DE102015215388A1 - Method for calculating the quality of a reducing agent solution - Google Patents

Abstract

The invention relates to a method for quality calculation of a reducing agent solution by means of a quality sensor, wherein a sensor value of the quality sensor is used as input for the signal processing in a transmitter, which has two filters having different time constants, and wherein (16) (17) is checked the slower of the two filters violates a first predefinable threshold value (b1) and checks whether the difference between the two filters violates a second predefinable threshold value (b2) and an error (E1, E2) is detected if at least one of the threshold values (b1, b2) is injured.

Description

The present invention relates to a method for the quality calculation of a reducing agent solution by means of a quality sensor. Furthermore, the invention relates to a computer program, which executes each step of the method according to the invention, while it runs on a computing device, as well as a machine-readable storage medium, which stores the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method according to the invention.

State of the art

To reduce nitrogen oxide emissions from motor vehicles, exhaust aftertreatment units are known in which a urea-water solution (HWL), which is stored in a storage device, for example in a tank, is fed to the exhaust gas line of a combustion unit, for example an internal combustion engine. To reduce nitrogen oxide emissions, the so-called Selective Catalytic Reduction (SCR) process is used. Since the HWL is consumed by the injection into the exhaust system of the internal combustion engine in the area of an SCR catalyst, it must be refilled from time to time.

The reduction of nitrogen oxides is only possible if the HWL has a sufficiently high quality. When filling the HWL tank with a HWL of inferior quality, however, a sufficient reduction of nitrogen oxides in the exhaust gas of the combustion unit is not ensured.

From the DE 10 2005 012 393 B4 A system for diagnosing the quality of a reagent solution, in particular an aqueous urea solution, is already known. The system includes, among other things, a reagent solution source, a device for determining the determination of a quality value according to the quality of the reagent solution, a first and a second filter, and a first and a second comparator. For example, the quality value is the concentration of the reagent in the reagent solution. The two filters each receive the quality value and each generate a first and a second filtered quality value. The first filtered quality value is compared by the first comparator with two thresholds, and an error value is generated when the first filtered quality value is outside the range indicated by the thresholds. The second filtered quality value is compared by means of the second comparator with a third threshold value and another error value is generated if the second filtered quality value exceeds or falls short of the third threshold value. Depending on the two error values obtained, the reagent quality monitoring logic block may be enabled or disabled.

Disclosure of the invention

The core of the invention is a method for the quality calculation of a reducing agent solution by means of a quality sensor, wherein a sensor value of the quality sensor serves as an input for the signal processing in an evaluation electronics. This transmitter has two filters, which have different time constants. The method checks whether the slower of the two filters violates a first predefinable threshold value and whether the difference between the two filters violates a second predefinable threshold value. An error is detected if at least one of the two thresholds is violated. Thus, advantageously, a misfueling can be carried out on the basis of the quality of the reducing agent solution by means of a relative comparison.

In particular, the two filters of the transmitter are designed as a PT1 filter. This is very advantageous because the PT1 filters have a simple and well-known transmission behavior known from the prior art.

In the method, a drift of the quality sensor is preferably detected when the first filter violates a first predefinable threshold value. Thus, a measurement-related error, in this case an error of the sensor, can be easily distinguished from an actually poor quality of the reducing agent solution.

Preferably, it is recognized in the method that there is a dilution of the reducing agent solution if the difference between the two filters violates the second predefinable threshold value. By means of this advantageous procedure, a poor quality of the reducing agent solution can be detected in a simple manner.

According to a preferred embodiment, the upper and lower frequencies of the sensor tube signal are cut off by the two filters and only one medium frequency range required for the evaluation is taken into account. This procedure is very advantageous because in this way the amount of data to be processed is reduced and thus a shorter computing time is achieved.

According to an advantageous embodiment of the invention, the method for the quality calculation of a reducing agent solution comprises several steps. First, a temperature change rate of the reducing agent solution in a refueling of a reducing agent tank with a reducing agent solution detected by means of a temperature sensor. In the second step, it is checked whether the detected temperature change rate is within predefinable limits. As soon as the temperature change rate is outside these limits, the calculation of the quality of the reducing agent solution is interrupted for a predeterminable period of time. This procedure is very advantageous because errors are avoided in this way, resulting from an excessive change in temperature.

Preferably, the calculation of the quality of the reducing agent solution is also interrupted as soon as the temperature of the reducing agent solution is outside predeterminable limits. This procedure is very advantageous, since on the one hand it is ensured that the reducing agent tank is thawed and, on the other hand, it is determined whether the reducing agent tank has an extreme temperature, ie a temperature outside the predefinable limits. The latter would lead to an inaccurate measurement.

Furthermore, the calculation of the quality of the reducing agent solution is preferably interrupted as soon as a value representing the quality of measurement of the quality sensor is below a predefinable threshold value. This procedure is very advantageous, since a faulty measured value is detected in a simple manner.

The invention further comprises a computer program which is set up to carry out each step of the method according to the invention, in particular if it is executed on a computing device or electronic control device. It allows the implementation of the method according to the invention on an electronic control unit, without having to make any structural changes thereto.

The invention also comprises a machine-readable storage medium on which the computer program is stored, and an electronic control unit which is set up to carry out the method according to the invention.

Further advantages and features of the invention will become apparent from the following description of embodiments in conjunction with the drawings. In this case, the individual features can be implemented individually or in combination with each other.

Brief description of the drawings

In the drawings show:

1 a schematic representation of the reducing agent solution tank and

2 a flowchart illustrating the flow of an embodiment of the method according to the invention for the quality calculation of a reducing agent solution.

Embodiments of the invention

To reduce nitrogen oxides in the exhaust of motor vehicles, the so-called Selective Catalytic Reduction (SCR) method is used. In this method, a reducing agent solution, eg urea water solution (HWL), which is also known under the name AdBlue ^® , injected into the exhaust system of the internal combustion engine. A correct reduction of nitrogen oxides is only possible if the reducing agent solution has a sufficiently high quality. Therefore, monitoring the quality of reducing agents is essential. The quality of the reducing agent solution is determined on the basis of the concentration of the reducing agent in the solution.

In 1 is a reducing agent solution tank 1 of an SCR catalyst system in which HWL acts as a reductant solution 2 located. At the bottom of the reducing agent solution tank 1 are in a structural unit 3 a quality sensor 31 and a temperature sensor 32 arranged. The quality sensor 31 is designed as an ultrasonic sensor. For removal of the reducing agent solution 2 from the reducing agent solution tank 1 is a sampling tube 4 intended.

In 2 are the individual steps of an embodiment of the method according to the invention for the quality calculation of a reducing agent solution 2 shown. First, a temperature change rate ( dT / dt ) of the reducing agent solution 2 when refueling a reducing agent tank 1 with the reducing agent solution 2 detected 10 , In this case, the temperature profile of the mixture of the refueled reducing agent solution 2 and already in the tank 1 contained reducing agent solution 2 in the course of time by means of the structural unit 3 included temperature sensor 32 measured. In the second step of the procedure is checked 11 whether the detected temperature change rate ( dT / dt ) within predefinable limits ( dT / dt ) _min and ( dT / dt ) _max , the difference of ( dT / dt ) _min and ( dT / dt ) is 3 K _max . Once the detected temperature change rate ( dT / dt ) is not within the predeterminable limits, the calculation becomes 18 the quality of the reducing agent solution 2 t _wait interrupted for a predefinable period of time 20 , Is the detected temperature change rate ( dT / dt ) within the predefinable limits ( dT / dt ) _min and ( dT / dt ) _max , so in the following step of the process, the absolute temperature T _tank in the tank 1 located reducing agent solution 2 by means of in the structural unit 3 included temperature sensor 32 detected 12 and it will checked 13 whether it is within the specifiable limits T _{tank, min} = -2 ° C and T _{tank, max} = +50 ° C. Once T _tank falls outside of these predeterminable limits, the calculation will turn 18 the quality of the reducing agent solution 2 for the predeterminable time t _wait = 60 seconds interrupted 20 , If the absolute temperature T _{tank is} within the specifiable limits T _{tank, min} and T _{tank, max} , then in the next step, the measuring quality of the quality sensor 31 representing value q detected 14 and it is being tested 15 whether the value q is below a predefinable threshold value q _s . An example of the value q is the number of echoes that the quality sensor 31 receives from the emitted ultrasonic pulses. If an echo is received for each emitted ultrasonic pulse, then the quality of measurement of the quality sensor is 31 very well. If, on the other hand, no echo is received, then the quality sensor has 31 a very bad quality of measurement. If the value q is greater than the threshold value q _s , the calculation will also be made in this case 18 the quality of the reducing agent solution 2 t _wait interrupted for a predefinable period of time 20 , If the value q is less than the threshold value q _s , the following is used to check whether the calculation of the quality of the reducing agent solution uses two filters that are part of an evaluation unit 2 can be carried out. As input value, both filters receive a sensor value of the quality sensor 31 , The two filters are designed as PT1 filters, have different time constants and intersect the upper and lower frequencies of the sensor tube signal of the quality sensor 31 so that only one medium frequency range required for the evaluation is considered. In the next step 16 The method checks whether one of the slower of the two PT1 filters violated a first predefinable threshold value b ₁ . If this is the case, then a first error E _{1 is} set, according to which a drift of the quality sensor 31 is present. If threshold b _{1 is} not violated, then in the next step 17 checked whether the difference of the two PT1 filter violated a second predetermined threshold b ₂ . If this is the case, then a second error E _{2 is} set, according to which a dilution of the reducing agent solution 2 is present. If the threshold b _{2 is} not violated, the calculation becomes 18 the quality of the reducing agent solution 2 carried out.

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

• DE 102005012393 B4 [0004]

Claims (11)

Method for calculating the quality of a reducing agent solution ( 2 ) by means of a quality sensor ( 31 ), characterized in that a sensor value of the quality sensor ( 31 ) is used as input for the signal processing in an evaluation electronics, which has two filters, which have different time constants, and that is checked ( 16 ) ( 17 ), whether the slower of the two filters a first predetermined threshold (b ₁ ) violated and that it is checked whether the difference of the two filters violated a second predetermined threshold (b ₂ ) and that an error (E ₁ , E ₂ ) is detected if at least one of the threshold values (b ₁ , b ₂ ) is violated. Method according to one of the preceding claims, characterized in that the two filters of the evaluation are designed as a PT1 filter. Method according to claim 1 or 2, characterized in that a drift of the quality sensor ( 31 ) is detected when the first filter violates the first predefinable threshold (b ₁ ). A method according to claim 1 or 2, characterized in that it is recognized that a dilution of the reducing agent solution ( 2 ) is present if the difference of the two filters violates the second predefinable threshold value (b ₂ ). Method according to one of the preceding claims, characterized in that the upper and lower frequencies of the sensor tube signal are cut off from the filters and only one medium frequency range required for the evaluation is taken into account. Method for calculating the quality of a reducing agent solution ( 2 ) according to one of the preceding claims, characterized in that the method comprises the following steps: a. Capture ( 10 ) a temperature change rate ( dT / dt ) of the reducing agent solution ( 2 ) during refueling of a reducing agent tank ( 1 ) with a reducing agent solution ( 2 ) by means of a temperature sensor ( 32 b. Check (11) whether the detected rate of change of temperature ( dT / dt ) within predefinable limits ( dT / dt ) _min and ( dT / dt ) _max is and c. Interruption ( 20 ) of a calculation ( 18 ) the quality of the reducing agent solution ( 2 ) for a predeterminable time period t _wait as soon as the temperature change rate ( dT / dt ) outside the specified limits ( dT / dt ) _min and ( dT / dt ) _max is. Method according to claim 6, characterized in that the calculation ( 18 ) the quality of the reducing agent solution ( 2 ) is also interrupted as soon as the temperature (T _tank ) of the reducing agent solution ( 2 ) outside specifiable limits (T _{tank, min} ) and (T _{tank, max} ). Method according to claims 6 and 7, characterized in that the calculation ( 18 ) the quality of the reducing agent solution ( 2 ) is interrupted as soon as the measuring quality of the quality sensor ( 31 ) representing value (q) is below a predefinable threshold value (q _s ). A computer program adapted to perform each step of the method of any one of claims 1 to 8. A machine-readable storage medium on which a computer program according to claim 9 is stored. Electronic control unit which is set up to carry out the method according to one of Claims 1 to 8.

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