JP6945139B2 - Refrigeration cycle system, outdoor unit, control unit - Google Patents

Description

The present invention relates to a refrigeration cycle system, an outdoor unit, and a control unit, and more particularly to a refrigeration cycle system, an outdoor unit, and a control unit capable of recovering oil accumulated in a refrigeration cycle.

Conventionally, as a refrigeration cycle system, for example, a multi-type air conditioner in which one or a plurality of indoor units are connected to one or a plurality of outdoor units has been known.
In such an air conditioner, if the air conditioner is operated for a predetermined time, oil may accumulate in the indoor unit and the piping depending on the operating condition, and the oil in the compressor may be insufficient. Therefore, in the indoor unit and the piping. Control is performed to collect the oil accumulated in the water.

As such oil recovery control, conventionally, for example, a multi-type in which a plurality of indoor units equipped with an indoor heat exchanger and an indoor expansion valve are connected to an outdoor unit equipped with a variable capacity compressor and an outdoor heat exchanger. The air conditioner includes a means for detecting the pressure of the discharged refrigerant during the cooling operation, a means for detecting the outside temperature, and a means for counting the operation time and the stop time below a predetermined frequency of the variable capacity compressor. , A technique including means for changing the cycle of the oil recovery operation for controlling the oil recovery by adjusting the opening degree of the indoor expansion valve of each indoor unit based on these detected values is disclosed (for example, Patent Document). See 1).

Japanese Unexamined Patent Publication No. 09-170828

However, in the conventional technique, the indoor expansion of each indoor unit including the stop machine is performed by continuously or integrating the time during which the compressor is operated below the predetermined operating frequency or below the predetermined refrigerant discharge pressure. By increasing the valve opening all at once, the oil accumulated in the indoor unit and piping is recovered together with the liquid refrigerant, so a large amount of liquid refrigerant flows into the low pressure side and excessive liquid back occurs. There was a risk.

The present invention has been made in view of the above points, and an object of the present invention is to provide a refrigeration cycle system, an outdoor unit, and a control unit capable of recovering oil without generating excessive liquid back. Is what you do.

In order to solve the above-mentioned conventional problems, the refrigeration cycle system of the present invention is connected to an outdoor unit equipped with a compressor having a variable capacity whose capacity changes according to an operating frequency in the refrigeration cycle system. An indoor unit provided with an indoor expansion valve and a control unit for comprehensively controlling the refrigeration cycle system are provided, and the control unit includes the operating frequency of the compressor, the discharge superheat degree of the compressor, and the compressor. It is characterized in that oil recovery control is performed to raise the operating frequency of the compressor after lowering the operating frequency of the compressor based on the suction superheat degree and the maximum opening degree of the indoor expansion valve.

According to the present invention, by lowering the operating frequency of the compressor by the control unit during oil recovery control, the pressure of the refrigerant pipe on the low pressure side rises, and the refrigerant is in the liquid phase in all of the indoor unit and the pipe on the low pressure side. Since the state is likely to occur, the oil staying in all the indoor units and the refrigerant pipes on the low pressure side dissolves in the refrigerant in the liquid phase state, and the fluidity of the oil is improved. Therefore, the oil accumulated in all of the low-pressure side refrigerant pipes and the indoor unit can be recovered together with the liquid-phase refrigerant.

According to the present invention, in a refrigeration cycle system, oil recovery control can be performed at an appropriate timing according to the scale and operating conditions, and a state in which oil is always present in the compressor while suppressing fluctuations in air conditioning. Can be kept.

The block diagram which shows the refrigeration cycle system in Embodiment 1 of this invention. The block diagram which shows the control structure of Embodiment 1. FIG. (A) is a timing chart showing the control operation in the outdoor unit of the first embodiment, (b) is a timing chart showing the control operation in the indoor unit operating the cooling thermo-ON operation, and (c) is the cooling thermo-OFF operation. A timing chart showing the control operation of the indoor unit being blown, (d) is a timing chart showing the control operation of the indoor unit that is blowing air, and (e) is a timing chart showing the control operation of the indoor unit that is stopped. The flowchart which shows the operation of Embodiment 1. The figure which shows the example of the weighting value in Embodiment 2. FIG. The flowchart which shows the operation of Embodiment 2.

In the refrigeration cycle system, the present invention comprehensively controls an outdoor unit equipped with a compressor having a variable capacity whose capacity changes according to an operating frequency, an indoor unit connected to the outdoor unit, and the refrigeration cycle system. The compressor is provided with a control unit for the compressor, when the cumulative time of the cooling operation in a state where the condition for oil to be accumulated on the low pressure side of the refrigeration cycle system is equal to or longer than the first predetermined time. Oil recovery control is performed to raise the operating frequency of the compressor after lowering the operating frequency of the compressor.
According to this, at the time of oil recovery control, the control unit is controlled to lower the operating frequency of the compressor and increase the operating frequency of the compressor after a lapse of a predetermined time, so that excessive liquid backing is performed. The oil staying in the low-pressure side refrigerant pipe or the indoor unit can be recovered together with the liquid-phase refrigerant, whereby the amount of oil recovered can be increased.
In the present invention, the oil recovery control performed by the control unit lowers the operating frequency of the compressor by a preset second predetermined time, and is preset after the second predetermined time has elapsed. The control may be such that the operating frequency of the compressor is increased by the predetermined time of 3.

The present invention includes a superheat degree detecting means for detecting the superheat degree of the suction side of the compressor, and the control unit has a superheat degree of the suction side detected by the superheat degree detecting means of a first predetermined value or more. When this happens, it is determined that the condition for oil to accumulate on the low pressure side of the refrigeration cycle system is satisfied, and the oil recovery control is performed.
According to this, the oil recovery control is performed by judging the retention state of the oil in the low pressure side refrigerant pipe and the indoor unit from the suction superheat degree of the compressor, so that unnecessary oil recovery operation is suppressed. It is possible to keep the compressor in a state where oil is always present while suppressing fluctuations in air conditioning.

According to the present invention, when the operating frequency of the compressor becomes equal to or higher than the second predetermined value, the control unit determines that the condition for oil to be accumulated on the low pressure side of the refrigeration cycle system is satisfied, and controls the oil recovery. conduct.
According to this, the oil recovery control is performed by judging the oil retention state in the low pressure side refrigerant pipe and the indoor unit from the operating frequency of the compressor, so that unnecessary oil recovery operation is suppressed. It is possible to keep the compressor in a state of oil while suppressing fluctuations in air conditioning.

The present invention includes a superheat degree detecting means for detecting the superheat degree on the suction side of the compressor, and the control unit has a superheat degree on the suction side detected by the superheat degree detecting means of a first predetermined value or more. When the operating frequency of the compressor becomes equal to or higher than the second predetermined value, it is determined that the condition for oil to be accumulated on the low pressure side of the refrigeration cycle system is satisfied, and the oil recovery control is performed.
According to this, it is unnecessary because the oil recovery control is performed by judging the retention state of the oil in the refrigerant pipe on the low pressure side and the indoor unit from the suction superheat degree of the compressor and the operating frequency of the compressor. It is possible to suppress the oil recovery operation, and it is possible to keep the compressor in a state where oil is always present while suppressing fluctuations in air conditioning.

In the present invention, while the control unit is executing the oil recovery control, the indoor expansion valve of the indoor unit during the cooling operation is operated by superheat degree control.
According to this, it is possible to suppress the fluctuation of the air conditioning property due to the fluctuation of the refrigeration cycle at the time of oil recovery, and it is possible to suppress a large amount of liquid back to the compressor due to the liquid phase state of the refrigerant.

In the present invention, the indoor expansion valve is provided with an indoor expansion valve, and when the control unit performs the oil recovery control, the indoor expansion valve is opened to a predetermined set opening degree.
According to this, during the oil recovery control, the oil staying in the indoor unit can be efficiently recovered together with the refrigerant in the liquid phase state.

In the refrigeration cycle system, the present invention comprises an outdoor unit equipped with a compressor having a variable capacity whose capacity changes according to an operating frequency, an indoor unit connected to the outdoor unit and provided with an indoor expansion valve, and the refrigeration cycle system. The control unit is provided with a control unit that comprehensively controls the above, and the control unit has the operating frequency of the compressor, the discharge superheat degree of the compressor, the suction superheat degree of the compressor, and the maximum opening degree of the indoor expansion valve. Based on this, oil recovery control is performed to raise the operating frequency of the compressor after lowering the operating frequency of the compressor.

The present invention integrates a refrigeration cycle system including an outdoor unit equipped with a compressor having a variable capacity whose capacity changes according to an operating frequency, and an indoor unit connected to the outdoor unit and provided with an indoor expansion valve. A control unit for controlling the compressor, based on the operating frequency of the compressor, the degree of discharge superheat from the compressor, the degree of suction superheat of the compressor, and the maximum opening degree of the indoor expansion valve. After lowering the operating frequency, oil recovery control is performed to raise the operating frequency of the compressor.

The present invention is an outdoor unit equipped with a compressor having a variable capacity whose capacity changes according to an operating frequency, and includes an indoor unit having an indoor expansion valve and a control unit for controlling the system in an integrated manner. Connected to the refrigeration cycle system, the control unit is based on the operating frequency of the compressor, the discharge superheat degree of the compressor, the suction superheat degree of the compressor, and the maximum opening degree of the indoor expansion valve. After lowering the operating frequency of the compressor, a command to raise the operating frequency of the compressor is transmitted, and the operating frequency of the compressor is changed according to the transmitted signal.
According to this, in the refrigeration cycle system, oil recovery control can be performed at an appropriate timing according to the scale and operating conditions, and while suppressing fluctuations in air conditioning, the compressor always has oil in it. Can be kept.

In the present invention, the indoor unit includes an indoor expansion valve, and the control unit determines the ease with which the oil flows out based on the degree of superheat discharge of the compressor and the operating frequency of the compressor, and the oil. The difficulty of returning is determined based on the suction superheat degree of the compressor and the maximum opening degree of the indoor expansion valve.
According to this, it is possible to determine the amount of oil inside the compressor.

(Embodiment 1)
Hereinafter, Embodiment 1 of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a refrigeration cycle system of the present invention.
As shown in FIG. 1, the refrigeration cycle system 1 of the present embodiment includes an outdoor unit 10, a plurality of indoor units 20 connected to the outdoor unit 10 via a refrigerant pipe 11, and a control unit 40 (FIG. 2). See) and. However, in the present embodiment, an example in which two indoor units 20 are installed is shown, but the present invention is not limited to this, and for example, even if one indoor unit 20 is installed, or three or more indoor units 20 are installed. The indoor unit 20 may be installed.

The outdoor unit 10 includes a compressor 12 having a variable capacity whose capacity is variable by changing the operating frequency using an inverter, that is, the capacity is changed according to the operating frequency. An oil separator 13 is connected to the discharge side of the compressor 12 via a refrigerant pipe 11.
An outdoor heat exchanger 16 is connected to the oil separator 13 via a check valve 14 and a four-way valve 15 through a refrigerant pipe 11.
An indoor unit 20 is connected to the outdoor heat exchanger 16 via a refrigerant pipe 11, and an expansion valve 17 is provided in the middle of the refrigerant pipe 11 between the outdoor heat exchanger 16 and the indoor unit 20. Has been done.

The indoor unit 20 includes an indoor heat exchanger 21 and an indoor expansion valve 22. A four-way valve 15 is connected to the indoor unit 20 via a refrigerant pipe 11, and the four-way valve 15 is connected to the suction side of the compressor 12 via an accumulator 18.
A U-shaped refrigerant pipe 11 is housed inside the accumulator 18, and an oil return hole 19 is provided in the lower portion of the refrigerant pipe 11.

Further, the oil separator 13 is connected to an oil pipe 25 whose other end is connected to the refrigerant pipe 11 on the suction side of the compressor 12. The oil pipe 25 is provided with a capillary tube 26 for returning oil. Further, the oil pipe 25 is provided with an on-off valve 27 connected in parallel to the capillary tube 26.

On the discharge side of the compressor 12, a discharge temperature sensor 30 for detecting the temperature of the refrigerant discharged from the compressor 12 is provided. A high-pressure sensor 31 and a high-pressure switch 32 for detecting the pressure of the refrigerant discharged from the compressor 12 are provided between the oil separator 13 and the check valve 14, respectively. Here, the high-pressure switch 32 is a switch for stopping the operation of the system when the pressure of the discharged refrigerant reaches a predetermined maximum pressure.

Further, on one side of the outdoor heat exchanger 16 (the refrigerant inflow side during cooling operation), a heat exchange gas temperature sensor 33 for detecting the temperature of the gas refrigerant of the outdoor heat exchanger 16 is provided, and outdoor heat is provided. On the other side of the exchanger 16 (the outflow side of the refrigerant during cooling operation), a heat exchange liquid temperature sensor 34 for detecting the temperature of the liquid refrigerant of the outdoor heat exchanger 16 is provided. Further, the outdoor heat exchanger 16 is provided with an outside air temperature sensor 35 that detects the outside air temperature.

The refrigerant pipe 11 on the suction side of the compressor 12 is provided with a suction temperature sensor 36 for detecting the temperature of the refrigerant sucked into the compressor 12 and a low pressure sensor 37 for detecting the pressure of the refrigerant sucked into the compressor 12, respectively. There is. In the present embodiment, the suction temperature sensor 36 and the low pressure sensor 37 constitute a superheat degree detecting means.
Further, on one side of the indoor heat exchanger 21 (the refrigerant inflow side during cooling operation), an indoor liquid temperature sensor 38 for detecting the temperature of the liquid refrigerant of the indoor heat exchanger 21 is provided to exchange indoor heat. On the other side of the vessel 21 (refrigerant outflow side during cooling operation), an indoor gas temperature sensor 39 for detecting the temperature of the gas refrigerant of the indoor heat exchanger 21 is provided.

The control unit 40 is provided inside the outdoor unit 10 and is electrically connected to a component or device to be controlled. However, the control unit 40 does not necessarily have to be provided inside the outdoor unit 10, and the arrangement location may be changed as appropriate.
In FIG. 1, the connection of the control unit 40 is omitted in consideration of the legibility of the diagram. As described below, the control unit 40 is electrically connected to electronic components such as sensors to appropriately transmit necessary commands and communicate information with each other.
However, the electrical connection may be a connection form in which wireless communication or the like is used in addition to the connection by electric wires or cables.

Next, the control configuration of this embodiment will be described.
FIG. 2 is a block diagram showing a control configuration. The refrigeration cycle system 1 includes a control unit 40 that controls the refrigeration cycle system 1. The control unit 40 comprehensively controls each part of the refrigeration cycle system 1, and as shown in FIG. 2, a CPU as an arithmetic execution unit, a basic control program that can be executed by this CPU, predetermined data, and the like. It is equipped with a non-volatile storage ROM, a memory such as a RAM that volatilely stores data, and other peripheral circuits. The control unit 40 includes, as a counting means, an integration timer 41 that counts and integrates an arbitrary time during the cooling operation.

Further, the control unit 40 includes a discharge temperature sensor 30, a high pressure sensor 31, a heat exchange gas temperature sensor 33, a heat exchange liquid temperature sensor 34, an outside temperature sensor 35, a low pressure sensor 37, a suction temperature sensor 36, an indoor liquid temperature sensor 38, and the like. The value detected by the indoor gas temperature sensor 39 is input. Then, the control unit 40 controls the operation frequency of the compressor 12, the outdoor fan 42 of the outdoor heat exchanger 16, the indoor fan 43 of the indoor heat exchanger 21, and the indoor expansion valve 22 based on these detected values. It is configured to control the opening degree such as.

Further, in the present embodiment, the control unit 40 performs oil recovery control when a predetermined condition is reached during the cooling operation.
In the present embodiment, the oil recovery control refers to the control for recovering the oil accumulated in the indoor unit 20 or the refrigerant pipe of the refrigeration cycle during operation or stop. Specifically, the oil recovery control by the control unit 40 is performed by lowering the operating frequency of the compressor 12 by td for a predetermined time and then raising the operating frequency of the compressor 12 by tu for a predetermined time.

When the operating frequency of the compressor 12 is lowered, the pressure of the refrigerant pipe 11 and the indoor unit 20 on the low pressure side rises, so that the refrigerant of the refrigerant pipe 11 and the indoor unit 20 becomes less dry and in a liquid phase state. It becomes. When the dryness of the refrigerant decreases to a liquid phase state, the oil staying in the low pressure side refrigerant pipe 11 and the indoor unit 20 dissolves in the liquid phase refrigerant, and the fluidity of the oil becomes good.
Therefore, the control unit 40 reduces the operating frequency of the compressor 12 by td for a predetermined time to increase the fluidity of the oil, and then controls the operating frequency of the compressor 12 to increase the operating frequency by tu for a predetermined time, thereby increasing the flow velocity in the pipe. By increasing the amount of oil, the oil staying in the low-pressure side refrigerant pipe 11 and the indoor unit 20 can be recovered together with the liquid-phase refrigerant.

In the present embodiment, the oil recovery control after reaching a predetermined condition is performed based on the suction superheat degree of the compressor 12 and the operating frequency of the compressor 12.
Specifically, the time during which the compressor 12 is operated is integrated in a state where the suction superheat degree of the compressor 12 satisfies the condition of the predetermined value Sa or more and the operating frequency of the compressor 12 satisfies the predetermined value fa or more. The timer 41 continues to accumulate, and the oil recovery control is started when the integrated time becomes the predetermined time ta or more as the preset first predetermined time. When the suction superheat degree is the predetermined value Sa or more. Is in a state where the refrigerant flowing through the refrigerant pipe 11 and the indoor unit 20 is gasified, the viscosity of the oil is high, and the fluidity is poor. Further, when the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa, the amount of oil discharged from the compressor 12 increases, so that the low pressure side of the compressor 12 such as the indoor unit 20 side or the suction side of the compressor 12 Oil is likely to collect in the air.

Therefore, when the suction superheat degree is equal to or higher than the predetermined value Sa and the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa, the integrated time of the control unit 40 is compressed when the cumulative time is equal to or longer than the predetermined time ta. It is determined that the amount of oil inside the machine 12 has decreased and the conditions for oil accumulation on the low pressure side of the compressor 12, such as the indoor unit 20 side and the suction side of the compressor 12, have been satisfied, and the oil recovery control is performed.

In performing the oil recovery control, the control unit 40 calculates the low pressure saturation temperature of the refrigerant based on the refrigerant pressure on the suction side detected by the low pressure sensor 37, and the low pressure saturation temperature and the suction detected by the suction temperature sensor 36. The suction superheat degree is calculated from the difference from the temperature of the refrigerant.
Then, the control unit 40 integrates the operating time of the compressor 12 in a state where the suction superheat degree is equal to or higher than the predetermined value Sa and the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa by the integration timer 41. Then, the control unit 40 has an integrated time in which the compressor 12 is operated for a predetermined time ta or more in a state where the suction superheat degree is a predetermined value Sa or more and the operating frequency of the compressor 12 is a predetermined value fa or more. If it is determined that the problem has occurred, oil recovery control is performed.

After the oil recovery control is started, the control unit 40 lowers the operating frequency of the compressor 12, and when this operation elapses for a predetermined time td, the oil staying in the refrigerant pipe 11 on the low pressure side and the indoor unit 20 becomes liquid. It is considered that the oil is dissolved in the refrigerant in the phase state and the fluidity of the oil is improved. Therefore, the control unit 40 controls so that the operating frequency of the compressor 12 is increased (increased in frequency) after the operation in which the operating frequency of the compressor 12 is decreased is performed for a predetermined time td.
As a result, the oil staying in the low-pressure side refrigerant pipe 11 and the indoor unit 20 is sent to the accumulator 18 together with the liquid-phase refrigerant. The refrigerant sent to the accumulator 18 is separated into a gas refrigerant and a liquid refrigerant, and the oil dissolved in the liquid refrigerant is separated from the refrigerant.
The gas refrigerant separated by the accumulator 18 is sent to the compressor 12 via the refrigerant pipe 11. On the other hand, the oil accumulated below the accumulator 18 is sent to the compressor 12 through the oil return hole 19.

The oil discharge rate with respect to the operating frequency of the compressor 12 tends to increase as the operating frequency of the compressor 12 increases. Therefore, when the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa, the oil discharge rate becomes too high and may be lower than the amount of oil required by the compressor 12.
In the present embodiment, when the operating frequency of the compressor 12 becomes equal to or higher than the predetermined value fa, it is determined that the amount of oil inside the compressor 12 has decreased.
For example, in the present embodiment, the predetermined value fa of this operating frequency is set to 70 Hz.

Further, the predetermined value Sa of the suction superheat degree is set to a superheat degree at which the refrigerant density inside the low-pressure refrigerant pipe 11 on the suction side and the indoor unit 20 may decrease and the oil return may deteriorate. For example, in the present embodiment, the predetermined value Sa of the suction superheat degree is set to 10K.
Further, oil recovery control is performed when the suction superheat degree is equal to or higher than the predetermined value Sa and the operating frequency of the compressor 12 is operated at the predetermined value fa or higher for a predetermined time ta or higher. However, in the present embodiment, this predetermined time ta is set to, for example, 150 minutes as a time during which the amount of oil inside the compressor 12 becomes equal to or less than a certain required amount.
However, the predetermined value fa of the operating frequency of the compressor 12, the predetermined value Sa of the suction superheat degree, and the predetermined time ta of the integrated operation time are not limited to these values, and the capacity of the refrigeration cycle system 1 is not limited to these values. It is appropriately set according to the output of the compressor 12, the number of connected indoor units 20, and the like.

Next, the control operation including the oil recovery control in the present embodiment will be specifically described.
FIG. 3 is a timing chart showing the control operation in the present embodiment, and FIG. 3A shows the control operation in the outdoor unit. FIG. 3B shows a control operation in the indoor unit that is operating the cooling thermostat ON, and FIG. 3C shows a control operation in the indoor unit that is operating the cooling thermostat OFF. FIG. 3D shows a control operation of the indoor unit that is blowing air, and FIG. 3E shows a control operation of the indoor unit that is stopped.

In FIG. 3A, the waveform A shows the temporal change of the frequency of the compressor 12. Assuming that the time t1 in FIG. 3 is the time when the suction superheat degree is equal to or higher than the predetermined value Sa and the integrated time during which the compressor 12 is operated at the predetermined value fa or higher is equal to or higher than the predetermined time ta, FIG. In a), the control performed between the time t1 and the time t2 (that is, the time td as the second predetermined time + the time tu as the third predetermined time) is the oil recovery control in the present embodiment. ..

As shown in FIG. 3A, during normal operation control before and after the oil recovery control (time t <time t1 or time t> time t2), the control unit 40 sets the compressor 12 in the indoor heat exchanger 21. The operating frequency is controlled based on the evaporation temperature of the refrigerant.
Then, the control unit 40 is operated with a suction superheat degree of a predetermined value Sa or more as a first predetermined value and an operating frequency of the compressor 12 of a predetermined value fa or more as a second predetermined value. The oil recovery control is started at the time t1 when it is determined that the accumulated time is equal to or longer than the predetermined time ta.

In the oil recovery control, first, the control unit 40 lowers the operating frequency of the compressor 12 in the outdoor unit 10. At this time, the operating frequency of the compressor 12 is started to be lowered at time t1 with the target frequency set to f1. When the target frequency f1 is reached within the time td, the operation is maintained with the operating frequency set to f1 until the time td elapses. In the example shown in FIG. 3A, the target frequency f1 is set to 15 Hz. The target frequency f1 is the lowest frequency of the compressor 12, or a frequency that seems to be sufficient to increase the pressure of the piping portion or the indoor unit 20 that becomes low pressure in the refrigeration cycle system 1. At this time, the outdoor fan 42 is driven in the ON state by performing normal control.

Then, the control unit 40 raises the operating frequency of the compressor 12 after a predetermined time td has elapsed from the start of lowering the operating frequency of the compressor 12. At this time, the target frequency is set to f2, and the operating frequency of the compressor 12 is started to be increased after the time t1 has elapsed from the time td. In the example shown in FIG. 3A, the target frequency f2 is set to 60 Hz. The target frequency f2 is an operating frequency that can be set as the flow velocity in the pipe required for the outdoor unit 10 to recover the oil accumulated in the indoor unit 20 or the refrigerant pipe 11.

During the time tu, the control unit 40 controls to raise (increase) the operating frequency of the compressor 12 toward the target frequency f2 until a predetermined time tu elapses. When the target frequency f2 is reached within the time tu, the operation is maintained with the operating frequency set to f2 until the time tu elapses.
By increasing the operating frequency of the compressor 12 in this way, the oil staying in the refrigerant pipe 11 on the low pressure side and the indoor unit 20 is recovered together with the refrigerant in the liquid phase state.

Further, the waveform B shown in FIG. 3B shows the indoor unit when the indoor unit 20 connected to the outdoor unit 10 is in the cooling thermo-ON state in the situation where the oil recovery control of the present embodiment is implemented. The time change of the opening degree of the indoor expansion valve 22 of the unit 20 is shown.
When the indoor unit 20 connected to the outdoor unit 10 is in the cooling thermo-ON state, the opening degree of the indoor expansion valve 22 of the indoor unit 20 is controlled according to the degree of superheat of the refrigerant passing through the indoor heat exchanger 21. Will be done. At this time, the indoor fan 43 is usually driven by control.
Here, the normal control of the indoor fan 43 is a control performed based on the air volume or the wind speed set by the user using a remote controller or the like, and the same applies to the following description.

The waveform C shown in FIG. 3C shows the indoor unit 20 when the indoor unit 20 connected to the outdoor unit 10 is in the cooling thermo-off state in the situation where the oil recovery control of the present embodiment is implemented. The time change of the opening degree of the indoor expansion valve 22 of the above is shown.
When the indoor unit 20 is in the cooling thermo-OFF state, the indoor expansion valve 22 of the indoor unit 20 is closed during normal operation control before and after the oil recovery control (time t <time t1 or time t> time t2). However, at the time of oil recovery control (time t1 ≦ time t ≦ t2), it is controlled so as to open at a predetermined set opening degree. At this time, the indoor fan 43 is usually driven by control.

Here, the predetermined set opening is an opening necessary and sufficient for flowing the refrigerant, and may be, for example, an opening that opens when the refrigeration cycle system 1 is started. By opening the indoor expansion valve 22 to a predetermined set opening degree, the oil accumulated in the indoor unit 20 other than the indoor unit 20 in the cooling thermo-ON state can also be recovered. The same applies to the predetermined set opening degree in the following description.

The waveform D shown in FIG. 3D shows the indoor unit 20 when the indoor unit 20 connected to the outdoor unit 10 is in a blowing operation state in the situation where the oil recovery control of the present embodiment is implemented. The time change of the opening degree of the indoor expansion valve 22 is shown.
When the indoor unit 20 is in the ventilation operation state, the indoor expansion valve 22 of the indoor unit 20 is closed during normal operation control before and after the oil recovery control (time t <time t1 or time t> time t2). However, during oil recovery control (time t1 ≦ time t ≦ time t2), it is controlled to open at a predetermined set opening. At this time, the indoor fan 43 is normally operated by control.

The waveform E shown in FIG. 3E shows the time of the opening degree of the indoor expansion valve 22 of the indoor unit 20 when the indoor unit 20 is in the stopped state in the situation where the oil recovery control of the present embodiment is implemented. Show change.
When the indoor unit 20 is in the stopped state, the indoor expansion valve 22 of the indoor unit 20 is closed before and after the oil recovery control (time t <time t1 or time t> time t2) during normal operation control. However, during oil recovery control (time t1 ≦ time t ≦ t2), it is controlled to open at a predetermined set opening. At this time, the fan is stopped and controlled.
When the oil recovery control is performed in this way, the oil staying in the indoor heat exchanger 21 can be flowed to the low-pressure side refrigerant pipe 11 by opening the indoor expansion valve 22.

Next, the operation of the first embodiment will be described.
During the cooling operation, the four-way valve 15 is switched to the connected state shown by the solid line in FIG. Then, when the compressor 12 is driven, the high-temperature and high-pressure refrigerant from the compressor 12 flows in the direction indicated by the solid arrow in the figure.
The high-temperature and high-pressure refrigerant discharged from the compressor 12 flows to the outdoor heat exchanger 16 via the oil separator 13, the check valve 14, and the four-way valve 15, and is condensed by exchanging heat with the outside air in the outdoor heat exchanger 16. The refrigerant is sent to the indoor unit 20 via the refrigerant pipe 11.

After depressurizing with the indoor expansion valve 22, the refrigerant sent to the indoor heat exchanger 21 exchanges heat with the indoor air and evaporates, and the evaporated refrigerant flows to the four-way valve 15 via the refrigerant pipe 11 and presses the accumulator 18. It is returned to the suction side of the compressor 12 via. As a result, the room is cooled by the cooled room air.

Further, during the heating operation, the four-way valve 15 is switched to the connected state shown by the broken line in FIG. Then, when the compressor 12 is driven, the high-temperature and high-pressure refrigerant from the compressor 12 flows as shown by the broken line arrow in the figure.
The high-temperature and high-pressure refrigerant discharged from the compressor 12 flows to the indoor heat exchanger 21 via the oil separator 13, the check valve 14, and the four-way valve 15, and is condensed by exchanging heat with the indoor air in the indoor heat exchanger 21. NS. The flow rate of the condensed refrigerant is adjusted by the indoor expansion valve 22, the pressure is reduced by the outdoor expansion valve 17 via the refrigerant pipe 11, and then the condensed refrigerant is sent to the outdoor heat exchanger 16. The refrigerant sent to the outdoor heat exchanger 16 exchanges heat with the outside air, evaporates, and is returned to the compressor 12 via the four-way valve 15 and the accumulator 18. As a result, the room is heated by the heated room air.

Next, the control operation of the first embodiment will be described.
FIG. 4 is a flowchart showing a control process executed by the control unit 40. However, the start time of the flow shown in FIG. 4 may be the start time of the cooling operation.
Further, in the following description, for convenience of explanation, the integration timer 41 will be divided into three integration timers 41a, 41b, and 41c.

The integration timer 41a is a timer that counts (counts) ta for a predetermined time, the timer 41b is a timer that counts the time for lowering the operating frequency of the compressor 12 during oil recovery control, and the timer 41c is the frequency of the compressor 12 during oil recovery control. It is a timer that counts the time to raise. However, as a realization means, one integration timer may be used, or a plurality of integration timers may be appropriately used.
In the present embodiment, the integration timer 41 integrates the time when the control unit 40 determines that the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa and the suction superheat degree is equal to or higher than the predetermined value Sa. Do the action.

As shown in FIG. 4, first, during the cooling operation of the refrigeration cycle system 1, the control unit 40 determines whether or not the operating frequency of the compressor 12 under its control is equal to or higher than a predetermined value fa. (ST1).
When the control unit 40 determines that the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa (ST1: YES), the control unit 40 determines whether or not the suction superheat degree is equal to or higher than the predetermined value Sa (ST2).
When it is determined in step ST2 that the suction superheat degree is equal to or higher than the predetermined value Sa (ST2: YES), the integration timer 41a is timed (ST3). When the integration timer 41a starts the timing operation, the integration timer 41a continues to clock (count up) while the operating frequency of the compressor 12 continues to be at least a predetermined value fa and the suction superheat degree is at least a predetermined value Sa.

On the other hand, if it is determined that the operating frequency of the compressor 12 is not equal to or higher than the predetermined value fa (ST1: NO), or if it is determined that the suction superheat degree is not equal to or higher than the predetermined value Sa (ST2: NO), the process returns to step ST1. The process of determining the operating frequency of the compressor 12 and the degree of suction superheat (ST1, ST2) is sequentially repeated.

While the timekeeping operation in step ST3 is being performed, the control unit 40 determines the operating time when the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa and the suction superheat degree is equal to or higher than the predetermined value Sa, as counted by the integration timer 41a. It is determined whether or not the predetermined time ta or more has passed (ST4).
In step ST4, the operating time when the operating frequency of the compressor 12 counted by the integration timer 41a is equal to or higher than the predetermined value fa and the suction superheat degree is equal to or higher than the predetermined value Sa has not elapsed by the predetermined time ta or more (ST4: NO). ), The process is returned to step ST1, and the processes from step ST1 to step ST4 are repeated.

In step ST4, the operation time of the compressor 12 when the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa and the suction superheat degree is equal to or higher than the predetermined value Sa, as counted by the integration timer 41a, has elapsed by the predetermined time ta or more. If it is determined that ST4: YES), the oil recovery control is started and the integration time of the integration timer 41a is reset (ST5).
When the oil recovery control is started after step ST5, the control unit 40 executes the timekeeping operation of the integration timer 41b (ST6) and lowers the operating frequency of the compressor 12 to the target frequency f1 (ST7). ..
When the operating frequency of the compressor 12 is lowered, the internal pressure of the low-pressure side refrigerant pipe 11 and the indoor unit 20 rises, so that the refrigerant of the refrigerant pipe 11 and the indoor unit 20 is in a liquid phase state, and the low-pressure side refrigerant pipe The oil staying in the 11 and the indoor unit 20 dissolves in the refrigerant in the liquid phase state, and the fluidity of the oil becomes good.

Then, the control unit 40 determines the time accumulated by the timer 41b. That is, it is determined whether or not the operation in which the operating frequency of the compressor 12 is lowered has elapsed the predetermined time td (ST8).
When the control unit 40 determines in step ST8 that the operation of lowering the operating frequency of the compressor 12 has elapsed the predetermined time td (ST8: YES), the control unit 40 resets the timer 41b (ST9) and operates the timer 41c in a timed manner. Is started (ST10). After step ST10, the operating frequency of the compressor 12 is raised to the target frequency f2 (ST11).

By increasing the operating frequency of the compressor 12, the oil staying in the low-pressure side refrigerant pipe 11 and the indoor unit 20 can be recovered together with the refrigerant in the liquid phase state, and the amount of oil recovered can be increased.
After that, the control unit 40 determines the time accumulated by the timer 41c. That is, it is determined whether or not the operation of increasing the operating frequency of the compressor 12 has elapsed for a predetermined time (ST12).
In step ST12, when the control unit 40 determines that the operation of increasing the operating frequency of the compressor 12 has elapsed for a predetermined time (ST12: YES), the integration timer 41c is cleared (ST13), and the compressor 12 is executed. Shifts the operation control of to normal control (evaporation temperature control) operation.
After clearing the integration timer 41c, the above processing may be repeated by returning to the start of the processing flow shown in FIG. 4 during the cooling operation.
The determination process of step ST1 or step ST2, which is a process for determining that the condition for oil to be accumulated on the low pressure side of the refrigeration cycle system 1 is satisfied, may be performed by only one of these.

According to the present embodiment, the oil recovery control is performed by judging the retention state of the oil in each indoor unit 20 and the refrigerant pipe 11 from the suction superheat degree of the compressor 12 and the operating frequency. The necessary oil recovery operation can be suppressed, and the state in which the compressor 12 has oil can be maintained at all times while suppressing fluctuations in air conditioning.
At this time, even during the oil recovery control, the fluctuation of the air conditioning property due to the fluctuation of the refrigeration cycle can be suppressed by continuing the normal superheat degree control operation of the indoor expansion valve 22 of the cooling thermo-ON machine. , It is possible to suppress a large amount of liquid back to the low pressure side due to the liquid phase state of the refrigerant.

As described above, in the present embodiment, the control unit 40 is provided with an integration timer 41 (counting means) that integrates the operating time of the cooling operation, and the control unit 40 is a compressor 12 by the integration timer 41. When the integrated time of the operating time in a state where the condition for oil to be accumulated on the low pressure side is equal to or longer than the predetermined time ta, the operating frequency of the compressor 12 is lowered, and the predetermined time td elapses after the operating frequency is lowered. After that, oil recovery control is performed to raise the operating frequency of the compressor 12 for a predetermined time.
As a result, at the time of oil recovery control, the control unit 40 lowers the operating frequency of the compressor 12, and after a lapse of a predetermined time td, the control unit 40 controls to raise the operating frequency of the compressor 12, which is excessive. The oil staying in the low-pressure side refrigerant pipe 11 and the indoor unit 20 can be recovered together with the refrigerant in the liquid phase state without generating liquid back, whereby the amount of oil recovered can be increased.
As a condition for oil to collect on the low pressure side of the compressor 12, it is determined from the suction superheat degree and the operating frequency of the compressor 12, but it may be judged using only one of the suction superheat degree and the operating frequency. ..

Further, in the present embodiment, the suction temperature sensor 36 and the low pressure sensor 37 (superheat detection means) for detecting the degree of superheat on the suction side of the compressor 12 are provided, and the control unit 40 includes the suction temperature sensor 36 and the low pressure sensor 37. When the degree of superheat on the suction side detected by the above is equal to or higher than the predetermined value Sa, it is determined that the condition for oil to be accumulated on the low pressure side of the compressor 12 is satisfied, and the oil recovery control is performed.
As a result, the oil retention state in the low-pressure side refrigerant pipe 11 and the indoor unit 20 is judged from the suction superheat degree of the compressor 12 to perform oil recovery control, so that unnecessary oil recovery operation can be performed. It can be suppressed, and the state in which oil is always present in the compressor 12 can be maintained while suppressing fluctuations in air conditioning.

Further, in the present embodiment, the control unit 40 determines that the condition for oil to be accumulated on the low pressure side of the refrigeration cycle system 1 is satisfied when the operating frequency of the compressor 12 is equal to or higher than the predetermined value fa, and recovers the oil. Take control.
As a result, the oil retention state in the low-pressure side refrigerant pipe 11 and the indoor unit 20 is judged from the operating frequency of the compressor 12 to perform oil recovery control, so that unnecessary oil recovery operation is suppressed. It is possible to keep the compressor 12 in a state where oil is always present while suppressing fluctuations in air conditioning.

Further, in the present embodiment, the indoor unit 20 is provided with an indoor expansion valve 22, and when the control unit 40 performs oil recovery control, the indoor unit 20 connected to the refrigeration cycle system 1 is in a state where the cooling thermostat is ON. (It is a cooling thermo-ON machine), the indoor expansion valve 22 of the cooling thermo-ON machine is operated under the same superheat degree control as in normal operation.
As a result, fluctuations in the refrigeration cycle during oil recovery can be suppressed, and a large amount of liquid back to the low pressure side due to the liquid phase state of the refrigerant can be suppressed.

Further, in the present embodiment, the indoor unit 20 is provided with an indoor expansion valve 22, and when the control unit 40 performs oil recovery control, the indoor unit 20 connected to the refrigeration cycle system 1 is turned off by the cooling thermostat. When it is in a state (cooling thermo-off machine), in a blower operation state (blower), or in a stopped state (stop machine), each indoor expansion valve 22 is opened to a predetermined opening degree. Control.
Thereby, during the oil recovery control, the oil staying in the indoor unit 20 can be efficiently recovered together with the refrigerant in the liquid phase state.

(Embodiment 2)
Next, Embodiment 2 of the present invention will be described.
The configuration of the refrigeration cycle system according to the second embodiment is the same as the configuration described with reference to FIGS. 1 and 2 in the first embodiment, and the detailed description thereof will be omitted.
In the first embodiment, the oil recovery control was shifted (the oil recovery control was started) according to the value of the suction superheat degree, the value of the operating frequency of the compressor 12, and the integrated time ta, but in the second embodiment. Determines the ease with which the oil flows out from the compressor 12 and the difficulty with the oil returning to the compressor 12, and the control unit 40 performs oil recovery control based on this determination. As a result, oil recovery control can be performed at a more appropriate timing.

In the refrigeration cycle system 1, the ease of oil outflow can be determined from the discharge superheat degree So of the compressor 12 and the operating frequency f. As the discharge superheat degree So of the compressor 12 decreases, the oil tends to flow out, and as the operating frequency f of the compressor 12 increases, the oil tends to flow out. Further, the difficulty of returning the oil can be determined from the suction superheat degree Si of the compressor 12 and the maximum opening degree O of the indoor expansion valve 22. As the suction superheat degree Si of the compressor 12 increases, it becomes difficult for the oil to return, and as the maximum opening degree O of the indoor expansion valve 22 of the indoor unit 20 increases, it becomes difficult for the oil to return.
Therefore, in the present embodiment, the discharge superheat degree of the compressor 12 and the weighting value (weight value) with respect to the operating frequency of the compressor 12 are set in advance for the ease of oil outflow. Further, regarding the difficulty of returning the oil, a weighting value (weight value) for the suction superheat degree of the compressor 12 and the maximum opening degree of the indoor expansion valve 22 is set in advance. Each set weighting value (weighting value) is stored in advance in the control unit 40 as, for example, a data table.

FIG. 5 is a diagram showing an example of each weight value.
In the present embodiment, the discharge superheat degree So (unit: K) of the compressor 12 and the operating frequency f (unit: Hz) of the compressor 12, which are indicators of “easiness of oil outflow”, and “oil The range in which each numerical value of the suction superheat degree Si (unit: K) of the compressor and the maximum opening O (unit: pulse) of the indoor expansion valve 22 of the indoor unit 20, which are indicators of "difficulty in returning", can be taken. It is divided into a plurality of ranges, and the corresponding weight values C1 to C4 are set.
As shown in FIG. 5, in the present embodiment, the number of divisions for weighting is set to 3 or 4 as an example, but the number of divisions may be plural and is not limited to 3 or 4.

As shown in FIG. 5, the weight value C1 of the discharge superheat degree So of the compressor 12 is C1 = 7.2 when the discharge superheat degree So is in the range of 0 ≦ So <5K, and C1 in the range of 5K ≦ So <10K. = 3.0 and C1 = 0.2 in the range of 10K ≦ So, respectively. That is, the lower the discharge superheat degree So of the compressor 12, the more easily the oil flows out. Therefore, the lower the discharge superheat degree So, the larger the weight value of the oil outflow easiness is set.

Similarly, the weight value C2 of the operating frequency f of the compressor 12 is C2 = 0.5 in the range of the operating frequency f of 0 ≦ f <46 Hz, C2 = 0.6 in the range of 46 Hz ≦ f <65 Hz, and 65 Hz. In the range of ≦ f <80 Hz, C2 = 0.8 is set, and in the range of 80 Hz ≦ f, C2 = 1.8 is set. That is, the higher the operating frequency f of the compressor 12, the easier it is for oil to flow out. Therefore, the higher the operating frequency f, the larger the weight value of the ease of oil flowing out.
Note that the weight value C1 and the weight value C2 may be arbitrarily changed as long as they have a magnitude relationship indicating the ease of oil outflow.

The weight value C3 of the suction superheat degree Si of the compressor 12 is C3 = 0.6 when the suction superheat degree Si is in the range of 0 ≦ Si <5K, and C3 = 0.7 in the range of 5K ≦ Si <10K. In the range of ≦ Si, C3 = 0.8 is set respectively. That is, the higher the suction superheat degree Si of the compressor 12, the more difficult it is for the oil to return. Therefore, the higher the suction superheat degree Si, the greater the weight value of the difficulty of returning the oil.

The weight value C4 of the maximum opening degree O of the indoor expansion valve 22 in the indoor unit 20 is C4 = 0.6 when the maximum opening degree O is in the range of O <200 pulses and C4 in the range of 200 pulses ≤ O <340 pulses. = 0.7, and C4 = 0.8 in the range of 340 pulses ≤ O ≤ 480, respectively. That is, the larger the maximum opening degree O of the indoor expansion valve 22, the more difficult it is for the oil to return. Therefore, the higher the maximum opening degree O, the greater the weight value of the difficulty of returning the oil.
When a plurality of indoor units 20 are connected, the opening degree of all the connected indoor units 20 is detected, and the largest of the detected opening degree is adopted as the maximum opening degree O. Weight.

Note that the weight values C3 and C4 may be arbitrarily changed as long as they have a magnitude relationship indicating the difficulty of returning the oil. Further, the classification of the range in which each weight value and each detected value (So, f, Si, O) can be taken is not limited to the value shown in FIG. 5, and the scale of the refrigeration cycle system 1 and the compressor 12 It may be adjusted to an arbitrary value or range as necessary, such as the capacity of the unit and the performance of the indoor unit 20.

Further, in the present embodiment, the control unit 40 calculates the discharge superheat degree So of the compressor 12 based on the detected values of the temperature and pressure of the discharge refrigerant of the compressor 12 detected by the discharge temperature sensor 30 and the high pressure sensor 31. The control unit 40 acquires the operating frequency f of the compressor 12 that it controls.
Further, the control unit 40 calculates the suction superheat degree Si of the compressor 12 based on the detected values of the temperature and pressure of the suction refrigerant of the compressor 12 detected by the suction temperature sensor 36 and the low pressure sensor 37. The control unit 40 acquires the maximum opening degree O of the indoor expansion valve 22 that it controls.

The control unit 40 has a weight value C1 of the discharge superheat degree of the compressor 12 and a weight value of the operating frequency of the compressor 12 based on the calculated discharge superheat degree So of the compressor 12 and the acquired operating frequency f of the compressor 12. Set C2.
Similarly, the control unit 40 has a weight value C3 of the suction superheat degree of the compressor 12 and an indoor expansion valve 22 based on the calculated suction superheat degree Si of the compressor 12 and the acquired maximum opening degree O of the indoor expansion valve 22. The weight value C4 of the maximum opening degree of is set.

Further, the control unit 40 obtains the determination count value C5 of the weighted value by the following formula based on each weighted value.
Judgment count value C5 = (weight value C1 of discharge superheat degree x weight value C2 of operating frequency) + (weight value C3 of suction superheat degree x weight value C4 of maximum opening of indoor expansion valve)
The control unit 40 calculates the determination count value C5 at arbitrary interval times (for example, every minute), integrates the calculation results, and stores the integrated value as the integrated count value C5Σ.

Further, acquisition of the weight value C1 of the discharge superheat degree of the compressor 12, the weight value C2 of the operating frequency of the compressor 12, the weight value C3 of the suction superheat degree of the compressor 12, and the weight value C4 of the maximum opening degree of the indoor expansion valve. And the determination of the weighting value based on these acquired values is also performed every predetermined interval time ti (arbitrary interval time). The predetermined time in this case is measured by the integration timer 41.
Then, in the present embodiment, the control unit 40 determines whether or not the integrated count value C5Σ exceeds the predetermined count value Ct, and if it is determined that the integrated count value Ct exceeds the predetermined count value Ct, performs oil recovery control. In the present embodiment, the predetermined count value Ct is set to, for example, 150 counts.

Next, the operation of the second embodiment will be described.
However, in the following description, for convenience of explanation, the integration timer 41 will be divided into three integration timers 41i, 41b, and 41c.
The integration timer 41i is a timer for counting (counting) the predetermined interval time ti, and the timers 41b and 41c are the same as those in the first embodiment. 41b, and the timer 41c is a timer that counts the time for raising the frequency of the compressor 12 during oil recovery control. Further, as the realization means, one integration timer may be used, or a plurality of integration timers may be appropriately used.

FIG. 6 is a flowchart showing a control process executed by the control unit 40.
When the operating state of the refrigeration cycle system 1 is the cooling operation (ST21: YES), the control unit 40 starts the counting (timekeeping) operation of the integration timer 41i (ST22).
After that, when the predetermined interval time ti elapses (ST23: YES), the discharge superheat degree So of the compressor 12 is calculated and the operating frequency f of the compressor 12 is acquired. Then, the weighted values C1 and C2 are determined based on the discharge superheat degree So of the compressor 12 and the operating frequency f of the compressor 12 (ST24).
Subsequently, the control unit 40 acquires the calculated suction superheat degree Si of the compressor 12 and the maximum opening degree O of the indoor expansion valve 22, and the suction superheat degree Si of the compressor 12 and the maximum opening degree O of the indoor expansion valve 22. Based on, the respective weight values C3 and C4 are determined (ST25).

The control unit 40 calculates the determination count value C5 of the weight value by using each weight value determined in step ST24 and step ST25 and the above-mentioned equation (ST26). The current determination count value C5 calculated in step ST26 is integrated with the integrated count value C5 (C5 = 0 in the initial state) accumulated up to the previous time, and the current integrated count value ΣC5 is calculated (ST27). The calculated current integrated count value ΣC5 is stored in the RAM or the like of the control unit 40.
The control unit 40 compares the stored integrated count value ΣC5 with a preset predetermined count value Ct, and determines whether or not the integrated count value ΣC5 exceeds the predetermined count value Ct (ST29). When the control unit 40 determines in step ST29 that the integrated count value ΣC5 exceeds the predetermined count value Ct (ST29: YES), the control unit 40 starts the oil recovery control.

On the other hand, if it is determined in step ST29 that the integrated count value ΣC5 does not exceed the predetermined count value Ct (ST29: NO), the integrated timer 41i is reset (the time counting time of the integrated timer 41i is set to zero (ST30)). After initializing the integration timer 41i in step ST30, the processing flow is returned to step ST21.

When it is determined in step ST29 that the integrated count value ΣC5 exceeds the predetermined count value Ct and the oil recovery control is started, the control unit 40 sets the operating frequency of the compressor 12 to the target frequency as in the first embodiment. Along with reducing the frequency to f1 (ST31), the timekeeping operation of the integration timer 41b is executed (ST32).
Then, the control unit 40 determines the time accumulated by the timer 41b. That is, it is determined whether or not the predetermined time td has elapsed in the operation in which the operating frequency of the compressor 12 is lowered (ST33).

In step ST33, when the control unit 40 determines that the operation of lowering the operating frequency of the compressor 12 has elapsed the predetermined time td (ST33: YES), the timer 41b is reset (ST34), and the compressor Control is performed so that the tu operating frequency f is increased for a predetermined time while increasing the operating frequency of 12 to the target frequency f2 (ST35). At this time, the time counting operation of the integration timer 41c is started (ST36).

After that, the control unit 40 determines the time accumulated by the timer 41c. That is, it is determined whether or not the predetermined time tu has elapsed in the operation in which the operating frequency of the compressor 12 is increased (ST37).
In step ST37, when it is determined that the operation of increasing the operating frequency of the compressor 12 has elapsed for a predetermined time (ST37: YES), the control unit 40 resets the integration timer 41c (ST38) and retains the memory. The integrated count value ΣC5 is reset (changed to zero or the initial value), and the control returns to the normal cooling operation (ST40).
After returning to the normal cooling operation, the process may be returned to step ST21, but the process of step S21 may be started after an arbitrary time has elapsed.

As described above, in the present embodiment, the control unit 40 determines the ease of oil outflow from the compressor 12 and the difficulty of returning the oil to the compressor 12, and the ease of oil outflow. Weighting is performed based on the difficulty of returning, and oil recovery control is performed based on the integrated value of this weighting.
As a result, the amount of oil inside the compressor 12 can be determined, and the oil recovery control is performed according to the amount of oil inside the compressor 12, so that unnecessary oil recovery operation can be suppressed and air conditioning can be achieved. It is possible to maintain a state in which sufficient oil is always present in the compressor 12 while suppressing fluctuations in the compressor 12.

Further, in the present embodiment, the indoor unit 20 includes an indoor expansion valve 22, and the ease of oil outflow from the control unit 40 is based on the degree of superheat discharged from the compressor 12 and the operating frequency of the compressor 12. The difficulty of returning the oil is determined based on the suction superheat degree of the compressor 12 and the maximum opening degree of the indoor expansion valve 22.
This makes it possible to determine whether or not the amount of oil inside the compressor 12 is appropriate.
The predetermined count value Ct takes into consideration the numerical value of the weight value, the scale of the refrigeration cycle system 1 (the number of connected outdoor units 10 and indoor units 20, the length of the refrigerant pipe 11, etc.), the capacity of the compressor 12, and the like. Then, it may be set as an appropriate value.

As described above, according to the present invention, the problems of the prior art are solved.
That is, in the conventional technique, the operating frequency of the compressor for the purpose of keeping the refrigerant at a certain flow velocity or higher is increased immediately after the oil recovery operation is started, so that the evaporation pressure during the oil recovery operation is performed. Will decrease, and it will be difficult for liquid refrigerant to exist in the low-pressure piping section. Therefore, in order to return the oil, a large amount of liquid refrigerant must flow into the low pressure side, which may cause excessive liquid backing and impair the reliability of the compressor. In particular, if there is a stop machine that has been stopped for a long time and the temperature of the indoor heat exchanger and connecting pipes has risen to the ambient temperature, is it difficult for the liquid refrigerant to flow in that part, resulting in insufficient oil recovery? Alternatively, if the operation is focused on collecting oil in that portion, a large amount of liquid will be backed up from another indoor unit during cooling operation.

On the other hand, the refrigeration cycle system of the present invention includes an outdoor unit equipped with a compressor and an outdoor heat exchanger whose capacity can be changed by changing the operating frequency, and a plurality of indoor units connected to the outdoor unit. The refrigeration cycle apparatus provided with the above is provided with a control unit provided with a counting means for accumulating the operating time of the cooling operation, and the control unit satisfies the condition that oil is accumulated on the low pressure side of the compressor by the counting means. When the integrated time of the operating time in the state becomes a predetermined time or more, the oil recovery control is performed to lower the operating frequency of the compressor and increase the operating frequency of the compressor after the elapse of the predetermined time.
Therefore, when the operating frequency of the compressor is lowered by the control unit during oil recovery control, the pressure of the refrigerant pipe on the low pressure side rises, and the refrigerant tends to be in a liquid phase state in all of the low pressure pipe parts. The oil staying in all the refrigerant pipes dissolves in the refrigerant in the liquid phase state, and the fluidity of the oil is improved. Therefore, it is possible to recover the oil accumulated in all of the low-pressure side refrigerant pipes and the indoor unit together with the liquid-phase refrigerant.

Further, according to the present invention, even if there is an indoor unit (stopper) whose operation has been stopped for a long time so that the temperature of the low-pressure piping portion rises to the ambient temperature, the inside of the stopper is indoors. Since the evaporation pressure is also raised for the heat exchanger and the connecting pipe, the oil can be easily dissolved in the liquid phase refrigerant, which makes the oil recovery more reliable than the conventional one. It can be done easily.
Further, according to the present invention, since the generation of the refrigerant in the liquid phase state for improving the fluidity of the oil is performed by increasing the evaporation pressure, it evaporates in the process of returning to the normal operating state. Since the pressure drops and the liquid refrigerant evaporates, excessive liquid backing can be prevented.

INDUSTRIAL APPLICABILITY The present invention can appropriately recover the oil accumulated in the piping and the indoor unit in the refrigeration cycle system, and can be applied to applications such as a refrigerator, an air conditioner, and a hot water supply / air conditioning complex.

1 Refrigeration cycle system 10 Outdoor unit 11 Coolant piping 12 Compressor 13 Oil separator 16 Outdoor heat exchanger 18 Accumulator 19 Oil return hole 20 Indoor unit 21 Indoor heat exchanger 22 Indoor expansion valve 30 Discharge temperature sensor 31 High pressure sensor 32 High pressure switch 33 Heat exchange gas temperature sensor 34 Heat exchange liquid temperature sensor 35 Outside temperature sensor 36 Suction temperature sensor 37 Low pressure sensor 38 Indoor liquid temperature sensor 39 Indoor gas temperature sensor 40 Control unit 41 Integration timer

Claims (3)

In the refrigeration cycle system
An outdoor unit equipped with a compressor with variable capacity whose capacity changes according to the operating frequency, an indoor unit connected to the outdoor unit and equipped with an indoor expansion valve, and a control unit that comprehensively controls the refrigeration cycle system. With
The control unit lowers the operating frequency of the compressor based on the operating frequency of the compressor, the discharge superheat degree of the compressor, the suction superheat degree of the compressor, and the maximum opening degree of the indoor expansion valve. A refrigeration cycle system characterized in that oil recovery control for increasing the operating frequency of the compressor is performed after the operation. Control that comprehensively controls a refrigeration cycle system equipped with an outdoor unit equipped with a compressor with variable capacity whose capacity changes according to the operating frequency, and an indoor unit connected to the outdoor unit and equipped with an indoor expansion valve. It ’s a unit,
After lowering the operating frequency of the compressor based on the operating frequency of the compressor, the degree of discharge overheating from the compressor, the degree of suction overheating of the compressor, and the maximum opening degree of the indoor expansion valve, the compression is performed. A control unit characterized by performing oil recovery control that raises the operating frequency of the machine. It is an outdoor unit equipped with a compressor with variable capacity whose capacity changes according to the operating frequency.
It is connected to an indoor unit equipped with an indoor expansion valve and a refrigeration cycle system equipped with a control unit that controls the system in an integrated manner.
The control unit lowered the operating frequency of the compressor based on the operating frequency of the compressor, the discharge superheat degree of the compressor, the suction superheat degree of the compressor, and the maximum opening degree of the indoor expansion valve. An outdoor unit characterized in that a command for increasing the operating frequency of the compressor is later transmitted, and the operating frequency of the compressor is changed according to the transmitted signal.

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