Automobile environment wind tunnel low temperature and humidity control method

Abstract

This invention relates to the field of automotive environmental wind tunnel system control technology, and discloses a low-temperature humidity control method for automotive environmental wind tunnels. This method is applied to an automotive environmental wind tunnel control system, which includes a wind tunnel and a low-temperature humidity control section. The low-temperature humidity control section is equipped with a cryogenic coil. The low-temperature humidity control method includes feedforward control and closed-loop control. By obtaining the final humidity value of the wind tunnel and the final humidity value of the low-temperature humidity control section, the opening degree of the steam regulating valve is determined to control the humidity of the wind tunnel. Simultaneously, the cryogenic coil is used to control the temperature of the fresh air to match the wind tunnel test set temperature. The fresh air, cooled and humidified by the cryogenic coil, is then sent into the wind tunnel. This solves the problem in the prior art of accurately controlling the humidity of the wind tunnel in low-temperature environments.

Description

Technical Field

[0001] This invention relates to the field of automotive environmental wind tunnel system control technology, specifically to a method for low-temperature humidity control in an automotive environmental wind tunnel. Background Technology

[0002] Automotive environmental wind tunnels are crucial testing laboratories in automotive R&D, simulating real-world climate conditions to test vehicle performance. Humidity simulation is a core system within these wind tunnels, designed to mimic actual ambient air humidity. Most current automotive environmental wind tunnels can simulate humidity at both ambient and high temperatures, achieving relative humidity ranges from 5% to 95% with a control accuracy of ±3%. However, in cryogenic environments (-40°C to 0°C), automotive environmental wind tunnels cannot precisely control humidity; they can only dehumidify at low temperatures. This means that under low-temperature conditions, the humidity inside the wind tunnel will decrease progressively, making it difficult to maintain a fixed value.

[0003] Patent application number 201711480498.6 discloses a low-temperature air-cooled heat exchanger performance monitoring test bench. This bench controls humidity in a low-temperature environment, with a wind speed of 0.3–10 m / s. Humidity is adjusted by directly spraying steam into the wind tunnel. However, due to the high wind speeds in automotive environmental wind tunnels (reaching 200–250 km / h), such high wind speeds blowing through the steam nozzles cause severe stratification of the steam and wind tunnel air, resulting in extremely poor humidity uniformity. Furthermore, the steam nozzles increase wind resistance within the wind tunnel, significantly increasing the power of the main fan, which is extremely detrimental to the safety and wind speed simulation of the entire automotive environmental wind tunnel. Additionally, the temperature of the refrigerant oil in the main heat exchanger is lower than the temperature inside the wind tunnel. If low-temperature humidity control is performed, such as at -20°C and 90% humidity, the surface temperature of the main heat exchanger will be around -25°C. This can cause the main heat exchanger to freeze and become blocked, requiring the test to be stopped and defrosted after a short period, ultimately leading to test failure. For example, in the patent with application number 201810132378.5, humidity can only be controlled above 0°C. If this patent is directly used for humidity control in cryogenic low temperature conditions, there are shortcomings: the air temperature in the high flow range is at least 10°C. If steam is injected to adjust the humidity, the air temperature will be even higher. A large amount of high-temperature air entering the cryogenic low temperature wind tunnel will cause great temperature field disturbance, resulting in a decrease in temperature simulation performance.

[0004] In recent years, with the booming development of new energy vehicles, comprehensive technological advancements have been achieved. In winter, the heat pump air conditioning system of pure electric vehicles uses an external heat exchanger as an evaporator to absorb heat from the outside environment, while the internal condenser releases heat to the interior environment for winter heating. However, due to the low outside temperature in winter, if the surface temperature of the external heat exchanger is lower than the air dew point, moisture in the air will condense and frost on its surface. This frost layer hinders heat exchange between the external heat exchanger and the external environment, negatively impacting the system's normal operation and potentially preventing proper heating. Therefore, defrosting in winter has become a crucial issue for pure electric vehicle heat pump air conditioning systems. Testing and verifying heat pump anti-frost control strategies has become a mandatory test for automakers, necessitating that automotive environmental wind tunnels possess excellent low-temperature humidity control capabilities to provide superior environmental simulation for similar tests. Summary of the Invention

[0005] The present invention aims to provide a method for low-temperature humidity control in automotive environmental wind tunnels, in order to solve the problem in the prior art that it is difficult to accurately control the humidity of wind tunnels in low-temperature environments.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a low-temperature humidity control method for an automotive environmental wind tunnel, applied to an automotive environmental wind tunnel control system. The automotive environmental wind tunnel control system includes a wind tunnel and a low-temperature humidity control section, wherein a cryogenic coil is provided in the low-temperature humidity control section. The low-temperature humidity control method includes feedforward control and closed-loop control. By obtaining the final humidity value of the wind tunnel and the final humidity value of the low-temperature humidity control section, the opening degree of the steam regulating valve is determined to achieve humidity control of the wind tunnel. At the same time, the temperature of the fresh air is controlled to be consistent with the set temperature of the wind tunnel test using the cryogenic coil, and then the fresh air cooled and humidified by the cryogenic coil is sent into the wind tunnel.

[0007] The beneficial effects of this solution are: precise control of humidity in the ultra-low temperature (-40~0℃) and extremely high wind speed automotive wind tunnel environment; and prevention of icing in cooling devices such as the main heat exchanger and ultra-low temperature coils through feedforward control and closed-loop control, which would affect the precise control of humidity.

[0008] 1. By using feedforward control, the preset value of the valve opening of the steam regulating valve is obtained through theoretical calculation, thereby timely compensating for interference in the humidity control process, stabilizing the controlled variable, eliminating errors, and achieving the goal of precise humidity control in the automotive environment wind tunnel; This solves the problem that in the low-temperature humidity control process, due to the long length of the air duct in the entire low-temperature humidity control section and the long distance from the fresh air inlet of the system to the humidity sensor installation position inside the wind tunnel, the control has a large delay and inertia, resulting in a long time from the action of the steam regulating valve to the humidity response in the wind tunnel, making the control difficult, difficult to achieve fast response, and prone to oscillation in the humidity control inside the wind tunnel;

[0009] 2. Closed-loop control introduces a main loop and a secondary loop. During the low-temperature humidity control process, the secondary loop can be used for rapid coarse adjustment, which speeds up the response speed of the entire control system. At the same time, the main loop is used for fine adjustment, which makes minor corrections to the humidity control after the coarse adjustment of the secondary loop, thereby achieving precise control of wind tunnel humidity in low-temperature environments.

[0010] 3. The newly added low-temperature humidity control section cools and humidifies the fresh air before sending it into the wind tunnel, avoiding the situation where steam above 100°C enters the low-temperature wind tunnel directly, causing fluctuations in the wind tunnel environment temperature and stratification of steam and air, which makes it impossible to accurately control the humidity inside the wind tunnel.

[0011] Preferably, when determining the opening degree of the steam regulating valve, if the differential pressure of the cryogenic coil is higher than the first differential pressure threshold, the steam regulating valve is closed and the heating and de-icing program is started.

[0012] The beneficial effects of this solution are as follows: when the differential pressure of the cryogenic coil in the low-temperature humidity control section is higher than the first differential pressure threshold, it indicates that the cryogenic coil has become blocked by ice. At this time, the steam regulating valve is closed and the electric heating device is started to heat and defrost the cryogenic coil, so as to correct the low-temperature humidity control environment in a timely manner.

[0013] Preferably, if the differential pressure of the cryogenic coil is higher than the second differential pressure threshold, the steam regulating valve is closed, the heating and de-icing program is started, and the first differential pressure threshold is greater than the second differential pressure threshold.

[0014] The beneficial effects of this solution are as follows: by setting the first differential pressure threshold to be greater than the second differential pressure threshold, the system can be guaranteed to return to low-temperature humidity control as soon as possible after the ice in the cryogenic coil is removed, while ensuring safe operation of the system. This reduces the situation where the air temperature in the low-temperature humidity control section rises too much due to the electric heating device working for too long in the low-temperature test environment, which would require too much energy to lower the fresh air temperature to the test set temperature later.

[0015] Preferably, if the differential pressure of the cryogenic coil falls below the second differential pressure threshold, the heating and de-icing process is stopped, the steam regulating valve is opened, and the system returns to the low-temperature humidity control mode.

[0016] The beneficial effect of this solution is: timely return to a low-temperature and humidity-controlled environment.

[0017] Preferably, if the differential pressure of the main heat exchanger exceeds the third differential pressure threshold, the main fan is turned off, the main heat exchanger is adjusted to heating mode, and the steam regulating valve is closed to dehumidify the wind tunnel at low temperature.

[0018] The beneficial effects of this solution are as follows: If the differential pressure of the main heat exchanger is higher than the third threshold, it indicates that the main heat exchanger has iced up. At this time, the main fan is immediately shut down, and the cooling mode of the main heat exchanger is adjusted to the heating mode, so that the main heat exchanger can heat up and defrost on its own. At the same time, the steam regulating valve is closed, while the fresh air of the low-temperature humidity control section continues to be blown into the wind tunnel to perform low-temperature dehumidification operation on the wind tunnel, so as to blow away the moisture that appears on the surface of the main heat exchanger after the ice melts, avoid the situation of excessive local humidity in the wind tunnel, and further ensure the accurate control of the wind tunnel humidity when returning to the low-temperature humidity control program.

[0019] Preferably, if the differential pressure of the main heat exchanger is higher than the fourth differential pressure threshold, the main fan is turned off, the main heat exchanger is adjusted to the heating mode, the steam regulating valve is closed, and the wind tunnel is dehumidified at low temperature, and the third differential pressure threshold is greater than the fourth differential pressure threshold.

[0020] The beneficial effects of this scheme are: the third differential pressure threshold is greater than the fourth differential pressure threshold, which is also to enable the system to return to the low temperature humidity control program as soon as possible after the main heat exchanger is de-iced, thereby reducing energy consumption during the experiment.

[0021] Preferably, if the differential pressure of the main heat exchanger is lower than the fourth differential pressure threshold, the main heat exchanger is adjusted to cooling mode until the wind tunnel temperature returns to the test set temperature. Then, the main fan is started, the steam regulating valve is opened, and the system returns to low temperature humidity control mode.

[0022] The beneficial effect of this solution is: timely return to a low-temperature and humidity-controlled environment.

[0023] Preferably, determining the opening degree of the steam regulating valve includes the following steps:

[0024] S1, obtain the actual humidity value of the wind tunnel, determine the humidity setpoint of the low temperature humidity control section from the actual humidity value of the wind tunnel, and then determine the final humidity value of the low temperature humidity control section from the humidity setpoint of the low temperature humidity control section.

[0025] S2, obtain the actual humidity value of the low temperature humidity control section, and obtain the opening setting correction value of the steam regulating valve from the final humidity value of the low temperature humidity control section and the actual humidity value of the low temperature humidity control section;

[0026] S3, determine the opening feedforward value of the steam regulating valve;

[0027] S4. Determine the final opening setting value of the steam regulating valve based on the opening feedforward value and the opening setting correction value of the steam regulating valve.

[0028] S5 automatically controls the opening degree of the steam regulating valve based on the final opening degree setting value of the steam regulating valve.

[0029] The beneficial effects of this scheme are as follows: First, the opening setting correction value of the steam regulating valve is obtained through closed-loop control. The correction value is obtained by combining PID calculation based on parameters such as humidity and temperature inside the wind tunnel.

[0030] Then, parameters such as the absolute temperature of the incoming air, the saturated steam pressure of the incoming air, the air pressure, the relative humidity of the incoming air, and the absolute humidity of the incoming air are obtained. The opening feedforward value of the steam regulating valve is determined by calculation. The opening feedforward value of the steam regulating valve is added to the opening setting correction value of the steam regulating valve to obtain the final opening setting value of the steam regulating valve, so as to achieve precise control of air humidity in low temperature environment.

[0031] Preferably, in S1, the wind tunnel humidity required for the test is the wind tunnel humidity setpoint; then, by obtaining the wind tunnel dew point temperature, the wind tunnel humidity setpoint limit is determined, and the final wind tunnel humidity value is obtained by taking the smaller value between the wind tunnel humidity setpoint and the wind tunnel humidity setpoint limit, and the humidity setpoint of the low temperature humidity control section is determined by the final wind tunnel humidity value.

[0032] The beneficial effects of this scheme are as follows: During the main loop control process, the humidity setpoint for the wind tunnel test is limited. The final humidity value of the wind tunnel is obtained by taking the smaller value between the wind tunnel humidity setpoint and the wind tunnel humidity limit value. Limiting the humidity setpoint prevents icing of the main heat exchanger in the wind tunnel. The principle for preventing icing is that the dew point temperature of the air inside the wind tunnel can be calculated from the wind tunnel temperature and relative humidity under that condition. By controlling the surface temperature of the main heat exchanger to not be lower than this dew point temperature, icing of the main heat exchanger can be prevented.

[0033] Preferably, in S1, the humidity setting limit value of the low-temperature humidity control section is determined by obtaining the dew point temperature of the low-temperature humidity control section, and the final humidity value of the low-temperature humidity control section is determined by taking the smaller value between the humidity setting limit value of the low-temperature humidity control section and the actual humidity value of the low-temperature humidity control section.

[0034] The beneficial effects of this scheme are as follows: In the secondary loop control, the humidity setpoint in the low-temperature humidity control section is limited. The final humidity value of the low-temperature humidity control section is obtained by taking the smaller value between the humidity setpoint and the humidity limit value. The purpose of limiting the humidity setpoint in the low-temperature humidity control section is to prevent the cryogenic coil from freezing. The principle of preventing freezing is as follows: Based on the surface temperature of the cryogenic coil, the outlet air temperature of the low-temperature humidity control section, and the relative humidity of the outlet air in the low-temperature humidity control section, the dew point temperature of the air in the low-temperature humidity control section under this condition can be calculated. The surface temperature of the cryogenic coil cannot be lower than this dew point temperature, thus preventing the cryogenic coil from freezing. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the low-temperature humidity control process in an embodiment of the present invention;

[0036] Figure 2This is a schematic diagram of the low-temperature humidity control strategy in an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the structure of the automotive environmental wind tunnel in an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of the low-temperature humidity control section in an embodiment of the present invention. Detailed Implementation

[0039] The following detailed description illustrates the specific implementation method:

[0040] The reference numerals in the accompanying drawings include: wind tunnel 1, dehumidification section 2, low flow rate section 3, low temperature humidity control section 4, first corner 101, second corner 102, third corner 103, fourth corner 104, nozzle 105, sump chamber 106, insulation plate 107, collection port 108, tracked drum pit cover 109, drum 110, drum pit 111, main fan 112, main heat exchanger 113, sunlight simulation system 114, main heat exchanger temperature sensor 115, wind tunnel humidity sensor 116. 119. Outlet valve; 121. Main heat exchanger differential pressure sensor; 401. Inlet air temperature sensor; 402. Inlet air volume sensor; 403. Drainage and antifreeze structure; 404. Steam nozzle; 405. Compensating fan; 406. Electric heating device; 407. Cryogenic coil differential pressure sensor; 408. Outlet air temperature sensor; 409. Outlet air humidity sensor; 410. Cryogenic coil; 411. Cryogenic coil temperature sensor; 412. Drain pipe; 413. Steam regulating valve; 414. Air pressure sensor; 415. Inlet air humidity sensor.

[0041] Example

[0042] The basic implementation examples are as follows: Figure 1-4 As shown, Figure 1 This invention discloses a low-temperature humidity control method for automotive environmental wind tunnels, applied to the wind tunnel control system. By combining feedforward control and closed-loop control, the final humidity values ​​of the wind tunnel and the low-temperature humidity control section are obtained to determine the opening of the steam regulating valve. Based on the obtained valve opening, the control system adjusts the steam addition amount in real time to achieve precise humidity control within the wind tunnel under low-temperature conditions. The steam regulating valve is located within the low-temperature humidity control section, which maintains the temperature of the fresh air consistent with the wind tunnel test setpoint. The cooled and humidified fresh air enters the wind tunnel after passing through the low-temperature humidity control section. This ensures precise humidity control while preventing temperature fluctuations within the wind tunnel, thus achieving low-temperature humidity control in the automotive environmental wind tunnel.

[0043] like Figure 1As shown, during the low-temperature humidity control process, when the differential pressure of the cryogenic coil in the low-temperature humidity control section is higher than the first differential pressure threshold ΔP1 (ΔP1 needs to be adjusted and confirmed according to the specific conditions of the low-temperature humidity control section), it indicates that the cryogenic coil has become blocked by ice. At this time, the steam regulating valve should be closed immediately, the steam input should be stopped, and the electric heating device should be started to heat and defrost the cryogenic coil. After heating and defrosting for a period of time, if the differential pressure of the cryogenic coil is lower than the second differential pressure threshold ΔP2 (ΔP2 also needs to be adjusted and confirmed), it indicates that the ice in the cryogenic coil has been removed. Heating and defrosting should be stopped immediately, the steam regulating valve should be opened, and the system should return to low-temperature control. Furthermore, ΔP2 < ΔP1. This ensures that the system can return to low-temperature humidity control as soon as possible after the ice in the cryogenic coil is removed, while ensuring safe operation of the system. This reduces the possibility that the air temperature in the low-temperature humidity control section will rise too much due to the electric heating device working for too long in the low-temperature test environment, resulting in excessive energy consumption when lowering the fresh air temperature to the test set temperature. Meanwhile, if the differential pressure of the cryogenic coil is higher than the second differential pressure threshold ΔP2, the steam regulating valve needs to be closed and the heating and de-icing program needs to be started to further ensure the safe operation of the wind tunnel's low-temperature humidity control.

[0044] The temperature inside the wind tunnel is controlled by the main heat exchanger, and the wind speed is controlled by the main fan. If the differential pressure of the main heat exchanger is higher than the third threshold ΔP3 (ΔP3 needs to be adjusted and confirmed according to the specific conditions of the wind tunnel), it indicates that the main heat exchanger has iced. At this time, the main fan should be turned off immediately, and the cooling mode of the main heat exchanger should be adjusted to the heating mode to allow the main heat exchanger to heat up and defrost itself. At the same time, the steam regulating valve should be closed and the steam input should be stopped. Fresh air should continue to be blown into the wind tunnel from the low-temperature humidity control section to perform low-temperature dehumidification operation on the wind tunnel, so as to blow away the moisture that appears on the surface of the main heat exchanger after the ice melts, avoid the situation of excessively high local humidity in the wind tunnel, and further ensure accurate control of the wind tunnel humidity when returning to the low-temperature humidity control program.

[0045] After a period of low-temperature dehumidification, if the differential pressure of the main heat exchanger falls below the fourth differential pressure threshold ΔP4 (ΔP4 also needs to be confirmed through debugging), the heating mode of the main heat exchanger is switched back to cooling mode to bring the temperature inside the wind tunnel back to the set temperature required for the experiment. Simultaneously, the main fan is started and the steam regulating valve is opened to humidify the fresh air, thus returning the wind tunnel to its original low-temperature humidity, with ΔP4 < ΔP3. This is also to ensure a rapid return to the low-temperature humidity control program after the main heat exchanger defrosts, reducing energy consumption during the experiment. Meanwhile, if... Figure 1As shown, if the differential pressure of the main heat exchanger is higher than the fourth differential pressure threshold ΔP4, the main fan will be shut down, the cooling mode of the main heat exchanger will be adjusted to the heating mode, the steam regulating valve will be closed, and the steam input will be stopped to perform low-temperature dehumidification operation on the wind tunnel. In addition, before returning to low-temperature humidity control in the wind tunnel, it is necessary to ensure that the internal temperature of the wind tunnel has been reduced to the set temperature required for the test, and simultaneously check that the differential pressure of the cryogenic coil is lower than the second differential pressure threshold ΔP2 to ensure the safe operation of the automotive environment wind tunnel system.

[0046] like Figure 2 The low-temperature humidity control strategy shown includes feedforward control and closed-loop control. The closed-loop control further includes a main loop and a secondary loop, wherein: φ set The wind tunnel humidity setpoint (directly input into the control system according to automotive environmental wind tunnel testing requirements), φ set (limit) sets the limit value for wind tunnel humidity, with min being φ. set With φ set (limit) Takes the smaller value between the two, Φ Set final The final humidity value in the wind tunnel (i.e., φ) set With φ set (limit) The value obtained by taking the smaller value between the two); φ act The actual humidity value in the wind tunnel is E1(s), which is Φ. Set final With φ act The difference (i.e., the deviation value) is used by PID1 for the PID calculation of the main loop, φ 2set The humidity setpoint for the low-temperature humidity control section is obtained from the PID calculation of the main loop;

[0047] φ 2set (limit) sets the humidity limit for the low-temperature humidity control section, Φ 2Set final φ represents the final humidity value of the low-temperature humidity control section. 2act This represents the actual humidity value in the low-temperature humidity control section, where E2(s) is Φ. 2Set final With φ 2act The difference (also the deviation value) is used for PID2, which is the PID operation of the secondary loop.

[0048] u(s) is the setting correction value for the steam regulating valve opening obtained from the PID calculation of the secondary loop. feedford (s) represents the steam regulating valve opening feedforward value, Add represents the summation operation, and u final (s) represents the final opening value of the steam regulating valve;

[0049] G1(s) represents the actual opening degree of the steam regulating valve to the actual humidity value φ in the low-temperature humidity control section. 2act The transfer function; G2(s) is the actual humidity value φ in the low-temperature humidity control section.2act Actual humidity value φ in the environmental wind tunnel act The transfer function.

[0050] The main loop starts from the final humidity value Φ in the wind tunnel. Set final The final humidity value Φ in the low-temperature humidity control section 2Set final The control loop between the two circuits, and the secondary loop from the final humidity value Φ of the low-temperature humidity control section. 2Set final Actual humidity value φ at the low temperature humidity control section 2act Control loop between them.

[0051] During low-temperature humidity control, the long duct length of the entire low-temperature humidity control section and the long distance from the system's air inlet to the humidity sensor installation location inside the wind tunnel result in significant control delays and inertia. This leads to a long time required for the humidity response from the steam regulating valve's action to the wind tunnel's humidity response. In other words, the control process between the steam regulating valve and the wind tunnel humidity is a highly inertial, high-delay, and nonlinear control system, making it extremely difficult to control. Simply using PID control directly is insufficient for rapid response, resulting in large overshoot and potential oscillations in the humidity control within the wind tunnel. Therefore, feedforward control is added to the closed-loop control to theoretically calculate the preset value of the steam regulating valve opening. This allows for timely compensation for disturbances during the humidity control process, stabilizing the controlled variable, eliminating errors, and achieving precise humidity control in the automotive environment wind tunnel. Simultaneously, by introducing a main loop and a secondary loop for closed-loop control, the secondary loop performs rapid coarse adjustments to accelerate the overall control system's response speed, while the main loop performs fine adjustments, making minor corrections to the humidity control after the secondary loop's coarse adjustments. This further ensures precise humidity control in the wind tunnel under low-temperature conditions.

[0052] Next, using a specific automotive environmental wind tunnel system as an example, we will explain the low-temperature humidity control method in detail:

[0053] The automotive environmental wind tunnel control system in this embodiment is as follows: Figure 3As shown, the system includes a wind tunnel 1, a dehumidification section 2, a low-flow section 3, and a low-temperature humidity control section 4. The wind tunnel 1 has a first bend 101, a second bend 102, a third bend 103, and a fourth bend 104. A main fan 112 is located between the second bend 102 and the third bend 103. When the main fan 112 is turned on, the air inside the wind tunnel 1 flows counterclockwise, providing the wind speed required for automotive testing. The system also includes a sump chamber 106, which is the test section of the automotive environmental wind tunnel 1. The sump chamber 106 contains an insulated panel 107, a tracked drum pit cover 109, a drum 110, a drum pit 111, and a sunlight simulation system 114. A nozzle 105 is located at one end of the fourth bend 104 extending into the sump chamber 106, and a collection port is located at one end of the first bend 101 extending into the sump chamber 106. At the third corner 103, a main heat exchanger 113 is installed. The main heat exchanger 113 can selectively circulate hot oil or cooling oil, meaning it includes both heating and cooling modes. A wind tunnel humidity sensor 116 is also installed at the third corner 103 to detect the humidity inside the wind tunnel 1. A main heat exchanger temperature sensor 115 and a main heat exchanger differential pressure sensor 121 are connected to the main heat exchanger 113. The temperature sensor 115 monitors the surface temperature of the main heat exchanger 113, and the differential pressure sensor 121 monitors the differential pressure across the main heat exchanger 113. When the value monitored by the differential pressure sensor 121 is greater than ΔP3, it indicates that the main heat exchanger 113 has experienced icing. Simultaneously, the system also includes a temperature sensor to monitor the temperature inside the wind tunnel 1 in real time.

[0054] Dehumidification section 2, low-flow section 3, and low-temperature humidity control section 4 are connected in series. Low-temperature humidity control section 4 is connected to wind tunnel 1 through a pipeline with an outlet valve 119. When the low-temperature humidity control is started, the outlet valve 119 is opened, and the outside air first enters dehumidification section 2 for dehumidification and drying. The dried air after dehumidification enters low-flow section 3 from dehumidification section 2. Low-flow section 3 cools and slows down the dried air before sending it into low-temperature humidity control section 4. Pre-cooling the air in low-flow section 3 reduces the cooling load in low-temperature humidity control section 4, ensuring that low-temperature humidity control section 4 can accurately control the fresh air temperature to be consistent with the test set value of wind tunnel 1, avoiding high-temperature fresh air entering wind tunnel 1 and causing temperature field fluctuations in wind tunnel 1, which would affect the test.

[0055] The interior of the low-temperature humidity control section 4 is as follows Figure 4As shown, the duct of the low-temperature humidity control section 4 is equipped with, from front to back, an inlet air temperature sensor 401, an inlet air volume sensor 402, an air pressure sensor 414, an inlet air humidity sensor 415, several steam nozzles 404, a steam regulating valve 413, a hydrophobic antifreeze structure 403, a compensating fan 405, an electric heating device 406, a cryogenic coil 410, an outlet air temperature sensor 408, and an outlet air humidity sensor 409. A cryogenic coil temperature sensor 411 is connected to the cryogenic coil 410, and a cryogenic coil differential pressure sensor 407 is connected to both ends of the cryogenic coil 410. When the cryogenic coil differential pressure sensor 407 detects that the differential pressure across the cryogenic coil 410 is greater than ΔP1, it indicates that the cryogenic coil 410 has become blocked by ice. The steam nozzles 404 all spray in the direction of the incoming airflow, so that the steam sprayed out in a mist form from the steam nozzles 404 can be fully and evenly mixed with the air entering the duct. Figure 4 The image below shows a left view of the steam nozzles 404 in the low-temperature humidity control section 4. All steam nozzles 404 are evenly distributed. The steam regulating valve 413 is connected to the steam generator and simultaneously connects to all steam nozzles 404. A small-flow steam regulating valve 413 is used because the amount of steam required for low-temperature humidity control is relatively small. This small-flow steam regulating valve ensures precise control of the steam addition, thereby further ensuring precise control of the humidity in the wind tunnel 1 under low-temperature conditions. Simultaneously, the automotive environmental wind tunnel control system also includes a controller. Sensors such as the main heat exchanger temperature sensor 115 and the duct humidity sensor 116 transmit the collected data to the controller. After analysis and judgment, the controller controls the steam regulating valve 413, the electric heating device 406, etc., to take action, achieving automatic control.

[0056] The hydrophobic antifreeze structure 403 is connected to a condensate drain pipe 412. Since a small amount of steam from the steam nozzle 404 reaches the inner wall of the duct and condenses, the hydrophobic antifreeze structure 403 collects this condensate and discharges it through the drain pipe 412. This prevents the condensate from flowing down the duct towards the cryogenic coil 410, causing ice formation on the surface of the cooling coil, affecting cooling performance, and accelerating icing of the cryogenic coil 410. A compensating fan 405 is located at the rear end of the hydrophobic antifreeze structure 403. The use of the steam nozzle 404 and the hydrophobic antifreeze structure 403 increases air resistance within the duct. The compensating fan 405 compensates for this pressure drop, achieving precise control of the air pressure within the low-temperature humidity control section 4. Furthermore, during rotation, the compensating fan 405 thoroughly mixes the steam and air, further improving the uniformity of air humidity and preventing excessively high humidity in certain areas, which could lead to icing of the cooling coil.

[0057] The intake air volume sensor 402 monitors the intake air volume, measured in cubic meters per second (m³). 3 / h; Wind pressure sensor 414 monitors the pressure of the incoming air, in Pa; Intake air humidity sensor 415 monitors the air humidity in the intake section, and this humidity is relative humidity; Cryogenic coil temperature sensor 411 monitors the surface temperature of the cryogenic coil 410; Outlet air temperature sensor 408 monitors the outlet air temperature; Outlet air humidity sensor 409 monitors the outlet air relative humidity.

[0058] like Figure 2 The low-temperature humidity control strategy shown:

[0059] S1, during the main loop control process, limits were imposed on the humidity setpoint for wind tunnel 1. The humidity setpoint φ in the wind tunnel... set The final wind tunnel humidity value Φ is obtained by taking the smaller value between the wind tunnel humidity setting limit φset(limit) and the limit value φset(limit). Set final The humidity setpoint is limited to prevent the main heat exchanger 113 in wind tunnel 1 from freezing. The principle of preventing freezing is as follows: the temperature inside wind tunnel 1 and the relative humidity inside wind tunnel 1 (monitored by wind tunnel humidity sensor 116) can be used to calculate the dew point temperature of the air inside wind tunnel 1 under this condition. By controlling the surface temperature of the main heat exchanger 113 (monitored by main heat exchanger temperature sensor 115) to be no lower than the dew point temperature, freezing of the main heat exchanger 113 can be prevented.

[0060] Wind tunnel humidity setting limit φ set The formula for calculating (limit) is derived from the formula for calculating dew point temperature, as follows:

[0061]

[0062] tHXC Main heat exchanger surface temperature, in °C; tmain The wind tunnel temperature is obtained by monitoring the wind tunnel control system, and the unit is °C; in formula (1), (t) HXC -1) is to make φ set (limit) humidity and tmain The dew point temperature calculated from the temperature is higher than the temperature calculated from ... tHXC The temperature is reduced by 1°C, thus further ensuring that the main heat exchanger does not freeze.

[0063] Wind tunnel humidity final value Φ Set final Actual humidity value φ in the environmental wind tunnel act The difference is used to obtain the deviation value E1(s). The deviation value E1(s) is then processed by a PID controller (the parameters inside the PID controller need to be adjusted and confirmed according to the actual situation in the wind tunnel) to obtain the humidity setpoint φ for the low-temperature humidity control section. 2set ;

[0064] In the secondary loop control, the humidity setpoint in the low-temperature humidity control section is limited. The humidity setpoint φ in the low-temperature humidity control section... 2setHumidity setting limit φ for low temperature humidity control section 2set (limit) The smaller of the two values ​​is used to obtain the final humidity value Φ for the low-temperature humidity control section. 2Set final The purpose of limiting the humidity setting value of the low-temperature humidity control section is to prevent the cryogenic coil 410 from freezing. The principle of preventing freezing is as follows: based on the surface temperature of the cryogenic coil 410 (monitored by the cryogenic coil temperature sensor 411), the outlet air temperature of the low-temperature humidity control section 4 (monitored by the outlet air temperature sensor 408), and the outlet air relative humidity of the low-temperature humidity control section 4 (monitored by the outlet air humidity sensor 409), the dew point temperature of the air in the low-temperature humidity control section 4 under this condition can be calculated. The surface temperature of the cryogenic coil 410 cannot be lower than the dew point temperature, thus preventing the cryogenic coil 410 from freezing.

[0065] Low temperature humidity control section humidity setting limit φ 2set The formula for calculating (limit) is also derived from the formula for calculating dew point temperature, as follows:

[0066]

[0067] t deep cooling t represents the surface temperature of the cryogenic coil, in °C. exit The outlet air temperature of the low-temperature humidity control section is expressed in °C; in formula (2), (t) deep cooling -1) is to make φ 2set (limit) humidity and t exit The dew point temperature calculated from the temperature is equal to t. deep cooling Lowering the temperature by 1°C further ensures that the cryogenic coils do not freeze.

[0068] S2, Φ 2Set final The actual humidity value φ of the low-temperature humidity control section 2act Subtracting the values ​​yields E2(s), and the deviation value E2(s) is used for PID calculation (the internal parameters of PID2 also need to be adjusted and confirmed) to obtain the steam regulating valve opening setting correction value u(s).

[0069] S3, obtain relevant parameters and determine the opening feedforward value of the steam regulating valve;

[0070] Steam regulating valve opening feedforward value u feedford (s) The specific calculation process is as follows:

[0071] T1=t1+273 (3)

[0072]

[0073]

[0074]

[0075] m1=ρ1×V1 (7)

[0076]

[0077] Where: t1 is the temperature value monitored by the inlet air temperature sensor 401, in °C; T1 is the absolute temperature of the inlet air, in K; p sac,1 φ1 is the inlet saturated steam pressure, in Pa; p1 is the pressure value monitored by the wind pressure sensor 414, in Pa; φ1 is the relative humidity monitored by the inlet humidity sensor 415, in %; χ1 is the absolute humidity of the inlet air, in kg / kg; R air R is the gas constant for air, which is 287.06, with units of J / (kg kJ); V ρ1 is the gas constant for water vapor, 461.04, in J / (kg·K); ρ1 is the inlet air density, in kg / m³; V1 is the inlet air volumetric flow rate, obtained by the inlet air volume sensor 402, in m³ / h; m1 is the inlet air mass flow rate, in kg / h; m max The steam mass flow rate at the maximum opening of steam regulating valve 413 is expressed in kg / h; feedford (s) is the feedforward value of the steam regulating valve opening, and 0≤u feedford (s)≤100.

[0078] S4, u(s) and the feedforward value of the steam regulating valve opening u feedford Adding (s) together yields the final value u of the steam regulating valve opening. final (s).

[0079] S5 automatically controls the opening degree of the steam regulating valve based on its final opening value. The steam regulating valve opening is adjusted to the actual humidity value φ in the low-temperature humidity control section. 2act The transfer function is G1(s), and the actual humidity value φ in the low-temperature humidity control section is... 2act Actual humidity value φ in the environmental wind tunnel act The transfer function is G2(s), and both G1(s) and G2(s) can be obtained by performing step response tests during debugging.

[0080] The specific implementation process is as follows: First, according to the specific automotive environment wind tunnel 1 test requirements, the temperature inside the wind tunnel 1 is controlled by the main heat exchanger 113 to be consistent with the wind tunnel 1 test set temperature, and the required wind tunnel 1 humidity set value is input into the automotive environment wind tunnel system to start the low temperature humidity control of the wind tunnel 1.

[0081] The system determines the final opening setting value of the steam regulating valve 413 according to the program in the closed-loop control, and adjusts the opening of the steam regulating valve 413 in real time according to this value to control the amount of steam injected into the low temperature humidity control section 4. Since the low temperature humidity control section 4 has reduced the fresh air temperature to be consistent with the test setting temperature of wind tunnel 1, the fresh air after low temperature humidification entering wind tunnel 1 will not cause fluctuations in the internal temperature of wind tunnel 1, thus ensuring that the test can be carried out smoothly.

[0082] During the low-temperature humidity control process, feedforward control and closed-loop control are used to prevent icing of the cryogenic coil 410 and the main heat exchanger 113, thus ensuring accurate humidity control in a low-temperature environment. If icing occurs in the cryogenic coil 410 and the main heat exchanger 113, the differential pressure sensor 121 of the main heat exchanger and the differential pressure sensor 407 of the cryogenic coil will detect and provide feedback, allowing the test to be paused in time to deal with the icing and avoid safety issues.

[0083] This low-temperature humidity control method combines feedforward control and closed-loop control. During the low-temperature humidity control process, feedforward control uses theoretical calculations to obtain the preset value of the valve opening of the steam regulating valve 413, compensating for interference affecting the humidity stability of wind tunnel 1, stabilizing the controlled variable, eliminating errors, and solving the problem that the control process between the steam regulating valve 413 and the humidity in wind tunnel 1 takes a long time to respond, resulting in large overshoot and oscillations. Closed-loop control introduces a main loop and a secondary loop. During the low-temperature humidity control process, the secondary loop allows for rapid coarse adjustment, accelerating the response speed of the entire control system. Simultaneously, the main loop performs fine adjustment, providing minor corrections to the humidity control after the coarse adjustment in the secondary loop, thereby achieving precise humidity control of wind tunnel 1 under low-temperature conditions.

[0084] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for low-temperature humidity control in an automotive environmental wind tunnel, characterized in that: This technology is applied to automotive environmental wind tunnel control systems, which include a wind tunnel and a low-temperature humidity control section. The low-temperature humidity control section is equipped with cryogenic coils and steam regulating valves. The low-temperature humidity control method includes feedforward control and closed-loop control. By obtaining the final humidity value of the wind tunnel and the final humidity value of the low-temperature humidity control section, the opening degree of the steam regulating valve is determined to control the humidity of the wind tunnel. At the same time, the temperature of the fresh air is controlled to be consistent with the set temperature of the wind tunnel test using cryogenic coils, and then the fresh air, which has been cooled by cryogenic coils and humidified by steam, is sent into the wind tunnel. Determining the opening degree of a steam regulating valve includes the following steps: S1, obtain the actual humidity value of the wind tunnel, determine the humidity setpoint of the low temperature humidity control section from the actual humidity value of the wind tunnel, and then determine the final humidity value of the low temperature humidity control section from the humidity setpoint of the low temperature humidity control section. S2, obtain the actual humidity value of the low temperature humidity control section, and obtain the opening setting correction value of the steam regulating valve from the final humidity value of the low temperature humidity control section and the actual humidity value of the low temperature humidity control section; S3, determine the opening feedforward value of the steam regulating valve; S4. Determine the final opening setting value of the steam regulating valve based on the opening feedforward value and the opening setting correction value of the steam regulating valve. S5 automatically controls the opening degree of the steam regulating valve based on the final opening degree setting value of the steam regulating valve.

2. The method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 1, characterized in that: When determining the opening degree of the steam regulating valve, if the differential pressure across the cryogenic coil exceeds the first differential pressure threshold, close the steam regulating valve and start the heating and de-icing program.

3. The method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 2, characterized in that: If the differential pressure across the cryogenic coil exceeds the second differential pressure threshold, close the steam regulating valve, start the heating and de-icing program, and ensure that the first differential pressure threshold is greater than the second differential pressure threshold.

4. The method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 3, characterized in that: If the differential pressure across the cryogenic coil falls below the second differential pressure threshold, stop the heating and de-icing process, open the steam regulating valve, and return to the low-temperature humidity control mode.

5. The method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 4, characterized in that: The wind tunnel has a first corner, a second corner, a third corner, and a fourth corner. A main fan is located between the second and third corners. It also includes a sump chamber, which is the test section of the automotive environmental wind tunnel. A nozzle is installed at the end of the fourth corner that extends into the sump chamber, and a collection port is installed at the end of the first corner that extends into the sump chamber. A main heat exchanger is located at the third corner. If the differential pressure across the main heat exchanger exceeds the third differential pressure threshold, the main fan is turned off, the main heat exchanger is adjusted to heating mode, and the steam regulating valve is closed to dehumidify the wind tunnel at low temperature.

6. The method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 5, characterized in that: If the differential pressure across the main heat exchanger exceeds the fourth differential pressure threshold, shut down the main fan, adjust the main heat exchanger to heating mode, close the steam regulating valve, and perform low-temperature dehumidification on the wind tunnel, while ensuring that the third differential pressure threshold is greater than the fourth differential pressure threshold.

7. The method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 6, characterized in that: If the differential pressure across the main heat exchanger falls below the fourth differential pressure threshold, the main heat exchanger will be switched to cooling mode until the wind tunnel temperature returns to the test set temperature. Then, the main fan will be started, the steam regulating valve will be opened, and the system will return to low-temperature humidity control mode.

8. The method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 1, characterized in that: In S1, the wind tunnel humidity required for the test is the wind tunnel humidity setpoint; then, by obtaining the wind tunnel dew point temperature, the wind tunnel humidity setpoint limit is determined. The final wind tunnel humidity value is obtained by taking the smaller value between the wind tunnel humidity setpoint and the wind tunnel humidity setpoint limit. The humidity setpoint of the low temperature humidity control section is determined by the final wind tunnel humidity value and the actual wind tunnel humidity value.

9. A method for low-temperature humidity control in an automotive environmental wind tunnel according to claim 8, characterized in that: In S1, the humidity setting limit value of the low-temperature humidity control section is determined by obtaining the dew point temperature of the low-temperature humidity control section, and the final humidity value of the low-temperature humidity control section is determined by taking the smaller value between the humidity setting limit value and the humidity setting value of the low-temperature humidity control section.

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