DE102013207999A1 - Method and device for operating an internal combustion engine - Google Patents

Abstract

Method and device for operating an internal combustion engine with an exhaust tract, in which a nitrogen oxide sensor is arranged, the measurement signal of which is representative of a nitrogen oxide content in a measurement recording area of the nitrogen oxide sensor. A corrected measurement signal (MS_NOX_K) of the nitrogen oxide sensor is determined depending on the measurement signal and an adaptation value (AD). In the event that a predetermined operating situation (BS) is recognized, which is representative of the fact that there is essentially no nitrogen oxide in the measurement area of the nitrogen oxide sensor, a calibration process is carried out. During the calibration process, an estimated course of an estimate measurement signal (MS_NOX_EST) of the nitrogen oxide sensor is determined, depending on a measurement value of the corrected measurement signal (MS_NOX_K) of the nitrogen oxide sensor, correlating to a start of the calibration process. Furthermore, an adaptation value is assigned to the calibration process as a function of the corrected measurement signal (MS_NOX_K) of the nitrogen oxide sensor and as a function of a comparison characteristic value (IQ), which is representative of a comparison between the course of the estimation measurement signal (MS_NOX_EST) and the corrected measurement signal (MS_NOX_K ) of the nitrogen oxide sensor.

Description

The invention relates to a method and a device for operating an internal combustion engine.

Increasingly stringent statutory regulations regarding permissible pollutant emissions of motor vehicles, in which internal combustion engines are arranged, make it necessary to keep the pollutant emissions during operation of the internal combustion engine as low as possible. This can be done by reducing the pollutant emissions that occur during the combustion of the air / fuel mixture in the respective cylinder of the internal combustion engine. On the other hand, exhaust gas aftertreatment systems are used in internal combustion engines, which convert pollutant emissions that are generated during the combustion process of the air / fuel mixture in the respective cylinders, into harmless substances.

For this purpose, for example, an oxidation catalyst is used, which is adapted to oxidize carbon monoxide to carbon dioxide and to oxidize unburned hydrocarbons to water and carbon dioxide.

Further, for this purpose, a particulate filter may be provided, which is designed to store soot and to oxidize it at regular intervals to carbon dioxide.

Furthermore, a so-called nitrogen oxide reduction system may be provided which comprises a metering unit for ammonia and an SCR catalyst. The SCR catalyst is designed to use ammonia to reduce the nitrogen oxide formed during combustion.

From the DE 100 03 219 A1 It is known on the basis of a signal curve of a NOx-sensitive measuring device after switching the internal combustion engine into a lean operating mode to determine a reference time and to use this as a time zero point for the NOx storage catalytic converter related control processes.

From the DE 199 26 139 A1 For example, a method is known for determining the NOx concentration of an exhaust gas flow of an internal combustion engine by means of a NOx sensor calibrated by selected operating points, which is arranged downstream of a NOx storage catalytic converter. The reference point used for calibration is the minimum of the sensor signal curve after a regeneration phase.

From the EP 1 227 234 A2 For example, a method is known for operating an NOx sensor disposed in an exhaust passage of an internal combustion engine, wherein the signal values of the NOx sensor are compared with signal values previously determined at a known NOx concentration. The resulting references are used to correct the currently determined signal values.

The object on which the invention is based is to provide a method and a device which makes a contribution to a reliable and low-emission operation of an internal combustion engine.

The object is solved by the features of the independent claims. Advantageous embodiments of the invention are characterized in the subclaims.

The invention is characterized by a method and a corresponding device for operating an internal combustion engine with an exhaust gas tract, in which a nitrogen oxide sensor is arranged, whose measurement signal is representative of a nitrogen oxide content in a measurement receiving area of the nitrogen oxide sensor. A corrected measurement signal of the nitrogen oxide sensor is determined as a function of the measurement signal and an adaptation value.

In the event that a predetermined operating situation is detected, which is representative that there is substantially no nitrogen oxide in a measuring range of the nitrogen oxide sensor, a calibration process is performed. During the calibration process, an estimated course of an estimated measurement signal of the nitrogen oxide sensor is determined, specifically as a function of a measured value of the corrected measurement signal of the nitrogen oxide sensor, correlating to a beginning of the calibration process. Furthermore, in the context of the calibration process, the adaptation value is determined as a function of the corrected measurement signal of the nitrogen oxide sensor and dependent on a comparison characteristic value that is representative of a comparison between the profile of the estimated measurement signal and the corrected measurement signal of the nitrogen oxide sensor.

In this way, any deviations from an expected gas composition that may occur during the calibration process can be taken into account in a particularly suitable manner. In this way, for example, unexpectedly occurring NOx components in the exhaust gas or other components, such as ammonia, which have an influence on the measurement signal, can be suitably taken into account and thus the adaptation value can be determined with a particularly high quality.

The predetermined operating situation can be done, for example, based on an evaluation of predetermined operating variables of the internal combustion engine. It can thus be detected, for example, depending on a detection of a push operation. The estimated course of the estimated measurement signal can not of course take into account influences that emanate from unexpected exhaust gas compositions during the calibration phase. However, the comparison characteristic value allows precisely such unexpected influences to be taken into account.

According to an advantageous embodiment, the comparison characteristic value is determined as a function of an integral of an amount of the deviation between the estimated measurement signal and the corrected measurement signal. In this way, the comparison characteristic value can be determined particularly easily and then also suitably represents exactly the unexpected deviations of the exhaust gas composition.

According to a further advantageous embodiment, the value of the integral is reduced in the determination of the comparison characteristic value by a predetermined integral correction value, which depends on a time duration of the calibration process.

It has surprisingly been found that in this way a particularly high quality of the adaptation value can be achieved.

According to a further advantageous embodiment, the course of the estimated measuring signal is determined as a function of a low-pass filtering. In this way, the course of the estimated measuring signal can simply be determined computationally and represents an expected course of the corrected measuring signal with sufficient accuracy if no unexpected disturbances in the exhaust gas composition occur during the calibration process. In this context, the use of the integral correction value, with a suitable specification, is particularly advantageous in order to reproduce an actual response of the nitrogen oxide sensor even more precisely within the course of the estimation measurement signal.

According to a further advantageous embodiment of the calibration process is terminated when the corrected measurement signal is predetermined quasi stationary. This can be detected particularly easily by evaluating the changes in the corrected measurement signal and is then an indicator that the measurement signal is representative of an exhaust gas, in which essentially no nitrogen oxides are present, in particular, close to the end of the calibration process.

According to a further advantageous embodiment, the adaptation value is determined as a function of a minimum value of the corrected measurement signal during the calibration process. In this way, the value of the corrected measurement signal which best represents the corrected measurement signal at a substantially non-existent nitrogen oxide concentration in the exhaust gas can be determined particularly easily and with high quality.

According to a further advantageous embodiment, a gas mass flow characteristic value is determined, which is representative of a gas mass flow during the calibration process, and the adaptation value is determined as a function of the gas mass flow characteristic value.

In this way, the adaptation value can be determined particularly precisely. Here, the knowledge is used that an amount of the gas mass flow influences the quality of the determination of the adaptation value. In this way, therefore, a so-called purging of the nitrogen oxide sensor is considered suitable.

According to a further advantageous embodiment, a gradient characteristic value is determined which is representative of a gradient of the gradient of the corrected measurement signal during the calibration process and the adaptation value is determined as a function of the gradient characteristic value. In this way, in particular a degree of stationarity of the measurement signal and / or the exhaust gas composition can be suitably taken into account and thus also its influence on the determination of the adaptation value. Thus, a particularly effective contribution can be made to suitably determine the adaptation value and in particular to adapt it with the aim that the corrected measurement signal represents the actual nitrogen oxide content of the exhaust gas as accurately as possible.

According to a further advantageous embodiment of the calibration process is only started after a predetermined waiting time after the detection of the predetermined operating situation. In this way, a so-called sensor dead time can be taken into account particularly simply, which is due in particular to the fact that the exhaust gas has to pass through a predetermined flow path to the respective actual sensor element.

Embodiments of the invention are explained in more detail below with reference to the schematic drawings. Show it:

1 an internal combustion engine and a control device associated therewith,

2 a flowchart of a program that is executed in the control device during operation,

3A to 3E first signal curves,

4 second signal curves,

5 third signal curves,

6A to 6G fourth waveforms and

7A to 7G fifth signal curves.

Elements of the same construction or function are identified across the figures with the same reference numerals.

An internal combustion engine ( 1 ) comprises an intake tract 1 , a motor unit 3 and an exhaust tract 5 , The engine unit 1 includes one or more cylinders associated with respective injectors. In the exhaust tract 5 is an oxidation catalyst 7 and a particle filter 9 arranged. Furthermore, the exhaust tract 5 associated with a nitrogen oxide reduction system comprising a metering device 11 for ammonia or urea and an SCR catalyst 13 includes. Furthermore, a first exhaust gas recirculation 15 and / or a second exhaust gas recirculation 17 provided with respective associated exhaust gas recirculation valves.

A control device 18 is provided, the sensors are assigned, which detect different parameters and each determine the value of the measured variable. Operating variables also include variables derived from this in addition to the measured variables.

The control device 18 is designed to determine, depending on at least one of the operating variables manipulated variables, which are then converted into one or more actuating signals for controlling the actuators by means of corresponding actuators. The control device 18 may also be referred to as a device for operating the internal combustion engine. The control device 18 preferably comprises a data and program memory and a computing unit, which may include, for example, a microprocessor and / or a microcontroller.

The sensors are for example a pedal position sensor which detects an accelerator pedal position of an accelerator pedal, an air mass sensor which detects an air mass flow, a temperature sensor which detects an intake air temperature, or a crankshaft angle sensor which detects a crankshaft angle to which a rotational speed is then assigned.

Furthermore, there is a lambda probe 19 provided upstream of the oxidation catalyst 7 is arranged and detects a residual oxygen content of the exhaust gas and the measurement signal is characteristic of the air / fuel ratio in the respective combustion chamber of the respective cylinder and upstream of the lambda probe 19 before the oxidation of the fuel. In principle, a second lambda probe can also be used 21 downstream of the oxidation catalyst 7 be arranged, for example, downstream of the particulate filter 9 can be arranged.

In addition, the exhaust gas system is associated with at least one nitrogen oxide sensor whose measurement signal is representative of a nitrogen oxide content in a measurement receiving area of the nitrogen oxide sensor. So can a first nitric oxide sensor 23 upstream of the oxidation catalyst 7 in the exhaust tract 5 be arranged. Alternatively or additionally, a second nitrogen oxide sensor 25 downstream of the SCR catalyst 13 be arranged.

The first nitric oxide sensor 23 is used to control the metering device 11 , The second nitric oxide sensor 25 is used to indicate a particular state of the SCR catalyst 13 to monitor.

In principle, legal regulations require compliance with specified nitrogen oxide limit values. If by means of the second nitrogen oxide sensor 25 For example, the exceeding of predetermined limits is detected, if necessary, an error entry in an error memory area of the data and program memory of the control device 18 take place, in particular with an activation of a MIL lamp. In this context, MIL means "malfunction indication lamp", which thus performs an error signaling for the driver.

In principle, the second nitrogen oxide sensor can detect a fault with regard to the exceeding of limit values 25 be used.

The technically possible signal accuracy is potentially influenced by the manufacturing process and / or the aging process of the sensor electronics and the respective sensor element. The respective signal characteristic of the measurement signal of the respective nitrogen oxide sensor has different characteristics. A signal characteristic is the additive deviation from an actually correct measured value, which is also referred to as offset or signal offset. Another signal characteristic is the characteristic slope, which is also referred to as signal gain. The signal offset can drift in the positive or negative direction over the sensor lifetime. The signal gain usually decreases over the lifetime. Ideally, the signal offset equals zero and the signal gain equals one. The signal offset leads to a small relative deviation for large signal values. A relative error due to the signal offset, on the other hand, is very large for small signal values. Changes in the signal gain lead to a large absolute deviation for large signal values.

In the case of internal combustion engines, the aging of nitrogen oxide sensors or lambda probes fundamentally leads to a system deviation and, as a consequence, to a deterioration of the pollutant emissions and, in particular, premature failure of one or more of the oxidation catalytic converter 7 , the particulate filter 9 and the SCR catalyst 13 ,

Basically, there are phases without combustion in the motor unit 3 suitable for carrying out a calibration of the respective nitrogen oxide sensor. However, it has been shown that even in such phases basically an influence, for example, of the oxidation catalyst 7 and / or the particulate filter 9 and / or the SCR catalyst 13 and / or the first exhaust gas recirculation 15 and / or the second exhaust gas recirculation 17 done in terms of the exhaust gas composition. Thus, it was found that during SCR catalyst overrun operation 13 can lose ammonia by cooling. Since the nitrogen oxide sensor has a cross-sensitivity to ammonia, it has been shown that such a situation, which is difficult to predict, can lead to a changed measurement signal of the nitrogen oxide sensor.

A program for operating the internal combustion engine is in the program and data memory of the control device 18 stored and is processed during operation of the internal combustion engine. The following is the program based on the flowchart of 2 explained in more detail.

The program is started in a step S1 in which variables can be initialized if necessary.

In a step S3, it is checked whether a predetermined operating situation BS has been detected. The predetermined operating situation BS is representative of the fact that there is essentially no nitrogen oxide in the measurement acceptance region of the nitrogen oxide sensor, that is, depending on which nitrogen oxide sensor the program is processed with respect to the first nitrogen oxide sensor 23 or the second nitrogen oxide sensor 25 ,

The predetermined operating situation BS is detected as a function of one or more operating variables in a predefined manner. Thus, for example, the predetermined operating situation BS can be detected depending on whether an operating state of the fuel cut is assumed, in which no fuel is metered through the injectors during operation of the internal combustion engine.

The presence of the predetermined operating situation BS can also be detected as a function of whether the respective exhaust gas recirculation valves are in their closed state.

In addition, in step S3, it is also possible to check for the presence of one or more further activation conditions. These can be one or more of the following:
Exhaust gas recirculation is not activated.

The respective SCR catalyst 13 is ready for operation, in particular normal temperature range, only up to a limit loaded with ammonia and there is no urea injection instead.

The oxidation catalyst 7 is ready for use, so its temperature is in particular within a predetermined range.

The respective nitrogen oxide sensor has a stable operating temperature and a Einschalteinschwingvorgang is completed.

A gas temperature in the measurement receiving area of the respective nitrogen oxide sensor is within a predetermined range.

The gas flow at the respective nitrogen oxide sensor is within a predetermined range.

The oxygen concentration was stable for a given period of time.

The oxygen concentration was above a predetermined threshold for a predetermined period of time.

The activation conditions also contribute to the fact that the same conditions as possible are present for the respective performance of a calibration on the respective nitrogen oxide sensor, which reduces scattering when adjusting a respective adaptation value AD.

If the conditions of step S3 are not met, that is, the predetermined operating situation BS is not recognized and the respectively tested activation conditions are not met, then the processing, if appropriate after a predetermined waiting period, is continued again in step S3.

On the other hand, if the conditions of the step S3 are met, the processing is continued in a step S5. In the step S5, the program preferably remains for a predetermined one Waiting period. By means of these, it is particularly taken into account that the respective nitrogen oxide sensor has a so-called sensor dead time, which is representative of the fact that the gas in each case requires a given time duration in order to reach the respective sensor element within the nitrogen oxide sensor.

Subsequently, the processing is continued in a step S7, whereby a calibration process begins. In step S7, an estimated course of an estimated measuring signal MS_NOX_EST of the nitrogen oxide sensor is determined, specifically as a function of a measured value of a corrected measuring signal MS_NOX_K of the nitrogen oxide sensor, correlated to the beginning of the calibration process. The measured value is thus detected in particular very soon after the beginning of the processing of step S7. The corrected measurement signal MS_NOX_K of the nitrogen oxide sensor is determined as a function of the measurement signal MS_NOX of the nitrogen oxide sensor and an adaptation value AD, which is explained in more detail below.

With regard to the estimated course, it is assumed that the estimated measurement signal changes from the detected measured value to a default value which it assumes depending on the sensor characteristic, in particular after a predetermined settling time, if the nitrogen oxide content in the exhaust gas containing the Measuring pickup range of the nitrogen oxide sensor flows past this, is substantially zero or has only such a nitrogen oxide content, which is optionally contained in air. Depending on the configuration of the adaptation value, this default value may be zero, for example.

Thus, the estimated signal course MS_NOX_EST represents, in particular, a step response of the nitrogen oxide sensor from the measured value of the corrected measurement signal MS_NOX_K, which is correlated to the beginning of the calibration process, up to its default value.

In the context of determining the estimated course of the estimated measuring signal MS_NOX_EST, for example, a low-pass filter is used, which can optionally be realized as a first, second or third order.

In a subsequent step S9, it is checked whether the calibration process is to be ended. In this connection, it is checked, for example, whether the corrected measurement signal MS_NOX_K is quasi-stationary in a predetermined manner, for example also stationary. In this context, other conditions can be checked, which are explained below after the explanation of steps S11 to S19.

If the conditions of the step S9 are not satisfied, the processing in the step S11 is continued. In step S11, a comparison characteristic value IQ is determined, which is representative of a comparison between the course of the estimated measuring signal MS_NOX_EST and the corrected measuring signal MS_NOX_K of the nitrogen oxide sensor.

In this case, the passage through steps S11 to S19 preferably takes place cyclically and in particular with a predetermined sampling interval T, specifically during the execution of the calibration process.

The determination of the comparison characteristic value IQ preferably takes place by means of the calculation rule specified in step S11, where t denotes the time and thus then represents the respectively current instant. ABS denotes an absolute value, that is the amount. By the calculation rule in step S11 thus takes place a numerical integration. Thus, the comparison characteristic value IQ is determined as a function of the integral of the magnitude of the deviation between the estimated measurement signal MS_NOX_EST and the corrected measurement signal MS_NOX_K.

In this case, a scanning integral correction value CIQ is used as the subtrahend in the respective passage through step S11. Thus, overall, during the entire calibration process, the value of the integral is reduced by a predetermined integral correction value, which depends on a period of the calibration process. By a suitable specification of the Abtastintegralkorrekturwertes CIQ, which can be determined by appropriate tests, in particular non-relevant signal deviations can be reduced from the comparison characteristic IQ and in particular eliminated. A small value of the comparison characteristic value IQ is indicative of a good analysis situation, while large values of the comparison parameter IQ are indicative of a poor analysis situation and thus the comparison parameter IQ is representative of a statement about the quality of the selected analysis situation. In addition, during the execution of the calibration process, the detected measured values, that is to say in particular the measured values of the corrected measuring signal MS_NOX_K of the respective nitrogen oxide sensor, are temporarily stored in the program and data memory for a subsequent evaluation.

In a step S13, a gradient characteristic value G is determined. In this case, the gradient characteristic value G is determined so that it is representative of a gradient of the gradient of the corrected measurement signal MS_NOX_K during the calibration process. In this case, it is determined, for example, by forming an integral over the magnitude of the gradient of the corrected measurement signal. This can also be achieved, for example, by a quasi-moving averaging respectively. In addition, the gradient can also be determined as a function of a respective current measured value and minus a low-pass filtered preceding measured value of the corrected measuring signal MS_NOX_K. In this case, a constant value can be provided which is used as a subtrahend for each execution of step S13 for reducing the respective gradient characteristic value G, which thus heals the gradient characteristic value G again in the direction of zero after a dynamic phase.

In a subsequent step S15, a gas mass flow characteristic value D is determined, which is representative of a gas mass flow during the calibration process. Thus, in particular, an integral is formed via the gas mass flow, which flows past the nitrogen oxide sensor in particular during the calibration process in the measurement receiving region. He is thus representative of a so-called rinsing time.

In a subsequent step S17, a quality characteristic value Q_KW is determined, specifically depending on a product of the comparison characteristic value IQ, the gradient characteristic value G and the gas mass flow parameter D.

In a step S19, a filter value K_FIL is determined as a function of a predetermined filter basic value K_FIL_FIX and the quality characteristic value Q_KW.

Subsequent to step S19, the processing in step S9 is continued. In particular, it is also checked in step S9 whether the quality characteristic value Q_KW is greater than a predefined threshold value THD. Furthermore, a minimal measured value of the corrected measurement signal MS_NOX_K is determined during the previous calibration process and it is checked whether it lies within a predefined plausible range

If it has thus been recognized in step S9 that the corrected measurement signal MS_NOX_K is predetermined quasi stationary, the calibration process is terminated. Further, in the step S9, in this case, it is decided whether the processing is continued in a step S21, which is the case when the quality characteristic Q_KW is greater than the predetermined threshold THD and the minimum measured value of the corrected measurement signal MS_NOX_K within a predetermined plausible range lies. Otherwise, the processing is continued again, optionally after the predetermined waiting period, again in step S3.

In a step S21, a base adaptation value AD_BAS is determined, specifically as a function of the stored course of the corrected measurement signal MS_NOX_K during the calibration process and the filter value K_FIL determined last in the step S19. In this case, the filter value is in particular predetermined such that, given the presence of the quality characteristic Q_KW, in the case of a high quality during the calibration process, the adaptation value AD is influenced more strongly. This is determined in particular during the processing of the subsequent step S23, in which the adaptation value AD is determined as a function of the base adaptation value AD_BAS and a reference value REF, which is explained with reference to the step S25.

In addition, an offset value OFFS can also be determined in step S23, specifically as a function of the reference value REF and the base adaptation value AD_BAS, for example, a difference of the reference value REF and the base adaptation value AD_BAS. In contrast, the adaptation value AD is determined in particular as a function of a sum of the reference value REF and the base adaptation value AD_BAS.

Subsequent to step S23, the processing is continued again in step S3.

The reference value REF is determined in particular in a timely manner for a first startup of the respective nitrogen oxide sensor. In this case, the determination of the reference value REF is carried out analogously to the determination of the base adaptation value AD_BAS, only in a learning phase after initial startup of the respective nitrogen oxide sensor.

The reference value REF is frozen, in particular after the training phase, that is permanently stored in the data and program memory.

In the context of step S21, in particular a minimum of the course of the corrected measurement signal MS_NOX_K is determined and used to adapt the base adaptation value AD_BAS. In this context, averaging or filtering can also take place within the scope of the determination.

In the 3A to 3E are plotted over the time t, the temporal reference in the 3A to 3E corresponds to each other. In the 3A the time profile of a calibration indicator KAL_I is plotted, wherein this takes a value of one, while the calibration process is performed.

In the 3B the time profile of the measured signal MS_NOX of the nitrogen oxide sensor is plotted. In the 3C is the time course of the reference value REF plotted over the time t. In the 3D is the time course of the adaptation value AD plotted over time t in the 3E the course of the offset value OFFS is plotted over the time t.

The adaptation value AD is used for an additive correction of the measurement signal MS_NOX.

In the 4 exemplary profiles of the corrected measurement signal MS_NOX_K of the nitrogen oxide sensor and of the estimated measurement signal MS_NOX_EST of the nitrogen oxide sensor are plotted over the time t. Furthermore, the 4 the course of the comparison characteristic IQ is plotted during the calibration process. It can be clearly seen from the course of the comparison characteristic value IQ that in the example case the 4 a less suitable situation for strongly adapting the adaptation value AD is present. In contrast, the comparison characteristic value IQ in the courses according to the 5 significantly lower values, in particular towards the end of the calibration process, and thus a particularly suitable situation exists at least with regard to the comparison characteristic value IQ for adapting and thus determining the adaptation value AD.

6A shows further exemplary courses of the corrected measurement signal MS_NOX_K and the estimated measurement signal MS_NOX_EST during the calibration process. In the 6C . 6E and 6G first to third characteristic curves KF1, KF2, KF3 are plotted, via which an assignment of the values determined during the calibration process in accordance with 6B . 6C respectively 6F to the respective comparison characteristic value IQ, gradient characteristic value G or gas mass flow characteristic value D is effected. In the case of the 6A to 6G The calibration process shown here is a less suitable situation for strongly adapting the adaptation value AD, which is shown by the fact that the quality characteristic Q_KW has a value which is representative of a low quality.

In contrast, in the further exemplary signal curves of the 7A to 7G 1 shows a calibration process that represents a good situation for strongly adapting the adaptation value AD, which is shown by the quality characteristic Q_KW resulting from the comparison characteristic value IQ, the gradient characteristic value G and the gas mass flow characteristic value D.

LIST OF REFERENCE NUMBERS

1

intake system

3

motor unit

5

exhaust tract

7

oxidation catalyst

9

particulate Filter

11

Metering device NH3

13

SCR catalyst

15

first exhaust gas recirculation

17

second exhaust gas recirculation

18

control device

19

first lambda probe

21

second lambda probe

23

first nitric oxide sensor

25

second nitric oxide sensor

ms_NOx

Measurement signal of the nitrogen oxide sensor

MS_NOX_K

corrected measurement signal of the nitrogen oxide sensor

AD

adaptation value

REF

reference value

AD_BAS

Based adaptation value

OFFS

offset value

KAL_I

Kalibrationsindikator

MS_NOX_EST

Estimated measurement signal

IQ

Comparative characteristics

D

Gas mass flow value

G

Gradientenkennwert

t

Time

Q_KW

Quality parameter

K_FIL_FIX

Filtergrund value

K_FIL

filter value

THD

threshold

CIQ

Integral correction value

CFIG

Abtastanpassungswert

BS

predetermined operating situation

T

sampling

KF1, KF2, KF3

first, second, third characteristic

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

• DE 10003219 A1 [0006]
• DE 19926139 A1 [0007]
• EP 1227234 A2 [0008]

Claims (10)

Method for operating an internal combustion engine with an exhaust gas tract ( 5 ), in which a nitrogen oxide sensor is arranged, whose measurement signal (MS_NOX) is representative of a nitrogen oxide content in a measuring range of the nitrogen oxide sensor, wherein a corrected measurement signal (MS_NOX_K) of the nitrogen oxide sensor depending on the measurement signal (MS_NOX) and an adaptation value (AD) is determined, in which in the case that a predetermined operating situation (BS) is detected, which is representative that there is substantially no nitrogen oxide in the measurement receiving area of the nitrogen oxide sensor, a calibration process is performed at - an estimated course of an estimated measuring signal (MS_NOX_EST) of the nitrogen oxide sensor is determined, specifically as a function of a measured value of the corrected measuring signal (MS_NOX_K) of the nitrogen oxide sensor correlating to a beginning of the calibration process and - the adaptation value (AD) is determined depending on the corrected measurement signal (MS_NOX_K) of the nitric oxide sensor and dependent on a comparison characteristic value (IQ), which is representative of a comparison between the course of the estimated measuring signal (MS_NOX_EST) and the corrected measuring signal (MS_NOX_K) of the nitrogen oxide sensor.  The method of claim 1, wherein the comparison characteristic value (IQ) is determined as a function of an integral of an amount of the deviation between the estimated measurement signal (MS_NOX_EST) and the corrected measurement signal (MS_NOX_K).  Method according to one of the preceding claims, wherein in determining the comparison characteristic value (IQ), the value of the integral is reduced by a predetermined integral correction value that is dependent on a time duration of the calibration process.  Method according to one of the preceding claims, in which the course of the estimated measuring signal (MS_NOX_EST) is determined as a function of a low-pass filtering.  Method according to one of the preceding claims, in which the calibration process is ended when the corrected measurement signal (MS_NOX_K) is predetermined quasi stationary.  Method according to one of the preceding claims, in which the adaptation value (AD) is determined as a function of a minimum value of the corrected measurement signal (MS_NOX_K) during the calibration process.  Method according to one of the preceding claims, wherein a gas mass flow characteristic (D) is determined, which is representative of a gas mass flow during the calibration process, and the adaptation value (AD) is determined depending on the gas mass flow characteristic (D).  Method according to one of the preceding claims, in which a gradient characteristic value (G) is determined which is representative of a progression of the gradient of the corrected measurement signal (MS_NOX_K) during the calibration process and the adaptation value (AD) is determined as a function of the gradient characteristic value (G).  Method according to one of the preceding claims, in which the calibration process is only started after a predetermined waiting time has elapsed after the detection of the predetermined operating situation (BS). Device for operating an internal combustion engine with an exhaust gas tract ( 5 ), in which a nitrogen oxide sensor is arranged, whose measurement signal (MS_NOX) is representative of a nitrogen oxide content in a measurement receiving area of the nitrogen oxide sensor, which is designed to carry out a method according to one of the preceding claims.

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