DE102017214749A1 - Method for diagnosing a humidity sensor of a vehicle - Google Patents

Abstract

The invention relates to a method for diagnosing a moisture sensor (104) of a vehicle (100), wherein water is detected on a surface by use of a sensor device (102), and if water is detected on the surface, a measured value of a humidity of the moisture sensor (104) is detected is compared to a lower threshold, wherein at least one measure is performed depending on a result of the comparison. The invention further relates to a computing unit and a computer program for carrying out the method.

Description

The present invention relates to a method for diagnosing a moisture sensor of a vehicle and to a computing unit and a computer program for carrying it out.

State of the art

In combustion engines, the knowledge of the humidity is helpful to better control the combustion. The determination of the humidity is of particular importance for vehicles with low-pressure exhaust gas recirculation (low-pressure EGR) for optimizing combustion or reducing pollutant emissions. For example, such reveal US 2012/279200 A . US 2012/024271 A and US 2012/012088 A Processes in which the humidity has an influence on the setting of the low-pressure EGR mass flow. The low pressure EGR mass flow tends to be reduced with increasing humidity of the intake air to counteract the risk of condensation in the intake tract. Condensation may contaminate or damage components in the intake manifold downstream of the low pressure EGR supply line such as compressor, intercooler, charge air cooler bypass valve, throttle, temperature sensors or pressure sensors. Low-pressure EGR is an important technology for reducing nitrogen oxide emissions, especially in vehicles with a diesel engine.

For this reason, a humidity sensor may be located in the intake tract of the internal combustion engine, with which the moisture of the intake air is determined. For example, a moisture sensor may also be integrated in an air mass flow meter. It is desirable to be able to monitor the functioning of such a sensor during operation.

One difficulty of a diagnostic method for a humidity sensor is, in particular, the determination of a humidity humidity reference value determined independently of the humidity sensor, with which the measured value of the humidity sensor can be compared.

DE 102013203123 A1 shows a method in which a reference value for the humidity is obtained via the Internet.

JP 2016142142 A shows a method in which a lower limit for the humidity is determined when it is concluded from the activation of the windshield wiper that it is raining.

Disclosure of the invention

According to the invention, a method for diagnosing a moisture sensor in a vehicle as well as a computing unit and a computer program for carrying it out with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

In the method according to the invention for the diagnosis of a moisture sensor of a vehicle, water is detected on a surface by the use of a sensor device and, when water is detected on the surface, a measured value of a humidity of the moisture sensor is compared with a lower threshold value, wherein at least one of them is dependent on a result of the comparison Action is performed.

The invention makes it possible to improve the accuracy of such a sensor during operation by means of an adjustment method and to monitor the functionality of such a sensor during operation. Depending on the use of the moisture sensor signal, the type of vehicle and the country in which the vehicle is to be marketed, it may be required to monitor its functionality through statutory on-board diagnostics.

Preferably, water is detected on a surface in an environment of the vehicle that is within range of the sensor device. It is conceivable that water is detected on a surface at a distance of up to 5 m, preferably 2 m of the vehicle. In this case, the surface may advantageously have a roadway or an outer surface, e.g. a disc of the vehicle, so that in particular a wet road surface and / or a wet outer surface of the vehicle can be detected.

When it rains, the relative humidity in ground-level air layers reaches a value close to 100%. If the signal of the moisture sensor indicates a substantially lower value, then a deviation can be deduced and a corresponding measure, for example, depending on the size of the deviation, taken.

In particular, a deviation of the measured value of the moisture sensor downwards can be recognized by the invention and prevented or reduced by suitable countermeasures. This is advantageous over methods that only recognize other types of deviations (eg, upward, slow response time), since a measured humidity reading of the moisture sensor, for example, presents the risk of setting too high a mass flow of the low pressure EGR, condensation occurs and components are dirty or damaged.

The expression by the recognition of a wet roadway has opposite solutions as in the JP 2016142142 A the advantage that it can be carried out not only when the rain takes place at the moment of vehicle operation, but also when the rain is recent.

Opposite solutions like in the DE 102013203123 A1 The invention has the advantage that it is independent of an Internet connection. Thus it is applicable in a higher number of vehicles and independent of possible errors in the Internet connection. In addition, there is a higher chance of acceptance as an OBD procedure by an approval authority.

In an advantageous embodiment, the sensor device has an optical sensor by means of which it is detected whether the surface is wet, e.g. by determining a wavelength fraction of a frequency band absorbed by water. Since water preferably absorbs certain wavelength ranges, it is easy to deduce a wet surface in this way.

In a further advantageous embodiment, the sensor device has an image capture device, by means of which it is detected whether the surface is wet, e.g. by using an image recognition method to detect the reflection of a light source on the wet surface. This is advantageous since image capture devices are now available, in particular from the smartphone sector, small, inexpensive and in good quality.

Advantageously, the sensor device has a rain sensor, which preferably detects water on an outer surface, in particular a pane, of the vehicle. In this way, rain can be closed quickly and easily. This is advantageous because rain sensors are often already present in a windshield wiper control. This expression has opposite solutions as in the JP 2016142142 A the advantage that it can also be performed when the wiper is not activated, for example because the vehicle is stationary.

In a further advantageous embodiment, especially for detecting a wet road surface, the sensor device has an ultrasonic sensor. For example, an ultrasound caused by tires of the vehicle may be measured to detect if the road surface is wet. It is also possible to measure the reflection of emitted ultrasound on the road, since dry roads reflect diffusely, whereas wet roads reflect sound more directionally. This embodiment is advantageous since an ultrasonic sensor can be mounted relatively flexibly in the vehicle and may already be present in parking assistance systems.

In a further advantageous embodiment, especially for the detection of a wet road surface, the sensor device has a device for determining a coefficient of friction of the roadway, as used, for example, in driving assistance systems, such as e.g. ESP (vehicle dynamics control) or anti-slip control is used. This device is in particular part of the associated driver assistance control device and can be realized in particular in software. This is advantageous since such a device is often already present. From the coefficient of friction can be concluded that the road is wet. This is possible because the coefficient of friction is around 1 on a dry road but typically in the range of 0.4 to 0.8 on a wet road.

Conveniently, when the measured value of the humidity of the humidity sensor is lower than the lower threshold value, the at least one measure corrects the measured value of the humidity in the sequence. "In the sequence" here means that the measured value of the air humidity is corrected in future measurements. So it is conceivable that due to the deviation of the measured value of the humidity sensor a correction term is formed from the lower threshold value, which is used in further measurements to correct the measured value of the air humidity. In other words, the raw value supplied by the sensor is corrected with the correction term to obtain a corrected measured value. Such a measure is commonly referred to as sensor matching.

In a further advantageous development of the measured value of the humidity of the humidity sensor is further compared with an upper threshold, wherein, depending on the result of the comparison, at least a second measure is performed. In this way, the measured value of the air humidity is advantageously secured against deviations upward. This is also possible if no water is detected on a surface, since the maximum relative humidity value is always 100%.

Equally expedient, if the measured value of the humidity of the humidity sensor is higher than the upper threshold value, the measured value of the air humidity is corrected as the at least one second measure in the sequence. In this way, even if the measured value of the humidity of the humidity sensor deviates upwards, preferably a correction term is created with which further measured values can then be corrected continuously. Such a measure is commonly referred to as sensor matching.

In a further advantageous embodiment, the correction of the measured value of the air humidity takes place by means of an additive correction term. Just as easily, the correction of the measured value of the air humidity additionally or alternatively by a multiplicative correction term. This is advantageous because it can be ensured in a simple manner, a continuous correction of the measured value of the humidity.

In a further advantageous embodiment, the at least one measure comprises comparing the measured value of the air humidity with a second lower threshold value and determining a defect of the moisture sensor when the second lower threshold value is undershot. This is advantageous because it provides a diagnostic method that detects a defect of the humidity sensor. For minor deviations of the measured value of the moisture sensor accuracy can be improved by a correction term usually sufficient, larger deviations should be concluded that a malfunction of the moisture sensor better.

Preferably, the at least one second measure comprises comparing the measured value of the air humidity with a second upper threshold value and determining a defect of the moisture sensor when the second upper threshold value is exceeded. In this way, a diagnostic method is advantageously provided that also recognizes an excessively high measured value as an error of the moisture sensor.

An arithmetic unit according to the invention, e.g. a control device of a (power) vehicle, is, in particular programmatically, configured to perform a method according to the invention.

Also, the implementation of the method in the form of a computer program is advantageous because this causes very low costs, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as e.g. Hard drives, flash memory, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described below with reference to the drawing.

list of figures

• 1 schematically shows a preferred embodiment of a motor vehicle with a humidity sensor and an evaluating arithmetic unit, which is adapted to perform a preferred embodiment of a method according to the invention.
• 2 shows a preferred embodiment of a method according to the invention schematically as a block diagram.

Embodiment (s) of the invention

In 1 is a motor vehicle shown schematically and with 100 designated. The car 100 includes an engine control unit 101 , which receives various sensor data and evaluates for controlling an internal combustion engine.

Furthermore, the motor vehicle includes 100 a humidity sensor 104 , which is preferably provided in an intake tract (not shown) of the internal combustion engine (not shown) and measures there a humidity. Furthermore, the motor vehicle includes 100 an exhaust gas recirculation, of which an EGR valve 106 is shown schematically in the figure. The EGR valve 106 is from the engine control unit 101 controlled depending on a measured humidity. Here, the low-pressure EGR mass flow is expediently reduced with increasing humidity of the intake air to counteract the risk of condensation in the intake tract, as by condensation components in the intake downstream of the low-pressure EGR supply line, such as compressor, intercooler, intercooler bypass valve, throttle valve, temperature sensors or pressure sensors, can become dirty or damaged.

For diagnosis of the humidity sensor used 104 , ie in particular for plausibility of the measured value, is the engine control unit 101 with at least one sensor device 102 . 103 connected and for carrying out a method according to 2 set up

The engine control unit 101 is in the example shown with an ultrasonic sensor 102 as part of the sensor device 102 . 103 connected and set up to detect whether the road surface is wet by here one of tires 105 of the vehicle 100 Ultrasound is measured to detect if the road surface is wet.

Instead of the ultrasonic sensor or in addition to it is also conceivable that the engine control unit 101 with an optical sensor as part of the sensor device 102 . 103 is connected and is adapted to detect whether the road surface is wet, for example, by determining a wavelength portion of a frequency band absorbed by water.

Alternatively or additionally, it is also conceivable that the engine control unit 101 with an image capture device with a light source as part of the sensor device 102 . 103 connected and configured to recognize whether the road surface is wet, for example, by using an image recognition method to detect the reflection from the light source on the wet roadway.

In addition, the motor vehicle here includes a rain sensor 103 as a further component of the sensor device, to detect whether a surface of an outer surface of the motor vehicle is wet, and in this way to determine whether it is raining. The rain sensor 103 can be linked to a windscreen wiper control.

The control unit 101 is particularly adapted to carry out a preferred embodiment of a method according to the invention, which in 2 is shown schematically as a block diagram. In the example shown, a sensor device is used both for detecting a wet road surface and for detecting a wet vehicle surface. However, one of the two options is sufficient.

The procedure begins in one step 201 in which by means of the sensor device 102 it is detected whether a surface is wet in an environment of the vehicle. For example, by means of the ultrasonic sensor 102 Check if the road surface is wet.

If it is detected that the surface is wet, this is done in one step 202 noted, for example, by a corresponding first status indicator (so-called flag) in a memory of the executing engine control unit 101 is set to TRUE (or TRUE) otherwise set to FALSE.

Will in step 201 not realizing that the surface is wet, will step 201 repeated.

In a parallel step 203 is by means of the sensor device 103 detects whether a surface of the vehicle is wet. For example, water is detected on the windshield as a surface by means of the rain sensor.

If it is detected that the surface is wet, this is done in one step 204 noted, for example, by a corresponding second status indicator in a memory of the executing engine control unit 101 is set to TRUE (or TRUE) otherwise set to FALSE.

Will in step 203 not realizing that the surface is wet, will step 203 repeated.

Optionally, one check step each 211 be provided, which checks whether the first or second status indicator remain set over a certain minimum time T. If so, go to step 205 continued. Otherwise, start over.

In step 205 a third status indicator (so-called rain flag) is set to TRUE if both the first and the second status indicator (possibly long enough) are set. This means that a high humidity of close to 100% is expected.

If the rain flag is set to TRUE, then in step 206 a lower threshold h_ref_low is set with h_ref_low≤100%, which represents a lower threshold for the real humidity. This threshold can, for example, in a memory of the engine control unit 101 be stored and read from there and / or calculated according to a calculation rule.

The lower threshold h_ref_low corresponds to a high relative humidity, but is expediently less than 100% in order to take into account that the increase in atmospheric humidity due to evaporation of the water does not occur abruptly. The calculation of h_ref_low may be such that h_ref_low starts at a start value (eg 90%), thereafter increases as long as the rain flag is at TRUE, and finally reaches or meets a target value close to or equal to a relative humidity of 100% approaching asymptotically.

Advantageously, in step 206 Furthermore, an upper threshold h_ref_high with eg h_ref_high ≥ 95%, preferably h_ref_high = 100% set, which represents an upper threshold for the humidity. This threshold can, for example, in a memory of the engine control unit 101 be stored and read from there and / or calculated according to a calculation rule.

The lower threshold h_ref_low or the upper threshold h_ref_high are either a value for the absolute or for the relative humidity, depending on whether the value determined from the humidity sensor is an absolute or relative air humidity.

At least in the case that the threshold values are values for the absolute air humidity, the ambient temperature or the intake air temperature is also included in their calculation. This temperature value may e.g. measured by a corresponding sensor.

In addition, the ambient pressure can also be included in the calculation of the reference values. The ambient pressure can be measured by a corresponding sensor.

In step 207 For example, the upper threshold h_ref_high and the lower threshold h_ref_low are set to one from the humidity sensor 104 output raw value h_sens _raw as a measured value compared. If h_ref_low ≤ h_sens _raw ≤ h_ref_high, will step 205 repeated. It is assumed in this case that the humidity sensor 104 outputs a correct value.

h_sens_raw is to be understood as a raw value in the sense that no correction value according to the invention has yet been included. However, h_sens raw may already include other corrections, such as temperature. These other corrections are not the subject of the invention.

If h_sens_raw <h_sens_raw, ie the measured value of the humidity h_sens_raw is lower than the lower threshold h_ref_low, then in step 208 as the first measure calculates a correction term. This correction term is expediently stored in the non-volatile memory of the control unit.

If h_sens_raw> h_ref_high, the measured value of the humidity of the humidity sensor h_sens_raw is therefore higher than the upper threshold h_ref_high becomes in step 212 as the second measure also calculates a correction term. This correction value is expediently stored in the non-volatile memory of the control unit.

For example, as a measure in the steps 208 respectively. 212 an additive correction value c_add and / or a multiplicative correction value c mult is calculated, wherein the raw value of the air humidity in the sequence is corrected according to the formula h_corr = h_sens_raw + c_add and / or according to the formula h_corr = c_mult x h_sens_raw in order to provide the most accurate possible moisture value which is used for the other functions implemented in the control units, for example the setting of the low-pressure EGR by the engine control unit. Such a measure is commonly referred to as sensor matching.

For example, an additive correction value c_add can be calculated according to the following formula: $$c\_add=\left\{\begin{array}{c}H\_ref\_lOw-H\_sens\_raw.wenn:H\_sens\_raw<H\_ref\_lOw\\ 0wenn:H\_ref\_lOw\le H\_sens\_raw\le H\_ref\_HiGH\\ H\_ref\_HiGH-H\_sens\_raw.wenn:H\_sens\_raw>H\_ref\_HiGH\end{array}\right\}$$

The corresponding formulas for a multiplicative correction value c_mult are: $$c\_mult=\left\{\begin{array}{c}H\_ref\_lOw/H\_sens\_raw.wenn:H\_sens\_raw<H\_ref\_lOw\\ l.wenn:H\_ref\_lOw\le H\_sens\_raw\le H\_ref\_HiGH\\ H\_ref\_HiGH/H\_sens\_raw.wenn:H\_sens\_raw>H\_ref\_HiGH\end{array}\right\}$$

It can be provided that step 206 is performed only when the rain flag has been TRUE for a certain time. Alternatively it can be provided that step 206 is performed only when the rain flag has been TRUE for a certain time and then reset to FALSE, and then for h_sens_raw, h_ref_low, and h_ref_high values are used immediately before the reset. The advantage is that then the lower reference value may be larger (according to the calculation method described above), which causes a higher accuracy of the correction value.

Furthermore, in order to increase the robustness, it may be provided that h_sens_raw and / or h_ref_low and / or h_ref_high are not currently formed values, but mean values formed over a relatively long period of time and / or low-pass filtered values.

To increase the robustness, it can furthermore be provided that the determined correction value is itself filtered, for example according to the following calculation rule: $$c\_add\left(0\right)=0$$

Given the conditions for forming a new reference value, c_add_unfiltered is calculated according to equation (1). $$c\_add\left(n\right)=\left(1-k\right)\times c\_add\left(n-1\right)+k\times c\_add\_unifiltered$$

n

Zählindes, n=1, 2, ...

c_add(0)

Initialwert für den Korrekturwert

c_add(n)

Korrekturwert nach Abgleichschritt Nummer n

k

Filterkonstante

There are

n

Counting index, n = 1, 2, ...

c_add (0)

Initial value for the correction value

c_add (n)

Correction value after adjustment step number n

k

filter constant

For a multiplicative correction value, the corresponding calculation rule is: $$c\_mult\left(0\right)=1$$

Given the conditions for forming a new reference value, c_mult_unfiltered is calculated according to equation (2). $$c\_mult\left(n\right)=\left(1-k\right)\times c\_mult\left(n-1\right)+k\times c\_mult\_unifiltered$$

In the case of a filtering, the last calculated value c_add (n) or c_mult (n) is to be understood as c_add or c mult without specifying the count.

The correction value c_add or c mult is preferably stored in the nonvolatile memory of the control unit so that it is also available after a restart.

In step 209 will after the correction in the steps 208 . 212 checks whether the deviation between the raw value and the respective threshold value is implausibly large. A second upper threshold value T_high and a second lower threshold value T_low are determined for the largest plausible positive or negative deviation. If h_ref_low-T low≤h_sens _raw≤h_ref high + T_high, then no error will be issued and it will go back to step 205 continued. If h_sens_raw <h_ref_low - T_low or h_sens raw> h_ref_high + T high, there will be a defect of the humidity sensor 104 in step 210 detected.

In particular, with h_sens_raw <h_ref_low - T low an error with a negative deviation is detected, and with h_sens raw> h_ref_high + T high an error with a positive deviation is detected.

It can be provided that the diagnosis decision in step 209 is hit only when the rain flag has been TRUE for a certain time.

Since, regardless of the weather situation, an air humidity value corresponding to a relative humidity of 100% represents an upper limit for the real humidity, the formation of a correction value and the diagnosis by the comparison between h_sens_raw and h_ref_high is not tied to the detection of water on the road surface and can regardless of the rain flag.

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

• US 2012279200 A [0002]
• US 2012024271 A [0002]
• US 2012012088 A [0002]
• DE 102013203123 A1 [0005, 0014]
• JP 2016142142 A [0006, 0013, 0017]

Claims (14)

A method for diagnosing a humidity sensor (104) of a vehicle (100), wherein water is detected on a surface by using a sensor device (102) and when detecting water on the surface a measured value of humidity of the humidity sensor (104) compared with a lower threshold is performed, wherein at least one measure is performed depending on a result of the comparison. Method according to Claim 1 wherein the surface is an outer surface of the vehicle or a road surface. Method according to Claim 1 or 2 wherein the sensor device has an optical sensor and / or an image acquisition device and / or a rain sensor and / or an ultrasonic sensor, by means of which it is respectively detected whether the surface is wet. Method according to one of the preceding claims, wherein the sensor device has a device for determining a coefficient of friction of the roadway. The method of any one of the preceding claims, wherein the humidity sensor (104) is located in an intake tract of the vehicle (100). Method according to one of the preceding claims, wherein, when the measured value of the humidity of the humidity sensor is lower than the lower threshold value, as the at least one measure, the measured value of the humidity in the sequence is corrected. Method according to one of the preceding claims, wherein the at least one measure comprises comparing the measured value with a second lower threshold value and determining a defect of the moisture sensor when the second lower threshold value is undershot (208). Method according to one of the preceding claims, wherein the measured value of the humidity of the humidity sensor is further compared with an upper threshold (205), wherein at least a second measure is performed depending on the result of the comparison. Method according to Claim 8 wherein if the humidity reading of the humidity sensor is higher than the upper threshold, the humidity reading is corrected as the at least one second measure in the sequence. Method according to Claim 8 or 9 wherein the at least one second measure comprises comparing the measured value with a second upper threshold value and determining a defect of the moisture sensor when the second upper threshold value is exceeded (208). Method according to one Claim 6 or 9 wherein the correction of the measured value of the air humidity is effected by an additive and / or a multiplicative correction term. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims. Computer program that causes a computing unit, a method according to one of Claims 1 to 11 when executed on the computing unit. Machine-readable storage medium with a computer program stored thereon Claim 13 ,

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