DE102017200533A1 - Method for monitoring a quality sensor - Google Patents

Abstract

A method for monitoring a quality sensor for a reducing agent solution includes detecting a change in a concentration signal (cmess) of the quality sensor in an evaluation period (Δt), measuring a temperature change (ΔT) of the reducing agent solution in an evaluation period (Δt), and calculating an expected change in one Concentration signal (c) from the change in temperature (.DELTA.T). Depending on a comparison of the change of the concentration signal (c) with the expected change of the concentration signal (c), an error of the quality sensor is inferred.

Description

The present invention relates to a method for monitoring a quality sensor for a reducing agent solution. Furthermore, the present invention relates to a computer program executing each step of the method and to a machine-readable storage medium storing the computer program. Finally, the invention relates to an electronic control device which is set up to carry out the method.

State of the art

For the reduction of nitrogen oxides in the exhaust of motor vehicles SCR catalysts (Selective Catalytic Reduction) can be used. These reduce nitrogen oxide molecules to elemental nitrogen in the presence of ammonia as a reducing agent on the catalyst surface. The reducing agent is provided in the form of an ammonia-splitting urea-water solution (HWL), which is injected into the exhaust line through a metering device upstream of the SCR catalyst.

The HWL is commercially available as AdBlue ^® and is stored in a reducing agent tank. In order to save the cost of the HWL, it happens that drivers refuel the reducing agent tank with dilute HWL or with water. The legislation of various countries therefore requires that a quality sensor be installed in the reducing agent tank, which monitors the concentration of the HWL. This may be, for example, an optical sensor which measures the refractive index of the HWL or an ultrasonic sensor which measures the transit time of an ultrasonic signal in the HWL. If a too low HWL concentration is detected, a warning is issued to the driver. If this does not then replace the dilute HWL within a certain time by HWL the required concentration, the vehicle is automatically shut down.

In order to avoid this monitoring, manipulations are known in which the quality sensor is removed from the reducing agent tank and hung in a small separate vessel with HWL of the required concentration. The legislation of several states therefore calls for monitoring the quality sensor in order to rule out such manipulation.

Disclosure of the invention

The method for monitoring a quality sensor for a reducing agent solution comprises detecting a change of a concentration signal of the quality sensor in an evaluation period. In the evaluation period, a temperature change of the reducing agent solution is measured. An expected change in the concentration signal is calculated from the temperature change. In response to a comparison of the change in the concentration signal with the expected change in the concentration signal, an error of the quality sensor is inferred.

This method makes use of the fact that the measuring principles used by conventional quality sensors are temperature-dependent. For example, the refractive index of a HWL, which is evaluated in the optical concentration determination depends not only on the urea concentration of the HWL, but also on their temperature. Furthermore, the speed of sound of ultrasound in a HWL depends not only on their concentration, but also on their temperature. Since these relationships are known, it is possible to calculate from the temperature change how the measured concentration signal should change during the evaluation period. If it deviates significantly from the expected behavior, then a defect or a manipulation of the quality sensor can be inferred.

The measurement of the temperature change can be carried out in particular by means of a permanently installed in the reducing agent tank temperature sensor. Such temperature sensors belong to the standard equipment of reducing agent tanks, so that no additional temperature sensor has to be installed specifically for carrying out the method.

The evaluation period is preferably selected such that a predetermined increase in the temperature of the reducing agent solution takes place in it. In this way, a sufficient trustworthiness of the monitoring result can be ensured. A rise in temperature occurs after the start of an internal combustion engine, in whose exhaust system the reducing agent solution is injected, due to a pressure build-up and a return flow of HWL into the reducing agent tank from a metering valve.

Closing to an error of the quality sensor can be realized in various ways in different embodiments of the method:

In one embodiment, the closure is for a quality sensor fault by comparing an absolute change in the concentration signal between the beginning and end of the evaluation period with an expected absolute change in the concentration signal between the beginning and end of the evaluation period.

In another embodiment of the method, the closure is based on an error of the quality sensor in that an integral of all changes of the concentration signal in the evaluation period is compared with an expected integral of all changes of the concentration signal in the evaluation period.

In yet another embodiment, the closure is responsive to an error of the quality sensor by comparing an integral of the gradients of all changes in the concentration signal in the evaluation period with an expected integral of the gradients of all changes in the concentration signal in the evaluation period.

If the reducing agent tank is very large or thermally insulated well installed, the temperature of the reducing agent solution may increase too slowly to allow for trustworthy monitoring of the quality sensor. In this case, it is preferable that the reducing agent solution is heated in the evaluation period. For this purpose, in particular a tank heater can be used, which is installed in the reducing agent tank to thaw frozen frozen water. In particular, it can also be provided that the method is initially carried out without active heating of the reducing agent solution. If it is concluded that an error of the quality sensor, carried out a new implementation of the process while heating the reducing agent solution to make the monitoring result plausible.

In order to avoid erroneous monitoring results, the implementation of the method can be coupled to release conditions. In particular, the release condition may be that no fault of the quality sensor and / or the temperature sensor is present, that the quality sensor and / or the temperature sensor is ready for measurement, and that at least a predetermined volume fraction of the HWL at an ambient temperature which is below the freezing temperature of the HWL thawed.

The computer program is set up to carry out each step of the method, in particular if it runs on a computing device or an electronic control unit. It allows the implementation of the method on an electronic control unit, without having to make any structural changes. For this purpose it is stored on the machine-readable storage medium.

By loading the computer program onto a conventional electronic control unit, the electronic control unit is set up, which is set up to monitor a quality sensor for a reducing agent solution by means of the method.

list of figures

• 1 zeigt schematisch einen Reduktionsmitteltank, in dem ein Qualitätssensor angeordnet ist, welcher mittels eines Verfahrens nach einem Ausführungsbeispiel der Erfindung überwacht werden kann.
• 2 zeigt ein Ablaufdiagramm eines Verfahrens gemäß einem Ausführungsbeispiel der Erfindung.
• 3 zeigt in einem Diagramm den zeitlichen Verlauf von Konzentrationssignalen in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens, in dem der Reduktionsmitteltank nicht beheizt wird, wenn der überwachte Qualitätssensor intakt ist.
• 4 zeigt in einem Diagramm den zeitlichen Verlauf von Konzentrationssignalen in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens, in dem der Reduktionsmitteltank nicht beheizt wird, wenn der Qualitätssensor manipuliert wurde.
• 5 zeigt in einem Diagramm den zeitlichen Verlauf von Konzentrationssignalen in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens, in dem der Reduktionsmitteltank aktiv beheizt wird, wenn der überwachte Qualitätssensor intakt ist.
• 6 zeigt in einem Diagramm den zeitlichen Verlauf von Konzentrationssignalen in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens, in dem der Reduktionsmitteltank aktiv beheizt wird, wenn der Qualitätssensor manipuliert wurde.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

• 1 schematically shows a reducing agent tank in which a quality sensor is arranged, which can be monitored by a method according to an embodiment of the invention.
• 2 shows a flowchart of a method according to an embodiment of the invention.
• 3 shows in a diagram the time course of concentration signals in an embodiment of the inventive method in which the reducing agent tank is not heated when the monitored quality sensor is intact.
• 4 shows a diagram of the time course of concentration signals in an embodiment of the inventive method in which the reducing agent tank is not heated when the quality sensor has been manipulated.
• 5 shows in a diagram the time course of concentration signals in an embodiment of the inventive method in which the reducing agent tank is actively heated when the monitored quality sensor is intact.
• 6 shows in a diagram the time course of concentration signals in an embodiment of the inventive method in which the reducing agent tank is actively heated when the quality sensor has been manipulated.

Embodiments of the invention

A reducing agent tank 10 for an SCR catalyst system is in 1 shown. He has a reducing agent line 11 on, with a reducing agent solution 20 from the reducing agent tank 10 can be pumped to a metering valve, not shown, of the SCR catalyst system. In the reducing agent tank 10 are a quality sensor 12 and a temperature sensor 13 arranged to increase the concentration and temperature of the reducing agent solution 20 to measure and to an electronic control unit 30 pass. A tank heater 14 is at the bottom of the reducing agent tank 10 arranged.

A start 40 an embodiment of the method according to the invention takes place, as in 2 is shown, if any required release conditions for the method are met. A change of a concentration signal of the quality sensor 12 is detected 42. In addition, by means of the temperature sensor 13 a temperature change of the reducing agent solution 20 measured 43. This will continue until a test 44 shows that a given temperature change ΔT of the reducing agent solution 20 is done. Then, from the temperature change .DELTA.T, an expected change in the concentration signal is calculated 46. By comparing the change in the concentration signal with the expected change in the concentration signal, it is concluded 47 whether the quality sensor 12 okay is 48 or if a mistake 49 the quality sensor 20 is present. This error can be a manipulation. This first embodiment of the method according to the invention does not provide for active heating of the reducing agent solution 20 in front. Rather, the temperature change .DELTA.T is due to a reflux of heated reductant solution 20 into the reducing agent tank 10 ,

In a second embodiment of the method according to the invention takes place after the start 40 a heating 41 the reducing agent solution 20 by means of the tank heater 14 , When the exam 44 indicates that the desired temperature change .DELTA.T has occurred, the tank heating 14 switched off again 45.

The closing 47 to a mistake of the quality sensor 20 takes place in different embodiments of the method according to the invention by an absolute change of the concentration signal between the beginning and the end of an evaluation period in which the temperature change is compared with an expected absolute change of the concentration signal between the beginning and the end of the evaluation period, or by a Integral of all changes of the concentration signal in the evaluation period with an expected integral of all changes of the concentration signal in the evaluation period, or by comparing an integral of the gradients of all changes of the concentration signal in the evaluation period with an expected integral of the gradients of all changes of the concentration signal in the evaluation period ,

3 shows as in the evaluation period .DELTA.t the temperature T of the reducing agent solution 20 from an initial value T ₁ at the beginning t _{1 of} the evaluation period Δt increases by the temperature change ΔT to a final value T ₂ at the end t _{2 of} the evaluation period .DELTA.t. In this evaluation period Δt, the measured concentration _signal c _{mess increases} . The course of the expected concentration signal c _{is to} follow that of the measured signal c _mess . It is therefore concluded 47 that the quality sensor 12 okay is 48.

In contrast to the representation in 3 the measured concentration _signal c _{mess changes} in 4 in the evaluation period .DELTA.t substantially not, while due to the temperature change .DELTA.T is expected that the concentration signal c _soll increases. Therefore it is concluded 47 that the quality sensor 12 has an error 49.

5 shows the time course of the temperature T and the concentration _signals c _mess , c _should in an embodiment of the method according to the invention, in which an active heating 41 the reducing agent solution 20 he follows. This results in a faster temperature change .DELTA.T, whereby the evaluation period .DELTA.t shortened. Nevertheless, the expected change of the concentration signal c _soll in the evaluation period Δt is so significant that the result of the monitoring is trustworthy. If, as in 5 is shown, the measured concentration _signal c _mess the expected concentration signal c _should follow, it is concluded 47, that the quality sensor 12 okay is 48.

6 shows a case in which the measured concentration _signal c _mess does not change significantly in the evaluation period .DELTA.t. Since it deviates significantly from the expected concentration signal c _soll , it is concluded 47 that the quality sensor 20 has an error 49.

Claims (9)

Method for monitoring a quality sensor (12) for a reducing agent solution (20), comprising the following steps: - detecting (42) a change in a concentration signal (cmess) of the quality sensor (12) in an evaluation period (Δt), - measuring (43) a Temperature change (ΔT) of the reducing agent solution (20) in an evaluation period (Δt), - calculating (46) an expected change in the concentration signal (c _soll ) from the temperature change (ΔT), - closing (47) to an error of the quality sensor (20) as a function of a comparison of the change in the concentration signal (cmess) with the expected change in the concentration signal (c _soll ). Method according to Claim 1 , characterized in that the evaluation period (Δt) is selected such that in it a predetermined increase in temperature of the reducing agent solution (20) takes place. Method according to Claim 1 or 2 characterized in that the closure (47) is for an error of the quality sensor (12) by an absolute change of the concentration signal (cmess) between the beginning (t ₁ ) and the end (t2) of the evaluation period (Δt) with an expected absolute change of the concentration signal (c _soll ) between the beginning (t ₁ ) and the end (t ₂ ) of the evaluation period (.DELTA.t) is compared. Method according to Claim 1 or 2 characterized in that the closure (47) is for an error of the quality sensor (12) by an integral of all changes in the concentration signal (cmess) in the evaluation period (Δt) with an expected integral of all changes in the concentration signal (c _soll ) in the Evaluation period (.DELTA.t) is compared. Method according to Claim 1 or 2 characterized in that the closure (47) is for an error of the quality sensor (12) in that an integral of the gradients of all changes of the concentration signal (cmess) in the evaluation period (Δt) with an expected integral of the gradients of all changes of the concentration signal (c _should ) in the evaluation period (.DELTA.t) is compared. Method according to one of Claims 1 to 5 , characterized in that in the evaluation period (.DELTA.t), the reducing agent solution (20) is heated (41). Computer program, which is set up, each step of the procedure according to one of Claims 1 to 6 perform. Machine-readable storage medium on which a computer program is based Claim 7 is stored. An electronic control device (30) arranged to provide a quality sensor (12) for a reductant solution (20) by a method according to any one of Claims 1 to 6 to monitor.

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