KR20180089301A - Method for detecting an error in an scr system by means of an ammonia slip - Google Patents

Abstract

The present invention relates to a method of detecting fault in an SCR system of a combustion engine including two SCR catalytic converters of a vehicle by using an ammonia slip. The invention includes two SCR catalytic converters and at least two nitrogen oxide sensors. A first nitrogen oxide sensor is disposed between two SCR catalytic converters and a second nitrogen oxide sensor is arranged downstream of the two SCR catalytic converters. The method includes the steps of: continuously detecting a signal (y_1) on the first nitrogen oxide sensor to calculate an ammonia mass (NH_3z) on the first nitrogen oxide sensor; and performing overdose step (203) by increasing an amount of a reducing agent mass (m_Dos). The converted ammonia mass of the first SCR catalytic converter exceeds the ammonia mass required for the reduction of nitrogen oxides until the ammonia charge level in the first SCR catalytic converter exceeds the maximum ammonia charge level of the first SCR catalytic converter. Thus, a first inspection step for checking the presence of ammonia slip in the first SCR catalytic converter is performed according to the signal of the first nitrogen oxide sensor. If there is ammonia slip in the first SCR catalytic converter, at least a first error detection step of the second SCR catalytic converter is performed.

Description

METHOD FOR DETECTING AN ERROR IN AN SCR SYSTEM BY MEANS OF AN AMMONIA SLIP [0002]

The present invention relates to a method for error detection using ammonia slip in an SCR system comprising two SCR catalytic converters. The present invention also relates to a computer readable storage medium storing a computer program as well as a computer program for executing each step of the method when executed on a computer. Finally, the present invention relates to an electronic control unit configured to execute the method.

In the exhaust gas of automobile internal combustion engine widespread technique today for the reduction of nitrogen oxides (NOx) is a selective catalytic reduction: a (SCR S elective- C atalytic- R eduction). In the SCR system, urea water, also known commercially as AdBlue 占 as a reducing agent solution, is injected through the dosing module into the exhaust pipe upstream of at least one SCR catalytic converter. The ammonia produced in the urea water reacts with nitrogen oxides in SCR catalytic converters during selective catalytic reduction to produce elemental nitrogen.

Through 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 converters for reducing nitrogen oxide emissions in the exhaust pipe is inadequate, error detection using vehicle specific inspection methods (usually implemented in electronic control units) is required. For this reason, continuous monitoring is performed during the normal mode of the vehicle.

In the case of the already known monitoring strategy, for example, the ammonia storage capacity of the SCR catalytic converters considered as a feature for failure of the SCR catalytic converter due to aging or damage is calculated. In this case, the SCR catalytic converter is first charged through the over-stoichiometric metering (so-called over-metering) of the reducing agent solution to the maximum ammonia charge level. When the maximum ammonia charge level is reached, the ammonia can no longer be stored by the SCR catalytic converter, and an ammonia slip occurs, where pure ammonia flows out downstream of the SCR catalytic converter. Nitrogen oxide sensors have cross sensitivity to ammonia, and thus, ammonia slip can be indirectly detected and used as a defined starting point. Subsequently, the metering addition of the reducing agent solution is reduced or reduced to a negligible extent, so that the stored ammonia is decomposed by selective catalytic reduction. On the other hand, for example, the efficiency of the SCR catalytic converter can be calculated, from which the storage capacity of the SCR catalytic converter can be deduced. Although this method can in principle be applied to two SCR catalytic converters, the metering input of the reducing agent solution is very strongly suppressed by the upstream SCR catalytic converter.

From DE 10 2012 202 671 A1 a method for the diagnosis of two SCR catalytic converters is known. Here, the aging state of the second SCR catalytic converter is detected based on the difference between the sensor signal of the first sensor and the sensor signal of the second sensor during emptying of the two SCR catalytic converters.

 DE 10 2012 220 151 A1 relates to a method for the inspection of two SCR catalytic converters. The inspection of the first SCR catalytic converter disposed upstream is carried out in such a manner that the nitrogen oxide concentration is controlled through the change of operating parameters of the internal combustion engine and / or the system. When the signal of the sensor disposed between the SCR catalytic converters is attenuated, the storage capability of the first SCR catalytic converter is judged to be insufficient. Similarly, the inspection of the downstream second SCR catalytic converter can be accomplished by first verifying the functionality of the first SCR catalytic converter and then again modulating the nitrogen oxide concentration through alteration of the operating parameters of the internal combustion engine and / or the system . When the signal of the sensor disposed downstream of the second SCR catalytic converter attenuates, the storage capability of the second SCR catalytic converter is judged to be insufficient.

The present method relates to an SCR system of an internal combustion engine for an automobile. In this case, the SCR system includes two SCR catalytic converters arranged in succession in one common exhaust pipe. The exhaust gas is first passed through a first SCR catalytic converter and then to a second SCR catalytic converter, whereby both SCR catalytic converters act on the exhaust gas. Further, the SCR system includes two or more ammonia sensors similarly disposed in the exhaust pipe. A first ammonia sensor is disposed between the two SCR catalytic converters, from which the ammonia mass can be measured after the exhaust after-treatment through the first SCR catalytic converter. A second ammonia sensor is disposed downstream of the two SCR catalytic converters, where it is possible to measure the ammonia mass after the exhaust after-treatment via the two SCR catalytic converters. The ammonia concentration corresponds to the ammonia slip that occurs when the ammonia charge level exceeds the maximum ammonia charge level for each SCR catalytic converter. The components described above may be coupled to one common electronic control unit that controls these components. In this method, the signal of the first ammonia sensor is continuously detected and the mass of ammonia in the first ammonia sensor is calculated therefrom.

In the case of active diagnosis, the amount of reducing agent added to the metric is increased, in other words excess metering is performed. In this case, the ammonia mass of the first SCR catalytic converter converted from the metering dosing reducing agent mass exceeds the ammonia mass required for reduction in the first SCR catalytic converter. Thereby, the first SCR catalytic converter is supplied with more ammonia mass than is used through SCR. As a result, the ammonia charge level in the first SCR catalytic converter rises. If the maximum ammonia charge level is exceeded, ammonia is not used and passes through the first SCR catalytic converter, resulting in ammonia slip in the first SCR catalytic converter. The occurrence of the ammonia slip is detected according to the signal of the first ammonia sensor during the first inspection step for the presence of the ammonia slip. In particular, the ammonia slip is detected when the ammonia mass in the first ammonia sensor exceeds a second threshold value. Finally, if the ammonia slip in the first SCR catalytic converter has been detected, the first error detection of the second SCR catalytic converter is performed through the evaluation criteria described below.

Alternatively, after the signal of the first ammonia sensor is continuously detected and the ammonia mass in the first ammonia sensor is calculated therefrom, before the excess metering input, the parameters for normal metering input, i. E. A passive diagnosis of unmodified dosing is performed. In the case of passive diagnosis, a second inspection step for the presence of the ammonia slip likewise is carried out in accordance with the signal of the first ammonia sensor. Eventually, if ammonia slip in the first SCR catalytic converter is detected, a second error detection of the second SCR catalytic converter is performed through the evaluation criteria described below. If an error is output at the second error detection during passive diagnostics, the excess metering step is initiated and the active method proceeds.

Conversely, during passive diagnosis, if an error is not output at the second error detection, the steps of the excess metering input stage and the first-mentioned active diagnostics following it are suppressed. Preferably, in this case, a ghost counter may be started. The ghost counter simulates the feasibility of active diagnostics and calculates the point at which errors may have been detected through active diagnostics. If active diagnostics may have been performed in the current operating cycle, the IUMPR (in-use performance ratio) increases. If at least one of the operating parameters of the internal combustion engine appears opposite, the ghost counter is stopped and / or reset. Operating parameters considered in this regard include the temperature level and temperature slope of the second SCR catalytic converter, the mass flow rate of the reducing agent solution flowing through the second SCR catalytic converter, and switch on / off conditions. Therefore, the ghost counter indicates how much probability an error can be detected by proportioning the operating cycles including diagnostics executed to all operating cycles. Therefore, legal regulations related to this are observed. In particular, it should not be less than the established threshold for IUMPR.

As a possible evaluation criterion, a difference between the mass of ammonia in the first ammonia sensor and the mass of ammonia in the second ammonia sensor can be calculated. Whereby the difference is integrated over time. If the integrated difference falls below the third threshold value at the time of the determination, an error in the second SCR catalytic converter is detected because the ammonia can not be sufficiently stored by the second SCR catalytic converter. Otherwise, it is detected that there is no error in the second SCR catalytic converter. Optionally, the integration of the difference is normalized to a preset temperature-dependent maximum value.

Alternatively, an absolute value of the difference may be used instead of using the difference itself for evaluation. In this case, error detection is performed as described above. In particular, when the ammonia charge level of the second SCR catalytic converter is very close to the maximum ammonia charge level for the SCR catalytic converter, or even reaches the maximum ammonia charge level, evaluation of the absolute value of the difference is desirable. In this case, the minimum temperature variation in the second SCR catalytic converter alternately allows the ammonia to be released and then stored again. Each calculated difference has a varying sign that allows a reliable evaluation through calculation of the absolute value.

As another possible evaluation criterion, a correlation coefficient between the signal of the first ammonia sensor and the signal of the second ammonia sensor can be calculated. If the correlation coefficient exceeds the sixth threshold, an error in the second SCR catalytic converter is detected because both signals are too similar to each other than when there may be enough ammonia stored. If the correlation coefficient does not exceed the sixth threshold value, it is detected that there is no error in the second SCR catalytic converter. Even in this case, the above-described phenomenon in which ammonia is alternately released and then stored again can be evaluated. In this case, the signals of the first ammonia sensor and the signals of the second ammonia sensor are different from each other, thereby decreasing the correlation coefficient.

Both metrics, by themselves, demonstrate proper error detection for the second SCR catalytic converter.

The detection of the ammonia slip can preferably be stopped when it is ascertained that the temperature gradient at the time of inspection is reduced below the first threshold value. When the temperature falls, the probability of occurrence of ammonia slip is lowered by emptying the new storage locations in the SCR catalytic converters, and as a result, the error detection may be distorted. Alternatively, this dependence can be considered in the detection of the ammonia slip, for example, in such a way that the second threshold value is adjusted accordingly.

Preferably, the error detection is performed only when the integrated ammonia mass in the first ammonia sensor exceeds a second threshold value. Thus, it can be ensured that the ammonia mass which can be used in the second SCR catalytic converter for reduction is provided in a sufficiently large amount to be reliable.

If there is an ammonia slip on the first SCR catalytic converter and the integrated ammonia mass in the first ammonia sensor exceeds a third threshold, additional detection of the ammonia slip may be initiated via the signal of the first ammonia sensor.

Preferably, in the case of active diagnostics, if the ammonia mass in the second ammonia sensor is higher than the fourth threshold, the excess metering step may be terminated. For direct comparison with the fourth threshold instead of the ammonia mass in the second ammonia sensor, the ammonia mass may be integrated and the integrated ammonia mass may then be compared to a suitable fourth threshold in the second nitrogen oxide sensor. Alternatively, the ammonia concentration of the exhaust gas in the second ammonia sensor may instead be compared with a suitable fourth threshold value. The resulting ammonia slip is sufficient for a reliable evaluation. Now, in order to prevent excessive use of the reducing agent, it may be sufficient to meter the reducing agent mass required for the reduction of the nitrogen oxides.

In addition, the over-metering input may be performed intermittently rather than continuously during the active diagnosis. Compared to continuous dosing, during intermittent dosing, a relatively small amount of ammonia mass can be used for further evaluation after the end of the excess metering. As a result, the excitation of the SCR system is reduced, resulting in less emissions.

The computer program of the present disclosure is configured to execute each step of the method, particularly when executed on a computer or a control unit. The computer program of the present invention enables the implementation of the method in the conventional electronic control unit without the necessity of implementing a structural change in the conventional electronic control unit. To this end, the computer program of the present invention is stored in a machine-readable storage medium.

By installing the computer program of the present invention in a conventional electronic control unit, an electronic control unit configured to execute error detection in the SCR system is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

1 is a schematic diagram illustrating an SCR system capable of performing error detection using one embodiment of a method according to the present invention, including two SCR catalytic converters and two ammonia sensors.
Figure 2a is a flow chart illustrating one embodiment of a method according to the present invention in which active diagnosis is implemented.
Figure 2b is a further portion of a flow chart diagram illustrating another embodiment of a method according to the present invention in which passive diagnostics preceding the active diagnosis of Figure 2a are implemented.
FIG. 3A is a graph showing the integrated difference of the reductant mass, the signals of ammonia sensors, the integrated ammonia mass in the first ammonia sensor, and the ammonia masses on the first ammonia sensor and the second ammonia sensor over time, It can be seen here that no error is detected for the second SCR catalytic converter through one embodiment of the method according to the invention.
FIG. 3B is a graph showing the integrated amount of the reducing agent mass, the signals of the ammonia sensors, the integrated ammonia mass in the first ammonia sensor, and the integrated difference of the ammonia masses in the first ammonia sensor and the second ammonia sensor over time , Where an error is detected for the second SCR catalytic converter through one embodiment of the method according to the present invention.

1, there is shown an SCR system 100 of an internal combustion engine, not shown, in a vehicle, including a first SCR catalytic converter 101 and a second SCR catalytic converter 102, An error can be detected by one embodiment of the following method. Two SCR catalytic converters 101 and 102 are arranged in the exhaust pipe 120 and the first SCR catalytic converter 101 injects urea water upstream of the two SCR catalytic converters 101 and 102 into the exhaust pipe 120 Is closer to the metering input module (130). The SCR system 100 is also disposed between the first SCR catalytic converter 101 and the second SCR catalytic converter 102 so that the ammonia mass thereafter after exhaust gas treatment through the first SCR catalytic converter 101 A first ammonia sensor 111 which can be measured; A second ammonia sensor 112 disposed downstream of the second SCR catalytic converter 102 and capable of measuring the ammonia mass there after exhaust gas treatment through the two SCR catalytic converters 101 and 102; . Not only the two ammonia sensors 111 and 112 but also the metering input module 130 are connected to the electronic control unit 140 and controlled through the electronic control unit.

2A, a flow diagram of one embodiment of a method according to the present invention in which active diagnosis is implemented is shown. At the start time, the signal y ₁ of the first ammonia sensor 111 is detected 200 and the ammonia mass NH ₃ z in the first ammonia sensor 111 is calculated 201 from this signal y ₁ .

Accordingly, at query step 202, it is checked whether the temperature slope dT exceeds the first threshold S ₁ . In yet other embodiments, additional conditions for passive diagnostics may be examined in query step 202. [ The possible conditions are as follows.

Readiness of the SCR system 100;

The readiness of the ammonia sensors 111 and 112;

- evaluation of the signals y ₁ and y _{2 of the} ammonia sensors 111 and 112;

- evaluation of exhaust gas mass flow rate;

The temperature level of the SCR catalytic converters 101 and 102; And

The modeled ammonia charge level of the SCR catalytic converters 101 and 102;

If at least one of the conditions is not met, the detection (200) of the signal y ₁ of the first ammonia sensor 111 continues until all conditions are met.

If all of the conditions checked in the query step 202 are met then an active diagnostic is performed in which the excess metering input step 203 of the SCR system 100 is executed by increasing the reducing agent mass m _ds dosed into the exhaust pipe 120 Is performed. The excess metering input step 203 is adjusted so that the converted ammonia mass of the first SCR catalytic converter 101 exceeds the ammonia mass required for the reduction of nitrogen oxides. In this case, the excess metering input step 203 is executed continuously or intermittently according to the embodiment and the operating conditions. As a result, the ammonia charge level in the first SCR catalytic converter 101 rises until it exceeds the maximum ammonia charge level of the first SCR catalytic converter 101. In this case, ammonia slip occurs in the first SCR catalytic converter 101.

The ammonia slip is detected according to a signal y ₁ of the first ammonia sensor 111 in a first checking step 204 of the presence of ammonia slip. To this end, the ammonia mass (NH ₃ z) in the first ammonia sensor 111 detected 201 from the signal y _{1 of} the first ammonia sensor 111 is compared with the second threshold value S ₂ do. When the ammonia mass (NH ₃ z) exceeds the second threshold value (S ₂ ), the ammonia slip in the first SCR catalytic converter (101) is detected. In other embodiments, other methods for detection of ammonia slip may be applied.

If the ammonia slip is detected, the ammonia mass (NH ₃ z) in the first ammonia sensor 111 is integrated (205). The integrated ammonia mass? NH ₃ z is then used for error detection for the first SCR catalytic converter 101. A first checking step 206 is performed as to whether the integrated ammonia mass? NH ₃ z in the first ammonia sensor 111 exceeds the third threshold value S ₃ . If it is exceeded, it is assumed that enough ammonia can be utilized from this to the second SCR catalytic converter 102 to effect error detection. The integral mass ammonia (∫NH z ₃₎ is below the third threshold (S _3), or if it is the same as the third threshold (S _3), is the iterative method of the present application.

When ammonia by weight in the second NOx sensor 112 in the testing step 207 (NH ₃ n) is greater than the fourth threshold, greater than quantitative In step 203 at this point is terminated (207), the metering The reducing agent mass (m _Dos ) is reduced to the required amount. In yet another embodiment, instead of the ammonia mass, the integrated ammonia mass at the second nitrogen oxide sensor 112 may be used for the inspection step 207. In yet another embodiment, the ammonia concentration of the exhaust gas in the second nitrogen oxide sensor 112 may be used for the checking step 207. The fourth threshold value is correspondingly adjusted in these cases.

In this embodiment, the integrated ammonia mass? NH ₃ z in the first ammonia sensor 111 corresponds to the third threshold value S ₃ as well as the result of the first checking step 204 on the presence or absence of ammonia If the result of the first checking step 206 as to whether it is exceeded is also positive, the first error detection step 210 is initiated.

At the same time, according to an embodiment of the method according to the invention, a selection criterion is selected. In an embodiment of the method according to the present invention, the integrated difference (?) Between the ammonia mass (NH ₃ z) in the first ammonia sensor (111) and the ammonia mass (NH ₃ n) in the second ammonia sensor D) is calculated according to the following formula 1 (209a).

(공식 1).

(Formula 1).

Following this, the first error detection step 210 of the second SCR catalytic converter 102 is performed through a selection criterion. If the integrated difference D is below the fifth threshold S ₅ , an error 211 is output because ammonia can not be sufficiently stored by the second SCR catalytic converter 102 to be. If the integrated difference? D is above the fifth threshold S ₅ or equal to the fifth threshold S ₅ , no error 212 is output.

In still another embodiment of the method according to the present invention, the first ammonia signal (y ₁₎ and the correlation coefficient (E) of the signal (y ₂₎ of the second ammonia sensor in the sensor 112 to calculate according to formula 2 (209b).

(공식 2)

(Formula 2)

The correlation coefficients, shows how determination signal (y ₂₎ is similar to how the signal (y ₁₎ and a second ammonia sensor 112 of the first ammonia sensor (111) and the time (t _E). Following this, the first error detection step 209 of the second SCR catalytic converter 102 is performed through a selection criterion. If the correlation coefficient exceeds the sixth threshold S ₆ , an error 210 is output, since both signals y ₁ and y ₂ are too similar to the case where enough ammonia may have been stored Because. Correlation coefficient is smaller than the sixth threshold value (S _6), or a sixth surface equal to a threshold (S _6), no error (211) is output.

It should be noted that the calculation steps 209a and 209b of the selection criterion are different from the integration step 205 of the ammonia mass NH ₃ z and the integrated ammonia mass ∫NH ₃ z in the first ammonia sensor 111 ) Is greater than the third threshold value (S ₃ ).

The transition position (1) shown by the dashed line in Fig. 2A shows the connection with the flowchart shown in Fig. 2 as another embodiment of the passive diagnosis preceding the active diagnosis.

2B, firstly, a signal y ₁ of the first ammonia sensor 111 is detected (200) similar to the active diagnosis, from which the ammonia mass (NH ₃ z) in the first ammonia sensor 111 (201). Accordingly, similarly, in query step 202, it is checked whether the temperature slope dT exceeds the first threshold S ₁ . Likewise, in still other embodiments, additional conditions for passive diagnostics may be examined in query step 202. [ These conditions correspond to the conditions described above for active diagnosis. The same reference numerals as in Fig. 2A indicate that the steps correspond to each other. Therefore, the three steps (200, 201, and 202) listed above can also be borrowed from active diagnostics, so see the discussion there.

In the case of manual diagnosis, the operating parameters of the metering dosing are not changed, and normal metering dosing is performed at this point. A second checking step 220 for the presence of an ammonia slip is performed according to the signal y ₁ of the first ammonia sensor 111. In this case, similarly, the ammonia mass (NH ₃ z) in the first ammonia sensor 111 is compared with the second threshold value S ₂ . The second threshold value (S ₂ ) can be chosen differently from the active diagnosis in the case of passive diagnosis, since the metering doses of the reducing agent also differ. Similarly, when the ammonia mass (NH ₃ z) exceeds the second threshold value (S ₂ ), the ammonia slip in the first SCR catalytic converter 101 is detected. Again, other methods may be applied to detect ammonia slip in other embodiments.

If the ammonia slip is detected, the ammonia mass (NH ₃ z) in the first ammonia sensor 111 is integrated (221) in the same manner. The integrated ammonia mass (∫NH ₃ z) is generally distinguished from the integrated ammonia mass (∫NH ₃ z) in active diagnostics and usually appears to be less. And a second checking step 222 is performed to determine whether the integrated ammonia mass? NH ₃ z in the first ammonia sensor 111 exceeds a third threshold value S ₃ , wherein the third threshold value? (S ₃ ) are similarly adjusted accordingly. The integral mass ammonia (∫NH z ₃₎ is below the third threshold (S _3), or if it is the same as the third threshold (S _3), is the iterative method of the present application.

In this embodiment, the integrated ammonia mass? NH ₃ z in the first ammonia sensor 111 corresponds to the third threshold value S ₃ as well as the result of the second checking step 221 on the presence or absence of ammonia If the result of the second checking step 222 as to whether it is exceeded is also positive, the second error detection step 224 is initiated. A selection criterion is selected according to an embodiment of the method according to the invention. As in the active diagnosis, the integrated difference (D) of the ammonia mass (NH ₃ z) in the first ammonia sensor (111) and the ammonia mass (NH ₃ z) in the second ammonia sensor (112) calculated or (223a), or the first correlation coefficient (E) of the signal (y ₂₎ of the signal (y ₁₎ and a second ammonia sensor 112 of the ammonia sensor (111) is calculated according to formula 2 (223b ).

Following this, in accordance with the selection criteria, a second error detection step 224 is performed. Similar to the passive diagnosis, if the integrated difference? D is below the fifth threshold S ₅ or if the correlation coefficient E exceeds the sixth threshold S ₆ , . If this is not the case, no error 226 is output.

If an error 225 is output in the passive diagnosis, the active diagnosis shown in FIG. 2B is executed from the transition position 1, that is, the excess metering injection step 203 is performed. Otherwise, the execution of the excess metering input step 203 and the subsequent steps of active diagnosis in FIG. 2A are suppressed.

In the embodiment shown in FIG. 2B, as no error 226 is output in the passive diagnosis, the ghost counter 227 is started. For these cases, the ghost counter 227 is used to calculate the point in time when the active diagnostic may have detected an error. If active diagnostics may have been performed in the current operating cycle, the IUMPR (in-use performance ratio) increases. If at least one of the operating parameters of the internal combustion engine appears opposite, the ghost counter 227 is stopped and / or reset. The ghost counter 227 will proportion the operating cycles including diagnostics to all operating cycles, thereby indicating the probability that an error will be detected.

3a and 3b show the results of the measurement of the reductant mass (m _Dos ), the signals of the ammonia sensors (y ₁ and y ₂ ), the integration at the first ammonia sensor 111 (∫NH ₃ z) of the first ammonia sensor 111 and the integrated difference (∫NH ₃ z) between the ammonia mass (NH ₃ z) in the first ammonia sensor 111 and the ammonia mass (NH ₃ n) in the second ammonia sensor 112 D are shown respectively. The metered dose of reducing agent mass (m _Dos ) increases during the excess metering dosing step (203). As a result, by the ammonia slip generated in the first SCR catalytic converter 101, the integrated ammonia mass? NH ₃ z in the first ammonia sensor 111 can be detected by the first inspection for the presence or absence of ammonia slip Until this fact is confirmed at step 204. [ In the figures, the presence or absence of ammonia slip is determined in such a manner that whether or not the ammonia mass (NH ₃ z) in the first ammonia sensor 111 exceeds the second threshold value S ₂ A first checking step 204 is performed. If there is an ammonia slip, the excess metering step 203 ends (208).

In this case, only the integrated difference? D is used as the selection criterion. In Fig. 4A, an example in which no error 211 is detected is shown. The integrated difference? D is greater than the fifth threshold S ₅ at the determination time t _{E as} shown. In contrast, in FIG. 4B, an example in which an error 210 is detected is shown. The integrated difference? D is below the fifth threshold S ₅ at the determination time t _{E as} shown.

Claims (14)

A method for error detection in an SCR system (100) of an internal combustion engine for an automotive vehicle, comprising two SCR catalytic converters (101, 102) and two or more ammonia sensors (111, 112) Is disposed between the two SCR catalytic converters 101 and 102 and the second ammonia sensor 112 is disposed downstream of the two SCR catalytic converters 101 and 102,
For active diagnosis,
I. a detection step (200) of continuously detecting the signal (y ₁ ) of the first ammonia sensor (111);
II. A calculation step (201) of calculating the ammonia mass (NH ₃ z) in the first ammonia sensor (111);
III. And an excess metering input step of inputting an excess metering through an increase of a reducing agent mass (m _Dos ) to be metered in, wherein an ammonia filling level in the first SCR catalytic converter (101) is higher than a maximum ammonia filling , Wherein the converted ammonia mass of the first SCR catalytic converter (101) exceeds the ammonia mass required for the reduction of nitrogen oxides until the first SCR catalytic converter (101) level is exceeded.
IV. A first checking step (204) of checking whether ammonia slip exists in the first SCR catalytic converter (101) according to the signal (y ₁ ) of the first ammonia sensor (111);
V. A first error detection step (209) for detecting an error in at least a second SCR catalytic converter (102) via an evaluation criterion if ammonia slip is present in the first SCR catalytic converter (101). In the error detection method. 2. The method of claim 1, wherein after step II of the method and before step III of the method,
- a second checking step (220) of checking whether there is ammonia slip in the first SCR catalytic converter (101) according to the signal (y ₁ ) of the first ammonia sensor (111);
- a second error detection step (224) for detecting an error in at least the second SCR catalytic converter (102) via an evaluation criterion if ammonia slip is present in the first SCR catalytic converter (101);
- suppressing the method steps III-V if no error 226 is output in the second error detection step 224,
Wherein a passive diagnosis for a regular metering input is performed. 3. The method of claim 2, wherein the ghost counter (227) is started when no error (226) is output in the second error detection step (224) during the passive diagnosis. 4. The method according to any one of claims 1 to 3, wherein the ammonia mass (NH ₃ z) in the first ammonia sensor (111) and the ammonia mass (NH ₃ n) in the second ammonia sensor , The difference D is integrated over a time period t and the integrated difference D is multiplied by a fifth threshold value S ₅ at a determination time t _E If errors 210 and 225 in the second SCR catalytic converter 102 are detected and the integrated difference D is above the fifth threshold S ₅ at the determination time t _E , (211, 226) is detected in the second SCR catalytic converter (102) if the second threshold value (S ₅ ) is equal to the fifth threshold value (S ₅ ). Any one of claims 1 to A method according to any one of claim 3, wherein for the evaluation criteria, the signal of the first ammonia sensor (111) (y ₁₎ and the correlation coefficient based on the signal (y ₂₎ of the second ammonia sensor 112 (210, 225) in the second SCR catalytic converter 102 is detected when the correlation coefficient E is above the sixth threshold S ₆ at the determination time t _E and correlation coefficient (E) an error in the determined time (t _E) a sixth threshold (S ₆₎ a lower than, or the sixth threshold value (S _6), and the 2 SCR catalytic converter (102) plane as the (211, 226) are detected in the SCR system. 6. The method according to any one of claims 1 to 5, wherein in the checking step (204, 220) for the presence of ammonia slip in the first SCR catalytic converter (101) mass ammonia (NH ₃ z) is the second threshold value when exceeding the (S _2), the error detection method for, SCR system, characterized in that the ammonia slip is detected in the ammonia sensor (111) for. 7. Method according to any one of the preceding claims, characterized in that, in the checking step (202), if the temperature slope (dT) decreases below the first threshold (S ₁ ) An error detection method in an SCR system. 8. The method according to any one of claims 1 to 7, wherein the error detection step (209, 224) is performed when the integrated ammonia mass (? NH ₃ z) in the first ammonia sensor (111) ₃ ). ≪ / RTI > The method of claim < RTI ID = 0.0 > 1, < / RTI > 9. The method according to any one of claims 1 to 8, wherein, in the case of active diagnosis, if the ammonia mass (NH ₃ n) in the second ammonia sensor (112) exceeds the fourth threshold value (S ₄ ) (203) is terminated (207). ≪ Desc / Clms Page number 13 > 9. The method according to any one of claims 1 to 8, wherein, in the case of active diagnosis, if the integrated ammonia mass at the second ammonia sensor (112) exceeds a fourth threshold (S ₄ ) (203) is terminated (207). 9. The method according to any one of claims 1 to 8, wherein, in the case of active diagnosis, if the ammonia concentration of the exhaust gas in the second ammonia sensor (112) exceeds the fourth threshold value (S ₄ ) (203) is terminated (207). ≪ Desc / Clms Page number 24 > 12. A computer program configured to execute each step of the method according to any one of claims 1-11. 13. A machine-readable storage medium having stored thereon a computer program according to claim 12. An electronic control unit (140) configured to perform error detection in an SCR system (100) using a method according to any one of the preceding claims.

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