JP2017032163A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make oil return amount to a compressor appropriate to improve efficiency of the compressor in an air conditioner.SOLUTION: An air conditioner includes: a compressor 16; an oil separator 18 provided on a refrigerant discharge side of the compressor 16; and an oil return pipe 70 connecting the oil separator 18 with a suction side of the compressor 16. The oil return pipe 70 includes: a first return pipe 71 for steadily returning oil from the oil separator 18 to the suction side; and a second return pipe 72 provided in parallel with the first return pipe 71. The second return pipe 72 includes an oil return valve 72b for opening/closing a flow passage. The oil return valve 72b is closed when the refrigerant recirculation by using the compressor 16 reaches a predetermined circulation amount threshold value Thc or lower.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an air conditioner.

  Conventionally, in an air conditioner having an oil separator provided on the discharge side of a compressor and an oil return pipe connecting the oil separator and the suction side of the compressor, oil shortage is detected by an oil level sensor of the compressor. An air conditioner that opens the valve of the oil return pipe and returns the oil from the oil separator to the compressor is known (for example, see Patent Document 1).

JP-A-7-103584

By the way, in the structure which returns oil from an oil separator to a compressor like the said conventional air conditioning apparatus, if the oil of a compressor increases too much by the oil which returns from an oil separator, the efficiency of a compressor will come out.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to optimize the return amount of oil to the compressor and improve the efficiency of the compressor in the air conditioner.

To achieve the above object, the present invention includes a compressor, an oil separator provided on the refrigerant discharge side of the compressor, and an oil return pipe connecting the oil separator and the suction side of the compressor. In the air conditioner, the oil return pipe includes a first return pipe that steadily returns oil from the oil separator to the suction side, and a second return pipe provided in parallel with the first return pipe. The second return pipe is provided with a valve for opening and closing the flow path, and the valve is closed when the refrigerant circulation amount by the compressor is equal to or less than a predetermined circulation amount threshold value. It is characterized by that.
Further, the present invention is characterized in that the valve is closed when the superheat degree of the refrigerant on the suction side of the compressor becomes equal to or higher than a predetermined superheat degree threshold value.
Further, the present invention is characterized in that the valve is closed when a pressure difference between the discharge side and the suction side of the compressor is within a predetermined pressure difference range.

Further, according to the present invention, when all the conditions within the circulation amount threshold value, the superheat degree threshold value, and the pressure difference range are satisfied, the timer starts counting, and all the conditions are satisfied. The valve is closed when it is determined by the timer that a predetermined time has elapsed.
The invention is characterized in that the timer count is stopped when at least one of the conditions is not satisfied during the timer count.
Further, the present invention is characterized in that the valve is an on-off valve that is open when not energized and closed when energized.

  According to the air conditioner of the present invention, the oil return pipe includes a first return pipe that returns oil from the oil separator to the suction side constantly, and a second return pipe that is provided in parallel with the first return pipe. The second return pipe is provided with a valve that opens and closes the flow path, and the valve is closed when the refrigerant circulation amount by the compressor becomes equal to or less than a predetermined circulation amount threshold value. Thereby, when the circulation amount of the refrigerant becomes equal to or less than the predetermined circulation amount threshold, the valve of the second return pipe is closed, and the oil returns to the compressor through the first return pipe. The amount of oil returning to the compressor through the return pipe is reduced. For this reason, when the circulating amount of the refrigerant becomes a predetermined amount or less and the amount of oil required by the compressor decreases, the amount of oil that returns to the compressor through the second return pipe can be reduced. By optimizing the amount of oil returned to the compressor, the efficiency of the compressor can be improved.

It is a lineblock diagram of the air harmony device concerning an embodiment of the invention. It is a figure which shows the refrigerant circuit of the vicinity of an oil return pipe | tube. It is a block diagram which shows the functional structure of an air conditioning apparatus. It is a time chart of control of optimization of oil quantity. It is a flowchart of control which optimizes the amount of oil.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an air-conditioning apparatus according to an embodiment of the present invention.
The air conditioner 10 includes an outdoor unit 11 and a plurality of indoor units 12 (... indicates a plurality. The same applies hereinafter). The outdoor unit 11 and the indoor units 12... Are connected by an inter-unit pipe 13 including a liquid pipe 13a and a gas pipe 13b, thereby constituting a refrigeration cycle circuit for performing an air conditioning operation. The outdoor unit 11 houses a gas engine 15 (engine) and a compressor 16 that compresses the refrigerant by the driving force of the gas engine 15. Specifically, the compressor 16 includes a first compressor 16c and a second compressor 16d provided in parallel. The gas engine 15 generates a driving force by burning an air-fuel mixture of a fuel such as a gas supplied via a fuel adjustment valve (not shown) and air supplied via a throttle valve (not shown).

The compressor 16 is driven by the gas engine 15 via a drive belt 17 that is stretched between the driven shaft of the compressor 16 and the output shaft of the gas engine 15.
An oil separator 18, a four-way valve 19, and outdoor heat exchangers 20, 20 are connected in order to the discharge pipe 16 a of the compressor 16, and the outdoor heat exchangers 20, 20 are connected to each indoor via the liquid pipe 13 a. It is connected to one end of the indoor heat exchangers 21 of the units 12. An expansion valve 22... Is provided on one end side of each indoor heat exchanger 21. The heat exchange between the outdoor heat exchangers 20 and 20 is promoted by the ventilation of the blower 20a.
A four-way valve 19 is connected to the other end of each indoor heat exchanger 21... Via a gas pipe 13 b, and a suction pipe 16 b of the compressor 16 is connected to the four-way valve 19. An accumulator 23 is provided in the vicinity of the compressor 16 in the suction pipe 16b. Each indoor heat exchanger 21... Has a blower (not shown).

The liquid pipe 13 a is provided with a motor-operated valve 24, a check valve 25, and a liquid pipe 81 connected to the inflow side of the accumulator 23.
In the discharge pipe 16a, a pressure switch 28 and a high-pressure sensor 29 for detecting the refrigerant pressure in the discharge pipe 16a are provided between the compressor 16 and the oil separator 18. The pressure switch 28 has a function of detecting the high pressure abnormality of the refrigerant and stopping the compressor 16.
In the suction pipe 16b, a low-pressure sensor 30 that detects the pressure of the refrigerant in the suction pipe 16b is provided between the compressor 16 and the accumulator 23. In addition, a refrigerant pipe 82 that connects the suction pipe 16b to the liquid pipe 13a side is connected to the suction pipe 16b, and an electric valve 80 is provided in the refrigerant pipe 82. The refrigerant pipe 82 includes the plate heat exchanger 31 at a portion between the motor operated valve 80 and the suction pipe 16b.

The outdoor unit 11 includes a bypass pipe 35 that connects the discharge pipe 16a and the suction pipe 16b. Specifically, one end of the bypass pipe 35 is connected to a portion of the discharge pipe 16a between the oil separator 18 and the four-way valve 19, and the other end of the bypass pipe 35 is connected to the accumulator 23 and the four-way valve 19 in the suction pipe 16b. Connected to the part between. A part of the refrigerant in the discharge pipe 16a flows through the bypass pipe 35 to the suction pipe 16b due to a pressure difference.
The bypass pipe 35 is provided with a bypass valve 36 that changes the area of the flow path of the bypass pipe 35. The bypass valve 36 is an electric valve controlled by the outdoor side control unit 37 (control unit) of the outdoor unit 11, and the flow path area is arbitrarily set stepwise or steplessly between the open state and the closed state. Can be adjusted.

  The outdoor unit 11 includes an oil return pipe 70 that connects the oil separator 18 and the suction pipe 16b. The lubricating oil stored in the oil separator 18 flows to the suction pipe 16b through the oil return pipe 70 due to a pressure difference between the discharge pipe 16a side and the suction pipe 16b.

FIG. 2 is a view showing a refrigerant circuit in the vicinity of the oil return pipe 70. In FIG. 2, the flow of the refrigerant and oil is indicated by arrows.
The oil separator 18 has a cylindrical shape and is a centrifugal type that separates oil from a refrigerant flowing into the inside by centrifugal force. The oil separator 18 includes a cylindrical main body 18a whose upper end and lower end are closed. The refrigerant inlet 18b of the oil separator 18 is provided along the cylindrical inner wall at the top of the main body 18a, and the refrigerant flows into the main body 18a from the discharge pipe 16a connected to the refrigerant inlet 18b.
The oil outlet 18c of the oil separator 18 is provided at the bottom of the main body 18a. The refrigerant outlet 18d of the oil separator 18 is provided in the upper part of the main body 18a, and the discharge pipe 16a extends from the refrigerant outlet 18d to the four-way valve 19.
The refrigerant flowing into the main body 18a from the refrigerant inlet 18b flows downward while turning along the cylindrical inner peripheral surface of the main body 18a as shown in FIG. 2, and oil is removed from the refrigerant by centrifugal force at this time. To be separated. The separated oil is stored in the lower part of the main body 18a, and the gaseous refrigerant flows out from the refrigerant outlet 18d.

The oil return pipe 70 includes a first return pipe 71 that connects the oil outlet 18c of the oil separator 18 and the suction pipe 16b, and a second return pipe 72 that is provided in parallel to the first return pipe 71. Prepare.
One end of the first return pipe 71 is connected to the oil outlet 18c, and the other end of the first return pipe 71 is connected to a portion of the suction pipe 16b downstream of the accumulator 23. The first return pipe 71 includes a decompression unit 71a configured by a capillary tube.

The second return pipe 72 is connected to the first return pipe 71 so as to bypass the decompression section 71 a, and one end of the second return pipe 72 is upstream of the decompression section 71 a in the first return pipe 71. The other end of the second return pipe 72 is connected to the downstream side of the decompression unit 71 a in the first return pipe 71.
The second return pipe 72 includes a decompression unit 72a configured by a capillary tube and an oil return valve 72b (valve) provided downstream of the decompression unit 72a. The oil return valve 72 b is an electromagnetic valve (open / close valve) that opens when not energized and closes when energized, and is controlled to be opened and closed by the outdoor control unit 37.

When the four-way valve 19 is switched to the heating operation, the refrigerant discharged from the compressor 16 to the discharge pipe 16a is transferred to the oil separator 18, the four-way valve 19, and the gas pipe 13b as shown by broken arrows in FIG. , Indoor heat exchanger 21..., Liquid pipe 13a, outdoor heat exchangers 20, 20, four-way valve 19, plate heat exchanger 31, accumulator 23, and compressor 16 are circulated in this order, and the indoor heat exchanger The room is heated by the heat of condensation of the refrigerant at 21.
When the four-way valve 19 is switched to the cooling operation, the refrigerant discharged from the compressor 16 to the discharge pipe 16a is transferred to the oil separator 18, the four-way valve 19, and the outdoor heat exchange as shown by solid line arrows in FIG. 20, 20, liquid pipe 13 a, indoor heat exchanger 21..., Gas pipe 13 b, four-way valve 19, plate-type heat exchanger 31, accumulator 23, and compressor 16 circulate in this order, and the indoor heat exchanger The room is cooled by the evaporation heat of the refrigerant at 21.
Since the indoor heat exchangers 21 are connected in parallel, the refrigerant can be individually supplied to the indoor heat exchangers 21 and the indoor heat exchangers 21 are operated independently. It is possible.

The gas engine 15 includes a cooling water circuit 40.
The cooling water circuit 40 includes a cooling water three-way valve 41, radiators 43 and 43, a cooling water pump 44, an exhaust gas heat exchanger 45 of the gas engine 15, which are sequentially connected from the gas engine 15 through a cooling water pipe. The cooling water pump 44 circulates cooling water in this circuit. The piping of the cooling water circuit is indicated by a thick line in FIG. 1, and the flow of the cooling water is indicated by a solid arrow.
The radiators 43 and 43 are arranged in parallel inside the outdoor heat exchangers 20 and 20. In the radiator 43, heat exchange between the outside air and the cooling water is performed.
In the plate heat exchanger 31, the refrigerant returning to the compressor 16 is heated by the cooling water flowing in the cooling water circuit 40 by the operation of the motor operated valve 80. Thereby, the low-pressure pressure of the refrigerant increases, and the heating efficiency is improved.
An exhaust muffler 46 and an exhaust top 47 for exhausting the exhaust gas are sequentially connected to the exhaust gas heat exchanger 45.

The coolant circuit 40 can form a first path through which the coolant flows in the order of the gas engine 15, the coolant three-way valve 41, the radiators 43 and 43, the coolant pump 44, the exhaust gas heat exchanger 45, and the gas engine 15. It is.
The cooling water circuit 40 supplies the cooling water in the order of the gas engine 15, the cooling water three-way valve 41, the plate heat exchanger 31, the cooling water pump 44, the exhaust gas heat exchanger 45, and the gas engine 15. A second path through which the cooling water flows can be formed.
Further, a reservoir tank 83 for replenishing cooling water is connected to the cooling water circuit 40.

FIG. 3 is a block diagram showing a functional configuration of the air conditioning apparatus 10.
A gas engine 15, a compressor 16, a four-way valve 19, a bypass valve 36, and an oil return valve 72b including each part of the cooling water circuit 40 are connected to the outdoor control unit 37 of the outdoor unit 11. The outdoor control unit 37 includes a high-pressure side pressure sensor 29, a low-pressure side pressure sensor 30, a pressure switch 28, an outside air temperature sensor 48 that detects the temperature of outside air, and an engine speed that detects the engine speed of the gas engine 15. The control means 49 etc. to which the instruction | indication of the driving | operation etc. to the detection means 73 and the outdoor unit 11 etc. are input are connected.
An indoor side control unit 50 that controls the indoor units 12... Is connected to the outdoor side control unit 37, and the outdoor side control unit 37 and the indoor side control unit 50 communicate with each other. The indoor control unit 50 is connected to the expansion valves 22..., A room temperature sensor 51 that detects the room temperature, and a remote controller 52 to which an operation instruction to the indoor units 12.
The outdoor side control unit 37 and the indoor side control unit 50 include a CPU, a ROM as a storage unit, a RAM, an EEPROM, and the like.

The outdoor side control unit 37 closes the oil return valve 72b and optimizes the amount of oil returning from the oil separator 18 to the compressor 16 when it is determined that the amount of oil required by the compressor 16 has decreased. I do.
FIG. 4 is a time chart of control for optimizing the oil amount.
In FIG. 4, time is shown on the horizontal axis, and the engine speed of the gas engine 15, the superheat degree on the suction side of the compressor 16, and the open / close state of the oil return valve 72b are shown on the vertical axis.

The engine speed of the gas engine 15 has a correlation with the circulation amount of the refrigerant in the refrigerant circuit of the air conditioner 10, and the higher the engine rotation speed, the higher the rotation speed of the compressor 16 and the refrigerant circulation amount. growing. For this reason, the circulation amount of the refrigerant can be estimated by detecting the engine speed.
In the air conditioner 10, a predetermined circulation amount threshold Thc in the refrigerant circulation amount is set as one of the indicators for determining whether or not the amount of oil required by the compressor 16 has decreased. As described above, since the circulation amount of the refrigerant can be estimated from the engine speed, in the present embodiment, the circulation amount threshold Thc is a predetermined engine speed corresponding to the predetermined circulation amount of the refrigerant.
The circulation amount threshold value Thc is set to a value that can be considered that the circulation amount of the refrigerant due to the discharge from the compressor 16 is relatively small and the amount of oil required by the compressor 16 is reduced. Desired. That is, when the engine speed is equal to or less than the circulation amount threshold value Thc, it can be determined that the amount of oil required by the compressor 16 has decreased.

Further, in the air conditioner 10, a predetermined superheat degree threshold Ths in the superheat degree on the suction side of the compressor 16 is set as one index for determining whether or not the amount of oil required by the compressor 16 has decreased. Has been. Here, the degree of superheat can be obtained based on the pressure and temperature on the suction side of the compressor 16 and is calculated by the outdoor side control unit 37.
When the degree of superheat on the suction side of the compressor 16 is high, it can be determined that the oil and the refrigerant are properly separated and are circulating in the refrigerant circuit. Further, when the degree of superheat on the suction side of the compressor 16 is low, it can be determined that the refrigerant and oil are mixed and returned to the compressor 16, and in this case, the refrigerant returned to the compressor 16 is evaporated. However, the amount of oil that substantially returns to the compressor 16 is smaller than when the oil is properly separated.
The superheat degree threshold Ths is set to a value at which it is determined that the oil and the refrigerant are properly separated and circulated, and the oil returned from the second return pipe 72 can be reduced. That is, when the superheat degree is equal to or higher than the superheat degree threshold Ths, it can be determined that the oil returned from the second return pipe 72 can be reduced. The superheat degree threshold Ths is obtained by experiment or calculation.

Further, in the air conditioner 10, as one of the indexes for determining whether or not the amount of oil required by the compressor 16 has decreased, the pressure difference between the discharge pipe 16a and the suction pipe 16b is a predetermined pressure difference range ( A condition is set as to whether it is within (not shown). Here, the pressure difference is the difference between the detection value of the high pressure side pressure sensor 29 and the detection value of the low pressure side pressure sensor 30.
When this pressure difference is small and within a predetermined pressure difference range, it can be determined that the operation of the compressor 16 and the circulation of the refrigerant are stable, and the amount of oil required by the compressor 16 has decreased.

  As shown in FIG. 4, at the time t1, the engine speed of the gas engine 15 is in a transient state of increase, the engine speed is equal to or less than the circulation amount threshold value Thc, and the superheat degree is smaller than the superheat degree threshold value Ths. The pressure difference (not shown) between the suction side and the suction side is large and is outside the predetermined pressure difference range. Therefore, at time t1, the amount of oil required by the compressor 16 is determined to be a normal amount, the energization of the oil return valve 72b is turned off (the valve is open), and the oil in the oil separator 18 is , Return to the compressor 16 through both the first return pipe 71 and the second return pipe 72. Here, the normal amount of oil in the compressor 16 is set to be large with a margin so as to cope with fluctuations in the load on the compressor.

  At time t2, the engine speed is equal to or less than the circulation amount threshold value Thc, the superheat degree is equal to or greater than the superheat degree threshold value Ths, and the pressure difference (not shown) is within the predetermined pressure difference range. For this reason, at time t2, the operation of the compressor 16 is in a stable state, and it is determined that the amount of oil required by the compressor 16 may be smaller than the normal amount. At time t2, the energization of the oil return valve 72b remains off.

  At time t3 after a predetermined time h has elapsed from time t2, the engine speed is equal to or less than the circulation amount threshold Thc, the superheat is equal to or greater than the superheat threshold Ths, and the pressure difference (not shown) is within the predetermined pressure difference range. The stable state of operation of the compressor 16 continues for a predetermined time h from the time t2. At time t3, the energization of the oil return valve 72b is turned on (the valve is closed), and the oil in the oil separator 18 returns to the compressor 16 through the first return pipe 71.

  At time t4, the engine speed is higher than the circulation amount threshold Thc, the superheat is equal to or greater than the superheat threshold Ths, and the pressure difference (not shown) is within the predetermined pressure difference range. At time t4, since the engine speed is high and the speed of the compressor 16 is also high, a normal amount of oil in the compressor 16 is required. For this reason, at time t4, the energization of the oil return valve 72b is turned off, and the oil return valve 72b is opened. Therefore, at time t4, the oil in the oil separator 18 returns to the compressor 16 through both the first return pipe 71 and the second return pipe 72.

  At time t5, the engine speed is equal to or less than the circulation amount threshold Thc, the superheat is equal to or greater than the superheat threshold Ths, and the pressure difference (not shown) is within the predetermined pressure difference range. For this reason, at time t5, the operation of the compressor 16 is in a stable state, and it is determined that the amount of oil required by the compressor 16 may be smaller than the normal amount. At time t5, the energization of the oil return valve 72b remains off.

  At time t6 when a predetermined time h has elapsed from time t5, the engine speed is equal to or less than the circulation amount threshold Thc, the superheat is equal to or greater than the superheat threshold Ths, and the pressure difference (not shown) is within the predetermined pressure difference range. And the stable state of operation of the compressor 16 continues for a predetermined time h from time t5. At time t6, the energization of the oil return valve 72b is turned on (the valve is closed), and the oil in the oil separator 18 returns to the compressor 16 through the first return pipe 71.

FIG. 5 is a flowchart of control for optimizing the oil amount. The process of FIG. 5 is repeatedly executed at predetermined time intervals.
First, the outdoor control unit 37 determines whether the engine speed of the gas engine 15 is equal to or less than the circulation amount threshold value Thc based on the output value of the engine speed detection means 73 during the operation of the air conditioner 10. Is determined (step S1).
When the engine speed is equal to or less than the circulation amount threshold value Thc (step S1: Yes), the outdoor side control unit 37 determines whether or not the superheat degree is equal to or higher than the superheat degree threshold value Ths (step S2).
When the superheat degree is equal to or higher than the superheat degree threshold Ths (step S2: Yes), the outdoor side control unit 37 determines whether or not the pressure difference is within the predetermined pressure difference range (step S3).

When the pressure difference is within the predetermined pressure difference range (step S3: Yes), the outdoor side control unit 37 starts counting (adding) the timer (step S4), and then the timer reaches the predetermined value ( It is determined whether or not time is up (step S5). The state of Yes in step S3 corresponds to time t2 and time t5 in FIG.
If the timer has not reached the predetermined value (step S5: NO), the outdoor control unit 37 sets the oil return valve 72b in a non-energized state to open (step S6), then ends the process and proceeds to step S1. To do. The state of Nо in step S5 corresponds to the state between time t2 and time t3 and the state between time t5 and time t6, and the oil in the oil separator 18 flows through the first return pipe 71. And through the second return pipe 72 back to the compressor 16.

When the engine speed is higher than the circulation amount threshold Thc (step S1: No), the outdoor control unit 37 resets (ends) the timer counted in step S4 (step S7), and proceeds to step S6. The oil return valve 72b is opened.
When the engine speed is equal to or less than the circulation amount threshold Thc but the superheat is smaller than the superheat threshold Ths (step S2: No), the outdoor control unit 37 resets (ends) the timer count (step S7). In step S6, the oil return valve 72b is opened. This state corresponds to time t1.
When the engine speed is equal to or less than the circulation amount threshold Thc and the superheat is equal to or greater than the superheat threshold Ths, but the pressure difference is not within a predetermined pressure difference range (step S3: Nо), the outdoor control unit 37 uses a timer Is reset (finished) (step S7), the process proceeds to step S6, and the oil return valve 72b is opened.
That is, if any one of the circulation amount threshold value Thc, the superheat degree threshold value Ths, and the condition within the predetermined pressure difference range is not satisfied, the timer is reset even after the timer starts counting. .

When the timer reaches a predetermined value (step S5: Yes), that is, when the predetermined time h has elapsed in FIG. 4, the outdoor side control unit 37 sets the oil return valve 72b in an energized state and closes it (step S8). The process ends and the process proceeds to step S1. This state corresponds to time t3 and time t6.
As described above, when it is determined that the amount of oil required by the compressor 16 may be smaller than the normal amount based on the circulation amount threshold value Thc, the superheat degree threshold value Ths, and the conditions within the predetermined pressure difference range. In addition, the oil return valve 72b is fully closed and the amount of oil returning from the second return pipe 72 is reduced, whereby the amount of oil returning to the compressor 16 can be optimized. For this reason, the resistance by oil can be reduced and the efficiency of the compressor 16 can be improved.

  After the oil return valve 72b is energized and closed in step S8, if it becomes NO in any of steps S1 to S3, the outdoor control unit 37 proceeds to step S6 via step S7, and returns to the oil return. The valve 72b is opened. As a result, the oil in the oil separator 18 returns to the compressor 16 through both the first return pipe 71 and the second return pipe 72. This state corresponds to time t4 in FIG.

As described above, according to the embodiment to which the present invention is applied, the air conditioner 10 includes the compressor 16, the oil separator 18 provided on the refrigerant discharge side of the compressor 16, the oil separator 18 and the compression. The oil return pipe 70 is connected to the suction side of the machine 16, and the oil return pipe 70 is connected to the first return pipe 71 and the first return pipe 71 that regularly return the oil from the oil separator 18 to the suction side. The second return pipe 72 is provided with an oil return valve 72b that opens and closes the flow path, and the oil return valve 72b circulates the refrigerant by the compressor 16. The amount is closed based on the fact that the amount has become equal to or less than a predetermined circulation amount threshold Thc. Thereby, when the circulation amount of the refrigerant becomes equal to or less than the circulation amount threshold value Thc, the oil return valve 72b of the second return pipe 72 is closed, and the oil returns to the compressor 16 through the first return pipe 71. However, the amount of oil returning to the compressor 16 through the second return pipe 72 is reduced. For this reason, when the circulation amount of the refrigerant becomes equal to or less than the circulation amount threshold Thc and the amount of oil required by the compressor 16 decreases, the amount of oil that returns to the compressor through the second return pipe 72 is reduced. The amount of oil returned to the compressor 16 can be optimized and the efficiency of the compressor 16 can be improved.
The oil return valve 72b is closed based on the fact that the superheat degree of the refrigerant on the suction side of the compressor 16 is equal to or higher than a predetermined superheat degree threshold Ths. Accordingly, when it is determined that the superheat degree of the refrigerant on the suction side of the compressor 16 is high and the oil and the refrigerant are properly separated and circulated, the compressor 16 passes through the second return pipe 72. The amount of oil returning to can be reduced. For this reason, the efficiency of the compressor 16 can be improved by optimizing the return amount of the oil to the compressor 16.

The oil return valve 72b is closed when the pressure difference between the discharge side and the suction side of the compressor 16 is within a predetermined pressure difference range. Thus, when the pressure difference between the discharge side and the suction side is within a predetermined pressure difference range, the operation of the compressor 16 is stable, and the amount of oil required by the compressor 16 is reduced, the second The amount of oil returning to the compressor 16 through the return pipe 72 can be reduced. For this reason, the return amount of oil to the compressor 16 can be optimized and the efficiency of the compressor can be improved.
Further, when the circulation amount threshold value Thc or less, the superheat degree threshold value Ths or more, and the conditions within the pressure difference range are all satisfied, the timer starts counting, and the timer sets the predetermined time h while all the conditions are satisfied. When it is determined that the time has elapsed, the oil return valve 72b is closed. As a result, when the operation of the compressor 16 is in a stable state for a predetermined time h, the oil return valve 72b is closed and the amount of return of the oil is reduced, so that the oil is returned when the operation of the compressor 16 is unstable. It can be prevented that the return valve 72b is closed and the return amount of oil is reduced.

In addition, when at least one of the above conditions is not satisfied during the timer count, the timer count is stopped, so that the oil return valve 72b is prevented from being closed when the operation of the compressor 16 is unstable. it can.
Since the oil return valve 72b is an open / close valve that is open when not energized and closed when energized, when the oil return valve 72b is not energized due to a failure or the like, the oil return valve 72b is open. It becomes. Therefore, even when the oil return valve 72b is not energized, the oil can be returned from the second return pipe 72 to the compressor 16, and the risk of oil shortage can be reduced.

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 circulation amount threshold value Thc has been described as being a predetermined engine speed corresponding to a predetermined circulation amount of the refrigerant, but the present invention is not limited to this. Since the circulation amount of the refrigerant can also be estimated from the rotation speed of the compressor 16, the circulation amount threshold Thc may be the rotation speed of the predetermined compressor 16 corresponding to the predetermined circulation amount of the refrigerant.
In the above embodiment, the oil return valve 72b has been described as an electromagnetic valve (open / close valve). However, the present invention is not limited to this, and the opening degree is stepwise or stepless between the open state and the closed state. May be an adjustable electric valve. In this case, the opening degree may be reduced without fully closing the oil return valve when the predetermined time h elapses.

DESCRIPTION OF SYMBOLS 10 Air conditioning apparatus 16 Compressor 18 Oil separator 70 Oil return pipe 71 1st return pipe 72 2nd return pipe 72b Oil return valve (valve)
Thc Circulation volume threshold Ths Superheat threshold

Claims (6)

In an air conditioner comprising a compressor, an oil separator provided on a refrigerant discharge side of the compressor, and an oil return pipe connecting the oil separator and a suction side of the compressor,
The oil return pipe includes a first return pipe that constantly returns oil from the oil separator to the suction side, and a second return pipe that is provided in parallel to the first return pipe, The second return pipe is provided with a valve for opening and closing the flow path,
The air conditioner is characterized in that the valve is closed on the basis that the amount of refrigerant circulated by the compressor becomes equal to or less than a predetermined circulation amount threshold.   2. The air conditioner according to claim 1, wherein the valve is closed when the superheat degree of the refrigerant on the suction side of the compressor becomes equal to or higher than a predetermined superheat degree threshold value.   The air conditioner according to claim 2, wherein the valve is closed based on a pressure difference between the discharge side and the suction side of the compressor being within a predetermined pressure difference range.   When the conditions below the circulation amount threshold value, the superheat degree threshold value and the pressure difference range are all satisfied, the timer starts counting, and a predetermined time elapses by the timer while all the conditions are satisfied. 4. The air conditioner according to claim 3, wherein the valve is closed when it is determined that a failure has occurred.   The air conditioner according to claim 4, wherein the timer count is stopped when at least one of the conditions is not satisfied during the timer count.   The air conditioning apparatus according to any one of claims 1 to 5, wherein the valve is an on-off valve that is open when not energized and closed when energized.

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