A method and device for controlling exhaust pressure of a vehicle CO2 heat pump air conditioning system

Abstract

The present invention proposes a method and device for controlling the exhaust pressure of a vehicle CO2 heat pump air conditioning system based on correction of heat exchanger performance degradation. T in , supply air temperature T out , ambient temperature T amb and the current compressor discharge pressure P ;according to T in , T out and T amb Calculate the theoretical optimal exhaust pressure P opt1 ;According to the service life of the system, the performance degradation correction coefficient is obtained to calculate the corrected optimal exhaust pressure P opt2 ; Determine the current compressor exhaust pressure P and P opt2 Is the deviation between them within the allowable range? If so, ensure that the original electronic expansion valve opening remains unchanged; otherwise, adjust the electronic expansion valve opening to make the current compressor exhaust pressure P With optimal exhaust pressure P opt2 The deviation is within the allowable range. Even after the performance of the heat exchanger degrades, the optimal exhaust pressure prediction accuracy can still be guaranteed to be high, so that the heating coefficient of the system can be maintained at a high level.

Description

Technical Field

[0001] The present invention relates to the field of controllers for electric vehicle air source CO2 heat pump air conditioners, and in particular to a method and device for controlling exhaust pressure of a vehicle CO2 heat pump air conditioner system based on correction of heat exchanger performance degradation. Background Art

[0002] Electric vehicle CO2 heat pump air conditioners have the advantages of both environmental protection and energy saving, and have excellent heating capacity in cold conditions. They actively respond to my country's long-term goal of "carbon neutrality and carbon peak", and are expected to become the ultimate solution in my country's automotive air-conditioning field. How to control the exhaust pressure has always been an important issue for transcritical CO2 heat pump systems. The exhaust pressure is a key indicator that determines the performance of transcritical CO2 heat pump systems. Studies have confirmed that due to the unique thermodynamic properties of CO2 working fluid, there is an optimal exhaust pressure in the system, and the heating coefficient (COP) at this pressure is the highest. A slight deviation from the optimal exhaust pressure may cause the system's heating coefficient (COP) to be significantly reduced. Therefore, controlling the performance of the CO2 heat pump system through the optimal exhaust pressure is the current mainstream method.

[0003] Unlike commercial CO2 heat pump water heater systems, the limitations of the gas cooler's heat exchange area due to the interior space of the vehicle, as well as changes in operating mode and cooling medium, lead to significant temperature slip at the gas cooler outlet. The coefficient of operation (COP) varies significantly with the system's operating parameters. The exhaust pressure correlation equation previously established for CO2 heat pump water heaters is no longer applicable to air-source vehicle CO2 heat pump air conditioners, resulting in excessive deviations. In addition, due to the long-term and complex use of vehicle CO2 heat pump systems, the heat exchanger will experience severe performance degradation due to practical reasons such as fouling, refrigerant corrosion, and carbonization of the lubricating oil. Specifically, the heat exchange efficiency of the heat exchanger continues to decrease with operating time. However, the degradation of component performance is difficult to measure experimentally in practice. This will cause the prediction results of the optimal exhaust pressure correlation equation designed for the initial state to gradually deviate from the actual value during long-term operation, making it difficult to maintain a high coefficient of operation (COP) throughout the entire life cycle. Although the use of intelligent algorithms can obtain the optimal exhaust pressure after the performance degradation of the heat exchanger, during the adjustment process, it is necessary to repeatedly adjust the opening of the electronic expansion valve at high frequency to achieve a gradient search of the exhaust pressure, which causes rapid fluctuations in the flow rate within the system and periodic oscillations in the exhaust pressure in the compressor, which will destroy the stability of the system and the service life of key components.

[0004] In summary, existing technologies are unable to directly obtain the real-time and accurate optimal exhaust pressure for automotive CO2 heat pump air conditioning systems with different degrees of heat exchanger degradation based on the current system operating parameters while ensuring system stability, so that the system can maintain a high heating coefficient (COP) during long-term operation. Summary of the Invention

[0005] In view of this, it is necessary to provide an exhaust pressure control method and device for a vehicle CO2 heat pump air-conditioning system based on heat exchanger performance degradation correction, so as to solve the technical problems that the existing technology has poor adaptability in automotive application scenarios and it is difficult to ensure a high optimal exhaust pressure prediction accuracy throughout the entire life cycle.

[0006] The technical solution provided by the present invention is:

[0007] A method for controlling exhaust pressure of a vehicle CO2 heat pump air conditioning system based on heat exchanger performance degradation correction is described. The method is applied to passenger vehicles and operates under a heating cycle. The specific steps of the method are as follows:

[0008] S1: In the operation of the vehicle CO2 heat pump air conditioning system, the temperature sensor is used to obtain the inlet air temperature T of the heat exchanger under the current working conditions. in , supply air temperature T out， Ambient temperature T amb and the current compressor exhaust pressure P;

[0009] S2: Set the inlet air temperature of the heat exchanger to T in , air supply temperature T out and ambient temperature T amb Substitute the correlation formula to calculate the theoretical optimal exhaust pressure P opt1 ;

[0010] S3: Calculate the heat exchanger performance degradation compensation coefficient U opt , calculate the corrected optimal exhaust pressure P opt2 ;

[0011] S4: Determine the current compressor exhaust pressure P and the optimal exhaust pressure P opt2 Is the relative error between them within the allowable range? If so, maintain the current opening of the electronic expansion valve; otherwise, execute step S5;

[0012] S5: By adjusting the opening of the electronic valve, the current compressor exhaust pressure P and the optimal exhaust pressure P are achieved. opt2 The relative error between them is within the allowable range;

[0013] S6: Monitor the temperature sensor for the inlet air temperature of the heat exchanger in the vehicle ΔT in , supply air temperature variable ΔT out and ambient temperature variable ΔT amb If the change amplitude of any variable exceeds a certain amplitude, return to step S1; otherwise, continue to maintain the current electronic expansion valve opening.

[0014] In step S1, the vehicle CO2 heat pump system is a basic CO2 heat pump air conditioning system consisting of an in-vehicle heat exchanger, an out-vehicle heat exchanger, a gas-liquid separator, an electronic expansion valve, and a compressor.

[0015] In the above-mentioned step S2, the theoretical optimal exhaust pressure calculation formula of the vehicle CO2 heat pump air conditioner is:

[0016]

[0017] Among them, T amb is the ambient temperature; T in and T out are the inlet and supply air temperatures of the heat exchanger in the vehicle, respectively.

[0018] In the step S3, the compensation coefficient U opt There are two calculation methods: if the degradation factor DF of the current heat exchanger is known HE , can be calculated as follows:

[0019]

[0020]

[0021] Where U is the total heat transfer coefficient; A is the heat exchange area; ΔT m is the temperature difference of the working fluid at the inlet and outlet of the heat exchanger; Q is the heating capacity.

[0022] If the operating life of the current vehicle CO2 heat pump air conditioning unit is known, it can be estimated using the following method:

[0023] Service life ≤ 4 years, U opt =100%; service life = 5 years, U opt =102.5%; service life = 6 years, U opt =103.8%; service life = 7 years, U opt =105.8%; service life = 8 years, U opt =108.4%; service life = 9 years, U opt =113.5%; service life = 10 years, U opt =118.2%.

[0024] Corrected optimal exhaust pressure P opt2 The calculation method is as follows:

[0025]

[0026] Among them, U opt is the compensation coefficient; P opt1 is the theoretical optimal exhaust pressure.

[0027] In the step S4, the current compressor exhaust pressure P is compared with the corrected optimal exhaust pressure P opt2 The permissible range of deviations between them satisfies the following relationship:

[0028]

[0029] In the step S5, the PID controller automatically increases the opening of the electronic expansion valve to reduce the exhaust pressure P; or automatically decreases the opening of the electronic expansion valve to increase the exhaust pressure P, so that the exhaust pressure P is equal to the corrected optimal exhaust pressure P. opt2 The deviation between them reaches the permissible range.

[0030] In the step S6, the monitored temperature sensor information includes the ambient temperature variable ΔT amb , In-vehicle heat exchanger inlet air temperature variable ΔT in and supply air temperature variable ΔT out , the permissible variation range should satisfy the following relationship:

[0031]

[0032] The exhaust pressure control device of a vehicle CO2 heat pump air conditioning system based on heat exchanger performance degradation correction is composed of a vehicle CO2 heat pump air conditioning information acquisition module, a theoretical optimal exhaust pressure calculation module, a heat exchanger degradation correction module, a pre-adjustment judgment module, an electronic expansion valve opening adjustment module, and a vehicle CO2 heat pump air conditioning operation monitoring module.

[0033] The vehicle CO2 heat pump air conditioning information acquisition module is used to record the ambient temperature T collected by the vehicle CO2 heat pump air conditioning system temperature sensor. amb 、In-vehicle heat exchanger air intake module T in , In-vehicle heat exchanger air supply temperature T out and the current compressor discharge pressure P;

[0034] The theoretical optimal exhaust pressure calculation module is used to calculate the theoretical optimal exhaust pressure P under the current working conditions. opt1 ;

[0035] The heat exchanger degradation correction module: Considering the long-term performance degradation of the heat exchanger, calculates the compensation coefficient under the current operating conditions, and calculates the corrected optimal exhaust pressure P opt2 ;

[0036] The judgment module before adjustment: judges the current compressor exhaust pressure P and the corrected optimal exhaust pressure P opt2 Is it satisfied The mathematical relationship between

[0037] The electronic expansion valve opening adjustment module adopts a PID controller to adjust the electronic expansion valve opening so that the real-time compressor exhaust pressure P is consistent with the corrected optimal exhaust pressure P. opt2 Ultimate Satisfaction The mathematical relationship between

[0038] The vehicle CO2 heat pump air conditioning operation monitoring module is used to monitor the ambient temperature variable ΔT collected by the temperature sensor of the vehicle CO2 heat pump air conditioning system. amb , In-vehicle heat exchanger inlet air temperature variable ΔT in , supply air temperature variable T out Does the following mathematical relationship satisfy?

[0039]

[0040] The beneficial effects of the present invention are:

[0041] 1. The present invention utilizes a new empirical correlation formula for theoretical optimal exhaust pressure fitted from a large amount of low-temperature operating test data of automotive CO2 heat pump air conditioners. Based on only three operating parameters of the automotive CO2 heat pump air conditioner, the theoretical optimal exhaust pressure can be directly calculated with high accuracy, and the system can be rapidly stabilized. This effectively addresses the problems of existing empirical correlation formulas not matching automotive application scenarios, as well as the shortcomings of complex calculations in intelligent algorithms, high-frequency adjustment of the expansion valve opening caused by gradient search, periodic system oscillations, and long stabilization time.

[0042] 2. Based on the mechanism of heat exchanger performance degradation, this invention proposes a correction method to perform real-time correction on the theoretical optimal exhaust pressure. This effectively solves the problem of the current optimal exhaust pressure control method's gradually decreasing prediction accuracy over the entire life cycle, enabling the automotive CO2 heat pump system to maintain a high heating coefficient (COP) for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The following is a flow chart of the control method of the present invention.

[0044] Figure 2 Schematic diagram of the structure of a CO2 heat pump air-conditioning system for a vehicle in an embodiment of the present invention.

[0045] Figure 3 It is the composition structure of the control device.

[0046] Figure 4 This is a structural block diagram of the control method of the present invention.

[0047] Figure 5 This is a corresponding diagram of the estimation method of the correction coefficient of the present invention based on the service life of the system. DETAILED DESCRIPTION

[0048] The present invention will be further described below with reference to specific implementation examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0049] Figure 1 is a flow chart of the control method of the present invention, which illustrates the implementation process of the control method of the present invention; Figure 2 It is a structural diagram of a vehicle CO2 heat pump air-conditioning system in an embodiment of the present invention. Figure 3 It is the composition structure of the control device.

[0050] The vehicle CO2 heat pump air conditioning system is composed of an external heat exchanger, namely an evaporator, an internal heat exchanger, namely a gas cooler, an electronic expansion valve, a CO2 dedicated compressor and a gas-liquid separator.

[0051] The operating principle of the vehicle CO2 heat pump air conditioning system is as follows: saturated CO2 vapor flowing out of the vehicle's external heat exchanger enters the compressor and is compressed to a high-temperature, high-pressure state. Due to CO2's relatively low critical pressure of 7.2 MPa and critical temperature of 31.1°C, the CO2 is typically in a supercritical state at the compressor outlet. Supercritical CO2 is a single-phase state, distinct from that between gas and liquid, with a density close to that of a liquid and a viscosity close to that of a gas, resulting in excellent thermal conductivity and low flow resistance. The high-temperature, high-pressure supercritical CO2 then enters the vehicle's internal heat exchanger for cooling. Throughout the isobaric heat release process, the CO2 remains in a supercritical state, and no condensation phase transition occurs in the internal heat exchanger, acting as a gas cooler. The low-temperature, supercritical CO2 flowing out of the internal heat exchanger enters an electronic expansion valve for pressure reduction, transforming it into wet vapor. It then enters the external heat exchanger for isobaric evaporation and heat absorption, returning to saturated CO2 vapor to complete the heating cycle. During the entire cycle, it absorbs ambient heat from the external heat exchanger and releases heat in the internal heat exchanger to heat the passenger compartment.

[0052] The speed of the compressor of the vehicle CO2 heat pump air conditioning system is controlled by the constant air supply temperature system. The air supply temperature T out The higher the value, the faster the compressor speed, and vice versa. The CO2 working medium flow rate involved in the system circulation is controlled by the electronic expansion valve. out Under these conditions, the larger the opening of the electronic expansion valve, the greater the CO2 flow rate in the system, and the lower the corresponding compressor exhaust pressure. Conversely, the greater the exhaust pressure. In any working condition, there is a specific optimal exhaust pressure P opt Maximize the system's heating coefficient COP. Optimal exhaust pressure P opt and ambient temperature T amb , air supply temperature T out and inlet air temperature T in There is a linear coupling relationship between them.

[0053] The optimal exhaust pressure P of the vehicle CO2 heat pump air conditioning system opt and ambient temperature T amb , air supply temperature T out , Inlet air temperature T in The linear coupling relationship between the four is not static. As the heat exchanger ages, problems such as fin aging and fouling will cause the heat exchange efficiency of the heat exchanger to decrease, which will cause the physical state of the CO2 working fluid inside the system to change under the same working conditions, that is, the optimal exhaust pressure P opt and ambient temperature T amb , air supply temperature T out , Inlet air temperature T in The linear coupling relationship between them will change.

[0054] If the current control strategy is used, it is difficult to adjust the heat exchanger performance according to the ambient temperature T in the vehicle CO2 heat pump air conditioner after the heat exchanger performance deteriorates. amb , Inlet air temperature T in , air supply temperature T out Directly calculate the current accurate optimal exhaust pressure P opt This may require rapid and high-frequency adjustment of the electronic expansion valve opening to find the optimal exhaust pressure P opt , the compressor exhaust pressure oscillates greatly, which prolongs the system stabilization time, reduces the service life of system components, and there is also the risk of falling into a local optimal solution.

[0055] To quickly and accurately predict the optimal exhaust pressure of a vehicle CO2 heat pump air conditioning system, maintaining high accuracy even after heat exchanger performance degradation, avoid the loss of system components associated with current methods, improve system stability, and maintain a high heating coefficient (COP) throughout its lifecycle, this paper proposes a method for controlling the exhaust pressure of a vehicle CO2 heat pump air conditioning system based on heat exchanger performance degradation correction, comprising the following steps. Figure 4 This is a structural block diagram of the control method of the present invention.

[0056] S1: During the operation of the vehicle CO2 heat pump air conditioning system, the temperature sensor is used to obtain the inlet air temperature T of the heat exchanger under the current working conditions. in , supply air temperature T out， Ambient temperature T amb and the current compressor exhaust pressure P;

[0057] S2: Set the inlet air temperature of the heat exchanger to T in , air supply temperature T out and ambient temperature T amb Substitute the correlation formula to calculate the theoretical optimal exhaust pressure P opt1 ;

[0058] S3: Calculate the heat exchanger performance degradation compensation coefficient U opt , calculate the corrected optimal exhaust pressure P opt2 ;

[0059] S4: Determine the current compressor exhaust pressure P and the optimal exhaust pressure P opt2 Is the relative error between them within the allowable range? If so, maintain the current opening of the electronic expansion valve; otherwise, execute step S5;

[0060] S5: By adjusting the opening of the electronic expansion valve, the current compressor exhaust pressure P and the optimal exhaust pressure P are achieved. opt2 The relative error between them is within the allowable range;

[0061] S6: Monitor the temperature sensor for the inlet air temperature of the heat exchanger in the vehicle ΔT in , supply air temperature variable ΔT out and ambient temperature variable ΔT amb If the change amplitude of any variable exceeds a certain amplitude, return to step S1; otherwise, continue to maintain the current electronic expansion valve opening.

[0062] In step S1, the vehicle CO2 heat pump air conditioning system is a basic CO2 heat pump air conditioning system consisting of an in-vehicle heat exchanger, an out-vehicle heat exchanger, a gas-liquid separator, an electronic expansion valve, and a compressor.

[0063] In the above-mentioned step S2, the theoretical optimal exhaust pressure calculation formula of the vehicle CO2 heat pump air conditioner is:

[0064]

[0065] Among them, T amb is the ambient temperature; T in and T out are the inlet and supply air temperatures of the heat exchanger in the vehicle, respectively.

[0066] In the step S3, the compensation coefficient U opt There are two calculation methods: if the degradation factor DF of the current heat exchanger is known HE ,

[0067] It can be calculated as follows:

[0068]

[0069]

[0070] Where U is the total heat transfer coefficient; A is the heat exchange area; ΔT m is the temperature difference of the working fluid at the inlet and outlet of the heat exchanger; Q is the heating capacity.

[0071] If the operating life of the current vehicle CO2 heat pump air conditioning system is known, it can be estimated using the following method:

[0072] Service life ≤ 4 years, U opt =100%; service life = 5 years, U opt =102.5%; service life = 6 years, U opt =103.8%; service life = 7 years, U opt =105.8%; service life = 8 years, U opt =108.4%; service life = 9 years, U opt =113.5%; service life = 10 years, U opt =118.2%.

[0073] Corrected optimal exhaust pressure P opt2 The calculation method is as follows:

[0074]

[0075] Among them, U opt is the compensation coefficient; P opt1 is the theoretical optimal exhaust pressure.

[0076] In the step S4, the current compressor exhaust pressure P is compared with the corrected optimal exhaust pressure P opt2 The permissible range of deviations between them satisfies the following relationship:

[0077] .

[0078] In the step S5, the PID controller automatically increases the opening of the electronic expansion valve to reduce the current compressor exhaust pressure P; or automatically decreases the opening of the electronic expansion valve to increase the current compressor exhaust pressure P, so that the current compressor exhaust pressure P is consistent with the corrected optimal exhaust pressure P. opt2 The deviation between them reaches the permissible range.

[0079] In the step S6, the monitored temperature sensor information includes the ambient temperature variable ΔT amb , In-vehicle heat exchanger inlet air temperature variable ΔT in and supply air temperature variable ΔT out , the permissible variation range should satisfy the following relationship:

[0080] .

[0081] The present invention also provides an exhaust pressure control device for a vehicle CO2 heat pump air conditioning system based on heat exchanger performance degradation correction. This control device comprises a vehicle CO2 heat pump air conditioning system information acquisition module, a theoretically optimal exhaust pressure calculation module, a heat exchanger degradation correction module, a pre-adjustment judgment module, an electronic expansion valve opening adjustment module, and a vehicle CO2 heat pump air conditioning system operation monitoring module.

[0082] The vehicle CO2 heat pump air conditioning system information acquisition module is used to record the ambient temperature T collected by the vehicle CO2 heat pump air conditioning system temperature sensor. amb 、In-vehicle heat exchanger air intake module T in , In-vehicle heat exchanger air supply temperature T out and the current compressor discharge pressure P;

[0083] The theoretical optimal exhaust pressure calculation module is used to calculate the theoretical optimal exhaust pressure P under the current working conditions. opt1 ;

[0084] The heat exchanger degradation correction module: Considering the long-term performance degradation of the heat exchanger, calculates the compensation coefficient under the current operating conditions, and calculates the corrected optimal exhaust pressure P opt2 ;

[0085] The judgment module before adjustment: judges the current compressor exhaust pressure P and the corrected optimal exhaust pressure P opt2 Is it satisfied The mathematical relationship between

[0086] The electronic expansion valve opening adjustment module adopts a PID controller or a remote controller to adjust the opening of the electronic expansion valve so that the real-time exhaust pressure P of the compressor is consistent with the corrected optimal exhaust pressure P. opt2 Ultimate Satisfaction The mathematical relationship between

[0087] The vehicle CO2 heat pump air conditioning system operation monitoring module:

[0088] Used to monitor the ambient temperature variable ΔT collected by the temperature sensor of the vehicle CO2 heat pump air conditioning system amb , In-vehicle heat exchanger inlet air temperature variable ΔT in , supply air temperature variable ΔT out Does the following mathematical relationship satisfy?

[0089] .

[0090] In a specific embodiment of the present invention, the system monitors the ambient temperature T amb =-10℃, the inlet air temperature of the heat exchanger in the vehicle is T in =0℃, the air supply temperature of the heat exchanger in the vehicle is Tout =42℃, current exhaust pressure P=70bar.

[0091] According to the formula , the theoretical optimal exhaust pressure is calculated to be 36.1211+0.2819×(-10)+0.3048×0+1.0376×42=76.88bar. HE =0.8, formula The current correction factor U can be calculated opt =250×0.8^2-417×0.8+276=102.4%. Then according to the formula , calculate the corrected optimal exhaust pressure P opt2 =102.4%×76.88=78.73bar.

[0092] According to the formula It can be seen that P=70bar<0.98P opt2 =77.16bar. At this time, the difference is not within the allowable range, and the opening of the electronic expansion valve needs to be reduced. After the adjustment, the compressor exhaust pressure = 79.0bar. According to the formula It can be seen that 0.98P opt2 =77.16bar <P=79.0bar<1.02P opt2 =80.3bar. At this time, the difference is within the allowable range, and the opening of the electronic expansion valve remains unchanged. At this time, the sensor signal ΔT in =0.20℃, ΔT out =0.15℃, ΔT amb =0.40℃, formula It is determined that the current system operating conditions are stable, the system adjustment is completed, and the system heating coefficient (COP) can reach 3.15.

[0093] In another specific embodiment of the present invention, the system monitors the ambient temperature T amb =0℃, the inlet air temperature of the heat exchanger in the vehicle is T in =5℃, the air supply temperature of the heat exchanger in the vehicle is T out =44℃, current exhaust pressure P=100bar.

[0094] According to the formula , the theoretical optimal exhaust pressure is calculated to be 36.1211+0.2819×0+0.3048×5+1.0376×44=83.30bar. It is known that the current service life of the heat exchanger in this system is 7 years. Figure 5 The current correction factor U can be estimated opt =105.8%. Then according to the formula , calculate the corrected optimal exhaust pressure P opt2 =105.8% ×83.30=88.13bar. According to the formula It can be seen that P=100bar>1.02P opt2 = 89.89bar. At this time, the difference is not within the allowable range, and the opening of the electronic expansion valve needs to be increased. The compressor exhaust pressure after the adjustment is reduced = 90.0bar. According to the formula It can be seen that 0.98P opt2 =88.10bar< P=90.0bar<1.02P opt2 =91.69bar. At this time, the difference is within the allowable range, and the opening of the electronic expansion valve remains unchanged. At this time, the sensor signal ΔT in =0.10℃, ΔT out =0.30℃, ΔT amb =0.40℃, according to the formula It can be determined that the current system operating conditions are stable, the system adjustment is completed, and the system heating coefficient (COP) can reach 3.40.

[0095] The above describes in detail the exhaust pressure control method and apparatus for a vehicle CO2 heat pump air conditioning system based on heat exchanger performance degradation correction. This article describes its specific application in applicable practical scenarios. While the above implementation examples are intended to facilitate understanding of the principles and application of the present invention, it should be noted that practitioners in related fields may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are considered to be within the scope of protection of the present invention.

Claims

1. A method for controlling exhaust pressure of a vehicle CO2 heat pump air conditioning system based on heat exchanger performance degradation correction, characterized in that: The specific steps of this method are as follows: S1: During the operation of the vehicle CO2 heat pump air conditioning system, the temperature sensor is used to obtain the inlet air temperature T of the heat exchanger under the current working conditions. in , the air supply temperature of the heat exchanger in the vehicle is T out， Ambient temperature T amb and the current compressor exhaust pressure P; S2: Set the inlet air temperature of the heat exchanger to T in , In-vehicle heat exchanger air supply temperature T out and ambient temperature T amb Substitute the correlation formula to calculate the theoretical optimal exhaust pressure P opt1 ; S3: Calculate the heat exchanger performance degradation compensation coefficient U opt , calculate the corrected optimal exhaust pressure P opt2 ; S4: Determine the current compressor exhaust pressure P and the optimal exhaust pressure P opt2 Is the relative error between them within the allowable range? If so, keep the current opening of the electronic expansion valve; otherwise, execute step S5; S5: By adjusting the opening of the electronic expansion valve, the current compressor exhaust pressure P and the optimal exhaust pressure P are achieved. opt2 The relative error between them is within the allowable range; S6: Monitor the inlet air temperature variable ΔT of the heat exchanger in the vehicle in , the air supply temperature variable of the heat exchanger in the vehicle ΔT out and ambient temperature variable ΔT amb If the change amplitude of any variable exceeds a certain amplitude, return to step S1; otherwise, continue to maintain the current electronic expansion valve opening.

2. The control method according to claim 1, characterized in that: In the step S1, the vehicle CO2 heat pump air conditioning system is a CO2 heat pump air conditioning system composed of an in-vehicle heat exchanger, an out-vehicle heat exchanger, a gas-liquid separator, an electronic expansion valve, and a compressor.

3. The control method according to claim 1, wherein: In the above-mentioned step S2, the theoretical optimal exhaust pressure calculation formula of the vehicle CO2 heat pump air conditioning system is: Among them, T amb is the ambient temperature; T in and T out are the inlet and supply air temperatures of the heat exchanger in the vehicle, respectively.

4. The control method according to claim 1, wherein: In the step S3, the compensation coefficient U opt There are two calculation methods: if the degradation factor DF of the current heat exchanger is known HE , calculated as follows: Where U is the total heat transfer coefficient; A is the heat exchange area; ΔT m is the temperature difference of the working fluid at the inlet and outlet of the heat exchanger; Q is the heating capacity; If the operating life of the current vehicle CO2 heat pump air conditioning system is known, estimate it using the following method: Service life ≤ 4 years, U opt =100%; service life = 5 years, U opt =102.5%; service life = 6 years, U opt =103.8%; service life = 7 years, U opt =105.8%; service life = 8 years, U opt =108.4%; service life = 9 years, U opt =113.5%; service life = 10 years, U opt =118.2%.

5. The control method according to claim 1, characterized in that: In the step S3, the corrected optimal exhaust pressure P opt2 The calculation method is as follows: Among them, U opt is the compensation coefficient; P opt1 is the theoretical optimal exhaust pressure.

6. The control method according to claim 1, characterized in that: In the step S4, the current compressor exhaust pressure P is compared with the corrected optimal exhaust pressure P opt2 The permissible range of relative error between them satisfies the following relationship: 。 7. The control method according to claim 1, characterized in that: In the step S5, the PID controller automatically increases the opening of the electronic expansion valve to reduce the current compressor exhaust pressure P; or automatically decreases the opening of the electronic expansion valve to increase the current compressor exhaust pressure P, so that the current compressor exhaust pressure P is consistent with the corrected optimal exhaust pressure P. opt2 The relative error between them reaches the allowable range.

8. The control method according to claim 1, characterized in that: In the step S6, the monitored temperature sensor information includes the ambient temperature variable ΔT amb , In-vehicle heat exchanger inlet air temperature variable ΔT in and the supply air temperature variable ΔT of the heat exchanger inside the vehicle out , the allowable variation amplitude should satisfy the following relationship: .

9. An exhaust pressure control device for a vehicle CO2 heat pump air conditioning system based on heat exchanger performance degradation correction, characterized in that: The control device consists of a vehicle CO2 heat pump air conditioning system information acquisition module, a theoretical optimal exhaust pressure calculation module, a heat exchanger degradation correction module, a pre-adjustment judgment module, an electronic expansion valve opening adjustment module, and a vehicle CO2 heat pump air conditioning system operation monitoring module. The vehicle CO2 heat pump air conditioning system information acquisition module is used to record the ambient temperature T collected by the vehicle CO2 heat pump air conditioning system temperature sensor. amb , In-vehicle heat exchanger inlet air temperature T in , In-vehicle heat exchanger air supply temperature T out and the current compressor discharge pressure P; The theoretical optimal exhaust pressure calculation module is used to calculate the theoretical optimal exhaust pressure P under the current working conditions. opt1 ; The heat exchanger degradation correction module: Considering the long-term performance degradation of the heat exchanger, calculates the compensation coefficient under the current operating conditions, and calculates the corrected optimal exhaust pressure P opt2 ; The judgment module before adjustment: judges the current compressor exhaust pressure P and the corrected optimal exhaust pressure P opt2 Is it satisfied The mathematical relationship between The electronic expansion valve opening adjustment module adopts a PID controller to adjust the electronic expansion valve opening so that the real-time compressor exhaust pressure P is consistent with the corrected optimal exhaust pressure P. opt2 Ultimate Satisfaction The mathematical relationship between The vehicle CO2 heat pump air conditioning system operation monitoring module is used to monitor the ambient temperature variable ΔT collected by the vehicle CO2 heat pump air conditioning system temperature sensor. amb , In-vehicle heat exchanger inlet air temperature variable ΔT in , In-vehicle heat exchanger air supply temperature variable ΔT out Does the following mathematical relationship satisfy? 。

Images