DE102011084278A1 - Method for preventing fogging of window panes of motor car, involves activating anti-fogging operation if time variation of measurement values of air humidity sensor or time variation of dew point temperature is larger than threshold level - Google Patents

Abstract

The method involves activating anti-fogging operation of a ventilation and/or air conditioning apparatus of a vehicle based on measurement values of an air humidity sensor and an inside temperature sensor and measurement values of an external temperature sensor. The anti-fogging operation is activated if dew point temperature is larger than external temperature or if the time variation of the measurement values of the air humidity sensor or the time variation of the dew point temperature is larger than a preset threshold level. An independent claim is also included for a device for preventing fogging of window panes of a vehicle.

Description

The present invention relates to a method and a device for avoiding the fogging of the windows of a vehicle, in particular a motor vehicle, according to the preambles of the independent claims.

Such a method and such a device are known from EP 2 202 107 A1 known. A sensor unit mounted on an inner surface of a windshield of the vehicle includes a humidity sensor, a first temperature sensor detecting the temperature of the inner surface of the windshield, and a second temperature sensor detecting the temperature of the air contacting the humidity sensor which detects the air temperature in the vicinity of the inner surface the windscreen is. In addition, an outside temperature sensor is provided, which detects the air temperature outside the vehicle, and a coolant temperature sensor. From the measured values, a dew point temperature is determined. If the temperature of the inner surface of the windscreen is lower than the dew point temperature, anti-fog operation is activated.

It has been found that the reliability of the known anti-fogging methods is still unsatisfactory and that thus a satisfactory compromise between safety and comfort can not be achieved.

The invention is based on the object to avoid the fogging of the windows of a vehicle in a particularly simple and reliable manner.

This object is achieved by a method and a device having the features of the independent patent claims.

Advantageous developments of the invention are specified in the dependent claims.

• – die Taupunkttemperatur ist größer als die Außentemperatur; oder
• – die zeitliche Änderung der Taupunkttemperatur ist größer als ein voreingestellter Schwellenwert;

wobei an die Stelle des – bevorzugten – Vergleichs der zeitlichen Änderung der Taupunkttemperatur mit einem Schwellenwert alternativ ein Vergleich der zeitlichen Änderung der Messwerte des Luftfeuchtigkeitssensors mit einem – anderen – Schwellenwert treten kann.According to the invention, the anti-fog operation is activated when one of the following two conditions is met:

• - the dew point temperature is greater than the outside temperature; or
• The time change of the dew point temperature is greater than a preset threshold value;

wherein, instead of the - preferred - comparison of the temporal change of the dew point temperature with a threshold value, alternatively a comparison of the temporal change of the measured values of the humidity sensor with a - another - threshold value can occur.

That is, in the invention, the dew point temperature is not compared with the temperature of the inner surface of the windshield, as in the above-mentioned. State of the art, but with the outside temperature. At the same time, the time change of the dew point temperature or the measured values of the humidity sensor is observed. The second of the last two alternatives is also from the o.g. As is well known in the prior art, namely from the description of the underlying art, the change in humidity is to be used there to correct a value that determines whether or not a window glass will mist up. That is, the activation of the defogging operation does not start from a certain change in the humidity as in the invention, but also depends on the uncorrected determinate value.

It has been found that the invention makes it possible to avoid the fogging of the window panes of a vehicle in a particularly reliable manner, and this with a particularly low sensory expenditure. Namely, instead of a window glass sensor unit, it is possible to resort to an internal temperature sensor which is disposed at an arbitrary position in the vehicle, e.g. in the instrument panel, on the steering column, in the air conditioning unit, on the center console, on the B-pillar, etc. Such an internal temperature sensor is usually already present in the vehicle, as well as an outside temperature sensor, so that you add to implement the invention only a humidity sensor and can modify the software of an already existing control module for the ventilation or air conditioning of the vehicle.

In a preferred embodiment, the relative humidity measured in the interior of the vehicle by means of the air humidity sensor is corrected on the basis of a preset function of the measured values of the internal temperature sensor. This measure is based on the knowledge that there is a temperature dependency of the measured values of the humidity sensor on its own temperature, especially if the humidity sensor is of the condenser type. The finding that the capacitive humidity measurement is temperature-dependent was investigated and confirmed with many measurements of the response behavior of capacitive humidity sensors. The temperature dependence determined for a specific type of sensor can be used within the scope of the invention to correct the measured relative humidity.

Furthermore, it was recognized that the measured values of the humidity sensor are influenced by aging effects, which is why the correction of the measured relative air humidity preferably also on the basis of a measure of the aging of the Humidity sensor is done, which measure can be or include the time, for example.

As is known per se, the dew point temperature can then be calculated as a preset function of the measured values of the internal temperature sensor and of the measured or corrected relative air humidity.

As mentioned, in the invention, the dew point temperature is not compared with the temperature of the inner surface of a window pane, as in the prior art, but with the much easier to measure outside temperature, i. the air temperature outside the vehicle. However, since it is the temperature of the disk inner surface that is actually critical for fogging, in a preferred embodiment of the invention, the dew point temperature is compared before it is compared with the outside temperature based on a preset function of the difference of the measured values of the outside temperature sensor and the inside temperature sensor , By means of this correction function, the temperature gradient is modeled by the window pane.

For the preferred case that anti-fog operation is activated under the condition that the time change of the dew point temperature is greater than a preset threshold, it has been found that a preset threshold of about 3 ° C per minute or greater is favorable. But measurements in the range of 1 to 10 ° C / min are possible.

The humidity sensor and the interior temperature sensor are preferably located so far away from the windows of the vehicle that their measurements are not or not significantly affected by a cold window surface, and preferably have thermal contact with each other.

The following is a description of embodiments with reference to the drawings. Show:

1 Measured values of a typical humidity sensor as a function of the actual humidity for different sensor temperatures;

2 Dew point curves for different warm air compared with corresponding dew point curves for excessively high measured air humidity;

3 a flowchart for explaining a method for avoiding the fogging of the windows of a vehicle; and

4 Time profiles of the measured and the actual humidity with a test measurement with variable temperature.

In order to determine in a motor vehicle the probability that fogged windows, one uses an air humidity sensor. On the basis of the measured relative humidity and other measured values, a control module determines the dew point temperature of the air in the vehicle interior and therefrom the probability that fogged windows. If there is a risk of fogging the windows, the control module will cause the anti-fog operation of the ventilation or air conditioning, e.g. by blowing air or more air or warmer air onto the inner surfaces of the discs to avoid fogging. This may affect the comfort of the vehicle occupants, e.g. if warm air is not available after a cold start. Thus, in the winter often no recirculation mode for faster warming of the passenger compartment is possible if windows threaten to fog, since recirculation mode increases the humidity in the passenger compartment. Therefore, it is important to achieve a good compromise between comfort and window dressing. To make this possible, an accurate measurement of the humidity in the passenger compartment is required. However, the measurement signal of common humidity sensors, which is essential for the determination of the dew point temperature, is very inaccurate. The inaccuracies are based on 1) different sensor elements (usually capacitors) and components of the electronic circuit for detecting and amplifying the sensor signal, 2) aging effects of the sensor elements and 3) temperature dependencies of the sensor elements and associated components.

The dependence of the measured values of a typical humidity sensor on the sensor temperature is in 1 for the temperatures 10 ° C, 25 ° C and 46 ° C shown. It can be seen that this sensor only provides measured values for the relative air humidity at 25 ° C, which correspond to the relative air humidity supplied by a measuring-accurate reference sensor. For lower or higher temperatures, the measured relative humidity typically deviates by approximately ± 5% from the actual relative humidity.

Such large deviations of the measured relative humidity can lead to deviations of the calculated dew point temperature from the actual dew point temperature, which are in the range of ± 3 ° C and at low relative humidity are still significantly larger. This is recognizable 2 , which calculated dew point curves, ie dew point temperatures as a function of the relative humidity, for air of 10 ° C and 20 ° C compared to corresponding dew point curves for air at 10 ° C and from 20 ° C for 5% too high relative humidity (RH).

If a dew point temperature calculated with such inaccuracies is used to determine if windshield fogging is to be expected in the vehicle, this method is too inaccurate and there is a risk that either windshield fogging will not be reliably predicted or the comfort of the vehicle occupant will be unnecessarily compromised ,

Based on the flowchart of 3 Now, an improved method of avoiding fogging the windows of a motor vehicle by activating anti-fog operation of a ventilation and / or air conditioning system of the vehicle will be described. The motor vehicle includes a humidity sensor and an indoor temperature sensor, which are arranged close to each other, but not in the vicinity of the disc, in an interior of the vehicle, for. B. in the instrument panel, on the steering column, in the air conditioning unit, on the center console, on the B-pillar, etc. In addition, the motor vehicle includes an outside temperature sensor, the z. B. may be located behind the front bumper, and a control device for performing the method steps explained below.

In step S1, the measured value of the relative humidity RH humidity _{sensor is} read. In step S2, it is checked whether sensor aging effects are to be considered. If the humidity _sensor has not aged, the measured RH RH _sensor remains unchanged, and if the humidity _{sensor aged,} an aging _correction value RH _{sensor aged is added} to the measured relative humidity in step S3. In step S4, the measured value of the inside temperature _{sensor is} read, which indicates the air temperature T _incar close to the humidity _sensor .

Subsequently, a corrected relative air humidity RH _{correct is} calculated in step S5 on the basis of the measured relative humidity RH _sensor , possibly plus the aging _{correction value} RH _{sensor, aged} , and the air temperature T _incar close to the air humidity _sensor . To a stored 3D correction table can be used, can be read as a function of RH _sensor and T _incar from which RH _correct. In this way, temperature dependencies of the measured relative humidity RH _{sensor are} compensated, as they are in 1 are illustrated. Generally speaking, in step S5 a relative humidity measured in the interior of the vehicle by means of the humidity sensor is corrected on the basis of a preset function of the measured values of the internal temperature sensor and possibly also a measure for the aging of the humidity sensor. Incidentally, this correction has nothing to do with the fact that a constant absolute humidity results in different relative humidities at different temperatures.

Subsequently, in step S6, based on the air temperature T _incar and the corrected relative humidity RH _correct, a dew point temperature T _{dewp is} calculated, as determined from dew point _curves as in _FIG 2 shown results. Again, a saved 3D table can be used. Generally speaking, in step S6, the dew point temperature is calculated as a preset function of the measured values of the indoor temperature sensor and the measured or corrected relative humidity.

In step S7, the measured value of the outside temperature sensor for the temperature T _{amb of} the air in the vicinity of the vehicle is then read.

If the calculated dew point temperature T _{dewp is} greater than the measured outdoor temperature T _amb , this may be an indicator for window _fogging . However, it is actually the temperature of the inner surface of the window pane that is comparable to the dew point temperature. In order not to have to measure them directly, the calculated dew point temperature T _{dewp is} still corrected in step S8. For this purpose, a stored 3D correction _table can be used, from which a corrected dew point temperature T _{dewp, correct} as the sum of the dew point temperature T _dewp and a function of (T _incar - T _amb ) can be read out. That is, the dew point temperature is corrected based on a preset function of the difference of the measured values of the outside temperature sensor and the inside temperature sensor. In this way, the temperature gradient is taken perpendicularly through the glass of the window, without the temperature of the inner surface of the window must be measured directly.

Only now, in step S9, the corrected dew point temperature T _{dewp, correct is} compared with the outside temperature T _amb , and if T _{dewp, correct is} greater than T _amb , the process proceeds to step S11, in which it is assumed that There is a risk that window panes mist up and an anti-fog operation is started.

However, if T _{dewp, correct is} less than T _amb , it is not certain that there is no danger of _fogging windows. In this case, it is still checked in step S10 whether the temporal change of the corrected dew point temperature T _{dewp, correct} greater than a preset threshold limit of z. B. 3 ° C per minute. If T _{dewp, correct is} greater than limit, the process proceeds to step S11, where antifogging operation is started, and otherwise, the routine returns to step S1 to be re-run.

It has been found that the test criterion of step S10 is an excellent criterion in certain situations in order to assess the risk of windshield fogging. A rapid increase in the (corrected) dew point temperature announces a window fogging, even if the test criterion of step S9 is not met. Such a situation occurs z. B. on when the ventilation works in recirculation mode and in the vehicle significantly moisture is produced, what the breathing of the occupants is sufficient. Such a situation could also occur if the outside temperature sensor incorrectly measures too high an outside temperature T _amb , for example if the radiator fan is driving warmer air toward the outside temperature sensor when the vehicle is moving slowly or when the vehicle is at a standstill. Although one can try to prevent such erroneous measurements, for example, by using only outside temperature readings below a certain rate of increase and / or measuring the outside temperature only while driving and / or freezing their value when the vehicle with warm engine, but can be incorrect measurements of the outside temperature not completely avoid.

4 shows the temporal course of the measured and the actual relative humidity with a test measurement of a humidity sensor in a climatic cabinet, whereby the air temperature between -20 ° C and +64 ° C was varied and in addition the air humidity was varied, as in 1 shown. Out 4 one recognizes, firstly, that the humidity sensor used has a temperature-dependent error, and secondly, however, that the temporal change of the air humidity measurement from the sensor largely corresponds to the reference. Thus, the change with time of the dew point temperature calculated with the sensor measured values is robust against the temperature-dependent error and other sensor tolerances.

It has been confirmed by many wind tunnel and road tests that the execution of the step S10 in FIG 3 significantly improves the reliability of fitting detection. From certain increase rates of the dew point temperature, one can reliably assume that the moisture production in the vehicle interior is a problem and threatens a window fogging.

Step S10 in FIG 3 could be modified so that the temporal change of the relative humidity RH _sensor or RH _correct instead of the temporal change of the dew point temperature T _dewpt or T _{dewp, correct is} monitored for exceeding a threshold, the routine of 3 possibly something to modify. However, it is better to use the dew point temperature in step S10, since the relative humidity is coupled with the temperature and the relative humidity falls when the temperature inside the vehicle increases, which might need to be considered.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 2202107 A1 [0002]

Claims (8)

A method for avoiding fogging the windows of a vehicle, in particular a motor vehicle, by activating an anti-fog operation of ventilation and / or air conditioning of the vehicle (S11) based on measured values (S1, S4) of a humidity sensor and an indoor temperature sensor, which are close to each other in an interior space of the vehicle, and measured values (S7) of an outside temperature sensor in the surroundings of the vehicle, wherein a dew point temperature is determined from the measured values (S6, S8), characterized in that an anti-fog operation is activated when the dew point temperature is greater than the outside temperature is (S9) or when either the time change of the measured values of the humidity sensor or more preferably the time change of the dew point temperature is greater than a preset threshold (S10). A method according to claim 1, characterized in that a measured by means of the humidity sensor relative humidity in the interior of the vehicle on the basis of a preset function of the measured values of the internal temperature sensor and optionally also a measure for the aging of the humidity sensor is corrected (S5). A method according to claim 1 or 2, characterized in that the dew point temperature is calculated as a preset function of the measured values of the internal temperature sensor and the measured or the corrected relative air humidity (S6). A method according to claim 3, characterized in that the dew-point temperature is corrected on the basis of a preset function of the difference of the measured values of the outside temperature sensor and the inside temperature sensor (S8). Method according to one of the preceding claims, characterized in that in the case that the anti-fog operation is activated under the condition that the time change of the dew point temperature is greater than a preset threshold, the threshold value is about 3 ° C per minute or greater. Method according to one of the preceding claims, characterized in that the humidity sensor and the internal temperature sensor are not arranged close to the window panes of the vehicle. Method according to one of the preceding claims, characterized in that the humidity sensor and the internal temperature sensor have thermal contact with each other. Device for avoiding the fogging of the window panes of a vehicle, characterized in that the device is arranged for carrying out the method according to one of the preceding claims.

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