WO2020052867A1

WO2020052867A1 - Method for diagnosing the function of an exhaust gas aftertreatment system of an internal combustion engine, and exhaust gas aftertreatment system

Info

Publication number: WO2020052867A1
Application number: PCT/EP2019/071211
Authority: WO
Inventors: Hong Zhang
Original assignee: Vitesco Technologies GmbH
Priority date: 2018-09-13
Filing date: 2019-08-07
Publication date: 2020-03-19
Also published as: DE102018215629A1

Abstract

The invention relates to a method for diagnosing the function of an exhaust gas aftertreatment system of an internal combustion engine (1) and to a corresponding exhaust gas aftertreatment system. The method includes the step of testing the functionality of a particle filter (5) of the exhaust gas aftertreatment system with respect to the filter effect of the filter in that a defined lambda value change upstream of the particle filter (5) is induced by changing a fuel addition by means of a fuel supply device upstream of the particle filter, the corresponding lambda value change downstream of the particle filter (5) is measured in a time frame (TW) immediately following the aforementioned lambda value change, and a lambda comparison value (LVgW) based thereon is provided. A comparison of the lambda comparison value (LVgW) with specified thresholds (GW) is then used to diagnose the particle filter (5) as being damaged or intact. The exhaust gas aftertreatment system according to the invention is designed to carry out the aforementioned method. By using the method as well as the exhaust gas aftertreatment system, a functional diagnosis of the particle filter (5) can be carried out with a high degree of reliability and robustness against interference as an onboard diagnosis.

Description

description

Procedure for the functional diagnosis of a

Exhaust gas aftertreatment system of an internal combustion engine and

Exhaust aftertreatment system

The present invention relates to a method for the function diagnosis of an exhaust gas aftertreatment system of an internal combustion engine, in particular a diesel engine, which has a particle filter arranged in an exhaust pipe and one

Fuel supply device for adding fuel to the exhaust gas mass flow in the exhaust gas mass flow upstream, that is, upstream of the particle filter, and a lambda sensor, in the exhaust gas mass flow downstream, that is to say downstream of the particle filter.

In particular vehicles with diesel internal combustion engines

(Diesel engine), but increasingly also vehicles with

Otto internal combustion engines (petrol engines) nowadays have a particle filter (DPF) to avoid particles (soot, particulate matter) in the exhaust gas emissions and, if necessary, a so-called oxidation catalyst to reduce the proportion of pollutants 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. So nowadays the particle filters of such a, frequent and exact

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). 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 regard to particle filtering in the operation of the

Enable 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.

The invention relates to a method for functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine

presented, wherein the exhaust gas aftertreatment system has a 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, upstream of the particle filter, and a lambda sensor (10), in the exhaust gas mass flow downstream , that is, after the particle filter.

A so-called lambda sensor, also known as an l-sensor or l-probe, detects the combustion air ratio in the exhaust gas. The combustion air ratio is the ratio of the air mass 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 air or fuel excess in the exhaust gas. At l> 1 there is excess air and thus a so-called lean combustion, conversely at l <1 there is excess fuel and thus a so-called rich combustion.

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

- Setting and / or verifying a stationary loading

Mode of operation 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 induction of a lambda value change 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 mentioned;

- Measuring the lambda value change in the exhaust gas mass flow after the particle filter within a, directly following the aforementioned lambda value change in the exhaust gas mass flow in front of the particle filter, following specified time window, by means of the lambda sensor;

- Providing a correlating lambda comparison value on the basis of the measured lambda value change after the particle filter;

- Evaluation of 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 steady-state operating mode of the internal combustion engine and the constant lambda value are to be understood to mean that the relevant operating parameters, such as, for example, the speed under certain load and in particular the

Lambda value, lie or move within a predetermined range of fluctuation, which is dimensioned such that its effects on the implementation of the method are negligible if the diagnostic result is sufficiently accurate. It is therefore also possible to speak of a quasi-static 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 not to be understood here 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 into 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, that is, after the particle filter.

This exhaust gas aftertreatment system is further characterized in that it has an electronic computing and Control unit is assigned, 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 fuel supply device mentioned and for detecting one of the

Lambda sensor output measurement signal, wherein the electronic computing and control unit is further 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 consists of a lambda sensor according to a

Particle filter to use in conjunction with a

Lambda value change in the exhaust gas mass flow upstream of the particle filter, the particle filter, and thus the exhaust gas treatment system, a function check

undergo.

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 value, the corresponding particle emission exceeds a diagnostic threshold value (OBD threshold value).

In order to detect this state, starting from a steady or stationary or quasi-stationary operating state, for example when the internal combustion engine and is idling

for example, at a constant particle filter temperature, the lambda value upstream of the particle filter, preferably in one Step, increased, starting from a 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

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 a short period of time within a defined time window that immediately follows the increase in lambda value upstream of the particle filter, and

for example between 3 and 5 seconds, is only a comparatively small increase and a correspondingly smaller gradient, that is to say a lower one

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 entire 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 relationship between the

Lambda value change after the particle filter and

Lambda value change in front of the particle filter 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, the

Particulate filter classified as defective.

In this case, a corresponding change in the lambda value upstream of the particle filter is made by adding fuel to the

Exhaust gas mass flow in front of the particle filter, using a

Fuel supply device, which enables an accurate metering of the amount of fuel. Such

Fuel supply devices are common to many

Internal combustion engines, in particular in internal combustion engines for medium and heavy-duty vehicles, are already in use in order to achieve a regeneration required for the particle filter

Generate temperature increase in the exhaust gas by adding fuel.

A desired lambda value increase or

Lambda value reduction predefined in front of the particle filter and the required amount of fuel added

Appropriate control of the fuel supply device, metered into the exhaust gas mass flow. The necessary ones

Control values are, for example, based on, in

Dependency on different operating states, empirically created, stored maps, or by means of

corresponding calculation models determined.

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

Figure 1 is a schematic representation of an embodiment of a

Internal combustion engine with exhaust gas aftertreatment system according to the invention; Figure 2 is a schematic representation of another

Execution of an internal combustion engine with exhaust gas aftertreatment system according to the invention;

Figure 3 is a block diagram showing the

Procedure of an execution of the

method according to the invention;

Figure 4 is a qualitative representation of curves of

Lambda values before and after the particle filter if the particle filter is intact and defective; and

Figure 5 is a qualitative representation of traces of the

Lambda values before and after the particle filter for successive changes in lambda values.

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

Figure 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 3 and an intake tract 12.

The intake tract 12 includes an intake manifold 12a connected to the internal combustion engine 1 with an intake pipe 12b connected to it. A throttle valve 15 for regulating the air mass flow 20 in the intake pipe 12b and the air supply to the combustion chambers of the internal combustion engine 1 is arranged in the intake pipe 12b.

The exhaust tract 3 contains an exhaust manifold 3a, which also includes the exhaust line 3b and thus the exhaust gas aftertreatment system 2 connects the internal combustion engine 1. The exhaust gas aftertreatment system 2 includes the exhaust gas line 3b for guiding the exhaust gas mass flow 10 and a particle filter 5 arranged in the exhaust gas line 3b, and a fuel supply device 7 for adding fuel 7d into the exhaust gas mass flow 10 upstream, that is to say upstream of the particle filter 5 and Lambda sensor 6, in the exhaust gas mass flow 10 downstream, that is after the particle filter 5.

Furthermore, the exhaust gas aftertreatment system 2 includes an electronic computing and control unit 30, hereinafter also abbreviated to ECU, which is set up to specifically and specifically bring about a change in the lambda value in the exhaust gas mass flow 10 upstream of the particle filter 5 by changing the fuel addition by means of the fuel supply device 7 and for detecting a measurement signal output by the lambda sensor 6.

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

In this embodiment, the fuel supply device 7 has, in particular, a metering device 7b arranged upstream of the particle filter 5 on the exhaust gas line 3b, which is arranged on the exhaust gas line 3b for precise metering and introduction of the fuel 7d into the exhaust gas mass flow 10. The fuel 7d is stored in a storage container 7a, which in turn is connected to the metering device 7b via a fuel line 7e. An embodiment of the exhaust gas aftertreatment system 2, as described above, is characterized in that the ECU 30 is a integral part of a central control unit 32 of the internal combustion engine, which is also referred to as CPU 32 for short, the method to be carried out being part of an on-board diagnosis. nose system for monitoring the exhaust-gas-related functional units of the internal combustion engine in normal operation.

FIG. 2 also shows an internal combustion engine 1 with a further embodiment of an exhaust gas aftertreatment system 2 according to the invention, which, in a further embodiment of the embodiment shown in FIG. 1, has an exhaust gas mass flow 10 between the particle filter 5 and the fuel supply device 7, in particular the metering device 7b , in the exhaust pipe 3b on an ordered oxidation catalyst 8. In this example, the ECU 30 is further configured to carry out the method for the functional diagnosis of the exhaust gas aftertreatment system 2 of an internal combustion engine 1 in such a way that the setting or verification of the stationary operating mode includes an immediately preceding regeneration of the oxidation catalytic converter 8.

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 illustrated in the essential method steps using the simplified block sequence program shown in FIG. 3.

After the start of the method, the internal combustion engine is set to a stationary operating mode in the first method step, identified by "BP_Stat", a specific, constant lambda value in the Exhaust gas mass flow 10 before the particle filter 5 of the internal combustion engine 1 is adjusted. . Because in real operation the

If certain minor fluctuations in the operating parameters cannot be avoided in the internal combustion engine, the stationary operating mode and the constant lambda value are characterized by values of the corresponding operating parameters which are within a predetermined fluctuation range which is considered to be negligible for the method or lie within them.

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 identified by “BP_Stat = ok?”, Checks whether the current operating mode corresponds to the specified operating mode if this is not the case, the operating parameters of the internal combustion engine 1 will continue to be adjusted until the desired stationary operating mode is available, if the stationary operating mode is present, the next method step can follow.

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

In the following process step, identified by “X_Var”, the targeted, defined induction of a lambda value change X_Var in the exhaust gas mass flow 10 upstream of the particle filter 5 is then carried out, starting from the aforementioned constant lambda value, by changing the force Addition of substance by means of the fuel supply device 7 mentioned, in particular by correspondingly controlling the metering device 7b, by the ECU 30, as shown in FIG.

In one embodiment of the method according to the invention, the defined lambda value change X_Var upstream of the particle filter 5 can include a reduction and / or 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. This is done, for example, by correspondingly controlling the metering device 7b

Fuel supply device 7 by means of the ECU 30.

In another embodiment of the method according to the invention, the lambda value change X_Var in front of the particle filter 5 can 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 for the functional diagnosis of the particle filter, as will be explained further below and with the aid of FIG. 5.

In the further course of the method according to the invention, the lambda value change X_Sig in the exhaust gas mass flow 10 after the particle filter 5 is then measured within a defined time window TW immediately after the aforementioned lambda value change X_Var before the particle filter 5, in accordance with the method step identified with “X_Sig”. This takes place by means of the lambda sensor 6, which emits a corresponding measurement signal, which is fed to the ECU 30 for further processing via the signal line 6c, as symbolized by the dashed line in FIG. 2. In the following process step, marked “LVgW”, a correlating Lamb is provided

da comparison value LVgW based on the measured lambda value change.

As a lambda comparison value LVgW, for example, a subsequent time period TF from the time tO of the start of the lambda value change X_Var before the particle filter 5 to a time t1 at which the lambda value change X_Var after the particle filter 5 has a certain proportionate value L_% of the maximum lambda value change X_Var has reached 5 in front of the particle filter. This is also shown in Figure 4. Here the lambda value change X_Sig-l reaches a proportional value L_% of the maximum lambda value change X_Var at 63% after a subsequent time period TF at the time t1.

In another embodiment of the method, a respective maximum value L_Max_l, L_Max_2, or minimum value of the lambda value change X_Sig_l, X_Sig_2, after the particle filter and / or a gradient determined within the defined time window TW, is used as the lambda comparison value LVgW Gl the lambda value change used. This is also shown using the example of an increase in lambda value in FIG. 4, the change in lambda value X_Sig-1 having reached a maximum value L_Max_l by the end of the defined time window TW. The

Lambda value change X_Sig_l a gradient Gl, which can optionally also be used as a lambda comparison value LVgW. The same applies accordingly to a lambda value reduction not shown in FIG. 4.

In a further embodiment of the method, in order to provide a lambda comparison value LVgW, the before the Particle filters predefined and, within the defined time window TW, lambda values measured after the particle filter at a specific point in time and / or the gradients of the lambda value changes X_Var, X_Sig_l, X_Sig_2, are related to one another, as will be explained in more detail below using FIG. 4 should. This enables a particularly reliable Lamb to be provided

da comparison value LVgW and increases the diagnostic certainty of the procedure.

A further embodiment of the method according to the invention is characterized in that, in order to provide a lambda comparison value LVgW, the lambda values and / or the gradients of successive opposite lambda value changes, as described above, are used in combination with one another after and before the particle filter 5 , as will be explained further below using the example shown in FIG. 5.

In the following process step, identified by “LVgW - GW”, the lambda value change X_Sig_l, X_Sig_2, X_Sig measured within the defined time window TW is evaluated according to the particle filter 5 on the basis of the respective lambda comparison value LVgW and predetermined 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 Particle filter 5 measured values or gradients of the lambda value change can be used, which enables a wide variance in the design of the method according to the invention and the adaptation to the needs in the respective application. The comparative value LVgW must then be given correspondingly adjusted limit values GW. These can be determined beforehand, for example, empirically or by means of a model calculation and are stored, for example, in an electronic memory area of the electronic computing and control unit ECU and are called up from there for evaluating the lambda value change. Such an electronic memory area is identified in FIG. 3 by E_Sp2 and contains the corresponding limit values GW, which are shown as “(1) GW”.

On the basis of the previously described evaluation of the change in concentration after the particle filter 5, the following step, labeled “LVgW> GW”, then diagnoses the particle filter 5 as defective, “DPF = nok” if the evaluation shows that the lamb

since the comparison value LVgW has exceeded at least a predetermined limit value GW. Otherwise, the particle filter is diagnosed as functional "DPF = ok" if the lambda comparison value LVgW has not reached or exceeded a limit value. Depending on the type of lambda comparison value (LVgW), the respective limit value may be exceeded, as already explained above 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, after the particle filter 5 has been diagnosed, the targeted, defined lambda value change in front of the particle filter 5 is withdrawn again, and the internal combustion engine 1 is switched back to the normal working mode BP_Norm depending on the diagnosis result and is operated or operated as intended limited to an emergency operation BP Not. As can be seen from FIG. 3, different further measures can now be initiated based on and depending on the diagnostic result, and the method can thus be expanded.

If the diagnosis shows that the particle filter 5 is intact and functioning correctly, DPF = ok, the internal combustion engine can continue to be operated after the method has been carried out, that is to say after the diagnosis of the functionality of the particle filter 5, again in the normal working mode, BP_Norm is shown in the process step labeled "BP_Norm".

However, if the diagnosis shows that the particle filter is defective, DPF = nok, an emergency operation, BP_Not, of the internal combustion engine can be initiated instead, which, for example, still enables a workshop to be visited with reduced engine output. At the same time, an error message can be issued to the driver, prompting him to visit the nearest workshop immediately or to have the repair carried out. This is shown in FIG. 3 in the method step labeled "BP_Not".

In order to ensure permanently fault-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 TW for measuring the lambda value change in the exhaust gas mass flow 10 after the particle filter 5 has a duration of less than or equal to 5 seconds, in particular less than or equal to 3 seconds on. The length of this time window ensures that only a rapid change in lambda value after the particle filter 5, as occurs exclusively when the particle filter 5 is defective, has an effect in the determination of the lambda comparison value LVgW and thus in the diagnosis of the particle filter 5.

Figure 4 shows an example of the course of the lambda value change over time. The curve marked with X_Var shows the lambda value change upstream of the particle filter 5, starting from a lambda value regulated in the diagnostic mode of operation at time tO, a defined, abruptly shown lambda value change 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.

The curve marked X_Sig_l shows the lambda value recorded downstream of the particle filter in the event of a defective particle filter. Shortly after the time tO, i.e. immediately after the lambda value change X_Var has been brought about in front of the particle filter 5, the lambda value begins to rise with a gradient Gl within the time window TW and rises to a maximum value L_Max_l at the 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 X_Var before the particle filter.

The curve marked X_Sig_2, on the other hand, shows the lambda value recorded downstream of the particle filter with an intact particle filter. Immediately after the point in time tO, the lambda value also begins to increase within the time window TW here, but with a gradient G2 that is significantly smaller than the curve X_Sig_l. Accordingly, until Time tw, at the end of the time window TW, only a significantly smaller maximum value L_Max_2 is reached.

As the lambda comparison value LVgW, as can be seen from the aforementioned exemplary embodiments and FIG. 4, the respective lambda maximum value L_Max_l, L_Max_2 reached by the specific time tw at the end of the time window TW or the respective gradient Gl, G2 of the lambda value increase within the Time window TW can be used.

In another embodiment, a follow-up time period TF from the time tO of the start of the lambda value change X_Var before the particle filter 5 to a time t1 at which the lambda value change X_Sig_l, X_Sig_2, after the particle filter 5, can also optionally have a specific proportional value as a lambda comparison value LVgW L_% (here, for example, 63%) of the maximum lambda value change X_Var before the particle filter has been reached. As can be seen from FIG. 4, in the case of an intact particle filter 5, that is to say in the case of the curve X_Sig_2, the certain proportionate value L_% of 63% is only reached at a much later time t2. The faster the value L_% is reached, the greater the damage to the particle filter 5. The limit value GW for the subsequent time period used as the lambda comparison value could be set here, for example, at 63% / 1.5 seconds. If the value L_% of 63% of the maximum lambda value change X_Var is already reached after 1.2 seconds, the result is 63% / l, 2 seconds, which means that the limit value GW is exceeded and the particle filter is to be rated as defective (DPF = nok) is.

Furthermore, it is possible to consider the lambda values measured downstream of the particle filter and the upstream predetermined lambda values in combination and combine them from one Lambda comparison value to determine LVgW. The lambda value change X_Var upstream of the particle filter can be based on the default values or can be determined using model considerations.

To determine a lambda comparison value LVgW, the gradient Gl of the lambda value change downstream of the particle filter 5 determined within the time window TW can be divided by the grade rule LSpl of the lambda value change X_Var upstream of the particle filter. The result is used as the lambda comparison value LVgW.

Gl / LSpl = 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:

(30% / s) / 100% = 0.03 / s.

If there is now a limit value 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.

A further embodiment of the method, as shown qualitatively in FIG. 5, is characterized in that the lambda value change X_Var upstream of the particle filter has a lambda value change in one direction and a subsequent lambda value change in the opposite direction. In order to make it easier to understand, in this example it is assumed that there is a sudden increase in lambda value by a grade rule LSpl and a subsequent sudden decrease in lambda value by a grade rule LSp2, the reverse case also being possible. The values and or the gradients of the lambda value increase and the lambda value value are Reduction in each case before and in front of the particle filter 5 in combination with each other for evaluating the particle filter 5.

For example, a ratio value of the gradient Gla of the lambda value increase downstream and the grade rule LSpl of the lambda value increase upstream of the particle filter and of the gradient Give the subsequent lambda value drop downstream and the associated grade rule LSp2 of the lambda value reduction upstream of the particle filter and the sum thereof can be calculated.

This is shown qualitatively in FIG. 5. Shown is the curve X_Var of the lambda value change upstream and the resulting curve X_Sig of the lambda value downstream of the particle filter 5. The curve X_Var shows a deliberate and defined sudden increase in lambda value by the grade rule LSpl with a certain amount at time t10 and a persistence of the increased

Lambda values over time window TW1 up to time t20. This is followed by an abrupt reduction of the lambda value by the grade rule LSp2, which is brought about in a targeted and defined manner, by the same amount, that is to say a complete withdrawal of the lambda value increase, at time t20. The resulting curve of the lambda value downstream of the particle filter shows an increase with the gradient Gla following the time t10, within the time window TW1 immediately following the change in the lambda value before the particle filter, until the time t20 and a subsequent drop in the

Lambda values with a gradient give within the immediately following the lambda value change in front of the particle filter

Time window TW2 that lasts until time t30. The lambda comparison value LVgW can be determined according to the following relationship: (Gla / LSpl) + (Glb / LSp2) = LVgW

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

Claims

1. Method for the functional diagnosis of an exhaust gas aftertreatment

tion system (2) of an internal combustion engine (1), which has an exhaust pipe (3b) for guiding an exhaust gas mass flow (10) and a particle filter (5) arranged in the exhaust pipe (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), arranged 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 present (BP_Stat = ok),

- targeted, defined induction of a Lambda

change (X_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 (X_Sig) in the exhaust gas mass flow (10) after the particle filter (5) within a time frame (TW) following the above-mentioned lambda value change (X_Var) in the exhaust gas mass flow (10) before the particle filter (5) the lambda sensor (6);

- Providing a correlating lambda comparison value (LVgW) based on the measured lambda value change after the particle filter (X_Sig);

- Evaluate the change in lambda value (X_Sig) measured within the specified time window (TW) after the parti- kelfilter (5) based on the respective Lamb

da comparison value (LVgW) and predefined 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).

2. The method of claim 1, wherein the defined lambda

Value change (X_Var) before the particle filter (5) includes a reduction and / or an increase in the lambda value, which is set by means of a defined increase and / or reduction in the addition of fuel by means of the fuel supply device (7) mentioned.

3. The method according to any one of claims 1 or 2,

where as the lambda comparison value (LVgW) a subsequent time period (TF) from the time (tO) of the start of the lambda value change (X_Var) before the particle filter (5) to a time (tl) at which the lambda value change (X_Sig_l, X_Sig_2) after the particle filter (5) has reached a certain proportionate value (L_%) of the maximum lambda value change (X_Var) before the particle filter (5) is used.

4. The method according to any one of claims 1 or 2,

whereby as a lambda comparison value (LVgW) a respective maximum value (L_Max_l, L_Max_2) reached within the defined time window (TW) or minimum value of the lambda value or a gradient (Gl, G2) of the lambda value change determined within the defined time window (TW)

(X_Sig_l, X_Sig_2) after the particle filter (5) is used.

5. The method according to any one of claims 1 or 2, characterized in that to provide a Lamb

da comparison value (LVgW), the lambda values predefined and measured after the particle filter 5 at a specific point in time and / or the gradients of the lambda value changes within the defined time window (TW) in relation to one another.

6. The method according to any one of claims 1 or 2, characterized in that the lambda value change (X_Var) before the particle filter has a lambda value change in one direction (LSpl) and a subsequent lambda value change in the opposite direction (LSp2).

7. The method 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 (LSpl, LSp2, Gla, Gib)) respectively after and before the particle filter (5 ) can be used in combination.

8. The method according to any one of claims 1 to 7, characterized ge

indicates 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.

9. The method according to any one of claims 1 to 8, characterized ge

indicates 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) and continues depending on the diagnosis result is operated or limited to an emergency operation (BP Not).

10. The method according to any one of claims 1 to 9, characterized in that between the fuel supply device (7) and the particle filter (5), an oxidation catalyst (8) is arranged in the exhaust pipe (3b) and that the stationary mode ( BP_Stat) is additionally characterized by an immediately preceding regeneration of the oxidation catalyst (8).

11. exhaust gas aftertreatment system (2) of an internal combustion engine (1), which has an exhaust pipe (3b) for guiding an exhaust gas mass flow (10) and one in the exhaust pipe (3b) to ordered particle filter (5) and a force

Substance supply device (7) for adding fuel into 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 that the exhaust gas aftertreatment system is assigned an electronic computing and control unit (30), which is set up for the targeted, defined induction of a lambda value change (X_Var) in the exhaust gas mass flow (10) upstream of the particle filter (5) by changing the fuel addition by means of the fuel Feeding device (7) and for detecting a measurement signal output by the lambda sensor (6), the electronic computing and control unit (30) also being set up to perform the method for functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1) according to one of the Execute claims 1 to 9.

12. The exhaust gas aftertreatment system according to claim 11, characterized in that it is arranged in the exhaust gas mass flow (10) between the particle filter (5) and the fuel supply device (7) in the exhaust line (3b) Oxidation catalyst (8), wherein the electronic computing and control unit (30) is further set up to carry out the method for functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1) according to claim 10.