DE102010001892B3 - Method for controlling operation of e.g. diesel engine, involves performing corrective action for oxygen sensor, when error value exceeds sensitivity valve of observer during actual operating condition of internal combustion engine - Google Patents

Abstract

The method involves determining an error value based on the difference between a sensor value obtained by an oxygen sensor and a model-based estimation value of an observer, where the sensor value represents the oxygen content in an intake manifold of an internal combustion engine. A sensitivity valve of the observer is calculated. A corrective action for the oxygen sensor is performed by adding an adjustment term to or removing the adjustment term from the error value, when the error value exceeds the sensitivity valve during an actual operating condition of the engine. An independent claim is also included for a device for controlling the operation of an internal combustion engine.

Description

The invention relates to a method and a device for controlling the operation of an internal combustion engine.

It has been known for many years, both diesel engines and gasoline engines with an exhaust gas recirculation (EGR = "Exhaust Gas Recirculation") equip, in which exhaust gases are fed back to the intake manifold to u. A. To reduce the temperature peaks in the cylinder (due to the setting of a lower oxygen concentration in the mixture). This in turn can be achieved a reduction or limitation of NO _x - (= nitrogen oxide) emissions, which is necessary to the z. B. in the EURO-6 emission standard prescribed strict limits.

To reduce pollutant emissions - such. B. NO _x emissions - is it u. A. known to provide an oxygen sensor in the intake manifold. On the basis of the supplied by this oxygen sensor FMAN value (which denotes the oxygen content in the intake manifold), a closed FMAN control can be realized by means of which in turn the combustion process in the cylinder can be improved.

The basic correlation between NO _x emissions and FMAN value is well known. For accurate closed loop FMAN control and for the most accurate estimation of NO _x emissions (without the use of a NO _x sensor), as required for On Board Diagnostics (OBD); However, due to the changing conditions with respect to soot and moisture as well as due to the considerable temperature variation, an adjustment or correction of the FMAN value supplied by the oxygen sensor is necessary.

From the DE 44 22 414 A1 a generic method for controlling the operation of an internal combustion engine with an exhaust gas recirculation and an oxygen sensor for measuring the oxygen content in the exhaust manifold is known in which a regulation of the exhaust gas recirculation takes place on the basis of the oxygen measured value.

From the US 2009/0320577 A1 a method for determining errors in the air system of an internal combustion engine is known, in which an exhaust oxygen measured value is compared with a model-based estimated value and when a predetermined error threshold values are exceeded, an error mode is detected.

Against the above background, it is an object of the present invention to provide a method and apparatus for controlling the operation of an internal combustion engine which enables a reliable estimation of the NO _x emissions and a correspondingly precise regulation of the exhaust gas recirculation.

This object is achieved by a method according to the features of independent claim 1 and a device according to the features of claim 8.

• – Ermitteln eines Fehlerwertes auf Basis der Differenz zwischen einem durch den Sauerstoffsensor erfaßten Sensorwert sowie einem mittels eines Beobachters modellgestützt abgeschätzten Wert;
• – Berechnen eines Empfindlichkeitswertes des Beobachters; und
• – Durchführen einer Korrekturanpassung des Sauerstoffsensors unter der Bedingung, dass der Fehlerwert den Empfindlichkeitswert am aktuellen Arbeitspunkt übersteigt.

An inventive method for controlling the operation of an internal combustion engine, wherein the internal combustion engine has an exhaust gas recirculation and an oxygen sensor for measuring a characteristic of the oxygen content in the intake manifold sensor value and wherein a control of the exhaust gas recirculation is made on the basis of this sensor value comprises the following steps:

• Determining an error value on the basis of the difference between a sensor value detected by the oxygen sensor and a value modeled using a model by an observer;
• - calculating a sensitivity value of the observer; and
• - Perform a correction adjustment of the oxygen sensor under the condition that the error value exceeds the sensitivity value at the current operating point.

According to the invention, the difference between the detected by the oxygen sensor FMAN value and the model-based estimated FMAN value (hereinafter referred to as "ΔFMAN") is determined or monitored. Furthermore, the sensitivity of the FMAN observer or observer according to the invention (referred to below as "dFMAN") is calculated. A sensor correction or adaptation of the FMAN sensor is only carried out under the condition that at the current operating point the value of the control deviation ΔFMAN exceeds the value of the sensitivity dFMAN. Otherwise (ie if ΔFMAN <dFMAN), no adaptation of the FMAN sensor takes place. According to the invention, an adaptation term is thus added to the sensor-based detected FMAN value only if, on the basis of the calculation of the FMAN value. Control deviation ΔFMAN and the sensitivity dFMAN of the FMAN Observer is considered necessary.

The corresponding values can be stored in a fitting table and written to non-volatile memory (NVRAM) with the ignition off. A control program controls the reading of the adaptive offset values, e.g. B. can be done during normal driving.

The invention further relates to a device for controlling the operation of an internal combustion engine, which is designed to carry out a method according to the invention. For preferred embodiments of the device reference is made to the statements in connection with the method according to the invention.

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

The invention will be explained below with reference to preferred embodiments with reference to the accompanying drawings.

Show it:

1 the course of the characteristic value for the oxygen content in the intake manifold sensor value (FMAN) for two different equilibrium states in each case in comparison between measurement and model;

2 a schematic diagram for explaining the correction adjustment of the oxygen sensor according to the invention;

3 a schematic diagram for explaining the inventive calculation of the sensitivity value in two different ranges of values of the oxygen sensor; and

4 a flowchart for explaining the sequence of the method according to the invention according to a preferred embodiment.

The mathematical description of the algorithm according to the invention is based on the following equation describing the dynamic behavior of the FMAN value in the intake manifold: F. _man = RT / pV [(F _egr - F _man ) W _egr - F _man W _comp ] (1) where P denotes the pressure, T the temperature, R the general or universal gas constant and W _egr the exhaust gas recirculation rate.

The assumption of the equilibrium state (dFMAN / dt = 0) as well as a change from equation (1) gives:

1 shows the course of the oxygen content in the intake manifold characteristic sensor value (FMAN) for two different states of equilibrium, namely at 750 revolutions / min and a mean induced pressure of BMEP = 1 bar (= curves "204_NADI") and the other at 2,000 revolutions / min. (= "195_NADI") and a mean induced pressure of BMEP = 6 bar, respectively in Homogeneous Charge Compression Ignition (HCCI) mode and in comparison between measurement and model, with the arrow "P" pointing toward increasing exhaust gas recirculation flow shows. How out 1 As can be seen, the approximate calculation already leads to a good accuracy.

2 shows a schematic diagram for explaining the correction adjustment of the oxygen sensor according to the invention. According to 2 becomes an adjustment unit 260 both by means of an observer or observer 250 determined, model-based estimated value (FMAN_obs) as well as a by the Oxygen sensor detected sensor value (FMAN_sens) supplied. The observer 250 are the inputs required for model-based estimation from an engine control unit (ECU) 240 supplied, which controls the internal combustion engine 230 performs. In the equipped with an exhaust gas recirculation engine 230 Control of the oxygen content in the intake manifold (FMAN) via corresponding FMAN actuators according to control by a controller 220 ,

The adaptation unit 260 performs a correction adjustment of the oxygen sensor only under the condition that the observer's sensitivity value dFMAN based on the difference between a sensor value (FMAN) detected by the oxygen sensor and a model-estimated estimated value ΔFMAN 250 exceeds the current operating point.

According to 3 Here, the calculation of the sensitivity dFMAN of the FMAN Observer in two different areas "I" and "II". The range "I" corresponds to a closed FMAN control in HCCI mode (ie in the area of homogeneous compression ignition, HCCI = "Homogeneous Charge Compression Ignition"). In this range, the FMAN setpoint is relatively large, and there is a high exhaust gas recirculation rate (= EGR rate). The sensitivity dFMAN is calculated in the range of the current FMAN setpoint. The range "II" corresponds to FMAN values close to zero. There is no FMAN regulation in this area. However, the correlation between the FMAN value and the NO _x emissions for downstream NO _x -based onboard diagnostic (OBD) functionality may be used. The sensitivity is calculated by the value FMAN = 0.

oder in Kurzschreibweise dF_man = f₁(F_egr, W_egr, W_comp)dF_egr + f₂(F_egr, W_egr, W_comp)dW_comp + f₃(F_egr, W_egr, W_comp)dW_egr (4) Furthermore, the sensitivity dFMAN is calculated. The following applies:

or in shorthand dF _man = f ₁ (F _egr , W _egr , W _comp ) dF _egr + f ₂ (F _egr , W _egr , W _comp ) dW _comp + f ₃ (F _egr , W _egr , W _comp ) dW _egr (4)

In reality, the exhaust gas recirculation rate W _{egr is} dependent on the temperature in the intake manifold, so that the equations (3) and (4) can be extended accordingly if necessary.

A possible extension of the exhaust gas recirculation rate is shown below, where P is the pressure, T is the temperature, N is the engine speed, VD is the engine displacement, R is the universal gas constant and η _{vol is} the volumetric efficiency, and where the index "int" applies to the intake manifold and Index "asp" indicates the air sucked into the cylinders:

A conversion from equation (5) and the calculation of the total differential result in a summary: dW _egr = g ₁ (η _vol , P _int , T _int , N, W _comp ) dP _int + g ₂ (η _vol , P _int , T _int , N, W _comp ) dT _int + g ₃ (η _vol , P _int , T _int , N, W _comp ) dη _vol + g ₄ (η _vol , P _int , T _int , N, W _comp ) dW _comp (6-7), where g () denotes the sensitivity function. Here, both the temperature in the intake manifold and the effects of the volumetric efficiency are taken into account.

4 shows a flowchart of the sequence of the method according to the invention according to a preferred embodiment. In a step S10, it is checked whether the ignition is turned on. If this is the case, a transition is made to step S20, in which (in normal driving operation) an adaptation table explained below is read in.

If the ignition is not switched on in accordance with the query of step S10, then it is checked or queried in step S30 whether the necessary activation prerequisites (in particular with regard to the equilibrium state, value range of the oxygen sensor, ambient pressure and temperature) are fulfilled for the adaptation according to the invention.

Then, in step S40, the determination of a control deviation .DELTA.FMAN is carried out according to the difference between the sensor value FMAN detected by the oxygen sensor and the value estimated by the observer, as well as the calculation of a sensitivity value dFMAN of the above explained with reference to equations (3) - (7) observer.

If the result of the query in step S50 determines whether the control deviation ΔFMAN exceeds the sensitivity value dFMAN at the current operating point, a correction adaptation of the oxygen sensor takes place in step S60 by adding an offset value to a fitting table for correcting the sensor value FMAN detected by the sensor ,

When the ignition is off (as requested in step S70), the adjustment table is stored in a nonvolatile data memory (NVRAM) in step S80 which is read in during normal running operation (i.e., when the ignition is turned on in accordance with in step S10) (step S20).

Claims (8)

Method for controlling the operation of an internal combustion engine, wherein the internal combustion engine has an exhaust gas recirculation and an oxygen sensor for measuring an oxygen content in the intake manifold characteristic sensor value (FMAN) and wherein an exhaust gas recirculation control based on this sensor value (FMAN) is performed, characterized in that the method comprises the steps of: determining an error value (ΔFMAN) on the basis of the difference between a sensor value (FMAN) detected by the oxygen sensor and a value estimated by a model based on an observer; Calculating a sensitivity value (dFMAN) of the observer; Performing a correction adjustment of the oxygen sensor under the condition that the error value (ΔFMAN) exceeds the sensitivity value (dFMAN) at the current operating point. A method according to claim 1, characterized in that the performing of a correction adaptation of the oxygen sensor comprises the addition of at least one adaptation term to the sensor value (FMAN) detected by the oxygen sensor. A method according to claim 2, characterized in that performing a correction adjustment of the oxygen sensor comprises storing the adjustment term in a fitting table. A method according to claim 3, characterized in that the adjustment table is written with the ignition off in a nonvolatile data memory (NVRAM). Method according to claim 3 or 4, characterized in that the calculation of the sensitivity value (dFMAN) in a first value range of the sensor value (FMAN) in accordance with dF _man = f ₁ (F _egr , W _egr , W _comp ) dF _egr + f ₂ (F _egr , W _egr , W _comp ) dW _comp + f ₃ (F _egr , W _egr , W _comp ) dW _egr where F _{EGR is} the oxygen fraction in the exhaust gas recirculation system, W _{egr is} the exhaust gas recirculation rate and W _{comp is} the cylinder air intake rate W _asp minus the exhaust gas recirculation rate W _egr . A method according to claim 5, characterized in that the calculation of the sensitivity value (dFMAN) in a second value range of the sensor value (FMAN) below the first value range according to dF _man = f ₁ (F _egr , W _comp , ...) dF _egr + f ₂ (F _egr , W _comp , ...) dW _comp + ... he follows. A method according to claim 5 or 6, characterized in that in the first value range of the sensor value (FMAN) is a closed control of the oxygen content in the intake manifold in HCCI mode. Device for controlling the operation of an internal combustion engine, wherein the internal combustion engine has an exhaust gas recirculation and an oxygen sensor for measuring an oxygen content in the intake manifold characteristic sensor value (FMAN), characterized in that the device is adapted to perform a method according to one of the preceding claims.

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