DE102019112311A1 - Method for monitoring a particulate filter - Google Patents

Abstract

Method for monitoring a particulate filter in an exhaust stream of an internal combustion engine, wherein for monitoring a arranged in the flow direction of the exhaust stream behind the particulate filter particle sensor is used, wherein accumulating at the particulate sensor soot particles lead to a current flow, wherein the current flow is measured.

Description

The invention relates to a method for monitoring a particulate filter in an exhaust gas stream of an internal combustion engine, wherein for monitoring a arranged in the flow direction of the exhaust stream downstream of the particulate filter particle sensor is used, wherein at the particulate sensor accumulating soot particles lead to a current flow, wherein the current flow is measured.

Diesel particulate filters (DPF) are typically monitored for filter efficiency. This is done for example by means of a particle sensor, also known as Particulate Matter Sensor (PMS). A DPF is considered defective if, in a test cycle such as the WLTC (Worldwide Harmonized Light Duty Test Cycle), it exceeds the limits, in this case usually the particulate emissions. Such a DPF, which no longer complies with the limits, is also called BPU (Best Performing Unaccapable). The mode of operation of the PMS is based on the fact that soot particles that pass through a DPF and enter the tailpipe also settle on the sensor tip of the particle sensor. The sensor tip consists - in simplified terms - of an anode and cathode pair. If a soot layer forms, this leads to a flow of current. As the soot loading progresses, the current flow increases. Determining whether or not a current measured by the particulate sensor is caused by a defective DPF is a challenge.

The publication US 8 561 388 B2 discloses a device for fault detection for particulate filter, wherein for monitoring a arranged in the flow direction of the exhaust stream downstream of the particulate filter particle sensor is used. In this case, a time is estimated, which goes by a defective particulate filter until a certain current flows at the particle sensor. In turn, an amount of particulates entering the particulate filter is estimated, a filter efficiency estimated, and finally an amount of particulate exiting the particulate filter estimated. For this purpose, for example, corresponding maps are stored in the engine control. This approach, which is based on the amount of particles, has the disadvantage that time-consuming and costly test bench measurements must be carried out for the mapping of the characteristic maps, which in particular must include a particle concentration measurement and a mass flow measurement in order to determine the particle quantity therefrom.

An object of the invention is to propose a method for monitoring a particle filter by means of a particle sensor, which detects a defective particle filter independently of an estimate of the amount of particles.

The object is achieved by the method according to claim 1. In the dependent claims preferred embodiments and advantageous developments are given.

In the method according to the invention for monitoring a particulate filter in an exhaust gas stream of an internal combustion engine, a particle sensor arranged downstream of the particulate filter in the flow direction of the exhaust gas stream is used for monitoring purposes. At the particle sensor accumulating soot particles lead to a flow of current, wherein the current flow is measured. According to the invention, at least one reference period is determined in a calibration step, wherein within the reference period the measured current flow increases at a defective particle filter by a specified value. Furthermore, according to the invention, the at least one reference period is taken into account in the monitoring of the particulate filter. For the purposes of the invention, the defective particle filter, in particular a BPU particle filter, is to be distinguished from the particle filter to be monitored in the calibration step. The monitored particulate filter is functional and is then checked continuously during operation of the internal combustion engine. The defective particulate filter is used only in the calibration step to determine the at least one reference period.

The method is used in particular for monitoring a diesel particulate filter, which is intended to filter soot particles from the exhaust gas stream. For the purposes of the invention, the term "particle sensor" is understood to mean any sensor which, due to the accumulation of particles, in particular soot particles, is capable of permitting a measurable electrical current flow, the current flow increasing with the amount of accumulated particles. It is known to the person skilled in the art that, instead of the measurand current, it is also possible to measure a voltage and / or an electrical conductance in order to obtain a measurand which increases with the accumulating amount of particles on the particle sensor.

The calibration step provided according to the invention comprises, in particular, the creation of a model, wherein the decision as to whether the particle filter is defective or is functional is made on the basis of the model during the monitoring of the particle filter. As a rule, the calibration step comprises a parameterization of a control unit which performs the monitoring task. In the control unit, for example of a motor vehicle, said model for monitoring the diesel particulate filter is implemented alongside other function models, the models usually consisting of mathematical functions for approximating characteristics and, for example, by characteristics, maps and be defined. The models are based on model parameters, which are usually preset and are not changed after the controller has been started up. Such a model parameter reflects the measured reference period. Taking into account the at least one reference period in the monitoring of the particulate filter is thus to be understood that the reference period is used in the form of a model parameter in a model for monitoring the particulate filter.

Determining the reference period at the defective particulate filter in the calibration step and considering the reference period in monitoring the functional particulate filter during operation is advantageous because the time-based model can be used independent of a proportional amount of soot. The measurements necessary for the determination of the reference period are advantageously carried out without complex test bench measurements, namely preferably in the context of driving tests, for example on a test track. This is more effective in terms of time and especially cost than measurements on an engine test bench.

According to a preferred embodiment of the method, a first set of a plurality of reference periods in different stationary operating states of the internal combustion engine is determined in the calibration step. The reference period, within which the flow of current at the particle sensor increases by a fixed value in the case of a defective particle filter, varies depending on the operating state of the internal combustion engine. It is therefore particularly advantageous to determine not only a reference period, but a set of reference periods. From this first set of reference periods, a parameter set is created for the control unit's rating.

An operating state of the internal combustion engine is to be understood as a state in which the internal combustion engine runs with specific operating parameters. Among the essential operating parameters include a speed of the internal combustion engine, an injection amount of injected fuel per stroke and a percentage of recirculated exhaust gas, which is guided via an exhaust gas recirculation from the exhaust system in an intake tract of the internal combustion engine. The selection of the operating state characterizing parameters of the internal combustion engine can be extended or changed, for example, depending on the use and application of the internal combustion engine.

In the context of the invention, a stationary operating state of the internal combustion engine is understood as an operating state in which the parameters characterizing the operating state are constant, or in which the gradient of the change of the relevant parameters lies below a limit value to be defined. The parameters used to distinguish the stationary operating state of the internal combustion engine from a transient operating state change need not necessarily coincide with those operating parameters which are varied in determining the first set of reference periods in different stationary operating states of the internal combustion engine.

• - Ein Verhältnis einer Ist-Luftzahl zu einer Soll-Luftzahl, wobei die Luftzahl auch als Verbrennungsluftverhältnis A bezeichnet wird. Wenn das Verhältnis einen vorbestimmten Grenzwert unterschreitet, ist die Bedingung für eine transiente Betriebszustandsänderung der Brennkraftmaschine für diesen Parameter erfüllt.
• - Ein Gradient einer Stellung eines Steuerungselements, mit dem die Leistung der Brennkraftmaschine geregelt wird, auch als Pedalstellung bezeichnet. Liegt der Gradient der Pedalstellungsänderung über einem vorbestimmten Grenzwert oder, bei negativen Gradienten, unterhalb eines vorbestimmten Grenzwerts, dann ist die Bedingung für eine transiente Betriebszustandsänderung der Brennkraftmaschine für diesen Parameter erfüllt.
• - Ein Drehzahlgradient der Drehzahl der Brennkraftmaschine. Liegt ein Anstieg der Drehzahl pro Zeiteinheit über einem vorbestimmten Grenzwert oder, bei negativen Gradienten, unterhalb eines vorbestimmten Grenzwerts, dann ist die Bedingung für eine transiente Betriebszustandsänderung der Brennkraftmaschine für diesen Betriebsparameter erfüllt.

According to a further preferred embodiment of the method is detected in the monitoring of the particulate filter, if the internal combustion engine is running in a steady-state operating state, or if there is a transient operating state change of the internal combustion engine. In particular, the following parameters are used:

• - A ratio of an actual air ratio to a desired air ratio, wherein the air ratio is also referred to as the combustion air ratio A. If the ratio falls below a predetermined limit, the condition for a transient operating state change of the internal combustion engine for this parameter is satisfied.
• - A gradient of a position of a control element, with which the power of the internal combustion engine is controlled, also referred to as pedal position. If the gradient of the pedal position change is above a predetermined limit value or, in the case of negative gradients, below a predetermined limit value, then the condition for a transient operating state change of the internal combustion engine for this parameter is fulfilled.
• - A speed gradient of the speed of the internal combustion engine. If an increase in the speed per unit time is above a predetermined limit value or, in the case of negative gradients, below a predetermined limit value, then the condition for a transient operating state change of the internal combustion engine for this operating parameter is fulfilled.

In the method according to the invention, a transient change in the operating state of the internal combustion engine is particularly preferably determined when the three aforementioned conditions are met simultaneously. The person skilled in the art knows that a transient change in the operating state of the internal combustion engine can alternatively be detected on the basis of other and / or further parameters.

According to a further preferred embodiment of the method, it is provided that a second set of a plurality of reference periods during transient operating state changes of Internal combustion engine is determined. Like the first set of reference periods, the second set of reference periods can also be advantageously performed by trial runs on a vehicle with a defective diesel particulate filter. Elaborate measurements on the engine test bench are not required. If necessary, the vehicle can alternatively be driven on a chassis dynamometer. The first set of reference periods and the second set of reference periods are determined in the calibration step using a defective particulate filter. The data obtained in the calibration step are used for the control of the control unit for controlling the internal combustion engine. The monitoring of the particulate filter is then carried out by the control unit. During monitoring, unlike in the calibration step, the particulate filter is monitored in use. It is therefore not a defective particulate filter, as in the calibration step.

Particularly preferably, the first set and / or the second set of reference periods is taken into account in the monitoring of the particulate filter.

According to a further preferred embodiment of the method, an operating state of the internal combustion engine is determined during the monitoring of the particulate filter, wherein the operating state is assigned a stationary time value on the basis of the first set of reference periods. The operating state of the internal combustion engine is represented for example by the parameters speed, exhaust gas recirculation rate and injection quantity. Each combination of these parameters is assigned a steady-state time value which results from the reference periods of the first set determined in the calibration step. Each of the reference periods has also been determined at a certain operating condition of the internal combustion engine. Thus, for example, that reference period is assigned to a current operating state of the internal combustion engine as a stationary time value, which was determined in a similar or identical operating state. Particularly preferably, the stationary time value is determined by interpolation from a plurality of adjacent reference periods closest to the operating point.

As soon as the operating state of the internal combustion engine changes, so does the associated time value changes. This course of the stationary time value is inverted according to a further preferred embodiment and integrated over time. The result of the integration is referred to below as a stationary addend. The value of the stationary addend is written, for example, in a memory and updated continuously. In practical application, the operating state of the internal combustion engine is not detected as an analog signal, but interrogated at regular intervals, for example, with a sampling rate of one thousandth of a second. Accordingly, a steady-state time value is assigned to the operating state of the internal combustion engine for the period from one sampling to the subsequent sampling, this time value being inverted and summed up to the stationary summand once per sampling period.

An advantage of integrating the inverse stationary time values is that there is an easy way of monitoring the particulate filter. As soon as the value integrated over time, or accumulated value, reaches the value one, this means that the internal combustion engine has generated a particle quantity which has led to an increase in the measured current flow by the specified value in the calibration step.

Thus, if the particle sensor measures a lower current flow at the time, it means that the monitored particulate filter works better than the defective particulate filter used in the calibration step. On the other hand, if the measured current flow at the time is just as high or larger, this would be to conclude that the monitored particulate filter has a defect.

A further preferred embodiment of the method will be described below, which also takes into account the effects of transient operating state changes of the internal combustion engine. For this purpose, in particular when monitoring the particle filter, it is detected whether the internal combustion engine is in a stationary operating state or in a transient operating state change, as already described above. Particularly preferably, a duration of each transient operating state change is determined. The method is described below with reference to a transient operating state change, wherein the described method steps are repeated for each transient operating state change.

According to a preferred embodiment of the method, a starting rotational speed of the internal combustion engine is determined at the beginning of the transient operating state change and a final rotational speed of the internal combustion engine is determined upon termination of the transient operating state change. The end of a transient operating state change is determined by the fact that the parameters monitored for the determination no longer fulfill the specified conditions for a transient operating state change. The start speed and the end speed of the transient operating state change form a value pair to which an index from an index table is assigned. The assignment by means of an index table is a simple and effective Possibility to evaluate the speed change or the effect of the speed change on the particle emission. Since the particle emission depends not only on the speed difference during a transient operating state change, but also on the speed range within which the speed change occurs, the assignment of an index from an index table is an easy way of evaluation.

According to a further preferred embodiment of the method, an injection quantity of injected fuel is determined during the transient operating state change. For this purpose, in particular the time profile of the injection quantity is integrated and stored from the beginning of the transient operating state change to the end of the transient operating state change.

During the monitoring of the particle filter, a transient time value is taken from the index of the transient operating state change and the determined injection quantity during the transient operating state change from a time value table. The time value table contains in particular the second set of reference periods. In particular, the transient time value is calculated by interpolation of the reference periods closest to the time value table.

In a further step, a transient addend is preferably determined as the ratio of the duration of the transient operating state change to the transient time value. In a further step, a sum is preferably formed from the stationary summand and the transient summand. If this sum is the value 1 is reached, the current flow is measured at the particle sensor, where errors are detected when the measured current flow is greater than the set value.

Furthermore, the integration of the inverted stationary time values is continued during a transient operating state change. In order to avoid double detection of this steady state fraction, the transient summand is corrected by subtracting the ratio of the duration of the transient operating state change and the steady state value of the transient state change from the transient summand.

Another object of the invention relates to a computer program product, which is designed to perform steps of the method described above in the monitoring of the particulate filter. In monitoring the particulate filter, those steps of the method are performed which are not performed in the calibration step.

Another object of the invention relates to an electronic storage medium, wherein the computer program product described above is stored.

Another object of the invention relates to a control device for controlling an internal combustion engine, designed to monitor a particulate filter in an exhaust stream of the internal combustion engine according to the method described above. The control device preferably has the electronic storage medium described above.

The invention will be explained in more detail with reference to an embodiment with reference to the accompanying drawings. The embodiments are merely exemplary and do not limit the general inventive concept.

• 1 eine schematische Darstellung einer beispielhaften Brennkraftmaschine, bei der das erfindungsgemäße Verfahren anwendbar ist;
• 2 eine schematische Darstellung zur Erläuterung einer Zuordnung von stationären Zeitwerten zu Betriebszuständen der Brennkraftmaschine gemäß einer Ausführungsform des erfindungsgemäßen Verfahrens;
• 3 ein Ablaufschema zur Erläuterung der Verfahrensschritte zur Berücksichtigung einer transienten Betriebszustandsänderung der Brennkraftmaschine gemäß einer bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens;
• 4 ein Schema zur Erläuterung eines Verfahrensschritts der Zuordnung eines transienten Zeitwerts anhand von Zuordnungstabellen gemäß einer bevorzugten Ausführungsform des erfindungsgemäßen Verfahrens.

Show it

• 1 a schematic representation of an exemplary internal combustion engine, in which the inventive method is applicable;
• 2 a schematic representation for explaining an assignment of stationary time values to operating states of the internal combustion engine according to an embodiment of the method according to the invention;
• 3 a flowchart for explaining the method steps for taking into account a transient operating state change of the internal combustion engine according to a preferred embodiment of the method according to the invention;
• 4 a diagram for explaining a method step of the assignment of a transient time value based on assignment tables according to a preferred embodiment of the method according to the invention.

In the 1 is an exemplary internal combustion engine 2 shown schematically, the inventive method, for example, in such an internal combustion engine 2 with a particle filter 1 is applicable. The internal combustion engine 2 in the embodiment is with an exhaust gas turbocharger 7 shown. In the internal combustion engine 2 is injected fuel together with intake air from an intake air tract 5 burned. The combustion exhaust gases are via an exhaust tract 6 derived. An exhaust gas recirculation 4 is intended to return some of the exhaust gas back to the intake air tract 5 to lead. The remaining exhaust gas flows through a turbine of the exhaust gas turbocharger 7 and subsequently through the particulate filter 1 , which is intended to filter and collect particles in the exhaust stream. A flow direction of the exhaust gas flow is indicated by an arrow 9 characterized. In which The method according to the invention becomes a particle sensor 3 used, being attached to the particle sensor 3 Accumulate particles that are not passing through the particulate filter 1 were filtered out of the exhaust stream. At the particle sensor 3 particles collect and lead to a measurable current flow. This is indicated by the particle sensor 3 two electrodes, not shown, between which an electrical resistance decreases with increasing Rußbeladung. By heating the electrodes, the soot is burned at regular intervals, so that a new measurement with the thus regenerated particle sensor 3 is possible. Corresponding circuits of the electrodes for measuring a current flow, or else a voltage or the electrical resistance, are known to the person skilled in the art and will not be explained in more detail here. The internal combustion engine 2 further includes a controller 8th on which serves to numerous processes of the internal combustion engine 2 and the associated components to control. These are in the controller 8th various software program products are stored and processed by this. The inventive method is also used as a software program product in the control unit 8th saved and processed. In addition to the measured current flow at the particle sensor 3 Numerous other measured values and measuring signals are sent to the control unit 8th fed, such as a speed of the internal combustion engine 2 , a rate of exhaust gas recirculation 4 , An injection amount of injected fuel per power stroke of the internal combustion engine 2 and a power request of an operator of the internal combustion engine, which is also referred to as pedal position. The corresponding signal connections of the control unit 8th are known in the art and have been omitted in the drawing for clarity.

In a calibration step, parameters are determined to determine the functions of the controller 8th adapt, for example, to the respective internal combustion engine 2 or to a particular vehicle in which the internal combustion engine 2 is installed. In this calibration step, at least one reference period is determined in the method according to the invention. The reference period is the time in which the measured current flow at the particle sensor 3 increases to a predetermined value, this value can be advantageously set arbitrarily in the inventive method. In the calibration step, this reference period is determined with a defective particle filter (not shown). As a defective particulate filter, in particular, such a particulate filter is used for the calibration, which can no longer guarantee the prescribed limit values for particulate emissions. Since only the time until reaching the specified current flow is measured in the calibration step, this can be determined particularly advantageous in driving tests, so that a complex test stand operation is omitted at a motor test.

The measured reference period represents one of the parameters for the so-called control unit 8th Based on the reference period, which was determined in the calibration step, later after parameterization of the control unit 8th when monitoring a particulate filter in use 1 decided whether this is functional or defective. Thus, in the monitoring of the usually functional particulate filter 1 the reference period is taken into account.

The reference period, determined in the calibration step, for reaching the set value for the flow of current at the particle sensor 3 is usually significantly on the operating condition of the internal combustion engine 2 dependent. Is an internal combustion engine 2 provided that they are always operated in a steady operating condition, a single reference period may be sufficient to monitor the particulate filter 1 to ensure. Especially with internal combustion engines 2 , whose operating state is varied during operation, are preferably in the calibration step several reference periods in different operating conditions of the internal combustion engine 2 determined. Depending on the application of the internal combustion engine 2 The operating state can also change abruptly, which is referred to below as a transient operating state change. If the additional influences of such transient operating state changes are to be taken into account, further reference time periods for different transient operating state changes are preferably determined in the calibration step.

In a preferred embodiment of the method, in the calibration step, a first set of multiple reference periods 16 . 19 ( 2 ) in various stationary operating states of the internal combustion engine 2 determined. From the first set of reference periods 16 . 19 becomes a parameter set for the control unit's rating 8th created. According to a further preferred embodiment of the method, it is provided that a second set of a plurality of reference periods 44 ( 4 ) during transient operating state changes of the internal combustion engine 2 is determined. Like the first set of reference periods 16 . 19 can also be the second set of reference periods 44 Carry out advantageous by test drives with a vehicle with a defective diesel particulate filter. Particular preference is also given to the second set of reference periods 44 becomes a parameter set for the control unit's rating 8th created.

With reference to the 2 is explained below, as with the first set of reference periods 16 . 19 in different stationary operating states of the internal combustion engine 2 when monitoring the particulate filter 1 A decision is made as to whether the particulate filter in question 1 is still functional or defective.

The 2 shows a schematic diagram 10 in which a three-dimensional space 15 possible operating states of an internal combustion engine 2 schematically represents. The operating state of the internal combustion engine 2 is characterized by three parameters, but this is only to be understood as an example. The space 15 the possible operating states of the internal combustion engine 2 can be characterized by further or other parameters, so that a higher dimensional space 15 would result. In the present example, the first parameter is on the first axis 11 the speed of the engine signed off. On the second axis 12 is an injection amount of injected fuel removed and on the third axis 13 a degree of exhaust gas recirculation 4 , In the room 15 are points 16 . 19 drawn in each case for an operating state of the internal combustion engine 2 stand. The points 16 . 19 are not all provided with reference numerals for clarity. In the with points 16 . 19 designated operating states are the reference periods in a stationary operation of the internal combustion engine in the calibration step 2 been determined. This means that each of these operating points is assigned a reference period, so that subsequent to the reference periods 16 . 19 Reference is made. The diagram 10 thus exemplifies the first set of stationary reference periods 16 . 19 used as a parameter in the control unit's configuration 8th for monitoring the particulate filter 1 be taken into account.

During operation of the internal combustion engine 2 becomes the particle filter 1 supervised. The operating state of the internal combustion engine 2 , here characterized by the three on the axes 11 . 12 . 13 specified parameters, is known at any time, as the corresponding parameters in the control unit 8th be fed. Thus, each operating state of the internal combustion engine 2 A stationary time value can be assigned on the basis of the first set of reference periods. An exemplary current operating state of the internal combustion engine 2 during the monitoring of the particulate filter 1 is in the diagram 10 with a cross with reference number 17 shown. The number of operating states of the internal combustion engine 2 by testing one of the stationary reference periods 16 . 19 is assigned, is small compared to the possible number of different operating states of the internal combustion engine 2 , Therefore, the operating conditions of the stationary reference periods 16 . 19 as meaningful as possible in the room 15 distributed. The stationary time value is preferred 17 for the current operating state by interpolation from the neighboring reference periods closest to the current operating point 19 determined. The current operating point with the stationary time value to be assigned 17 , as well as the nearest adjacent reference periods 19 are out of the room for clarity's sake 15 shown again to illustrate this interpolation. Broken Guides 18 clarify the actual location of the points 19 and the cross 17 in the room 15 , The interpolation is by lines 14 , which are the closest reference periods 19 connect, graphically displayed. By means of the interpolation, the current operating point advantageously has a stationary time value which is as realistic as possible 17 assigned, even if no stationary reference period was determined for this operating point. The current operating state of the internal combustion engine 2 associated stationary time values 17 are continuously determined, or determined at regular intervals, according to a sampling rate for the operating parameters of the internal combustion engine 2 ,

In the control unit 8th become the consecutively determined stationary time values 17 inverted and integrated over time. The use of the inverted time values has the advantage that when the value reaches one for the sum, the internal combustion engine 2 has emitted an equivalent of particulate emission, which in the calibration step results in the increase of the amperage at the particle sensor 3 to the specified value. As in the monitoring but a functional particulate filter 1 is monitored, it is expected that by the time the sum reaches one, the measured current flow at the particle sensor 3 is lower than the set value for the current flow. Thus, the inventive method allows in a simple manner to decide whether the particulate filter 1 is defective or functional. The in the control unit 8th Integration of the inverted stationary time values ti_steady is called stationary addend R_steady, which is calculated according to the following formula: $$\text{R\_steady}={\displaystyle \int 1\text{/ ti\_steady dt}}$$

The stationary summand R_steady covers the contribution of the stationary operating states or those operating state changes that are not classified as transient operating state changes.

To see if the particle filter 1 is functional or defective, a proportion is also preferably taken into account by transient operating state changes. With reference to the 3 and 4 the determination of the proportion of transient operating state changes is explained below.

In the 3 is a flowchart for explaining the method steps for taking into account the transient operating state changes of the internal combustion engine 2 shown. The lines or arrows 24 . 25 in the diagram represent signals, where links and branches by nodes 23 are shown, so that simple intersections of the lines 24 . 25 not to be considered as connections. To transient operating state changes of the internal combustion engine 2 to consider, for example, is a logic 20 provided to detect a transient operating state change. This is the case, for example, when an actual value for the air value λ differs greatly from a desired value for the air value λ or the ratio falls below a certain limit value. Furthermore, there is a transient operating state change when the power demand, also called pedal position, is subject to a sharp change over time. Also for this gradient, a limit is provided. A third criterion is, for example, exceeding a limit value for the gradient of the rotational speed of the internal combustion engine 2 , If all criteria are met simultaneously, the logic sends 20 the signal "TRUE" or "1". If at least one of the criteria is not met, the logic sends 20 the signal "FALSE" or a logical zero. A transition from FALSE to TRUE will cause the block 21 a trigger signal 24 while switching from TRUE to FALSE causes the block 22 in turn, a trigger signal 25 sends. The trigger signal 24 causes the current engine speed 26 as start speed 28 the transient operating state change is stored. Furthermore, the trigger signal leads 24 to that integration 30 about the injection quantity 27 is started. Another integration 32 over time is also triggered by the trigger signal 24 started. Will the trigger signal 25 sent on completion of the transient operating state change, so the current speed 26 as final speed 29 the transient operating state change stored. Furthermore, the integration 30 stopped and the value for the amount of fuel injected during the transient operating state change 31 saved. Also the integration 32 over time is triggered by the trigger signal 25 terminated and the duration of the transient operating state change 33 saved. According to this scheme, every transient operating state change is detected.

With reference to the 4 is shown below, as from the stored values of a single transient operating state change their contribution to the monitoring of the particulate filter 1 is determined.

The 4 shows a scheme for explaining method steps that are used to assign a transient time value 43 be carried out for a transient operating state change. This is a first mapping table 40 provided in the control unit 8th is deposited. This is every pair of starting speed 28 and final speed 29 the transient operating state change assigned an index value. The determined index 41 the transient operating state change serves in a second allocation table 42 together with the previously determined total quantity 31 injected fuel during the transient operating state change thereto, a transient time value 43 to determine. The second mapping table 42 is filled with the transient reference periods determined in the calibration phase 44 , If none of the identified reference periods 44 to the pairing from the index 41 and the injection quantity 31 fits, becomes the transient time value 43 determined by interpolation. The first mapping table 40 is also called index table 40 designated. The second mapping table 42 is also called the time value table 42 designated. From the transient time value 43 , which has been determined for a transient operating state change, subsequently becomes a transient summand R_dyn as a ratio of the duration 33 (tijump) in transient mode to the transient time value 43 (ti_dyn) is calculated. As the previously with respect to the 2 described integration of the inverse stationary time value continues during the transient operating state change, the accumulated during the transient operating state change stationary component must be subtracted as a correction value. This correction value is calculated as the ratio of the duration 33 (tijump) the transient operating state change to the steady state time value (ti_steady) of the transient operating state change (see 17 in FIG 2 ). The result is the transient summand R_dyn for each transient change in operating state according to the following formula: $$\text{r\_dyn}=\text{ti\_jump / ti\_dyn}-\text{ti\_jump / ti\_steady}$$

The stationary summand R_steady is added with the transient summand R_dyn to a total sum, which is called the cumulative inverse time R_tix: $$\text{R\_ti}=\text{R\_steady}+\text{r\_dyn}$$

The person skilled in the art recognizes that every transient operating state change results in a further summand R_dyn, which is included in the total. As soon as this sum of the cumulative inverse time reaches the value one (R_tix = 1), the current flow at the particle sensor becomes 3 measured, being on error is detected when the measured current flow is greater than the specified value.

LIST OF REFERENCE NUMBERS

1

particulate Filter

2

Internal combustion engine

3

particle sensor

4

Exhaust gas recirculation

5

Ansauglufttrakt

6

exhaust tract

7

turbocharger

8th

control unit

9

Flow direction, arrow

10

diagram

11

First axis, speed

12

Second axis, injection quantity

13

Third axle, exhaust gas recirculation rate

14

interpolation lines

15

Space, operating range of the internal combustion engine

16

Operating status with assigned reference period

17

Stationary time value in the determined operating state

18

guides

19

Nearest adjacent operating states

20

Logic for detecting a transient operating state change

21

Transition from FALSE to TRUE

22

Transition from TRUE to FALSE

23

node

24

Signal Start of the transient operating state change

25

Signal End of transient operating state change

26

Engine speed

27

Injection quantity

28

Speed at the beginning of the transient operating state change

29

Speed at the end of the transient operating state change

30

Integration of injection quantity

31

Total injection quantity

32

Integration of time

33

Total duration of the transient operating state change

40

First table, index table

41

index

42

Second table, time value table

43

Transient time value

44

Reference period

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 8561388 B2 [0003]

Claims (10)

Method for monitoring a particle filter (1) in an exhaust gas stream of an internal combustion engine (2), wherein a particle sensor (3) arranged behind the particle filter in the flow direction (9) of the exhaust gas flow is used for monitoring, wherein particles collecting at the particle sensor lead to a flow of current , wherein the current flow is measured, characterized in that in a calibration step at least one reference period is determined, in which the measured current flow increases at a defective particulate filter by a predetermined value, and wherein the at least one reference period in the monitoring of the particulate filter (1) into account becomes. Method according to Claim 1 characterized in that in the calibration step, a first set of a plurality of reference periods (16, 19) is determined in different stationary operating states of the internal combustion engine (2), a second set of a plurality of reference periods (44) being determined during transient operating state changes of the internal combustion engine, and wherein in the monitoring of the particulate filter (3) of the first sentence and / or the second sentence is taken into account. Method according to Claim 2 , characterized in that in the monitoring of the particulate filter, an operating condition of the internal combustion engine (2) is detected, wherein the operating state of the first set of reference periods, a stationary time value (17) is assigned. Method according to Claim 3 , characterized in that the stationary time value (17) is determined by interpolation from the neighboring reference periods (19) closest to the operating point. Method according to one of Claims 3 or 4 , characterized in that a stationary summand is calculated by inverting the time constant value (17) obtained by continuously determining the operating state and integrating it over time. Method according to one of the preceding claims, characterized in that it is detected in the monitoring of the particulate filter, whether a stationary operating state or a transient operating state change of the internal combustion engine (2) is present, wherein a duration (33) of each transient operating state change is determined. Method according to Claim 6 , characterized in that upon detection of a transient operating state change, a starting speed (28) of the internal combustion engine (2) is determined at the beginning and a final speed (29) of the internal combustion engine at the end of the transient operating state change, wherein a value pair of starting speed and final speed index (41) from an index table (40). Method according to one of Claims 6 or 7 , characterized in that from the beginning of the transient operating state change until the termination of the transient operating state change, an injection quantity (31) of injected fuel is determined. Method according to the Claims 7 and 8th , characterized in that a transient summand is determined as a ratio of the duration (33) of the transient operating state change to a transient time value (43), the transient time value being calculated from a time value table (41) and the determined injection quantity (31). 42), the time value table containing the second set of reference periods (44). Method according to the Claims 5 and 9 , characterized in that upon reaching a sum of the stationary summand and the transient summand equal to one, the current flow is measured at the particle sensor (3), wherein errors are detected when the measured current flow is greater than the predetermined value.

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