A method for detecting leakage of R407C refrigerant for a vehicle air conditioning unit

Abstract

The application discloses a kind of R407C refrigerant leakage detection methods for vehicle air conditioning unit, directly utilize the characteristics of fast response of pressure signal, little influence of refrigerant because of the composition change caused by refrigeration system leakage, by comparing the pressure difference between the two refrigeration systems of double refrigeration system passenger room air conditioning unit and the absolute value of the pressure of single system, combined with outdoor environment temperature partition, three layers of logic, logic 1, logic 2 and logic 3 are designed, which correspond to different leakage severity and operation mode respectively.All logic uses "three times alarm confirmation" mechanism to avoid false alarm caused by transient disturbance.The R407C refrigerant leakage detection method for vehicle air conditioning unit of the application adopts a new type of refrigerant leakage detection logic based on pressure detection, completely avoids the influence of boiling point drift between bubble point and dew point of R407C refrigerant, the nature of leakage detection does not change, and the speed of refrigerant leakage detection feedback is also faster, more accurate and more accurate.

Description

Technical Field

[0001] This invention belongs to the field of vehicle air conditioning system technology, specifically relating to a method for detecting R407C refrigerant leakage in vehicle air conditioning units. Background Technology

[0002] In the design of modern urban rail air conditioning systems, passenger compartment air conditioning units typically employ a dual-refrigeration system design. Each system has its own independent refrigerant circulation system and its own core components such as compressors, condensers, and expansion units. Each system can be controlled individually or together. If a refrigerant leak occurs during operation, the evaporator in the unit's refrigeration system may experience drastic fluctuations in airflow rate or temperature, far exceeding design values. This leads to excessively low low pressure in the refrigeration system. Under these conditions, the compressor and evaporator capacity will reach equilibrium as the unit's suction pressure and temperature continue to decrease, ultimately resulting in excessively low low pressure during operation. This causes frost to form on the coils and pipes, frequent compressor starts under low-pressure control, and may even lead to damage from drawing in liquid refrigerant.

[0003] Traditional refrigerant leak detection logic is based on the surface temperature of the copper inlet suction pipe of the air conditioning unit's compressor and related calculations. This detected temperature value is derived from the calculation of the superheat value ΔT. The compressor suction superheat of the passenger air conditioning unit's refrigeration system is equal to the temperature difference between the surface temperature of the copper pipe at the compressor suction port and the saturated boiling temperature derived from the low-pressure refrigerant in the compressor suction pipe, based on the characteristics of the refrigerant used in the air conditioning unit's refrigeration system.

[0004] During testing, it was found that the suction temperature sensor installed on the surface of the suction pipe of the compressor in the refrigeration system of the passenger air conditioning unit using R407C refrigerant had a long delay in detecting temperature.

[0005] The first reason is due to the unique characteristic of the mixed refrigerant R407C, which possesses two boiling temperatures (bubble point and dew point). R407C is a ternary non-azeotropic refrigerant composed of R32 (difluoromethane), R125 (pentafluoroethane), and R134a (tetrafluoroethane) in a specific ratio. Therefore, its boiling point is affected; it does not boil at a fixed temperature but rather exists within a temperature fluctuation range. This means its boiling point is represented as a range. The starting temperature (bubble point) and ending temperature (dew point) within this range correspond to the boiling points of different components. For example... Figure 1 As shown Please see Figure 1 The boiling point of R407C refrigerant includes both bubble point and dew point characteristics.

[0006] Bubble point: This is the temperature at which the first bubble forms when the liquid refrigerant is heated under constant pressure. For R407C, the bubble point is close to the saturation temperature of the lower boiling point component (R-32) in the mixture. Dew point: This is the temperature at which the first droplet forms when the vaporized refrigerant is cooled under constant pressure. For R407C, its dew point is closer to the saturation temperature of the higher boiling point component (R-125).

[0007] Boiling points of R407C components: Under standard atmospheric pressure, the boiling points of each component of R407C are as follows: R32 (difluoromethane, CH2F2): Boiling point is approximately -51.7°C.

[0008] R125 (pentafluoroethane, C2HF5): Boiling point is approximately -48.5°C.

[0009] R134a (tetrafluoroethane, C2H2F4): Boiling point is approximately -26.3°C.

[0010] Boiling point comparison explanation: The boiling point range of R407C (-43.6°C to -36.1°C) lies between the boiling points of its components R32 and R125 (approximately -51.7°C and -48.5°C, respectively) and the boiling point of R134a (approximately -26.3°C). Since R134a constitutes the largest proportion of the mixture (approximately 50%), the boiling point range of R407C is closer to that of R134a, but overall, its boiling point is still significantly lower than that of any single R134a. For example, as shown in the table below, at 54.5°C, with constant pressure for all refrigerants, the boiling point of R407C varies by approximately 5.4°C.

[0011] This change in boiling point is a key characteristic of R407C as a non-zeolite mixture, meaning that if a refrigerant leak occurs on the liquid side, R32 will leak first. However, if the leak occurs on the gas side, the proportion of refrigerant leaking will differ. This causes a change in the boiling point of the refrigeration system at the location of the leak, affecting the compressor inlet temperature and resulting in different superheats due to the refrigerant leaking from different locations. This makes it impossible to determine the refrigerant leakage proportion solely through temperature detection and superheat calculations—because these detections and calculations rely on the compressor inlet temperature (i.e., the refrigerant boiling point). Therefore, the refrigerant leakage logic based on compressor suction pipe surface temperature detection and superheat calculations is not accurate enough for R407C.

[0012] The practical impact of this situation lies in the fact that, since R407C is a non-azeotropic mixture, its bubble point and dew point differ at the same pressure, leading to temperature fluctuations. This affects system performance, requiring precise control of superheat. At typical operating pressures, the bubble point is lower than the dew point, which affects heat transfer and temperature detection of subcooling. Air conditioning systems need to be run in a laboratory for extended periods to stabilize conditions and facilitate suction temperature monitoring. There are also significant impacts on various changing operating conditions in the field, such as compressor on / off and bypass on / off. However, return gas temperature changes are less sensitive due to the unique properties of the R407C refrigerant mixture, which may lead to false alarms, especially when using R407C refrigerant in this project. The mixed refrigerant exhibits slip subcooling. Furthermore, the temperature sensor signal shows that the temperature signal transmission speed is slower than the pressure signal transmission speed.

[0013] The second reason is that the contact area between the cylindrical head 1′ of the temperature sensor and the copper tube 2′ is very limited, such as... Figure 2 As shown, the temperature of the refrigerant inside the copper tube needs to be transferred to the sensitive element in the temperature sensor through heat conduction within the copper tube and on the surface of the temperature sensor. During this heat transfer process, heat loss occurs, leading to significant temperature deviations. When the temperature of the R407C refrigerant inside the copper tube changes significantly, the speed and accuracy of temperature transfer are greatly affected due to the small contact area between the temperature sensor and the copper tube. Summary of the Invention

[0014] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for detecting R407C refrigerant leaks in vehicle air conditioning units. It adopts a new refrigerant leak detection logic based on pressure detection, replacing the detection logic based on temperature detection in the prior art. This completely avoids the influence of boiling point drift between the bubble point and dew point of R407C refrigerant. The essence of leak detection remains unchanged, and the speed of refrigerant leak detection feedback is faster, more accurate, and more precise.

[0015] The technical solution to achieve the above objective is as follows: A method for detecting R407C refrigerant leakage in a vehicle air conditioning unit, wherein the air conditioning unit comprises two independent refrigeration systems, each of which uses R407C refrigerant, and each of which is equipped with a high-pressure sensor for detecting compressor discharge pressure and a low-pressure sensor for detecting compressor suction pressure. The R407C refrigerant leakage detection method includes the following steps: S1, after the two refrigeration systems are running stably at the same time, obtain the low pressure value LP1 of the first refrigeration system, the low pressure value LP2 of the second refrigeration system, the high pressure value HP1 of the first refrigeration system, and the high pressure value HP2 of the second refrigeration system. S2, calculate the absolute value of the low-pressure difference ΔLP = |LP1 - LP2|, and the absolute value of the high-pressure difference ΔHP = |HP1 - HP2|; S3, compare the ΔLP with the preset low pressure differential threshold, and compare the ΔHP with the high pressure differential threshold obtained by looking up the table based on the outdoor ambient temperature; S4, when ΔLP is greater than the preset low pressure differential threshold, ΔHP is greater than the high pressure differential threshold, and the above state continues for a preset delay time, it is determined that the refrigeration system corresponding to the lower pressure value of LP1 and LP2 has a refrigerant leak, and a leak alarm is recorded. S5, repeat steps S1 to S4 to accumulate the number of leak alarms. When the accumulated number of alarms reaches the preset number of alarms, output a refrigerant leak fault signal.

[0016] The above-mentioned method for detecting R407C refrigerant leakage in a vehicle air conditioning unit includes a low-pressure differential threshold of 1.2 Bar and a second threshold of 1.5 Bar; the preset delay time includes a first delay of 30 seconds corresponding to the first threshold of 1.2 Bar and a second delay of 8 seconds corresponding to the second threshold of 1.5 Bar.

[0017] The above-mentioned method for detecting R407C refrigerant leakage in vehicle air conditioning units, wherein when ΔLP > 1.2 Bar and lasts for 30 seconds, it is determined to be a Class I leakage alarm; When ΔLP > 1.5 Bar and lasts for 8 seconds, it is determined to be a Class II leakage alarm; The first type of leakage alarm and the second type of leakage alarm share the same counter. Within the same detection cycle, before the alarm is reset, after the first type of leakage alarm is triggered, the second type of leakage alarm will not repeatedly increment the counter, and vice versa.

[0018] The next counting cycle will only begin after Class I and Class II leakage alarms have been reset.

[0019] The aforementioned method for detecting R407C refrigerant leaks in vehicle air conditioning units, wherein "stable operation" includes at least the following conditions: The compressors of both refrigeration systems have a continuous operating time of more than 120 seconds. If the refrigeration system is equipped with a hot gas bypass valve, the closing time of the hot gas bypass valve is greater than 30 seconds; The refrigeration system has no compressor fault alarms and no air valve fault alarms.

[0020] The aforementioned method for detecting R407C refrigerant leaks in vehicle air conditioning units stipulates that after a single leak alarm is recorded, the alarm state can only be reset and the next leak detection can only begin if any of the following conditions are met: 20 minutes have passed since this alarm was triggered; The corresponding refrigeration system compressor stops running.

[0021] The aforementioned method for detecting R407C refrigerant leaks in vehicle air conditioning units also includes a single-system severe leak detection mode: A leak alarm is recorded when only one refrigeration system is operating stably, the outdoor ambient temperature is above 20°C, and all of the following conditions are met for 10 seconds: the low-pressure value of the operating refrigeration system is ≤ 2.1 Bar; Furthermore, the high-pressure value of the operating refrigeration system is less than the high-pressure threshold obtained by looking up the table based on the outdoor ambient temperature. Once the low-pressure value of the operating refrigeration system rises to ≥ 2.7 Bar, the leakage alarm will automatically reset and the next detection will begin. When the cumulative number of alarms reaches the preset number, a refrigerant leakage fault signal will be output.

[0022] The above-mentioned method for detecting R407C refrigerant leakage in vehicle air conditioning units, wherein the high-pressure differential threshold or high-pressure threshold is obtained by looking up the following table: Table 1. Relationship between outdoor ambient temperature and high pressure differential threshold, as well as high pressure threshold: The above-mentioned method for detecting R407C refrigerant leakage in a vehicle air conditioning unit includes a preset alarm count of 3 times. After 3 consecutive leakage alarms, the refrigerant leakage fault signal is sent to the controller of the vehicle air conditioning unit, and the "refrigerant leakage fault" information is displayed on the control display screen.

[0023] The present invention also discloses a passenger compartment air conditioning unit for rail vehicles, comprising: Two independent refrigeration systems using R407C refrigerant; Each refrigeration system includes a compressor, condenser, evaporator, and expansion unit, as well as a high-pressure sensor and a low-pressure sensor; And an air conditioning unit central controller, the air conditioning unit central controller being configured to execute the above-described R407C refrigerant leak detection method and send the final alarm information to the vehicle control system terminal.

[0024] The R407C refrigerant leakage detection method for vehicle air conditioning units of the present invention has the following beneficial effects: (1) High design novelty. Because refrigerant R407C has both dew point and bubble point boiling points, different locations of refrigerant leakage result in different degrees of superheat. This makes the traditional refrigerant leak detection logic, which relies solely on temperature detection and superheat calculation to determine the refrigerant leakage ratio, impossible—because these detections and calculations depend on the compressor inlet temperature (i.e., the refrigerant boiling point temperature). Therefore, the refrigerant leak logic based on temperature detection and superheat calculation is not accurate enough for R407C. This design abandons the traditional logic of detecting refrigerant leaks by detecting the surface temperature of the compressor inlet copper pipes and calculating superheat in the air conditioning refrigeration system. Instead, it uses pressure sensors to collect the high-pressure values ​​of the compressor exhaust pipes and the low-pressure values ​​of the compressor suction pipes of the two refrigeration systems in the passenger compartment air conditioning unit. By comparing the pressure values ​​and pressure differences under different ambient temperature conditions, it accurately detects refrigerant R407C leaks in the passenger compartment air conditioning unit under different outdoor and indoor temperature conditions, demonstrating strong novelty.

[0025] (2) The design is highly comprehensive. For the design of passenger cabin air conditioning units that use R407C refrigerant in rail air conditioning, which adopt dual refrigeration systems and use high-pressure and low-pressure sensors, this R407C refrigerant leakage detection logic can be used to detect refrigerant leakage. It can be widely used in the design of similar systems.

[0026] (3) The design is highly consistent and fully covers the design requirements of dual refrigeration system with high pressure sensor and low pressure sensor for passenger cabin air conditioning units using R407C refrigerant in track air conditioning, and meets the design requirements of passenger cabin air conditioning units with dual refrigeration system using R407C refrigerant in different projects.

[0027] (4) High design reliability: The logic for detecting R407C refrigerant leakage faults in the passenger compartment air conditioning unit of the rail air conditioning system based on pressure detection has been verified by laboratory tests and tested in actual applications of related projects. This improves the operational safety, reliability, and stability of the dual refrigeration system of the passenger compartment air conditioning unit using R407C refrigerant in the rail air conditioning system. The test of the R407C refrigerant leakage fault monitoring and detection logic of the two refrigeration systems of the passenger compartment air conditioning unit is based on the working conditions specified in Clauses 8.2.12 and 8.2.16a of standard Q / CR 278-2015. Type test report: QSD-0695300-4400 refrigerant leakage logic test report A01. Attached Figure Description

[0028] Figure 1 Dew point and bubble point diagram for refrigerant R407C; Figure 2 This is a schematic diagram illustrating the use of a temperature sensor to detect the temperature of the refrigerant inside a copper tube in existing technologies. Figure 3 This is a schematic diagram of a dual-refrigeration system for a vehicle air conditioning unit that uses R407C refrigerant. Figure 4 This is a flowchart of the R407C refrigerant leakage detection method for vehicle air conditioning units according to the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solution of the present invention, its specific embodiments are described in detail below with reference to the accompanying drawings: Hardware basis of this invention: Please refer to Figure 3 The passenger compartment air conditioning unit of the rail vehicle includes two independent refrigeration systems, each using R407C refrigerant. Each refrigeration system includes a compressor 1, a condenser 2, and an evaporator 3. Each refrigeration system's piping is equipped with a sight glass 6, a dryer filter 7, a liquid circuit solenoid valve 8, a hot gas bypass valve 10, a check valve 12, a maintenance valve 13, an expansion valve 14, a gas-liquid separator 15, a pressure switch 17, a condenser outlet temperature sensor 19, and a compressor inlet temperature sensor 20. A condenser blower 4 is located next to condenser 2, and a blower 5 is located next to evaporator 3.

[0030] Each refrigeration system is equipped with a high-pressure sensor 21 for detecting the discharge pressure of compressor 1 and a low-pressure sensor 18 for detecting the suction pressure of compressor 1. The passenger compartment air conditioning unit of the rail vehicle also includes a central controller for the air conditioning unit. The central controller can read the high-pressure and low-pressure values ​​of the two refrigeration systems in real time, namely, the low-pressure value LP1 of the first refrigeration system, the low-pressure value LP2 of the second refrigeration system, the high-pressure value HP1 of the first refrigeration system, and the high-pressure value HP2 of the second refrigeration system. The central controller for the air conditioning unit is used to run the three-layer logic of the R407C refrigerant leakage detection method of the present invention.

[0031] The core idea of ​​this invention is to eliminate the need for superheat calculation. Instead, it leverages the rapid response and minimal impact of refrigerant composition changes on pressure signals. By comparing the pressure difference between two refrigeration systems and the absolute pressure value of a single system, and considering outdoor ambient temperature (fresh air temperature) zoning, a three-layer logic (Logic 1, Logic 2, and Logic 3) is designed, corresponding to different leakage severity levels and operating modes. All logic employs a "three-stage alarm confirmation" mechanism to avoid false alarms caused by momentary disturbances.

[0032] The common parameter table of the present invention pre-calibrates the high pressure differential threshold and high pressure threshold according to different outdoor ambient temperatures (fresh air temperature T), as shown in Table 1.

[0033] Table 1. Relationship between outdoor ambient temperature and high pressure differential threshold, as well as high pressure threshold: Please see Figure 4 An embodiment of the present invention provides a method for detecting R407C refrigerant leakage in vehicle air conditioning units.

[0034] Logic 1, corresponding to general leak detection in dual-system operation, is applicable under the following conditions: both refrigeration systems are running stably simultaneously. Stability prerequisites include: both compressors running continuously for >120 seconds; bypass valves (if present) in both systems closed for ≥30 seconds. There are no compressor, damper, or other fault alarms. Specifically, it includes the following steps: S1, obtain the low-pressure value LP1 of the first refrigeration system, the low-pressure value LP2 of the second refrigeration system, the high-pressure value HP1 of the first refrigeration system, and the high-pressure value HP2 of the second refrigeration system after the two refrigeration systems are running stably at the same time.

[0035] S2, calculate the absolute value of the low-pressure difference ΔLP = |LP1 - LP2|, and the absolute value of the high-pressure difference ΔHP = |HP1 - HP2|.

[0036] S3, compare ΔLP with the preset low pressure differential threshold, and compare ΔHP with the high pressure differential threshold obtained from Table 1 based on the outdoor ambient temperature.

[0037] S4, Judgment condition (must be met simultaneously for 30 seconds): The absolute value of the low-pressure difference ΔLP = |LP1 - LP2| > 1.2 Bar; The absolute value of the high pressure difference ΔHP = |HP1 - HP2| > the high pressure difference threshold corresponding to T in Table 1; Judgment action: Determine that the refrigeration system with both ΔLP and ΔHP lower (i.e., the lower pressure side) has a refrigerant leak, and record 1 leak alarm.

[0038] S5, Reset and Accumulation: Reset Condition: After a single alarm, wait 20 minutes or the compressor stops to reset the alarm status and prepare for the next test. Repeat steps S1 to S4 to accumulate the number of leak alarms. When the controller of the passenger compartment air conditioning unit has accumulated 3 leak alarms, it reports "refrigerant leak fault" to the vehicle control system terminal and displays the "refrigerant leak fault" information on the vehicle control system terminal display screen.

[0039] The two stable operating conditions set in Logic 1 are to prevent large fluctuations in the high pressure value (compressor discharge pressure) detected by the high pressure sensor and the low pressure value (compressor suction pressure) detected by the low pressure sensor during the initial operation of the air conditioning unit, which would lead to inaccurate pressure detection results and cause false alarms.

[0040] Logic 1 specifically emphasizes that the bypass valve must be closed for 30 seconds. When the hot gas bypass valve in the air conditioning unit's refrigeration system immediately closes, the low-pressure value will fluctuate for a few seconds. If the low-pressure value detected by the low-pressure sensor is sent to the air conditioning controller during this time to determine if there is a refrigerant leak, it can easily cause false alarms. Therefore, it is emphasized that a pressure signal must be sent to the central controller of the air conditioning unit 30 seconds after the bypass valve closes to initiate the logic for determining whether there is a refrigerant leak. For passenger air conditioning units without a bypass valve, the bypass valve control-related content in the refrigerant leak detection logic can be ignored.

[0041] Logic 1 specifically emphasizes that the prerequisite for refrigerant leak detection is that both refrigeration systems of the passenger compartment air conditioning unit are operating normally, and the absolute value of the low-pressure difference between the two refrigeration systems is greater than 1.2 bar, and the absolute value of the high-pressure difference is greater than the value in Table 1, lasting for 30 seconds. Because after a refrigerant leak, both the low-pressure and high-pressure values ​​of the corresponding refrigeration system will decrease. If the two independent refrigeration systems of the passenger compartment air conditioning unit are operating, and the low-pressure difference is greater than 1.2 bar, it indicates that the refrigerant leak in the refrigeration system with the lower low-pressure value is not very serious. Provided that the absolute value of the high-pressure difference is greater than the value in Table 1, the system suspected of refrigerant leakage (i.e., the refrigeration system with the lower low-pressure value) can operate for 30 seconds before performing R407C refrigerant leak fault detection and sending a refrigerant leak fault alarm to the control system. The settings of low-pressure difference > 1.2 bar and high-pressure difference greater than the value in Table 1, lasting for 30 seconds, along with these pressure values ​​and delay values, are unique to this patent.

[0042] Logic 1 specifically emphasizes that the setting of resetting the alarm value and starting the next detection after 20 minutes of each refrigerant leak alarm or compressor shutdown is unique to this patent. The purpose is to prevent the time interval between the three alarms from being too short, which would cause the compressor's discharge pressure and suction pressure to be unstable in the initial stage of the air conditioning unit's refrigeration system, resulting in false alarms.

[0043] II. Logic 2 corresponds to rapid severe leak detection during dual-system operation. Applicable conditions are: both refrigeration systems are operating stably simultaneously. Stability prerequisites: same as Logic 1 (compressor operation > 120 seconds, bypass valve closed ≥ 30 seconds, no compressor, damper, or other fault alarms). Specifically, it includes the following steps: S1, obtain the low-pressure value LP1 of the first refrigeration system, the low-pressure value LP2 of the second refrigeration system, the high-pressure value HP1 of the first refrigeration system, and the high-pressure value HP2 of the second refrigeration system after the two refrigeration systems are running stably at the same time.

[0044] S2, calculate the absolute value of the low-pressure difference ΔLP = |LP1 - LP2|, and the absolute value of the high-pressure difference ΔHP = |HP1 - HP2|.

[0045] S3, compare ΔLP with the preset low pressure differential threshold, and compare ΔHP with the high pressure differential threshold obtained from Table 1 based on the outdoor ambient temperature.

[0046] S4, Judgment condition (must be met simultaneously for 8 seconds): The absolute value of the low-pressure difference ΔLP = |LP1 - LP2| > 1.5 Bar; The absolute value of the high pressure difference ΔHP = |HP1 - HP2| > the high pressure difference threshold corresponding to T in Table 1; Judgment Action: Determine that the refrigeration system with both ΔLP and ΔHP lower (i.e., the side with lower pressure) has a refrigerant leak and record one leak alarm; the response time is shorter than logic 1 (logic 2 lasts 8 seconds vs. logic 1 lasts 30 seconds), and it is suitable for scenarios with a faster leakage rate.

[0047] S5, Reset and Accumulation: The reset condition is the same as logic 1. The counter shares the same logic as logic 1. The counter increments by 1 when either logic 1 or logic 2 is triggered. If logic 1 has been triggered and the leak alarm has not been reset during this detection cycle, logic 2 will not add an extra count (and vice versa), to avoid repeated accumulation.

[0048] After the leakage alarms of logic 1 and logic 2 are reset, the next detection count will begin.

[0049] When the controller of the air conditioning unit records a total of 3 leakage alarms, it reports "refrigerant leakage fault" to the vehicle control system terminal and displays the "refrigerant leakage fault" information on the control display screen of the vehicle control system terminal.

[0050] Logic 2 specifically emphasizes that under stable operating condition 1: the compressors of both refrigeration systems of the passenger compartment air conditioning unit have been running for more than 120 seconds. Stable operating condition 2: Both refrigeration system compressors are running (bypass valve closed for 30 seconds, no compressor fault alarm, no damper fault alarm). The above two conditions are set to avoid large fluctuations in the compressor's discharge pressure (the high-pressure value detected by the high-pressure sensor) and the compressor's suction pressure (the low-pressure value detected by the low-pressure sensor) during the initial operation of the air conditioning unit, which could lead to inaccurate pressure readings and false alarms.

[0051] Logic 2 specifically emphasizes that the bypass valve must be closed for 30 seconds. When the hot gas bypass valve in the air conditioning unit's refrigeration system immediately closes, the low-pressure value will fluctuate for a few seconds. If the low-pressure value detected by the low-pressure sensor is sent to the controller during this time to determine if there is a refrigerant leak, it can easily cause false alarms. Therefore, it is emphasized that a pressure signal must be sent to the central controller of the air conditioning unit 30 seconds after the bypass valve closes to initiate the logic for determining whether there is a refrigerant leak. For passenger air conditioning units without a bypass valve, the bypass valve control-related content in the refrigerant leak detection logic can be ignored.

[0052] Logic 2 specifically emphasizes that the prerequisite for refrigerant leak detection is that both refrigeration systems of the passenger compartment air conditioning unit are operating normally, and the absolute value of the low-pressure difference between the two refrigeration systems is greater than 1.5 bar, and the absolute value of the high-pressure difference is greater than the value in Table 1, lasting for 8 seconds. Because after a refrigerant leak, both the low-pressure and high-pressure values ​​of the corresponding refrigeration system will decrease. If the two independent refrigeration systems of the passenger compartment air conditioning unit are operating, and the low-pressure difference is greater than 1.5 bar, it indicates that the refrigerant leak in the refrigeration system with the lower low-pressure value is very serious and urgent. Under the premise that the absolute value of the high-pressure difference is greater than Table 1, the system suspected of refrigerant leakage, i.e., the refrigeration system with the lower low-pressure value, can operate for 8 seconds before performing R407C refrigerant leak fault detection and sending a refrigerant leak fault alarm to the control system. The settings of low-pressure difference > 1.5 bar and high-pressure difference greater than the value in Table 1, lasting for 8 seconds, along with these pressure values ​​and delay values, are unique to this patent.

[0053] Logic 2 specifically emphasizes that the setting of resetting the alarm value and starting the next detection after 20 minutes of each refrigerant leak alarm or compressor shutdown is unique to this patent. The purpose is to prevent the time interval between the three alarms from being too short, which would cause the compressor's discharge pressure and suction pressure to be unstable in the initial stage of the air conditioning unit's refrigeration system, easily leading to false alarms.

[0054] Logic 1 and Logic 2 are specifically emphasized. Both Logic 1 and Logic 2 require the air conditioning unit's controller to accumulate three refrigerant leak alarms before determining a refrigerant leak fault and sending an alarm to the vehicle control system terminal, displaying "Refrigerant Leak Fault" on the control screen. Because the low-pressure difference values ​​of Logic 1 and Logic 2 overlap, during the counting process of Logic 1 and Logic 2, they are not counted separately, but rather their counts are superimposed within the same detection cycle. In other words, the "Refrigerant Leak Fault" reports from both Logic 1 and Logic 2 are attributed to the air conditioning unit's control system logic. (1) If a leakage fault alarm occurs in logic 1 or logic 2, the counter triggered by the alarm will increment by 1; (2) If a leakage fault alarm occurs in logic 1, before the alarm is reset in the same detection cycle, the counter will not be increased by logic 2 at the same time. That is, if a leakage fault alarm occurs in logic 2, it will not be counted in the total of 3 alarms (and vice versa).

[0055] (3) After the leakage alarms of logic 1 and logic 2 are reset, the next detection count will begin.

[0056] The ambient temperature, running time, pressure, and pressure difference values ​​in Logic 1 and Logic 2 are unique to this invention and are based on the conclusions of logic verification experiments conducted in the laboratory.

[0057] 3. Logic 3, corresponding to severe leak detection in a single system, applicable conditions: Only one refrigeration system is operating stably (the other system is not started or is faulty). Environmental prerequisites: Outdoor ambient temperature (fresh air temperature) > 20℃. Stability prerequisites: The running compressor has been running continuously for > 120 seconds; the bypass valve of the running refrigeration system is closed (if present), and the compressor has no fault alarm. Specifically, it includes the following steps: S1, obtains the low-pressure value and high-pressure value of a single refrigeration system after it has been running stably.

[0058] S2, compare the low pressure value with the preset low pressure threshold (2.1 Bar), and compare the high pressure value with the high pressure threshold obtained from Table 1 based on the outdoor ambient temperature.

[0059] S3, Judgment condition (must be met simultaneously for 10 seconds): The low-pressure value of the refrigeration system is ≤ 2.1 Bar; The high pressure value of the refrigeration system is less than the high pressure threshold corresponding to T in Table 1; Action taken: Record one leakage alarm.

[0060] S4, Reset Condition: After detecting one leak alarm, the alarm is not immediately accumulated to three. Instead, it waits for the system's low-pressure level to rise to ≥ 2.7 Bar before automatically resetting and restarting the next detection. This design avoids continuous false alarms caused by brief pressure fluctuations or system self-adjustment.

[0061] S5, final fault output: When the controller of the air conditioning unit records a total of 3 leakage alarms (each alarm must go through a reset process of low pressure recovery to 2.7 Bar between each alarm), it reports "refrigerant leakage fault" to the vehicle's control system terminal and displays "refrigerant leakage fault" information on the vehicle control terminal display screen.

[0062] Logic 3 specifically addresses faults involving severe R407C refrigerant leakage in any one or two refrigeration systems of the passenger cabin air conditioning unit. According to laboratory leakage logic verification experiments, leakage alarm logic 3 will only be triggered when the refrigerant leakage in any one of the refrigeration systems of the passenger cabin air conditioning unit approaches 50%.

[0063] Logic 3 specifically emphasizes the prerequisites for determining refrigerant leak faults: Condition 1: When the ambient temperature is above 20°C, this is a prerequisite for determining that any refrigeration system of the unit must have a low-pressure value of 2.1 bar and a high-pressure value greater than the high-pressure value in Table 1 during operation. Only under these temperature conditions, if the low-pressure value is below 2.1 bar and the high-pressure value is below the high-pressure value in Table 1 for 10 seconds, a refrigerant leak fault count will be recorded once.

[0064] Condition 2: Either compressor in either of the two systems of the passenger cabin air conditioning unit has been running for 120 seconds.

[0065] Condition 3: Any refrigeration system of the passenger compartment air conditioning unit is powered on and running (bypass valve closed, compressor fault alarm, damper fault alarm).

[0066] The key difference here is that Logic 3 applies to the scenario where either of the two refrigeration systems in the passenger compartment air conditioning unit is operating, not the scenario where both systems are operating simultaneously. This needs to be clarified. And within that: Condition 2: Either compressor in either of the two systems of the passenger cabin air conditioning unit has been running for 120 seconds; Condition 3: Any refrigeration system of the passenger compartment air conditioning unit is powered on and running (bypass valve closed, compressor fault alarm not present, air conditioning valve fault alarm not present); These measures are all to prevent false alarms caused by unstable compressor discharge and suction pressures when any of the refrigeration systems in the unit are just starting to run.

[0067] Logic 3 specifically emphasizes the following judgment conditions: the low-pressure value of the refrigeration system of the passenger compartment air conditioning unit is 2.1 bar, and the high-pressure value is lower than the value in Table 1, and these conditions are maintained continuously for 10 seconds. If the above conditions are met, the passenger compartment air conditioning unit will detect a refrigerant leak. The pressure values ​​used here to determine whether there is a serious refrigerant leak, including the low-pressure value being lower than 2.1 bar and the high-pressure value being lower than the high-pressure value in Table 1, are unique to this application and are based on the conclusions of logic verification experiments conducted in the laboratory.

[0068] Logic 3 specifically emphasizes that, to prevent false alarms, after detecting the first refrigerant leak, the alarm will only reset when the low-pressure value of the relevant refrigeration system returns to 2.7 bar. Then, Logic 3 will restart the second R407C refrigerant leak detection, and so on for the third. Only after the air conditioning system controller has detected a total of three refrigerant leak faults will it report a "refrigerant leak fault" to the vehicle's control system terminal and display the "refrigerant leak fault" information on the vehicle control terminal display. The process of waiting for the low-pressure value to return to 2.7 bar before the first alarm resets and the air conditioning unit controller performs a second Logic 3 leak alarm detection is unique to this application and is based on the conclusion that the logic verification experiments conducted in the laboratory have proven its effectiveness.

[0069] The R407C refrigerant leakage detection method for vehicle air conditioning units of the present invention is applicable to passenger compartment air conditioning units in rail air conditioning systems that use R407C refrigerant. The refrigerant leakage detection logic comprehensively covers the design of dual refrigeration systems in passenger compartment air conditioning units of rail air conditioning systems that use R407C refrigerant and employ both high-pressure and low-pressure sensors.

[0070] In summary, the R407C refrigerant leakage detection method for vehicle air conditioning units of the present invention uses high-pressure and low-pressure sensors installed on the inlet and outlet pipes of the compressor in the refrigeration system to detect the high-pressure and low-pressure values ​​at the compressor inlet and outlet, as well as the calculated pressure difference. This optimizes the R407C refrigerant leakage detection logic in the refrigeration system, accurately detecting when the refrigerant leakage in the two independent refrigeration systems of the passenger compartment air conditioning unit exceeds a certain percentage. The control system promptly reports a "refrigerant leakage fault" alarm, reminding the user to take appropriate protective measures and maintenance checks to prevent damage to critical components such as the compressor caused by the low pressure exceeding the system's designed safe operating range during extreme operating conditions when the refrigerant leakage exceeds 30%. This method can be widely applied to the design of refrigeration systems for passenger compartment air conditioning units using R407C refrigerant in the rail air conditioning industry for refrigerant leakage detection. It can be comprehensively and effectively applied to the dual refrigeration system design of passenger compartment air conditioning units in different projects, meeting the needs of different customers and ensuring the safe, reliable, stable, and efficient operation of the air conditioning system.

[0071] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for detecting R407C refrigerant leakage in a vehicle air conditioning unit, wherein the air conditioning unit comprises two independent refrigeration systems, each of which uses R407C refrigerant, and each of which is equipped with a high-pressure sensor for detecting compressor discharge pressure and a low-pressure sensor for detecting compressor suction pressure, characterized in that... The R407C refrigerant leakage detection method includes the following steps: S1, after the two refrigeration systems are running stably at the same time, obtain the low pressure value LP1 of the first refrigeration system, the low pressure value LP2 of the second refrigeration system, the high pressure value HP1 of the first refrigeration system, and the high pressure value HP2 of the second refrigeration system. S2, calculate the absolute value of the low-pressure difference ΔLP = |LP1 - LP2|, and the absolute value of the high-pressure difference ΔHP = |HP1 - HP2|; S3, compare the ΔLP with the preset low pressure differential threshold, and compare the ΔHP with the high pressure differential threshold obtained by looking up the table based on the outdoor ambient temperature; S4, when ΔLP is greater than the preset low pressure differential threshold, ΔHP is greater than the high pressure differential threshold, and the above state continues for a preset delay time, it is determined that the refrigeration system corresponding to the lower pressure value of LP1 and LP2 has a refrigerant leak, and a leak alarm is recorded. S5, repeat steps S1 to S4 to accumulate the number of leak alarms. When the accumulated number of alarms reaches the preset number of alarms, output a refrigerant leak fault signal.

2. The method for detecting R407C refrigerant leakage in a vehicle air conditioning unit according to claim 1, characterized in that, The low-pressure differential threshold includes a first threshold of 1.2 Bar and a second threshold of 1.5 Bar; the preset delay time includes a first delay of 30 seconds corresponding to the first threshold of 1.2 Bar and a second delay of 8 seconds corresponding to the second threshold of 1.5 Bar.

3. The method for detecting R407C refrigerant leakage in a vehicle air conditioning unit according to claim 2, characterized in that, When ΔLP > 1.2 Bar and lasts for 30 seconds, it is determined to be a Class I leakage alarm; When ΔLP > 1.5 Bar and lasts for 8 seconds, it is determined to be a Class II leakage alarm; The first type of leakage alarm and the second type of leakage alarm share the same counter. Within the same detection cycle, after the first type of leakage alarm is triggered, the second type of leakage alarm will not repeatedly increment the counter count, and vice versa.

4. The method for detecting R407C refrigerant leakage in a vehicle air conditioning unit according to claim 1, characterized in that, The term "stable operation" includes at least the following conditions: The compressors of both refrigeration systems have a continuous operating time of more than 120 seconds. If the refrigeration system is equipped with a hot gas bypass valve, the closing time of the hot gas bypass valve is greater than 30 seconds; The refrigeration system has no compressor fault alarms and no air valve fault alarms.

5. The method for detecting R407C refrigerant leakage in a vehicle air conditioning unit according to claim 1, characterized in that, After a single leak alarm is recorded, the alarm status can only be reset and the next leak detection can only begin if any of the following conditions are met: 20 minutes have passed since this alarm was triggered; The corresponding refrigeration system compressor stops running.

6. The method for detecting R407C refrigerant leakage in a vehicle air conditioning unit according to claim 1, characterized in that, It also includes a single-system critical leak detection mode: A leak alarm is recorded when only one refrigeration system is operating stably, the outdoor ambient temperature is above 20°C, and all of the following conditions are met for 10 seconds: the low-pressure value of the operating refrigeration system is ≤ 2.1 Bar; Furthermore, the high-pressure value of the operating refrigeration system is less than the high-pressure threshold obtained by looking up the table based on the outdoor ambient temperature. Once the low-pressure value of the operating refrigeration system rises to ≥ 2.7 Bar, the leakage alarm will automatically reset and the next detection will begin. When the cumulative number of alarms reaches the preset number, a refrigerant leakage fault signal will be output.

7. A method for detecting R407C refrigerant leakage in a vehicle air conditioning unit according to claim 1 or 6, characterized in that, The high-pressure differential threshold or high-pressure threshold is obtained by looking up the following table: Table 1. Relationship between outdoor ambient temperature and high pressure differential threshold, as well as high pressure threshold:

8. A method for detecting R407C refrigerant leakage in a vehicle air conditioning unit according to claim 1 or 5, characterized in that, The preset alarm count is 3 times; when the controller of the air conditioning unit accumulates 3 consecutive leak alarms, the refrigerant leak fault signal is sent to the vehicle control system terminal, and the "refrigerant leak fault" information is displayed on the display screen of the vehicle control system terminal.

9. A passenger compartment air conditioning unit for a rail vehicle, characterized in that, include: Two independent refrigeration systems using R407C refrigerant; each refrigeration system includes a compressor, condenser, evaporator and expansion device, a high-pressure sensor and a low-pressure sensor; and an air conditioning unit central controller configured to perform the R407C refrigerant leak detection method as described in any one of claims 1 to 8 and send the final alarm information to the vehicle control system terminal.

Images