Low-temperature humidity control method for automobile environment test chamber

Abstract

The invention discloses a low-temperature humidity control method for an automobile environment test chamber, which relates to the technical field of automatic control of test chambers and comprises the following steps: acquiring dry-bulb temperature, relative humidity and atmospheric pressure in the chamber, front and back pressure difference of a coil pipe, air volume, surface temperature of the coil pipe and outlet temperature of the coil pipe, and calculating air mass flow and moisture content in the chamber; symmetrical temperature perturbation is applied with the current coil pipe surface temperature as the center, coil pipe air side channel impedance coefficients are calculated at different temperature points, and an impedance curvature index is calculated according to the coil pipe air side channel impedance coefficients; a continuous inhibition factor is generated based on the impedance curvature index, a basic dehumidification demand obtained by the moisture content deviation is continuously corrected, and a planned dehumidification mass flow rate is obtained; and the humidification mass flow rate, the coil pipe target temperature and the reheating power are further calculated and issued to a refrigerating loop, a humidifier and a reheater. The low-temperature humidity control stability of the test chamber can be improved.

Description

Technical Field

[0001] This invention relates to the field of automatic control technology for test chambers, and in particular to a method for low-temperature humidity control in an automotive environmental test chamber. Background Technology

[0002] Automotive environmental testing chambers are widely used for performance verification of vehicles and components in low-temperature environments, such as windshield defogging and defrosting, cold resistance testing of seals, risk assessment of volatile organic compounds and condensation in interior components, and low-temperature performance testing of battery packs. These tests typically require maintaining a specified humidity level at a low dry-bulb temperature and keeping the temperature and humidity stable throughout the test to ensure repeatable boundary conditions for condensation, frosting, and evaporation processes. Testing chambers often use cooling coils for both cooling and dehumidification, supplemented by humidifiers for replenishment and reheaters for temperature recovery. However, near freezing points in the low-temperature range, condensation and frost buildup on the coil surface can cause significant drift in the pressure difference between the windward and leeward sides of the coil, the airflow through the coil, and the coil outlet temperature. This can lead to changes in air mass flow rate and deviations in the humidity control within the chamber, resulting in overshooting, oscillation, or slowed convergence of temperature and humidity, thus affecting the stability and consistency of defogging tests.

[0003] Existing technologies typically employ multi-loop regulation strategies with cabin dry-bulb temperature and relative humidity as feedback parameters, or segmented control through preset dehumidification capacity, humidification output, and reheat power, triggering defrosting or limiting when there is a risk of coil frost formation. The main drawbacks of this approach are: firstly, relative humidity is significantly affected by temperature, and in the low-temperature range combined with reheat, the temperature may rise but the humidity criterion may change, leading to inconsistencies between the calculated humidity control and the actual humidity level; secondly, the air-side resistance of the coil exhibits a significant non-linearity with changes in coil temperature and frost condition. Simply relying on fixed settings or discrete thresholds for limiting makes it difficult to smoothly correct the dehumidification intensity during periods of rapid resistance change, easily causing amplified airflow fluctuations, abrupt changes in humidity control output, increased energy consumption, and decreased test repeatability, while also making it difficult to balance humidity control accuracy with operational stability in the low-temperature range. Summary of the Invention

[0004] The purpose of this invention is to solve the problems in the existing technology of low-temperature humidity control, such as nonlinear changes in the air pressure difference and air volume of the coil due to condensation and freezing on the surface of the coil and the growth of frost layer, which cause difficulty in smoothly adjusting the dehumidification intensity, easy overshoot and fluctuation of temperature and humidity in the chamber, and insufficient stability and repeatability of test conditions. Therefore, a low-temperature humidity control method for automotive environmental test chamber is proposed.

[0005] To address the problems existing in the prior art, the present invention adopts the following technical solution: A method for low-temperature humidity control in an automotive environmental testing chamber, comprising: S1. Collect environmental parameters, operating parameters of the air side of the coil, and temperature parameters of the coil in the test chamber, and calculate the current air mass flow rate and humidity in the chamber. S2. Apply temperature perturbation based on the current coil surface temperature, and collect the coil air-side operating parameters during the perturbation process. Calculate the coil air-side channel impedance coefficient at different temperature points. S3. Calculate the impedance curvature index based on the impedance coefficient of the air-side channel of the coil at different temperature points. S4. A continuous inhibition factor is generated based on the impedance curvature index. The deviation based on the moisture content in the chamber is corrected by the continuous inhibition factor to obtain the planned dehumidification mass flow rate. S5. Based on the planned dehumidification mass flow rate, air mass flow rate, and the set target moisture content and target temperature, calculate the humidification mass flow rate, coil target temperature, and reheat power, and send the calculation results to the corresponding actuators to adjust the temperature and humidity of the test chamber.

[0006] Preferably, environmental parameters within the test chamber, operating parameters on the air side of the coil, and temperature parameters of the coil are collected, and the current air mass flow rate and humidity content within the chamber are calculated, including: The environmental parameters inside the test chamber, the operating parameters of the air side of the coil, and the temperature parameters of the coil were collected. The environmental parameters included the dry bulb temperature, relative humidity, and atmospheric pressure inside the chamber; the operating parameters of the air side of the coil included the pressure difference before and after the coil and the air volume through the coil; and the temperature parameters included the surface temperature of the coil and the outlet temperature of the coil. The air density is determined based on the dry-bulb temperature and atmospheric pressure inside the cabin. The air mass flow rate is obtained by multiplying the air density by the air volume passing through the coil. The corresponding saturated vapor pressure is determined based on the dry-bulb temperature inside the cabin, and the partial pressure of water vapor is calculated based on the relative humidity and the saturated vapor pressure. Based on the conversion relationship of moisture content, the partial pressure of water vapor is converted to atmospheric pressure to obtain the moisture content inside the cabin.

[0007] Preferably, the formula for calculating the impedance coefficient of the air-side channel of the coil is: In the formula, The impedance coefficient of the air-side channel of the coil. The pressure difference across the coil. This refers to the airflow through the coil.

[0008] Preferably, the impedance curvature index is calculated based on the impedance coefficient of the air-side channel of the coil at different temperature points, including: Using the current coil surface temperature as the center, the preset temperature step value is increased and decreased respectively to form three sampling temperature points; The surface temperature of the coil is controlled to reach the three sampling temperature points in sequence, and the corresponding coil air-side channel impedance coefficient is calculated respectively. The impedance curvature index is calculated based on the coil air-side channel impedance coefficient at the three sampling temperature points. The formula for calculating the impedance curvature index is as follows: In the formula, The impedance curvature index. This is the temperature step value. The current coil surface temperature, The coil air-side channel impedance coefficient corresponding to the temperature point after adding a temperature step value to the current coil surface temperature. The air-side channel impedance coefficient of the coil corresponding to the temperature point after reducing the current coil surface temperature by a temperature step value.

[0009] Preferably, a continuous suppression factor is generated based on the impedance curvature index, and the deviation based on the moisture content inside the chamber is corrected by the continuous suppression factor to obtain the planned dehumidification mass flow rate, including: Calculate the difference between the moisture content inside the chamber and the set target moisture content, and take the positive part of the difference as the basic dehumidification requirement; Calculate the reciprocal of the sum of the numerical value 1 and the absolute value of the impedance curvature index, and use the reciprocal as the continuous suppression factor; The planned dehumidification mass flow rate is obtained by multiplying the air mass flow rate, the continuous inhibition factor, and the basic dehumidification requirement.

[0010] Preferably, calculating the humidification mass flow rate includes: Calculate the difference between the target moisture content and the moisture content inside the cabin, and take the positive part of the difference as the basic humidification requirement; Multiply the air mass flow rate by the basic humidification requirement to obtain the humidification mass flow rate.

[0011] Preferably, calculating the target temperature of the coil includes: Calculate the equivalent target supply air moisture content for this cycle based on the cabin moisture content, planned dehumidification mass flow rate, humidification mass flow rate, and air mass flow rate. Convert the equivalent target supply air moisture content into the corresponding supply air water vapor partial pressure target; Based on the relationship between saturated vapor pressure and temperature, the temperature value that makes the saturated vapor pressure equal to the partial pressure of the supply air vapor is calculated, and this temperature value is taken as the target temperature of the coil.

[0012] Preferably, calculating the reheat power includes: Calculate the difference between the target temperature and the coil outlet temperature, and multiply the air mass flow rate and the air constant pressure specific heat capacity by the difference to obtain the reheat power.

[0013] Preferably, the preset temperature step value is an integer multiple of the temperature control resolution of the test chamber's cooling circuit, and this integer multiple is greater than or equal to 1.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention calculates the air mass flow rate and cabin moisture content by collecting parameters such as dry-bulb temperature, relative humidity, atmospheric pressure, pressure difference before and after the coil, airflow through the coil, and coil temperature. A symmetrical temperature perturbation is applied centered on the coil surface temperature to calculate the coil air-side channel impedance coefficient at different temperature points and further obtain the impedance curvature index. This allows for the quantification of the nonlinear acceleration trend of the coil air-side flow resistance with temperature changes at low temperatures. Subsequently, a continuous suppression factor can be generated based on the impedance curvature index and directly applied to the basic dehumidification demand obtained from the moisture content deviation, forming a planned dehumidification mass flow rate. This ensures that the adjustment of dehumidification intensity during the rapid resistance change phase caused by frost growth is continuous rather than abrupt, reducing the risks of amplified airflow fluctuations, sudden changes in dehumidification output, and temperature and humidity overshoot oscillations. This improves the stability of low-temperature humidity control conditions and the repeatability of test results.

[0015] 2. After obtaining the planned dehumidification mass flow rate and air mass flow rate, this invention further calculates the humidification mass flow rate, coil target temperature, and reheat power by combining the target moisture content and target temperature. The calculation results are then sent to the refrigeration loop actuator, humidifier, and reheater to achieve closed-loop regulation of the temperature and humidity of the test chamber. This ensures that the three execution quantities of dehumidification, humidification, and reheat form consistent executable commands within the same cycle based on mass and heat conservation. This balances humidity control accuracy and temperature maintenance capability in low-temperature humidity control scenarios, reduces humidity control calculation deviations caused by changes in relative humidity criteria with temperature, and minimizes defects such as amplified airflow fluctuations, abrupt changes in humidity control output, and increased energy consumption. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 This is a schematic flowchart of a low-temperature humidity control method for an automotive environmental test chamber according to the present invention. Figure 2 This is a schematic diagram of the low-temperature humidity control system for the automotive environmental test chamber of the present invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0018] Example: This example provides a low-temperature humidity control method for an automotive environmental test chamber. See [link to example]. Figure 1 Specifically, including: S1. Collect environmental parameters, operating parameters of the air side of the coil, and temperature parameters of the coil in the test chamber, and calculate the current air mass flow rate and humidity in the chamber. In embodiments of the present invention, environmental parameters within the test chamber, operating parameters on the air side of the coil, and temperature parameters of the coil are collected, and the current air mass flow rate and humidity content within the chamber are calculated, including: The environmental parameters inside the test chamber, the operating parameters of the air side of the coil, and the temperature parameters of the coil were collected. The environmental parameters included the dry bulb temperature, relative humidity, and atmospheric pressure inside the chamber; the operating parameters of the air side of the coil included the pressure difference before and after the coil and the air volume through the coil; and the temperature parameters included the surface temperature of the coil and the outlet temperature of the coil. The air density is determined based on the dry-bulb temperature and atmospheric pressure inside the cabin. The air mass flow rate is obtained by multiplying the air density by the air volume passing through the coil. The corresponding saturated vapor pressure is determined based on the dry-bulb temperature inside the cabin, and the partial pressure of water vapor is calculated based on the relative humidity and the saturated vapor pressure. Based on the conversion relationship of moisture content, the partial pressure of water vapor is converted to atmospheric pressure to obtain the moisture content inside the cabin; Specifically, the test chamber controller synchronously collects environmental parameters, operating parameters on the air side of the coil, and temperature parameters of the coil within each control cycle. Environmental parameters include the dry-bulb temperature, relative humidity, and atmospheric pressure inside the chamber. Operating parameters on the air side of the coil include the pressure difference across the coil and the airflow through the coil. Temperature parameters include the coil surface temperature and the coil outlet temperature. The dry-bulb temperature inside the chamber is measured by temperature sensors located in the return air area or at representative measuring points. Relative humidity is measured by humidity sensors at the same measuring points and input as a dimensionless quantity from 0 to 1. Atmospheric pressure is measured by pressure sensors inside or outside the chamber and used to uniformly calculate air conditions. The pressure difference across the coil is measured by differential pressure sensors located at pressure taps on the windward and leeward sides of the coil, and the pressure is measured through the coil. The air volume is directly measured by an air volume meter or calculated based on the fan speed and duct calibration curve. The coil surface temperature is measured by a temperature sensor attached to the coil surface or fin root, and the coil outlet temperature is measured by a temperature sensor on the coil outlet side. To suppress the impact of random sensor fluctuations on computation, the controller samples each sensor multiple times at a fixed sampling frequency within a control cycle and takes the arithmetic mean as the effective value for that cycle. The fixed sampling frequency is 5Hz and the sampling duration is 2s. At this frequency and duration, industrial temperature, humidity, and differential pressure acquisition can reduce short-term noise without introducing significant control lag. After obtaining the dry-bulb temperature and atmospheric pressure inside the chamber, the controller determines the air density based on the ideal gas state relation. The air density is calculated using the following formula: in, air density, Atmospheric pressure The dry-bulb temperature inside the cabin. The gas constant for air is 287 J / (kg·K), a universal constant used in air thermodynamic calculations. The controller calculates the air mass flow rate based on the product of air density and airflow through the coil, using the following formula: in, Air mass flow rate, The air volume passing through the coil, The air mass flow rate is used to characterize the mass of air flowing through the coil per unit time, and serves as a benchmark for subsequent calculations of planned dehumidification and humidification mass flow rates. Before obtaining the humidity content inside the chamber, the controller determines the corresponding saturated vapor pressure based on the dry-bulb temperature inside the chamber. The saturated vapor pressure is obtained using an empirical formula suitable for real-time calculation by the controller. The empirical formula adopts the Magnus-Tetens formula and is in the following form: in, The saturated vapor pressure, The dry-bulb temperature inside the cabin. The formula is an exponential function, with 610.78, 17.27, and 237.3 being fixed coefficients. This form provides a fitting accuracy for saturated vapor pressure within the commonly used temperature range that meets the engineering calculation requirements for temperature and humidity control. The controller calculates the partial pressure of water vapor based on relative humidity and saturated vapor pressure, which is calculated using the following formula: in, For water vapor partial pressure, Relative humidity, The saturated water vapor pressure is used to convert relative humidity, a temperature-dependent parameter, into absolute water vapor partial pressure, eliminating the interference of temperature on humidity characterization. Based on the physical definition of moisture content, the water vapor partial pressure is converted to atmospheric pressure to obtain the cabin moisture content, which is calculated using the following formula: in, The value represents the humidity inside the chamber. 0.62198 is the constant coefficient corresponding to the ratio of water vapor to dry air gas constant (the molar mass of water vapor is 18.015 g / mol, the molar mass of dry air is 28.964 g / mol, 18.015 / 28.964≈0.62198, determined according to the physical definition of molar mass). Atmospheric pressure As the water vapor partial pressure, this process can obtain absolute moisture content parameters that are not affected by temperature, providing a stable and accurate state criterion for subsequent dehumidification and humidification adjustment, and avoiding the distortion of relative humidity characterization caused by temperature changes, which would affect the humidity control accuracy; thus, the air mass flow rate and cabin moisture content of the current cycle are formed, which are used for subsequent calculation of planned dehumidification mass flow rate under impedance curvature index constraints and calculation of target moisture content deviation, respectively.

[0019] S2. Apply temperature perturbation based on the current coil surface temperature, and collect the coil air-side operating parameters during the perturbation process. Calculate the coil air-side channel impedance coefficient at different temperature points. In an embodiment of the present invention, a temperature perturbation is applied based on the current coil surface temperature, and the operating parameters of the coil air side are collected during the perturbation process. The coil air side channel impedance coefficient at different temperature points is calculated, including: Using the current coil surface temperature as the center, the preset temperature step value is increased and decreased respectively to form three sampling temperature points; The surface temperature of the coil is controlled to reach the three sampling temperature points in sequence, and the corresponding coil air-side channel impedance coefficient is calculated respectively. Specifically, after obtaining the current coil surface temperature and the corresponding coil air-side operating parameters, the controller constructs a symmetrical temperature perturbation sampling sequence centered on the current coil surface temperature to calculate the coil air-side channel impedance curvature index, and defines three sampling temperature points as... , and ,in The reference sampling temperature point corresponding to the current coil surface temperature is used. The sampling temperature points for heating perturbation and cooling perturbation are determined by the following formulas: In the formula, The preset temperature step value is used to limit the perturbation amplitude and ensure sampling symmetry; the temperature step value The value of is jointly determined by the temperature control resolution of the test chamber's cooling circuit and the measurement resolution of the coil surface temperature. Specifically, it is taken as an integer multiple of the cooling circuit temperature control resolution and must not be less than the primary temperature control resolution. This ensures that perturbations are distinguishable in both the actuator output and the temperature sensor readings, and that sampling points do not overlap due to quantization errors. The preferred integer multiple is 2, which improves the numerical stability of subsequent three-point differential calculations without significantly altering the macroscopic operating conditions within the chamber. To ensure that the coil surface temperature sequentially reaches the three sampling temperature points, the controller sequentially sets the control setpoint of the coil surface temperature to . Or set sequentially to A sampling window is maintained at each sampling temperature point to calculate the coil air-side channel impedance coefficient under near-steady-state conditions. The duration of the sampling window is 10 seconds. Within this time scale, the coil surface temperature can converge to near the set value under the common adjustment bandwidth of the refrigeration circuit, and the pressure difference across the coil and the airflow reading through the coil reach a repeatable level. Within each sampling window, the controller samples the pressure difference across the coil and the airflow through the coil multiple times at a fixed sampling frequency and takes the arithmetic mean to obtain the effective pressure difference and effective airflow at that temperature point. Then, the coil air-side channel impedance coefficient corresponding to that temperature point is calculated. The coil air-side channel impedance coefficient is calculated by the following formula: In the formula, The impedance coefficient of the air-side channel of the coil. The pressure difference across the coil. For the airflow through the coil, the squared term is used to eliminate the difference in pressure drop scale at different airflow levels, so that More directly characterizing the geometric blockage and frictional resistance changes in the air-side channel of the coil; through The impedance coefficients were obtained at the three sampling temperature points. , and This provides consistent, symmetrical, and repeatable discrete samples for the subsequent second-order difference calculation of the impedance curvature index, thereby quantifying the nonlinear bending trend of the coil air-side channel impedance as the coil surface temperature changes during low-temperature humidity control. The quantification results of the coil air-side channel impedance coefficient are used to characterize the structural abrupt change tendency of the coil air-side channel from a flowable state to a frost-dominated blockage state, and provide a calculable basis for the subsequent generation of continuous inhibition factors to correct dehumidification requirements.

[0020] S3. Calculate the impedance curvature index based on the impedance coefficient of the air-side channel of the coil at different temperature points. In embodiments of the present invention, the impedance curvature index is calculated based on the impedance coefficient of the air-side channel of the coil at different temperature points, including: Calculate the impedance curvature index based on the coil air-side channel impedance coefficient at three sampling temperature points; Specifically, after calculating the impedance coefficients of the air-side channel of the coil at three sampling temperature points, the controller defines the three sets of impedance coefficients as follows: , and ,in This indicates that the coil surface temperature is at the reference sampling temperature point. The impedance coefficient of the air-side channel of the coil at that time This indicates that the surface temperature of the coil is at the sampling temperature point of the heating perturbation. The impedance coefficient of the air-side channel of the coil at that time This indicates that the surface temperature of the coil is at the sampling temperature point of the cooling perturbation. The impedance coefficient of the air-side channel of the coil is calculated, and based on this, the impedance curvature index is calculated. The impedance curvature index is defined as the discrete second-order variation intensity of the air-side channel impedance coefficient of the coil with respect to the coil surface temperature, and its calculation adopts a symmetrical three-point difference form. In the formula, The impedance curvature index. For temperature step values, the numerator term This term is used to characterize the bending or curvature trend of the impedance coefficient near a reference temperature point. When the impedance coefficient changes nearly linearly with the surface temperature of the coil, the numerator term approaches zero, thus... The absolute value of the numerator term is relatively small; when the geometric blockage or frictional resistance of the air-side channel of the coil changes nonlinearly with the surface temperature of the coil, the absolute value of the numerator term increases, thereby... The increase in the absolute value of corresponds to the physical process in which the flow area and pressure drop characteristics change abruptly or rapidly due to states such as condensation and frosting on the coil surface; denominator term This is used to scale the temperature step amplitude, ensuring comparability of curvature quantities obtained under different device resolutions or perturbation amplitudes and avoiding inconsistencies in the dimensions of curvature caused by changes in temperature step values; the impedance curvature index is obtained through the above calculation. As a nonlinear sensitivity measure of the air-side channel of the coil under the current low-temperature humidity control conditions, it is used to provide a calculable basis for subsequent steps, so that the dehumidification demand of the coil can be continuously suppressed when the impedance curvature increases. This achieves the goal of identifying and avoiding the air-side channel of the coil from entering the strong nonlinear blockage zone without relying on discrete threshold judgment.

[0021] S4. A continuous inhibition factor is generated based on the impedance curvature index. The deviation based on the moisture content in the chamber is corrected by the continuous inhibition factor to obtain the planned dehumidification mass flow rate. In an embodiment of the present invention, a continuous suppression factor is generated based on the impedance curvature index, and the deviation based on the moisture content inside the chamber is corrected by the continuous suppression factor to obtain the planned dehumidification mass flow rate, including: Calculate the difference between the moisture content inside the chamber and the set target moisture content, and take the positive part of the difference as the basic dehumidification requirement; Calculate the reciprocal of the sum of the numerical value 1 and the absolute value of the impedance curvature index, and use the reciprocal as the continuous suppression factor; Multiply the air mass flow rate, the continuous inhibition factor, and the basic dehumidification requirement to obtain the planned dehumidification mass flow rate; Specifically, after obtaining the cabin humidity, air mass flow rate, and impedance curvature index within the same control cycle, the controller directly maps the nonlinear bending trend of the coil air-side channel impedance to the dehumidification execution quantity during low-temperature humidity control to obtain the set target humidity. This target humidity is given by the test condition document or test program and serves as a reference value for the controlled quantity in this cycle. The controller calculates the difference between the cabin humidity and the target humidity, defining the positive part of this difference as the basic dehumidification requirement. The positive part means that the difference is taken when it is positive and zero when it is negative, thus ensuring that the dehumidification requirement is positive only when the cabin humidity is higher than the target humidity. After forming the basic dehumidification requirement, the controller generates a continuous suppression factor. This continuous suppression factor is a dimensionless coefficient used to continuously weaken the dehumidification intensity borne by the coil, and it decreases monotonically as the absolute value of the impedance curvature index increases. The continuous suppression factor is calculated using the following formula: In the formula, The constant 1 is the impedance curvature exponent, and its value is determined based on the following: Shishi To ensure that the dehumidification requirement is not weakened, and in Ensure when increasing Stay The range is within which the changes are continuous, thus avoiding control jumps caused by using discrete threshold judgments; based on this, the controller combines air mass flow rate, continuous inhibition factor, and basic dehumidification requirements. The planned dehumidification mass flow rate is obtained by multiplying the two values. The planned dehumidification mass flow rate represents the target output of dehumidified water mass handled by the coil in this cycle. The reason for using the product form is that the air mass flow rate provides a scale of the air mass participating in heat and mass exchange per unit time, and the planned dehumidification mass flow rate provides a scale of the excess moisture content per unit mass of dry air to be removed. The continuous suppression factor maps the risk of strong second-order bending of the coil air-side channel impedance with the coil surface temperature to the dehumidification execution quantity in a continuous manner. This causes the planned dehumidification mass flow rate to automatically decrease when the impedance curvature increases, thereby reducing the impact on the low-temperature humidity control stability and test repeatability when the coil air-side channel enters the strong nonlinear blockage region. It also provides a dehumidification plan quantity that can be directly issued for subsequent calculations of humidification mass flow rate, coil target temperature and reheat power.

[0022] S5: Based on the planned dehumidification mass flow rate, air mass flow rate, and the set target moisture content and target temperature, calculate the humidification mass flow rate, coil target temperature, and reheat power, and send the calculation results to the corresponding actuators to adjust the temperature and humidity of the test chamber. In an embodiment of the present invention, based on the planned dehumidification mass flow rate, air mass flow rate, and set target moisture content and target temperature, the humidification mass flow rate, coil target temperature, and reheat power are calculated, and the calculation results are sent to the corresponding actuators to adjust the temperature and humidity of the test chamber, including: Calculate the difference between the target moisture content and the moisture content inside the cabin, and take the positive part of the difference as the basic humidification requirement; Multiply the air mass flow rate by the basic humidification requirement to obtain the humidification mass flow rate; Calculate the equivalent target supply air moisture content for this cycle based on the cabin moisture content, planned dehumidification mass flow rate, humidification mass flow rate, and air mass flow rate. Convert the equivalent target supply air moisture content into the corresponding supply air water vapor partial pressure target; Based on the relationship between saturated vapor pressure and temperature, the temperature value that makes the saturated vapor pressure equal to the target vapor pressure of the supply air is calculated, and this temperature value is taken as the target temperature of the coil. Calculate the difference between the target temperature and the coil outlet temperature, and multiply the air mass flow rate and air constant pressure specific heat capacity by the difference to obtain the reheat power; Specifically, after obtaining the cabin humidity, air mass flow rate, planned dehumidification mass flow rate, coil outlet temperature, set target humidity, and set target temperature within the same control cycle, the controller first calculates the difference between the target humidity and the cabin humidity and takes its positive part as the basic humidification demand in order to generate the humidification mass flow rate, coil target temperature, and reheat power that can be directly sent to the actuator. The positive part means that the difference is taken when it is positive and zero when it is negative, thus ensuring that humidification demand is generated only when the cabin humidity is lower than the target humidity. The physical meaning of the basic humidification demand is the mass of water vapor that needs to be added per unit mass of dry air. Based on the law of conservation of mass, the controller multiplies the air mass flow rate by the basic humidification demand to obtain the humidification mass flow rate, which represents the mass of water vapor that needs to be added by the humidifier per unit time. Specifically, after obtaining the humidification mass flow rate, the controller, combining the cabin humidity, planned dehumidification mass flow rate, humidification mass flow rate, and air mass flow rate, calculates the equivalent target supply air humidity for this cycle. The equivalent target supply air humidity is the target humidity that the supply air side should achieve after the combined effect of the planned removal of water vapor by the coil and the replenishment of water vapor by the humidifier within this cycle. This is used to uniformly map the planned dehumidification mass flow rate and the humidification mass flow rate to the target temperature of the coil. The calculation is as follows: In the formula, The equivalent target supply air moisture content for this cycle. This refers to the humidity level inside the cabin. Air mass flow rate, To determine the planned dehumidification mass flow rate, For humidification mass flow rate, This indicates the mass of water vapor that needs to be removed by the coil per unit mass of dry air. This indicates the mass of water vapor that needs to be added by the humidifier per unit mass of dry air; to convert the equivalent target supply air moisture content into a target quantity that can be used to solve for the coil temperature, the controller calculates the target supply air water vapor partial pressure based on the conversion relationship between moisture content and partial pressure. The calculation is as follows: In the formula, Atmospheric pressure The equivalent target supply air moisture content for this cycle is given by the constant 0.62198, which is the constant coefficient corresponding to the ratio of water vapor to dry air gas constants. Then, based on the relationship between saturated water vapor pressure and temperature, the temperature value that makes the saturated water vapor pressure equal to the target supply air water vapor partial pressure is calculated, and this temperature value is defined as the target coil temperature. The solution satisfies the following: In the formula, Since the saturated vapor pressure is a function with temperature as the independent variable, the same formula for calculating saturated vapor pressure as that for calculating moisture content can be used to ensure consistency in conversion. To achieve a repeatable deterministic solution, Newton's iteration is used to calculate the target temperature of the coil, with the initial value of the iteration taken as the current surface temperature of the coil. To shorten the convergence time, the iterative format is as follows: In the formula, For the first The target temperature of the coil obtained in the next iteration. For the first The target temperature of the coil obtained in the next iteration. Let be the derivative of the saturated vapor pressure function with respect to temperature, and take the iteration termination condition as... The The resolution of the coil surface temperature measurement is set to one times the accuracy of the measurement. This is because if the temperature update is less than the measurement resolution, further iteration will not improve the achievable accuracy and will introduce unnecessary computational fluctuations. After obtaining the target temperature of the coil, in order to converge the cabin temperature to the target temperature and offset the temperature deviation caused by the air handled by the coil, the difference between the target temperature and the coil outlet temperature is calculated. The reheat power is obtained by multiplying the air mass flow rate and the air constant pressure specific heat capacity by the difference. The air constant pressure specific heat capacity is taken as... It is a commonly used engineering constant for the specific heat capacity of air at constant pressure and temperature, which can meet the accuracy requirements for estimating the control power of the test chamber.

[0023] The humidification mass flow rate is used as the mass flow rate control target of the humidifier, the coil target temperature is used as the coil temperature control target of the refrigeration circuit, and the reheat power is used as the power control target of the reheater. Based on the conservation of mass and heat, the moisture content target and temperature target are transformed into executable continuous control quantities and kept consistent with the planned dehumidification mass flow rate. This ensures the coordinated action of dehumidification, humidification and reheating during low-temperature humidity control and improves the stability and reliability of temperature and humidity control.

[0024] Specifically, after obtaining the humidification mass flow rate, coil target temperature, and reheat power within this control cycle, the controller sends the calculated results as execution setpoints to the corresponding actuators to complete temperature and humidity regulation. Specifically, the coil target temperature is sent to the temperature regulation actuator in the refrigeration circuit and converted into a cooling capacity regulation command, causing the coil surface temperature to converge towards the coil target temperature. This cooling capacity regulation command corresponds to at least one of compressor speed setting, electronic expansion valve opening setting, or refrigerant flow rate setting. The humidification mass flow rate is sent to the humidifier and converted into a humidification output command, causing the refrigerant to be injected per unit time... The water vapor mass is consistent with the humidification mass flow rate. The humidification output command corresponds to at least one of the humidifier's duty cycle, valve opening, or spray volume setting. The reheat power is sent to the reheater and converted into a heating power command, so that the reheater provides heat input matching the reheat power to the air after passing through the coil. After the command is sent, the controller continuously collects the dry bulb temperature and humidity in the chamber and updates the deviation with the target temperature and target humidity, so that the execution quantities of the refrigeration circuit, humidifier, and reheater are adjusted in a rolling manner with the control cycle, thereby achieving stable convergence and maintenance of the test chamber temperature and humidity under the target temperature and humidity conditions.

[0025] like Figure 2 As shown, Figure 2 This is a schematic diagram of the low-temperature humidity control system of an automotive environmental test chamber. It includes a test chamber shell 10, within which are installed a fan / duct 30 for generating circulating airflow and a coil 20 for cooling and dehumidifying the circulating airflow. Downstream of the coil 20 are a humidifier 40 and a reheater 50 to respectively humidify and compensate for the treated air and raise its temperature. Temperature and humidity sensors 11 are installed inside the test chamber to collect dry-bulb temperature and relative humidity, a pressure sensor 12 to collect atmospheric pressure, differential pressure sensors 13 on both sides of the coil 20 to collect the pressure difference across the coil, and an airflow meter 14 inside the duct to collect the airflow through the coil. The coil 20 is equipped with… The coil surface temperature sensor 15 is used to collect the coil surface temperature. The coil inlet temperature sensor 16 and the coil outlet temperature sensor 17 are respectively set at the inlet and outlet of the coil 20 to collect the coil inlet temperature and the coil outlet temperature. The collected signals from each sensor 11 to 17 are input to the controller 60. The controller 60 completes the control quantity calculation based on the collected environmental parameters, coil air-side operating parameters and coil temperature parameters, and sends the control command to the refrigeration loop actuator 70 to adjust the refrigeration output of the coil 20. At the same time, the humidification command is sent to the humidifier 40 and the reheat power command is sent to the reheater 50, thereby realizing the closed-loop regulation and stable maintenance of the temperature and humidity of the test chamber.

[0026] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for low-temperature humidity control in an automotive environmental testing chamber, characterized in that, Includes the following steps: S1. Collect environmental parameters, operating parameters of the air side of the coil, and temperature parameters of the coil in the test chamber, and calculate the current air mass flow rate and humidity in the chamber. S2. Apply temperature perturbation based on the current coil surface temperature, and collect the coil air-side operating parameters during the perturbation process. Calculate the coil air-side channel impedance coefficient at different temperature points. S3. Calculate the impedance curvature index based on the impedance coefficient of the air-side channel of the coil at different temperature points. S4. A continuous inhibition factor is generated based on the impedance curvature index. The deviation based on the moisture content in the chamber is corrected by the continuous inhibition factor to obtain the planned dehumidification mass flow rate. S5. Based on the planned dehumidification mass flow rate, air mass flow rate, and the set target moisture content and target temperature, calculate the humidification mass flow rate, coil target temperature, and reheat power, and send the calculation results to the corresponding actuators to adjust the temperature and humidity of the test chamber.

2. The method for low-temperature humidity control in an automotive environmental test chamber according to claim 1, characterized in that, Collect environmental parameters, operating parameters on the air side of the coil, and temperature parameters of the coil within the test chamber, and calculate the current air mass flow rate and humidity level inside the chamber, including: The environmental parameters inside the test chamber, the operating parameters of the air side of the coil, and the temperature parameters of the coil were collected. The environmental parameters included the dry bulb temperature, relative humidity, and atmospheric pressure inside the chamber; the operating parameters of the air side of the coil included the pressure difference before and after the coil and the air volume through the coil; and the temperature parameters included the surface temperature of the coil and the outlet temperature of the coil. The air density is determined based on the dry-bulb temperature and atmospheric pressure inside the cabin. The air mass flow rate is obtained by multiplying the air density by the air volume passing through the coil. The corresponding saturated vapor pressure is determined based on the dry-bulb temperature inside the cabin, and the partial pressure of water vapor is calculated based on the relative humidity and the saturated vapor pressure. Based on the conversion relationship of moisture content, the partial pressure of water vapor is converted to atmospheric pressure to obtain the moisture content inside the cabin.

3. The method for low-temperature humidity control in an automotive environmental testing chamber according to claim 2, characterized in that, The steps for calculating the impedance coefficient of the air-side channel of the coil include: Calculate the square of the airflow through the coil; The air-side channel impedance coefficient of the coil is obtained by comparing the pressure difference across the coil with the square of the airflow through the coil.

4. The method for low-temperature humidity control in an automotive environmental testing chamber according to claim 3, characterized in that, Based on the impedance coefficient of the air-side channel of the coil at different temperature points, the impedance curvature index is calculated, including: Using the current coil surface temperature as the center, the preset temperature step value is increased and decreased respectively to form three sampling temperature points; The surface temperature of the coil is controlled to reach the three sampling temperature points in sequence, and the corresponding coil air-side channel impedance coefficient is calculated respectively. The first sum is obtained by adding the coil air-side channel impedance coefficient corresponding to the temperature point after the current coil surface temperature increases by a temperature step value, and the coil air-side channel impedance coefficient corresponding to the temperature point after the current coil surface temperature decreases by a temperature step value. Multiply the current coil surface temperature by two to obtain twice the reference impedance value. Calculate the difference between the first sum and twice the reference impedance, and obtain the impedance curvature index based on the ratio of the difference to the square of the temperature step value.

5. The method for low-temperature humidity control in an automotive environmental testing chamber according to claim 1, characterized in that, A continuous suppression factor is generated based on the impedance curvature index. This continuous suppression factor is then used to correct deviations based on the cabin moisture content, resulting in the planned dehumidification mass flow rate, including: Calculate the difference between the moisture content inside the chamber and the set target moisture content, and take the positive part of the difference as the basic dehumidification requirement; Calculate the reciprocal of the sum of the numerical value 1 and the absolute value of the impedance curvature index, and use the reciprocal as the continuous suppression factor; The planned dehumidification mass flow rate is obtained by multiplying the air mass flow rate, the continuous inhibition factor, and the basic dehumidification requirement.

6. The method for low-temperature humidity control in an automotive environmental testing chamber according to claim 5, characterized in that, Calculating the humidification mass flow rate includes: Calculate the difference between the target moisture content and the moisture content inside the cabin, and take the positive part of the difference as the basic humidification requirement; Multiply the air mass flow rate by the basic humidification requirement to obtain the humidification mass flow rate.

7. The method for low-temperature humidity control in an automotive environmental testing chamber according to claim 6, characterized in that, Calculate the target temperature of the coil, including: Calculate the equivalent target supply air moisture content for this cycle based on the cabin moisture content, planned dehumidification mass flow rate, humidification mass flow rate, and air mass flow rate. Convert the equivalent target supply air moisture content into the corresponding supply air water vapor partial pressure target; Based on the relationship between saturated vapor pressure and temperature, the temperature value that makes the saturated vapor pressure equal to the partial pressure of the supply air vapor is calculated, and this temperature value is taken as the target temperature of the coil.

8. The method for low-temperature humidity control in an automotive environmental test chamber according to claim 2, characterized in that, Calculating reheat power includes: Calculate the difference between the target temperature and the coil outlet temperature, and multiply the air mass flow rate and the air constant pressure specific heat capacity by the difference to obtain the reheat power.

9. The method for low-temperature humidity control in an automotive environmental test chamber according to claim 4, characterized in that, The preset temperature step value is an integer multiple of the temperature control resolution of the test chamber's cooling circuit, and this integer multiple is greater than or equal to 1.

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