DE102018216402A1 - Process for quality detection of a reducing agent - Google Patents

Abstract

The invention relates to a method for quality detection of a reducing agent (2) in a reducing agent tank (1) of an SCR system for an internal combustion engine by means of a measuring system (3), which has a sound source, a sound sensor and a stationary object (5), which is defined in a Distance to the sound source and the sound sensor is arranged. If the temperature of the reducing agent (2) is above a freezing point of the reducing agent (2) with the desired concentration, a sound wave (S) is emitted in the direction of the stationary object (5) from the sound source and the stationary object (5) reflects the sound wave (S) in the direction of the sound sensor as a reflection wave (R). If the reflection wave (R) is not received by the sound sensor, an error is concluded. If an error has been concluded and if the reducing agent tank (1) is at least filled to such an extent that the measuring system (3) is covered and if the measuring system (3) is recognized as error-free, it is concluded that the concentration of the reducing agent (2) deviates from the target concentration.

Description

The present invention relates to a method for quality detection of a reducing agent in a reducing agent tank of an SCR system. The invention further relates to a computer program that executes every step of the method when it runs on a computing device, and to a machine-readable storage medium that 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

Nowadays, the aftertreatment of exhaust gases from an internal combustion engine uses the SCR (Selective Catalytic Reduction) process to reduce nitrogen oxides (NOx) in the exhaust gas. The DE 103 46 220 A1 describes the basic principle. A 32.5% urea-water solution (HWL), also known commercially as AdBlue ^® , is metered into the exhaust gas. A metering system with a metering module is typically provided for this purpose in order to meter the HWL upstream of an SCR catalytic converter into the exhaust gas stream. Ammonia is split off from the HWL, which is then bound to the reactive surface of the SCR catalytic converter. There the ammonia combines with the nitrogen oxides, from which water and nitrogen arise. The HWL is conveyed from a reducing agent tank through a pressure line to the dosing module by means of a delivery module with a delivery pump.

The mass of the ammonia split off depends directly both on the mass of the metered urea-water solution and on the concentration of the urea in the urea-water solution - which is also referred to as the quality of the reducing agent or the urea-water solution - from.

It is therefore relevant for the functioning of the SCR system to monitor the quality of the HWL. If the concentration of urea or the quality of the reducing agent is too low, less nitrogen oxide is converted and the efficiency of the SCR catalyst drops. If the concentration of urea is too high or the quality of the reducing agent is too high, the converted ammonia does not react with the nitrogen oxides and passes through the SCR catalytic converter; Ammonia slip occurs.

The US 9,038,442 B2 describes a system and a method for determining the quality and the quantity of the reducing agent. To determine the quality, the system has a transducer and a stationary object attached at a known distance from the transducer. The transducer is set up to emit a sound wave in the horizontal direction onto a stationary object and to receive a reflection wave (an echo) from the stationary object. A temperature sensor is also provided, which measures the temperature of the reducing agent. The quality is now determined on the basis of the sound wave and the reflection wave as well as the temperature by a control unit. A transducer is also called a transducer and can be designed as an ultrasonic transducer or ultrasonic head in special cases. Accordingly, (measuring) transducers, (ultrasound) transducers and ultrasound heads are each ultrasound sources.

However, this process assumes that the reducing agent is in the liquid state. The freezing point of the 32.5% urea-water solution mentioned above is approx. -11 ° C, so that in practice it can happen that the reducing agent to be investigated is frozen. When frozen, the transmission for the sound waves changes so that the reflection wave no longer reaches the transducer. Therefore, the quality cannot be determined by the above method.

In the event that the reflection wave does not reach the converter, an error is output. In general, however, it cannot be directly concluded that if the transducer does not receive a reflection wave, the reducing agent is frozen, rather other sources of error, in particular an empty reducing agent tank or a defective transducer, have to be considered. Fill level sensors are known to determine the fill level of the reducing agent tank and thus also to recognize the case that the reducing agent tank is empty. In addition, methods for monitoring the converter are known.

Disclosure of the invention

A method for quality detection of a reducing agent in a reducing agent tank of an SCR system for an internal combustion engine is proposed. A measuring system is provided which has a sound source, a sound sensor and a stationary object which is arranged at a defined distance from the sound source and the sound sensor. As a preferred embodiment, the sound source is an ultrasound source. The sound source and the sound sensor preferably form a unit and are designed, for example, as measuring transducers, also called transducers, and specifically as ultrasonic heads.

Conventionally, it is provided to determine the concentration of the reducing agent in the liquid state. It is one Temperature threshold provided, which represents the freezing point of the reducing agent at the target concentration. The target concentration is the concentration from which it is assumed that the reducing agent used has it and which is assumed in further operation, for example as part of metering strategies. The temperature threshold is therefore selected depending on the reducing agent used and can be read, for example, from a table or determined in advance by tests. It can therefore be assumed according to the definition of the temperature threshold that the reducing agent is in the liquid state at the target concentration at a temperature above the temperature threshold. The preferred temperature threshold is the freezing point of a typically used urea-water solution, which is around -11 ° C. The temperature is preferably measured by a temperature sensor on or in the reducing agent tank.

If the temperature is above the freezing point of the reducing agent with the target concentration, the diagnosis is made. Here, a sound wave is emitted from the sound source in the direction of the stationary object. There the stationary object reflects the sound wave in the direction of the sound sensor. The reflected sound wave is referred to below as the “reflection wave”. If the reflection wave is not received by the sound sensor, an error is concluded. General sources of error are a malfunction of the measuring system or an insufficient fill level of the reducing agent, in which the sound sensor and the stationary object as well as the sound path in between, i.e. the measuring system, are not covered.

If an error has been concluded, it is checked whether the other sources of error can be excluded. Devices and methods for recognizing these sources of error are already known. Specifically, this means that the reducing agent tank is filled with the reducing agent solution at least to such an extent that the measuring system is covered, ie. H. Both the sound source and the sound sensor - or the transducer - as well as the stationary object and the sound path in between are covered by the reducing agent. The fill level can preferably be monitored by a fill level sensor. In addition, the measuring system is recognized as error-free by means of a diagnostic method, i. H. the sound source and the sound sensor - or the transducer - are functional and correctly set and adjusted for use, and the stationary object is correctly aligned. Depending on the diagnosis, the measuring system can be checked during use or during maintenance. If the temperature is measured by a temperature sensor as described above, its functionality and calibration are also checked.

According to the method, in this case, in which the temperature is above the temperature threshold and in which an error has been concluded, but the above-mentioned sources of error can be excluded, it is concluded that the concentration of the reducing agent deviates from the target concentration. The reason for this is that if all other sources of error can be excluded, only the transmission properties of the reducing agent can be responsible for the error. These change particularly strongly when the reducing agent is frozen, to such an extent that the sound wave can no longer be reflected in the intended manner and therefore no reflection wave can be detected by the sound sensor. The error therefore comes from a frozen reducing agent. However, since the temperature is above the temperature threshold that represents the freezing point of the reducing agent at the target concentration, the reducing agent can only freeze if the concentration of the reducing agent deviates from the target concentration.

This method enables the reducing agent to be recognized in quality even in the frozen state.

A urea-water solution is typically used as the reducing agent. The freezing point for a 32.5% urea-water solution is -11 ° C at the target concentration. The temperature is advantageously above this freezing point of the urea-water solution at the desired concentration. As a result, the frequently occurring case that the reducing agent tank is filled with water instead of the urea-water solution can be recorded. Because the additional water introduced reduces the concentration of the urea-water solution and the freezing point shifts to 0 ° C as the concentration decreases.

Accordingly, it is advantageous that the method is only carried out when the temperature in the case of water-based reducing agents is below 0 ° C., since a freezing point which is above this is not reached.

The method is preferably carried out immediately after the start of the internal combustion engine. At this point, additional heaters that are used to thaw the reducing agent are not yet fully operational.

A fill level meter already mentioned is typically not able to measure the fill level of the reducing agent in the frozen state. A fill level last stored as valid, which was previously determined by the fill level sensor, is preferably used to assess whether the measuring system is covered.

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

By loading the computer program onto a conventional electronic control device, the electronic control device is obtained which is set up to carry out the quality detection of the reducing agent.

Figure list

• 1 zeigt eine schematische Darstellung eines Reduktionsmitteltanks mit einem Messsystem, bei dem das erfindungsgemäße Verfahren durchgeführt werden kann.
• 2 zeigt ein Ablaufdiagramm eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens.

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

• 1 shows a schematic representation of a reducing agent tank with a measuring system in which the inventive method can be carried out.
• 2nd shows a flow chart of an embodiment of the inventive method.

Embodiment of the invention

1 shows a schematic representation of a reducing agent tank 1 for an SCR system of an internal combustion engine, not shown, which is equipped with a reducing agent 2nd is filled. The preferred reducing agent 2nd for the SCR is a 32.5% urea-water solution. At the bottom of the reducing agent tank 1 is a measuring system 3rd for quality detection of the reducing agent 2nd arranged. The measuring system 3rd has a transducer 4th and a stationary object 5 on, which are formed in one piece in this embodiment. In this embodiment, the stationary object 5 horizontal to the transducer 4th and arranged at a predetermined distance from it. The transducer 4th serves as a sound source for a sound wave S he towards the stationary object 5 broadcasts. The stationary object 5 is set up and aligned so that the sound wave S is reflected and as a reflection wave R to the transducer 4th runs back. At the same time is the transducer 4th set up the reflection wave R to receive and thus serves as a sound sensor. The transducer 4th is on a circuit board 6 within the measurement system 3rd trained, which as an interface to an electronic control unit 7 serves, the electronic control unit 7 the transducer 4th controls and records and processes the received signals. On the circuit board 6 is also a temperature sensor 8th provided the the temperature T of the reducing agent 2nd measures and the measured value to the electronic control unit 7 passes on. It is also inside the reducing agent tank 1 a level meter 9 arranged. This records how far the reducing agent tank 1 is filled, ie the height up to which the reducing agent 2nd in the reducing agent tank 1 stands. The fill level is sent to the electronic control unit 7 transferred, validated and saved there.

2nd shows a flow chart of an embodiment of the inventive method. The process is carried out immediately after the engine starts and starts when in a query 10th the currently measured temperature T of the reducing agent above a temperature threshold T _S which is the freezing point of the reducing agent 2nd represented at target concentration. In this exemplary embodiment, the target concentration is the concentration which is assumed for the typically used 32.5% urea-water solution and which is assumed in the dosing strategy for the SCR. In this embodiment, the temperature threshold is T _S at -11 ° C, because the freezing point of the 32.5% urea-water solution is here. Is the temperature T below the temperature threshold Ts or corresponds to this, the procedure is ended 11 and the quality of the reducing agent 2nd can be determined by other, already known methods which are not described further here. Is the temperature T however, above the temperature threshold T _S , it can be assumed that the 32.5% urea-water solution, i.e. the reducing agent 2nd , is not frozen, but is in the liquid state. With the urea-water solution it is also provided that for temperatures T above 0 ° C, the process is also not carried out, since in this case the urea-water solution freezes at any concentration, even with pure water. It is done as in 1 shown sending out 12th the sound wave S through the transducer 4th , the reflection of the sound wave S at the fixed object 5 and the return of the reflection wave R to the transducer 4th . Reaches the reflection wave R the transducer 4th , it will be captured by it 13 . Will be when capturing 13 the reflection wave R in a query 14 If no error is found, the process is ended 11 and the quality of the reducing agent 2nd can be determined by other, already known methods.

However, is in the query 14 an error detected because no reflection wave R through the transducer 4th detected 13 the type of error is first determined. For this purpose, the various sources of error are checked by known diagnostic methods, which are described in 2nd as different queries 15 , 16 , 17th are shown. The queries 15 , 16 , 17th or the diagnostic procedures can be carried out simultaneously or in succession. It is also possible that diagnostic methods have already been carried out in advance, provided that the robustness of the respective diagnostic method makes it possible and the result is still valid during the method according to the invention. Firstly, the fill level of the reducing agent 2nd in the reducing agent tank 1 checked 15 . Since, according to the invention, it cannot be assumed that the reducing agent 2nd is not frozen, the current level, which is in the frozen state with the conventionally used level meters, is not 9 can not be determined anyway, but the last level saved as valid F _lgs used. Is the measuring system 3rd , more precisely the transducer 4th , the stationary object 5 and that of the gush waves S and the reflection waves R passed sound path through the reducing agent 2nd covered, this source of error can be excluded. The second is the measuring system 3rd checked for functionality 16. It is checked more precisely whether the transducer 4th is able to emit and also receive sound waves. The third is the functionality and the calibration of the temperature sensor 8th checked 17th . If both are the case, the measuring system itself can be excluded as a source of error.

If the source of the error is through one of these queries 15 , 16 , 17th found, in other words, is one of the diagnostic procedures provided by these queries 15 , 16 , 17th represents the error, the method is ended 11 . No statements can then be made about the quality of the reducing agent 2nd be taken because the cause of the error lies in the measurement itself. However, the source of the error is not one of the queries mentioned 15 , 16 , 17th determined, in other words, if the error is not found by any of the diagnostic methods mentioned, it is determined according to the invention 18 that the error can only result from the fact that the reducing agent 2nd is frozen. Taking into account the beginning of the query 10th established premise that the temperature T of the reducing agent above the temperature threshold T _S lies, which represents the freezing point for the reducing agent at the desired concentration, according to the invention from the knowledge that the reducing agent 2nd is still frozen, concluded that the concentration of the reducing agent 2nd deviates from the target concentration 19th . In the event that the reducing agent is the urea-water solution already mentioned, the higher temperature indicates T , in which the urea-water solution is frozen, to a lower concentration in relation to the target concentration and thus to an increased water content.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• DE 10346220 A1 [0002]
• US 9038442 B2 [0005]

Claims (9)

Method for quality detection of a reducing agent (2) in a reducing agent tank (1) of an SCR system for an internal combustion engine by means of a measuring system (3), which has a sound source, a sound sensor and a stationary object (5) which is at a defined distance from the sound source and is arranged to the sound sensor, in which, when the temperature (T) of the reducing agent (2) lies above a freezing point of the reducing agent (2) with the desired concentration, a sound wave (S) from the sound source in the direction of the stationary object (5 ) is emitted (12) and the stationary object (5) reflects the sound wave (S) in the direction of the sound sensor as a reflection wave (R), and if the reflection wave (R) is not received by the sound sensor, an error is concluded ( 14), characterized in that if an error has been concluded (14) and if the reducing agent tank (1) is filled at least to the extent that the measuring system em (3) is covered and if the measuring system (3) is recognized as error-free, it is concluded that the concentration of the reducing agent (2) deviates from the target concentration (19). Procedure according to Claim 1 , characterized in that the temperature (T) is above the freezing point for a urea-water solution with the desired concentration. Procedure according to Claim 1 or 2nd , characterized in that the temperature (T) is below 0 ° C. Method according to one of the preceding claims, characterized in that it is carried out directly after starting the internal combustion engine. Method according to one of the preceding claims, characterized in that the temperature (T) is determined by a temperature sensor (8). Method according to one of the preceding claims, characterized in that for evaluating (15) whether the measuring system (3) is covered by the reducing agent _solution (2), a fill level (F _lgs ) last stored as valid which was previously stored by a fill level sensor (9 ) was determined, is used. Computer program, which is set up each step of the method according to one of the Claims 1 to 6 perform. Machine-readable storage medium on which a computer program Claim 7 is saved. Electronic control device (7), which is set up to use a method according to one of the Claims 1 to 6 perform the quality detection of the reducing agent (2).

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