CN112443380A

CN112443380A - Method for monitoring a particle filter by means of a particle sensor

Info

Publication number: CN112443380A
Application number: CN202010871092.6A
Authority: CN
Inventors: M·埃特尔; S·考茨施曼; T·汉德勒
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-08-27
Filing date: 2020-08-26
Publication date: 2021-03-05
Also published as: DE102019212807A1

Abstract

The invention relates to a method for monitoring a particle filter (16) by means of a particle sensor (20) which is arranged downstream of the particle filter (16) in an exhaust gas line (17) of an internal combustion engine (10), comprising: defining a first diagnostic phase (52) comprising: a soot emission model of a limiting particulate filter arranged downstream of the internal combustion engine is specified, and according to the soot emission model, the particulate sensor (20) can provide a first measurable signal when the limiting particulate filter is used after a period of time which is determined after a complete sensor regeneration (50), wherein the period of time (t) thus determined₁) An end of the first diagnostic phase (52) is defined, wherein the method further comprises: detecting an output signal (40, 42) of the particle sensor; and determining that the particulate filter (16) is damaged if the signal of the particulate sensor occurs in the defined first diagnostic phase (52).

Description

Method for monitoring a particle filter by means of a particle sensor

Technical Field

The present invention relates to a method for monitoring a particle filter by means of a particle sensor, as well as to a computing unit for carrying out the method and to a computer program for carrying out the method.

Background

Internal combustion engines inevitably produce soot particles in the exhaust gas, for which increasingly stringent limit values apply. Thus, in diesel engines, but also in gasoline engines, soot filters or particulate filters are used in exhaust gas aftertreatment systems. The operating capacity of a particle filter built into the exhaust gas flow can be monitored, for example, by means of suitable soot particle sensors, the output signals of which are evaluated by a control unit in order to deduce the soot particle content in the exhaust gas. The respective sensor can be arranged in front of the particle filter and/or behind the particle filter for different purposes.

Such a sensor may, for example, comprise two comb-shaped electrodes engaging into one another on a ceramic substrate, wherein the accumulation of conductive carbon black particles leads to a change in the impedance of the electrodes as a function of the amount of carbon black accumulated. As the particle concentration on the sensor surface increases, in this way a decrease in resistance or an increase in current can be measured with a constant voltage applied between the electrodes. However, a certain minimum amount of accumulated carbon black particles is required before a conductive connection is made and thereby a measurable signal is produced. I.e. before the minimum amount of particles is constructed at the sensor, the resistive particle sensor will not provide a signal and then exhibit a change in resistance, i.e. a current signal related to the applied measurement voltage.

Also, resistive particle sensors can only provide a meaningfully analyzable signal within a certain maximum load; above this maximum load, the resistance will no longer drop significantly or the measured current will no longer rise significantly. Thus, the particle sensor may be regenerated by pyrolysis by heating the particle sensor to a suitable temperature at which the accumulated carbon black particles may be burned off. The sensor may be heated, for example, by a heating element on the back side of the ceramic substrate. These heating elements can also be used to maintain the sensor at a relatively constant operating temperature, since the electrical conductivity is also affected by the temperature. In general, a measurement cycle in a vehicle for diagnostic purposes begins with such a regeneration of the sensor and is completely regenerated again after the diagnostic result has been obtained.

Future legislation on monitoring particulate filters contains significantly reduced limit values and specifies: small damage to the particle filter can be reliably and promptly detected even in on-board diagnostics (OBD). Therefore, it is required that: when the soot concentration in the exhaust gas is low, the corresponding particle sensor has to provide a diagnostic result immediately. These limits and reaction times cannot be achieved with the methods hitherto.

Disclosure of Invention

According to the invention, a method for monitoring a particle filter is proposed, as well as a computing unit for carrying out the method and a computer program for carrying out the method, having the features of the independent patent claims. Advantageous embodiments are the subject matter of the dependent claims and the subsequent description.

In particular, a method for monitoring a particle filter by means of a particle sensor, which is arranged downstream of the particle filter in an exhaust gas line of an internal combustion engine, is proposed, wherein a first diagnostic phase is defined, which comprises: specifying a soot emission model of a limiting particulate filter arranged downstream of the internal combustion engine; and, according to the soot emission model, determining how long after a complete sensor regeneration the particulate sensor can provide the first measurable signal with the use of the limiting particulate filter, wherein the time length thus determined defines the end of the first diagnostic phase. Based on this, the output signal of the particle sensor is then continuously detected and, if the signal of the particle sensor occurs in the defined first diagnostic phase, a particle filter damage is determined. By defining a limiting particle filter, that is to say a particle filter which is just still permissible or no longer permissible, on the basis of the desired limit value and the emission model, it is possible to ascertain already at a first diagnostic stage very early whether the particle filter is damaged more than this limiting particle filter, so that for example a replacement is necessary. Soot emission models are well known in the prior art.

A second diagnostic phase can then be further defined, which follows the first diagnostic phase, wherein at least one output signal of the particle sensor within at least one predefined time period within the second diagnostic phase is detected and evaluated for detecting damage to the particle filter. In this second phase, damage below the damage level of the defined limit particle filter can now also be ascertained, since each increase indicates a particle re-accumulation.

According to an exemplary embodiment, the expected soot concentration in the exhaust gas of the internal combustion engine is modeled for this purpose, and if there is an increase in the expected soot concentration, the time period specified for detecting the sensor signal is specified such that it begins to increase at the expected soot concentration. It is thereby possible to ascertain whether the corresponding signal of the particle sensor corresponds to the expected increase in the soot concentration in the exhaust gas, in order to monitor the functional capability of the sensor on the basis thereof.

For example, it can be provided that: if the at least one detected increase (i.e. the difference) in the output signal exceeds a predetermined limit value within a predetermined time period within the second diagnostic phase, the particle filter is damaged. In this case, it is optionally possible to select very small limiting values (up to a value of 0) or limiting values such that at least insignificant fluctuations do not lead to the triggering of a diagnostic result. However, more than one output signal may be analyzed for this purpose.

According to one specific embodiment, the sensor regeneration can be carried out, for example, after a predefined number of analyses of the output signal of the particle sensor and/or for the case in which the output signal of the particle sensor is above a maximum load threshold. Sensor regeneration may be performed in whole or in part. In this case, the sensor regeneration can be carried out, for example, in such a way that a residual load of the sensor in the case of soot particles remains, which corresponds to the sensor load at the end of the first diagnostic phase. In this way, the sensor is again in the second diagnostic phase immediately after the partial regeneration and can reliably measure the minimum signal rise without a time delay.

Alternatively, a count value may be stored, the count value being indicative of the number of sensor signals analyzed so far in the second diagnostic stage; additionally or alternatively, a time period may also be stored, which describes the time period since the last complete and/or partial sensor regeneration. In this way, the monitoring can also be continued directly in the last diagnostic phase at the restart after the interruption of the measurement cycle, for example due to the vehicle being stopped. This is particularly suitable for brief interruptions of the engine operation of an internal combustion engine, for example in a hybrid vehicle.

Preferably, measures can be taken if it is determined that the particle filter is damaged, for example an alarm signal is output. Furthermore, optionally, at least a part of the detected sensor signals can also be output via a diagnostic interface of the control unit.

The computing unit according to the invention, for example, a control device of a motor vehicle, is designed in a program-controlled manner in particular to carry out the method according to the invention.

The implementation of the method according to the invention in the form of a computer program or a computer program product with program code for carrying out all method steps is also advantageous, in particular when the control device which carries out the method is also used for other tasks and is therefore always present, since this results in particularly low costs. Data carriers suitable for providing the computer program are, in particular, magnetic, optical and electronic memories, such as hard disks, flash memories, EEPROMs, DVDs and others. It is also possible to download the program via a computer network (internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the accompanying drawings.

The invention is schematically illustrated in the drawings and will be described below with reference to the drawings according to embodiments.

Drawings

FIG. 1 schematically illustrates a system in which embodiments of the invention may be applied;

FIG. 2 illustrates a signal variation process of a resistive particle sensor according to an embodiment of the present invention in case of filter damage; and

fig. 3 shows the signal profile of the resistive particle sensor without damage to the filter.

Detailed Description

Fig. 1 schematically shows a system in which exemplary embodiments of the present invention may be applied. The air supply device 11 supplies air for combustion to the internal combustion engine 10, which may be embodied as a diesel engine. The exhaust gases of the internal combustion engine 10 are discharged via an exhaust gas line 17, in which at least one particle filter 16 is arranged. In the exhaust gas line 17, various sensors can also be arranged, such as a temperature sensor 15, a particle sensor 12 arranged upstream of the filter, and an exhaust gas sensor (not shown) in the form of an oxygen sensor, whose signals are supplied to the engine controller 14. Downstream of the particle filter, a particle sensor is arranged, which is designed here as a resistive particle sensor 20. Particulate filter 16 may also be connected to engine controller 14 or other control unit.

The particle sensor can output a signal when a measuring voltage is applied, which signal reproduces the load of the sensor in the case of soot particles. The signal may be output as a current or as a resistance of the particle sensor element. The exhaust gas line and other customary components of the exhaust gas aftertreatment system, such as a catalytic converter, are not shown in this figure.

The engine controller 14 determines the amount of fuel that can be delivered to the internal combustion engine 10 by means of the fuel metering device 13, for example on the basis of data delivered to it. The engine controller 14 may, for example, further process and analyze the sensor signals, for example by means of suitable software modules, and/or control the heating of the respective elements for filter regeneration and/or sensor regeneration, as will be described later.

With the illustrated apparatus, both observation of the particulate emissions of the internal combustion engine 10 (on-board diagnostics) and prediction of the load of the particulate filter are possible. The particulate filter may be, for example, a wall-flow filter or a bypass filter.

In the case of diesel engines, particulate filters are often used, while gasoline engines are increasingly also equipped with particulate filters. The invention may be applied not only to monitoring a diesel particulate filter but also to monitoring a gasoline particulate filter or similar filtering system.

According to a first embodiment of the invention, in order to achieve a more sensitive detection of defects and damage of the particle filter, a two-stage analysis of the signal of the particle sensor may be used.

In this case, a first diagnostic phase is defined by determining the expected particle load for a theoretical particle filter which is still considered intact after the limit value to be applied. The modeled particulate filter is used as a limit case (limit particulate filter). Next, based on the limit particle filter with critical damage, it is determined: after which period of time soot may accumulate at the particle sensor 20 used, the particle load is still just too small to result in a measurable sensor signal. In this way, the duration t is obtained₁As a limit of the first diagnostic phase, the time period t₁It is stated how long later the first sensor signal can be measured in the case of a limiting particle filter. To calculate the time length t₁In particular, a model of the particle emissions of the internal combustion engine 10 can be used as a function of the operating point, which in turn can be constructed from the modeled and/or detected data. The end of a complete sensor regeneration can be used as the beginning of a measurement cycle or a first diagnostic phaseTime t₀。

If it is now possible to operate the diagnostic device already in this first phase, i.e. for a time period t₁Detecting a measurable signal at particle sensor 20 before expiration, this indicates: the particle load is still higher than in the case of a predefined limiting particle filter. Then, from this, it can be immediately concluded: the measured particle filter should be considered as damaged because it has poorer filtration properties than the limiting particle filter. In general, a current rise during the first phase can conclude that the degree of damage of the particle filter is high.

Whereas in the case of a critically good particle filter or even better filter, from the point in time t₀To t₁Should be performed without a measurable sensor signal.

At a time t₁After expiration, the second diagnostic phase begins. At this stage, a diagnostic result can be obtained by detecting the sensor signal, i.e. the current output by the particle sensor, for example, during the time period Δ t, respectively. Here, a model of the soot emissions of the engine can be used in order to determine the expected increase Δ s of the particulate emissions during this time period. If at least some of these emissions are not blocked by the particle filter and are detected by the particle sensor, then measurable sensor signals Δ I can be expected at these times in the second diagnostic phase, since in the first diagnostic phase at time t₁At the end there is already a minimum sensor load for signal generation. Preferably, the degree of the current change Δ I is also here the degree of DPF damage, so that when the signal change is large, it can be assumed that the damage is more severe.

Fig. 2 shows the course of the output signal of the resistive particle sensor 20 over time after a critically damaged particle filter (i.e. a particle filter corresponding to a critical particle filter) together with the corresponding soot concentration in the exhaust gas flow 17. The upper line 30 is the soot concentration and the lower line 40 is the sensor signal. Here, these emissions can be calculated by means of a suitable model of the engine, including the operating conditions. At the beginning of the presented curve, a complete sensor regeneration 50 is performed (after the end of the dew point is reached). The regeneration phase 50 may be performed at engine start-up or independently thereof. During the regeneration phase, the particulate sensor may be heated to a higher temperature at which the accumulated soot may be burned off. The temperature required for this depends, inter alia, on the gas composition present. The regeneration phase 50 may be introduced and controlled by the control unit 14 in connection with the sensors. The control unit may be, for example, an engine control unit 14, which may be connected to the sensors 20 and other components, for example, via a bus system, but other suitable control units may also assume these tasks. After sensor regeneration 50 ends, a measurement cycle for diagnostic purposes begins.

As can be seen in fig. 2: the sensor signal 40 reaches the first diagnostic phase 52 up to the time t₁Despite the correspondingly present soot concentration, the latter is not increased by definition, since the diagnosis phase is defined on this basis. Once a measurable signal is expected for the limiting particulate filter, a first diagnostic stage 52 (time t)₁) It ends and the second diagnostic phase 53 begins. Now, in the case of at least one modeled increase Δ s1, Δ s 2. (as seen in the short marked part of the upper curve), the associated sensor signal Δ I of the particle filter 20 is detected₁, ΔI₂, ΔI₃,.... For a limiting particle filter, this would also expect a measurable sensor signal, i.e. a current rise. The time during which the rise in the sensor signal is measured is the duration Δ t. The diagnostic time period Δ t is variable and depends on the level and duration of the positive change in soot concentration. The diagnosis is started when the positive gradient of the soot concentration exceeds a predefined limit value and is ended when the positive gradient of the soot concentration falls below a predefined limit value, respectively. Here, if the initial carbon black concentration is minute, for example, when the vehicle shifts from the engine idling/thrust phase/engine stop phase to strong acceleration, carbon blackThe probability of a positive change in concentration and correspondingly analyzable diagnostic result rises.

The signal increase Δ I over the time period can then be evaluated in the corresponding control unit 14 and either only evaluated as a qualitative indication of the presence of a certain damage or quantitatively, wherein, for example, a correlation between the degree of the current increase Δ I with a predetermined increase Δ s of the soot concentration and the degree of damage of the particle filter, for example, a ratio Δ I/Δ s, can be found or can be predetermined. Immediately thereafter, the next increase Δ s in modeled soot concentration₂In this way, a further diagnostic result can be obtained, i.e. a renewed passing of the sensor signal Δ I₂Corresponding to the expected carbon black concentration deltas₂To obtain further diagnostic results.

Alternatively, the sensor signal 40 can also be detected in a similar manner without continuous monitoring or modeling of the soot concentration 30, wherein then an increase in the sensor signal 40 also indicates a new particle load and thus a damage of the particle filter 20. In this case, the sensor signal can be detected at regular time intervals or continuously, for example, without it being mandatory here to use the change in the soot concentration as a trigger.

Preferably, a plurality of sensor signals Δ I can be evaluated in the second diagnostic phase 53₁, ΔI₂, ΔI₃Or

diagnostic results

54, 55, 56, 57 without regenerating the sensor 20 between diagnostic stages. I.e. the particle sensor may remain in the previously described second diagnostic stage 53 and there is continued accumulation of soot. The associated sensor signal 40 will correspondingly continue to rise in absolute value, however, until the maximum measurable load is reached. Generally, an approximately linear increase in terms of particle loading will be expected. However, other variations are possible depending on the type of sensor, load and other conditions like temperature.

In this case, for example, the number n of diagnostic results that should be analyzed before the regeneration of the sensor can be specified. This may be done, for exampleTo do so by a simple counter that is raised by one at each diagnostic analysis and reset with sensor regeneration 58. Such a counter (or a predetermined number of other implementations of the diagnostic result) can also be stored in the non-volatile memory element, so that the vehicle can be stopped in the second phase 53 and the diagnosis can be continued correctly in the second phase 53 immediately after the next vehicle start, without a preceding sensor regeneration. Additionally or alternatively, the modeled soot load 30 in the exhaust gas flow and the time t determined therefrom up to the end of the first phase can also be stored when the vehicle is stopped₁Together with the length of time that has expired in this phase, it is also possible in this case to continue the

diagnostic phases

52, 53 immediately after the start. In this case, special parameters, which take account, for example, of the restart of the engine and its influence on the soot loading, can also influence the modeling.

If the sensor regeneration 58 is to be carried out, for example because a predetermined number of diagnostic events have been detected or the current of the sensor signal 40 exceeds a predetermined limit value, a complete or partial regeneration 58 of the sensor element can be carried out. For example, partial regeneration may only proceed to the extent that the conductive connection on sensor 20 has been burned off but a residual load remains on the sensor. This means that: the sensor after partial regeneration 58 may preferably always be loaded to such an extent that a measurable increase in sensor 40 occurs immediately after further particle loading. I.e. the sensor immediately resumes another second diagnostic phase 53 in the case of such a scheduled partial regeneration, in which one or more diagnostic results can then be further analyzed as described above. However, it is also possible to carry out a partial regeneration to a large extent up to a complete regeneration, i.e. the entire soot load on the sensor is burnt off.

The different triggering causes for regenerating the sensor element 20, such as exceeding the limit value of the measured current 40 and/or reaching the maximum number n of diagnostic results, can also be combined with one another as desired. According to one embodiment, regeneration 58 can always be triggered, for example, if the current is detected to be above a predetermined limit value. Correspondingly, for example, a current can be specified as a limit value, which current corresponds to the soot loading of the sensor 20 above the measurement limit. In this case, different regeneration cycles can also be specified for different trigger events, so that, for example, a complete regeneration can be carried out if the current is too high, and only a partial regeneration is carried out after a maximum number of diagnostic results. However, it is equally possible to use the same regeneration process for all triggering reasons. Furthermore, the sensor regeneration can optionally also be triggered by other events, such as the vehicle being switched off, a limit value being exceeded in terms of the modeled soot loading being exceeded, and/or a sensor regeneration taking place simultaneously with the filter regeneration. In one possible embodiment, it may be provided that: after a predefined number of passages of the second diagnostic phase with a corresponding partial regeneration of the filter 16, a complete regeneration is carried out, after which the first diagnostic phase 52 begins again. Here, in the control unit 14, there may be stored: which

diagnostic stage

52, 53 the sensor system is currently in. Likewise, it may also be provided that: sensor regeneration is performed at least when or only when regeneration of the filter 16 is triggered as long as the current 40 or sensor load is below a maximum load limit.

In fig. 3, an exemplary sensor signal 42 is shown for comparison purposes in the presence of an intact particle filter 16, wherein the sensor current 42 and the soot concentration 30 are plotted over time. The course of the change in the soot concentration in this example corresponds to the course of the change shown in fig. 2, and the

diagnostic phases

52, 53 and the regeneration phases 50, 58 defined in terms of the limiting particle filter are correspondingly identical. In this case of an undamaged or hardly damaged particle filter, the signal 42 in the first diagnostic stage 52 will be the same as in the case of the limiting particle filter 40, since in both cases no signal should occur in the first diagnostic stage 52. Thereby, in the first phase, only a conclusion is meaningful as to whether the particle filter is worse than the limit particle filter.

However, unlike the example in fig. 2, no sensor signal or at least only a small sensor signal (for example below a threshold value considered as a correlation limit) can now be measured in the second diagnostic phase 53. This indicates that: the upstream particle filter 16 functions normally and filters the particles from the exhaust gas flow 17 to such an extent that no significant amount of soot is accumulated at the downstream particle sensor 20. As also in the previous example, the standard-compliant partial regeneration 58 of the sensor can then optionally be carried out after a predefined number n of diagnostic results. Alternatively, it is also possible: such a periodic regeneration 58 is partially stopped, in particular when, depending on the sensor signal (or the cessation of the signal rise), it can be concluded therefrom that there is no soot loading exceeding the limit value of the first phase 52. In this case, a partial or complete sensor regeneration 58 may be carried out, for example, only if the measured sensor current 42 rises above a predetermined limit value. The same (partially loaded) initial state is thus always reached if, for example, a partial regeneration 58 of the sensor is only carried out if the measured sensor current 42 rises above a predetermined limit value.

It is also possible that: provision is made for periodic partial regeneration of the sensor after a predetermined number of diagnostic results; and/or to carry out these partial regenerations only if a measurable sensor current has occurred at least once in the last diagnostic phase, which indicates that damage or insufficient filtering has begun.

After a complete regeneration of the sensor, the diagnostic method can be reset to the beginning of the first diagnostic phase 52 independently of the cause of the regeneration, so that the predetermined period t is reached₁After expiry, the second diagnostic phase 53 is restarted, the predetermined period t₁Corresponding to the measurable load of the limiting particulate filter.

The number of diagnostic results in the second diagnostic phase, i.e. the number of detected sensor signal rises and the optional analysis of these sensor signal rises, may be the same in each of the repeated second phases 53 or differ due to certain conditions as explained above. At least one diagnostic result 54 should be detected here, but significantly

more results

55, 56, 57, for example 5 to 10 results, can be detected in the second diagnostic phase 53 before the sensor regeneration is carried out. It should be assumed that: the current does not rise so much that the sensor can also be operated for a long time in the second diagnostic phase with the limiting particle filter operating. Generally, it is not necessary to give an upper limit to the number of diagnostics performed per diagnostic stage, as long as the sensor is still capable of outputting a meaningful signal and is below its maximum measurable load.

Each of these obtained

diagnosis results

54, 55, 56, 57 can be analyzed individually and/or information from a plurality of diagnosis results can also be analyzed, for example over a plurality of diagnosis periods Δ t₁, Δt₂, Δt₃A plurality of signal rise values Δ I in₁, ΔI₂, ΔI₃The average value of (a,) is either in the form of or by taking into account the highest current rise max (Δ I) during the second diagnostic phase 53₁, ..., ΔI_n) To analyze the information in the plurality of diagnostic results. Other analysis options are also possible. Here, it is also possible: for example, if it is ascertained by means of the temperature sensor 15 that the exhaust gas temperature exceeds the appropriate operating conditions, certain diagnostic results are excluded from the analysis. Here, portions of the diagnostic results from the second stage 53 may continue to be used. It is also conceivable that: the diagnostic results from a plurality of diagnostic phases, in particular from a plurality of second diagnostic phases which are carried out one after the other with partial regeneration 58 in between, are jointly evaluated and further conclusions regarding the filter state are drawn, for example, from the increasing increase in the rise of the respective sensor signal over time.

In the event that a filter damage or at least a current lack of filter function of the particle filter 16 is detected, a corresponding signal can be generated by the control unit. This signal can be forwarded, for example, via an interface, in order to enable diagnostics at the connected device; and/or may result in a visible or audible warning signal to the driver. For example, the need to replace the filter or at least to inspect it can be indicated by an alarm signal or an alarm display. The diagnostic results obtained can optionally be stored partially or completely, so that further information about the degree of damage can be obtained, for example, in a repair shop by reading these values via an interface of the control unit. In this case, it can be provided how many diagnostic results must be detected with a measurable sensor signal in order to determine filter damage and a corresponding warning signal, so that, for example, brief fluctuations do not have to trigger a false alarm.

For all embodiments, a suitable particle sensor 20 may be arranged immediately behind the particle filter 16 to be monitored, or other elements of the exhaust gas aftertreatment system (e.g. one or more catalytic converters) may be between the filter and the sensor. Other catalytic converters or other exhaust gas aftertreatment components may likewise be arranged in front of or behind the particle filter system, as appropriate. The particulate filter may also be combined with a catalytic purification element, for example in an SCR-F (selective catalytic reduction on filter) system. Likewise, there may also be a plurality of particle filters 16 with individual assigned particle sensors 20, or in the case of a plurality of particle filters, only one particle sensor 20 may be used for monitoring. The diagnostic information obtained from the particle sensor may also be combined in the control unit 14 with other diagnostic results, for example with the measured pressure or counter pressure before or after the filter system.

Claims

1. A method for monitoring a particulate filter (16) by means of a particulate sensor (20) which is arranged downstream of the particulate filter (16) in an exhaust gas line (17) of an internal combustion engine (10), the method comprising:

defining a first diagnostic phase (52) comprising:

-specifying a soot emission model of a limiting particulate filter arranged downstream of the internal combustion engine;

-determining from the soot emission model how long after a complete sensor regeneration (50) the particle sensor (20) can provide the first measurable signal with the use of an extreme particle filter, wherein the time duration (t) thus determined is based on the soot emission model₁) Defining the end of the first diagnostic phase (52),

wherein the method further comprises:

detecting an output signal (40, 42) of the particle sensor;

and determining that the particulate filter (16) is damaged if the signal of the particulate sensor occurs in the defined first diagnostic phase (52).

2. The method of claim 1, further comprising:

defining a second diagnostic phase (53) which follows the first diagnostic phase (52); and is

Detecting and analyzing at least one predefined time period (Δ t) within the second diagnosis phase (53)₁, Δt₂, Δt₃Said.) at least one output signal (Δ I) of the particle sensor (20)₁, ΔI₂, ΔI₃..) for identifying damage to the particulate filter (16).

3. The method of claim 2, further comprising:

modeling an expected soot concentration (30) in an exhaust gas of the internal combustion engine; and is

If at the expected carbon black concentration (. DELTA.s)₁, Δs₂, Δs₃Said) there is an increase, said predetermined period of time (Δ t) will be set₁, Δt₂, Δt₃A.) is specified such that the time period begins with the expected beginning of the increase in carbon black concentration.

4. According to claim 2 or 3The method of (a), wherein provision is made for: if it is within the second diagnostic phase (53) for the predetermined time period (Δ t)₁, Δt₂, Δt₃..) at least one detected increase (Δ I) in the output signal₁, ΔI₂, ΔI₃And..) the particle filter is damaged (16) if a predetermined limit value is exceeded.

5. The method according to one of claims 2 to 4, the method further comprising:

at the output signal (Δ I) to the particle sensor₁, ΔI₂, ΔI₃A.) is followed by a sensor regeneration (58).

6. The method according to one of claims 2 to 5, the method further comprising:

if the output signal of the particle sensor (40, 42) is above a maximum load threshold, a sensor regeneration (58) is performed.

7. Method according to one of claims 5 or 6, wherein the sensor regeneration (50, 58) is carried out such that a residual load of the particle sensor (16) in the case of soot particles remains which corresponds to the end (t) of the first diagnostic phase (52)₁) The sensor load at time.

8. The method according to one of claims 2 to 7, the method further comprising:

storing a counter value which indicates the sensor signal (Δ I) analyzed up to now in the second diagnostic phase (53)₁, ΔI₂, ΔI₃..

9. The method according to one of the preceding claims, the method further comprising:

a storage period, which describes the period since the last complete and/or partial regeneration (50, 58) of the sensor.

10. The method according to one of the preceding claims, the method further comprising:

if it is determined that the particulate filter (16) is damaged, an alarm signal is output.

11. The method according to one of the preceding claims, the method further comprising:

outputting the detected sensor signal (Δ I) via a diagnostic interface₁, ΔI₂, ΔI₃..

12. A computing unit (14) which is set up to carry out all method steps of a method according to one of the preceding claims.

13. A computer program which, when being executed on a computing unit (14), causes the computing unit to carry out all the method steps of the method according to one of claims 1 to 11.

14. A machine readable storage medium having stored thereon a computer program according to claim 13.