Low-temperature-resistant quasi-two-stage compression variable frequency carbon dioxide heat pump air conditioner for rail vehicle

Abstract

Disclosed in the present invention is a low-temperature-resistant quasi-two-stage compression variable frequency carbon dioxide heat pump air conditioner for a rail vehicle, comprising a compressor, a four-way valve, an outdoor heat exchanger, a first regenerator, a first filter drier, a second filter drier, an indoor heat exchanger, and a gas-liquid separator which are sequentially communicated by means of pipelines. A second regenerator is further provided between the first filter drier and the second filter drier, a high-pressure side and a medium-pressure side of the second regenerator are each provided with a one-way electronic expansion valve, and an air outlet on the medium-pressure side of the second regenerator is connected to a vapor injection port of the compressor. By means of the design of quasi-two-stage compression-intermediate vapor injection, the quasi-two-stage compression variable frequency carbon dioxide heat pump air conditioner for the vehicle disclosed in the present invention can achieve ultralow-temperature operation of a carbon dioxide heat pump, increase the energy efficiency ratio, and widen the application environment temperature range of the heat pump; during heating, by means of intermediate vapor injection, the circulation amount is increased and the exhaust temperature is reduced; and during cooling, the quality at an inlet of an evaporator is reduced by means of the first regenerator, so that the quasi-two-stage compression carbon dioxide heat pump operates efficiently under all working conditions.

Description

A low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles Technical Field

[0001] The present invention relates to the technical field of rail vehicle air conditioning, in particular to a low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles. Background Art

[0002] Existing rail vehicle carbon dioxide heat pump air conditioners include a compressor, a four-way valve, an outdoor heat exchanger, a first heat regenerator, a first drying filter, a second drying filter, an indoor heat exchanger, and a gas-liquid separator, which are connected in sequence through pipelines. However, existing rail vehicle carbon dioxide heat pump air conditioners have poor heating effects in low-temperature environments.

[0003] Summary of the Invention

[0004] In view of the above problems, the present invention proposes a low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles.

[0005] The technical means adopted in the present invention are as follows:

[0006] A low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner, comprising a compressor, a four-way valve, an outdoor heat exchanger, a first regenerator, a first drying filter, a second drying filter, an indoor heat exchanger, and a second regenerator;

[0007] The exhaust port of the compressor is connected to the first valve port of the four-way valve through a pipeline, the second valve port of the four-way valve is connected to the first interface of the outdoor heat exchanger through a pipeline, the second interface of the outdoor heat exchanger is connected to the first interface on the high-pressure side of the first regenerator through a pipeline, the second interface on the high-pressure side and the first interface on the high-pressure side of the first regenerator are respectively connected to the first interface of the first drier through pipelines, the second interface of the first drier is respectively connected to the first interface of the second drier and the first interface on the high-pressure side of the second regenerator through pipelines, the second interface on the high-pressure side of the second regenerator is connected to the first interface of the second drier through a pipeline, the second interface on the second drier is connected to the first interface of the indoor heat exchanger through a pipeline, the second interface of the indoor heat exchanger is connected to the third valve port of the four-way valve through a pipeline, the fourth valve port of the four-way valve is connected to the first interface on the low-pressure side of the first regenerator through a pipeline, and the second interface on the low-pressure side of the first regenerator is connected to the air inlet of the compressor through a pipeline;

[0008] The first interface on the medium-pressure side of the second regenerator is connected to the second interface on the high-pressure side of the second regenerator through a pipeline, and the second interface on the medium-pressure side of the second regenerator is connected to the air supply port of the compressor through a pipeline;

[0009] A second one-way valve and a first one-way valve are respectively provided on the pipelines connecting the second high-pressure side interface and the first high-pressure side interface of the first regenerator and the first interface of the first drying filter;

[0010] A first one-way electronic expansion valve and a second one-way electronic expansion valve are respectively provided on two pipelines connecting the second interface of the first filter drier, the first interface of the second filter drier, and the first interface on the high-pressure side of the second regenerator;

[0011] A third one-way electronic expansion valve is provided on the pipeline connecting the first interface on the medium-pressure side of the second heat regenerator and the second interface on the high-pressure side of the second heat regenerator.

[0012] Furthermore, it also includes the gas-liquid separator arranged on the pipeline connecting the fourth valve port of the four-way valve and the first interface on the low-pressure side of the first regenerator.

[0013] Furthermore, it also includes a high-pressure pressure transmitter, a high-pressure pressure switch, a first stop valve and a safety valve arranged on a pipeline connecting the exhaust port of the compressor and the first valve port of the four-way valve;

[0014] A low-pressure switch, a low-pressure transmitter, and a second stop valve are provided on a pipeline connecting the air inlet of the compressor and the second interface on the low-pressure side of the first regenerator; and

[0015] A medium-pressure pressure transmitter is provided on a pipeline connecting the second interface on the medium-pressure side of the second regenerator and the air supply port of the compressor.

[0016] Furthermore, it also includes a first pipe temperature sensor, a second pipe temperature sensor and a third pipe temperature sensor;

[0017] The first pipe temperature sensor is arranged on a pipe connecting the second interface of the outdoor heat exchanger and the first interface on the high-pressure side of the first regenerator;

[0018] The second pipeline temperature sensor is provided on the pipeline connecting the second low-pressure side interface of the first regenerator and the air inlet of the compressor;

[0019] The third pipeline temperature sensor is arranged on the pipeline connecting the second interface on the medium-pressure side of the second regenerator and the air supply port of the compressor.

[0020] Furthermore, the exhaust port and the air inlet of the compressor are respectively provided with an exhaust shock-absorbing pipe and an intake shock-absorbing pipe.

[0021] Furthermore, an exhaust temperature switch is provided at the exhaust port of the compressor.

[0022] Furthermore, it also includes a first fan and a second fan which are arranged corresponding to the outdoor heat exchanger and the indoor heat exchanger.

[0023] Furthermore, the outdoor heat exchanger is a copper tube aluminum fin heat exchanger; the first fan is an axial flow fan; the first heat regenerator and the second heat regenerator are both plate heat exchangers; the indoor heat exchanger is a copper tube aluminum fin heat exchanger; and the second fan is a centrifugal fan.

[0024] Compared with the existing technology, the low-temperature resistant rail vehicle quasi-two-stage compression variable frequency carbon dioxide heat pump air conditioner disclosed in the present invention has the following beneficial effects: the existing rail carbon dioxide heat pump air conditioners have poor heating effect in low-temperature environments. The low-temperature resistant rail vehicle quasi-two-stage compression variable frequency carbon dioxide heat pump air conditioner disclosed in the present invention can realize ultra-low temperature operation of the carbon dioxide heat pump through a quasi-two-stage compression-intermediate air supply design, improve energy efficiency, and broaden the application environment temperature range of the carbon dioxide heat pump.

[0025] The heating process increases the circulation volume and reduces the exhaust temperature through intermediate air supply, and the cooling process reduces the evaporator inlet dryness through the first regenerator, allowing the quasi-two-stage compression carbon dioxide heat pump to operate efficiently under all working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic diagram of a low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed in the present invention;

[0027] FIG2 is a refrigerant flow diagram of the refrigeration process of the low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner disclosed in the present invention;

[0028] FIG3 is a refrigerant flow diagram of the heating process of the low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner disclosed in the present invention;

[0029] In the figure: 1. Compressor; 2. Four-way valve; 3. Outdoor heat exchanger; 4. First regenerator; 5. First filter drier; 6. Second filter drier; 7. Indoor heat exchanger; 8. Second regenerator; 9. First one-way valve; 10. Second one-way valve; 11. First one-way electronic expansion valve; 12. Second one-way electronic expansion valve; 13. Third one-way electronic expansion valve; 14. Gas-liquid separator; 15. High-pressure pressure transmitter; 16. High-pressure pressure switch; 17. First stop valve; 18. Safety valve; 19. Low-pressure pressure switch; 20. Low-pressure pressure transmitter; 21. Second stop valve; 22. Medium-pressure pressure transmitter; 23. First pipeline temperature sensor; 24. Second pipeline temperature sensor; 25. Third pipeline temperature sensor; 26. Exhaust shock absorber pipe; 27. Intake shock absorber pipe; 28. Exhaust temperature switch; 29. ​​First fan; 30. Second fan DETAILED DESCRIPTION

[0030] As shown in FIG1 , the low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner disclosed in the present invention includes a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, a first regenerator 4, a first drying filter 5, a second drying filter 6, an indoor heat exchanger 7, and a second regenerator 8;

[0031] The exhaust port of the compressor 1 is connected to the first valve port A of the four-way valve 2 through a pipeline, the second valve port B of the four-way valve 2 is connected to the first interface of the outdoor heat exchanger 3 through a pipeline, the second interface of the outdoor heat exchanger 3 is connected to the first interface on the high-pressure side of the first regenerator 4 through a pipeline, the second interface on the high-pressure side and the first interface on the high-pressure side of the first regenerator 4 are respectively connected to the first interface of the first drier 5 through pipelines, the second interface of the first drier 5 is respectively connected to the first interface of the second drier 6 and the first interface on the high-pressure side of the second regenerator 8 through pipelines, the second interface on the high-pressure side of the second regenerator 8 is connected to the first interface of the second drier 6 through a pipeline, the second interface of the second drier 6 is connected to the first interface of the indoor heat exchanger 7 through a pipeline, the second interface of the indoor heat exchanger 7 is connected to the third valve port C of the four-way valve 2 through a pipeline, the fourth valve port D of the four-way valve 2 is connected to the first interface on the low-pressure side of the first regenerator 4 through a pipeline, and the second interface on the low-pressure side of the first regenerator 4 is connected to the air inlet of the compressor 1 through a pipeline;

[0032] The first interface on the medium-pressure side of the second regenerator 8 is connected to the second interface on the high-pressure side of the second regenerator 8 through a pipeline, and the second interface on the medium-pressure side of the second regenerator 8 is connected to the air supply port of the compressor 1 through a pipeline;

[0033] A second one-way valve 10 and a first one-way valve 9 are respectively provided on the pipelines connecting the second high-pressure side interface and the first high-pressure side interface of the first regenerator 4 with the first interface of the first drying filter 5;

[0034] The two pipelines connecting the second interface of the first filter drier 5, the first interface of the second filter drier 6, and the first interface on the high-pressure side of the second regenerator 8 are respectively provided with a first one-way electronic expansion valve 11 and a second one-way electronic expansion valve 12;

[0035] A third one-way electronic expansion valve 13 is provided on the pipeline connecting the first interface on the medium-pressure side of the second regenerator 8 and the second interface on the high-pressure side of the second regenerator 8 .

[0036] Furthermore, it also includes the gas-liquid separator 14 arranged on the pipeline connecting the fourth valve port D of the four-way valve 2 and the first interface on the low-pressure side of the first regenerator 4.

[0037] Furthermore, it also includes a high-pressure pressure transmitter 15, a high-pressure pressure switch 16, a first stop valve 17 and a safety valve 18 provided on the pipeline connecting the exhaust port of the compressor 1 and the first valve port A of the four-way valve 2;

[0038] A low-pressure switch 19, a low-pressure transmitter 20 and a second stop valve 21 are provided on the pipeline connecting the air inlet of the compressor 1 and the second interface on the low-pressure side of the first regenerator 4; and

[0039] A medium-pressure transmitter 22 is provided on the pipeline connecting the second interface on the medium-pressure side of the second regenerator 8 and the air supply port of the compressor 1 .

[0040] Furthermore, it also includes a first pipe temperature sensor 23, a second pipe temperature sensor 24 and a third pipe temperature sensor 25;

[0041] The first pipe temperature sensor 23 is provided on the pipe connecting the second interface of the outdoor heat exchanger 3 and the first interface on the high-pressure side of the first regenerator 4;

[0042] The second pipeline temperature sensor 24 is provided on the pipeline connecting the second low-pressure side interface of the first regenerator 4 and the air inlet of the compressor 1;

[0043] The third pipeline temperature sensor 25 is provided on the pipeline connecting the second interface on the medium-pressure side of the second regenerator 8 and the air supply port of the compressor 1 .

[0044] Furthermore, the exhaust port and the air inlet of the compressor 1 are respectively provided with an exhaust shock-absorbing pipe 26 and an intake shock-absorbing pipe 27 .

[0045] Furthermore, an exhaust temperature switch 28 is provided at the exhaust port of the compressor 1 .

[0046] Furthermore, the system further includes a first fan 29 and a second fan 30 which are provided corresponding to the outdoor heat exchanger 3 and the indoor heat exchanger 4 .

[0047] Furthermore, the outdoor heat exchanger 3 is a copper tube aluminum fin heat exchanger; the first fan 29 is an axial flow fan; the first regenerator 4 and the second regenerator 8 are both plate heat exchangers; the indoor heat exchanger 7 is a copper tube aluminum fin heat exchanger; and the second fan 30 is a centrifugal fan.

[0048] The low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner disclosed in the present invention can realize refrigeration cycle, heating cycle and heating and defrosting functions. The specific working process of each function is as follows:

[0049] Refrigeration cycle:

[0050] In the following description, the first interface and the second interface of each component are referred to as the air inlet and the air outlet in sequence according to the flow direction of the refrigerant;

[0051] As shown in FIG2 , in the low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air-conditioning system disclosed by the present invention, the compressor is the power source for the entire cycle process. During the cooling process, it cooperates with the first one-way electronic expansion valve to establish a system pressure difference. During the heating process, it cooperates with the second one-way electronic expansion valve to establish a system pressure difference. The compressor is a variable-frequency compressor that can adapt to a wide range of heating and cooling needs. The compressor has three ports: an intake port, an exhaust port, and an air supply port. The exhaust port of the compressor is connected to the first valve port of the four-way valve through a pipeline, and an exhaust shock absorber pipe is provided on the pipeline. The intake port of the compressor is connected to the low-pressure side outlet of the first regenerator through a pipeline, and an intake shock absorber pipe is provided on the pipeline. The exhaust shock absorber pipe and the intake shock absorber pipe are both corrugated hoses, and their main function is to absorb the vibration of the compressor and prevent the amplitude from being transmitted to the system pipeline.

[0052] The four-way valve is a cooling and heating switching valve. When cooling, AB is connected (the first valve port and the second valve port are connected), and CD is connected (the third valve port and the fourth valve port are connected); when heating, AC is connected (the first valve port and the third valve port are connected), and BD is connected (the second valve port and the fourth valve port are connected).

[0053] The second valve port of the four-way valve is connected to the air inlet of the outdoor heat exchanger via a pipeline. In this embodiment, the outdoor heat exchanger is a small-diameter copper tube and aluminum fin heat exchanger with an outer diameter of 5 mm, which has low air resistance and high heat exchange efficiency. The first fan for the outdoor heat exchanger is an axial flow fan with a high air volume.

[0054] During the refrigeration process, the refrigerant (R744) is discharged from the compressor exhaust port, enters the four-way valve inlet A (first valve port) through the exhaust shock absorber pipe, flows through the four-way valve port B (second valve port), and enters the outdoor heat exchanger. The first fan and the outdoor heat exchanger are in countercurrent form, and the two cooperate to force the refrigerant (R744) to cool down. Then the refrigerant (R744) enters the high-pressure side of the first reheater.

[0055] The first regenerator uses a plate heat exchanger, a type of partition-type heat exchanger. The heat exchanger is made of textured heat exchanger fins bonded together, with a refrigerant flow path between the fins. The heat source and cold source refrigerants are located on either side of the fin. The high-pressure inlet is connected to the outdoor heat exchanger outlet, which is connected to the inlet of the second one-way valve. The low-pressure inlet is connected to the indoor heat exchanger outlet, which is connected to the compressor suction shock absorber inlet. In this embodiment, the first regenerator has a total of 30 heat exchanger fins, with a size of 191x77 mm. 2 The number and volume of heat exchange plates in the regenerator can be set as needed.

[0056] The refrigerant (R744) flows out of the outdoor heat exchanger, passes through the high-pressure side of the first reheater, and then passes through the second one-way valve to enter the first drier. The drier mainly filters impurities in the pipeline to prevent the electronic expansion valve from clogging. At the same time, it can absorb moisture in the refrigerant and purify the refrigerant. The drier is a two-way filter element with low resistance.

[0057] During the cooling process, the second and third one-way electronic expansion valves are closed. Refrigerant passes through the first filter drier and then enters the first one-way electronic expansion valve. The electronic expansion valve has a built-in throttling orifice that acts as a throttling and pressure-reducing device. After passing through the first one-way electronic expansion valve, the high-pressure, low-temperature liquid refrigerant expands into a low-temperature, low-pressure gas-liquid mixture, which then passes through the second filter drier. In this embodiment, the first, second, and third one-way electronic expansion valves all function as one-way expansion valves.

[0058] The second drier is the same as the first drier, which is a two-way filter element with very low resistance. Its main function is to filter impurities in the pipeline during the heating process to prevent the electronic expansion valve from being blocked. At the same time, it can absorb moisture in the refrigerant and purify the refrigerant.

[0059] After exiting the second filter dryer, the low-temperature, low-pressure gas-liquid mixed refrigerant enters the indoor heat exchanger. Working in conjunction with the second fan, it exchanges heat with the indoor air, removing heat from the humid air and liquefying the water vapor in the humid air into condensed water, achieving a dehumidifying and cooling effect. In this embodiment, the indoor heat exchanger is a 7.94mm outer diameter copper tube and aluminum fin heat exchanger. The fins have a hydrophilic coating to facilitate the separation of condensed water. The second fan is an EC fan (centrifugal fan), which can meet the different ventilation volume requirements of the user end and can also achieve various heat and moisture load regulation requirements. The second fan and the indoor heat exchanger are in a downstream configuration.

[0060] The refrigerant flows out of the indoor heat exchanger, passes through the third and fourth valve ports of the four-way valve, and enters the gas-liquid separator. In this embodiment, the gas-liquid separator has a volume of 2L and is mainly used to store refrigerant that does not participate in the circulation during heating conditions to prevent liquid shock in the compressor.

[0061] After passing through the gas-liquid separator, the refrigerant becomes 100% saturated steam. It then enters the low-pressure side of the first regenerator, where the low-pressure refrigerant and the high-pressure refrigerant undergo a partitioning heat exchange. The plate heat exchanger offers high heat exchange efficiency, reducing the refrigerant dryness after the valve while superheating the refrigerant at the evaporator outlet, improving energy efficiency. In the first regenerator, the high-pressure and low-pressure refrigerants flow in countercurrent.

[0062] The refrigerant flows out from the low-pressure side outlet of the first regenerator into the suction shock absorber pipe, and then enters the compressor to complete the entire refrigeration cycle.

[0063] In the low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air-conditioning system disclosed in the present invention, a high-pressure side branch is provided between the exhaust shock absorber pipe and the first valve port of the four-way valve, and the high-pressure side branch comprises a first stop valve, a high-pressure pressure transmitter, a high-pressure pressure switch, and a safety valve; a low-pressure side branch is provided between the intake shock absorber pipe and the low-pressure side outlet of the first regenerator, and the low-pressure side branch comprises a second stop valve, a low-pressure pressure transmitter, and a low-pressure pressure switch.

[0064] The primary shutoff valve facilitates maintenance and repair, allowing replacement of the high-pressure switch, high-pressure pressure sensor, and safety valve without draining the refrigerant. The first shutoff valve has three ports: inlet, outlet, and charging port. The inlet connects to the main line, while the outlet connects to the high-pressure switch, high-pressure pressure transmitter, and safety valve. When the stem of the first shutoff valve is open, the inlet and outlet of the first shutoff valve are connected, and the charging port is open to the atmosphere, but not to the inlet and outlet. When the stem of the first shutoff valve is closed, the inlet and outlet of the shutoff valve are disconnected, and the charging port is connected to the inlet.

[0065] In this embodiment, the safety valve is a resettable pressure relief valve with an operating value of 14MPa±0.2MPa and a reset value of 12MPa±0.2MPa. The high-pressure switch is a normally closed type with an operating value of 12.5±0.5MPa and a reset value of 9MPa±1MPa. The high-pressure pressure transmitter is a current-type transmitter with an output of 4-20mA, corresponding to a pressure range of 0-16MPa, with a linear relationship. The safety valve functions as a third-level pressure protection. The characteristic of CO2 refrigerant is its high transcritical cycle operating pressure. Under equivalent operating conditions, the high-pressure pressure is five times that of R407c refrigerant, reaching 10MPa. For safety reasons, three levels of protection are designed on the high-pressure side. The first level is implemented by a high-pressure pressure transmitter and an electronic expansion valve, with a high-pressure threshold set at 12 MPa. When the high-pressure pressure transmitter detects that the high-pressure pressure exceeds 12 MPa for 1 second, the electronic expansion valve opens wider to control the pressure within 12 MPa. The second level of pressure protection is a high-pressure pressure switch. If the first-level pressure protection fails due to force majeure, the high-pressure switch will shut down the compressor when the high-pressure pressure exceeds 12.5 MPa. The specific working principle is that the high-pressure pressure switch contains a normally closed bimetallic structure. When the pressure exceeds the activation value, the bimetallic structure opens, breaking the circuit. The air conditioning controller receives a high-level to low-level signal, controls the compressor to stop, ensures the air conditioning is shut down, and restores the piping system pressure to normal. The third level of pressure protection is a safety valve. If both the first and second levels of pressure protection fail due to force majeure, the high-pressure pressure continues to rise. When the high-pressure pressure exceeds the safety valve activation value, the safety valve will open, discharging carbon dioxide to the outside, thereby reducing the pressure and protecting the compressor.

[0066] The second shut-off valve primarily facilitates maintenance and inspection, allowing replacement of the low-pressure switch and low-pressure sensor without draining the refrigerant. The second shut-off valve has three ports: an inlet, an outlet, and a charging port. The inlet connects to the main line, and the outlet connects to the low-pressure switch and low-pressure sensor. When the second shut-off valve stem is open, the inlet and outlet of the second shut-off valve communicate, and the charging port is open to the atmosphere, but the charging port is not connected to either the inlet or outlet. When the second shut-off valve stem is closed, the inlet and outlet of the second shut-off valve are disconnected, and the charging port is connected to the inlet.

[0067] In this embodiment, the low-pressure switch is a normally open type, with an action value of 2.5±0.2MPa and a recovery value of 3.5MPa±0.2Mpa; the low-pressure pressure transmitter is a current type, with an output of 4-20mA, corresponding to a pressure range of 0-16MPa, which is a linear correspondence; the refrigerant charge is 1.8Kg; two-level protection is designed on the low-pressure side: the first level is achieved by the low-pressure pressure transmitter in conjunction with the electronic expansion valve, and the low-pressure threshold is set to 3.3MPa. When the low-pressure pressure transmitter detects that the low-pressure pressure is less than 3.3MPa for 1 second, the low-pressure pressure transmitter will be turned off. At s, the electronic expansion valve opens wider to maintain the pressure above 3.3 MPa. The second-level pressure protection is a low-pressure switch. If the first-level pressure protection fails due to force majeure, the low-pressure switch shuts down the compressor when the low-pressure drops below 2.5 MPa. The low-pressure switch incorporates a normally open bimetallic strip. When the pressure falls below the actuation level, the strip opens, breaking the circuit. The air conditioner controller receives a high-to-low signal, shutting down the compressor and restoring normal system pressure. A pipe temperature sensor is located at the outlet of the outdoor heat exchanger. This temperature sensor calculates the optimal system high pressure and adjusts the opening of the first one-way electronic expansion valve to ensure efficient system operation. An exhaust temperature switch is installed at the compressor outlet, set to 120°C. When the exhaust temperature exceeds the actuation level, the compressor shuts down. Normal compressor control resumes when the exhaust temperature drops below 90°C.

[0068] Heating cycle:

[0069] As shown in Figure 3, during the heating process, the refrigerant (R744) is discharged from the compressor exhaust port, enters the four-way valve inlet (first valve port) through the exhaust shock absorber pipe, flows through the four-way valve C port (third valve port), and enters the indoor heat exchanger. The second fan and the indoor heat exchanger are in countercurrent form, and the two cooperate to force the refrigerant (R744) to cool. Then the refrigerant (R744) enters the second drying filter.

[0070] During the heating process, the first one-way electronic expansion valve is closed, and the refrigerant flows out of the second drying filter in two ways, one of which enters the high-pressure side of the second regenerator, and the other enters the third one-way electronic expansion valve.

[0071] In this embodiment, the second regenerator has a total of 15 heat exchanger fins, with an outer shape of 191X77 mm. 2 The regenerator is divided into a high-pressure side and an intermediate-pressure side. The number and volume of heat exchangers can be adjusted as needed. The high-pressure side refrigerant is secondary cooled by the intermediate-pressure side refrigerant. The intermediate-pressure side refrigerant is then superheated by the high-pressure side refrigerant to form a supply air that enters the compressor supply air pipe. The fluids on both sides of the second regenerator are in countercurrent flow.

[0072] The refrigerant is throttled and reduced in pressure to medium-pressure wet steam by a third one-way electronic expansion valve. This valve also serves two functions: first, controlling the supply air flow rate; and second, controlling the supply air superheat through the coordination of an intermediate pressure transmitter and a third pipe temperature sensor. In this application, the second regenerator improves the circulation flow rate and cycle energy efficiency, and is therefore also referred to as an economizer.

[0073] The compressor has two-stage compression inside. The low-temperature and low-pressure refrigerant gas enters from the air intake port, and is compressed by the first stage of the compressor to discharge the medium-pressure and medium-temperature refrigerant gas into the compressor cavity. At this time, the refrigerant entering from the air supply port is mixed with the compressor cavity, and is compressed by the second stage of the compressor and discharged to the compressor exhaust port.

[0074] The main refrigerant flows out from the high-pressure side of the second regenerator and enters the second one-way electronic expansion valve. The second one-way electronic expansion valve is a main throttle valve. It has the same function as the first one-way electronic expansion valve in the refrigeration cycle. The refrigerant passes through the second one-way electronic expansion valve and is throttled and reduced in pressure to low-temperature, low-pressure wet steam.

[0075] The refrigerant flows out of the second one-way electronic expansion valve and into the first drier. The first and second drier filters protect the three one-way electronic expansion valves in the system, preventing impurities from entering the electronic expansion valves and causing system damage.

[0076] The refrigerant flows from the first filter drier into the first check valve. During the heating cycle, the first regenerator is short-circuited and inoperative. The refrigerant then flows out of the first check valve and into the outdoor heat exchanger. The first fan cooperates with the outdoor heat exchanger for forced heat exchange, converting the refrigerant from low-temperature, low-pressure wet vapor to low-pressure, superheated steam.

[0077] The refrigerant flows out from the outdoor heat exchanger outlet, enters the four-way valve B port (the second valve port), then flows out from the four-way valve D port (the fourth valve port) and enters the gas-liquid separator.

[0078] In the heating cycle, the gas-liquid separator can store the remaining refrigerant that does not participate in the circulation in the piping system to prevent the refrigerant from migrating and forming liquid hammer.

[0079] Refrigerant flows from the gas-liquid separator into the low-pressure side of the first regenerator. At this point, because the high-pressure side of the first regenerator is short-circuited, the first regenerator is inoperative, effectively acting as a section of piping. Refrigerant then flows from the low-pressure side of the first regenerator into the suction shock absorber pipe, and then into the compressor intake, completing the cycle. A second pipe temperature sensor is attached to the compressor intake pipe. During the heating cycle, this second pipe temperature sensor and the low-pressure pressure transmitter work in conjunction with the second one-way electronic expansion valve to control the suction superheat, which is set at 4K. A heating tape is attached to the compressor cavity for preheating during the heating cycle.

[0080] Heating and defrosting:

[0081] When the ambient temperature is between -5℃ and 5℃ and the humidity is high, the outdoor heat exchanger is particularly prone to frost. Over time, the heat transfer of the outdoor heat exchanger deteriorates, seriously affecting the heating of the heat pump, so defrosting is required.

[0082] The low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioning system disclosed in the present invention uses the low-pressure pressure transmitter reading and the second pipe temperature sensor reading as defrost judgment conditions. Specifically, the low-pressure pressure transmitter reading is recorded as P1, and the second pipe temperature sensor reading is recorded as T2. The defrost judgment conditions are:

[0083] (1) Pl<3.5MPa;

[0084] (2)0.0612*Pl 5 -0.9466*Pl 4 +6.0791*Pl 3 -21.643*Pl 2 +55.273*Pl-78.923-T2>-3;

[0085] When the above conditions are met at the same time, the cycle enters heating and defrosting

[0086] Heating and defrosting is a refrigeration cycle, but fan A does not work.

[0087] The reading of the first pipe temperature sensor is recorded as T1. When T1>5℃, the defrost process is terminated and the cycle returns to normal control.

[0088] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A cryogenic-resistant quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles, characterized in that: It includes a compressor, a four-way valve, an outdoor heat exchanger, a first regenerator, a first dryer filter, a second dryer filter, an indoor heat exchanger, and a second regenerator; The exhaust port of the compressor is connected to the first valve port of the four-way valve through a pipeline. The second valve port of the four-way valve is connected to the first interface of the outdoor heat exchanger through a pipeline. The second interface of the outdoor heat exchanger is connected to the first interface of the high-pressure side of the first regenerator through a pipeline. The second interface of the high-pressure side and the first interface of the high-pressure side of the first regenerator are respectively connected to the first interface of the first dryer filter through pipelines. The second interface of the first dryer filter is respectively connected to the first interface of the second dryer filter and the first interface of the high-pressure side of the second regenerator through pipelines. The second interface of the high-pressure side of the second regenerator is connected to the first interface of the second dryer filter through a pipeline. The second interface of the second dryer filter is connected to the first interface of the indoor heat exchanger through a pipeline. The second interface of the indoor heat exchanger is connected to the third valve port of the four-way valve through a pipeline. The fourth valve port of the four-way valve is connected to the first interface of the low-pressure side of the first regenerator through a pipeline. The second interface of the low-pressure side of the first regenerator is connected to the intake port of the compressor through a pipeline; The first interface of the medium-pressure side of the second regenerator is connected to the second interface of the high-pressure side of the second regenerator through a pipeline. The second interface of the medium-pressure side of the second regenerator is connected to the gas replenishing port of the compressor through a pipeline; A second check valve and a first check valve are respectively provided on the pipelines connecting the second interface of the high-pressure side and the first interface of the high-pressure side of the first regenerator to the first interface of the first dryer filter; A first one-way electronic expansion valve and a second one-way electronic expansion valve are respectively provided on the two pipelines connecting the second interface of the first dryer filter to the first interface of the second dryer filter and the first interface of the high-pressure side of the second regenerator; A third one-way electronic expansion valve is provided on the pipeline connecting the first interface of the medium-pressure side of the second regenerator to the second interface of the high-pressure side of the second regenerator.

2. The cryogenic-resistant orbit vehicle quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner according to claim 1, wherein: It further includes the gas-liquid separator provided on the pipeline connecting the fourth valve port of the four-way valve to the first interface of the low-pressure side of the first regenerator.

3. The cryogenic-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles according to claim 1, characterized in that: It further includes a high-pressure pressure transmitter, a high-pressure pressure switch, a first stop valve, and a safety valve provided on the pipeline connecting the exhaust port of the compressor to the first valve port of the four-way valve; A low-pressure pressure switch, a low-pressure pressure transmitter, and a second stop valve provided on the pipeline connecting the intake port of the compressor to the second interface of the low-pressure side of the first regenerator; and, A medium-pressure pressure transmitter provided on the pipeline connecting the second interface of the medium-pressure side of the second regenerator to the gas replenishing port of the compressor.

4. The cryogenic-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles according to claim 1, characterized in that: It further includes a first pipeline temperature sensor, a second pipeline temperature sensor, and a third pipeline temperature sensor; The first pipeline temperature sensor is provided on the pipeline connecting the second interface of the outdoor heat exchanger to the first interface of the high-pressure side of the first regenerator; The second pipeline temperature sensor is provided on the pipeline connecting the second interface of the low-pressure side of the first regenerator to the intake port of the compressor; The third pipeline temperature sensor is arranged on the pipeline connecting the second interface on the medium-pressure side of the second regenerator and the gas supplementing port of the compressor.

5. The cryogenic-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles according to any one of claims 1 to 4, characterized in that: An exhaust shock-absorbing pipe and a suction shock-absorbing pipe are respectively arranged at the exhaust port and the intake port of the compressor.

6. The cryogenic-resistant orbit vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner according to claim 5, characterized in that: A discharge temperature switch is also arranged at the exhaust port of the compressor.

7. The cryogenic-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles according to claim 6, characterized in that: It further includes a first fan and a second fan which are correspondingly arranged with the outdoor heat exchanger and the indoor heat exchanger.

8. The cryogenic-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles according to claim 7, wherein: The outdoor heat exchanger is a copper tube-aluminum fin heat exchanger; the first fan is an axial flow fan; both the first regenerator and the second regenerator are plate heat exchangers; the indoor heat exchanger is a copper tube-aluminum fin heat exchanger; the second fan is a centrifugal fan.

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