KR20180002058A - Error detection in a scr-system by means of efficiency - Google Patents

Abstract

The present invention relates to a method of detecting an error in a SCR system of an internal combustion engine of a vehicle, wherein the SCR system has two SCR catalytic converters and two nitrogen oxide sensors. One nitrogen oxide sensor is arranged upstream of the two SCR catalytic converters, and the other nitrogen oxide sensor is arranged downstream of the SCR catalytic converters. The method comprises: a step (307) of establishing an ammonia charge level (NH3_charge level) in the established first SCR catalytic converter, wherein the ammonia charge level (NH3_charge level) is set to be lower than the maximum ammonia charge level of the SCR catalytic converter; a step (308) in which the concentration of the nitrogen oxide (NOx_ before treatment) is measured at the upstream of the SCR catalytic converters, and the concentration of NOx (NOx_ after treatment) is measured at the downstream of the SCR catalytic converters (NOx_ after treatment); a step (311) in which during an evaluation step, a comparison (311) of the predicted efficiency ( prediction) of the first SCR catalytic converter (201) and the actual efficiency ( actual) of the first SCR catalytic converter (201) is performed; and a step (320, 330) in which finally, an error is detected in at least one of the two SCR catalytic converters according to the comparison (311) of the predicted efficiency ( prediction) and the actual efficiency ( actual).

Description

ERROR DETECTION IN A SCR-SYSTEM BY MEANS OF EFFICIENCY < RTI ID = 0.0 >

The present invention relates to a method for error detection in an SCR system with two SCR catalytic converters, using efficiency. The invention also relates to a computer program for executing each step of the method when the invention is implemented on a computing device and to a machine-readable storage medium storing the computer program. Finally, the present invention relates to an electronic control device configured to perform this method.

Current widespread technology for reducing emissions of nitrogen oxides (NOx) in the automotive internal combustion engine, which is a selective catalytic reduction: the (S elective C atalytic R eduction SCR). In the SCR system, urea aqueous solution, which is also commercially available as AdBlue ^® , is injected by the injection module into the exhaust gas line upstream of at least one SCR catalytic converter. The ammonia separated from the urea aqueous solution reacts with the nitrogen oxides in the SCR catalytic converter in the selective catalytic reduction system to form elemental nitrogen.

With the introduction of stricter emission regulations, a plurality of SCR catalytic converters acting on the same exhaust gas are used. If the efficiency of the SCR catalytic converter is not sufficient to reduce nitrogen emissions in the exhaust gas line, error detection using a vehicle specific inspection method (typically implemented in an electronic control unit) is required. For this reason, continuous monitoring is performed during normal operation of the vehicle. In a typical test method, one or more nitrogen sensors are used upstream of the SCR catalytic converter, and one or more nitrogen sensors are used downstream of the SCR catalytic converter. In the case of only one SCR catalytic converter, two nitrogen sensors are sufficient to calculate the efficiency of the SCR system while monitoring the nitrogen emissions.

An extension of the SCR system to a plurality (n) of SCR catalytic converters in the same exhaust line, in order to determine one or more SCR catalytic converters with no function or malfunction, using a pin point strategy N + 1 < / RTI > nitrogen sensors of the conventional system as a precondition. Correspondingly, SCR catalytic converters with no function or poor performance can be repaired or replaced as desired, while SCR catalytic converters or SCR systems with good function are not affected. Of course, the use of a pinpoint strategy is not necessary during normal operation of the vehicle, since in this case it is sufficient to monitor the efficiency. In the case of a SCR catalytic converter which does not function at all or which is malfunctioning, for example, an alarm is transmitted to the driver through a signal lamp on the instrument panel, which causes the driver to drive the vehicle, for example, to a workshop. During operation at the workshop, the pinpoint strategy described above is used in the inspection method to detect SCR catalytic converters that do not function at all or are malfunctioning.

The method according to the invention relates to the SCR system of an automotive internal combustion engine. In this case, the SCR system has two SCR catalytic converters arranged in succession in one common exhaust gas line. The exhaust gas first passes through the first SCR catalytic converter and then to the second SCR catalytic converter, so that both of the two SCR catalytic converters act on the exhaust gas. Further, the SCR system also has two nitrogen sensors disposed in the exhaust gas line. A first nitrogen sensor is disposed upstream of the two SCR catalytic converters, wherein the nitrogen oxide concentration can be measured before treatment of the exhaust gas by the SCR catalytic converter. A second nitrogen sensor is disposed downstream of the two SCR catalytic converters, wherein the nitrogen oxide concentration after exhaust gas treatment by the SCR catalytic converter can be measured.

The method includes the following steps. First, the established ammonia charge level in the first SCR catalytic converter is set. This established ammonia charge level is lower than the maximum ammonia charge level that can be stored in the SCR catalytic converter. As a result, the amount of ammonia separated from the urea aqueous solution injected into the exhaust gas system is all stored in the first SCR catalytic converter. Accordingly, in the second SCR catalytic converter, ammonia is not provided for reduction, thereby not contributing to the reduction of nitrogen oxides.

Then, the nitrogen oxide concentration is measured not only upstream but also downstream of the SCR catalytic converters. Preferably the actual efficiency of the first SCR catalytic converter can be calculated from the ratio of the two nitrogen oxide concentrations. As the exhaust gas passes through both of the two SCR catalytic converters, the calculated actual efficiency is related only to the first SCR catalytic converter, since no ammonia is present in the second SCR catalytic converter and no reduction occurs.

According to one preferred aspect, with respect to the first SCR catalytic converter, the predictive efficiency of the first SCR catalytic converter can be determined from a characteristic curve representing the correlation between the efficiency and the ammonia charge level.

Subsequently, during the evaluation step, a comparison is made between the predicted efficiency and the actual efficiency of the first SCR catalytic converter. Finally, an error in at least one of the two SCR catalytic converters is detected based on the comparison result. At this time, particularly preferably, when the prediction efficiency and the actual efficiency of the first SCR catalytic converter are different from each other, an error is detected in the first SCR catalytic converter.

Optionally, at the beginning of the method, a measurement of the nitrogen oxide concentration upstream of the SCR catalytic converters and a measurement of the nitrogen oxide concentration downstream of the two SCR catalytic converters can be performed. In this case, the two SCR catalytic converters operate in the normal operating mode. If the nitrogen oxide concentration at the downstream of the two SCR catalytic converters does not match the predicted nitrogen oxide concentration, an error in the SCR system is detected. Particularly preferably, as described, if an error is detected in the SCR system and, furthermore, the predicted efficiency and the actual efficiency of the first SCR catalytic converter match each other, an error is detected in the second SCR catalytic converter.

According to another aspect, after the errory catalytic converter is repaired or replaced based on the above method, the vehicle travels over a determined interval and / or a fixed time, and the method can then be performed again . Therefore, a rare case in which two SCR catalytic converters have functional errors at the same time is also considered. Optionally, a larger error spectrum can be covered, since the evaluation step can be changed during the re-execution of the method.

A computer program according to the present invention is configured to perform each step of the method according to the present invention, particularly when executed in a computing device or a control device. This computer program makes it possible to carry out the method according to the invention without having to carry out a structural change in a conventional electronic control unit. To this end, the computer program is stored in a machine-readable storage medium.

An electronic control device configured to perform error detection in the SCR system is obtained by executing a computer program on a conventional electronic control device. In this case, the electronic control device may be a vehicle-specific control device or an external control device, for example, a diagnostic device connected to the SCR system during error detection to control the method.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are illustrated in the drawings and will be described in more detail in the following detailed description.
1 is a schematic diagram of an SCR system that includes two SCR catalytic converters and three nitrogen oxide sensors and in which error detection can be performed using conventional methods.
2 is a schematic diagram of an SCR system that includes two SCR catalytic converters and two nitrogen oxide sensors and in which error detection can be performed using the method according to the present invention.
Figure 3 is a flow diagram of one embodiment of a method according to the present invention.
4 is a graph of a characteristic curve of the efficiency of an SCR catalytic converter for an ammonia charge level, which can be used in an embodiment of the method according to the present invention.

1, there is shown a typical SCR system 100 of an automotive internal combustion engine, not shown, having a first SCR catalytic converter 101 and a second SCR catalytic converter 102, An error can be detected. Two SCR catalytic converters 101 and 102 are arranged in succession in one exhaust gas line 120 wherein a first SCR catalytic converter 101 is connected upstream of the two SCR catalytic converters 101 and 102, And is disposed closer to the injection module 130 that injects the aqueous solution into the exhaust gas line 120. The SCR system 100 also includes a first nitrogen oxide sensor 110 that is disposed between the injection module 130 and the first SCR catalytic converter 101 where the SCR catalytic converters 101 and & 102) can measure the nitrogen oxide concentration of the exhaust gas before the exhaust gas treatment (before the NOx_ treatment). The SCR system 100 also includes a second nitrogen oxide sensor 111 which is disposed downstream of the second SCR catalytic converter 102 and into which two SCR catalytic converters 101 and 102 are connected It is possible to measure the nitrogen oxide concentration (after NOx_ treatment) of the exhaust gas after the exhaust gas treatment. In addition, the SCR system includes another third NOx sensor 112, which is disposed between the first SCR catalytic converter 101 and the second SCR catalytic converter 102, The nitrogen oxide concentration of the exhaust gas after the exhaust gas treatment by the SCR catalytic converter 101 can be measured. The three nitrogen oxide sensors 110, 111 and 112 and the injection module 130 described above are connected to the electronic control unit 140 and are controlled by the electronic control unit.

In a conventional method for detecting an error, the actual difference between the nitrogen oxide concentration at the first nitrogen oxide sensor 110 and the nitrogen oxide concentration at the third nitrogen oxide sensor 112 or the actual difference between the nitrogen oxide concentration at the third nitrogen oxide sensor 112 The actual difference between the nitrogen oxide concentration of the second nitrogen oxide sensor 111 and the nitrogen oxide concentration of the second nitrogen oxide sensor 111 is calculated and compared with the predicted difference. If one or more of the actual differences do not match the corresponding expected difference, an error in the SCR catalytic converter 101 or 102 lying therebetween is estimated.

Figure 2 shows an SCR system 200 of an automotive internal combustion engine, not shown, which also includes a first SCR catalytic converter 201 and a second SCR catalytic converter 202, An error can be detected using the embodiment. The two SCR catalytic converters 201 and 202 are arranged in succession in one exhaust gas line 220 in which case the first SCR catalytic converter 201 is placed closer to the injection module 230 as described above do. Of course, the SCR system 200 shown in this figure may be provided downstream of the first NO x sensor 210 and the second SCR catalytic converter 202 disposed between the injection module 230 and the first SCR catalytic converter 201 Only the second nitrogen oxide sensor 211 is disposed. The two SCR catalytic converters 210 and 211 and the injection module 230 are connected to the electronic control unit and are controlled by the electronic control unit at least during error detection. In another embodiment, the electronic control device may be an external device coupled to the SCR system 200 during error detection.

The first nitrogen oxide sensor 210 measures the nitrogen oxide concentration (before NOx_treatment) of the exhaust gas before the exhaust gas treatment by the SCR catalytic converters 101 and 102, and the second nitrogen oxide sensor 211 measures two (After NOx_treatment) of the exhaust gas after the exhaust gas treatment by the SCR catalytic converters 101 and 102 is measured. Therefore, the SCR system 200 shown in Fig. 2 differs from the SCR system shown in Fig. 1 only in that a third nitrogen oxide sensor 112 is unnecessary.

One embodiment of a method according to the present invention for detecting errors in the SCR system 200 described above is shown in the flow chart in Fig. In the first step, a measurement 300 of the nitrogen oxide concentration (before NOx_treatment) in the first nitrogen oxide sensor 210 and the nitrogen oxide concentration (after NOx_treatment) in the second nitrogen oxide sensor 211 . (After NOx_treatment) after the exhaust gas treatment by the two SCR catalytic converters 201 and 202 deviates from the predicted value derived from the nitrogen oxide concentration (before NOx_treatment) and the conversion rate of the two SCR catalytic converters , An error in the SCR system 200 is detected (301). In other words, in at least one (201 or 202) of the two SCR catalytic converters, rarely both, functional errors and / or at least a reduction in conversion rate occur. If no error is detected 301 within the SCR system 200, the method ends (302).

Otherwise, in the next step, the internal combustion engine of the stationary vehicle is switched to the no-load mode (303) and then operated (304) at the determined operating point. Thereafter, the process waits until the nitrogen oxide concentration (before the NOx_ treatment) in the first nitrogen oxide sensor 210 becomes equal to the nitrogen oxide concentration (after the NOx_ treatment) in the second nitrogen oxide sensor 211 Next, urea aqueous solution is injected 306 into the exhaust gas line 220. As a result, 1 SCR catalytic converter 201 ammonia charge level (NH ₃ _ charge level) increases until reaching the value determined is the maximum ammonia charge level of the final value of claim 1 SCR catalytic converter than low. As a result, the second SCR catalytic converter is no longer supplied with ammonia, and does not contribute to the reduction of nitrogen oxides in the exhaust gas. The final ammonia charge level is reached (NH ₃ _ charge level), on the one hand, the nitrogen in the first NOx sensor 210 NOx concentration (NOx_ before treatment) and the second NOx sensor 211 in the oxide The measurement 308 of the concentration (after NOx_treatment) is performed again and the actual efficiency ([eta] actual) of the first SCR catalytic converter 201 is determined based on the measurement 308. [ On the other hand, it is determined the prediction efficiency (η prediction) of claim 1 SCR catalytic converter 201 in the charge level on the basis of ammonia (NH ₃ _ charging level), the SCR catalyst converter 1 201 confirmed. To this end, the characteristic curve 400 of the first SCR catalytic converter shown in FIG. 4 is used.

In the comparison (311), the actual efficiency (? Actual) and the prediction efficiency (? Prediction) are compared during the evaluation step. An error is detected 320 in the first SCR catalytic converter 201 if only the first SCR catalytic converter is present in the exhaust gas, It contributes to reduction. As another step 321, the first SCR catalytic converter 201 in error is repaired or replaced. If the actual efficiency (? Actual) and the prediction efficiency (? Prediction) coincide with each other, an error in the first SCR catalytic converter (201) can not be confirmed. However, it can be assumed that there is an error in the second SCR catalytic converter 202 because an error in the SCR system 200 has been detected in the measurement 300. Correspondingly, in this case, an error is detected at the second SCR catalytic converter 202 (330). In this case also, as the next step 331, the second SCR catalytic converter 202 with the error is repaired or replaced.

In order to rule out the rare case of errors in both SCR catalytic converters 201 and 202, particularly when an error is detected (320) in the first SCR catalytic converter 201, And travels through the determined section (340). Then, the method is repeated from the beginning. In another embodiment, the evaluation step at the iteration of the method can be changed.

4, there as described above, the characteristic curve 400 of the efficiency (η) according to the charge level of ammonia (NH ₃ _ charge level) is shown. Point 401, the charge level of ammonia (NH ₃ _ charge level) determined at step 307 is written. Point 402 also indicates the coincidence of the actual efficiency (? Actual) and the predictive efficiency (? Prediction) that can be read with respect to the point 401 from the characteristic curve (400). On the other hand, the point 403 indicates the actual efficiency (? Actual) that does not coincide with the prediction efficiency (? Prediction) because it does not match the characteristic curve 400.

Claims (11)

A method for detecting an error in an SCR system (200) of an automotive internal combustion engine having two SCR catalytic converters (201, 202) and two nitrogen oxide sensors (210; 211) The upstream of the two SCR catalytic converters 201, 202 and the downstream of the nitrogen oxide sensor 211 are arranged in the following steps:
- confirmation of claim 1 SCR catalytic converter 201 ammonia charge level, the method comprising: setting a (NH ₃ _ charging level), the ammonia charge level (NH ₃ _ charge level) up to ammonia of the SCR catalytic converter (201) Setting (307) to be less than the charge level,
- measuring the nitrogen oxide concentration (after NOx_treatment) upstream of the SCR catalytic converter 201 (202) and the NOx concentration (after NOx_treatment) downstream of the SCR catalytic converter 201 ),
- comparing (311) the predicted efficiency (? Prediction) of the first SCR catalytic converter (201) to the actual efficiency (? Actual) of the first SCR catalytic converter (201) during the evaluation phase; And
- detecting (320; 330) an error in at least one of the two SCR catalytic converters (201; 202) according to a comparison (311) of the predictive efficiency , An error detection method in the SCR system. The method according to claim 1, wherein an error is detected (320) in the first SCR catalytic converter (201) when the actual efficiency (η actual) of the first SCR catalytic converter (201) Wherein the error is detected in the SCR system. 2. The method according to claim 1, wherein the concentration of nitrogen oxides upstream of the SCR catalytic converters (before NOx_treatment) and the concentration of NOx downstream of the two SCR catalytic converters (after NOx_treatment) A measurement 300 is performed and the two SCR catalytic converters 201 and 202 operate in a normal operating mode and the NOx concentration (after NOx_treatment) downstream of the two SCR catalytic converters 201 and 202 is predicted Wherein an error is detected (301) in the SCR system (200) if it does not match the nitrogen oxide concentration. 4. The method of claim 3, wherein if an error is detected (301) in the SCR system (200) and the actual efficiency (? Actual) of the first SCR catalytic converter (201) , And an error is detected (330) in the second SCR catalytic converter (202). 5. The method according to any one of claims 1 to 4, wherein after the errored SCR catalytic converter (201; 202) has been repaired or replaced (321; 331), the vehicle travels over a determined interval and / (340), and then the method is repeated. 6. The method of claim 5, wherein the evaluation step in the iteration of the method is changed. 5. A method according to any one of claims 1 to 4, wherein the actual efficiency (? Actual) of the first SCR catalytic converter (201) is determined by the NOx concentration (309) from the nitrogen oxide concentration (after NOx_treatment) at the upstream and downstream of the NOx treatment (309). 5. A method according to any one of claims 1 to 4, wherein the predictive efficiency (? Prediction) of the first SCR catalytic converter (201) is determined from a characteristic curve (400) for the first SCR catalytic converter ≪ / RTI > in the SCR system. A computer program configured to perform each step of the method according to any one of claims 1 to 4 and stored in a machine-readable storage medium. 10. A machine-readable storage medium having stored thereon a computer program according to claim 9. An electronic control device configured to perform error detection in an SCR system using the method according to any one of claims 1 to 4.

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