DE102018215629A1 - Method for functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine and exhaust gas aftertreatment system - Google Patents

Abstract

A method for the functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine (1) and a corresponding exhaust gas aftertreatment system are described. The method relates to the checking of a particle filter (5) of the exhaust gas aftertreatment system for functionality with regard to its filter effect, by bringing about a defined lambda value change upstream of the particle filter (5) by changing a fuel supply by means of a fuel supply device upstream of the particle filter the specified lambda value change following the specified time window (TW), the corresponding lambda value change downstream of the particle filter (5) is measured and a lambda comparison value (LVgW) is provided on the basis thereof. The particle filter (5) is then diagnosed as defective or intact on the basis of a comparison of the lambda comparison value (LVgW) with predetermined limit values (GW). The exhaust gas aftertreatment system according to the invention is set up to carry out the aforementioned method. Using the aforementioned method and the exhaust gas aftertreatment system, a functional diagnosis of the particle filter (5) can be carried out with high reliability and robustness against interference as on-board diagnosis.

Description

The present invention relates to a method for functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine, in particular a diesel engine, a particle filter arranged in an exhaust gas line and a fuel supply device for adding fuel to the exhaust gas mass flow in the exhaust gas mass flow upstream, i.e. upstream of the particle filter, and a lambda sensor in Exhaust gas mass flow downstream, that is, after the particle filter.

In particular, vehicles with diesel internal combustion engines (diesel engine), but increasingly also vehicles with gasoline internal combustion engines (petrol engine), nowadays have a particle filter ( DPF ) to avoid particles (soot, fine dust) in the exhaust gas emissions and, if necessary, a so-called oxidation catalyst to reduce the pollutant content in the exhaust gas emissions.
Legislators are continually lowering the emission limit values for exhaust gases from vehicles with internal combustion engines (internal combustion engines) and are issuing regulations to monitor their proper functioning. This applies in particular to the so-called OBD diagnosis (on-board diagnosis, ongoing, automatic self-diagnosis in the intended operation of the vehicle) in such vehicles. Nowadays, the particle filter must also be subjected to such a frequent and precise OBD diagnosis.

It is known to carry out such a diagnosis in relation to the particle emissions with a so-called PM sensor (Particulate Matter Sensor, particle sensor). If the PM emission measured with the particle sensor after the particle filter is higher than a threshold value, the particle filter is diagnosed as faulty. However, a relatively long period of time is required for such a diagnosis. Furthermore, the diagnosis is limited to the particle emission and the accuracy of the diagnosis is also not good enough to meet the requirements of future, even lower emission threshold values.

The present invention is therefore based on the object of providing a method and a corresponding exhaust gas aftertreatment system of an internal combustion engine which enable particularly rapid and accurate automatic functional diagnosis of a particle filter with respect to particle filtering during operation of the internal combustion engine.

This object is achieved according to the invention with a method and an exhaust gas aftertreatment system according to the independent claims.

According to the invention, a method for functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine is presented, wherein the exhaust gas aftertreatment system has an exhaust gas line for guiding an exhaust gas mass flow and a particle filter arranged in the exhaust gas line, and wherein a fuel supply device for adding fuel into the exhaust gas mass flow upstream, that is to say upstream of the particle filter, and a lambda sensor ( 10th ), is arranged downstream in the exhaust gas mass flow, i.e. after the particle filter.

A so-called lambda sensor, also known as a λ sensor or λ probe, detects the combustion air ratio in the exhaust gas. The combustion air ratio is the ratio of the air mass that is available in the combustion chamber of an internal combustion engine for the combustion of the supplied fuel mass to the air mass required for complete combustion of the supplied fuel mass and thus provides information about an excess of air or fuel in the exhaust gas. At λ> 1 there is excess air and thus a so-called lean combustion, conversely at λ <1 there is excess fuel and thus a so-called rich combustion.

• - Einstellen und/oder Verifizieren einer stationären Betriebsart der Brennkraftmaschine, die gekennzeichnet ist durch einen konstanten Lambdawert im Abgasmassenstrom vor dem Partikelfilter; bei Vorliegen der stationären Betriebsart,
• - gezieltes, definiertes Herbeiführen einer Lambdawertänderung im Abgasmassenstrom vor dem Partikelfilter, ausgehend von dem vorgenannten konstanten Lambdawert, durch Änderung der Kraftstoffzugabe mittels der genannten Kraftstoff-Zuführeinrichtung;
• - Messen der Lambdawertänderung im Abgasmassenstrom nach dem Partikelfilter innerhalb eines, unmittelbar auf die vorgenannte Lambdawertänderung im Abgasmassenstrom vor dem Partikelfilter folgenden, festgelegten Zeitfensters, mittels des Lambdasensors;
• - Bereitstellen eines korrelierenden Lambda-Vergleichswertes auf Basis der gemessenen Lambdawertänderung nach dem Partikelfilter;
• - Bewerten der innerhalb des festgelegten Zeitfensters gemessenen Lambdawertänderung nach dem Partikelfilter anhand des jeweiligen Lambda-Vergleichswertes und vorgegebener Grenzwerte; und
• - Diagnostizieren des Partikelfilters als schadhaft, wenn die Bewertung ergibt, dass der Lambda-Vergleichswert zumindest einen vorgegebenen Grenzwert überschritten hat.

The method according to the invention has the steps shown below:

• - Setting and / or verifying a stationary operating mode of the internal combustion engine, which is characterized by a constant lambda value in the exhaust gas mass flow upstream of the particle filter; if the stationary operating mode is available,
• - Targeted, defined bringing about a change in the lambda value in the exhaust gas mass flow upstream of the particle filter, starting from the aforementioned constant lambda value, by changing the fuel addition by means of the fuel supply device;
• - Measuring the lambda value change in the exhaust gas mass flow after the particle filter within a specified time window immediately following the aforementioned lambda value change in the exhaust gas mass flow before the particle filter, by means of the lambda sensor;
• - Providing a correlating lambda comparison value based on the measured lambda value change after the particle filter;
• - Evaluating the change in lambda measured after the particle filter within the defined time window on the basis of the respective lambda comparison value and predetermined limit values; and
• - Diagnosing the particle filter as defective if the evaluation shows that the lambda comparison value has exceeded at least a predetermined limit value.

In this context, the stationary operating mode of the internal combustion engine and the constant lambda value should be understood to mean that the relevant operating parameters, such as, for example, the speed under a certain load and in particular the lambda value, lie or move within a predetermined fluctuation range, which is dimensioned in this way that their effects on the implementation of the method, with sufficient accuracy of the diagnostic result, are negligible. It is also possible to speak of a quasi-stationary operating mode and a quasi-constant lambda value. The specified fluctuation range can be determined empirically or with the help of model calculations.

Furthermore, depending on the type of the lambda comparison value, a predetermined limit value can be exceeded both in the positive and in the negative direction. Exceeding is therefore not to be understood in the sense of "getting bigger" but in the sense of "crossing the border" regardless of the direction.

The invention further relates to an exhaust gas aftertreatment system of an internal combustion engine, which has an exhaust gas line for guiding an exhaust gas mass flow and a particle filter arranged in the exhaust gas line, and a fuel supply device for adding fuel to the exhaust gas mass flow upstream, that is to say upstream of the particle filter, and a lambda sensor in the exhaust gas mass flow downstream. after the particle filter.

This exhaust gas aftertreatment system is further characterized in that an electronic computing and control unit is assigned to it, which is set up for the targeted, defined induction of a lambda value change in the exhaust gas mass flow upstream, in front of the particle filter, by changing the fuel addition by means of the aforementioned fuel supply device and for recording a measurement signal output by the lambda sensor, the electronic computing and control unit also being set up to carry out the method for functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine, according to a method according to the invention as described above or below.

It can thus be summarized that the basic idea of the invention is to use a lambda sensor after a particle filter in order to subject the particle filter, and thus the exhaust gas treatment system, to a function check in connection with a change in the lambda value in the exhaust gas mass flow upstream of the particle filter.

Functional damage to particle filters usually consists of openings or holes in the substrate of the filter, the number or cross-sectional area of which determine the degree of damage and through which a corresponding part of the exhaust gas can pass through unfiltered and untreated. If the total cross section of the breakthroughs or open holes is above a threshold, the corresponding particle emission exceeds a diagnostic threshold (OBD threshold).

In order to detect this state, the lambda value upstream of the particle filter, preferably in one step, is increased, starting from a steady or stationary or quasi-stationary operating state, for example when the internal combustion engine is idling and for example at a constant particle filter temperature previously given lambda value and the signal curve representing the lambda value after the particle filter is observed. The corresponding change in lambda value is therefore measured after the particle filter.

If the filter substrate is intact, the passage of the exhaust gas through the particle filter is delayed. Therefore, the lambda value measured after the filter has only a comparatively small increase and a correspondingly smaller gradient, i.e. one, for a short period of time, within a defined time window that immediately follows the lambda value increase in front of the particle filter, and for example between 3 and 5 seconds lower slew rate.

If a lambda comparison value determined from the lambda value measurement is now below or above a correspondingly predetermined limit value, it can be assumed that the total cross section of openings in the filter substrate is so small that the full functionality can be assumed to be given. However, if the limit value is exceeded, the entire cross-section of breakthroughs in the filter substrate is so large that the exhaust gas flows unfiltered through the particle filter to a large extent and almost without delay, so that the corresponding lambda sensor after the particle filter unites within the specified, immediately following time window immediate, lambda value increase registered with a much higher gradient.

It has been shown that the ratio between the change in lambda value after the particle filter and the change in lambda value before Particle filter is directly proportional to the total cross section of the openings in the filter substrate of the particle filter. If this ratio is above a certain threshold or limit value, the particle filter is classified as defective.

A corresponding change in the lambda value upstream of the particle filter is in this case brought about by adding fuel to the exhaust gas mass flow upstream of the particle filter, by means of a fuel supply device which enables an exact metering of the fuel quantity. Such fuel supply devices are already in use in many internal combustion engines, in particular in internal combustion engines for medium and heavy-duty vehicles, in order to generate a temperature increase in the exhaust gas required for the particle filter regeneration by adding fuel.

A desired lambda value increase or lambda value reduction is predefined in front of the particulate filter and the amount of fuel required for this is metered into the exhaust gas mass flow by appropriately controlling the fuel supply device. The control values required for this are determined, for example, on the basis of stored, empirically created, dependent maps of different operating states, or by means of corresponding computing models.

• 1 eine schematische Darstellung einer Ausführung einer Brennkraftmaschikne mit erfindungsgemäßer Abgasnachbehandlungsanlage;
• 2 eine schematische Darstellung einer weiteren Ausführung einer Brennkraftmaschikne mit erfindungsgemäßer Abgasnachbehandlungsanlage;
• 3 ein Blockdiagramm zur Darstellung des Verfahrensablaufs einer Ausführung des erfindungsgemäßen Verfahens;
• 4 eine qualitative Darstellung von Verlaufskurven von Lambdawerten vor und nach dem Partikelfilter bei intaktem und defektem Partikelfilter; und
• 5 eine qualitative Darstellung von Verlaufskurven der Lambdawerte vor und nach dem Partikelfilter bei aufeinanderfolgenden Lambdawertänderungen.

The invention and further advantageous exemplary embodiments and developments of the invention are explained in detail below with reference to the figures. Show it:

• 1 a schematic representation of an embodiment of an internal combustion engine with exhaust gas aftertreatment system according to the invention;
• 2nd a schematic representation of a further embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention;
• 3rd a block diagram to illustrate the process flow of an embodiment of the inventive method;
• 4th a qualitative representation of curves of lambda values before and after the particle filter with an intact and defective particle filter; and
• 5 a qualitative representation of curve curves of the lambda values before and after the particle filter with successive lambda value changes.

Objects with identical functions and names are identified throughout in the figures with the same reference symbols.

1 shows schematically in a simplified representation an embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention, for example a diesel engine. The internal combustion engine 1 has an exhaust tract 3rd and an intake tract 12th on.

The intake tract 12th includes one with the internal combustion engine 1 connected intake manifold 12a with an attached intake pipe 12b . In the intake pipe 12b is a throttle valve 15 , to regulate the air mass flow 20th in the intake pipe 12b and the air supply to the combustion chambers of the internal combustion engine 1 , arranged.

The exhaust tract 3rd includes an exhaust manifold 3a that the exhaust pipe 3b and thus the exhaust gas aftertreatment system 2nd with the internal combustion engine 1 connects. To the exhaust gas aftertreatment system 2nd belongs to the exhaust pipe 3b to guide the exhaust gas mass flow 10th and one in the exhaust pipe 3b arranged particle filter 5 , as well as a fuel supply device 7 for adding fuel 7d in the exhaust gas mass flow 10th upstream, i.e. in front of the particle filter 5 and a lambda sensor 6 , in the exhaust gas mass flow 10th downstream, i.e. after the particle filter 5 .

Furthermore, belongs to the exhaust gas aftertreatment system 2nd an electronic computing and control unit 30th , further briefly ECU called, which is set up for the targeted, defined induction of a lambda value change in the exhaust gas mass flow 10th in front of the particle filter 5 , by changing the fuel supply by means of the fuel supply device mentioned 7 and for detecting one from the lambda sensor 6 output measurement signal.

The ECU 30th is furthermore set up to provide a method according to the invention for functional diagnosis of the exhaust gas aftertreatment system 2nd the internal combustion engine 1 as described above and below. This is the ECU , among other things, via electrical signal lines 6c , 7c and 15c with the lambda sensor 6 , the fuel supply device 7 and the throttle valve 15 connected.

The fuel supply device 7 has in this embodiment in particular an upstream of the particle filter 5 on the exhaust pipe 3b arranged metering device 7b on that for the exact metering and introduction of the fuel 7d in the exhaust gas mass flow 10th on the exhaust pipe 3b is arranged. The fuel 7d is in a storage container 7a stocked, which in turn with the dosing device 7b via a fuel line 7e connected is.

A version of the exhaust gas aftertreatment system 2nd , as described above, is characterized in that the ECU 30th is an integral part of a central control unit 32 of the internal combustion engine, which is also known as CPU 32 is referred to, the method to be carried out being part of an on-board diagnostic system for monitoring the exhaust-gas-relevant functional units of the internal combustion engine in normal operation.

Also 2nd shows an internal combustion engine 1 with a further embodiment of an exhaust gas aftertreatment system according to the invention 2nd which, in a further embodiment of the 1 shown embodiment, one in the exhaust gas mass flow 10th , between the particle filter 5 and the fuel supply device 7 , especially the dosing device 7b , in the exhaust pipe 3b arranged oxidation catalyst 8th having. In this example it is ECU 30th further set up the method for functional diagnosis of the exhaust gas aftertreatment system 2nd an internal combustion engine 1 To be carried out in such a way that the setting or verification of the steady-state operating mode involves an immediately preceding regeneration of the oxidation catalyst 8th includes.

An embodiment of the method according to the invention for the functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine in one of the embodiments described above is shown in FIG 3rd The simplified block sequence program shown is shown in the essential method steps.

After the start of the process, the first, with " BP_Stat “Process step marked, the internal combustion engine is set to a stationary operating mode, with a specific, constant lambda value in the exhaust gas mass flow being the decisive operating parameter 10th in front of the particle filter 5 the internal combustion engine 1 Since certain slight fluctuations in the operating parameters cannot be avoided in real operation of the internal combustion engine, the steady-state operating mode and the constant lambda value are characterized by values of the corresponding operating parameters which are within a predetermined range of fluctuation which is considered to be negligible for the method or lie in it.

Since the adjustment, setting and / or verification of the diagnostic operating parameters can take a certain amount of time, the following process step, which is marked with "BP_Stat = ok?", Is used to check whether the current operating mode matches the specified operating mode. As long as this is not the case, the operating parameters of the internal combustion engine will continue to be tried 1 to adjust until the desired stationary operating mode is available. If the stationary operating mode is present, the next process step can follow.

In the event that the exhaust gas aftertreatment system 2nd additionally an oxidation catalyst 8th between the fuel supply device 7 and the particle filter 5 has, as described above, is the stationary mode BP_Stat additionally characterized in that an immediately preceding regeneration of the oxidation catalyst ( 8th ) was satisfied. This ensures that the oxidation catalytic converter is “discharged” and has minimal influence on the lambda value in the exhaust gas.

In the following, with " λ_Var The marked process step then carries out the targeted, defined induction of a lambda value change λ_Var in the exhaust gas mass flow 10th upstream of the particulate filter 5 . This takes place on the basis of the aforementioned constant lambda value, by changing the fuel addition by means of the aforementioned fuel supply device 7 , in particular by appropriate control of the metering device 7b , through the ECU 30th , as in 3rd shown with a dashed line.

In one embodiment of the method according to the invention, the defined change in lambda value λ_Var in front of the particle filter 5 include a reduction and / or increase in the lambda value by a defined increase and / or reduction in fuel addition by means of the fuel supply device mentioned 7 is set. This is done, for example, by correspondingly controlling the metering device 7b the fuel supply device 7 by means of ECU 30th .

In another embodiment of the method according to the invention, the lambda value change can λ_Var in front of the particle filter 5 have a lambda value change in one direction and a subsequent lambda value change in the opposite direction. Thus, in the further sequence of the method, the lambda value changes in the positive and negative direction, in addition, can be used to diagnose the function of the particle filter, as further below and with the aid of the 5 still to be explained.

In the further course of the method according to the invention, according to the “ λ_Sig Marked process step, the lambda value change λ_Sig in the exhaust gas mass flow 10th after the particle filter 5 within one, directly on the aforementioned lambda value change λ_Var in front of the particle filter 5 following specified time window TW measured. This is done using the lambda sensor 6 , which emits a corresponding measurement signal that is sent via the signal line 6c the ECU 30th for further Processing is fed in as with the dashed line 2nd is symbolized.

In the following, with " LVgW The marked process step is the provision of a correlating lambda comparison value LVgW based on the measured lambda value change.

As a lambda comparison value LVgW can for example be a follow-up period TF from the time t0 the start of the lambda change λ_Var in front of the particle filter 5 up to a point in time t1 at which the lambda value change λ_Var after the particle filter 5 a certain proportional value L_% of the maximum lambda value change λ_Var in front of the particle filter 5 has reached. This is also in 4th shown. Here the lambda change occurs λ_Sig-1 a proportional value L_% of the maximum lambda value change λ_Var at 63% after a subsequent period TF at the time t1 .

In another embodiment of the method is used as a lambda comparison value LVgW a respective one, within the defined time window TW maximum value reached L_Max_1 , L_Max_2 , or minimum value of the lambda value change λ_Sig_1 , λ_Sig_2 , after the particle filter and / or within the defined time window TW determined gradient G1 the lambda value change. This is also the example of a lambda value increase in 4th shown, with the lambda value change λ_Sig-1 until the end of the defined time window TW a maximum value L_Max_1 has reached. The change in lambda value indicates λ_Sig_1 a gradient G1 on, which can also be used as a lambda comparison value LVgW can be used. The same applies accordingly to an in 4th Lambda value reduction, not shown.

In a further embodiment of the method, a lambda comparison value can be provided LVgW that are given in front of the particle filter and that are within the defined time window TW , Lambda values measured according to the particle filter at a specific point in time and / or the gradients of the lambda value changes λ_Var , λ_Sig_1 , λ_Sig_2 , are related to each other, as below using the 4th should be explained in more detail. This enables a particularly reliable lambda comparison value to be provided LVgW and increases the diagnostic certainty of the procedure.

A further embodiment of the method according to the invention is characterized in that a lambda comparison value is provided LVgW , the lambda values and / or the gradients of successive opposite lambda value changes, as described above, in each case after and in front of the particle filter 5 can be used in combination with each other, as shown below in the 5 shown example to be explained.

In the following, with " LVgW - GW Marked process step, the evaluation takes place within the specified time window TW measured lambda value change λ_Sig_1 , λ_Sig_2 , λ_Sig , after the particle filter 5 based on the respective lambda comparison value LVgW and specified limit values GW GW . As a lambda comparison value LVgW Depending on the execution of the method, as already explained above, a respective maximum value or minimum value of the lambda value change and / or a determined gradient of the lambda value change or also comparison or ratio values based on the respectively before and after the particle filter 5 measured values or gradients of the lambda value change can be used. This enables a wide variance in the design of the method according to the invention and the adaptation to the needs in the respective application. According to the Lambda comparison value used LVgW are then adjusted thresholds GW to specify. For example, these can be determined beforehand empirically or by means of model calculation and are, for example, in an electronic memory area of the electronic computing and control unit ECU stored and retrieved from there to evaluate the lambda value change. Such an electronic memory area is in 3rd , With E_Sp2 marked and contains the corresponding limit values GW , as " (λ) GW ”Are shown.

Based on the previously described evaluation of the change in concentration after the particle filter 5 The particulate filter is then diagnosed in the following process step, labeled “LVgW ≥ GW” 5 as defective, "DPF = nok" if the evaluation shows that the lambda comparison value LVgW at least one predetermined limit GW has exceeded. Otherwise, the particle filter is diagnosed as functional "DPF = ok" if the lambda comparison value LVgW has not reached or exceeded a limit. Depending on the type of lambda comparison value ( LVgW ) can, as already explained above, exceed the respective limit value both in the positive direction, in the sense of a higher value, and in the negative direction, in the sense of a lower value.

In a further embodiment of the method according to the invention, the particle filter is diagnosed 5 , the targeted, defined lambda value change before the particle filter 5 withdrawn again and the internal combustion engine 1 is returned to the depending on the diagnostic result normal working mode BP Standard transferred and operated as intended or is in an emergency mode BP_Not limited.

How from 3rd it can be seen that different further measures can now be initiated based on and depending on the diagnostic result, thus expanding the method.

The diagnosis reveals that the particulate filter 5 is intact and works correctly, DPF = ok, so the internal combustion engine can after the procedure, that is after the diagnosis of the functionality of the particle filter 5 back in normal working mode, BP_Norm , continue to operate, this is in the " BP_Norm Marked process step shown.

However, if the diagnosis shows that the particle filter is damaged, DPF = nok, an emergency operation can instead BP_Not , The internal combustion engine can be initiated, which, for example, still allows a workshop to be visited with reduced engine power. At the same time, an error message can be issued to the vehicle driver, prompting him to go to the nearest workshop or to have the repair carried out. This is in 3rd in which with " BP_Not Marked process step shown.

In order to ensure permanent, error-free operation of the exhaust gas aftertreatment system, the method according to the invention can be repeated in certain cycles during operation, wherein these cycles can be based on a specific operating time period, a specific operating performance or on demand values determined during operation.

In a further embodiment of the method, the respective defined time window has TW , for measuring the lambda value change in the exhaust gas mass flow 10th after the particle filter 5 , a duration of less than or equal to 5 seconds, in particular less than or equal to 3 seconds. The length of this time window ensures that only a quick change in the lambda value after the particle filter 5 , as only if the particle filter is defective 5 occurs when determining the lambda comparison value LVgW and so when diagnosing the particulate filter 5 Shows impact.

4th shows an example of the changes in the lambda value change over time. The shows with λ_Var marked curve the change in lambda value upstream of the particle filter 5 , starting from a lambda value set in the diagnostic mode at the time t0 a defined change in lambda value, shown here in leaps and bounds, is brought about. The change in lambda value is shown in% of the change value and can therefore be seen as an amount both positive and negative.

With λ_Sig_1 The marked curve shows the lambda value recorded downstream of the particle filter in the event of a defective particle filter. Shortly after the time t0 , i.e. immediately after the lambda value change has been brought about λ_Var in front of the particle filter 5 , the lambda value begins with a gradient G1 within the time window TW to rise and rise to a maximum L_Max_1 at time tw, at the end of the time window TW . In the further course of time, the lambda value after the particle filter increases to 100% of the predetermined lambda value change λ_Var in front of the particle filter.

With λ_Sig_2 The marked curve, on the other hand, shows the lambda value recorded downstream of the particle filter with an intact particle filter. Immediately after the time t0 Here, too, the lambda value begins within the time window TW to rise, but with a compared to the curve λ_Sig_1 much smaller gradients G2 . Accordingly, until the time tw, at the end of the time window TW , even a much smaller maximum value L_Max_2 reached.

As a lambda comparison value LVgW can, as from the aforementioned embodiments and 4th can be seen, the respective up to the certain point in time tw at the end of the time window TW Lambda maximum value reached L_Max_1 , L_Max_2 or the respective gradient G1 , G2 of the increase in lambda within the time window TW be used.

In another embodiment, it can be used as a lambda comparison value LVgW optionally also a subsequent time period TF from the time t0 the start of the lambda change λ_Var in front of the particle filter 5 up to a point in time t1 at which the lambda value change λ_Sig_1 , λ_Sig_2 , after the particle filter 5 a certain proportionate value L_% (here, for example, 63%) of the maximum lambda value change λ_Var before the particle filter has been reached. How from 4th can be seen with an intact particle filter 5 , in the case of the curve λ_Sig_2 , the determined proportional value L_% of 63% only at a much later point in time t2 reached. The following applies here: the faster the value L_% is reached, the greater the damage to the particle filter 5 . The limit GW for the subsequent time period used as the lambda comparison value, it could be set here, for example, at 63% / 1.5 seconds. So that is the value L_% of 63% of the maximum lambda value change λ_Var Already reached after 1.2 seconds, the result is 63% / 1.2 seconds, which means the limit GW exceeded and the particle filter is to be rated as defective (DPF = nok).

Furthermore, it is possible to consider the lambda values measured downstream of the particle filter and the upstream predetermined lambda values in combination and a lambda comparison value therefrom LVgW to investigate. The change in lambda λ_Var upstream of the particle filter can be based on the default values or can be determined using model considerations.

Liegt beispielsweise der Gradient des Konzentrationsanstieges stromabwärts des Partikelfilters bei 30%/s und der Sprungwert der Konzentrationsänderung stromaufwärts des Partikelfilters beträgt 100% so ergibt sich ein Lambda-Vergleichswert von: $$\left(30\%/\text{s}\right)/100\%=\mathrm{0,03}/\text{s}.$$

Liegt nun ein Grenzwert GW von zum Beispiel 0,015 /s vor, so wäre dieser überschritten (LVgW ≥ GW) und der Partikelfilter wäre als schadhaft zu bewerten (DPF=nok).
Diese Vorgehensweise erhöht die Robustheit des Verfahrens gegen Störeinflüsse.To determine a lambda comparison value LVgW can, in one embodiment, be within the time window TW determined gradient G1 the change in lambda downstream of the particulate filter 5 by the grade rule LSp1 the change in lambda λ_Var be divided upstream of the particle filter. The result is called the lambda comparison value LVgW used. $$\text{G1}/\text{LSp1}=\text{LVgW}$$

For example, if the gradient of the concentration increase downstream of the particle filter is 30% / s and the grade rule of the change in concentration upstream of the particle filter is 100%, a lambda comparison value of: $$\left(\mathrm{30th}\%/\text{s}\right)/100\%=0.03/\text{s}.$$

Now there is a limit GW of, for example, 0.015 / s, this would be exceeded (LVgW ≥ GW) and the particle filter should be rated as defective (DPF = nok).
This procedure increases the robustness of the method against interference.

Another implementation of the method is as in 5 represented qualitatively, characterized in that the lambda value change λ_Var has a lambda value change in one direction and a subsequent lambda value change in the opposite direction in front of the particle filter. To make it easier to understand, in this example we start with a sudden increase in lambda value by a grade rule LSp1 , and a subsequent abrupt reduction in lambda value by a grade rule LSp2 , assumed, the reverse case is also possible. The values and or the gradients of the lambda value increase and the lambda value reduction are in each case after and in front of the particle filter 5 in combination with each other to evaluate the particle filter 5 used.

For example, a ratio value of the gradient can be used in each case G1a of the lambda value increase downstream and the grade rule LSp1 the increase in lambda value upstream of the particle filter and the gradient G1b the subsequent lambda value drop downstream and the associated grade rule value LSp2 the lambda value reduction is formed upstream of the particle filter and the sum thereof is calculated.

Diese Vorgehensweise erhöht die Robustheit des Verfahrens gegen Störeinflüsse weiter.This is qualitative in 5 shown. The curve is shown λ_Var the lambda value change upstream and the resulting curve λ_Sig of the lambda value downstream of the particle filter 5 . The curve λ_Var shows a targeted and defined sudden increase in lambda value around the grade rule LSp1 with a certain amount at the time t10 and a persistence of the increased lambda value over the time window TW1 until the time t20 . Then there is an equally targeted and defined step-by-step reduction in lambda value around the grade rule LSp2 by the same amount, i.e. a complete withdrawal of the lambda value increase, at the time t20 . The resulting course of the lambda value downstream of the particle filter records one at the time t10 following increase with the gradient G1a , within the time window immediately following the lambda value change before the particle filter TW1 , up to the time t20 and a subsequent drop in the lambda value with a gradient G1b within the time window immediately following the lambda value change before the particle filter TW2 that until time t30 lasts. According to the scheme above, the lambda comparison value LVgW can be determined according to the following relationship: $$\left(\text{G1a}/\text{LSp1}\right)+\left(\text{G1b}/\text{LSp2}\right)=\text{LVgW}$$

This procedure further increases the robustness of the method against interference.

Claims (12)

Method for functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1), which has an exhaust gas line (3b) for guiding an exhaust gas mass flow (10) and a particle filter (5) arranged in the exhaust gas line (3b), a fuel supply device (7) for adding fuel (7d) in the exhaust gas mass flow (10) upstream, in front of the particle filter (5), and a lambda sensor (6), in the exhaust gas mass flow (10) downstream, after the particle filter (5), with the following steps : - Setting and / or verifying a stationary operating mode (BP_Stat) of the internal combustion engine (1), which is characterized by a constant lambda value in the exhaust gas mass flow (10) upstream of the particle filter (5); if the stationary operating mode is available (BP_Stat = ok), targeted, defined induction of a lambda value change (λ_Var) in the exhaust gas mass flow (10) upstream of the particle filter (5), starting from the aforementioned constant lambda value, by changing the fuel addition by means of the aforementioned fuel supply device (7); - Measuring the lambda value change (λ_Sig) in the exhaust gas mass flow (10) after the particle filter (5) within a fixed time window (TW) following the aforementioned lambda value change (λ_Var) in the exhaust gas mass flow (10) before the particle filter (5), using the Lambda sensor (6); - Providing a correlating lambda comparison value (LVgW) based on the measured lambda value change after the particle filter (λ_Sig); - Evaluating the change in lambda value (λ_Sig) measured within the defined time window (TW) after the particle filter (5) on the basis of the respective lambda comparison value (LVgW) and predetermined limit values (GW); and - diagnosing the particle filter (5) as defective (DPF = nok) if the evaluation shows that the lambda comparison value (LVgW) has exceeded at least a predetermined limit value (GW). Procedure according to Claim 1 , The defined lambda value change (λ_Var) before the particle filter (5) includes a reduction and / or an increase in the lambda value, which is set by a defined increase and / or reduction in fuel addition by means of the fuel supply device (7) mentioned. Procedure according to one of the Claims 1 or 2nd , where as a lambda comparison value (LVgW) a subsequent time period (TF) from the time (t0) of the start of the lambda value change (λ_Var) before the particle filter (5) to a time (t1) at which the lambda value change (λ_Sig_1, λ_Sig_2) after the particle filter (5) has reached a certain proportionate value (L_%) of the maximum lambda value change (λ_Var) before the particle filter (5) is used. Procedure according to one of the Claims 1 or 2nd , where as the lambda comparison value (LVgW) a respective maximum value (L_Max_1, L_Max_2) reached within the defined time window (TW) or minimum value of the lambda value or a gradient (G1, G2) of the lambda value change (λ_Sig_1) determined within the defined time window (TW) , λ_Sig_2) after the particle filter (5) is used. Procedure according to one of the Claims 1 or 2nd , characterized in that in order to provide a lambda comparison value (LVgW), the lambda values predefined within the defined time window (TW) in front of the particle filter 5 and measured after the particle filter 5 at a specific point in time and / or the gradients of the lambda value changes, in relation to one another be set. Procedure according to one of the Claims 1 or 2nd , characterized in that the lambda value change (λ_Var) before the particle filter has a lambda value change in one direction (LSp1) and a subsequent lambda value change in the opposite direction (LSp2). Procedure according to Claim 6 , characterized in that to provide a lambda comparison value (LVgW), the lambda values and / or the gradients of the successive opposite lambda value changes (LSp1, LSp2, G1a, G1b)) are used in combination with each other after and before the particle filter (5) . Procedure according to one of the Claims 1 to 7 , characterized in that the respective defined time window (TW) has a duration of less than or equal to 5 seconds or less than or equal to 3 seconds. Procedure according to one of the Claims 1 to 8th , characterized in that after the particle filter (5) has been diagnosed, the specific, defined lambda value change in front of the particle filter (5) is withdrawn and the internal combustion engine (1) is switched back to the normal working mode (BP_Norm) depending on the diagnosis result and continues is operated or limited to an emergency operation (BP_Not). Procedure according to one of the Claims 1 to 9 , characterized in that an oxidation catalytic converter (8) is arranged in the exhaust line (3b) between the fuel supply device (7) and the particle filter (5) and that the stationary operating mode (BP_Stat) is additionally characterized by an immediately preceding regeneration of the Oxidation catalyst (8). Exhaust gas aftertreatment system (2) of an internal combustion engine (1), which has an exhaust gas line (3b) for guiding an exhaust gas mass flow (10) and a particle filter (5) arranged in the exhaust gas line (3b) as well as a fuel supply device (7) for adding fuel to the Exhaust gas mass flow (10) upstream, in front of the particle filter (5), and a lambda sensor (6), in the exhaust gas mass flow (10) downstream, after the particle filter (5), characterized in that the exhaust gas aftertreatment system has an electronic computing and control unit (30 ) is assigned, which is set up for the targeted, defined induction of a lambda value change (λ_Var) in the exhaust gas mass flow (10) upstream of the particle filter (5), by changing the fuel addition by means of the aforementioned fuel supply device (7) and for detecting one of The measurement signal output to the lambda sensor (6), the electronic computing and control unit (30) also being set up to perform the method for the functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1) according to one of the Claims 1 to 9 to execute. Exhaust aftertreatment system after Claim 11 , characterized in that it has an oxidation catalyst (8) arranged in the exhaust gas mass flow (10) between the particle filter (5) and the fuel supply device (7) in the exhaust gas line (3b), the electronic computing and control unit (30) is furthermore set up to perform the method for functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1) Claim 10 to execute.

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