indoor expansion mechanism 13 are connected by the gas refrigerant pipe 10 and the refrigerant liquid pipe 11. The refrigeration circuit 50 for performing an air-conditioning operation is configured by connecting in an annular shape.

  The refrigerating circuit 50 according to the embodiment of the present invention communicates the discharge pipe 14 connecting the discharge port 4a of the compressor 4 and the oil separator 5, the case 22 of the compressor 4 and the inside of the oil separator 5. A connecting pipe 15 and a return circuit 16 for returning the oil accumulated in the oil separator 5 to the suction port 4b of the compressor 4 are provided. The return circuit 16 is configured by connecting an oil return pipe 31 that connects the oil separator 5 and the refrigerant return pipe 30 in the middle of the refrigerant return pipe 30 that connects the accumulator 9 and the suction port 4 b of the compressor 4. Yes. The refrigerant return pipe 30 constitutes a part of the gas refrigerant pipe 10.

The air conditioner 1 also includes a control unit 23. The control unit 23 has a four-way valve 6, an outdoor fan (not shown), and a desired air conditioning state set on an operation panel (not shown). The indoor fan (not shown), the outdoor expansion mechanism 8, the indoor expansion mechanism 13, and the compressor 4 are controlled.
The four-way valve 6 is interposed in the gas refrigerant pipe 10 and switches the circulation direction of the refrigerant discharged from the compressor 4 according to the operation mode (cooling mode and heating mode). In FIG. 1, the refrigerant flow in the cooling mode is indicated by solid arrows, and the refrigerant flow in the heating mode is indicated by dashed arrows.

The outdoor heat exchanger 7 receives air from the outdoor fan and exchanges heat between the outside air and the refrigerant. The outdoor heat exchanger 7 functions as a condenser in the cooling mode, and functions as an evaporator in the heating mode.
The outdoor expansion mechanism 8 expands the refrigerant flowing into the outdoor heat exchanger 7 in the heating mode under reduced pressure, and is provided in the refrigerant liquid pipe 11. For example, a capillary tube or an electronic expansion valve is used as the outdoor expansion mechanism 8.
The accumulator 9 is interposed in the gas refrigerant pipe 10 on the suction side of the compressor 4, gas-liquid separates the refrigerant flowing into the compressor 4, stores the liquid refrigerant inside, and only the gas refrigerant goes to the compressor 4. Send it out.

The indoor heat exchanger 12 performs heat exchange between the refrigerant flowing inside and the air blown from the indoor fan. The indoor heat exchanger 12 functions as an evaporator in the cooling mode and functions as a condenser in the heating mode.
The indoor expansion mechanism 13 is provided in the refrigerant liquid pipe 11, and decompresses and expands the refrigerant flowing into the indoor heat exchanger 12 in the cooling mode. As the indoor expansion mechanism 13, for example, a capillary tube or an electronic expansion valve is used.

FIG. 2 is a diagram illustrating a schematic configuration of the compressor 4.
The compressor 4 is a hermetic compressor including the case 22 in which a refrigerant and lubricating oil are sealed, and a cylinder 18 (compression unit) housed in the case 22. The cylinder 18 is driven by an external drive source, and is rotationally driven through, for example, a pulley 27 driven by a gas engine as an external drive source.

The vertically long cylinder 18 is arranged upright near the side surface of the case 22, and the end of the suction port 4 b is connected to the upper surface of the cylinder 18. The cylinder 18 includes a cylinder outlet 19 (an outlet of the compression unit) that discharges the refrigerant into the case 22 on the side surface, and the refrigerant sucked from the suction port 4b and compressed by the cylinder 18 passes from the cylinder outlet 19 into the case 22. It is discharged in the horizontal direction. The cylinder outlet 19 includes a net-like oil separator 20 that easily separates oil contained in the refrigerant discharged from the cylinder outlet 19 from the refrigerant. Further, the cylinder 18 includes an oil supply port 21 for sucking oil into the cylinder 18 below the cylinder outlet 19.
The oil stored in the case 22 accumulates in order from the bottom surface of the case 22, and the oil level L (oil level position) increases as the amount of stored oil increases. The gas refrigerant protruding from the cylinder outlet 19 exists above the oil level in the case 22.

FIG. 3 is a diagram showing a configuration around the compressor 4 and the oil separator 5. FIG. 4 is a cross-sectional view of the oil separator 5.
The oil separator 5 includes a separator case 40 formed so as to close both ends of a substantially cylindrical shape. The separator case 40 includes a substantially cylindrical tubular portion 41 extending in the vertical direction, a top portion 42 that closes the upper end portion of the tubular portion 41, and a bottom portion 43 that closes the lower end portion of the tubular portion 41.
One end of the discharge pipe 14 is connected to the discharge port 4 a on the upper part of the case 22 of the compressor 4, and the other end of the discharge pipe 14 is connected to the top connection part 42 a of the top part 42 of the separator case 40. Moreover, the gas refrigerant pipe 10 is connected to the top part 42, and the gas refrigerant separated by the oil separator 5 flows to the four-way valve 6 side through the gas refrigerant pipe 10.

One end of an oil return pipe 31 is connected to the bottom connection part 43 a of the bottom part 43 of the oil separator 5, and the other end of the oil return pipe 31 is connected to the refrigerant return pipe 30.
The oil return pipe 31 is provided with a resistance portion that adjusts the flow of oil in the oil return pipe 31. In this embodiment, an electronic expansion valve 17 (open / close valve) is used as the resistance portion. . The control unit 23 controls the electronic expansion valve 17 to open and close the flow path of the oil return pipe 31 and return the optimum amount of oil from the oil separator 5 to the compressor 4.

One end of the connection pipe 15 is connected to the case side surface 33 of the case 22 of the compressor 4, and the other end of the connection pipe 15 is connected to the side surface connection part 41 a of the cylindrical part 41 of the oil separator 5. The side connection part 41a is provided below the top connection part 42a and above the bottom connection part 43a in the vertical direction of the oil separator 5. That is, the connection pipe 15 opens into the separator case 40 at a height position between the top connection part 42a and the bottom connection part 43a.
Further, as shown in FIG. 2, the connecting pipe connecting portion 33 a in which one end of the connecting pipe 15 is connected to the case side surface 33 is disposed below the cylinder outlet 19 and above the oil supply port 21. That is, one end of the connecting pipe 15 opens into the case 22 at a height position between the cylinder outlet 19 and the fuel filler port 21.

  The oil separator 5 is a centrifugal separator. The other end of the discharge pipe 14 is a gas-liquid mixed fluid of gas refrigerant and oil discharged from the discharge pipe 14 along the inner peripheral surface of the cylindrical portion 41. So as to flow in the direction tangential to the inner peripheral surface of the tubular portion 41. Specifically, the gas-liquid mixed fluid that has flowed into the oil separator 5 descends while spirally swirling in the oil separator 5 along the inner peripheral surface of the tubular portion 41, and the oil mist is swirled during swirling. The oil is separated by adhering to the inner peripheral surface of the shaped portion 41. The separated oil moves downward and is stored in the separator case 40.

Further, referring to FIG. 4, the other end of the connection pipe 15 is similar to the other end of the discharge pipe 14, and the gas-liquid mixed fluid discharged from the connection pipe 15 flows along the inner peripheral surface of the cylindrical portion 41. It arrange | positions so that the tangent direction of the internal peripheral surface of the cylindrical part 41 may be directed so that it may flow. For this reason, the formation of the swirl flow can be promoted also by the gas-liquid mixed fluid discharged from the connection pipe 15, and the oil can be separated efficiently.
The opening diameter of the other end of the connection pipe 15 opening in the separator case 40 is smaller than the opening diameter of the discharge pipe 14 in the separator case 40 and larger than the opening diameter of the oil return pipe 31 in the separator case 40.

Operation in the cooling mode of the present embodiment will be described.
In the cooling mode, the refrigerant discharged from the compressor 4 is guided in the order of the oil separator 5, the four-way valve 6, and the outdoor heat exchanger 7, and is condensed and liquefied by the outdoor heat exchanger 7 receiving air from the outdoor fan. The Thereafter, the refrigerant flows in the order of the outdoor heat exchanger 7, the indoor expansion mechanism 13, and the indoor heat exchanger 12. In this indoor heat exchanger 12, the low-temperature and low-pressure refrigerant decompressed and expanded by the indoor expansion mechanism 13 evaporates by heat exchange with the air blown by the indoor fan, so that the air passing through the indoor heat exchanger 12 is To be cooled. Thereafter, the refrigerant flows through the indoor heat exchanger 12, the four-way valve 6, and the accumulator 9 in order, and is sucked into the compressor 4 again.

In the above operation, the oil contained in the gas refrigerant discharged from the compressor 4 is separated from the gas refrigerant by the oil separator 5, but is not completely separated, and a small amount of oil is combined with the gas refrigerant in the refrigeration circuit. 50 is circulated and returned to the compressor 4 again.
For this reason, the amount of oil circulating through the refrigeration circuit 50 increases depending on the installation status of the air conditioner 1, such as the installation distance between the outdoor unit 2 and the indoor unit 3 being far apart or there being a difference in height. 4 may lead to oil shortage.
Assuming such a situation, such an air conditioner usually responds by increasing the amount of oil filled in advance for safety.

  However, when the installation condition of the air conditioner 1 is close to the installation distance between the outdoor unit 2 and the indoor unit 3 and there is no difference in height, the oil in the case 22 of the compressor 4 becomes excessive and compressed by the cylinder 18. The gas refrigerant is discharged from the cylinder outlet 19 into the oil liquid. In this case, the compressed gas refrigerant diffuses into the oil liquid, and a so-called oil forming state is generated in which a large number of bubbles are generated. When oil forming occurs in the compressor 4, the amount of oil discharged from the compressor 4 increases and more oil than expected flows into the oil separator 5, exceeding the predetermined separation capacity of the oil separator 5, and the separation capacity is increased. descend. Furthermore, the oil that has flowed into the oil separator 5 with a reduced separation capacity flows into the refrigeration circuit 50 as it is, stays in the connecting pipe or heat exchanger, and narrows the flow path, thereby increasing the refrigerant pressure loss. The heat exchanger inhibits heat exchange between the refrigerant and the air, and causes the performance of the air conditioner 1 to deteriorate.

Here, when the oil in the case 22 of the compressor 4 becomes excessive, that is, when the oil level L in the case 22 is higher than the opening position of the connection pipe 15 in the case 22, the present embodiment. The operation will be described with reference to FIG.
The gas refrigerant compressed in the cylinder 18 flows into the oil separator 5 from the discharge port 4 a through the discharge pipe 14. When the gas refrigerant passes through the discharge pipe 14, a pressure loss occurs in the gas refrigerant. Therefore, a differential pressure is generated between the refrigerant pressure in the case 22 and the refrigerant pressure in the oil separator 5, and the refrigerant pressure in the case 22 becomes larger than the refrigerant pressure in the oil separator 5.

When the oil level L in the case 22 becomes excessive and the oil level L becomes higher than the opening position of the connection pipe 15, excess oil in the compressor 4 flows into the connection pipe 15 from the opening due to the pressure difference, and is connected. It moves through the tube 15 and into the oil separator 5. When the oil in the case 22 moves to the oil separator 5 through the connecting pipe 15 and the oil level L decreases to the same position as the opening of the connecting pipe 15, gas refrigerant and oil flow through the connecting pipe 15. When the oil level L falls below the opening position of the connecting pipe 15, the oil does not flow into the connecting pipe 15 and does not move to the oil separator 5.
As described above, when the oil level L in the case 22 becomes excessive, excess oil flows through the connecting pipe 15 to the oil separator 5, so that the oil level L can be prevented from reaching the cylinder outlet 19, and oil forming occurs. Can be prevented.

  The oil stored in the oil separator 5 passes through the oil return pipe 31 opened at the bottom 43 of the oil separator 5 and the refrigerant return pipe 30 and returns to the suction port 4 b of the compressor 4. The opening degree of the electronic expansion valve 17 provided in the oil return pipe 31 is determined based on the load conditions that the air conditioner 1 can use, the size of the air conditioner 1, and the rotational speed of the compressor 4. It is determined by the control unit 23 so that the level L is higher than the fuel filler 21. Therefore, the occurrence of oil forming can be prevented, the oil level L in the case 22 can be prevented from being lowered, and the lubrication failure of the cylinder 18 can be prevented.

The discharge pipe 14 is provided with a first temperature sensor 24 that detects the temperature of the gas refrigerant discharged from the compressor 4. The connecting pipe 15 is provided with a second temperature sensor 25 that detects the temperatures of the oil and gas refrigerant flowing into the connecting pipe 15 from within the case 22. The first temperature sensor 24 and the second temperature sensor 25 are connected to the control unit 23.
As shown in FIG. 2, when the oil level L in the case 22 is above the opening position of the connection pipe 15, the high-temperature and high-pressure gas refrigerant compressed by the compressor 4 flows through the discharge pipe 14 and is connected. Oil in the case 22 having a temperature lower than that of the compressed gas refrigerant flows through the pipe 15. For this reason, the detected temperature Tdis of the first temperature sensor 24 becomes higher than the detected temperature Toil of the second temperature sensor 25, and a difference occurs between the detected temperature Tdis and the detected temperature Toil.

FIG. 5 is a diagram showing the compressor 4 in a state where the oil level L is below the opening position of the connecting pipe 15.
As shown in FIG. 5, when the oil level L in the case 22 is below the opening position of the connection pipe 15, the high-temperature and high-pressure gas refrigerant flows through the discharge pipe 14 and the connection pipe 15. The detected temperature Tdis of the temperature sensor 24 and the detected temperature Toil of the second temperature sensor 25 are substantially the same.

  The control unit 23 determines the oil level L in the case 22 based on the detected temperature Tdis and the detected temperature Toil. As an example, the control unit 23 has a detection temperature Tdis-detection temperature Toil (hereinafter, only indicated by a symbol for simplification) that is a difference between detection temperatures of the first temperature sensor 24 and the second temperature sensor 25. If it is equal to or higher than (K), it is determined that the oil level L in the case 22 is above the opening position of the connecting pipe 15, and if Tdis-Toil is less than 5 (K), the oil level L in the case 22 It is determined that the oil level L is lower than the opening position of the connecting pipe 15.

  Further, when the control unit 23 determines that the oil level L in the case 22 is above the opening position of the connection pipe 15, the controller 23 reduces the opening of the electronic expansion valve 17 provided in the oil return pipe 31, and the case 22. When it is determined that the internal oil level L is below the opening position of the connecting pipe 15, control is performed to increase the opening of the electronic expansion valve 17.

FIG. 6 is a flowchart showing the opening degree control of the electronic expansion valve 17 by the control unit 23.
First, the control part 23 sets the initial opening degree of the electronic expansion valve 17 provided in the oil return pipe | tube 31 with the operation start of the air conditioning apparatus 1 (step S1). The initial opening is preferably an opening at which the electronic expansion valve 17 is fully opened. As an example, if the electronic expansion valve is adjustable in opening from 0 step to 480 steps, the control unit 23 sets the opening to 480 steps.

  Next, the control unit 23 waits for an arbitrary time from the setting of the initial opening of the electronic expansion valve 17 (step S2), and closes the opening of the electronic expansion valve 17 by a fixed step after the elapse of the arbitrary time (step S3). ), It is determined whether or not the opening degree of the electronic expansion valve 17 has reached a predetermined opening degree set in advance (step S4). When the opening degree of the electronic expansion valve 17 has not reached the predetermined opening degree (step S4: No), the control unit 23 returns to step S2. That is, the control unit 23 closes the opening of the electronic expansion valve 17 by a predetermined step every arbitrary time, and repeats this operation until a predetermined opening set in advance is reached. As an example, the control unit 23 performs a closing operation by 10 steps every minute after the start of operation, and repeats until the opening degree of the electronic expansion valve 17 reaches 240 steps, which is a half opening degree.

When the opening degree of the electronic expansion valve 17 has reached a predetermined opening degree of 240 steps (step S4: Yes), the control unit 23 determines whether or not Tdis-Toil, which is a difference in detected temperature, is greater than a predetermined temperature difference. Is discriminated (step S5). The predetermined temperature difference is, for example, 5 (K).
When it is determined that Tdis-Toil is larger than the predetermined temperature difference (step S5: Yes), that is, it is determined that the oil level L in the case 22 is above the opening position of the connecting pipe 15 as shown in FIG. In this case, the control unit 23 determines whether or not the opening degree of the electronic expansion valve 17 is 0 step (fully closed) (step S6).

When the opening degree of the electronic expansion valve 17 is not fully closed (step S6: No), the control unit 23 closes the opening degree of the electronic expansion valve 17 by a constant step, for example, 10 steps (step S7). It waits for a time, for example, 1 minute (step S8), returns to step S5, and determines again whether Tdis-Toil is larger than a predetermined temperature difference.
Thus, when the oil level L is excessive, the amount of oil passing through the oil return pipe 31 is reduced by closing the electronic expansion valve 17, and the oil returning from the oil separator 5 to the case 22 is reduced. For this reason, the amount of oil in the case 22 is reduced by the oil discharged from the discharge pipe 14 to the oil separator 5, and the oil level L of the case 22 is lowered.
Then, the control unit 23 performs the operations from step S5 to step S8 until it is determined that Tdis-Toil is smaller than the predetermined temperature difference (step S5: No), that is, the oil level L in the case 22 is The process is repeated until it is determined that the position is below the opening position of the connection pipe 15. When the opening of the electronic expansion valve 17 is fully closed (step S6: Yes), the control unit 23 waits for a certain time in that state (step S8), and returns to step S5.

  That is, when it is determined that the oil level L in the case 22 is above the opening position of the connection pipe 15, the control unit 23 performs an operation of closing the electronic expansion valve 17 in steps at regular intervals. This is performed until it is determined that the oil level L is below the opening position of the connecting pipe 15. In this way, when the oil level L is excessive, the electronic expansion valve 17 is closed in stages at regular intervals, so that the oil level L in the case 22 is prevented from being excessively reduced. Can be adjusted to an appropriate level.

If it is determined that Tdis-Toil is smaller than the predetermined temperature difference (step S5: No), that is, it is determined that the oil level L in the case 22 is below the opening position of the connecting pipe 15 as shown in FIG. If it is, the controller 23 opens the opening of the electronic expansion valve 17 by a certain step, for example, 10 steps (step S9), and determines whether or not the opening of the electronic expansion valve 17 is 480 steps (fully open). (Step S10). When the electronic expansion valve 17 is not fully open (step S10: No), the control unit 23 opens the opening of the electronic expansion valve 17 by a certain step, for example, 10 steps (step S11), and in this state for a certain time, for example, 1 The process waits for a minute (step S12), and returns to step S5 to determine again whether Tdis-Toil is larger than a predetermined temperature difference.
Thus, when the oil level L is low, by opening the electronic expansion valve 17, the amount of oil passing through the oil return pipe 31 increases, and the oil returning from the oil separator 5 to the case 22 increases. For this reason, the amount of oil in the case 22 is increased with respect to the oil discharged from the discharge pipe 14 to the oil separator 5, and the oil level L of the case 22 is increased.

Then, the control unit 23 performs the operations from Step S5 and Step S9 to Step S12 until it is determined that Tdis-Toil is larger than the predetermined temperature difference (Step S5: Yes), that is, in the case 22 This is repeated until it is determined that the oil level L is above the opening position of the connecting pipe 15. Moreover, when the opening degree of the electronic expansion valve 17 is fully open (step S10: Yes), the control part 23 waits for a fixed time in the state (step S12), and returns to step S5.
That is, when it is determined that the oil level L in the case 22 is below the opening position of the connection pipe 15, the control unit 23 performs an operation of opening the electronic expansion valve 17 step by step at regular intervals. This is repeated until it is determined that the oil level L is above the opening position of the connecting pipe 15. As described above, when the oil level L is lowered, the electronic expansion valve 17 is opened stepwise at regular intervals, so that the oil level L in the case 22 is prevented from being excessively increased. Can be adjusted to an appropriate level.

  Further, in the present embodiment, the control unit 23 opens and closes the electronic expansion valve 17 on the basis of a predetermined temperature difference that changes depending on whether or not the oil passes through the connecting pipe 15, and the oil level in the case 22. In order to adjust L, the oil level L moves up and down in the vicinity of the opening position of the connecting pipe 15. For this reason, the oil level L can be maintained at an appropriate position between the cylinder outlet 19 and the oil filler port 21, and the occurrence of oil forming and insufficient lubrication of the cylinder 18 can be prevented.

  As described above, according to the embodiment to which the present invention is applied, the refrigeration circuit 50 includes the compressor 4 in which the cylinder 18 is sealed in the case 22, and the oil separator 5 is provided in the discharge port 4 a of the compressor 4. A return circuit 16 that connects and returns the oil accumulated in the oil separator 5 to the suction port 4b of the compressor 4, and includes a connection pipe 15 that communicates the case 22 and the oil separator 5. The connection pipe 15 is a cylinder of the cylinder 18. It is connected to the case 22 at a position below the outlet 19. Accordingly, when the oil accumulated in the case 22 is filled up to the position of the connecting pipe 15 located below the cylinder outlet 19, the oil flows through the connecting pipe 15 to the oil separator 5. Can be prevented. For this reason, generation | occurrence | production of oil forming can be prevented and the performance fall of the refrigerating circuit 50 can be prevented.

  The connection pipe 15 is positioned below the discharge pipe 14 that connects the discharge port 4 a to the oil separator 5, and is positioned above the bottom connection part 43 a that is a connection part between the return circuit 16 and the oil separator 5. Thus, since the oil separator 5 is connected, the oil can be allowed to flow to the oil separator 5 without affecting the oil separating function of the oil separator 5, and the oil can be efficiently supplied from the oil separator 5 to the return circuit.

  The refrigeration circuit 50 includes a first temperature sensor 24 provided in the discharge pipe 14 and a second temperature sensor 25 provided in the connection pipe 15, and the first temperature sensor 24 and the second temperature sensor 25. Since the control unit 23 that detects the oil level L in the case 22 is provided based on the temperature difference detected by the, the oil level L in the case 22 can be detected with a simple configuration.

  Further, the return circuit 16 includes an electronic expansion valve 17 that opens at one end in the oil separator 5 and communicates with the suction port 4b of the compressor 4 at the other end, and opens and closes the flow path of the return circuit 16. When the unit 23 detects that the oil level L is higher than the connection position of the connection pipe 15, the unit 23 performs a closing control to close the electronic expansion valve 17, and the oil level L is higher than the connection position of the connection pipe 15. When it is detected that the electronic expansion valve 17 is in the lower position, the opening control for opening the electronic expansion valve 17 is performed. As a result, the oil level L in the case 22 repeats up and down in the vicinity of the connection position of the connecting pipe 15 and is kept substantially constant, so that the oil level L can be made appropriate and the occurrence of oil forming is prevented. Thus, the performance of the refrigeration circuit 50 can be prevented from degrading.

In addition, the said embodiment shows the one aspect | mode which applied this invention, Comprising: This invention is not limited to the said embodiment.
In the above embodiment, the control unit 23 has been described as detecting the temperature by the first temperature sensor 24 and the second temperature sensor. However, the temperature detection is performed by directly detecting the temperature of the fluid flowing through the pipe. Alternatively, it may be detected indirectly via the temperature of the tube.

4 compressors (sealed compressors)
4a Discharge port 4b Suction port 5 Oil separator 14 Discharge pipe 15 Connection pipe 16 Return circuit 17 Electronic expansion valve (open / close valve)
18 cylinders (compression section)
19 Cylinder outlet (compressor outlet)
22 Case 23 Control unit 24 First temperature sensor 25 Second temperature sensor 50 Refrigeration circuit

Claims (4)

  A sealed compressor having a compression section sealed in a case, an oil separator connected to a discharge port of the sealed compressor, and a return circuit for returning the oil accumulated in the oil separator to the suction port of the sealed compressor A connecting pipe that communicates the case with the oil separator, and the connecting pipe is connected to the case at a position lower than an outlet of the compression section of the hermetic compressor. Refrigeration circuit.   The connection pipe is connected to the oil separator at a position below a discharge pipe connecting the discharge port to the oil separator and above a connection portion between the return circuit and the oil separator. The refrigeration circuit according to claim 1.   A first temperature sensor provided in the discharge pipe; and a second temperature sensor provided in the connection pipe, based on a temperature difference detected by the first temperature sensor and the second temperature sensor. The refrigeration circuit according to claim 2, further comprising a control unit that detects an oil level in the case. The return circuit includes an open / close valve that opens at one end in the oil separator and communicates with the other end to the suction port of the hermetic compressor and opens and closes the flow path of the return circuit,
When the control unit detects that the oil level is above the connection position of the connection pipe, the control unit performs a closing control to close the on-off valve, and the oil level is higher than the connection position of the connection pipe. 4. The refrigeration circuit according to claim 3, wherein when it is detected that the valve is in a lower position, an opening control for opening the on-off valve is performed.

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