DE102009054817A1 - Method for on-board error diagnosis in operation of internal combustion engine of motor vehicle, involves determining actual emission value in actual operating condition, and generating error signal based on index value - Google Patents

Abstract

The method involves determining a reference value for emission i.e. soot- or nitrogen oxide emission, of an internal combustion engine based on a set value for air- and fuel path. An actual emission value is determined in an actual operating condition. An index value is determined, where the index value corresponds to quotients from integral of the actual emission value and integral of the reference value at a time interval. An error signal is generated based on the index value, and emission control of the engine is taken place based on the error signal. An independent claim is also included for a device for on-board error diagnosis in operation of an internal combustion engine.

Description

The invention relates to a method and a device for "on-board" fault diagnosis during operation of an internal combustion engine.

Since diesel particulate filters are used in motor vehicles, the analysis of the soot emissions of the internal combustion engine is increasingly taking place in the way of evaluating the soot loading of the diesel particulate filter. The evaluation of anomalies in the operation of the internal combustion engine, which can lead to an overload of the diesel particulate filter, is essential for the prediction of situations in which the diesel particulate filter is overloaded, and for avoiding replacement of the diesel particulate filter as a result of the addition of soot particles, if a safe, controlled regeneration is no longer possible. Another disadvantageous effect of the increased particulate filter loading is an increase in backpressure above the nominal value, thereby affecting fuel economy and performance of the internal combustion engine.

There is thus a need to obtain information about the effects of disturbances in the operation of the internal combustion engine on the soot emissions of the internal combustion engine.

Furthermore, an "on-board" measurement of NO _x emissions in the exhaust system of an internal combustion engine opens up a number of new possibilities for control and fault diagnosis during operation of the internal combustion engine. Although the fault diagnosis is currently performed using a sensor, there is also the possibility of feedback control with respect to the air and fuel paths.

The problem arises that in an "on-board" fault diagnosis, a restriction to a NO _x threshold is not trivial in that for a test drive leading from the same starting point to the same destination, a first driver will have different NOs depending on the driving habits _x emissions and can cause a different fuel consumption compared to a second driver because z. B. results in a more aggressive driving in higher NO _x emissions and increased fuel consumption. On the other hand, for a control test cycle, NO _x emission and fuel consumption are independent of drivability, because, by definition, the test cycle limits such dependence to acceptable variation between different test cycles.

So far, in the prior art, the use of "on-board" detection of NO _x emissions has not been intensively researched either for "on-board" failure diagnosis or for controlling the operation of the internal combustion engine.

It is an object of the present invention to provide a method and an apparatus for "on-board" fault diagnosis in the operation of an internal combustion engine, which with regard to the soot emission and / or the NOx emission, a reliable "on-board" fault diagnosis and optionally a allow suitable control.

This object is achieved by the method according to the features of independent patent claim 1 and the device according to the features of independent claim 9.

• – Ermitteln eines Emissions-Referenzwertes auf Basis einer Solleinstellung für den Luft- und Kraftstoffpfad;
• – Ermitteln eines aktuellen Emissions-Wertes in einem aktuellen Betriebszustand;
• – Ermitteln eines Indexwertes, wobei dieser Indexwert dem Quotienten aus dem Integral des aktuellen Emissions-Wertes über ein vorbestimmtes Zeitintervall und dem Integral des Emissions-Referenzwertes über dieses Zeitintervall entspricht; und
• – Erzeugen eines Fehlersignals auf Basis dieses Indexwertes.

A method for "on-board" fault diagnosis in the operation of an internal combustion engine comprises the following steps:

• - determining an emissions reference value based on a default setting for the air and fuel path;
• - determining a current emission value in a current operating state;
• - determining an index value, said index value corresponding to the quotient of the integral of the current emission value over a predetermined time interval and the integral of the emission reference value over this time interval; and
• - Generate an error signal based on this index value.

In particular, the present invention is based on the concept of calculating an emission reference value, which may be an emission reference value for the soot emission or for the NOx emission of the internal combustion engine, which to a certain extent represents a desired value for the emission level this emission reference value is used for "on-board" fault diagnosis and, where appropriate, emission control.

In accordance with the invention, the calculation of a reference value for the soot emission (in units of mg / m ³ ) as a function of target settings for the air and fuel paths takes into account the influence of the vehicle dynamics (ie, transient corrections) on the equilibrium state calibration values.

According to one embodiment, the determination of the emission reference value is based on a reference value (F _{exh, ref} ) of the burned mass fraction in the exhaust gas. Furthermore, the determination of the current emission value in a current operating state can be based on a value of the burned mass fraction in the exhaust gas (F _{exh, ref} ).

For a given operating state, the soot concentration produced by the combustion process essentially depends on the burned mass fraction in the exhaust gas (F _exh ). For the reference value of the soot emission, a reference value of the mass fraction burned in the exhaust gas (F _{exh, ref} ) is calculated for the target setting for the air and fuel path. A consideration of the driving behavior takes place insofar as a more aggressive driving style leads to a more pronounced correction of the desired value (ie to a greater deviation due to the high-pass filtering for transient corrections) and to larger deviations between the target settings and measured values, in particular the Air path concerns.

According to one embodiment, an emission control of the internal combustion engine takes place as a function of the error signal.

According to a further embodiment, a correction of the target setting for the air path and / or the fuel path takes place as a function of the error signal.

According to one embodiment, for a first value range of the error signal, a correction of the target setting for the air path, and for a second value range of the error signal, a correction of the target setting for the fuel path, wherein the second value range corresponds to larger deviations of the current emission from the reference value of the emission than that first value range.

The invention further relates to a device for "on-board" fault diagnosis during operation of an internal combustion engine, wherein the device is designed to carry out a method according to one of the preceding claims. For preferred embodiments of the device, reference is made to the above statements in connection with the method.

Further embodiments of the invention are described in the description and the dependent claims.

The invention will be explained below with reference to a preferred embodiment with reference to the accompanying figure.

Show it:

1 a schematic diagram for explaining the implementation of a method according to the invention for fault diagnosis according to an embodiment using the soot emission;

2 a schematic diagram for explaining a method according to the invention for controlling the soot emission;

3 a schematic diagram for explaining the implementation of a method according to the invention for fault diagnosis according to an embodiment with respect to the NOx emission; and

4 a schematic diagram for explaining a method according to the invention for controlling the NOx emission.

In addition, first with reference to 1 and 2 a possible implementation of the method according to the invention for fault diagnosis or for controlling an internal combustion engine with application to the soot emission explained.

According to 1 the calculation of a reference value for soot emission (in units of mg / m ³ ) is made essentially as a function of target settings for the air and fuel path.

As in 1 shown schematically, for a given operating condition, the soot concentration produced by a combustion process substantially dependent on the burned mass fraction in the exhaust gas (F _exh ). Accordingly, to determine a reference value of the soot emission, a reference value (F _{exh, ref)} the mass fraction burned in the exhaust gas calculated for the target setting for the air and fuel path.

In the case of a non-dynamic variation of the target fuel path setting, the reference value for the soot emission is calculated essentially based on the _exhausted mass fraction reference value (F _{exh, ref} ), which in turn essentially consists of MAF and MAP setpoint values the case of a non-model-based control of the air path is calculated. The reference value for the soot emission is then estimated for the emissions of the internal combustion engine in the target setting for the air and fuel path.

For the purpose of "on-board" fault diagnosis, see 1 calculates the integral of the current soot emission over a time interval and divides it by the integral of the reference value for the soot emission over the time interval. The selection of the time window used here is relevant to the timeframe of a pre-calibration mass fraction in the diesel particulate filter for the next operating cycle in order to ensure a correct fault diagnosis.

The index value thus calculated is evaluated with an OBD threshold index value for the Error diagnosis (OBD threshold index value, OBD = "on-board diagnostics"), this OBD threshold index value being the quotient of an OBD threshold (in g per operating cycle) and the integral of the reference value for soot emission (in grams per operating cycle) equivalent. For values above the OBD threshold index value, an error message is displayed during fault diagnosis or an error signal is output.

According to 2 For example, the deviation between the reference value for the soot level and the current value for the soot emission is used to generate an error signal. This error signal is used in the air and fuel path structure as follows:
Air and fuel path control coordination determines whether correction of the air path and / or fuel path target setting is required to bring the deviation between the soot emission reference value and the measured soot emission value within an acceptable tolerance range.

Depending on the operating range of the internal combustion engine, for large deviations of the soot emission (i.e., when fast dynamics are required), the target fuel path setting is corrected. In the case of comparatively small deviations in the soot emission and a good tracking between the reference value and the current target setting for the air path, the default setting for the air path is corrected.

Alternatively, in a closed loop (closed loop) air path feedback control, the soot error signal may be used directly to control the air path adjustment. Control in this approach is limited by linking with the NO _x emissions values tolerated by the NO _x emission OBD threshold when operating at another NO _x soot compensation curve operating point.

Depending on whether "on-board" control and / or monitoring of the soot emission is desired, a model of any exhaust aftertreatment component may be included to estimate the soot emission, which will determine the soot content in the exhaust pipe (or in the monitoring position ), z. For example, any diesel particulate filter catalyst elements that store or convert soot particles at the inlet to the diesel particulate filter substrate. Similarly, a model for the current soot emission may be used to evaluate soot emissions at the monitoring position, but in this case under on-board direct measurement and / or a suitable estimation algorithm. This may correspond to the estimation algorithm used in connection with the reference value for the soot emission, but based on the currently measured values for the air path (MAF, MAP, exhaust lambda value, intake lambda value) and the fuel path . be used.

With reference to 1 described method for "on-board" fault diagnosis can be used analogously for an emission reference value for the NOx emission. In addition, first with reference to 3 and 4 a possible implementation of the method according to the invention for fault diagnosis or for controlling an internal combustion engine with application to the NOx emission explained.

A NOx emission reference value may be calculated based on the following steps: estimating unburned NO _x emissions, applying a reduced-order thermal and kinetic model for the exhaust aftertreatment component, and estimating downstream NO _x emissions.

According to 3 For a given operating state, the NOx concentration produced by a combustion process is determined as a function of the burned mass fraction in the exhaust gas (F _exh ). Accordingly, to determine a reference value of the NOx concentration, a reference value (F _{exh, ref} ) of the burned mass fraction in the exhaust gas is calculated for the target setting for the air and fuel path.

In the case of a non-dynamic variation of the desired fuel level setting, the reference value for the NOx concentration is calculated essentially on the basis of the reference value for the combusted mass fraction in the exhaust gas (F _{exh, ref} ), which in turn essentially consists of MAF and MAP values. Setpoints are calculated for the case of a non-model-based control of the air path. The NOx concentration reference value is then estimated for the engine emissions at the air and fuel rail setpoint.

For the purpose of "on-board" fault diagnosis, see 3 calculates the integral of the current NOx emission over a time interval and divides by the integral of the NOx emission reference value over the time interval. The selection of the time window used here is relevant to the timeframe of a pre-calibration mass fraction in the diesel particulate filter for the next operating cycle in order to ensure a correct fault diagnosis.

The index value thus calculated is compared with an OBD Threshold Index value for the fault diagnosis (OBD threshold index value, OBD = "on-board diagnostics"), this OBD threshold index value being the quotient of an OBD threshold (in g per operating cycle) and the Integral of the reference value for NOx emission (in grams per operating cycle). For values above the OBD threshold index value, an error message is displayed during fault diagnosis or an error signal is output.

According to 4 For example, the deviation between the reference value for the NOx emission and the current value for the NOx emission is used to generate an error signal. This error signal is used in the air and fuel path structure as follows:
An air and fuel path control coordination determines whether a correction of the target air path and / or fuel path adjustment is required to set the deviation between the NOx emission reference value and the measured NOx emission value within an acceptable tolerance range bring.

Depending on the operating range of the internal combustion engine, for large variations in NOx emission (i.e., when fast dynamics are required), the fuel path set point adjustment is corrected. In the case of comparatively smaller deviations in the NOx emission as well as a good tracking between the reference value and the current target setting for the air path, the default setting for the air path is corrected.

Alternatively, in a closed loop (closed loop) air path feedback control, the NOx error signal may be used directly to control the air path setting.

Depending on whether "on-board" control and / or monitoring of NOx emission is desired, a model of any exhaust aftertreatment component may be included to estimate the NOx emission, which is the NOx emission in the exhaust pipe (or in the monitoring position) influenced, z. For example, any diesel particulate filter catalyst elements that store NOx conversion at the inlet to the diesel particulate filter substrate. Similarly, a model for the current NOx emission may be used to evaluate NOx emission at the monitoring position, but in this case under on-board direct measurement and / or a suitable estimation algorithm. This may be in accordance with the estimation algorithm used in conjunction with the NOx emission reference value but based on the currently measured values for the air path (MAF, MAP, exhaust lambda, intake lambda) and fuel path be placed or used.

Claims (9)

A method of "on-board" fault diagnosis in the operation of an internal combustion engine, characterized in that the method comprises the steps of: a) determining an emission reference value based on a target setting for the air and fuel path; b) determining a current emission value in a current operating state; c) determining an index value, said index value corresponding to the quotient of the integral of the current emission value over a predetermined time interval and the integral of the emission reference value over that time interval; and d) generating an error signal based on this index value. A method according to claim 1, characterized in that the emission reference value is a reference value for the soot emission of the internal combustion engine. A method according to claim 1, characterized in that the emission reference value is a reference value for the NOx emission of the internal combustion engine. Method according to one of the preceding claims, characterized in that the determination of the emission reference value takes place on the basis of a reference value (F _{exh, ref} ) of the burned mass fraction in the exhaust gas. Method according to one of the preceding claims, characterized in that the determination of the current emission value on the basis of a value of the combusted mass fraction in the exhaust gas (F _{exh, ref} ) takes place in a current operating state. Method according to one of the preceding claims, characterized in that an emission control of the internal combustion engine takes place as a function of the error signal. Method according to one of the preceding claims, characterized in that a correction of the target setting for the air path and / or the fuel path takes place as a function of the error signal. A method according to claim 7, characterized in that for a first value range of the error signal, a correction of the target setting for the air path takes place, and for a second value range of the error signal, a correction of The second value range corresponds to larger deviations of the current emission from the reference value of the emission than the first value range. Device for "on-board" fault diagnosis during operation of an internal combustion engine, characterized in that the device is designed to carry out a method according to one of the preceding claims.

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