Multi-connected simultaneous cooling and heating air conditioner and control method thereof

Abstract

The application provides a multiple simultaneous refrigeration and heating air conditioner and a control method thereof, and relates to the technical field of air conditioner oil retention. The air conditioner comprises an oil return four-way valve. In normal circulation, the compressor discharge pipe side of the high-pressure gas pipe and the high-pressure main gas pipe connection side of the high-pressure gas pipe are communicated, and the compressor suction pipe side of the low-pressure gas pipe and the low-pressure main gas pipe connection side of the low-pressure gas pipe are communicated. In oil return circulation, the compressor discharge pipe side and the low-pressure main gas pipe connection side are communicated, and the compressor suction pipe side and the high-pressure main gas pipe connection side are connected. The embodiment of the application can prevent insufficient compressor oil, does not need to increase the amount of compressor sealing oil, can prevent the refrigeration capacity or the heating capacity from decreasing, only needs to increase one four-way valve, does not need to control multiple valves, prevents the complication of the outdoor unit controller circuit board and the complication of the wiring, simplifies the control software of oil return operation, and shortens the time required for software production and debugging.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of air conditioner oil retention, and in particular, to a multi-connected simultaneous refrigeration and heating air conditioner and a control method thereof. BACKGROUND

[0002] In a multi-connected simultaneous refrigeration and heating air conditioner, under the condition that there is a drop (hereinafter referred to as an outside-to-inside drop) between the outdoor unit and the indoor unit, in the case of upward flow of the main gas pipe, oil cannot move together with the refrigerant and is retained in the main gas pipe. If this retained oil does not return to the compressor and increases, the compressor will be damaged due to insufficient oil.

[0003] The existing solution can prevent insufficient oil in the compressor by increasing the amount of oil sealed in the compressor. However, if the amount of oil sealed in the compressor is increased, the discharge amount of the compressor increases, and flows to the outdoor heat exchanger and the indoor heat exchanger together with the refrigerant, thereby reducing the heat exchange capacity and reducing the refrigeration or heating capacity.

[0004] Another existing solution can provide an electromagnetic valve in the high-pressure gas pipe and the low-pressure gas pipe of the outdoor unit, and provide a bypass connection between the high-pressure gas pipe and the low-pressure gas pipe provided with the electromagnetic valve. In the oil return operation of the outdoor unit with the outside-to-inside drop on the upper side, the high-pressure main gas pipe and the low-pressure main gas pipe make the high-pressure gas refrigerant flow downward. In the oil return operation of the outdoor unit with the outside-to-inside drop on the lower side, the high-pressure main gas pipe and the low-pressure main gas pipe make the low-pressure gas refrigerant flow downward. Through these actions, it is possible to prevent the oil from being retained in the low-pressure main gas pipe or the high-pressure main gas pipe to cause insufficient oil in the compressor. However, in the oil return operation of this method, the gas refrigerant is distributed to the high-pressure main gas pipe and the low-pressure main gas pipe. Therefore, in order to recover the retained oil in the main gas pipe, it is necessary to prolong the oil return time due to the slow flow rate of the respective refrigerants.

[0005] Another existing solution can provide an electromagnetic valve in the high-pressure gas pipe and the low-pressure gas pipe of the outdoor unit, and provide a bypass connection between the high-pressure gas pipe and the low-pressure gas pipe provided with the electromagnetic valve. In the oil return operation of the outdoor unit with the outside-to-inside drop on the upper side, the high-pressure main gas pipe and the low-pressure main gas pipe make the high-pressure gas refrigerant flow downward. In the oil return operation of the outdoor unit with the outside-to-inside drop on the lower side, the high-pressure main gas pipe and the low-pressure main gas pipe make the low-pressure gas refrigerant flow downward. Through these actions, it is possible to prevent the oil from being retained in the low-pressure main gas pipe or the high-pressure main gas pipe to cause insufficient oil in the compressor. However, in the oil return operation of this method, the gas refrigerant is distributed to the high-pressure main gas pipe and the low-pressure main gas pipe. Therefore, in order to recover the retained oil in the main gas pipe, it is necessary to prolong the oil return time due to the slow flow rate of the respective refrigerants. SUMMARY

[0006] To address the aforementioned problems, this invention provides a multi-split air conditioner capable of simultaneously cooling and heating, preventing insufficient compressor oil supply. The air conditioner includes a four-way oil return valve. The compressor discharge pipe side of the high-pressure gas pipe, the high-pressure main gas pipe connection side of the high-pressure gas pipe, the compressor suction pipe side of the low-pressure gas pipe, and the low-pressure main gas pipe connection side of the low-pressure gas pipe are respectively connected to their respective ports of the four-way oil return valve. The high-pressure main gas pipe connection is connected to the high-pressure main gas pipe, and the low-pressure main gas pipe connection is connected to the low-pressure main gas pipe. Under normal circulation conditions, the... The connection relationships of the four-way return oil valve are as follows: the compressor exhaust pipe side of the high-pressure gas pipe is connected to the high-pressure main gas pipe connection side of the high-pressure gas pipe, and the compressor suction pipe side of the low-pressure gas pipe is connected to the low-pressure main gas pipe connection side of the low-pressure gas pipe; under oil return circulation, the connection relationships of the four-way return oil valve are as follows: the compressor exhaust pipe side of the high-pressure gas pipe is connected to the low-pressure main gas pipe connection side of the low-pressure gas pipe, and the compressor suction pipe side of the low-pressure gas pipe is connected to the high-pressure main gas pipe connection side of the high-pressure gas pipe.

[0007] The multi-split air conditioner for simultaneous cooling and heating provided by this invention can prevent insufficient compressor oil by preventing oil from accumulating in the low-pressure main gas pipe or high-pressure main gas pipe when there is a height difference between the upper and lower sides of the outdoor unit, thus preventing insufficient compressor oil. It does not require increasing the amount of oil sealed in the compressor, thus preventing a decrease in cooling or heating capacity. It only requires adding a four-way valve, eliminating the need to control multiple valves, thus preventing the complexity of the outdoor unit controller circuit board and wiring. The control software for oil return operation can also be simplified, shortening the time required for software development and debugging.

[0008] Optionally, in the oil return circulation of the outdoor unit when there is a drop between the inside and outside, all high-pressure side switching valves of the conversion device are set to closed, and all low-pressure side switching valves are set to open.

[0009] In this embodiment of the invention, when the outdoor unit is on the lower side, the refrigerant during oil return operation is only distributed to the low-pressure main gas pipe, rather than simultaneously distributed to the high-pressure main gas pipe and the low-pressure main gas pipe. Therefore, the refrigerant flow rate in the main gas pipe becomes faster, and the stagnant oil can be recovered in a short time.

[0010] Optionally, it also includes an outdoor unit four-way valve; in the oil return circulation when there is a drop between the upper and lower sides of the outdoor unit, the outdoor unit four-way valve operates in heating circulation.

[0011] In this embodiment of the invention, when the four-way valve for oil return is in oil return circulation, the four-way valve of the outdoor unit switches to heating circulation accordingly to realize the refrigerant loop and move the oil remaining in the pipeline back to the compressor.

[0012] Optionally, in the oil return circulation of the outdoor unit when there is a drop between the inside and outside, all high-pressure side switching valves of the conversion device are set to open, and all low-pressure side switching valves are set to close.

[0013] In the embodiment of the present application, when the outdoor unit is on the downside, the gaseous refrigerant during the oil return operation is only distributed to the high-pressure main gas pipe, but not simultaneously distributed to the high-pressure main gas pipe and the low-pressure main gas pipe, so that the flow rate of the refrigerant in the main gas pipe is increased, and the stagnant oil can be recovered in a short time.

[0014] Optionally, the outdoor unit four-way valve is further included; in the oil return cycle when the outdoor unit is on the downside and has an indoor-outdoor difference, the outdoor unit four-way valve is operated in a refrigeration cycle.

[0015] In the embodiment of the present application, when the oil return four-way valve performs the oil return cycle, the outdoor unit four-way valve is switched to the refrigeration cycle correspondingly, the refrigerant loop is realized, and the oil stagnating in the pipeline is moved to the compressor.

[0016] Optionally, the high-pressure main gas pipe is connected to the first port of the indoor unit through a high-pressure side switching valve; and the low-pressure main gas pipe is connected to the first port of the indoor unit through a low-pressure side switching valve.

[0017] In the embodiment of the present application, the high-pressure main gas pipe and the low-pressure main gas pipe are arranged between the oil return four-way valve and the indoor unit, the refrigerant loop is realized, and the oil stagnating in the pipeline is moved to the compressor.

[0018] Optionally, a main liquid pipe is further included; the main liquid pipe is connected between the indoor unit and the outdoor unit, one end of the main liquid pipe is connected to the second port of the indoor unit, and the other end of the main liquid pipe is connected to the outdoor heat exchanger of the outdoor unit.

[0019] In the embodiment of the present application, the main liquid pipe is connected between the outdoor unit and the indoor unit, the refrigerant loop is realized, and the oil stagnating in the pipeline is moved to the compressor.

[0020] The embodiment of the present application provides a control method of a multi-connected simultaneous refrigeration and heating air conditioner, which is applied to the multi-connected simultaneous refrigeration and heating air conditioner in any of the above embodiments, and includes the following steps: if an oil return operation instruction is acquired and there is an indoor-outdoor difference, controlling an oil return four-way valve to operate in an oil return cycle; if it is determined that the outdoor unit is on the upside, controlling all high-pressure side switching valves of a switching device to be closed and all low-pressure side switching valves of the switching device to be opened; and if it is determined that the outdoor unit is on the downside, controlling all high-pressure side switching valves of the switching device to be opened and all low-pressure side switching valves of the switching device to be closed.

[0021] Optionally, the method further includes: if it is determined that the outdoor unit is on the upside, controlling an outdoor unit four-way valve to operate in a heating cycle; and if it is determined that the outdoor unit is on the downside, controlling the outdoor unit four-way valve to operate in a refrigeration cycle.

[0022] Optionally, the method further includes: if the oil return operation is ended, controlling the oil return four-way valve to operate in a normal cycle, and controlling the outdoor unit four-way valve to return to a state before the oil return operation.

[0023] The control method of the multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application can achieve the same technical effect as the multi-connected simultaneous refrigeration and heating air conditioner. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The refrigerant circulation diagram of the prior art three-pipe multi-connected simultaneous refrigeration and heating machine.

[0025] Figure 2 The setting schematic diagram of the outdoor unit on the upper side;

[0026] Figure 3 The setting schematic diagram of the outdoor unit on the lower side;

[0027] Figure 4 The refrigerant circulation diagram of the prior art 1;

[0028] Figure 5 The action schematic diagram of the outdoor unit on the upper side of the prior art 1;

[0029] Figure 6 The action schematic diagram of the outdoor unit on the lower side of the prior art 1;

[0030] Figure 7 The refrigerant circulation diagram of the prior art 2;

[0031] Figure 8 The action schematic diagram of the outdoor unit on the upper side of the prior art 2;

[0032] Figure 9 The action schematic diagram of the outdoor unit on the lower side of the prior art 2;

[0033] Figure 10 The refrigerant circulation diagram of the multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application, which can prevent the insufficient oil amount of the compressor;

[0034] Figure 11 The action schematic diagram of the outdoor unit on the upper side of the embodiment of the present application;

[0035] Figure 12 The action schematic diagram of the outdoor unit on the lower side of the embodiment of the present application;

[0036] Figure 13 The schematic flow chart of the control method of the multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application;

[0037] Figure 14 The control flow chart of the oil return operation of the multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application.

[0038] Explanation of reference signs:

[0039] 11 - indoor unit; 12 - outdoor unit; 13 - outdoor heat exchanger; 14 - indoor heat exchanger; 15 - four-way valve; 16 - compressor; 17 - compressor discharge pipe; 18 - low-pressure main gas pipe connection portion; 19 - high-pressure main gas pipe connection portion; 20 - outdoor expansion valve; 21 - indoor expansion valve; 22 - outdoor unit low-pressure gas pipe; 23 - oil return bypass pipe; 24 - low-pressure main gas pipe; 25 - high-pressure main gas pipe; 26 - low-pressure side switching valve; 27 - high-pressure side switching valve; 28 - branch box; 29 - main liquid pipe; 30 - low-pressure gas pipe solenoid valve; 31 - low-pressure gas pipe; 32 - oil return bypass solenoid valve; 33 - first bypass solenoid valve; 34 - second bypass solenoid valve; 35 - high-pressure gas pipe solenoid valve; 36 - first bypass pipe; 37 - second bypass pipe; 38 - compressor suction pipe; 39 - high-pressure gas pipe; 101 - outdoor unit four-way valve; 102 - oil return four-way valve. DETAILED DESCRIPTION

[0040] In order to make the above objects, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0041] Figure 1 A refrigerant circulation diagram of a conventional three-pipe type multi-connected simultaneous refrigeration and heating machine is shown.

[0042] Exemplarily, in a multi-connected simultaneous refrigeration and heating air conditioner in which a refrigeration indoor unit and a heating indoor unit can be used in combination, an outdoor unit and an indoor unit are connected with a high-pressure side gas pipe (hereinafter, referred to as a high-pressure main gas pipe), a low-pressure side gas pipe (hereinafter, referred to as a low-pressure main gas pipe), and a liquid pipe (hereinafter, referred to as a main liquid pipe) Figure 1 of the three-pipe type machine shown.

[0043] In a multi-connected air conditioner, under a setting condition in which there is a difference (hereinafter, referred to as an outside-indoor difference) between an outdoor unit and an indoor unit, in a case where a main gas pipe flows upward, oil cannot move together with refrigerant and is retained in the main gas pipe. If the retained oil does not return to a compressor and increases, the compressor can be damaged due to a lack of oil.

[0044] However, in a main gas pipe of a two-pipe type cooling and heating fixed machine in which an outdoor unit and an indoor unit are connected with a main gas pipe and a main liquid pipe, when a four-way valve is in a refrigeration cycle, low-pressure gas refrigerant flows from the indoor unit to the outdoor unit, and when the four-way valve is in a heating cycle, high-pressure gas refrigerant flows from the outdoor unit to the indoor unit. Therefore, even in a case where there is an outside-indoor difference, if there is a switch between a refrigeration operation and a heating operation, or a switch of a four-way valve cycle such as a defrosting operation, retained oil does not continuously increase without returning because the flow direction of the main gas pipe is switched in opposite directions.

[0045] As Figure 1As shown, in the case of the indoor unit 11 only for cooling operation, the four-way valve 15 becomes a cooling cycle. Further, the low-pressure side switching valve 26 of the branch box 28 is opened, and the high-pressure side switching valve 27 is closed. Then, the high-pressure refrigerant discharged from the compressor 16 flows to the outdoor heat exchanger 13 via the four-way valve 15. And, it is condensed to liquid refrigerant with the outdoor heat exchanger 13, and flows to the indoor unit 12 through the main liquid pipe 29. Further, the liquid refrigerant is two-phase after decompression in the indoor expansion valve 21, and evaporates in the indoor heat exchanger 14, and performs a cooling operation. The low-pressure gas refrigerant after cooling flows from the indoor unit side to the outdoor unit side through the low-pressure side switching valve 26 and the low-pressure main gas pipe 24 to return to the outdoor unit 12, and is sucked into the compressor 16 through the low-pressure gas pipe 31.

[0046] In Figure 1 The low-pressure main gas pipe connection portion 18 and the high-pressure main gas pipe connection portion 19 are also shown, and are used to connect the low-pressure main gas pipe 24 and the high-pressure main gas pipe 25, respectively.

[0047] In the case of the indoor unit only for heating operation, the four-way valve 15 becomes a heating cycle. Further, the low-pressure side switching valve 26 of the branch box 28 is closed, and the high-pressure side switching valve 27 is opened. Then, the high-pressure gas refrigerant discharged from the compressor 16 flows from the outdoor unit side to the indoor unit side through the high-pressure gas pipe 39 and the high-pressure main gas pipe 25, and moves to the indoor unit 11 via the high-pressure side switching valve 27. And, it is condensed with the indoor heat exchanger 14, and performs a heating operation. The liquid refrigerant after condensation returns to the outdoor unit 12 through the main liquid pipe 29. Then, it is decompressed to gas-liquid mixture with the outdoor expansion valve 20, and evaporates with the outdoor heat exchanger 20, and is sucked into the compressor 16 via the four-way valve 15.

[0048] In the case where the indoor unit of the refrigeration operation and the indoor unit of the heating operation are both present and the refrigeration load is greater than the heating load, the four-way valve 15 becomes a refrigeration cycle. In addition, in the branch box 28, the low-pressure side switching valve 26 connected to the indoor unit of the refrigeration operation is opened, and the high-pressure side switching valve 27 connected to the indoor unit of the heating operation is closed. Also, the low-pressure side switching valve 26 connected to the indoor unit of the heating operation is closed, and the high-pressure side switching valve 27 connected to the indoor unit of the refrigeration operation is opened. Also, the high-pressure gas refrigerant discharged from the compressor 16 is distributed to the high-pressure gas refrigerant flowing through the outdoor unit high-pressure gas pipe 39 via the four-way valve 15. Then, the high-pressure gas refrigerant distributed to the outdoor heat exchanger 13 via the four-way valve 15 is condensed to liquid refrigerant in the outdoor heat exchanger 13, and flows into the indoor unit of the refrigeration operation through the main liquid pipe 29. Further, the liquid refrigerant is depressurized in the indoor expansion valve 21 and gas-liquid mixed, and then evaporated in the indoor heat exchanger 14, and performs the refrigeration operation. The low-pressure gas refrigerant after the refrigeration operation flows from the indoor unit side to the outdoor unit side via the low-pressure side switching valve 26 and the low-pressure main gas pipe 24, and returns to the outdoor unit, and the outdoor unit is sucked into the compressor through the low-pressure gas pipe 31. In addition, the high-pressure gas refrigerant distributed to the outdoor unit high-pressure gas pipe 39 moves to the indoor unit of the heating operation through the high-pressure main gas pipe 25. The refrigerant is condensed in the indoor heat exchanger 14, and performs the heating operation. The condensed liquid refrigerant moves to the main liquid pipe 29, and is combined with the liquid refrigerant condensed in the outdoor heat exchanger 13, and flows into the indoor unit of the refrigeration operation. The refrigeration operation and the heating operation are simultaneously performed by the above operation.

[0049] In the case where the indoor unit of the refrigeration operation and the indoor unit of the heating operation are both present and the heating load is greater than the refrigeration load, the four-way valve 15 becomes a heating cycle. In addition, in the branch box 28, the low-pressure side switching valve 26 connected to the indoor unit of the refrigeration operation is opened, and the high-pressure side switching valve 27 connected to the indoor unit of the heating operation is closed. Also, the low-pressure side switching valve 26 connected to the indoor unit of the heating operation is closed, and the high-pressure side switching valve 27 connected to the indoor unit of the refrigeration operation is opened. Also, the high-pressure gas refrigerant discharged from the compressor 16 flows from the outdoor unit side to the indoor unit side through the outdoor unit high-pressure gas pipe 39 and the high-pressure main gas pipe 25, and moves to the indoor unit of the heating operation via the high-pressure side switching valve 27. The refrigerant is condensed in the indoor heat exchanger 14, and performs the heating operation. The condensed liquid refrigerant moves to the main liquid pipe 29, and is distributed to the liquid refrigerant flowing through the outdoor unit and the liquid refrigerant flowing through the indoor unit of the refrigeration operation. The liquid refrigerant distributed to the outdoor unit is depressurized in the outdoor expansion valve 20 and gas-liquid mixed, and then evaporated in the outdoor heat exchanger 13, and is sucked into the compressor 16 via the four-way valve 15. In addition, the liquid refrigerant distributed to the indoor unit of the refrigeration operation is depressurized in the indoor expansion valve 21 and gas-liquid mixed, and then evaporated in the indoor heat exchanger 14, and performs the refrigeration operation. The low-pressure gas refrigerant after the refrigeration operation flows through the low-pressure main gas pipe 24 via the low-pressure side switching valve 26, and returns to the outdoor unit, and is sucked into the compressor 16 through the outdoor unit low-pressure gas pipe 22 after passing through the outdoor unit. The refrigeration operation and the heating operation are simultaneously performed by the above operation.

[0050] As described above, in the three-pipe multi-connected simultaneous cooling and heating air conditioner, in either the refrigeration cycle or the heating cycle of the four-way valve, the refrigerant of the high-pressure main gas pipe flows from the outdoor unit side to the indoor unit side, and the refrigerant of the low-pressure main gas pipe flows from the indoor unit side to the outdoor unit side. Therefore, in the case where there is an outside-in drop, the refrigerant flow of either the high-pressure main gas pipe or the low-pressure main gas pipe goes upward. For example, Figure 2 A setting diagram is shown in which the outdoor unit is on the upper side, and in this case, the low-pressure main gas pipe goes upward, and the low-pressure main gas pipe always flows upward; Figure 3 A setting diagram is shown in which the outdoor unit is on the lower side, and in this case, the high-pressure main gas pipe goes upward, and the high-pressure main gas pipe always flows upward. Therefore, in the case where there is an outside-in drop, the low-pressure main gas pipe retains oil when the outdoor unit is on the upper side, and the high-pressure main gas pipe retains oil without returning and continuously increases when the outdoor unit is on the lower side.

[0051] In general multi-connected air conditioners, in order to return the retained oil of the main gas pipe to the compressor, the compressor is operated at a high number of revolutions, and oil return operation is performed to accelerate the refrigerant flow rate of the gas pipe. However, in the upwardly flowing main gas pipe, it is difficult to return oil even in the high number of revolutions of the compressor. Therefore, in the three-pipe simultaneous cooling and heating multi-connected machine in the setting condition where there is an outside-in drop, the low-pressure main gas pipe is used when the outdoor unit is on the upper side, and the high-pressure main gas pipe flows upward when the outdoor unit is on the lower side, and the compressor oil shortage easily occurs.

[0052] In order to prevent such a compressor oil shortage, there is a method of increasing the amount of oil sealed in the compressor. However, if the amount of oil sealed in the compressor is increased, the discharge amount of the compressor increases, and flows to the outdoor heat exchanger and the indoor heat exchanger together with the refrigerant. Thus, the heat exchange capacity decreases, and the refrigeration capacity or the heating capacity decreases.

[0053] Figure 4 A refrigerant cycle diagram of the prior art 1 is shown, and a high-pressure gas pipe solenoid valve 35 is provided in the high-pressure gas pipe 39 between the compressor discharge pipe 17 and the high-pressure main gas pipe connection portion 19. In addition, a low-pressure gas pipe solenoid valve 30 is provided in the low-pressure gas pipe 31 between the four-way valve 15 and the low-pressure main gas pipe connection portion 18. An oil return bypass pipe 23 is provided between the high-pressure gas pipe 39 connected between the high-pressure gas pipe solenoid valve 35 and the high-pressure main gas pipe connection portion 19, and the low-pressure gas pipe 31 connected between the low-pressure gas pipe solenoid valve 30 and the low-pressure main gas pipe connection portion 18. In addition, an oil return bypass solenoid valve 32 is provided in the oil return bypass pipe 23.

[0054] As Figure 5The action diagram shown in the prior art 1 of the outdoor unit upper side, the outdoor unit 12 in the case of the outside inside drop, low pressure main gas pipe 24 and four-way valve 15 cycle irrelevant, upward flow, produce the retention oil. Therefore, in the oil return operation, the four-way valve 15 of the outdoor unit 12 forms the heating cycle. In addition, open the high pressure gas pipe electromagnetic valve 35 and the oil return bypass electromagnetic valve 32, close the low pressure gas pipe electromagnetic valve 30. And, all the high pressure side switch valve 27 and all the low pressure side switch valve 26 of all the branch box 28 are set to open. Through these actions, the high pressure gas refrigerant not only flows to the high pressure main gas pipe 25, but also flows to the low pressure main gas pipe 24. And, because the high pressure gas refrigerant flows from the outdoor unit 12 to the indoor unit 11, the low pressure main gas pipe 24 flows from the upper side to the lower side. Therefore, the retention oil of the low pressure main gas pipe 24 will move to the indoor unit 11. Then mixed in the condensation liquefied refrigerant in the indoor unit 11, through the main liquid pipe 29, return to the compressor 16 through the outdoor heat exchanger 13. As a result, it can prevent the oil from being retained in the low pressure main gas pipe 24 to cause the compressor oil shortage.

[0055] As Figure 6 The action diagram shown in the prior art 1 of the outdoor unit lower side, the outdoor unit in the case of the outside inside drop, high pressure main gas pipe 25 and four-way valve cycle irrelevant, upward flow, produce the retention oil. Therefore, in the oil return operation, the four-way valve 15 of the outdoor unit 12 forms the refrigeration cycle. In addition, open the low pressure gas pipe electromagnetic valve 30 and the oil return bypass electromagnetic valve 32, close the high pressure gas pipe electromagnetic valve 35. And, all the high pressure side switch valve 27 and all the low pressure side switch valve 26 of all the branch device are set to open. Through these actions, the low pressure gas refrigerant not only flows to the low pressure main gas pipe 24, but also flows to the high pressure main gas pipe 25. And, because the low pressure gas refrigerant flows from the indoor unit 11 to the outdoor unit 12, the high pressure main gas pipe 25 flows from the upper side to the lower side. Therefore, the retention oil of the high pressure main gas pipe 25 moves to the outdoor unit 12, returns to the compressor 16. As a result, it can prevent the oil from being retained in the high pressure main gas pipe 25 to cause the compressor oil shortage.

[0056] But in the oil return operation of the method, the gas refrigerant is distributed to the high pressure main gas pipe and the low pressure main gas pipe, and the refrigerant flow rate is slow. In order to recover the retention oil of the main gas pipe, it is necessary to prolong the oil return time.

[0057] Figure 7A refrigerant circulation diagram of prior art 2 is shown. A high-pressure gas pipe solenoid valve 35 is installed on the high-pressure gas pipe 39 between the compressor discharge pipe 17 and the high-pressure main gas pipe connection 19. A low-pressure gas pipe solenoid valve 30 is installed on the low-pressure gas pipe 31 between the four-way valve 15 and the low-pressure main gas pipe connection 18. A first bypass pipe 36 is provided between the high-pressure gas pipe between the high-pressure gas pipe solenoid valve 35 and the high-pressure main gas pipe connection 19, and between the low-pressure gas pipe 31 between the four-way valve 15 and the low-pressure gas pipe solenoid valve 30. A first bypass solenoid valve 33 is also provided on the first bypass pipe 36. Furthermore, a second bypass pipe 37 is provided between the low-pressure gas pipe 31 between the low-pressure gas pipe solenoid valve 30 and the low-pressure main gas pipe connection 18, and between the high-pressure gas pipe 39 between the compressor discharge pipe 17 and the high-pressure gas pipe solenoid valve 35. A second bypass solenoid valve 34 is also provided on the second bypass pipe 37.

[0058] like Figure 8 The diagram shows the operation of the outdoor unit 12 with an upper section. When there is a height difference between the upper and lower sections of the outdoor unit 12, the low-pressure main gas pipe 24 and the four-way valve 15 are unrelated to the circulation, resulting in upward flow and oil stagnation. Therefore, during oil return operation, the four-way valve 15 of the outdoor unit 12 forms a heating cycle. Additionally, all low-pressure side switching valves 26 of all branch boxes 28 are opened, and all high-pressure side switching valves 27 are closed. The second bypass solenoid valve 34 is opened, and the high-pressure gas pipe solenoid valve 35, the low-pressure gas pipe solenoid valve 30, and the first bypass solenoid valve 33 are closed. Through these actions, the high-pressure refrigerant flows downward into the low-pressure main gas pipe 24, and the stagnant oil moves to the indoor unit 11. Then, it mixes with the condensed refrigerant in the indoor unit 11, and returns to the compressor 16 via the main liquid pipe 29 and the outdoor heat exchanger 13. As a result, oil stagnation in the low-pressure main gas pipe 24, preventing insufficient compressor oil, is prevented.

[0059] like Figure 9 The diagram shows the operation of the outdoor unit 12 located on the lower side of the prior art 2. When there is a height difference between the indoor and outdoor sides of the outdoor unit 12, the high-pressure main gas pipe 25 is unrelated to the four-way valve circulation, resulting in upward flow and oil stagnation. Therefore, during oil return operation, the four-way valve 15 of the outdoor unit 12 forms a refrigeration cycle. Additionally, all high-pressure side switching valves 27 of all branch boxes 28 are opened, and all low-pressure side switching valves 26 are closed. Furthermore, the first bypass solenoid valve 33 is opened, and the high-pressure gas pipe solenoid valve 35, the low-pressure gas pipe solenoid valve 30, and the second bypass solenoid valve 34 are closed. Through these actions, the low-pressure refrigerant evaporated by the indoor unit 11 flows downward in the high-pressure main gas pipe 25, and the stagnant oil returns to the compressor. As a result, oil stagnation in the high-pressure main gas pipe 25, preventing insufficient oil level in the compressor, can be prevented.

[0060] However, this method requires controlling 4 electromagnetic valves, and thus the relay or wiring of the outdoor unit controller circuit board is increased. In addition, the control software is complicated, and the time required for production and debugging is lengthened.

[0061] The multi-connected simultaneous refrigeration and heating air conditioner of the embodiment of the present application can prevent insufficient oil amount of the compressor.

[0062] Specifically, the compressor discharge pipe side of the high-pressure gas pipe, the high-pressure main gas pipe connecting portion side of the high-pressure gas pipe, the compressor suction pipe side of the low-pressure gas pipe, and the low-pressure main gas pipe connecting portion side of the low-pressure gas pipe are respectively connected to each interface of the oil return four-way valve.

[0063] The high-pressure main gas pipe connecting portion is connected to the high-pressure main gas pipe, and the low-pressure main gas pipe connecting portion is connected to the low-pressure main gas pipe. The other side of the high-pressure main gas pipe and the low-pressure main gas pipe is connected to the indoor unit. Specifically, the high-pressure main gas pipe can be connected to the first port of the indoor unit through the high-pressure side switching valve; and the low-pressure main gas pipe can be connected to the first port of the indoor unit through the low-pressure side switching valve.

[0064] Further, the main liquid pipe can be connected between the indoor unit and the outdoor unit. One end of the main liquid pipe is connected to the second port of the indoor unit, and the other end of the main liquid pipe is connected to the outdoor heat exchanger of the outdoor unit, thereby connecting the refrigerant pipeline of the indoor unit and the outdoor unit.

[0065] In the normal cycle, the oil return four-way valve has the following connection relationship: the compressor discharge pipe side of the high-pressure gas pipe and the high-pressure main gas pipe connecting portion side of the high-pressure gas pipe are connected, and the compressor suction pipe side of the low-pressure gas pipe and the low-pressure main gas pipe connecting portion side of the low-pressure gas pipe are connected. The normal cycle refers to the normal refrigeration and heating cycle of the air conditioner.

[0066] In the oil return cycle, the oil return four-way valve has the following connection relationship: the compressor discharge pipe side of the high-pressure gas pipe and the low-pressure main gas pipe connecting portion side of the low-pressure gas pipe are connected, and the compressor suction pipe side of the low-pressure gas pipe and the high-pressure main gas pipe connecting portion side of the high-pressure gas pipe are connected. The oil return cycle refers to the oil return operation of the air conditioner, which moves the oil remaining in the pipeline to the compressor.

[0067] Optionally, in the oil return cycle when the outdoor unit has an external and internal drop, all high-pressure side switching valves of the switching device are set to be closed, and all low-pressure side switching valves are set to be opened. The switching device functions as a high and low pressure switching device, and the opening and closing of the high-pressure side switching valve and the low-pressure side switching valve can change the flow path of the refrigerant. The gas refrigerant in the oil return operation is only distributed to the low-pressure main gas pipe, and is not simultaneously distributed to the high-pressure main gas pipe and the low-pressure main gas pipe. Therefore, the refrigerant flow rate of the main gas pipe is fast, and the remaining oil can be recovered in a short time.

[0068] Exemplarily, the air conditioner further comprises an outdoor unit four-way valve, which is the original four-way valve and functions to switch the refrigeration and heating. Alternatively, in the oil return circulation when the outdoor unit has an outside-to-inside difference on the upper side, the outdoor unit four-way valve is operated in the heating cycle.

[0069] Through these actions, the high-pressure gas refrigerant flows to the low-pressure main gas pipe, and since the high-pressure gas refrigerant flows from the outdoor unit to the indoor unit, the low-pressure main gas pipe flows from the upper side to the lower side. The stagnant oil in the low-pressure main gas pipe moves to the indoor unit and then mixes with the condensed and liquefied refrigerant in the indoor unit, returns to the compressor through the main liquid pipe and the outdoor heat exchanger, so that the insufficient oil amount of the compressor caused by the oil stagnation in the low-pressure main gas pipe can be prevented.

[0070] Alternatively, in the oil return circulation when the outdoor unit has an outside-to-inside difference on the lower side, all the high-pressure side switching valves of the switching device are set to be open, and all the low-pressure side switching valves are set to be closed. The gas refrigerant during the oil return operation is only distributed to the high-pressure main gas pipe, rather than being simultaneously distributed to the high-pressure main gas pipe and the low-pressure main gas pipe, so that the refrigerant flow rate of the main gas pipe is increased, and the stagnant oil can be recovered in a short time.

[0071] Exemplarily, in the oil return circulation when the outdoor unit has an outside-to-inside difference on the lower side, the outdoor unit four-way valve is operated in the refrigeration cycle.

[0072] Through these actions, the low-pressure gas refrigerant flows to the high-pressure main gas pipe, and since the low-pressure gas refrigerant flows from the outdoor unit to the indoor unit, the high-pressure main gas pipe flows from the upper side to the lower side. The stagnant oil in the high-pressure main gas pipe moves to the outdoor unit and returns to the compressor, so that the insufficient oil amount of the compressor caused by the oil stagnation in the high-pressure main gas pipe can be prevented.

[0073] The multi-connected simultaneous refrigeration and heating air conditioner capable of preventing insufficient oil amount of the compressor provided by the embodiment of the present application can prevent the oil from being stagnant in the low-pressure main gas pipe and the high-pressure main gas pipe to cause insufficient oil amount of the compressor when the outdoor unit has an outside-to-inside difference on the upper side or the lower side, does not need to increase the enclosed oil amount of the compressor, can prevent the refrigeration capacity or the heating capacity from being reduced, only needs to increase one four-way valve, does not need to control multiple valves, prevents the complication of the outdoor unit controller circuit board and the complication of the wiring, and can simplify the control software of the oil return operation, thereby shortening the time required for the software production and debugging.

[0074] Figure 10 A refrigerant circulation diagram of the multi-connected simultaneous refrigeration and heating air conditioner capable of preventing insufficient oil amount of the compressor provided by the embodiment of the present application is shown.

[0075] As Figure 10As shown, in the three-pipe multi-connected simultaneous refrigeration and heating air conditioner, there are indoor unit 11, outdoor unit 12 and diverging tank 28 (i.e. the above-mentioned conversion device). The outdoor unit 12 includes compressor 16, and the diverging tank 28 includes low-pressure side switching valve 26 and high-pressure side switching valve 27.

[0076] The compressor discharge pipe 17 side of the high-pressure gas pipe 39, the high-pressure main gas pipe connecting portion 19 side of the high-pressure gas pipe 39, the compressor suction pipe 38 side of the low-pressure gas pipe 31, and the low-pressure main gas pipe connecting portion 18 side of the low-pressure gas pipe 31 are connected with the oil return four-way valve 102. The high-pressure main gas pipe connecting portion 19 is connected with the high-pressure main gas pipe 25, and the low-pressure main gas pipe connecting portion 18 is connected with the low-pressure main gas pipe 24.

[0077] The above-mentioned oil return four-way valve 102, the compressor discharge pipe 17 of the high-pressure gas pipe 39 and the high-pressure main gas pipe connecting portion 19 of the high-pressure gas pipe 39 are communicated, and the compressor suction pipe 38 of the low-pressure gas pipe 31 and the low-pressure main gas pipe connecting portion 18 of the low-pressure gas pipe are communicated, forming a normal circulation. The compressor discharge pipe 17 of the high-pressure gas pipe 39 and the low-pressure main gas pipe connecting portion 18 of the low-pressure gas pipe 31 are communicated, and the compressor suction pipe 38 of the low-pressure gas pipe 31 and the high-pressure main gas pipe connecting portion 19 of the high-pressure gas pipe 39 are communicated, forming an oil return circulation. In addition, in order to distinguish the four-way valve, the existing four-way valve of the outdoor unit is denoted as outdoor unit four-way valve 101.

[0078] Figure 11 The action schematic diagram of the outdoor unit upper side provided by the embodiment of the present application is shown. In the oil return operation of the outdoor unit 12 in the case of the outer-infall difference on the upper side, the oil return circulation of the oil return four-way valve 102 is switched, so that the compressor discharge pipe 17 side of the high-pressure gas pipe 39 and the low-pressure main gas pipe connecting portion 18 side of the low-pressure gas pipe 31 are communicated. In addition, all the high-pressure side switching valves 27 of the diverging tank 28 are set to be closed, and all the low-pressure side switching valves 26 are set to be opened. Thus, the high-pressure gas pipe 39 of the outdoor unit 12 is connected with the indoor unit 11 via the low-pressure main gas pipe 24. In addition, the outdoor unit four-way valve 101 performs a heating circulation. Thus, the high-pressure gas refrigerant discharged from the compressor 16 flows from the outdoor unit 12 to the indoor unit 11.

[0079] Through these actions, the high-pressure gas refrigerant flows to the low-pressure main gas pipe 24. Since the high-pressure gas refrigerant flows from the outdoor unit 12 to the indoor unit 11, the low-pressure main gas pipe 24 flows from the upper side to the lower side. Therefore, the stagnant oil of the low-pressure main gas pipe 24 will move to the indoor unit 11. Then it is mixed into the condensed and liquefied refrigerant in the indoor unit 11, and returns to the compressor 16 through the main liquid pipe 29 via the outdoor heat exchanger 13. As a result, the oil stagnation in the low-pressure main gas pipe can be prevented, which causes the insufficient amount of compressor oil.

[0080] By these actions, the high-pressure gas refrigerant flows to the low-pressure main gas pipe. Since the high-pressure gas refrigerant flows from the outdoor unit to the indoor unit, the low-pressure main gas pipe flows from the upper side to the lower side, and thus the oil stagnating in the low-pressure main gas pipe moves to the indoor unit. Then the oil is mixed with the condensed and liquefied refrigerant in the indoor unit, and returns to the compressor through the main liquid pipe and the outdoor heat exchanger. As a result, the oil stagnation in the low-pressure main gas pipe that causes the insufficient oil amount of the compressor can be prevented.

[0081] Figure 12 An action diagram showing the lower side of the outdoor unit of the embodiment of the present application is shown. In the oil return operation of the outdoor unit in the case where the outdoor unit has the outside-in drop at the lower side, the switching of the oil return cycle of the oil return four-way valve 102 is performed so as to communicate the compressor suction pipe 38 side of the low-pressure gas pipe 31 and the high-pressure main gas pipe connection part 19 side of the high-pressure gas pipe 39. In addition, all of the high-pressure side switching valves 27 of the branch box 28 are set to be open, and all of the low-pressure side switching valves 26 are set to be closed. Thus, the low-pressure gas pipe 31 of the outdoor unit 12 is connected to the indoor unit 11 via the high-pressure main gas pipe 25. In addition, the outdoor unit four-way valve 101 forms a refrigeration cycle so that the low-pressure gas refrigerant sucked by the compressor 16 flows from the indoor unit 11 to the outdoor unit 12.

[0082] By these actions, the low-pressure gas refrigerant flows to the high-pressure main gas pipe. Since the low-pressure gas refrigerant flows from the outdoor unit to the indoor unit, the high-pressure main gas pipe flows from the upper side to the lower side, and thus the oil stagnating in the high-pressure main gas pipe moves to the outdoor unit and returns to the compressor. As a result, the oil stagnation in the high-pressure main gas pipe that causes the insufficient oil amount of the compressor can be prevented.

[0083] The multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application has the following advantages:

[0084] 1. The oil stagnation in the low-pressure main gas pipe that causes the insufficient oil amount of the compressor can be prevented when the outdoor unit has the outside-in drop at the upper side; 2. The oil stagnation in the high-pressure main gas pipe that causes the insufficient oil amount of the compressor can be prevented when the outdoor unit has the outside-in drop at the lower side; 3. The refrigeration capacity or the heating capacity can be prevented from being reduced without increasing the enclosed oil amount of the compressor; 4. The gas refrigerant during the oil return operation will not be distributed to the high-pressure main gas pipe and the low-pressure main gas pipe, but only flow to one of the main gas pipes. Thus the refrigerant flow rate of the main gas pipe becomes fast, and the stagnating oil can be recovered in a short time; 5. Only one four-way valve is needed, and the control of multiple valves is not needed. Thus the complication of the outdoor unit controller circuit board and the complication of the wiring can be prevented, and the control software of the oil return operation can also be simplified, and the time required for the production and debugging of the software can be shortened.

[0085] Figure 13 A schematic flow chart of a control method of a multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application is shown. The method is applied to the above-mentioned multi-connected simultaneous refrigeration and heating air conditioner, and includes the following steps:

[0086] S1, if the oil return operation instruction is acquired and there is an inside-outside difference, then control the oil return four-way valve to run in the oil return cycle as described above.

[0087] S2, if it is determined that the outdoor unit is on the upper side, then control all of the high-pressure side switching valves of the switching device to be closed and all of the low-pressure side switching valves to be opened. If it is determined that the outdoor unit is on the upper side, then control the outdoor unit four-way valve to run in the heating cycle.

[0088] S3, if it is determined that the outdoor unit is on the lower side, then control all of the high-pressure side switching valves of the switching device to be opened and all of the low-pressure side switching valves to be closed. If it is determined that the outdoor unit is on the lower side, then control the outdoor unit four-way valve to run in the cooling cycle.

[0089] Further, the method described above further comprises:

[0090] If the oil return operation ends, then control the oil return four-way valve to run in the normal cycle and control the outdoor unit four-way valve to return to the state before the oil return operation.

[0091] The control method of the multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application can prevent the oil from being retained in the low-pressure main gas pipe and the high-pressure main gas pipe when the outdoor unit is on the upper side or the lower side, which can cause insufficient oil amount of the compressor.

[0092] Figure 14 The control flow chart of the oil return operation of the multi-connected simultaneous refrigeration and heating air conditioner provided by the embodiment of the present application comprises the following steps:

[0093] S201, according to the upper and lower relationship between the outdoor unit and the indoor unit, select any one of

no inside-outside difference

outdoor unit on the upper side setting

outdoor unit on the lower side setting

[0094] Before the air conditioner starts to run, check whether there is an inside-outside difference on the upper side of the outdoor unit or whether there is an inside-outside difference on the lower side of the outdoor unit. The user can input the information of whether there is an inside-outside difference through the wire controller or the dial switch, and the controller of the outdoor unit stores the information.

[0095] S202, determine whether there is an instruction to start the oil return operation. If yes, execute S203; if no, repeat S202.

[0096] S203, determine whether there is no inside-outside difference. If yes, execute S210; if no, execute S204.

[0097] S204, control the oil return four-way valve to be in the oil return cycle.

[0098] S205, determine whether the outdoor unit is on the upper side. If yes, execute S206; if no, execute S208.

[0099] S206, the four-way valve of the outdoor unit is controlled to become a heating cycle.

[0100] S207, the high-pressure side switching valve is closed and the low-pressure side switching valve is opened.

[0101] S208, the four-way valve of the outdoor unit is controlled to become a refrigeration cycle.

[0102] S209, the high-pressure side switching valve is opened and the low-pressure side switching valve is closed.

[0103] S210, the oil return four-way valve is controlled to return to a normal cycle.

[0104] S211, oil return operation is implemented.

[0105] S212, it is determined whether the oil return operation is instructed to end. If yes, S213 is executed; if no, it returns to continue to execute S211.

[0106] S213, the four-way valve of the outdoor unit is controlled to return to a state before the oil return operation is started.

[0107] S214, the oil return four-way valve is controlled to return to a normal cycle.

[0108] In the three-tube multi-connected simultaneous refrigeration and heating air conditioner, the compressor discharge pipe side of the high-pressure gas pipe and the high-pressure main gas pipe connection part side of the high-pressure gas pipe and the compressor suction pipe side of the low-pressure gas pipe and the low-pressure main gas pipe connection part of the low-pressure gas pipe are connected to the oil return four-way valve. The compressor discharge pipe side of the high-pressure gas pipe and the high-pressure main gas pipe connection part side of the high-pressure gas pipe are communicated, and the compressor suction pipe side of the low-pressure gas pipe and the low-pressure main gas pipe connection part side of the low-pressure gas pipe are communicated to perform a normal cycle; the compressor discharge pipe side of the high-pressure gas pipe and the low-pressure main gas pipe connection part side of the low-pressure gas pipe are communicated, and the compressor suction pipe side of the low-pressure gas pipe and the high-pressure main gas pipe connection part of the high-pressure gas pipe are communicated, and the oil return cycle can be switched.

[0109] In the oil return operation of the outdoor unit when there is an outside-inside drop on the upper side, the oil return cycle of the oil return four-way valve is switched, and the compressor discharge pipe side of the high-pressure gas pipe is communicated with the low-pressure main gas pipe connection part side of the low-pressure gas pipe. In addition, all high-pressure side switching valves of the branching box are closed, and all low-pressure side switching valves are opened.

[0110] In the oil return operation of the outdoor unit when there is an outside-inside drop on the lower side, the oil return cycle of the oil return four-way valve is switched, and the compressor suction pipe side of the low-pressure gas pipe is communicated with the high-pressure main gas pipe connection part side of the high-pressure gas pipe. In addition, all high-pressure side switching valves of the branching box are opened, and all low-pressure side switching valves are closed.

[0111] The embodiment of the present application provides a computer readable storage medium, the computer readable storage medium stores a computer program, the computer program is read and run by a processor, and the method provided by the above embodiment is realized, and the same technical effects can be achieved. In order to avoid repetition, here is no longer tedious. Wherein, the computer readable storage medium, such as read-only memory (Read-Only Memory, ROM for short), random access memory (Random Access Memory, RAM for short), magnetic disk or optical disk and the like.

[0112] Of course, those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment method can be completed by computer degree to instruct the control device, and the program can be stored in a computer readable storage medium. The program can include the processes of each method embodiment described above when executed, and the storage medium can be a memory, a disk, an optical disk, etc.

[0113] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art can make various modifications and changes without departing from the spirit and scope of the present application, and the protection scope of the present application should be limited by the scope defined by the claims.

[0114] Finally, it should be noted that, in this paper, relationship terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitation, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or device including the element.

[0115] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts between various embodiments can be referred to each other.

[0116] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art can make various modifications and changes without departing from the spirit and scope of the present application, and the protection scope of the present application should be limited by the scope defined by the claims.

Claims

1. A multi-split air conditioner that simultaneously cools and heats, characterized in that, can prevent insufficient compressor oil. Including the return oil four-way valve; The compressor exhaust pipe side of the high-pressure gas pipe, the high-pressure main gas pipe connection side of the high-pressure gas pipe, the compressor suction pipe side of the low-pressure gas pipe, and the low-pressure main gas pipe connection side of the low-pressure gas pipe are respectively connected to the respective ports of the return oil four-way valve; the high-pressure main gas pipe connection is connected to the high-pressure main gas pipe, and the low-pressure main gas pipe connection is connected to the low-pressure main gas pipe. Under normal circulation, the connection relationship of the return oil four-way valve is as follows: the compressor exhaust pipe side of the high-pressure gas pipe is connected to the high-pressure main gas pipe connection part side of the high-pressure gas pipe, and the compressor suction pipe side of the low-pressure gas pipe is connected to the low-pressure main gas pipe connection part side of the low-pressure gas pipe. Under the return oil circulation, the connection relationship of the return oil four-way valve is as follows: the compressor exhaust pipe side of the high-pressure gas pipe is connected to the low-pressure main gas pipe connection side of the low-pressure gas pipe, and the compressor suction pipe side of the low-pressure gas pipe is connected to the high-pressure main gas pipe connection side of the high-pressure gas pipe.

2. The air conditioner as described in claim 1, characterized in that, When there is a drop between the outside and inside of the outdoor unit during the oil return circulation, all high-pressure side switching valves of the conversion device are set to closed, and all low-pressure side switching valves are set to open.

3. The air conditioner as described in claim 2, characterized in that, It also includes the outdoor unit four-way valve; When there is a drop between the inside and outside of the outdoor unit, the outdoor unit's four-way valve operates in heating cycle during the oil return circulation.

4. The air conditioner as described in claim 1, characterized in that, When there is a drop between the inside and outside of the outdoor unit during the oil return circulation, all high-pressure side switching valves of the conversion device are set to open, and all low-pressure side switching valves are set to close.

5. The air conditioner as described in claim 4, characterized in that, It also includes the outdoor unit four-way valve; When there is a drop between the inside and outside of the outdoor unit, the four-way valve of the outdoor unit operates in a cooling cycle during the oil return circulation.

6. The air conditioner as described in claim 1, characterized in that, The high-pressure main gas pipe is connected to the first port of the indoor unit through a high-pressure side switching valve; the low-pressure main gas pipe is connected to the first port of the indoor unit through a low-pressure side switching valve.

7. The air conditioner as described in claim 6, characterized in that, It also includes the main liquid pipe; The main liquid pipe is connected between the indoor unit and the outdoor unit. One end of the main liquid pipe is connected to the second port of the indoor unit, and the other end is connected to the outdoor heat exchanger of the outdoor unit.

8. A control method for a multi-split air conditioning unit that simultaneously cools and heats, characterized in that, The multi-split air conditioning unit for simultaneous cooling and heating as described in any one of claims 1-7 comprises: If a return oil operation command is received and there is an internal and external drop, the return oil four-way valve is controlled to operate in return oil circulation mode. If it is determined that the outdoor unit is on the top side, then all high-pressure side switching valves of the control conversion device are closed, and all low-pressure side switching valves are opened; If the outdoor unit is located on the lower side, all high-pressure side switching valves of the control conversion device will be opened, and all low-pressure side switching valves will be closed.

9. The method as described in claim 8, characterized in that, The method further includes: If it is determined that the outdoor unit is on the top, then control the four-way valve of the outdoor unit to operate in heating circulation mode; If it is determined that the outdoor unit is on the lower side, then control the four-way valve of the outdoor unit to operate in a cooling cycle.

10. The method as described in claim 8 or 9, characterized in that, The method further includes: If the oil return operation ends, control the oil return four-way valve to operate in normal circulation, and control the outdoor unit four-way valve to return to the state before the oil return operation.

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