Patent Description:
Conventionally, there has been a refrigeration apparatus including a container that temporarily stores a refrigerant returning from an evaporator to a compressor. Refrigerating machine oil is sealed in a refrigerant circuit of the refrigeration apparatus together with the refrigerant, and the refrigerant and the refrigerating machine oil may separate in the container depending on temperature and pressure conditions. For this problem, <CIT> discloses an invention that executes an operation of stirring the separated refrigerant and refrigerating machine oil to solve the separation state. Furthermore, <CIT> discloses a refrigeration apparatus according to the preamble of claim <NUM>.

The above-described <CIT> discloses the invention that operates the compressor at a high number of revolutions in order to stir the separated refrigerant and refrigerating machine oil, but it may not be preferable in some situations to increase the number of revolutions of the compressor in such a way.

A refrigeration apparatus according to claim <NUM> is provided. A refrigeration apparatus of a first aspect includes a refrigerant circuit, a detection unit, and a control unit. In the refrigerant circuit, a compressor, a radiator, an expansion valve, an evaporator, and a container are connected in order. The refrigerant flows inside the refrigerant circuit. The detection unit detects the temperature or pressure of the refrigerant. The control unit controls the number of revolutions of the compressor and the opening degree of the expansion valve. On determination that the refrigerant and a lubricating oil are separated inside the container based on a detection result of the detection unit, the control unit executes first control and second control. The first control is control to decrease the number of revolutions of the compressor. The second control sets the opening degree of the expansion valve to a predetermined opening degree.

Here, the first and second control to decrease the number of revolutions of the compressor and set the opening degree of the expansion valve to a predetermined opening degree is executed when the refrigerant and the lubricating oil are separated inside the container. Therefore, the pressure on the suction side of the compressor including the container (hereinafter referred to as low pressure value) can be increased. This makes it possible to change the pressure and temperature in the container to solve the separation state between the refrigerant and the lubricating oil.

The refrigeration apparatus of a second aspect is the refrigeration apparatus of the first aspect, in which in the second control, the control unit sets the opening degree of the expansion valve to an opening degree of a fully open position or <NUM>% or more of the fully open position.

Here, since the opening degree of the expansion valve is near the fully open position when the refrigerant and the lubricating oil are separated inside the container, a large amount of high-temperature refrigerant flows into the container. This solves the separation state of the refrigerant and the lubricating oil at an early stage.

The refrigeration apparatus of a third aspect is the refrigeration apparatus of the first aspect or the second aspect, in which in the first control, the control unit decreases the number of revolutions of the compressor to set the number of revolutions of the compressor to a predetermined number of revolutions.

Here, since the number of revolutions of the compressor decreases to the predetermined number of revolutions, the separation state between the refrigerant and the lubricating oil is solved at an early stage.

The refrigeration apparatus of a fourth aspect is the refrigeration apparatus of the third aspect, in which the control unit has an oil return operation other than the first control and the second control. The oil return operation is an operation of returning the lubricating oil staying in the refrigerant circuit except the compressor to the compressor.

The refrigeration apparatus of the fourth aspect also has the oil return operation of the conventional refrigeration apparatus. However, the oil return operation, in which the motor of the compressor is turned at a relatively high number of revolutions, may not be preferable as an operation to solve the separation state between the refrigerant and the lubricating oil inside the container. Therefore, the control unit of the refrigeration apparatus of the fourth aspect has, apart from the oil return operation, an operation to solve the separation between the refrigerant and the lubricating oil in the container by the first control and second control.

The refrigeration apparatus of a fifth aspect is the refrigeration apparatus of the fourth aspect, in which when a condition that an integrated value of an amount of the refrigerant circulating in the refrigerant circuit exceeds a threshold value is satisfied, the control unit executes the oil return operation.

The refrigeration apparatus of a sixth aspect is the refrigeration apparatus of the fourth aspect or the fifth aspect, in which the predetermined number of revolutions in the first control is smaller than the number of revolutions of the compressor in the oil return operation.

Here, in contrast to the oil return operation of turning the compressor at a relatively high number of revolutions, in the first control to solve the separation between the refrigerant and the lubricating oil in the container, the number of revolutions of the compressor is decreased. Since the compressor is turned at a lower number of revolutions (predetermined number of revolutions) unlike the oil return operation, the pressure in the container increases and the separation state between the refrigerant and the lubricating oil in the container is more easily solved.

The refrigeration apparatus of a seventh aspect is the refrigeration apparatus of any one of the first aspect to the sixth aspect, in which when a request for stopping the compressor is received, the control unit determines whether to execute the first control and the second control before stopping the compressor based on a detection result of the detection unit.

Here, when the refrigerant and the lubricating oil are separated inside the container, the first control and the second control are executed before stopping the compressor. Therefore, the situation in which the compressor is stopped while the refrigerant and the lubricating oil are separated in the container and the compressor runs out of lubricating oil when the compressor is started again is inhibited.

Note that the request for stopping the compressor is a stop request based on an operation stop manipulation by a user of the refrigeration apparatus, or a stop request when the request for refrigerant circulation in a user-side unit of the refrigeration apparatus is temporarily canceled. The latter stop request is, for example, a thermo-off signal in the indoor unit, which is the user-side unit of an air conditioning apparatus, when the room temperature in the cooling operation becomes less than the set temperature.

The refrigeration apparatus of an eighth aspect is the refrigeration apparatus of any one of the first aspect to the sixth aspect, in which when a request to stop the compressor is received, the control unit determines whether the refrigerant and the lubricating oil are separated inside the container by a first criterion based on the detection result of the detection unit. When the request to stop the compressor is not received, the control unit determines whether the refrigerant and the lubricating oil are separated inside the container by a second criterion different from the first criterion based on the detection result of the detection unit.

Here, when the request to stop the compressor is received or not, it is determined whether the refrigerant and the lubricating oil are separated inside the container based on the detection result of the detection unit. Therefore, both when the compressor is operating and when the compressor is stopped, the first control and second control to solve the separation state between the refrigerant and the lubricating oil can be executed. The criterion for determining whether the refrigerant and the lubricating oil are separated inside the container is changed depending on whether the request to stop the compressor is received or not. This makes it possible, for example, to decrease the frequency at which the first and second control is executed when the compressor is operating, and to increase the frequency at which the first and second control is executed when the compressor stops.

The refrigeration apparatus of a ninth aspect is the refrigeration apparatus of any one of the first aspect to the eighth aspect, in which the detection unit includes a sensor. The sensor measures the temperature of the refrigerant in the container or the temperature of the refrigerant flowing through the refrigerant pipe connected to the container.

Here, the temperature of the refrigerant in the container can be accurately detected from the measured values of the temperature sensor and/or pressure sensor.

The refrigeration apparatus of a tenth aspect is the refrigeration apparatus of any one of the first aspect to the ninth aspect, in which the refrigerant circulating through the refrigerant circuit is R32.

The refrigeration apparatus of an eleventh aspect is the refrigeration apparatus of any one of the first aspect to the tenth aspect, in which on determination that the refrigerant and the lubricating oil are separated inside the container from the detection result of the detection unit, the control unit executes the first control and the second control to keep operating the compressor for a predetermined period of <NUM> minute to <NUM> minutes.

Hereinafter, an air conditioning apparatus as a refrigeration apparatus will be described with reference to the drawings.

<FIG> is a schematic configuration diagram of an air conditioning apparatus <NUM> (refrigeration apparatus). The air conditioning apparatus <NUM> is an apparatus capable of cooling and heating a room of a building or the like by a vapor compression refrigeration cycle. The air conditioning apparatus <NUM> includes an outdoor unit <NUM> and an indoor unit <NUM>. The outdoor unit <NUM> and the indoor unit <NUM> are connected via a liquid-refrigerant connection pipe <NUM> and a gas-refrigerant connection pipe <NUM>. A refrigerant circuit <NUM> that constitutes the vapor compression refrigeration cycle of the air conditioning apparatus <NUM> is configured by the outdoor unit <NUM> and the indoor unit <NUM> being connected via the refrigerant connection pipes <NUM> and <NUM>. Difluoromethane (R32), which is a refrigerant, is charged in the refrigerant circuit <NUM>. Refrigerating machine oil, which is immiscible with the refrigerant, is also charged in the refrigerant circuit <NUM> together with the refrigerant.

The indoor unit <NUM> is installed indoors and constitutes part of the refrigerant circuit <NUM>. The indoor unit <NUM> includes an indoor heat exchanger <NUM>.

In a cooling operation, the indoor heat exchanger <NUM> functions as an evaporator for a refrigerant to cool indoor air, and in a heating operation, the indoor heat exchanger <NUM> functions as a radiator for a refrigerant to heat indoor air. A first end of the indoor heat exchanger <NUM> is connected to the liquid-refrigerant connection pipe <NUM>. A second end of the indoor heat exchanger <NUM> is connected to the gas-refrigerant connection pipe <NUM>.

The indoor unit <NUM> includes an indoor fan <NUM>. The indoor fan <NUM> sucks indoor air into the indoor unit <NUM>, exchanges heat with the refrigerant in the indoor heat exchanger <NUM>, and then supplies the air indoors as supply air. The indoor fan <NUM> is, for example, a centrifugal fan, a multi-blade fan, or the like driven by an indoor fan motor <NUM>. The indoor fan motor <NUM> can change a frequency (number of revolutions) by an inverter.

The indoor unit <NUM> includes various sensors. The indoor unit <NUM> includes a liquid pipe temperature sensor <NUM>, an intermediate temperature sensor <NUM>, and an indoor temperature sensor <NUM>. The liquid pipe temperature sensor <NUM> detects a temperature Trl of the refrigerant in the liquid side refrigerant pipe of the indoor heat exchanger <NUM>. The intermediate temperature sensor <NUM> detects a temperature Trm of the refrigerant in an intermediate portion of the indoor heat exchanger <NUM>. The indoor temperature sensor <NUM> detects a temperature Tra of the indoor air sucked into the indoor unit <NUM>.

The outdoor unit <NUM> is installed outdoors and constitutes part of the refrigerant circuit <NUM>. The outdoor unit <NUM> includes a compressor <NUM>, a four-way switching valve <NUM>, an outdoor heat exchanger <NUM>, an expansion valve <NUM>, a liquid-side shutoff valve <NUM>, a gas-side shutoff valve <NUM>, and an accumulator <NUM>. The outdoor unit <NUM> includes an outdoor fan <NUM>.

The compressor <NUM> compresses a low-pressure refrigerant in the refrigeration cycle until the refrigerant turns into a high-pressure refrigerant. The compressor <NUM> drives a positive-displacement compression element (not shown), such as a rotary type or scroll type, to rotate by a compressor motor 21a. Here, as the compressor <NUM>, a rotary compressor with closed structure is used. The compressor motor 21a can change a frequency (number of revolutions) by an inverter. A suction pipe <NUM> is connected to a suction side of the compressor <NUM>, and a discharge pipe <NUM> is connected to a discharge side. The suction pipe <NUM> connects the suction side of the compressor <NUM> to a first port 22a of the four-way switching valve <NUM>. The suction pipe <NUM> is provided with the accumulator <NUM>. The suction pipe <NUM> is divided into a first pipe 31a and a second pipe 31b before and after the accumulator <NUM>. The accumulator <NUM> is a container that temporarily stores the refrigerant sucked into the compressor <NUM>. The accumulator <NUM> will be described in detail later with reference to <FIG>. The discharge pipe <NUM> is a refrigerant pipe connecting the discharge side of the compressor <NUM> to a second port 22b of the four-way switching valve <NUM>.

The four-way switching valve <NUM> switches a refrigerant flow direction in the refrigerant circuit <NUM>.

When starting the cooling operation, the four-way switching valve <NUM> switches to the cooling cycle state in which the outdoor heat exchanger <NUM> functions as a radiator for the refrigerant compressed in the compressor <NUM>, and the indoor heat exchanger <NUM> functions as an evaporator for the refrigerant that has radiated heat in the outdoor heat exchanger <NUM>. When starting the cooling operation, the four-way switching valve <NUM> switches such that the second port 22b and a third port 22c communicate with each other, and the first port 22a and a fourth port 22d communicate with each other. Accordingly, the discharge side of the compressor <NUM> (discharge pipe <NUM>) is connected to a gas side of the outdoor heat exchanger <NUM> (first gas refrigerant pipe <NUM>) (see the solid line in the four-way switching valve <NUM> in <FIG>). Furthermore, the suction side of the compressor <NUM> (suction pipe <NUM>) is connected to the gas-refrigerant connection pipe <NUM> side (second gas refrigerant pipe <NUM>) (see the solid line in the four-way switching valve <NUM> in <FIG>).

When starting the heating operation, the four-way switching valve <NUM> switches to the heating cycle state in which the outdoor heat exchanger <NUM> functions as an evaporator for the refrigerant that has radiated heat in the indoor heat exchanger <NUM>, and the indoor heat exchanger <NUM> functions as a radiator for the refrigerant compressed in the compressor <NUM>. When starting the heating operation, the four-way switching valve <NUM> switches such that the second port 22b and the fourth port 22d communicate with each other, and the first port 22a and the third port 22c communicate with each other. Accordingly, the discharge side of the compressor <NUM> (discharge pipe <NUM>) is connected to the gas-refrigerant connection pipe <NUM> side (second gas refrigerant pipe <NUM>) (see the broken line in the four-way switching valve <NUM> in <FIG>). Furthermore, the suction side of the compressor <NUM> (suction pipe <NUM>) is connected to the gas side of the outdoor heat exchanger <NUM> (first gas refrigerant pipe <NUM>) (see the broken line in the four-way switching valve <NUM> in <FIG>). The first gas refrigerant pipe <NUM> is a refrigerant pipe that connects the third port 22c of the four-way switching valve <NUM> to the gas side of the outdoor heat exchanger <NUM>. The second gas refrigerant pipe <NUM> is a refrigerant pipe that connects the fourth port 22d of the four-way switching valve <NUM> to the gas-refrigerant connection pipe <NUM> side.

In the cooling operation, the outdoor heat exchanger <NUM> functions as a radiator for the refrigerant whose cooling source is outdoor air. In the heating operation, the outdoor heat exchanger <NUM> functions as an evaporator for the refrigerant whose heating source is outdoor air. A first end on the liquid side of the outdoor heat exchanger <NUM> is connected to a liquid refrigerant pipe <NUM>, and a second end on the gas side is connected to the first gas refrigerant pipe <NUM>. The liquid refrigerant pipe <NUM> is a refrigerant pipe that connects the first end on the liquid side of the outdoor heat exchanger <NUM> to the liquid-refrigerant connection pipe <NUM>.

In the cooling operation, the expansion valve <NUM> decompresses the high-pressure refrigerant that has radiated heat in the outdoor heat exchanger <NUM> in the refrigeration cycle to low pressure in the refrigeration cycle. In the heating operation, the expansion valve <NUM> decompresses the high-pressure refrigerant that has radiated heat in the indoor heat exchanger <NUM> in the refrigeration cycle to low pressure in the refrigeration cycle. The expansion valve <NUM> is provided in the liquid refrigerant pipe <NUM>. The expansion valve <NUM> is an electric expansion valve with a changeable opening degree.

The liquid-side shutoff valve <NUM> and the gas-side shutoff valve <NUM> are provided in connecting ports with external devices and pipes (specifically, liquid-refrigerant connection pipe <NUM> and gas-refrigerant connection pipe <NUM>). The liquid-side shutoff valve <NUM> is provided at an end of the liquid refrigerant pipe <NUM>. The gas-side shutoff valve <NUM> is provided at an end of the second gas refrigerant pipe <NUM>. The liquid-side shutoff valve <NUM> and the gas-side shutoff valve <NUM> are manual valves that are opened and closed by hand.

The outdoor fan <NUM> plays a role of sucking outdoor air into the outdoor unit <NUM> to exchange heat with the refrigerant in the outdoor heat exchanger <NUM>, and then discharging the air to the outside. The outdoor fan <NUM> is a propeller fan or the like driven by an outdoor fan motor <NUM>. The outdoor fan motor <NUM> can change a frequency (number of revolutions) by an inverter.

The outdoor unit <NUM> includes various sensors. The outdoor unit <NUM> includes a suction temperature sensor <NUM>, a discharge temperature sensor <NUM>, an intermediate temperature sensor <NUM>, a liquid pipe temperature sensor <NUM>, and an outside air temperature sensor <NUM>. The suction temperature sensor <NUM> detects a temperature Ts of the low-pressure refrigerant sucked into the compressor <NUM> in the refrigeration cycle. The discharge temperature sensor <NUM> detects a temperature Td of the high-pressure refrigerant discharged from the compressor <NUM> in the refrigeration cycle. The intermediate temperature sensor <NUM> detects a temperature Tom of the refrigerant in the intermediate portion of the outdoor heat exchanger <NUM>. The liquid pipe temperature sensor <NUM> detects a temperature Tol of the refrigerant on the liquid side of the outdoor heat exchanger <NUM>. The outside air temperature sensor <NUM> detects a temperature Toa of the outdoor air sucked into the outdoor unit <NUM>.

As described above, the accumulator <NUM> of the outdoor unit <NUM> is disposed between the suction side of the compressor <NUM> and the first port 22a of the four-way switching valve <NUM>. The accumulator <NUM> has a function of separating the refrigerant into gas and liquid, and storing excess refrigerant on the suction side of the compressor <NUM>. The accumulator <NUM> separates, into gas and liquid, the refrigerant returned from the indoor heat exchanger <NUM> or the outdoor heat exchanger <NUM> serving as an evaporator through the first pipe 31a of the suction pipe <NUM> connected to the four-way switching valve <NUM>. Out of the refrigerant separated into gas and liquid, the gas refrigerant is sent to the compressor <NUM>. As shown in <FIG>, the accumulator <NUM> includes a casing <NUM> forming an internal space IS, an inlet pipe <NUM>, and an outlet pipe <NUM>.

The casing <NUM> mainly includes a cylindrical body 71a, a bowl-shaped upper lid 71b closing an opening above the body 71a, and a bowl-shaped lower lid 71c closing an opening below the body 71a. The inlet pipe <NUM> introduces the refrigerant that has passed through the first pipe 31a of the suction pipe <NUM> into the internal space IS. The inlet pipe <NUM> penetrates a periphery of the upper lid 71b. A tip opening 72a of the inlet pipe <NUM> is disposed in an upper portion of the internal space IS.

The outlet pipe <NUM> of the accumulator <NUM> guides the gas refrigerant separated in the internal space IS to the second pipe 31b of the suction pipe <NUM> connected to the compressor <NUM>. The outlet pipe <NUM> is a J-shaped pipe. The outlet pipe <NUM> penetrates the upper lid 71b and makes a U-turn in a lower portion of the internal space IS. The height position of an opening 73a at an upper end (tip) of the outlet pipe <NUM> is located in an upper portion of the internal space IS. An oil return hole 73b is formed in the U-turn portion of the outlet pipe <NUM> in the lower portion of the internal space IS. The oil return hole 73b is provided to return the refrigerating machine oil accumulated together with the liquid refrigerant in the lower portion of the internal space IS of the casing <NUM> to the compressor <NUM>. A pressure equalizing hole 73c is formed in a portion of the outlet pipe <NUM> near the upper lid 71b.

The outlet pipe <NUM> of the accumulator <NUM> is connected to the compressor <NUM> by the second pipe 31b of the suction pipe <NUM>.

The refrigerant connection pipes <NUM> and <NUM> are refrigerant pipes constructed on the spot when the air conditioning apparatus <NUM> is installed at an installation location such as a building. The length and pipe diameter of the refrigerant connection pipes <NUM> and <NUM> are selected according to installation conditions such as the installation location and a combination of the outdoor unit <NUM> and the indoor unit <NUM>.

As described above, part of the refrigerant circuit <NUM> of the indoor unit <NUM> is connected to part of the refrigerant circuit <NUM> of the outdoor unit <NUM> by the refrigerant connection pipes <NUM> and <NUM>, constituting the refrigerant circuit <NUM> as a whole. In the refrigerant circuit <NUM>, mainly, the compressor <NUM>, the outdoor heat exchanger <NUM> which functions as a radiator or evaporator for the refrigerant, the expansion valve <NUM>, the indoor heat exchanger <NUM> which functions as an evaporator or radiator for the refrigerant, and the accumulator (container) <NUM> are connected in order.

<FIG> is a control block diagram of the air conditioning apparatus <NUM> (refrigeration apparatus). The air conditioning apparatus <NUM> includes a control unit <NUM> that controls constituent devices. The control unit <NUM> is configured by connecting an outdoor control unit <NUM>, an indoor control unit <NUM>, and a remote control device <NUM> via a transmission line or a communication line. The outdoor control unit <NUM> is provided in the outdoor unit <NUM>. The indoor control unit <NUM> is provided in the indoor unit <NUM>. The remote control device <NUM> is provided indoors. Here, the control units <NUM> and <NUM> and the remote control device <NUM> are connected by wire via a transmission line or a communication line, but may be wirelessly connected.

The outdoor control unit <NUM> is provided in the outdoor unit <NUM> as described above, and mainly includes an outdoor CPU 38a, an outdoor transmission unit 38b, and an outdoor storage unit 38c. The outdoor control unit <NUM> receives detection signals such as signals from the temperature sensors <NUM> to <NUM>.

The outdoor CPU 38a is connected to the outdoor transmission unit 38b and the outdoor storage unit 38c. The outdoor transmission unit 38b transmits control data and the like to and from the indoor control unit <NUM>. The outdoor storage unit 38c stores control data and the like. The outdoor CPU 38a controls constituent devices provided in the outdoor unit <NUM> (compressor <NUM>, four-way switching valve <NUM>, expansion valve <NUM>, outdoor fan <NUM>, and the like) while transmitting, reading, and writing control data and the like via the outdoor transmission unit 38b and the outdoor storage unit 38c.

The indoor control unit <NUM> is provided in the indoor unit <NUM> as described above, and mainly includes an indoor CPU 44a, an indoor transmission unit 44b, an indoor storage unit 44c, and an indoor communication unit 44d. The indoor control unit <NUM> receives detection signals such as signals from the temperature sensors <NUM> to <NUM>.

The indoor CPU 44a is connected to the indoor transmission unit 44b, the indoor storage unit 44c, and the indoor communication unit 44d. The indoor transmission unit 44b transmits control data and the like to and from the outdoor control unit <NUM>. The indoor storage unit 44c stores control data and the like. The indoor communication unit 44d sends and receives control data and the like to and from the remote control device <NUM>. The indoor CPU 44a controls constituent devices provided in the indoor unit <NUM> (indoor fan <NUM> and the like) while transmitting, reading, writing, sending, and receiving control data and the like via the indoor transmission unit 44b, the indoor storage unit 44c, and the indoor communication unit 44d.

The remote control device <NUM> is provided indoors as described above, and mainly includes a remote control CPU <NUM>, a remote control communication unit <NUM>, a remote control manipulation unit <NUM>, and a remote control display unit <NUM>.

The remote control CPU <NUM> is connected to the remote control communication unit <NUM>, the remote control manipulation unit <NUM>, and the remote control display unit <NUM>. The remote control communication unit <NUM> sends and receives control data and the like to and from the indoor communication unit 44d. The remote control manipulation unit <NUM> receives input such as a control command from a user. The remote control display unit <NUM> displays the operation and the like. The remote control CPU <NUM> receives input such as operation commands and control commands via the remote control manipulation unit <NUM>, and issues control commands and the like to the indoor control unit <NUM> via the remote control communication unit <NUM> while displaying the operating state, control state, and the like on the remote control display unit <NUM>.

Next, the basic operation of the air conditioning apparatus <NUM> (refrigeration apparatus) will be described with reference to <FIG> and <FIG>. As the basic operation, the air conditioning apparatus <NUM> executes the cooling operation and the heating operation.

When a cooling operation command is received via the remote control manipulation unit <NUM> of the remote control device <NUM> or the like, the control unit <NUM> sets the operating mode of the air conditioning apparatus <NUM> to the cooling operation. Then, the control unit <NUM> switches the four-way switching valve <NUM> to the cooling cycle state (state shown by the solid line in <FIG>), drives the compressor <NUM> and the fans <NUM> and <NUM>, and opens the expansion valve <NUM>.

Then, the low-pressure refrigerant in the refrigeration cycle in the refrigerant circuit <NUM> is sucked into the compressor <NUM>, compressed to high pressure in the refrigeration cycle, and then discharged.

The high-pressure gas refrigerant discharged from the compressor <NUM> is sent to the outdoor heat exchanger <NUM> through the four-way switching valve <NUM>.

The high-pressure gas refrigerant sent to the outdoor heat exchanger <NUM> radiates heat by heat exchange with outdoor air supplied as a cooling source by the outdoor fan <NUM> in the outdoor heat exchanger <NUM>, and becomes a high-pressure liquid refrigerant.

The high-pressure liquid refrigerant that has radiated heat in the outdoor heat exchanger <NUM> is sent to the expansion valve <NUM>. The high-pressure liquid refrigerant sent to the expansion valve <NUM> is decompressed by the expansion valve <NUM> to low pressure in the refrigeration cycle.

The low-pressure refrigerant decompressed in the expansion valve <NUM> is sent to the indoor heat exchanger <NUM> through the liquid-side shutoff valve <NUM> and the liquid-refrigerant connection pipe <NUM>.

The low-pressure refrigerant sent to the indoor heat exchanger <NUM> exchanges heat with the indoor air supplied by the indoor fan <NUM> as a heating source to evaporate in the indoor heat exchanger <NUM>. The indoor air is thus cooled and then supplied into the room, thereby cooling the room.

The low-pressure refrigerant evaporated in the indoor heat exchanger <NUM> is sent to the suction pipe <NUM> through the gas-refrigerant connection pipe <NUM>, the gas-side shutoff valve <NUM>, and the four-way switching valve <NUM>. Thereafter, the refrigerant is sucked into the compressor <NUM> again through the accumulator <NUM>.

When a heating operation command is received via the remote control manipulation unit <NUM> of the remote control device <NUM> or the like, the control unit <NUM> sets the operating mode of the air conditioning apparatus <NUM> to the heating operation. Then, the control unit <NUM> switches the four-way switching valve <NUM> to the heating cycle state (state shown by the broken line in <FIG>), drives the compressor <NUM> and the fans <NUM> and <NUM>, and opens the expansion valve <NUM>.

The high-pressure gas refrigerant discharged from the compressor <NUM> is sent to the indoor heat exchanger <NUM> via the four-way switching valve <NUM>, the gas-side shutoff valve <NUM>, and the gas-refrigerant connection pipe <NUM>.

The high-pressure gas refrigerant sent to the indoor heat exchanger <NUM> radiates heat by heat exchange with indoor air supplied as a cooling source by the indoor fan <NUM> in the indoor heat exchanger <NUM>, and becomes a high-pressure liquid refrigerant. The indoor air is thus heated and then supplied into the room, thereby heating the room.

The high-pressure liquid refrigerant that has radiated heat in the indoor heat exchanger <NUM> is sent to the expansion valve <NUM> through the liquid-refrigerant connection pipe <NUM> and the liquid-side shutoff valve <NUM>.

The high-pressure liquid refrigerant sent to the expansion valve <NUM> is decompressed by the expansion valve <NUM> to low pressure in the refrigeration cycle. The low-pressure refrigerant decompressed in the expansion valve <NUM> is sent to the outdoor heat exchanger <NUM>.

The low-pressure liquid refrigerant sent to the outdoor heat exchanger <NUM> exchanges heat with the outdoor air supplied as a heating source by the outdoor fan <NUM> to evaporate in the outdoor heat exchanger <NUM>.

The low-pressure refrigerant evaporated in the outdoor heat exchanger <NUM> is sent to the suction pipe <NUM> through the four-way switching valve <NUM>, and sucked again into the compressor <NUM> through the accumulator <NUM>.

In the above-described basic operation (cooling operation and heating operation), the control unit <NUM> executes compressor capacity control and expansion valve degree of subcooling control as basic control.

The compressor capacity control is control to change the frequency F of the compressor <NUM> based on the temperature difference ΔTra between the indoor temperature Tra and the indoor set temperature Trat. The set temperature Trat is a temperature value set via the remote control manipulation unit <NUM> of the remote control device <NUM>, or the like.

In the cooling operation, the control unit <NUM> obtains the temperature difference ΔTra by subtracting the set temperature Trat from the indoor temperature Tra. In the heating operation, the control unit <NUM> obtains the temperature difference ΔTra by subtracting the indoor temperature Tra from the set temperature Trat.

Since it is required to increase the air conditioning capacity (cooling capacity or heating capacity) as refrigerating capacity when the temperature difference ΔTra is positive (in other words, when the indoor temperature Tra does not reach the set temperature Trat), the control unit <NUM> increases the frequency F of the compressor <NUM>. Specifically, the control unit <NUM> determines the change width ΔF of the frequency F of the compressor <NUM> according to the magnitude of the temperature difference ΔTra to increase the frequency F of the compressor <NUM> by the change width ΔF. Since it is required to decrease the air conditioning capacity (cooling capacity or heating capacity) when the temperature difference ΔTra is negative (in other words, when the indoor temperature Tra reaches the set temperature Trat), the control unit <NUM> decreases the frequency F of the compressor <NUM>. Specifically, the control unit <NUM> determines the change width ΔF of the frequency F of the compressor <NUM> according to the magnitude of the temperature difference ΔTra to decrease the frequency F of the compressor <NUM> by the change width ΔF.

The expansion valve degree of subcooling control is control to change the opening degree MV of the expansion valve <NUM> based on the degree of subcooling SC of the refrigerant at an outlet of the radiator for the refrigerant. Specifically, the control unit <NUM> changes the opening degree MV of the expansion valve <NUM> such that the degree of subcooling SC becomes the target degree of subcooling SCt. The degree of subcooling SC is the degree of subcooling at the outlet of the outdoor heat exchanger <NUM> that functions as a radiator for the refrigerant in the cooling operation, and is the degree of subcooling at the outlet of the indoor heat exchanger <NUM> that functions as a radiator for the refrigerant in the heating operation.

In the cooling operation, the control unit <NUM> subtracts the refrigerant temperature Tol on the liquid side of the outdoor heat exchanger <NUM> from the refrigerant temperature Tom in the intermediate portion of the outdoor heat exchanger <NUM> to obtain the degree of subcooling SC. In the heating operation, the control unit <NUM> subtracts the temperature Trl from the temperature Trm of the indoor heat exchanger <NUM> to obtain the degree of subcooling SC.

When the degree of subcooling SC is greater than the target degree of subcooling SCt, the control unit <NUM> increases the opening degree MV of the expansion valve <NUM> in order to decrease the degree of subcooling SC. Specifically, the control unit <NUM> determines the change width ΔMV of the opening degree MV of the expansion valve <NUM> according to the degree of subcooling difference ΔSC between the degree of subcooling SC and the target degree of subcooling SCt, and increases the opening degree MV of the expansion valve <NUM> by the change width ΔMV. When the degree of subcooling SC is smaller than the target degree of subcooling SCt, the control unit <NUM> decreases the opening degree MV of the expansion valve <NUM> in order to increase the degree of subcooling SC. Specifically, the control unit <NUM> determines the change width ΔMV of the opening degree MV of the expansion valve <NUM> according to the degree of subcooling difference ΔSC between the target degree of subcooling SCt and the degree of subcooling SC, and decreases the opening degree MV of the expansion valve <NUM> by the change width ΔMV.

The oil return control is control in an oil return operation for returning the refrigerating machine oil that has flowed out from the compressor <NUM> to the refrigerant circuit <NUM> (except compressor <NUM>) to the compressor <NUM>. In the oil return operation, the compressor <NUM> is driven at a predetermined number of oil return revolutions for a predetermined time.

Note that the predetermined number of oil return revolutions is required at least to be set to the number of revolutions at which the desired amount of refrigerating machine oil out of the refrigerating machine oil that has flowed out to the refrigerant circuit <NUM> except the compressor <NUM> returns to the compressor <NUM> by driving the compressor <NUM> for a predetermined time, and to be determined as appropriate by simulation, experiment, calculation on paper, or the like. The predetermined number of oil return revolutions is usually set to some relatively high number of revolutions. This is to efficiently return the refrigerating machine oil in the refrigerant circuit <NUM> to the compressor <NUM>.

When the condition that the amount of refrigerant circulating in the refrigerant circuit <NUM> exceeds a threshold value is satisfied, the amount being integrated after the previous oil return operation, the control unit <NUM> executes the oil return operation. The threshold value of the integrated value of the refrigerant is set near the upper limit of the amount of discharged oil allowed for reliability of the compressor <NUM>.

Since the air conditioning apparatus <NUM> uses difluoromethane (R32) as a refrigerant, when the outside air temperature is low, the degree of miscibility between the refrigerant and the refrigerating machine oil, which is sealed with the refrigerant for lubrication of the compressor <NUM>, is very small. Therefore, on the low-pressure side in the refrigeration cycle, because of a decrease in the refrigerant temperature, the degree of miscibility between the refrigerating machine oil and the refrigerant greatly decreases. The refrigerant and the refrigerating machine oil are separated into two layers in the accumulator <NUM> that becomes low pressure in the refrigeration cycle, and it becomes difficult for the refrigerating machine oil to return to the compressor <NUM>. For example, in the heating operation when the outside air temperature is low, as shown in <FIG>, the lower portion of the internal space IS of the casing <NUM> tends to be filled with the liquid refrigerant and the refrigerating machine oil separated from the liquid refrigerant tends to gather in the upper portion of the internal space IS. Then, the oil return hole 73b of the outlet pipe <NUM> of the accumulator <NUM> is separated from the refrigerating machine oil, and therefore the refrigerating machine oil that has accumulated in the internal space IS of the accumulator <NUM> cannot be returned to the compressor <NUM>. In other words, since the amount of liquid refrigerant increases around the oil return hole 73b of the outlet pipe <NUM>, the amount of refrigerating machine oil sucked from the oil return hole 73b decreases, and a sufficient amount of refrigerating machine oil cannot be returned to the compressor <NUM>.

In view of this, when the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM>, the control unit <NUM> executes a separation solution operation to solve the separation state. Hereinafter, the separation solution control including the separation solution operation will be described with reference to the control flowchart shown in <FIG>.

In step S1, the control unit <NUM> determines whether there is an operation stop signal. The operation stop signal is a signal sent from the remote control device <NUM> to the indoor control unit <NUM> when a manipulation of stopping the operation of the air conditioning apparatus <NUM> is executed with the remote control manipulation unit <NUM> of the remote control device <NUM>. The operation stop signal is, for example, a thermo-off signal sent from the indoor control unit <NUM> to the outdoor control unit <NUM> when the room temperature becomes higher than the indoor heating set temperature by <NUM> or more.

On determination in step S1 that there is an operation stop signal, the process proceeds to step S12, and the control unit <NUM> determines whether the suction temperature Ts is lower than a first threshold temperature T1. The suction temperature Ts is a temperature of the refrigerant in front of the accumulator <NUM>, the temperature being detected by the suction temperature sensor <NUM>.

On determination in step S12 that the suction temperature Ts is equal to or higher than the first threshold temperature T1, the degree of separation between the refrigerant and the refrigerating machine oil in the accumulator <NUM> is within a permissible range while the compressor is stopped, and the control unit <NUM> stops the compressor <NUM> as it is (step S13).

On determination in step S1 that there is no operation stop signal, the process proceeds to step S2, and the control unit <NUM> determines whether the suction temperature Ts is lower than a second threshold temperature T2.

On determination in step S2 that the suction temperature Ts is equal to or higher than the second threshold temperature T2, the degree of separation between the refrigerant and the refrigerating machine oil in the accumulator <NUM> is within the permissible range while the compressor is operating, and thus the control unit <NUM> maintains normal control of the number of revolutions of the compressor <NUM> and control of the opening degree of the expansion valve <NUM> at that time, and returns to step S1.

Note that regarding the degree of separation between the refrigerant and the refrigerating machine oil in the accumulator <NUM>, the permissible range while the compressor is stopped is different from the permissible range while the compressor is operating. Since it is preferable to continue normal control as much as possible while the compressor is operating, the permissible range while the compressor is operating is set widely. The permissible range while the compressor is stopped is set narrower than the permissible range while the compressor is operating in order to ensure that the refrigerating machine oil in the compressor <NUM> is sufficient when restarting the compressor <NUM>. Therefore, the second threshold temperature T2 is lower than the first threshold temperature T1.

On determination in step S2 that the suction temperature Ts is below the second threshold temperature T2 or on determination in step S12 that the suction temperature Ts is below the first threshold temperature T1, the control unit <NUM> proceeds to steps S3 and S4. In steps S3 and S4, in order to alleviate and solve the separation state between the refrigerant and the refrigerating machine oil in the accumulator <NUM>, the number of revolutions of the compressor <NUM> is decreased to a predetermined number of revolutions, and the opening degree of the expansion valve <NUM> is increased until fully opened. The control unit <NUM> executes each of the operations of steps S3 and S4 in parallel.

Thereafter, after waiting for a certain period of time (step S5), the process proceeds to step S6, and the control unit <NUM> returns to normal control before executing steps S3 and S4 by which the opening degree of the expansion valve <NUM> and the number of revolutions of the compressor <NUM> are adjusted. The number of revolutions of the compressor <NUM> and the opening degree of the expansion valve <NUM> in normal control are determined as described in (<NUM>-<NUM>-<NUM>) and (<NUM>-<NUM>-<NUM>).

Note that the certain period of time in step S5 can be selected from the range from <NUM> minute to <NUM> minutes, and is set in advance when the air conditioning apparatus <NUM> is manufactured.

As described above, the control unit <NUM> determines whether the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM> based on the temperature Ts detected by the suction temperature sensor <NUM> (steps S2 and S12). Then, when it is detected that the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM>, the control unit <NUM> executes the separation solution operation (steps S3, S4, S5). In the separation solution operation, the compressor <NUM> is driven at a predetermined number of revolutions lower than in the oil return operation. Accordingly, the separation state of the refrigerant and the refrigerating machine oil in the internal space IS of the accumulator <NUM> is alleviated and solved.

In steps S12 and S2, it is determined whether the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM> by using respective threshold values (first threshold temperature T1 and second threshold temperature T2). This determination is made by the control unit <NUM> based on the temperature inside the accumulator <NUM>, here, the suction temperature Ts corresponding to the temperature.

The control unit <NUM> determines whether the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM> with reference to the graph shown in <FIG>. The graph shown in <FIG> is divided into a region A in an environment where the refrigerant and the refrigerating machine oil are separated, and a region B in an environment where the refrigerant and the refrigerating machine oil are not separated. The graph shown in <FIG> is a graph showing the relationship between oil concentration and two-layer separation temperature when the refrigerant is difluoromethane (R32) and the refrigerating machine oil is polyvinyl ether (PVE). For example, when the oil concentration is <NUM> wt%, the two-layer separation temperature is about <NUM> and each threshold value is set near <NUM>. For example, the second threshold temperature T2 is set to -<NUM> and the first threshold temperature T1 is set to <NUM>.

Note that in the separation solution operation, a decrease in the number of revolutions of the compressor <NUM> and an increase in the opening degree of the expansion valve <NUM> lead to an increase in the pressure in the accumulator <NUM> and an increase in the temperature of the refrigerant. With this configuration, even if the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM>, the temperature of the refrigerant increases to exceed the two-layer separation temperature shown in <FIG>, alleviating and solving the separation state.

Next, features of the air conditioning apparatus <NUM> (refrigeration apparatus) will be described.

(<NUM>-<NUM>)
In the air conditioning apparatus <NUM>, the suction temperature sensor <NUM> detects the temperature of the refrigerant flowing into the accumulator <NUM>. The control unit <NUM> controls the number of revolutions of the compressor <NUM> and the opening degree of the expansion valve <NUM>. On determination that the refrigerant and the refrigerating machine oil (lubricating oil) are separated inside the accumulator <NUM> based on the detection result of the suction temperature sensor <NUM>, the control unit <NUM> executes the separation solution operation including steps S3 and S4. In the control of step S3, the number of revolutions of the compressor <NUM> is decreased. In the control of step S4, the opening degree of the expansion valve <NUM> is set to the predetermined opening degree (fully open).

Here, the separation solution operation of decreasing the number of revolutions of the compressor <NUM> and increasing the opening degree of the expansion valve <NUM> is executed when the refrigerant and the refrigerating machine oil are separated inside the accumulator <NUM>. Therefore, the pressure (low pressure value) on the suction side of the compressor <NUM> including the accumulator <NUM> can be increased. This makes it possible to change the pressure and temperature in the accumulator <NUM> to solve the separation state between the refrigerant and the refrigerating machine oil.

(<NUM>-<NUM>)
In the air conditioning apparatus <NUM>, the control unit <NUM> fully opens the opening degree of the expansion valve <NUM> in the control of step S4. Therefore, since the separation solution operation is executed to fully open the opening degree of the expansion valve <NUM> when the refrigerant and the refrigerating machine oil are separated inside the accumulator <NUM>, a large amount of high-temperature refrigerant flows into the accumulator <NUM>. This allows the separation solution operation to solve the separation state between the refrigerant and the refrigerating machine oil at an early stage.

(<NUM>-<NUM>)
In the air conditioning apparatus <NUM>, the control unit <NUM> decreases the number of revolutions of the compressor <NUM> in the control of step S3 to set the number of revolutions of the compressor <NUM> to a predetermined number of revolutions. Here, the control to decrease the number of revolutions of the compressor <NUM> to the predetermined number of revolutions is adopted instead of the control to decrease the number of revolutions a little. Therefore, the separation state between the refrigerant and the refrigerating machine oil is solved in a short time. Note that as one example, in the control of step S3, the number of revolutions of the compressor <NUM> is decreased to a predetermined number of revolutions in the range from <NUM> to <NUM> rpm.

(<NUM>-<NUM>)
In the air conditioning apparatus <NUM>, the control unit <NUM> executes the oil return operation separately from the separation solution operation. As described above, the oil return operation is an operation of returning the refrigerating machine oil staying in the refrigerant circuit <NUM> except the compressor <NUM> to the compressor <NUM>.

Some conventional refrigeration apparatus, such as the air conditioning apparatus, also executes the oil return operation similar to the present embodiment. However, the oil return operation, in which the motor of the compressor is turned at a relatively high number of revolutions, may not be preferable as an operation to solve the separation state between the refrigerant and the refrigerating machine oil inside the container such as the accumulator. Therefore, the control unit <NUM> of the air conditioning apparatus <NUM> executes the separation solution operation shown in <FIG>, in addition to the oil return operation, to alleviate and solve the separation between the refrigerant and the refrigerating machine oil in the accumulator <NUM>.

Note that, in contrast to the oil return operation of turning the compressor <NUM> at a relatively high number of revolutions, in the separation solution operation to solve the separation between the refrigerant and the refrigerating machine oil in the accumulator <NUM>, the number of revolutions of the compressor <NUM> is decreased to the predetermined number of revolutions. Since the compressor <NUM> is turned at a lower number of revolutions (predetermined number of revolutions) unlike the oil return operation, the pressure in the accumulator <NUM> increases and the separation state between the refrigerant and the refrigerating machine oil in the accumulator <NUM> is alleviated and solved at an early stage.

(<NUM>-<NUM>)
In the air conditioning apparatus <NUM>, when the request to stop the compressor <NUM> is received, the control unit <NUM> determines whether to execute the separation solution operation before stopping the compressor <NUM>, based on the detection result of the suction temperature sensor <NUM> (see step S12 in <FIG>). If the suction temperature Ts is so low that stopping the compressor <NUM> as it is may lead to a situation where the refrigerating machine oil in the compressor <NUM> is insufficient when restarting, control is executed to stop the compressor (step S13 in <FIG>) after the separation solution operation is executed. When the suction temperature Ts is lower than the first threshold temperature T1 in step S12 and the separation solution operation is performed, the suction temperature Ts increases accordingly. When the determination is made again in step S12 after the separation solution operation is finished, it is determined in step S12 that the suction temperature Ts is higher than the first threshold temperature T1, and the process proceeds to step S13 to stop the compressor <NUM>.

Here, the situation in which the compressor <NUM> is stopped while the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM> and the compressor <NUM> runs out of refrigerating machine oil when the compressor <NUM> is started again is inhibited.

(<NUM>-<NUM>)
In the air conditioning apparatus <NUM>, when the request to stop the compressor <NUM> is received, the control unit <NUM> determines whether the refrigerant and the refrigerating machine oil are separated inside the accumulator <NUM> by a first criterion (first threshold temperature T1) based on the detection result of the suction temperature sensor <NUM>. Meanwhile, when the request to stop the compressor <NUM> is not received, the control unit <NUM> determines whether the refrigerant and the refrigerating machine oil are separated inside the accumulator <NUM> by a second criterion (second threshold temperature T2) different from the first criterion (first threshold temperature T1) based on the detection result of the suction temperature sensor <NUM>.

Here, both when the request to stop the compressor <NUM> is received and not received, it is determined whether the refrigerant and the refrigerating machine oil are separated inside the accumulator <NUM>. Therefore, both when the compressor <NUM> is operating and when the compressor <NUM> is stopped, the separation solution operation for solving the separation state between the refrigerant and the refrigerating machine oil can be executed. The criterion for determining whether the refrigerant and the refrigerating machine oil are separated inside the accumulator <NUM> is changed depending on whether the request to stop the compressor <NUM> is received or not. This makes it possible, for example, to decrease the frequency at which the first and second control is executed when the compressor <NUM> is operating, and to increase the frequency at which the first and second control is executed when the compressor <NUM> stops.

(<NUM>-<NUM>)
The embodiment determines the degree of separation between the refrigerant and the refrigerating machine oil in the accumulator <NUM> by using the measured value of the suction temperature sensor <NUM> that detects the temperature of the refrigerant flowing into the accumulator <NUM>.

However, instead of this, it is also possible to install a sensor that can directly measure the temperature inside the accumulator <NUM> and use the measured value of the sensor.

It is also possible to attach a temperature sensor to the outer peripheral surface of the accumulator <NUM>, or to attach a temperature sensor to a pipe downstream of the accumulator <NUM>.

Furthermore, it is possible to install a pressure sensor that measures the pressure of the refrigerant in the accumulator <NUM> or around the accumulator <NUM> instead of the temperature sensor, and to calculate the temperature of the refrigerant in the accumulator <NUM> from the measured value.

Instead of determining the degree of separation of the refrigerant and refrigerating machine oil in the accumulator <NUM> from the measured values of one sensor alone, the separation may be determined based on a plurality of parameters such as the measured value of the suction temperature sensor <NUM> and the evaporation temperature.

(<NUM>-<NUM>)
The air conditioning apparatus <NUM> of the embodiment is an air conditioning apparatus that can switch between the cooling operation and the heating operation, but is not limited to this apparatus. The above-described separation solution operation is also effective for an air conditioning apparatus that executes only the cooling operation. When the refrigerant and the refrigerating machine oil are separated in the accumulator <NUM> in both the cooling operation and the heating operation, the separation solution operation is effective.

(<NUM>-<NUM>)
In the embodiment, the expansion valve <NUM> is fully opened in the separation solution operation (step S4 in <FIG>), but is not necessarily required to be fully opened. This is because when the expansion valve <NUM> is fully opened, there is a disadvantage that it takes a little time to return to normal control after the separation solution operation. However, the opening degree of the expansion valve <NUM> in the separation solution operation is preferably <NUM>% or more of the fully open position. This is because the liquid refrigerant held inside the heat exchanger by the expansion valve degree of subcooling control finally flows into the accumulator <NUM>.

Claim 1:
A refrigeration apparatus (<NUM>) comprising:
a refrigerant circuit (<NUM>) in which a compressor (<NUM>), a radiator (<NUM>, <NUM>), an expansion valve (<NUM>), an evaporator (<NUM>, <NUM>), and a container (<NUM>) are connected in order, and a refrigerant flows therein;
a detection unit (<NUM>) configured to detect a temperature or pressure of the refrigerant; and
a control unit (<NUM>) configured to control a number of revolutions of the compressor and an opening degree of the expansion valve,
characterized in that on determination that the refrigerant and a lubricating oil are separated inside the container based on a detection result of the detection unit,
the control unit is configured to execute first control (S3) to decrease the number of revolutions of the compressor, and
to execute second control (S4) to set the opening degree of the expansion valve to a predetermined opening degree.