Method for calculating fogging probability of front windshield of automobile

Abstract

The invention relates to a fogging probability calculation method for an automobile front windshield. The fogging probability calculation method comprises the following steps: S1, data signal acquisition: acquiring an automobile exterior temperature Ta, an automobile interior temperature Ti, a glass temperature Tw, an evaporator temperature Te, a relative humidity H, an air blower gear signal, an automobile speed signal V, an air blowing mode signal, a windscreen wiper signal, an internal and external circulation signal of an automobile interior air conditioner and a compressor instruction signal at intervals; by the adoption of the technical scheme, starting from the fog drop condensation and fog drop evaporation process on the glass surface, the mass of water vapor, capable of being separated out to the glass surface, in air in a vehicle in the current state is calculated and accumulated, then the accumulated amount corresponds to the fogging probability, and on the basis of the actual physical principle of fogging and demisting, the vehicle speed and internal and external circulation are calculated. Signals such as a blowing mode and the like are merged into fogging probability calculation, so that the dependence of the current fogging probability on relative humidity change can be effectively solved.

Description

Technical Field

[0001] This invention relates to the field of vehicle engineering technology, and in particular to a method for calculating the probability of fogging on a car's windshield. Background Technology

[0002] A wide and clear field of vision is crucial for drivers while driving, directly impacting driving safety. The air distribution on the inner surface of the windshield is shown in the attached diagram. Figure 2 As shown, fogging affects the visibility of the car. The specific fogging and condensation of fog droplets are as follows: when the moisture content of the main air layer is high and the moisture content of the saturated air layer is also high, water vapor in the main air layer will adhere to the glass surface and form fog; conversely, if there are fog droplets on the glass surface, the surface of the fog droplets will evaporate, and the evaporated water vapor will be added to the main air layer.

[0003] Current methods for calculating the fogging probability of automatic defogging in automobiles generally involve collecting data on the windshield temperature, dew point temperature, interior temperature, exterior temperature, and interior relative humidity. The fogging probability is then calculated based on changes in relative humidity, the temperature difference between the windshield and dew point, and the temperature difference between the interior and windshield temperatures. This calculation is obtained through experimental calibration. However, the fogging probability calculated using this method depends on changes in relative humidity and cannot accurately match actual conditions. This can lead to situations requiring manual operation, distracting the driver. Furthermore, it does not consider the impact of vehicle speed, airflow mode, and internal / external air circulation mode on fogging and defogging, resulting in increased energy consumption of the vehicle's air conditioning system and increased driving safety risks. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a method for calculating the probability of fogging on a car windshield, which solves the problem of insufficient accuracy in fogging probability due to reliance on changes in relative humidity inside the vehicle and failure to consider the effects of vehicle speed, airflow mode, and internal / external circulation mode on fogging and defogging of the windshield.

[0005] The technical solution of the present invention: a method for calculating the probability of fogging of a car windshield, comprising the following steps: S1: data signal acquisition: acquiring the outside temperature, inside temperature, glass temperature, evaporator temperature, relative humidity H, blower gear signal, vehicle speed signal V, blowing mode signal, internal and external circulation signal of the in-vehicle air conditioner and compressor command signal at intervals;

[0006] S2: Determine the air temperature T of the main body layer: Based on the blowing mode signal, blower speed signal, and relative humidity H obtained in S1, determine the influence of airflow on the glass, and combine the internal and external circulation status and compressor command. At this time, the air temperature T of the main body layer is dynamically selected as the interior temperature, exterior temperature or evaporator temperature.

[0007] S3: Water vapor mass calculation: Based on the main layer air temperature T determined in S2 and the glass temperature obtained from the corresponding signal, determine the saturated water vapor mass at the corresponding temperature and calculate the theoretical value of the current precipitable water vapor mass.

[0008] S4: Calculate the mass of water vapor precipitated within the interval: Based on the water vapor mass m calculated in S3, determine whether the current state is fogging or defogging, and obtain the fogging rate or defogging rate based on the blower gear, blowing mode, internal and external circulation status, vehicle speed signal V and compressor command signal.

[0009] When calculated in S3, where is the wind speed corresponding to the blower speed setting, and is the amount of reduction in fogging rate caused by airflow inside the vehicle;

[0010] When calculated in S3, where is the droplet surface evaporation rate corresponding to the blower speed setting, is the mass transfer coefficient, is the convective heat transfer coefficient, is the density of water, and is the specific heat capacity of glass;

[0011] S5: Dynamic cumulative calculation of water vapor accumulation M: The water vapor mass change process is constrained nonlinearly by the decay rate β, and the effective precipitated water vapor mass in the current sampling interval is calculated, where v is the rate of the current state or β is the decay rate. The precipitated water vapor mass is accumulated to obtain the cumulative amount M.

[0012] S6: Mapping to fogging probability P: Mapping the accumulated amount M to the final fogging probability, where t is the time for water vapor to accumulate.

[0013] A further provision of the present invention is that the step of dynamically selecting the temperature of the main layer in step S2 specifically includes: when it is determined that no effective airflow is blowing towards the glass, T = T i ;

[0014] When it is determined that there is effective airflow blowing towards the glass: the compressor starts, then T = T e When the compressor is off and the air conditioner is in recirculation mode, T = T i When the compressor is off and the air conditioner is in external circulation mode, T = T a .

[0015] In a further embodiment of the present invention, the condition for determining that there is an effective airflow blowing towards the glass is: the blowing mode is a window blowing mode, or the relative humidity H is decreasing and the blower speed is higher than the preset speed value of the blowing mode.

[0016] In a further embodiment of the present invention, when the relative humidity H trend remains constant and the blower speed is higher than the preset speed in this blowing mode, the mass m of water vapor precipitated within the current sampling interval is... s =0.

[0017] In a further embodiment of the present invention, v in step S4 m Based on the wind speed v corresponding to the blower speed setting g According to function v m =f(v g )Sure.

[0018] In a further embodiment of the present invention, when the air conditioner is in external circulation mode, v in step S4... x Based on the vehicle speed signal V and the wind speed v corresponding to the blower speed setting. g According to function v x =f(v g , V) is determined.

[0019] In a further embodiment of the present invention, the method for obtaining β in step S5 is as follows:

[0020] When m > 0 as calculated in S3, D e =Mm max , where m max D represents the maximum cumulative mass of fog droplets adhering to the windshield when it fogs up. e The difference;

[0021] When m calculated in S3 < 0, D e =Mm min , where m min This is the minimum cumulative mass of fog droplets adhering to the windshield when it fogs up;

[0022] The attenuation rate β is based on the difference D. e According to the function β=fD e The function β = fD is determined. e (Obtained through calibration)

[0023] In a further embodiment of the present invention, in step S6, the cumulative amount M = m0 + m s Where m0 is the initial cumulative amount, and the initial cumulative amount m0 ​​is based on the relative humidity H and the in-vehicle temperature T. i and glass temperature T w The temperature difference is expressed by the function m0 = f(T) i -T w , H) is obtained.

[0024] In a further embodiment of the present invention, step S1 also acquires a windshield wiper signal, and determines whether it is raining based on the windshield wiper signal, thereby adjusting the outside temperature T acquired in step S1 accordingly. a Interior temperature T i Apply a compensation value determined based on the ambient temperature.

[0025] A further feature of the present invention is that the glass temperature T obtained in step S1... w Based on vehicle speed signal V and outside temperature Ta According to function T b =f(V,T) a The corrected value T obtained b Make corrections.

[0026] The beneficial effects of this invention are as follows: This method starts from the process of fog droplet condensation and evaporation on the glass surface, calculates the mass of water vapor that can be released from the air inside the vehicle onto the glass surface under the current state, and accumulates it. The accumulated amount corresponds to the fogging probability. Considering that fogging and defogging of the windshield are easily affected by the airflow velocity inside the vehicle, based on the actual physical principles of fogging and defogging, signals such as vehicle speed, internal and external air circulation, and airflow mode are incorporated into the fogging probability calculation. This effectively solves the dependence of the current fogging probability on changes in relative humidity, and comprehensively judges the current fogging state of the windshield. This not only reduces manual operation by the driver, but also makes accurate judgments during automatic defogging, thereby rationally distributing the airflow and reducing the energy consumption of the vehicle's air conditioning system. Attached Figure Description

[0027] Figure 1 This is a flowchart of a specific embodiment of the present invention;

[0028] Figure 2 This is a diagram showing the air distribution on the inner surface of a glass in the background art. Detailed Implementation

[0029] The technical solutions in this embodiment will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0031] As attached Figure 1 As shown, the present invention provides a method for calculating the probability of fogging of a car windshield. Starting from the process of fog droplet condensation and evaporation on the glass surface, the method calculates the mass of water vapor in the air inside the car that can be released onto the glass surface under the current state, and accumulates it, thereby using the accumulated amount to correspond to the fogging probability.

[0032] The specific calculation process is as follows:

[0033] S1: Signal Acquisition: The outside temperature T is acquired by sampling at certain time intervals through multiple temperature and humidity sensors and the vehicle's CAN signal.a Interior temperature T i Glass temperature T w Evaporator temperature T e The following signals are included in this solution: relative humidity (H), blower speed signal, vehicle speed signal (V), airflow mode signal, windshield wiper signal, vehicle air conditioning recirculation signal, and compressor command signal. Figure 2 As shown, with glass temperature T w As the saturated air layer temperature, the sampling interval for signal acquisition in this embodiment is preset to 0.1 seconds. This preset sampling interval can be modified, and some sensor signals need to be corrected:

[0034] 1) Determine if it's raining based on whether the windshield wipers are on. If it's raining, determine the outside temperature T. a Regarding the temperature inside the car (T) i Corrections are made, where the corrected compensation value can be obtained through experimental calibration;

[0035] 2) Depending on the vehicle model configuration, the presence of a power module around the sensor measuring the glass temperature in the car can affect the glass temperature measurement. The glass temperature T... w Through the correction value T b Make corrections, where the correction value T b This can be achieved through vehicle speed signal V and outside temperature T. a A defined function T b =f(V,T) a The function T is obtained. b =f(V,T) a It can be obtained through experimental calibration and fitting.

[0036] S2: Determine the air temperature T of the main layer:

[0037] 1) Determine if there is effective airflow reaching the windshield based on the airflow mode, fan speed setting, and relative humidity:

[0038] When the blowing mode is set to window blowing mode, it is assumed that there is effective airflow blowing onto the glass;

[0039] When the blowing mode is not the window blowing mode, but the relative humidity H shows a decreasing trend and the blower speed is higher than the preset speed of the blowing mode, it is determined that there is air blowing onto the glass. The relative humidity H is determined by hysteresis sampling after exponential filtering. The preset speed is obtained by experimental calibration.

[0040] When it is determined that there is an effective airflow blowing towards the glass:

[0041] If the compressor command is not equal to 0 when it starts, then T = T e ;

[0042] If the compressor command is 0 (shutdown) and the air conditioner's circulation mode is external circulation, then T = T a ;

[0043] If the compressor command is 0 (shutdown) and the air conditioner's recirculation mode is internal recirculation, then T = T i ;

[0044] In all other cases, it is determined that there is no effective airflow blowing towards the glass, and the air temperature of the main body layer is T = T i .

[0045] S3: Calculate the mass of water vapor that can be precipitated in the air of the main layer under the current data acquisition state: Based on the main layer temperature T obtained in S2, the mass of saturated water vapor m at that temperature can be determined by consulting relevant data. t And based on the glass temperature T obtained from the corresponding signal. w Determine the mass m of saturated water vapor at this temperature. tw And calculate the current mass of water vapor that can be precipitated, m = m, based on the relative humidity H. t ×Hm tw In this step, the calculated water vapor mass m is the theoretical value.

[0046] S4: Calculate the mass of water vapor precipitated during the sampling interval:

[0047] 1) Determine whether the current state is fogging or defogging based on the sign of the water vapor mass m calculated by S3. The calculated value is the theoretically precipitable water vapor mass m. When m>0, it is determined that water vapor can be precipitated from the air in the main layer and condensed on the glass, i.e., it is in a fogging state. When m<0, it is determined that the fog droplets on the glass can evaporate and the water vapor content in the air in the main layer will increase, i.e., it is in a defogging state.

[0048] When the relative humidity H obtained by interval sampling is flat and stable, and the blower speed is higher than the preset speed in this blowing mode, the mass m of water vapor precipitated during the sampling interval is set to 0, and it is determined that the water vapor content in the air of the main layer is stable at this time.

[0049] 2) Since the fogging rate is related to the air velocity, the higher the blower speed, the faster the air velocity inside the car. Under the same conditions, the air exchange near the glass is more intense, thus accelerating the fogging rate. Therefore, based on the blower speed corresponding to the wind speed v... g With the evaporation rate v of the droplet surface m A calibration experiment was conducted to obtain the evaporation rate v at the droplet surface through fitting. m Based on the blower wind speed v g A defined function v m =f(v g );

[0050] When the air conditioner is in external circulation mode, and the vehicle speed signal V or blower speed setting is greater than 0, the air flowing inside the vehicle has a certain defogging ability. At this time, it is necessary to reduce the fogging rate. Therefore, an experiment was conducted to calibrate the evaporation rate of fog droplets by adjusting the airflow speed inside the vehicle based on controlling the vehicle speed and blower speed. The reduction in fogging rate v caused by the airflow inside the vehicle was obtained through fitting. x function v x =f(v g ,V);

[0051] Therefore, when m > 0 as calculated in step S3, the fogging rate v q =v g -v x ;

[0052] 3) Due to the varying rates of water vapor mass transfer between the surface of fog droplets on the glass and the air in the bulk layer during defogging, the mass transfer coefficient h... m It is related to the surface area of ​​the droplets, and h m =h / (ρ×c p ), where h m where ρ is the mass transfer coefficient, h is the convective heat transfer coefficient, ρ is the density of water, and c is the density of water. p The specific heat capacity of glass can be found in various references.

[0053] The surface area of ​​fog droplets is correlated with the blower setting and blowing mode. Different blowing modes and blower settings correspond to different angles and wind speeds of air blowing towards the glass, resulting in different rates of water evaporation from the fog droplet surface. Therefore, calibration experiments can be conducted based on the water evaporation rate of the fog droplet surface under different blowing modes and blower settings to obtain the fog droplet surface evaporation rate v. m ;

[0054] Therefore, when m < 0 calculated in step S3, v c =v m ×h m .

[0055] S5: Calculate the cumulative amount of water vapor precipitated within the signal acquisition interval. This part of the calculation is divided into two modules: the cumulative attenuation rate of the interval and the initial cumulative value.

[0056] Since the mass of fog droplets that can adhere to the glass surface when the windshield fogs up is not infinite, and the fog layer will not increase further once it approaches a certain amount, the maximum cumulative amount m is set according to the fogging probability corresponding to the final cumulative amount. max and minimum value m min Determine the difference D between the current cumulative amount M and its value. e This allows us to obtain the attenuation rate β, where β is based on the difference D. e According to the function β=fD e It is determined that the function β = fD eThe results were obtained through calibration experiments and measurement fitting.

[0057] When m > 0 as calculated in step S3, the difference D e =Mm max According to the function β=fD e The value of β is obtained.

[0058] When m calculated in step S3 is less than 0, the difference D is... e =Mm min According to the function β=fD e The value of β is obtained.

[0059] And the cumulative amount M = m0 + m s m s = m × v × β, where v is the current state speed v q or v c m0 is the initial cumulative amount, which is based on the relative humidity H and the in-vehicle temperature T. i and glass temperature T w The temperature difference is expressed by the function m0 = f(T) i -T w H) is obtained, and the function m0 = f(T) i -T w H) is obtained by fitting the measurement results of the calibration test.

[0060] S6: Mapping to fog probability P: Mapping the accumulated amount M to the final fog probability P = f(M) = f(m) s ,t), where t is the time for water vapor accumulation. The fogging probability function P is obtained by calibration experiment fitting through the accumulation amount M.

Claims

1. A method for calculating the probability of fogging on a car windshield, characterized in that, Includes the following steps: S1: Data signal acquisition: Intermittently acquire the outside temperature T a Interior temperature T i Glass temperature T w Evaporator temperature T e Relative humidity H, blower speed signal, vehicle speed signal V, air blowing mode signal, vehicle air conditioning internal and external circulation signal and compressor command signal; S2: Determine the air temperature T of the main body layer: Based on the blowing mode signal, blower speed signal, and relative humidity H obtained in S1, determine the influence of airflow on the glass, and combine the internal and external circulation status and compressor commands. At this time, the air temperature T of the main body layer is dynamically selected as the interior temperature T. i Outside temperature T a Or evaporator temperature T e ; S3: Water vapor mass calculation: Based on the main air temperature T determined in S2 and the glass temperature T measured in the corresponding signal. w Determine the mass m of saturated water vapor at the corresponding temperature. t and m tw And calculate the current mass of water vapor that can be precipitated, m = m t ×Hm tw ; S4: Calculate the mass m of water vapor precipitated within the signal acquisition interval. s The system determines whether the fogging or defogging state is currently in progress based on the water vapor mass m calculated by S3, and obtains the fogging rate v based on the blower speed, blowing mode, internal / external circulation status, vehicle speed signal V, and compressor command signal. q Or defogging rate v c ; When m > 0 as calculated in S3, v q =v g -v x , where v g The fan speed corresponding to the different settings is v. x The amount by which the fogging rate is reduced due to airflow inside the vehicle; When m calculated in S3 is less than 0, v c =v m ×h m h m =h / (ρ×c p ), where v m The speed of the blower is set to v. g The corresponding evaporation rate on the droplet surface, h m where ρ is the mass transfer coefficient, h is the convective heat transfer coefficient, ρ is the density of water, and c is the density of water. p The specific heat capacity of glass; S5: Dynamic cumulative calculation of water vapor accumulation M: The attenuation rate β is used to apply nonlinear constraints to the water vapor mass change process to calculate the effective precipitated water vapor mass m within the current sampling interval. s = m × v × β, where v is the current state speed v q or v c β is the decay rate, which affects the mass of water vapor released, m. s The cumulative amount M is obtained by accumulating the total amount. S6: Mapping to fog probability P: Mapping the accumulated amount M to the final fog probability P = f(M) = f(m) s ,t), where t is the time for water vapor to accumulate.

2. The method for calculating the probability of fogging on a car windshield according to claim 1, characterized in that, The step of dynamically selecting the body layer temperature in step S2 specifically includes: When it is determined that there is no effective airflow blowing towards the glass, T = T i ; When it is determined that there is effective airflow blowing towards the glass: if the compressor is turned on, then T = T e If the compressor is off and the air conditioner is in recirculation mode, then T = T i If the compressor is off and the air conditioner is in external circulation mode, then T = T a .

3. The method for calculating the probability of fogging on a car windshield according to claim 2, characterized in that, The conditions for determining that there is an effective airflow blowing towards the glass are: the blowing mode is the window blowing mode, or the relative humidity H is decreasing and the blower speed is higher than the preset speed value of the blowing mode.

4. The method for calculating the probability of fogging on a car windshield according to claim 3, characterized in that, When the relative humidity H trend remains constant, and the blower speed is higher than the preset speed for this blowing mode, the mass m of water vapor precipitated within the current sampling interval is... s =0.

5. The method for calculating the probability of fogging on a car windshield according to claim 1, characterized in that, v in step S4 m Based on the wind speed v corresponding to the blower speed setting g According to function v m =f(v g )Sure.

6. The method for calculating the probability of fogging on a car windshield according to claim 1, characterized in that, When the air conditioner is in external circulation mode, v in step S4 x Based on the vehicle speed signal V and the wind speed v corresponding to the blower speed setting. g According to function v x =f(v g , V) is determined.

7. The method for calculating the probability of fogging on a car windshield according to claim 1, characterized in that, The method for obtaining β in step S5 is as follows: When m > 0 as calculated in S3, D e =Mm max , where m max D represents the maximum cumulative mass of fog droplets adhering to the windshield when it fogs up. e The difference; When m calculated in S3 < 0, D e =Mm min , where m min This is the minimum cumulative mass of fog droplets adhering to the windshield when it fogs up; The attenuation rate β is based on the difference D. e According to the function β=fD e )Sure.

8. The method for calculating the probability of fogging on a car windshield according to claim 1, characterized in that, In step S6, the cumulative amount M = m0 + m s Where m0 is the initial cumulative amount, based on relative humidity H and in-vehicle temperature T. i and glass temperature T w The temperature difference is expressed by the function m0 = f(T) i -T w , H) is obtained.

9. The method for calculating the probability of fogging on a car windshield according to claim 1, characterized in that, Step S1 also acquires the windshield wiper signal, and determines whether it is raining based on the windshield wiper signal to adjust the vehicle interior temperature T acquired in step S1. i Apply a temperature based on the outside temperature T a The compensation value is determined by degree.

10. The method for calculating the probability of fogging on a car windshield according to claim 1, characterized in that, The glass temperature T obtained in step S1 w Based on vehicle speed signal V and outside temperature T a According to function T b =f(V,T) a The corrected value T obtained b Make corrections.

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