Method for functional diagnosis of an exhaust aftertreatment system of an internal combustion engine and exhaust aftertreatment system

Abstract

Method for the functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1), which has an exhaust line (3b) for conducting an exhaust gas mass flow (10) and a particulate filter (5) arranged in the exhaust line (3b), wherein a fuel supply device (7) for adding fuel (7d) to the exhaust gas mass flow (10) is arranged upstream, before the particulate filter (5), and a lambda sensor (6) is arranged downstream in the exhaust gas mass flow (10), after the particulate filter (5), and wherein an oxidation catalyst (8) is arranged in the exhaust line (3b) between the fuel supply device (7) and the particulate filter (5), comprising the following steps: - Setting and / or verifying a steady-state 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 particulate filter (5) and an immediately preceding regeneration of the oxidation catalyst (8); in the steady-state operating mode (BP_Stat=ok), - targeted, defined induction of a lambda value change (λ_Var) in the exhaust gas mass flow (10) upstream of the particulate 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) downstream of the particulate filter (5) within a defined time window (TW) immediately following the aforementioned lambda value change (λ_Var) in the exhaust gas mass flow (10) upstream of the particulate filter (5), by means of 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 lambda value change (λ_Sig) measured within the specified time window (TW) after the particulate filter (5) using the respective lambda comparison value (LVgW) and specified limit values (GW); and - Diagnosing the particulate filter (5) as defective (DPF=nok) if the evaluation shows that the lambda comparison value (LVgW) has exceeded at least a specified limit value (GW).

Description

The present invention relates to a method for the functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine, in particular of a diesel engine, which has a particle filter arranged in an exhaust line and a fuel feed device for adding fuel into the exhaust gas mass flow in 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 to say downstream of the particle filter.Vehicles with diesel internal combustion engines (diesel engine), but increasingly also vehicles with Otto internal combustion engines (gasoline engine), nowadays have a particle filter (DPF) for avoiding particles (soot, fine dust) in the exhaust emissions and optionally a so-called oxidation catalyst for reducing the pollutant fractions in the exhaust emissions.The legislator decreases the emission limit values of the exhaust gases of vehicles with internal combustion engines (internal combustion engines) ever further and leaves regulations for monitoring their regulation function. This also relates in particular to the so-called OBD diagnosis (on-board diagnosis, ongoing automatic self-diagnosis during the intended operation of the vehicle) in such vehicles. Thus, nowadays, the particle filters must also be subjected to such a frequent and accurate OBD diagnosis.For example, JP 2005-90 324 A discloses a method in which fuel is supplied to the filter at an exhaust passage of the internal combustion engine via a fuel addition valve. A lambda sensor downstream of the filter is then used to detect the extent to which the air-fuel ratio changes and to diagnose whether or not the filter is broken on the basis of the result.Furthermore, document FR 2 979 949 A1 discloses a method which provides an oxygen probe upstream and downstream of a catalyst and a particle filter in an exhaust line, respectively. During a regeneration phase, the oxygen content in the exhaust gas upstream and downstream of the particulate filter is then compared, and the state of the particulate filter is diagnosed on the basis of the comparison result.Document WO 2017 / 220 083 A1 also relates to an exhaust gas purification device having a filter function, wherein the filter substrate is provided on its surface with an oxygen-storing coating. For the diagnosis of the exhaust gas purification device, the oxygen storage capacity of the oxygen-storing coating is detected by two lambda sensors.Furthermore, documents FR 2 958 971 A1 and US 2005 / 0 188 681 A1 each disclose a method for diagnosing a particulate filter having an oxidation catalyst in an exhaust line of an internal combustion engine. At this time, a development of the oxygen content at an inlet and an outlet of the particulate filter over a predetermined period of time is determined, and whether the particulate filter is present or has deteriorated in function is determined by comparing the changes of the oxygen content at the inlet and outlet of the particulate filter.Document DE 10 2011 106 933 A1 describes a method for testing a particle filter which simultaneously provides the function of a three-way catalytic converter, in particular with oxygen storage. The catalytic function of the coating is tested and the functionality for separating particles is deduced therefrom.Finally, document DE 10 2016 213 767 A1 discloses a method for diagnosing an exhaust system of an internal combustion engine, in which a check of the functionality of a lambda probe and / or of a four-way catalytic converter is carried out on the basis of a lambda change when the internal combustion engine changes from a lean operation to a rich operation.It is also known to carry out such a diagnosis with respect to the particle emissions with a so-called PM sensor (Particulate Matter Sensor). If the PM emission after the patient filter measured with the particle sensor 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. Further, the diagnosis is limited to the particulate emission, and the accuracy of the diagnosis is also not good enough to meet the requirements of future even lower emission thresholds.The present invention is therefore based on the object of creating a method and a corresponding exhaust gas aftertreatment system of an internal combustion engine which make possible a particularly rapid and accurate automatic functional diagnosis of a particle filter with respect to the particle filtering during operation of the internal combustion engine.This object is achieved according to the invention by a method and an exhaust gas aftertreatment system according to the independent claims.According to the invention, a method for the functional diagnosis of an exhaust gas aftertreatment system of an internal combustion engine is presented, wherein the exhaust gas aftertreatment system has an exhaust line for guiding an exhaust gas mass flow and a particle filter arranged in the exhaust line, and wherein a fuel feed device for adding fuel into the exhaust gas mass flow is arranged upstream, that is to say upstream of the particle filter, and a lambda sensor is arranged in the exhaust gas mass flow downstream, that is to say downstream of the particle filter, and wherein an oxidation catalyst is arranged in the exhaust line between the fuel feed device and the particle filter.A so-called lambda sensor, also referred to 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 available in the combustion chamber of an internal combustion engine for the combustion of the supplied fuel mass to the air mass required for a 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 an excess of air and thus a so-called lean combustion, conversely at λ<1 there is an excess of fuel and thus a so-called rich combustion.The method according to the invention has the steps shown below:setting and / or verifying a steady-state 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 and an immediately preceding regeneration of the oxidation catalytic converter; in the presence of the steady-state operating mode,specifically, defined generation 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 aforementioned fuel supply device;measuring the lambda value change in the exhaust gas mass flow downstream of the particle filter within a defined time window, directly following the aforementioned lambda value change in the exhaust gas mass flow upstream of the particle filter, by means of the lambda sensor;providing a correlating lambda comparison value based on the measured lambda value change downstream of the particle filter;evaluating the lambda value change after the particle filter measured within the defined time window on the basis of the respective lambda comparison value and predefined limit values; anddiagnosing the particulate filter as defective if the evaluation reveals that the lambda comparison value has exceeded at least one predefined limit value.In this context, the steady-state operating mode of the internal combustion engine and the constant lambda value are understood to mean that the relevant operating parameters, such as, for example, the rotational speed at a specific load and, in particular, the lambda value, lie or move within a predefined fluctuation range which is dimensioned such that their effects on carrying out the method, with sufficient accuracy of the diagnostic result, are negligible. It is therefore also possible here to refer to a quasi-stationary operating mode and a quasi-constant lambda value. The predetermined range of variation can be determined empirically or with the aid of model calculations.Furthermore, an exceeding of a predefined limit value can take place both in the positive and in the negative direction, depending on the type of lambda comparison value. Exceeding is therefore not to be understood here in the sense of "becoming greater", but rather in the sense of "exceeding a limit" independently of the direction.The invention further relates to an exhaust gas aftertreatment system of an internal combustion engine, which has an exhaust line for guiding an exhaust gas mass flow and a particle filter arranged in the exhaust line, and also a fuel feed 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 to say downstream of the particle filter.This exhaust gas aftertreatment system is further characterized in that it has an oxidation catalyst arranged in the exhaust gas mass flow between the particle filter and the fuel supply device in the exhaust gas line, and that it is assigned an electronic computing and control unit which is configured to specifically bring about a lambda value change in the exhaust gas mass flow upstream, upstream of the particle filter, by changing the fuel addition by means of the fuel supply device mentioned and to record a measurement signal output by the lambda sensor, wherein the electronic computing and control unit is furthermore configured 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 in using a lambda sensor downstream of a particle filter in order to subject the particle filter, and thus the exhaust gas treatment system, to a function check in conjunction with a lambda value change in the exhaust gas mass flow upstream of the particle filter.Functionally influencing damage to particle filters usually consist of apertures 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 unfiltered and untreated. If the total cross-section of the apertures or open holes is above a threshold, the corresponding particulate emission exceeds a diagnostic (OBD) threshold.In order to detect this state, starting from a steady or steady or quasi-steady operating state, for example, during idling of the internal combustion engine and, for example, at a constant particle filter temperature, the lambda value upstream of the particle filter is increased, preferably in one step, starting from a previously given lambda value, and the signal curve representing the lambda value downstream of the particle filter is observed. A measurement of the corresponding lambda value change takes place downstream of the particle filter.With the filter substrate 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. a lower rate of increase, during a short period of time, within a defined time window which immediately follows the lambda value increase in front of the particle filter and is, for example, between 3 and 5 seconds.If a lambda comparison value determined from the lambda value measurement is below or above a correspondingly predefined limit value, it is to be assumed that the entire cross section of apertures in the filter substrate is so small that the full functionality can be assumed to be given. If, however, the limit value is exceeded, the entire cross section of apertures in the filter substrate is so large that the exhaust gas flows through the particle filter to a large extent and virtually without delay in an unfiltered manner, so that the corresponding lambda sensor downstream of the particle filter registers an immediate lambda value increase with a much higher gradient within the defined, immediately following time window.It has been found that the ratio between the lambda value change downstream of the particle filter and the lambda value change upstream of the particle filter is directly proportional to the total cross section of the apertures in the filter substrate of the particle filter. If this ratio is above a certain threshold value or limit value, the particle filter is classified as defective.A corresponding change in 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 feed device which enables an accurate 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-duty and heavy-duty vehicles, in order to generate a temperature increase in the exhaust gas required for the particle filter regeneration by means of addition of fuel.In this case, a desired lambda value increase or lambda value reduction is predefined upstream of the particle filter and the quantity of fuel added required for this purpose is metered into the exhaust gas mass flow by appropriate actuation of the fuel feed device. The control values required for this are determined, for example, on the basis of stored characteristic maps that are created using a sensation depending on different operating states, or by means of corresponding calculation models.The invention and further advantageous exemplary embodiments and refinements of the invention are explained in detail below with reference to the figures. The following are shown: FIG. 1 shows a schematic illustration of an embodiment of an internal combustion engine with an exhaust gas aftertreatment system; FIG. 2 shows a schematic illustration of an embodiment of an internal combustion engine with an exhaust gas aftertreatment system according to the invention; FIG. 3 is a block diagram showing the method sequence of an embodiment of the method according to the invention; FIG. 4 shows a qualitative representation of curves of lambda values before and after the particle filter with the particle filter intact and defective; and FIG. 5 shows a qualitative representation of curves of the lambda values before and after the particle filter with successive lambda value changes.Objects having the same function and designation are identified throughout the figures by the same reference numerals.FIG. 1 shows schematically in a simplified representation an embodiment of an internal combustion engine with an exhaust gas aftertreatment system, for example a diesel engine. The internal combustion engine 1 has an exhaust tract 3 and an intake tract 12.The intake passage 12 includes an intake manifold 12a connected to the internal combustion engine 1 and having an intake pipe 12b connected thereto. A throttle valve 15 is arranged in the intake pipe 12 bto regulate the air mass flow 20 in the intake pipe 12 band the air supply into the combustion chambers of the internal combustion engine 1.The exhaust tract 3 contains an exhaust manifold 3 awhich connects the exhaust line 3 band thus the exhaust gas aftertreatment system 2 to the internal combustion engine 1. The exhaust gas treatment system 2 includes the exhaust gas line 3 bfor guiding the exhaust gas mass flow 10 and a particle filter 5 arranged in the exhaust gas line 3 band a fuel feed device 7 for adding fuel 7 dto the exhaust gas mass flow 10 upstream, i.e. upstream of the particle filter 5 and a lambda sensor 6 downstream, i.e. downstream of the particle filter 5, in the exhaust gas mass flow 10.Furthermore, the exhaust gas aftertreatment system 2 includes an electronic computing and control unit 30, also referred to below as an ECU for short, which is configured to specifically bring about a lambda value change 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 mentioned, and to record a measurement signal output by the lambda sensor 6.The ECU 30 is furthermore configured to execute 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 6 c, 7 cand 15 cto 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 7 barranged on the exhaust line 3 bupstream of the particulate filter 5, which metering device is arranged on the exhaust line 3 bfor precise metering and introduction of the fuel 7 dinto the exhaust gas mass flow 10. The fuel 7 dis stored in a storage container 7 a, which in turn is connected to the metering device 7 bvia a fuel line 7 e.An embodiment of the exhaust gas aftertreatment system 2, as described above, is characterized in that the ECU 30 is an integral component of a central control unit 32 of the internal combustion engine, which is also referred to for short as CPU 32, wherein the method to be executed is part of an on-board diagnostic system for monitoring the exhaust-gas-relevant functional units of the internal combustion engine during normal operation.FIG. 2 shows an internal combustion engine 1 with an 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 oxidation catalytic converter 8 arranged in the exhaust gas mass flow 10, between the particle filter 5 and the fuel feed device 7, in particular the metering device 7 b, in the exhaust gas line 3 b. In this example, the ECU 30 is further configured to execute the method for the functional diagnosis of the exhaust gas aftertreatment system 2 of an internal combustion engine 1 such that the setting or verifying of the steady-state 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 on the basis of the simplified block sequence program illustrated in FIG. 3.After the start of the method, the internal combustion engine is set to a steady-state operating mode in the first method step identified as "BP Stat", wherein a specific, constant lambda value in the exhaust gas mass flow 10 upstream of the particle filter 5 of the internal combustion engine 1 is adjusted as the decisive operating parameter. Since certain slight fluctuations of the operating parameters cannot be avoided during 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 move within a predefined range of fluctuation which is to be regarded as negligible for the method or lie therein.Since the setting, setting and / or verification of the diagnostic operating parameters can take a certain time, it is checked in the following method step, which is labeled "BP_Stat=ok?", whether the current operating mode matches the predefined operating mode. As long as this is not the case, the operating parameters of the internal combustion engine 1 continue to be attempted to be adjusted until the desired steady-state operating mode is present. If the stationary operating mode is present, the next method step can follow.In the case 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 steady-state operating mode BP_Stat is additionally characterized in that an immediately preceding regeneration of the oxidation catalytic converter (8) has taken place. This ensures that the oxidation catalyst is "discharged" and has minimal influence on the lambda value in the exhaust gas.In the following method step, marked "λ_Var", the targeted, defined establishment of a lambda value change λ_Var in the exhaust gas mass flow 10 upstream of the particle filter 5 is then effected starting from the aforementioned constant lambda value, by changing the fuel addition by means of the fuel supply device 7, in particular by corresponding actuation of the metering device 7 b, by the ECU 30, as illustrated in FIG. 3 with dashed line.In one embodiment of the method according to the invention, the defined lambda value change λ_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 a fuel addition by means of the fuel feed device 7. This is effected, for example, by corresponding actuation of the metering device 7 bof the fuel feed device 7 by means of the ECU 30.In another embodiment of the method according to the invention, the lambda value change λ_Var upstream 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 can be used, in addition, 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, according to the method step marked "λ_Ig", the lambda value change λ_Ig in the exhaust gas mass flow 10 downstream of the particle filter 5 is measured within a defined time window TW immediately following the aforementioned lambda value change λ_Var upstream of the particle filter 5. This is done by means of the lambda sensor 6, which emits a corresponding measurement signal, which is fed via the signal line 6 cto the ECU 30 for further processing, as symbolized by the dashed line in FIG. 2.In the following method step, denoted by "LVgW", a correlating lambda comparison value LVgW is provided on the basis of the measured lambda value change.As a lambda comparison value LVgW, for example, a subsequent time duration TF can be used from the time t0of the beginning of the lambda value change λ_Var upstream of the particle filter 5 to a time t1at which the lambda value change λ_Var downstream of the particle filter 5 has reached a specific proportional value L_ % of the maximum lambda value change λ_Var upstream of the particle filter 5. This is also shown in FIG. 4. Here, the lambda value change λ_Ig-1 reaches a proportional value L_ % of the maximum lambda value change λ_Var at 63% after a subsequent time period TF at time t 1.In another embodiment of the method, a respective maximum value L_Max_ 1, L_Max_ 2 reached within the defined time window TW or minimum value of the lambda value change λ_Ig_ 1, λ_Ig_ 2 after the particle filter and / or a gradient G 1 of the lambda value change determined within the defined time window TW is used as the lambda comparison value LVgW. This is also illustrated in FIG. 4 using the example of a lambda value increase, wherein the lambda value change λ_Ig-1 has reached a maximum value L_Max_ 1 until the end of the defined time window TW. In this case, the lambda value change λ_Ig_ 1 has a gradient G 1, 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 lambda values which are predetermined upstream of the particle filter and which are measured after the particle filter within the defined time window TW at a specific point in time and / or the gradients of the lambda value changes λ_Var, λ_Ig_ 1, λ_Ig_ 2 can be put into a relationship with one another, as will be explained in more detail below with reference to FIG. 4. This enables the provision of a particularly reliable lambda comparison value LVgW and increases the diagnostic reliability of the method.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 each used after and before the particle filter 5 in combination with one another, as will be explained further below with reference to the example shown in FIG. 5.In the following method step, labeled "LVgW - GW", the lambda value change λ_Ig_ 1, λ_Ig_ 2, λ_Ig measured within the defined time window TW is evaluated downstream of the particle filter 5 on the basis of the respective lambda comparison value LVgW and predefined limit values GW GW. 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 values or gradients of the lambda value change respectively measured before and after the particle filter 5 can be used as the lambda comparison value LVgW. This allows a wide variance in the design of the method according to the invention and the adaptation to the requirements in the respective application. According to the lambda comparison value LVgW used, correspondingly adapted limit values GW are then to be specified. These can be determined, for example, beforehand empirically or by means of 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 marked E_Sp2 in FIG. 3 and contains the corresponding limit values GW, which are represented as "(λ)G".On the basis of the previously described evaluation of the concentration change downstream of the particle filter 5, the particle filter 5 is then diagnosed as defective, "DPF=nok", in the following method step, identified as "LVgW≥GW", if the evaluation reveals that the lambda comparison value LVgW has exceeded at least one predefined 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), as already explained above, the respective limit value can be exceeded 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, after the particulate filter 5 has been diagnosed, the specific, defined lambda value change upstream of the particulate filter 5 is again reduced and the internal combustion engine 1 is transferred again into the normal operating mode BP_Norm as a function of the diagnostic result and is operated further as intended or is limited to an emergency mode BP_Not.As can be seen from FIG. 3, different further measures can now be initiated further on the basis of and as a function of the diagnostic result and the method can thus be extended.If the diagnosis reveals that the particle filter 5 is intact and functions without faults, DPF=ok, the internal combustion engine can continue to be operated in the normal operating mode, BP_Norm, after carrying out the method, that is to say after the diagnosis of the functionality of the particle filter 5, this is illustrated in the method step identified as "BP_Norm".If, however, the diagnosis reveals that the particle filter is defective, DPF=nok, an emergency operation, BP_Not, of the internal combustion engine can instead be initiated, which still enables, for example, a visit to a workshop with reduced engine output. At the same time, an error message can be output to the vehicle driver with the request to promptly visit the next workshop or to initiate the repair. This is shown in FIG. 3 in the method step labeled "BP_Not".In order to ensure a permanently fault-free operation of the exhaust gas aftertreatment system, the method according to the invention can be repeated in specific cycles during operation, wherein these cycles can be based on a specific operating time duration, a specific operating power 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 downstream of the particle filter 5 has 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 rapid change in lambda value downstream of the particle filter 5, as occurs exclusively in the event of a defect in the particle filter 5, has an effect in the determination of the lambda comparison value LVgW and thus in the diagnosis of the particle filter 5.FIG. 4 shows, by way of example, the curves of the lambda value change over time. The curve marked λ_Var shows the change in lambda value upstream of the particle filter 5, wherein, starting from a lambda value adjusted in the diagnostic operating mode, at the time t0, a defined change in lambda value, shown abruptly here, is brought about. The lambda value change is shown in % of the change value and can thus be seen as a value both positive and negative.The curve marked A_Ig_ 1 shows the lambda value recorded downstream of the particle filter in the case of a defective particle filter. Shortly after the time t0, i.e. immediately after the establishment of the lambda value change λ_Var in front of the particle filter 5, the lambda value starts to increase with a gradient G1 within the time window TW and increases up to a maximum value L_Max_1 at the time tw, at the end of the time window TW. In the further course of time, the lambda value downstream of the particle filter rises to 100% of the predefined lambda value change λ_Var upstream of the particle filter.The curve marked λ_Ig_ 2, on the other hand, shows the lambda value recorded downstream of the particle filter in the case of an intact particle filter. Immediately after the time t0, the lambda value also starts to rise within the time window TW here, but with a gradient G2 that is significantly smaller than the curve λ_Ig_1. Accordingly, up to the time tw, at the end of the time window TW, only a substantially smaller maximum value L_Max_2 is also reached.As can be seen from the aforementioned exemplary embodiments and FIG. 4, the respective lambda maximum value L_Max_ 1, L_Max_ 2 reached at the end of the time window TW up to the specific point in time tw or also the respective gradient G 1, G 2 of the lambda value increase within the time window TW can be used as the lambda comparison value LVgW.In another embodiment, a subsequent time duration TF from the time t0of the beginning of the lambda value change λ_Var upstream of the particle filter 5 to a time t1at which the lambda value change λ_Ig_ 1, λ_Ig_ 2 downstream of the particle filter 5 has reached a specific proportional value L_ % (here, for example, 63%) of the maximum lambda value change λ_Var upstream of the particle filter can also be used as the lambda comparison value LVgW. 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 course curve λ_Ig_ 2, the specific proportional value L_ % of 63% is only reached at a significantly later point in time t 2. The faster the value L_ % is reached, the greater is the damage to the particle filter 5 that is present. The limit value GW for the subsequent time duration used as a lambda comparison value could be defined here at 63% / 1.5 seconds, for example. If the value L_ % of 63% of the maximum lambda value change λ_Var is thus already reached after 1.2 seconds, 63% / 1.2 seconds result, as a result of which the limit value GW is exceeded and the particle filter is to be assessed as defective (DPF=nok).Furthermore, it is possible to consider the lambda values measured downstream of the particle filter and the lambda values predefined upstream in combination and to determine a lambda comparison value LVgW therefrom. The lambda value change λ_Var upstream of the particle filter can be based on the specified values or can be determined with the aid of model considerations.In order to ascertain a lambda comparison value LVgW, in one exemplary embodiment, the gradient G 1 of the lambda value change downstream of the particle filter 5 ascertained within the time window TW can be divided by the step value LSp 1 of the lambda value change λ_Var upstream of the particle filter. The result is used as lambda comparison value LVgW. If, for example, the gradient of the concentration increase downstream of the particle filter is 30% / s and the jump value of the concentration change upstream of the particle filter is 100%, a lambda comparison value is obtained: if a limit value GW of, for example, 0.015 / s is now present, this would be exceeded (LVgW≥GW) and the particle filter would be assessed as defective (DPF=nok).This procedure increases the robustness of the method against disturbing influences.A further embodiment of the method is, as shown qualitatively in FIG. 5, characterized in that the lambda value change λ_Var upstream of the particle filter has a lambda value change in one direction and a subsequent lambda value change in the opposite direction. For the sake of easier comprehension, in this example, a sudden lambda value increase by a jump value LSp1 and a subsequent sudden lambda value reduction by a jump value LSp2 are initially assumed, wherein the reverse case is also possible. In this case, the values and or the gradients of the lambda value increase and the lambda value reduction are each used after and before the particle filter 5 in combination with one another for evaluating the particle filter 5.Thus, for example, a ratio value of the gradient G1a of the lambda value increase downstream and of the jump value LSp1 of the lambda value increase upstream of the particle filter and of the gradient G1b of the subsequent lambda value decrease downstream and of the associated jump value LSp2 of the lambda value reduction upstream of the particle filter can be formed and their sum can be calculated.This is qualitatively illustrated in FIG. 5. The curve λ_Var of the lambda value change is shown upstream and the resulting curve λ_Ig of the lambda value downstream of the particle filter 5. This is followed by an abrupt lambda value reduction by the jump value LSp2 by the same amount, which is also specifically and in a defined manner, i.e. a complete reduction of the lambda value increase, at the time t20. The resulting profile of the lambda value downstream of the particle filter records an increase with the gradient G1a following the time t10, within the time window TW1 immediately following the lambda value change upstream of the particle filter, until the time t20 and a subsequent decrease of the lambda value with a gradient G1b within the time window TW2 immediately following the lambda value change upstream of the particle filter, which last until the time t30. According to the above-mentioned diagram, the lambda comparison value LVgW can be determined according to the following relationship:This procedure further increases the robustness of the method against disturbing influences.

Claims

Method for the functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1) which has an exhaust line (3b) for guiding an exhaust gas mass flow (10) and a particle filter (5) arranged in the exhaust line (3b), wherein a fuel feed device (7) for adding fuel (7d) into the exhaust gas mass flow (10) is arranged upstream, upstream of the particle filter (5), and a lambda sensor (6) is arranged downstream, downstream of the particle filter (5), in the exhaust gas mass flow (10), and wherein an oxidation catalyst (8) is arranged in the exhaust line (3b) between the fuel feed device (7) and the particle filter (5), having the following steps: - setting and / or verifying a steady-state 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) and a directly preceding regeneration of the oxidation catalytic converter (8); in the presence of the steady-state operating mode (BP_Stat=ok), a specific, defined bringing about 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 fuel supply device (7); the lambda value change (λ_Ig) in the exhaust gas mass flow (10) downstream of the particle filter (5) within a defined time window (TW) directly following the aforementioned lambda value change (λ_Var) in the exhaust gas mass flow (10) upstream of the particle filter (5) by means of the lambda sensor (6); providing a correlating lambda comparison value (LVgW) on the basis of the measured lambda value change downstream of the particle filter (λ_Ig); evaluating the lambda value change (λ_Ig) downstream of the particle filter (5) measured within the defined time window (TW) on the basis of the respective lambda comparison value (LVgW) and predefined limit values (GW); and diagnosing the particle filter (5) as defective (DPF=nok) if the evaluation reveals that the lambda comparison value (LVgW) has exceeded at least one predefined limit value (GW).Method according to claim 1, wherein the defined lambda value change (λ_Var) upstream of the particle filter (5) includes a reduction and / or an increase of the lambda value, which is set by a defined increase and / or reduction of a fuel addition by means of said fuel supply device (7).Method according to either of Claims 1 and 2, wherein a subsequent time duration (TF) from the time (t0) of the start of the lambda value change (λ_Var) upstream of the particle filter (5) to a time (t1) at which the lambda value change (λ_Ig_1, λ_Ig_2) downstream of the particle filter (5) has reached a specific proportional value (L_%) of the maximum lambda value change (λ_Var) upstream of the particle filter (5) is used as the lambda comparison value (LVgW).Method according to one of Claims 1 or 2, wherein a respective maximum value (L_Max_1, L_Max_2) or minimum value of the lambda value, which is reached within the defined time window (TW), or a gradient (G1, G2) of the lambda value change (λ_Ig_1, λ_Ig_2) downstream of the particle filter (5) determined within the defined time window (TW), is used as the lambda comparison value (LVgW).Method according to one of Claims 1 or 2, characterized in that, in order to provide a lambda comparison value (LVgW), the lambda values which are predetermined within the defined time window (TW) upstream of the particle filter 5 and measured downstream of the particle filter 5 at a specific point in time and / or the gradients of the lambda value changes are put into a relationship with one another.Method according to one of Claims 1 or 2, characterized in that the lambda value change (λ_Var) upstream of the particle filter has a lambda value change in one direction (LSp1) and a subsequent lambda value change in the opposite direction (LSp2).Method according to Claim 6, characterized in that, in order 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 one another in each case after and before the particle filter (5).Method according to one of 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.Method according to one of Claims 1 to 8, characterized in that, after the particulate filter (5) has been diagnosed, the specific, defined lambda value change upstream of the particulate filter (5) is canceled and the internal combustion engine (1) is transferred again into the normal operating mode (BP_Norm) and is operated further or is restricted to an emergency operation (BP_Not).Exhaust gas aftertreatment system (2) of an internal combustion engine (1), which has an exhaust line (3b) for guiding an exhaust gas mass flow (10) and a particle filter (5) arranged in the exhaust line (3b), and a fuel feed device (7) for adding fuel into the exhaust gas mass flow (10) upstream, upstream of the particle filter (5), and a lambda sensor (6), downstream, in the exhaust gas mass flow (10), downstream of the particle filter (5), 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 feed device (7) in the exhaust line (3b), and the exhaust gas aftertreatment system is assigned an electronic arithmetic and control unit (30) which is designed for the targeted, selective, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, automatic, In a defined manner, a change in lambda value (λ_Var) 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) mentioned and for detecting a measurement signal output by the lambda sensor (6), wherein the electronic computing and control unit (30) is furthermore configured to carry out the method for the functional diagnosis of an exhaust gas aftertreatment system (2) of an internal combustion engine (1) according to one of Claims 1 to 9.

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