EP2013464B1 - Method for adjusting the air/fuel ratio of an internal combustion engine - Google Patents

Method for adjusting the air/fuel ratio of an internal combustion engine Download PDF

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Publication number
EP2013464B1
EP2013464B1 EP07722105A EP07722105A EP2013464B1 EP 2013464 B1 EP2013464 B1 EP 2013464B1 EP 07722105 A EP07722105 A EP 07722105A EP 07722105 A EP07722105 A EP 07722105A EP 2013464 B1 EP2013464 B1 EP 2013464B1
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EP
European Patent Office
Prior art keywords
switching point
point
lambda
oscillation
sensor
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EP07722105A
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German (de)
French (fr)
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EP2013464A1 (en
Inventor
Sven Bruhn
Matthias Schultalbers
Thomas Von Der Ohe
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IAV GmbH Ingenieurgesellschaft Auto und Verkehr
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IAV GmbH Ingenieurgesellschaft Auto und Verkehr
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Priority claimed from DE200610017863 external-priority patent/DE102006017863B3/en
Priority claimed from DE200610049348 external-priority patent/DE102006049348A1/en
Priority claimed from DE200610049350 external-priority patent/DE102006049350A1/en
Application filed by IAV GmbH Ingenieurgesellschaft Auto und Verkehr filed Critical IAV GmbH Ingenieurgesellschaft Auto und Verkehr
Publication of EP2013464A1 publication Critical patent/EP2013464A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
    • F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
    • F02D41/1476—Biasing of the sensor

Definitions

  • the invention relates to a method for adjusting the air / fuel ratio of an internal combustion engine.
  • the signal of at least one exhaust gas sensor is evaluated and by adjusting the amount of fuel supplied to the internal combustion engine in a control or regulation, the setting of the desired air / fuel ratio.
  • lambda probes are already known, which measure the oxygen content in the exhaust gas. In this case, a distinction is made between continuously measuring probes with a virtually linear sensor characteristic that is specified over the entire range, and jump probes with a strongly nonlinear characteristic of the oxygen content relative to the output voltage of the probe.
  • Jump sensors used in the lambda control have a switching characteristic which causes a large change in the probe output voltage with a small change in the lambda value in the region around lambda equal to 1.
  • more and more jump probes are used for lambda control, which are precisely specified only in the characteristic range of the fat-lean transition in the lambda value close to 1 and have a large slope there. Therefore, this probe is usually used only in 2-point controller structures for Einregelung a mixture value near lambda 1. Lambda setpoint values deviating from the stoichiometric operating point can thus only be approached in a controlled manner.
  • the switching point of the jump probe is adapted in order to ensure a desired conversion rate of the catalytic converter.
  • the object of the invention is therefore to provide a method for adjusting a fuel / air mixture, which allows for a lambda control by means of at least one jump probe the most accurate control of the fuel / air mixture for lambda setpoints, which differ from the stoichiometric ratio. Furthermore, a regulation is created that allows a diagnosis of the lambda probe.
  • the object is achieved in that a two-step control takes place about a switching point, wherein for setting a desired lambda value of the switching point of the two-point controller is adapted.
  • the oscillation of the measuring signal of the lambda probe is recorded by the switching point, whereby a constant control stroke is ensured.
  • a desired value is preset around the respective switching point, and the setpoint value of the two-step controller is shifted in such a way that the nominal value of the oscillation sets.
  • various amplitude-related parameters of the oscillation are evaluated.
  • the control is carried out to a desired value of the oscillation, wherein the switching point of the two-point controller adjusts in dependence thereon.
  • the self-adjusting probe output voltage is measured with regard to the amplitude of its oscillation (so-called residual ripple).
  • residual ripple There is a control to the measured variable of the residual ripple such that the switching point of the two-point controller as long as is shifted until the desired, predetermined residual ripple sets.
  • the method is based on the knowledge that the probe characteristic drifts due to temperature or aging with respect to the assignment of the probe output voltage to the lambda value.
  • the residual ripple correlates with a predetermined control stroke largely aging and temperature stable with a assignable lambda value.
  • a desired adjustment of the lambda value is achieved by shifting the switching point until a predeterminable residual ripple is reached, without predetermining an absolute switching point for the controller.
  • the curvature of the probe characteristic which is specific for an associated lambda value.
  • the shape of the probe characteristic curve is analyzed, which is largely attributable to a defined lambda value with respect to temperature and aging.
  • the unbalance of the oscillation of the probe output voltage is determined in a two-point control.
  • the resulting probe output voltage is analyzed with regard to its oscillation.
  • the asymmetry of the oscillation with respect to the switching point is evaluated.
  • the amplitude of the half-waves or their areas in relation to the threshold value are determined.
  • the ratio of the half-waves or their amplitude and / or surface area is used as a reference variable for the control.
  • the curvature and its equivalent determined by the unbalance is independent of the absolute value of the probe output voltage and allows a controlled approach of lambda values in the unspecified and very flat "fat load" of the probe characteristic by means of the two-step control used for the regulation of the stoichiometric ratio.
  • the method is based on the knowledge that the probe characteristic
  • the characteristic is aging and temperature stable and can be formed at a predetermined control stroke by means of the analysis of the asymmetry of the oscillation, an equivalent of the characteristic shape due to temperature or aging.
  • a desired adjustment of the lambda value is achieved by adapting the switching point until a specifiable asymmetry of the oscillation of the probe output voltage is reached, without predetermining an absolute switching point for the regulator. This ultimately results from the regulation on the asymmetry.
  • the signal of the lambda probe is considered when shifting the switching point away from the stoichiometric ratio.
  • an asymmetry of the oscillation of the probe output voltage in a two-point control is produced while the control stroke remains constant.
  • the control stroke is in running two-point regulations preferably 1-2% deviation from the set fuel mass.
  • the amplitude of the half-waves or their areas in relation to the threshold value are determined.
  • the ratio of the half-waves or their amplitude and / or area can be used as a reference variable for the control and the resulting switching point is considered for diagnosis.
  • the control of the asymmetry of the oscillation of the probe output voltage is effected in such a way that the switching point of the two-point controller is shifted until the desired, definable asymmetry is established.
  • the existing structure of the control as it is present in the prior art for stoichiometric operation as a two-step control, is also used for the diagnosis.
  • the existing structure of the control as it is present in the prior art for stoichiometric operation as a two-step control, is also used for the diagnosis.
  • only a comparison with previously determined standard values takes place.
  • an evaluation of the probe output signal with regard to the residual ripple of the oscillation of the probe output signal at switching point displacement is carried out for diagnosis as an alternative or in addition to the ascertained asymmetry.
  • the diagnosis is advantageously carried out in operating ranges in which a regulated lambda value deviating from the stoichiometric ratio is regulated in a regulated manner (eg, catalyst heating or component protection).
  • a regulated lambda value deviating from the stoichiometric ratio is regulated in a regulated manner (eg, catalyst heating or component protection).
  • the lambda control is necessary for gasoline engines with a 3-way catalytic converter, since this is only able to control the pollutant components HC, CO and NO x within a very narrow range of the air / fuel ratio (lambda value) effectively reduce.
  • the lambda window (control range of the jump probe with two-step control according to the prior art) is in a range between lambda values of 0.99 to 1.
  • the required accuracy is only achieved with a control, which in the case of a jump probe as a two-step control with a switching point at a desired lambda value near 1 is executed. With the signal of the jump probes only qualitative statements about the lambda value can be made. Depending on the measured lambda value, the signal of the injection quantity is modified.
  • the control in the direction of the desired lambda value is influenced by a change in the manipulated variable (injection quantity) by a defined value or characteristic curve (control stroke).
  • injection quantity a change in the manipulated variable
  • control stroke a defined value or characteristic curve
  • Exemplary are different probe characteristics in FIG. 1 shown.
  • the lambda control adjusts the following injection on the basis of the previous measurement.
  • the adjustment of the injection quantity due to the lambda probe signal is referred to as a control stroke.
  • the computing time in the control unit and the response time of the lambda probe the measurement has a time offset to the injection, resulting in a minimum period of oscillation of the lambda value.
  • the control switching point is usually in the specified stable range at 450 mV. This corresponds to a lambda value close to 1. Due to aging and temperature influences on the probe characteristic, the probe characteristic changes especially in the unspecified edge regions. If a "lean” or “rich” fuel / air mixture is to be set with the present two-point control, the switching point must be shifted downwards (for example 200 mV) or above (for example 700 mV). It uses the unspecified lean or rich load of the probe characteristic.
  • the characteristic curve of a jump probe is in FIG. 1 shown. The probe output voltage is shown as a function of the lambda value.
  • the lambda probe was heated to different temperatures, and for one and the same probe, temperature-dependent different probe characteristics are formed. Exemplary are the different temperatures Deviations of the probe characteristic, in particular in the unspecified edge regions shown. Since these characteristic ranges are very flat, only a small change in the probe output voltage takes place in the edge regions of the characteristic with large changes in the lambda value. If the edge areas of the probe characteristic curve are affected by aging or temperature influences (as in Fig. 1 shown), a fixed switching point outside Lambda 1 would cause the adjusted lambda to drift strongly. In addition, it can happen that a fixed switching point is no longer reached.
  • this can be avoided by monitoring the oscillation of the probe output voltage during regulation by an adapted switching point during a predetermined control stroke.
  • the switching point is shifted piecewise and, according to a first embodiment of the invention, the resulting oscillation of the probe output voltage is evaluated with regard to its amplitude (so-called residual ripple).
  • residual ripple is thus a reference variable of the scheme.
  • This controller structure is also used for the inventive control outside the stoichiometric mixture, wherein the switching point is adapted and their Property to generate a vibration of the measuring signal of the lambda probe is used.
  • the switching point of the two-point controller is shifted and the resulting oscillation of the probe output voltage caused by the constant control stroke is evaluated with regard to its amplitude (so-called residual ripple). Furthermore, an evaluation of the measurement curve of the probe output voltage with respect to the symmetry of the oscillation takes place.
  • the measurement curve is evaluated with regard to the amplitude of the individual half-waves and / or the area enclosed between the respective half-waves and a straight line through the switching point.
  • An integration results in the area of the respective half-wave of the trace.
  • the two-step control works with a defined control stroke. Based on the current measured value of the probe output voltage, the current injection quantity is changed by a defined amount (for example 2% of the current injection quantity) so that the measured value approaches the switching threshold. If the switching threshold is exceeded or not reached, the injection quantity changes again by the same amount. It thus takes place a swing of the lambda value and thus the measurement signal of the probe output voltage by the switching threshold.
  • an asymmetrical oscillation takes place around the switching point.
  • An exemplary switching point at a probe output voltage of 700 mV is considered below.
  • the probe output voltage oscillates about the switching point, whereby, measured at the switching point, a stronger penetration of the vibration of the probe output voltage takes place in the direction of lower voltage values. This is caused by the constant control stroke when changing over the control range sonar characteristic.
  • a reduction in the injection quantity takes place, for example, by 2%, in accordance with the control strategy of the two-step controller.
  • the lambda value is thereby controlled in the direction of lean lambda values. Due to the gas run times, a reaction is delayed so that the lambda value is overshooted in the direction of rich mixture values. However, due to the sensor characteristic that becomes flatter in this area, this only occurs to a lesser extent in the probe output voltage than in the same overshoot in the direction the stoichiometric ratio.
  • the thus measurable asymmetry is thus indicative of the curvature of the probe characteristic.
  • the curvature of the probe characteristic curve described by the asymmetry of the half-waves of the oscillation of the probe output signal is used as a reference variable for lambda values deviating from the stoichiometric ratio. It thus takes place a controlled approach of switching points, which are on the unspecified lean or rich load of the probe characteristic.
  • the regulation can thus be preset with reference values for the lambda value, which are ultimately setpoints for a defined curvature value of the probe characteristic.
  • a prior identification for example, the ratio of the half-wave surfaces to each other at a predetermined control stroke, so that the ratio of the surfaces to each other or the amplitudes of the half-waves to a defined lambda value, for example from preliminary investigations on the test bench is known.
  • the specification on the basis of the lambda value to be adjusted, the specification of a corresponding ratio of the amplitudes and / or the areas of the half-waves describing the asymmetry takes place. The switching point is shifted until the required value of the asymmetry is reached.
  • the oscillation of the measuring signal of the lambda probe can be evaluated and used as a reference variable for the control.
  • a regulation with regard to the amplitude of the oscillation can be used for adjusting "fat" or "lean” operating states.
  • the residual ripple or its amplitude itself can be considered.
  • the amplitude of the residual ripple is also a measure of the lambda value independent of the absolute values of the probe output voltage.
  • FIG. 2 explains the regulation in detail with an example.
  • the asymmetry of the half-waves and / or the amplitude of the residual ripple are specific for the respective switching points. This is used to diagnose the lambda probe.
  • a prior identification of the asymmetry for example by determining the ratio of the half-wave surfaces to each other and / or by measuring the residual ripple at a predetermined control stroke for predetermined switching points with a functioning lambda probe, for example by preliminary investigations on the testbed.
  • a comparison of the standard values determined for a functioning probe with those determined during operation is required, and it is possible to draw conclusions about the operating state of the lambda probe from the deviation of the values.
  • a deviation of the asymmetry and / or residual ripple, in particular in the edge regions of the probe characteristic curve, is characteristic of an aging or fault-related drift of the probe characteristic curve.
  • the residual ripple or its amplitude can be considered.
  • the amplitude of the residual ripple is also a measure of the diagnosis of the lambda probe for a specific switching point.
  • FIG. 2 shows an example for the determination of the amplitude of the oscillation (ripple) of the measuring signal of the lambda probe to the switching point.
  • FIG. 2 the probe signal with adapted switching point is shown. There is a shift of the switching point in the direction of higher probe output voltage, wherein the control stroke is maintained. The subarea of the shift of the switching point is hidden. Shown is the Probe output voltage after adjusting to a residual ripple of 350 mV amplitude of the oscillation of the probe output voltage. Due to the flattening probe characteristic, oscillation occurs with a lower amplitude of the oscillation of the probe output voltage. According to the switching point is shifted so far until the desired amplitude of the vibration of the probe output voltage (for example, 350 mV) is reached. This value can be assigned to a lambda value.
  • lambda value The relationship between the lambda value and the amplitude of the oscillation of the probe output voltage must first be determined for a control stroke defined in the control algorithm.
  • the lambda controller continues to be in operating ranges at lambda near 1 a control by means of the two-point controller to a defined switching point, for example, 450 mV probe output voltage for the example present jump probe with a probe characteristic according to FIG. 1 ,
  • a switching point for example, 450 mV probe output voltage for the example present jump probe with a probe characteristic according to FIG. 1
  • the switching point is shifted in the direction of "rich” or "lean” (probe output voltage less than or greater than 450 mV).
  • the amplitude of the probe output voltage is measured and, with a constant control stroke (variation of the fuel quantity to be injected when the changing switching point is undershot or exceeded by 2% of the basic injection quantity), a regulation takes place to a predetermined amplitude of the probe output voltage.
  • the probe output voltage oscillates by a new switching point, which is defined by the amplitude of the oscillation of the probe output voltage.
  • the described control on the amplitude of the oscillation of the probe output voltage sets a switching point as a function of the real sonic characteristic.
  • the switching points determined for certain operating points in the "lean” or “rich” range can be used for diagnostic purposes. Based on the comparison of the set switching points with predefined switching points determined for ideal probe characteristics, the determined deviation from the switching points of the real probe gained diagnostic information. If the determined switching points deviate by a predefined amount from the values determined for an ideal probe, the probe is rated as defective.
  • FIG. 3 is further illustrated by another example, the two-step control with switching point adaptation.
  • An embodiment of the invention is described in which the oscillation of the measuring signal of the lambda probe is evaluated on the basis of the asymmetry of the oscillation about the switching point. It is in FIG. 3 the probe output voltage over time for a Einregelvorgang a deviating from the stoichiometric ratio rich mixture shown.
  • the known two-step control by means of a jump probe, which a characteristic probe characteristic of the probe output voltage to the lambda value - as in FIG. 1 shown - has.
  • the probe output voltage oscillates in subarea A by a switching point at 450 mV, which corresponds to a stoichiometric mixture. If a fuel-rich mixture is now to be set for special operating points, such as acceleration lubrication or component protection, this will continue to be regulated.
  • the reference variable used here is the asymmetry of the oscillation of the probe output signal. There is a shift of the switching point of the two-point controller (sub-area B) until the predefined, to the respective lambda value associated asymmetry is reached. This can be formed, for example, as a ratio of the amplitude of the half-waves upper half-wave Ao / lower half-wave Au. Furthermore, the ratio of the areas of the upper to the lower half-wave with respect to a straight line through the switching point can be used for evaluation.
  • a combined two-point control with switching point adaptation takes place such that the switching point is adapted on the basis of the residual ripple and the imbalance.
  • the control can be constructed as a cascade control, wherein the inner loop contains the ripple control and the outer loop control to a value of the curvature of the probe characteristic, which is expressed by the asymmetry of the vibration of the probe voltage to the switching threshold.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Testing Of Engines (AREA)

Abstract

A method is for adjusting a fuel/air ratio by means of an on-off controller as well as a diagnostic method in which a desired fuel/air mixture is regulated in accordance with a test signal of a lambda probe that is embodied as a jump probe. The switching point of the on-off controller is moved/adapted while the oscillation of the test signal of the lambda probe is analyzed regarding the amplitude and/or the asymmetry of the oscillation around the switching point at a constant control stroke. A desired value for the asymmetry or the amplitude of the oscillation of the test signal of the lambda probe around the respective switching point is predefined, the switching point of the on-off controller being moved such that the desired value is reached.

Description

Die Erfindung betrifft ein Verfahren zum Einstellen des Luft-/Kraftstoffverhältnisses eines Verbrennungsmotors. Zum Einstellen des Luft-/Kraftstoffverhältnisses eines Verbrennungsmotors wird das Signal wenigstens eines Abgassensors ausgewertet und durch Anpassung der dem Verbrennungsmotor zugeführten Kraftstoffmenge erfolgt in einer Steuerung oder Regelung die Einstellung des gewünschten Luft-/Kraftstoffverhältnisses. Als Abgassensoren sind sogenannte Lambdasonden vorbekannt, welche den Sauerstoffanteil im Abgas messen. Es wird dabei zwischen kontinuierlich messenden Sonden mit über den gesamten Bereich spezifizierter, nahezu linearer Sondenkennlinie und Sprungsonden mit stark nichtlinearer Kennlinie des Sauerstoffanteils zur Ausgangsspannung der Sonde unterschieden. In der Lambdaregelung verwendete Sprungsonden weisen eine Schaltcharakteristik auf, welche eine starke Änderung der Sondenausgangsspannung bei einer geringen Änderung des Lambdawertes im Bereich um Lambda gleich 1 hervorruft. Aus Kostengründen werden vermehrt Sprungsonden zur Lambdaregelung eingesetzt, welche nur im Kennlinienbereich des Fett-Mager-Überganges im Lambdawert nahe 1 präzise spezifiziert sind und dort eine große Steigung aufweisen. Daher wird diese Sonde üblicherweise nur in 2-Punkt-Reglerstrukturen zur Einregelung eines Gemischwertes nahe Lambda 1 genutzt. Vom stöchiometrischen Arbeitspunkt abweichende Lambdasollwerte können damit nur gesteuert angefahren werden. Es entstehen in gesteuert gefahrenen Betriebssituationen, wie Katalysatorheizen (Betrieb mit gewünscht "magerem" Kraftstoff-Luft-Gemisch Lambda >1, vorzugsweise zwischen 1.01 und 1.05) und Bauteilschutz sowie Anfettung beim Beschleunigen (Betrieb mit Lambda <1 typische Werte für Bauteilschutz und Beschleunigungsanfettung liegen im Bereich von 0.99 bis 0.85) teilweise große Abweichungen vom gewünschten Lambdawert.The invention relates to a method for adjusting the air / fuel ratio of an internal combustion engine. For adjusting the air / fuel ratio of an internal combustion engine, the signal of at least one exhaust gas sensor is evaluated and by adjusting the amount of fuel supplied to the internal combustion engine in a control or regulation, the setting of the desired air / fuel ratio. As exhaust gas sensors so-called lambda probes are already known, which measure the oxygen content in the exhaust gas. In this case, a distinction is made between continuously measuring probes with a virtually linear sensor characteristic that is specified over the entire range, and jump probes with a strongly nonlinear characteristic of the oxygen content relative to the output voltage of the probe. Jump sensors used in the lambda control have a switching characteristic which causes a large change in the probe output voltage with a small change in the lambda value in the region around lambda equal to 1. For reasons of cost, more and more jump probes are used for lambda control, which are precisely specified only in the characteristic range of the fat-lean transition in the lambda value close to 1 and have a large slope there. Therefore, this probe is usually used only in 2-point controller structures for Einregelung a mixture value near lambda 1. Lambda setpoint values deviating from the stoichiometric operating point can thus only be approached in a controlled manner. There arise in controlled driven operating situations, such as catalyst heating (operation with desired "lean" fuel-air mixture lambda> 1, preferably between 1.01 and 1.05) and component protection and enrichment during acceleration (operation with lambda <1 typical values for component protection and acceleration fats are in the range of 0.99 to 0.85) sometimes large deviations from the desired lambda value.

Vorbekannt ist aus der DE 198 44 994 C2 die Diagnose einer Lambdasonde, bei welcher der Adaptionswert eines den Lambdaregelkreis abbildenden Modells bei einer periodischen Zwangsanregung der Regelstrecke überwacht wird. Einer der Modellparameter ist die Sensorverzögerungszeit, deren Abweichen bei der Modelladaption überwacht wird und eine signifikante Abweichung eine fehlerhafte Lambdasonde markiert. Das Verfahren wird für stetige Lambdasonden angewandt.Previously known from the DE 198 44 994 C2 the diagnosis of a lambda probe, in which the adaptation value of a model representing the lambda control loop is monitored during a periodic forced excitation of the controlled system. One of the model parameters is the sensor delay time whose deviation in the Model adaptation is monitored and a significant deviation marked a faulty lambda probe. The method is used for continuous lambda probes.

Vorbekannt ist weiterhin aus der DE 44 22 115 C2 eine Diagnose für eine Sprungsonde in einem geschlossenen Regelkreis, wobei der Regelkreis mit einer periodischen Zwangsanregung überlagert wird und aus dem daraus resultierende Sondensignal im Vergleich zur Anregung eine Diagnose der Lambdasonde erfolgt. Eine Verschiebung des Schaltpunktes des Zweipunktreglers findet nicht statt.Previously known from the DE 44 22 115 C2 a diagnosis for a jump probe in a closed loop, wherein the control loop is superimposed with a periodic forced excitation and from the resulting probe signal in comparison to the excitation of a diagnosis of the lambda probe. A shift of the switching point of the two-point controller does not take place.

Vorbekannt ist aus der DE 100 04 416 A1 ein Verfahren zum Einstellen des Luft-/Kraftstoffverhältnisses mit einer Abgassensorik vor dem Katalysator und einer Abgassensorik nach dem Katalysator. In gesonderten Betriebsbereichen des Verbrennungsmotors, beispielsweise bei Bergabfahrt, in welcher vom stöchiometrischen Verhältnis abgewichen werden soll, erfolgt ein Umschalten in den gesteuerten Betrieb ("open loop"). Die Luft-/Kraftstoffmenge wird bei gesteuertem Betrieb ohne Rückkopplung des Messwertes von der Lambdasonde auf Basis vordefinierter Stellgrößen eingestellt. Hier treten aufgrund der Steuerung ohne Messwertrückkopplung große Abweichungen zum eigentlich gewünschten Lambdawert auf. Eine Regelung des Luft-/Kraftstoffgemisches in Betriebsbereichen, in welchen gewünscht ein Betrieb mit vom stöchiometrischen Verhältnis abweichendem Luft-/Kraftstoffverhältnis (Lambda ungleich 1) realisiert wird, erfolgt nicht. Beim Übergang vom gesteuerten zum geregelten Betrieb, in welchem ein stöchiometrisches Verhältnis erneut eingeregelt werden soll, erfolgt in einem kurzen zeitlich begrenzten Übergangsbereich ein geregelter Betrieb auf Basis des Signals der Sprungsonde vor dem Katalysator. Hierfür wird bei abgeschalteter Nachregelung mittels der Lambdasonde nach dem Katalysator der Schaltpunkt der Sprungsonde adaptiert, um eine gewünschte Umsatzrate des Katalysators sicherzustellen. Nachteilig für die Regelung des Kraftstoff-/Luftgemisches mittels einer Sprungsonde ist die sondenbedingte Form der Kennlinie, welche im Bereich um Lambda 1 eine starke Veränderung des Spannungswertes bei geringen Änderungen des Lambdawertes bereitstellt, jedoch in Bereichen Lambda ungleich 1 einen sehr flachen Verlauf der Kennlinie aufweist. Hierdurch wird in Bereichen, welche vom stöchiometrischen Verhältnis abweichen, lediglich eine geringe Spannungsänderung bei sich ändernden Lambdawerten gemessen. Die Regelung mittels eines Zweipunktreglers ist damit ungenau. Weiterhin problematisch ist die durch die Alterung der Sonden auftretende Drift der Kennlinie. Während die Sonde im Sprungbereich um Lambda gleich 1 noch für die Regelung ausreichend differenzierte Messwerte des Kraftstoff-/Luftgemisches liefert, führt eine Drift der Kennlinie in dem vom stöchiometrischen Verhältnis abweichenden Bereich dazu, dass vordefinierte Schaltpunkte in den nicht spezifizierten Randbereichen der Kennlinie nicht mehr erreicht werden. Eine Regelung mittels eines Zweipunktreglers ist im flachen Bereich der Kennlinie einer Sprungsonde stark fehlerbehaftet.Previously known from the DE 100 04 416 A1 a method for adjusting the air / fuel ratio with an exhaust gas upstream of the catalyst and an exhaust gas sensor downstream of the catalyst. In separate operating areas of the internal combustion engine, for example, downhill, in which to deviate from the stoichiometric ratio, there is a switch to the controlled mode ("open loop"). The air / fuel quantity is set in controlled operation without feedback of the measured value from the lambda probe on the basis of predefined manipulated variables. Here occur due to the controller without feedback value large deviations from the actually desired lambda value. A regulation of the air / fuel mixture in operating ranges, in which an operation is desired with the stoichiometric ratio deviating air / fuel ratio (lambda not equal to 1) is realized, does not occur. In the transition from controlled to controlled operation in which a stoichiometric ratio is to be adjusted again, in a short temporary transition region controlled operation based on the signal of the jump probe before the catalyst. For this purpose, with switched-off readjustment by means of the lambda probe downstream of the catalytic converter, the switching point of the jump probe is adapted in order to ensure a desired conversion rate of the catalytic converter. Disadvantageous for the regulation of the fuel / air mixture by means of a jump probe is the probe-related shape of the characteristic, which provides a strong change in the voltage value with small changes in the lambda value in the region around lambda 1, but has a very flat course of the characteristic in regions lambda not equal to 1 , As a result, in areas which deviate from the stoichiometric ratio, only a slight change in voltage occurs as the lambda values change measured. The control by means of a two-point controller is thus inaccurate. Another problem is the drift of the characteristic that occurs as a result of the aging of the probes. While the probe in the jump range around lambda equal to 1 still supplies sufficiently differentiated measured values of the fuel / air mixture for the control, a drift of the characteristic in the range deviating from the stoichiometric ratio leads to predefined switch points in the unspecified edge regions of the characteristic no longer being reached become. A control by means of a two-point controller is heavily flawed in the flat region of the characteristic of a jump probe.

Aufgabe der Erfindung ist es daher, ein Verfahren zum Einstellen eines Kraftstoff-/Luftgemisches anzugeben, welches für eine Lambdaregelung mittels wenigstens einer Sprungsonde eine möglichst genaue Regelung des Kraftstoff-/Luftgemisches für Lambdasollwerte erlaubt, welche vom stöchiometrischen Verhältnis abweichen. Weiterhin wird eine Regelung geschaffen, die eine Diagnose der Lambdasonde erlaubt.The object of the invention is therefore to provide a method for adjusting a fuel / air mixture, which allows for a lambda control by means of at least one jump probe the most accurate control of the fuel / air mixture for lambda setpoints, which differ from the stoichiometric ratio. Furthermore, a regulation is created that allows a diagnosis of the lambda probe.

Erfindungsgemäß wird die Aufgabe dadurch gelöst, dass eine Zweipunktregelung um einen Schaltpunkt erfolgt, wobei zum Einstellen eines gewünschten Lambdawertes der Schaltpunkt des Zweipunktreglers adaptiert wird.According to the invention the object is achieved in that a two-step control takes place about a switching point, wherein for setting a desired lambda value of the switching point of the two-point controller is adapted.

Hierbei wird die Oszillation des Messsignals der Lambdasonde um den Schaltpunkt aufgenommen, wobei ein gleichbleibender Regelhub gesichert wird. Es wird bezüglich der Oszillation des Messsignals der Lambdasonde um den jeweiligen Schaltpunkt ein Sollwert vorgegeben und der Sollwert des Zweipunktreglers wird derart verschoben, dass sich der Sollwert der Oszillation einstellt. Als Merkmal der Oszillation werden verschiedene amplitudenbezogene Parameter der Oszillation ausgewertet. Die Regelung erfolgt dabei auf einen Sollwert der Oszillation, wobei sich der Schaltpunkt des Zweipunktreglers in Abhängigkeit davon einstellt.In this case, the oscillation of the measuring signal of the lambda probe is recorded by the switching point, whereby a constant control stroke is ensured. With reference to the oscillation of the measuring signal of the lambda probe, a desired value is preset around the respective switching point, and the setpoint value of the two-step controller is shifted in such a way that the nominal value of the oscillation sets. As a characteristic of the oscillation, various amplitude-related parameters of the oscillation are evaluated. The control is carried out to a desired value of the oscillation, wherein the switching point of the two-point controller adjusts in dependence thereon.

Bei einem definierten Regelhub (vorzugsweise 2% Abweichung von der eingestellten Kraftstoffmasse) wird die sich einstellende Sondenausgangsspannung hinsichtlich der Amplitude ihrer Schwingung (sog. Restwelligkeit) gemessen. Es erfolgt eine Regelung auf die Messgröße der Restwelligkeit derart, dass der Schaltpunkt des Zweipunktreglers solange verschoben wird, bis sich die gewünschte, vorgebbare Restwelligkeit einstellt. Das Verfahren geht von der Erkenntnis aus, dass die Sondenkennlinie temperatur- oder alterungsbedingt hinsichtlich der Zuordnung der Sondenausgangsspannung zum Lambdawert driftet. Überraschenderweise korreliert die Restwelligkeit bei vorgegebenem Regelhub weitgehend alterungs- und temperaturstabil mit einem zuordenbaren Lambdawert. Erfindungsgemäß vorteilhaft wird durch das Verschieben des Schaltpunktes bis zum Erreichen einer vorgebbaren Restwelligkeit eine gewünschte Verstellung des Lambdawertes erreicht, ohne einen absoluten Schaltpunkt für den Regler vorzugeben.At a defined control stroke (preferably 2% deviation from the set fuel mass), the self-adjusting probe output voltage is measured with regard to the amplitude of its oscillation (so-called residual ripple). There is a control to the measured variable of the residual ripple such that the switching point of the two-point controller as long as is shifted until the desired, predetermined residual ripple sets. The method is based on the knowledge that the probe characteristic drifts due to temperature or aging with respect to the assignment of the probe output voltage to the lambda value. Surprisingly, the residual ripple correlates with a predetermined control stroke largely aging and temperature stable with a assignable lambda value. According to the invention, a desired adjustment of the lambda value is achieved by shifting the switching point until a predeterminable residual ripple is reached, without predetermining an absolute switching point for the controller.

Es erfolgt eine Auswertung der Krümmung der Sondenkennlinie, welche spezifisch für einen zugehörigen Lambdawert ist. Erfindungsgemäß vorteilhaft wird dabei die Form der Sondenkennlinie analysiert, welche weitgehend temperatur- und alterungsstabil einem definierten Lambdawert zuordenbar ist.There is an evaluation of the curvature of the probe characteristic, which is specific for an associated lambda value. Advantageously, according to the invention, the shape of the probe characteristic curve is analyzed, which is largely attributable to a defined lambda value with respect to temperature and aging.

Als Äquivalent der Krümmung der Sondenkennlinie wird die Unsymmetrie der Schwingung der Sondenausgangsspannung in einer Zweipunktregelung ermittelt. Bei einem definierten Regelhub (vorzugsweise 1-2% Abweichung von der eingestellten Kraftstoffmasse) wird die sich einstellende Sondenausgangsspannung hinsichtlich ihrer Schwingung analysiert. Erfindungsgemäß vorteilhaft wird die Unsymmetrie der Schwingung in Bezug zum Schaltpunkt ausgewertet. Hierfür werden die Amplitude der Halbwellen bzw. deren Flächeninhalte in Bezug zum Schwellwert ermittelt. Das Verhältnis der Halbwellen bzw. deren Amplitude und/oder Flächeninhalt wird als Führungsgröße für die Regelung genutzt. Die Krümmung und deren über die Unsymmetrie bestimmtes Äquivalent ist vom Absolutwert der Sondenausgangsspannung unabhängig und ermöglicht ein geregeltes Anfahren von Lambdawerten in den nicht spezifizierten und sehr flach verlaufenden "Fett- bzw. Magerast" der Sondenkennlinie mittels der für die Regelung des stöchiometrischen Verhältnisses genutzten Zweipunktregelung.As an equivalent of the curvature of the probe characteristic, the unbalance of the oscillation of the probe output voltage is determined in a two-point control. At a defined control stroke (preferably 1-2% deviation from the set fuel mass), the resulting probe output voltage is analyzed with regard to its oscillation. Advantageously according to the invention, the asymmetry of the oscillation with respect to the switching point is evaluated. For this purpose, the amplitude of the half-waves or their areas in relation to the threshold value are determined. The ratio of the half-waves or their amplitude and / or surface area is used as a reference variable for the control. The curvature and its equivalent determined by the unbalance is independent of the absolute value of the probe output voltage and allows a controlled approach of lambda values in the unspecified and very flat "fat load" of the probe characteristic by means of the two-step control used for the regulation of the stoichiometric ratio.

Es erfolgt eine Regelung auf die Unsymmetrie der Schwingung der Sondenausgangsspannung derart, dass der Schaltpunkt des Zweipunktreglers solange verschoben wird, bis sich die gewünschte, vorgebbare Unsymmetrie einstellt. Das Verfahren geht von der Erkenntnis aus, dass die Sondenkennlinie temperatur- oder alterungsbedingt hinsichtlich der Zuordnung der Sondenausgangsspannung zum Lambdawert driftet, jedoch überraschenderweise die Kennlinienform alterungs- und temperaturstabil ist und bei einem vorgegebenen Regelhub mittels der Analyse der Unsymmetrie der Schwingung ein Äquivalent für die Kennlinienform gebildet werden kann. Erfindungsgemäß vorteilhaft wird durch die Adaption des Schaltpunktes bis zum Erreichen einer vorgebbaren Unsymmetrie der Schwingung der Sondenausgangsspannung eine gewünschte Verstellung des Lambdawertes erreicht, ohne einen absoluten Schaltpunkt für den Regler vorzugeben. Dieser ergibt sich letztlich aus der Regelung auf die Unsymmetrie.There is a control on the asymmetry of the vibration of the probe output voltage such that the switching point of the two-point controller is moved until the desired, predetermined asymmetry is established. The method is based on the knowledge that the probe characteristic However, surprisingly, the characteristic is aging and temperature stable and can be formed at a predetermined control stroke by means of the analysis of the asymmetry of the oscillation, an equivalent of the characteristic shape due to temperature or aging. According to the invention, a desired adjustment of the lambda value is achieved by adapting the switching point until a specifiable asymmetry of the oscillation of the probe output voltage is reached, without predetermining an absolute switching point for the regulator. This ultimately results from the regulation on the asymmetry.

Vorteilhaft ist die Einstellung eines gewünschten Lambdawertes im geregelten Betrieb, so dass verglichen mit dem gesteuerten Betrieb eine große Abweichung des Lambdawertes vermieden wird.It is advantageous to set a desired lambda value in controlled operation, so that a large deviation of the lambda value is avoided compared to the controlled operation.

Erfindungsgemäß vorteilhaft wird die vorhandene Struktur der Regelung - wie sie im Stand der Technik für den stöchiometrischen Betrieb als Zweipunktregelung vorhanden ist - auch für das Einstellen von Lambdawerten, welche vom stöchiometrischen Verhältnis abweichen, genutzt.According to the invention, the existing structure of the control - as it is available in the prior art for stoichiometric operation as a two-step control - also for setting lambda values, which differ from the stoichiometric ratio used.

Ausgehend von der Erkenntnis, dass sich bei Alterung oder Temperaturdrift die Kennlinie, insbesondere in den Randbereichen der Sondenkennlinie verändert, wird das Signal der Lambdasonde bei Verschiebung des Schaltpunktes weg vom stöchiometrischen Verhältnis betrachtet. Hervorgerufen durch die sich über den Lambdawert ändernde Krümmung der Sondenkennlinie wird bei gleichbleibendem Regelhub eine Unsymmetrie der Schwingung der Sondenausgangsspannung in einer Zweipunktregelung hervorgerufen. Der Regelhub beträgt dabei bei ausgeführten Zweipunktregelungen vorzugsweise 1-2% Abweichung von der eingestellten Kraftstoffmasse. Es kann dabei sowohl die sich bei einem definierten Schaltpunkt einstellende Unsymmetrie der Schwingung um den Schaltpunkt als auch der sich bei einer vorgegebenen Unsymmetrie einstellende Schaltpunkt der Sondenausgangsspannung ermittelt werden. Für die Analyse der Unsymmetrie werden die Amplitude der Halbwellen bzw. deren Flächeninhalte in Bezug zum Schwellwert ermittelt. Das Verhältnis der Halbwellen bzw. deren Amplitude und/oder Flächeninhalt kann als Führungsgröße für die Regelung genutzt werden und der sich einstellende Schaltpunkt wird zur Diagnose betrachtet.Based on the knowledge that changes in the characteristic curve, especially in the edge regions of the probe characteristic in aging or temperature drift, the signal of the lambda probe is considered when shifting the switching point away from the stoichiometric ratio. As a result of the curvature of the probe characteristic which changes over the lambda value, an asymmetry of the oscillation of the probe output voltage in a two-point control is produced while the control stroke remains constant. The control stroke is in running two-point regulations preferably 1-2% deviation from the set fuel mass. Both the asymmetry of the oscillation about the switching point that occurs at a defined switching point and the switching point of the probe output voltage that sets itself for a given asymmetry can be determined. For the analysis of the asymmetry, the amplitude of the half-waves or their areas in relation to the threshold value are determined. The ratio of the half-waves or their amplitude and / or area can be used as a reference variable for the control and the resulting switching point is considered for diagnosis.

Die Regelung auf die Unsymmetrie der Schwingung der Sondenausgangsspannung erfolgt dabei derart, dass der Schaltpunkt des Zweipunktreglers solange verschoben wird, bis sich die gewünschte, vorgebbare Unsymmetrie einstellt.The control of the asymmetry of the oscillation of the probe output voltage is effected in such a way that the switching point of the two-point controller is shifted until the desired, definable asymmetry is established.

Erfindungsgemäß vorteilhaft wird die vorhandene Struktur der Regelung -wie sie im Stand der Technik für den stöchiometrischen Betrieb als Zweipunktregelung vorhanden ist - auch für die Diagnose genutzt. Es erfolgt als Erweiterung lediglich ein Vergleich mit vorher bestimmten Normwerten.Advantageously according to the invention, the existing structure of the control, as it is present in the prior art for stoichiometric operation as a two-step control, is also used for the diagnosis. As an extension, only a comparison with previously determined standard values takes place.

Erfindungsgemäß vorteilhaft erfolgt zur Diagnose eine Auswertung des Sondenausgangssignals hinsichtlich der Restwelligkeit der Schwingung des Sondenausgangssignals bei Schaltpunktverschiebung alternativ oder zusätzlich zur ermittelten Unsymmetrie.According to the invention, an evaluation of the probe output signal with regard to the residual ripple of the oscillation of the probe output signal at switching point displacement is carried out for diagnosis as an alternative or in addition to the ascertained asymmetry.

Erfindungsgemäß vorteilhaft erfolgt die Diagnose in Betriebsbereichen, bei welchen geregelt ein vom stöchiometrischen Verhältnis abweichender Lambdawert eingeregelt wird (z. B. Katalysatorheizen oder Bauteilschutz).According to the invention, the diagnosis is advantageously carried out in operating ranges in which a regulated lambda value deviating from the stoichiometric ratio is regulated in a regulated manner (eg, catalyst heating or component protection).

Die Erfindung wird nachfolgend anhand von Zeichnungen eines Ausführungsbeispieles beschrieben. Weitere vorteilhafte Ausgestaltungen sind den Patentansprüchen zu entnehmen.The invention will be described below with reference to drawings of an embodiment. Further advantageous embodiments can be found in the claims.

Es zeigen:

Figur 1:
Kennlinienverläufe der Sondenausgangsspannung über dem Lambdawert für eine Sprungsonde bei verschiedenen Temperaturen,
Figur 2:
den Signalverlauf der Sondenausgangsspannung über der Zeit bei einer Sprungsonde mit Schaltpunktverschiebung des Zweipunktreglers,
Figur 3:
den Signalverlauf der Sondenausgangsspannung über der Zeit bei einer Sprungsonde mit Schaltpunktverschiebung des Zweipunktreglers.
Show it:
FIG. 1:
Characteristic curves of the probe output voltage over the lambda value for a jump probe at different temperatures,
FIG. 2:
the waveform of the probe output voltage over time in a jump probe with shift point shift of the two-point controller,
FIG. 3:
the waveform of the probe output voltage over time at a jump probe with switching point shift of the two-point controller.

Die Lambdaregelung ist für Ottomotoren mit einem 3-Wege-Katalysator notwendig, da dieser nur in einem sehr engen Bereich des Kraftstoff-/Luftverhältnisses (Lambdawert) in der Lage ist, die Schadstoffkomponenten HC, CO und NOx wirkungsvoll zu reduzieren. Das Lambdafenster (Regelbereich der Sprungsonde bei Zweipunktregelung gemäß Stand der Technik) liegt in einem Bereich zwischen Lambdawerten von 0,99 bis 1. Die geforderte Genauigkeit wird nur mit einer Regelung erreicht, welche im Falle einer Sprungsonde als Zweipunktregelung mit einem Schaltpunkt bei einem gewünschten Lambdawert nahe 1 ausgeführt ist. Mit dem Signal der Sprungsonden können lediglich qualitative Aussagen über den Lambdawert getroffen werden. In Abhängigkeit vom gemessenen Lambdawert wird das Signal der Einspritzmenge modifiziert. Zeigt das Lambdasignal Werte größer oder kleiner 1 an, so wird durch Änderung der Stellgröße (Einspritzmenge) um einen definierten oder in Kennlinien abgelegten Wert (Regelhub) die Regelung in Richtung des gewünschten Lambdawertes beeinflusst. Es stellt sich damit ein Pendeln um den gewünschten Lambdawert ein, welches durch eine Schwingung des Signals der Sondenausgangsspannung messbar ist. Beispielhaft sind verschiedene Sondenkennlinien in Figur 1 dargestellt. Die Lambdaregelung passt die jeweils folgende Einspritzung auf Basis der vorhergehenden Messung an. Die Anpassung der Einspritzmenge aufgrund des Lambdasondensignals wird als Regelhub bezeichnet. Die Messung weist jedoch durch die Gaslaufzeiten, die Rechenzeit im Steuergerät und die Ansprechzeit der Lambdasonde einen zeitlichen Versatz zur Einspritzung auf, so dass sich eine minimale Periodendauer der Schwingung des Lambdawertes ergibt.The lambda control is necessary for gasoline engines with a 3-way catalytic converter, since this is only able to control the pollutant components HC, CO and NO x within a very narrow range of the air / fuel ratio (lambda value) effectively reduce. The lambda window (control range of the jump probe with two-step control according to the prior art) is in a range between lambda values of 0.99 to 1. The required accuracy is only achieved with a control, which in the case of a jump probe as a two-step control with a switching point at a desired lambda value near 1 is executed. With the signal of the jump probes only qualitative statements about the lambda value can be made. Depending on the measured lambda value, the signal of the injection quantity is modified. If the lambda signal indicates values greater than or less than 1, the control in the direction of the desired lambda value is influenced by a change in the manipulated variable (injection quantity) by a defined value or characteristic curve (control stroke). This sets a pendulum to the desired lambda value, which is measurable by a vibration of the signal of the probe output voltage. Exemplary are different probe characteristics in FIG. 1 shown. The lambda control adjusts the following injection on the basis of the previous measurement. The adjustment of the injection quantity due to the lambda probe signal is referred to as a control stroke. However, due to the gas running times, the computing time in the control unit and the response time of the lambda probe, the measurement has a time offset to the injection, resulting in a minimum period of oscillation of the lambda value.

Zur Einstellung eines stöchiometrischen Luft-/Kraftstoffverhältnisses liegt der Regelschaltpunkt üblicherweise im spezifiziert stabilen Bereich bei 450 mV. Dies entspricht einem Lambdawert nahe 1. Aufgrund von Alterungs- und Temperatureinflüssen auf die Sondenkennlinie verändert sich die Sondenkennlinie insbesondere in den nicht spezifizierten Randbereichen. Soll ein "mageres" oder "fettes" Kraftstoff-/Luftgemisch mit der vorliegenden Zweipunktregelung eingestellt werden, muss der Schaltpunkt nach unten (beispielsweise 200 mV) oder oben (beispielsweise 700 mV) verschoben werden. Dabei nutzt man den nicht spezifizierten Mager- bzw. Fettast der Sondenkennlinie. Die Kennlinie einer Sprungsonde ist in Figur 1 dargestellt. Die Sondenausgangsspannung ist als Funktion des Lambdawertes dargestellt. Mittels verschiedener Heizspannungen wurde die Lambdasonde auf verschiedene Temperaturen aufgeheizt und für ein und die selbe Sonde bilden sich damit temperaturabhängig unterschiedliche Sondenkennlinien ab. Beispielhaft sind für verschiedene Temperaturen die Abweichungen der Sondenkennlinie, insbesondere in den nicht spezifizierten Randbereichen dargestellt. Da diese Kennlinienbereiche sehr flach verlaufen, erfolgt in den Randbereichen der Kennlinie bei großen Änderungen des Lambdawertes lediglich eine kleine Änderung der Sondenausgangsspannung. Wenn sich die Randbereiche der Sondenkennlinie durch Alterung oder Temperatureinflüsse (wie in Fig. 1 dargestellt) verschieben, würde ein fest definierter Schaltpunkt außerhalb von Lambda 1 dazu führen, dass das eingeregelte Lambda stark driftet. Zudem kann es passieren, dass ein fest definierter Schaltpunkt gar nicht mehr erreicht wird.For setting a stoichiometric air-fuel ratio, the control switching point is usually in the specified stable range at 450 mV. This corresponds to a lambda value close to 1. Due to aging and temperature influences on the probe characteristic, the probe characteristic changes especially in the unspecified edge regions. If a "lean" or "rich" fuel / air mixture is to be set with the present two-point control, the switching point must be shifted downwards (for example 200 mV) or above (for example 700 mV). It uses the unspecified lean or rich load of the probe characteristic. The characteristic curve of a jump probe is in FIG. 1 shown. The probe output voltage is shown as a function of the lambda value. By means of different heating voltages, the lambda probe was heated to different temperatures, and for one and the same probe, temperature-dependent different probe characteristics are formed. Exemplary are the different temperatures Deviations of the probe characteristic, in particular in the unspecified edge regions shown. Since these characteristic ranges are very flat, only a small change in the probe output voltage takes place in the edge regions of the characteristic with large changes in the lambda value. If the edge areas of the probe characteristic curve are affected by aging or temperature influences (as in Fig. 1 shown), a fixed switching point outside Lambda 1 would cause the adjusted lambda to drift strongly. In addition, it can happen that a fixed switching point is no longer reached.

Erfindungsgemäß kann dies vermieden werden, indem bei einem vorgegebenen Regelhub die Oszillation der Sondenausgangsspannung bei Regelung um einen adaptierten Schaltpunkt überwacht wird. Es wird erfindungsgemäß der Schaltpunkt stückweise verschoben und gemäß einer ersten Ausführung der Erfindung die resultierende Oszillation der Sondenausgangsspannung hinsichtlich deren Amplitude (sog. Restwelligkeit) ausgewertet. Es erfolgt ein Verschieben des Schaltpunktes bei gleichbleibendem Regelhub bis zu einem definierten Schwellwert der Restwelligkeit. Die Restwelligkeit wird damit zu einer Führungsgröße der Regelung.According to the invention, this can be avoided by monitoring the oscillation of the probe output voltage during regulation by an adapted switching point during a predetermined control stroke. According to the invention, the switching point is shifted piecewise and, according to a first embodiment of the invention, the resulting oscillation of the probe output voltage is evaluated with regard to its amplitude (so-called residual ripple). There is a shift of the switching point at a constant control stroke up to a defined threshold value of the residual ripple. The residual ripple is thus a reference variable of the scheme.

Die Erfindung geht von der Erkenntnis aus, dass die Kennlinienform weitgehend alterungs- bzw. temperaturstabil ist. Das heißt, dass der absolute Messwert der Sondenspannung für einen zugehörigen Lambdawert über der Lebensdauer bzw. der Temperatur driftet, jedoch die Form der Sondenkennlinie Sondenspannung = f(Lambdawert) erhalten bleibt und somit ein schwaches oder starkes Ansteigen bzw. Verflachen der Sondenkennlinie jeweils einem definierten Lambdawert zugeordnet werden kann. Als Maß für den Lambdawert kann somit die Krümmung der Sondenkennlinie verwendet werden. Die Krümmung der Sondenkennlinie ist ohne eine vergleichende Messung im Betrieb der Regeleinrichtung nicht direkt messbar. Für die Regelung des stöchiometrischen Verhältnisses wird eine Zweipunktregelung genutzt, welche einen Schaltpunkt im Übergangsbereich der Sondenkennlinie nahe Lambda = 1 aufweist. Diese Reglerstruktur wird weiterhin auch für die erfindungsgemäße Regelung außerhalb des stöchiometrischen Gemisches eingesetzt, wobei deren Schaltpunkt adaptiert wird und deren Eigenschaft, eine Schwingung des Messsignals der Lambdasonde zu erzeugen, genutzt wird. Es wird der Schaltpunkt des Zweipunktreglers verschoben und die durch den gleichbleibenden Regelhub hervorgerufene resultierende Oszillation der Sondenausgangsspannung wird hinsichtlich deren Amplitude (sog. Restwelligkeit) ausgewertet. Weiterhin erfolgt eine Auswertung der Messkurve der Sondenausgangsspannung hinsichtlich der Symmetrie der Schwingung. Die Messkurve wird hinsichtlich der Amplitude der einzelnen Halbwellen und/oder der zwischen den jeweiligen Halbwellen und einer Geraden durch den Schaltpunkt eingeschlossenen Fläche ausgewertet. Eine Integration ergibt dabei den Flächeninhalt der jeweiligen Halbwelle der Messkurve. Die Zweipunktregelung arbeitet mit einem definierten Regelhub. Ausgehend vom aktuellen Messwert der Sondenausgangsspannung wird die aktuelle Einspritzmenge um einen definierten Betrag (beispielsweise 2% der aktuellen Einspritzmenge) verändert, so dass sich der Messwert der Schaltschwelle annähert. Bei Über- bzw. Unterschreiten der Schaltschwelle erfolgt wieder eine Änderung der Einspritzmenge um den gleichen Betrag. Es erfolgt damit ein Schwingen des Lambdawertes und somit des Messsignals der Sondenausgangsspannung um die Schaltschwelle. Aufgrund der nichtlinearen Sondenkennlinie mit sich ändernder Steigung zu den Randbereichen erfolgt in den Bereichen abweichend vom stöchiometrischen Verhältnis eine unsymmetrische Schwingung um den Schaltpunkt. Es wird nachfolgend ein beispielhafter Schaltpunkt bei einer Sondenausgangsspannung von 700 mV betrachtet. Bei aktiver Zweipunktregelung erfolgt eine Schwingung der Sondenausgangsspannung um den Schaltpunkt, wobei gemessen am Schaltpunkt ein stärkeres Durchtauchen der Schwingung der Sondenausgangsspannung in Richtung geringerer Spannungswerte erfolgt. Dies wird durch den gleichbleibenden Regelhub bei sich über den Regelbereich ändernder Sondenkennlinie hervorgerufen. Bei einem Überschreiten des Schaltpunktes von 700 mV erfolgt entsprechend der Regelstrategie des Zweipunktreglers eine Verminderung der Einspritzmenge um beispielsweise 2%. Der Lambdawert wird dadurch in Richtung magerer Lambdawerte gesteuert. Aufgrund der Gaslaufzeiten erfolgt eine Reaktion verzögert, so dass ein Überschwingen des Lambdawertes in Richtung fetter Gemischwerte erfolgt. Dies bildet sich aufgrund der in diesem Bereich flacher werdenden Sondenkennlinie jedoch nur in geringerem Maße in der Sondenausgangsspannung ab, als bei dem gleichen Überschwingen in Richtung des stöchiometrischen Verhältnisses. Aufgrund der Zweipunktregelstrategie erfolgt beim Unterschreiten des Schaltpunktes eine Rücksteuerung der Kraftstoffmenge in Richtung des fetten Bereiches um den gleichen Betrag (beispielsweise 2% der Einspritzmenge s.o.), wobei durch die Gaslaufzeiten wiederum ein Überschwingen des Lambdawertes in Richtung mager erfolgt, was sich durch den in diesem Bereich steiler ausgebildeten Ast der Sondenkennlinie im Signal der Sondenausgangsspannung stärker niederschlägt. Wertet man die Sondenausgangsspannung hinsichtlich des Unter- bzw. Überschwingens des Messsignals um den Schaltpunkt aus, so ergibt sich in Abhängigkeit vom Arbeitspunkt auf der Sondenkennlinie ein charakteristisches Verhältnis der Halbwellen zueinander. Dieses ist mittels einer Auswertung der Amplituden der Halbwellen oder einer Auswertung der Halbwellenflächen quantifizierbar. Die so messbare Unsymmetrie ist damit bezeichnend für die Krümmung der Sondenkennlinie. Die über die Unsymmetrie der Halbwellen der Schwingung des Sondenausgangssignals beschriebene Krümmung der Sondenkennlinie wird für vom stöchiometrischen Verhältnis abweichende Lambdawerte als Führungsgröße genutzt. Es erfolgt damit ein geregeltes Anfahren von Schaltpunkten, welche auf dem nicht spezifizierten Mager- oder Fettast der Sondenkennlinie liegen. Der Regelung können damit Sollwerte für den Lambdawert vorgegeben werden, welche letztlich Sollwerte für einen definierten Krümmungswert der Sondenkennlinie sind. Für die Vorgabe muss eine vorherige Identifikation, beispielsweise des Verhältnisses der Halbwellenflächen zueinander bei einem vorgegebenen Regelhub erfolgen, so dass das Verhältnis der Flächen zueinander oder der Amplituden der Halbwellen zu einem definierten Lambdawert, beispielsweise aus Voruntersuchungen am Prüfstand bekannt ist. Für die Regelung erfolgt auf Basis des einzuregelnden Lambdawertes die Vorgabe eines entsprechenden, die Unsymmetrie beschreibenden Verhältnisses der Amplituden und/oder der Flächen der Halbwellen. Es erfolgt ein Verschieben des Schaltpunktes, bis der geforderte Wert der Unsymmetrie erreicht ist.The invention is based on the recognition that the characteristic curve is largely resistant to aging or temperature. This means that the absolute measured value of the probe voltage for an associated lambda value drifts over the service life or the temperature, but the shape of the probe characteristic probe voltage = f (lambda value) is maintained and thus a weak or strong increase or flattening of the probe characteristic in each case corresponds to a defined one Lambda value can be assigned. As a measure of the lambda value, therefore, the curvature of the probe characteristic can be used. The curvature of the probe characteristic is not directly measurable without a comparative measurement in the operation of the control device. For the control of the stoichiometric ratio, a two-point control is used, which has a switching point in the transition region of the probe characteristic near lambda = 1. This controller structure is also used for the inventive control outside the stoichiometric mixture, wherein the switching point is adapted and their Property to generate a vibration of the measuring signal of the lambda probe is used. The switching point of the two-point controller is shifted and the resulting oscillation of the probe output voltage caused by the constant control stroke is evaluated with regard to its amplitude (so-called residual ripple). Furthermore, an evaluation of the measurement curve of the probe output voltage with respect to the symmetry of the oscillation takes place. The measurement curve is evaluated with regard to the amplitude of the individual half-waves and / or the area enclosed between the respective half-waves and a straight line through the switching point. An integration results in the area of the respective half-wave of the trace. The two-step control works with a defined control stroke. Based on the current measured value of the probe output voltage, the current injection quantity is changed by a defined amount (for example 2% of the current injection quantity) so that the measured value approaches the switching threshold. If the switching threshold is exceeded or not reached, the injection quantity changes again by the same amount. It thus takes place a swing of the lambda value and thus the measurement signal of the probe output voltage by the switching threshold. Due to the nonlinear sensor characteristic curve with changing gradient to the edge regions, in the areas deviating from the stoichiometric ratio, an asymmetrical oscillation takes place around the switching point. An exemplary switching point at a probe output voltage of 700 mV is considered below. When two-level control is active, the probe output voltage oscillates about the switching point, whereby, measured at the switching point, a stronger penetration of the vibration of the probe output voltage takes place in the direction of lower voltage values. This is caused by the constant control stroke when changing over the control range sonar characteristic. When the switching point of 700 mV is exceeded, a reduction in the injection quantity takes place, for example, by 2%, in accordance with the control strategy of the two-step controller. The lambda value is thereby controlled in the direction of lean lambda values. Due to the gas run times, a reaction is delayed so that the lambda value is overshooted in the direction of rich mixture values. However, due to the sensor characteristic that becomes flatter in this area, this only occurs to a lesser extent in the probe output voltage than in the same overshoot in the direction the stoichiometric ratio. Due to the two-point control strategy takes place when falling below the switching point, a feedback control of the amount of fuel in the direction of the rich area by the same amount (for example, 2% of the injection amount so), in turn by the gas running times overshoot of the lambda value in the direction of lean, which is characterized by the in this Steeper formed branch of the probe characteristic in the signal of the probe output voltage stronger reflected. If one evaluates the probe output voltage with respect to the undershoot or overshoot of the measurement signal by the switching point, then a characteristic ratio of the half-waves to each other results depending on the operating point on the probe characteristic. This can be quantified by means of an evaluation of the amplitudes of the half-waves or an evaluation of the half-wave surfaces. The thus measurable asymmetry is thus indicative of the curvature of the probe characteristic. The curvature of the probe characteristic curve described by the asymmetry of the half-waves of the oscillation of the probe output signal is used as a reference variable for lambda values deviating from the stoichiometric ratio. It thus takes place a controlled approach of switching points, which are on the unspecified lean or rich load of the probe characteristic. The regulation can thus be preset with reference values for the lambda value, which are ultimately setpoints for a defined curvature value of the probe characteristic. For the specification, a prior identification, for example, the ratio of the half-wave surfaces to each other at a predetermined control stroke, so that the ratio of the surfaces to each other or the amplitudes of the half-waves to a defined lambda value, for example from preliminary investigations on the test bench is known. For the regulation, on the basis of the lambda value to be adjusted, the specification of a corresponding ratio of the amplitudes and / or the areas of the half-waves describing the asymmetry takes place. The switching point is shifted until the required value of the asymmetry is reached.

Wie bereits beschrieben kann die Oszillation des Messsignals der Lambdasonde ausgewertet und als Führungsgröße für die Regelung verwendet werden. Eine Regelung hinsichtlich der Amplitude der Oszillation (Restwelligkeit) kann zum Einregeln "fetter" bzw. "magerer" Betriebszustände genutzt werden.As already described, the oscillation of the measuring signal of the lambda probe can be evaluated and used as a reference variable for the control. A regulation with regard to the amplitude of the oscillation (residual ripple) can be used for adjusting "fat" or "lean" operating states.

Weiterhin kann parallel zur Unsymmetrie die Restwelligkeit bzw. deren Amplitude selbst betrachtet werden. Die Amplitude der Restwelligkeit ist ebenfalls ein von den Absolutwerten der Sondenausgangsspannung unabhängiges Maß für den Lambdawert. Figur 2 erläutert die Regelung detailliert an einem Beispiel.Furthermore, parallel to the asymmetry, the residual ripple or its amplitude itself can be considered. The amplitude of the residual ripple is also a measure of the lambda value independent of the absolute values of the probe output voltage. FIG. 2 explains the regulation in detail with an example.

Die Unsymmetrie der Halbwellen und/oder die Amplitude der Restwelligkeit sind für die jeweiligen Schaltpunkte spezifisch. Dies wird zur Diagnose der Lambdasonde genutzt. Für die Diagnose muss eine vorherige Identifikation der Unsymmetrie, beispielsweise durch Ermittlung des Verhältnisses der Halbwellenflächen zueinander und/oder durch eine Messung der Restwelligkeit bei einem vorgegebenen Regelhub für vorgegebene Schaltpunkte mit einer funktionierenden Lambdasonde, beispielsweise durch Voruntersuchungen am Prüfstand erfolgen. Für die Diagnose der Lambdasonde ist dabei ein Vergleich der für eine funktionierende Sonde ermittelten Normwerte mit den im Betrieb ermittelten erforderlich und aus der Abweichung der Werte können Rückschlüsse auf den Betriebszustand der Lambdasonde gezogen werden. Ein Abweichen der Unsymmetrie und/oder Restwelligkeit, insbesondere in den Randbereichen der Sondenkennlinie ist kennzeichnend für eine alterungs- oder fehlerbedingte Drift der Sondenkennlinie. Eine Auswertung der Abweichungen im Vergleich mit Prüfstandsdaten einer Sonde mit idealer Sondenkennlinie lässt eine Klassifizierung der Sonde hinsichtlich deren Betriebszustand zu und erlaubt eine Abschätzung der alterungsbedingten Kennliniendrift und damit eine virtuelle Kennlinienkorrektur. Weiterhin kann die Sonde hinsichtlich ihres Ausfalls überwacht werden.The asymmetry of the half-waves and / or the amplitude of the residual ripple are specific for the respective switching points. This is used to diagnose the lambda probe. For the diagnosis, a prior identification of the asymmetry, for example by determining the ratio of the half-wave surfaces to each other and / or by measuring the residual ripple at a predetermined control stroke for predetermined switching points with a functioning lambda probe, for example by preliminary investigations on the testbed. For the diagnosis of the lambda probe, a comparison of the standard values determined for a functioning probe with those determined during operation is required, and it is possible to draw conclusions about the operating state of the lambda probe from the deviation of the values. A deviation of the asymmetry and / or residual ripple, in particular in the edge regions of the probe characteristic curve, is characteristic of an aging or fault-related drift of the probe characteristic curve. An evaluation of the deviations in comparison with test bench data of a probe with ideal probe characteristic allows a classification of the probe with regard to its operating state and allows an estimation of the age-related characteristic drift and thus a virtual characteristic correction. Furthermore, the probe can be monitored for its failure.

Weiterhin kann alternativ oder parallel zur Unsymmetrie die Restwelligkeit bzw. deren Amplitude betrachtet werden. Die Amplitude der Restwelligkeit ist für einen spezifischen Schaltpunkt ebenfalls ein Maß für die Diagnose der Lambdasonde. Figur 2 zeigt hierfür ein Beispiel für die Ermittlung der Amplitude der Oszillation (Restwelligkeit) des Messsignals der Lambdasonde um den Schaltpunkt.Furthermore, alternatively or in parallel to the asymmetry, the residual ripple or its amplitude can be considered. The amplitude of the residual ripple is also a measure of the diagnosis of the lambda probe for a specific switching point. FIG. 2 shows an example for the determination of the amplitude of the oscillation (ripple) of the measuring signal of the lambda probe to the switching point.

In Figur 2 ist das Sondensignal mit adaptiertem Schaltpunkt dargestellt. Es erfolgt eine Verschiebung des Schaltpunktes in Richtung höherer Sondenausgangsspannung, wobei der Regelhub beibehalten wird. Der Teilbereich der Verschiebung des Schaltpunktes ist ausgeblendet. Dargestellt ist die Sondenausgangsspannung nach dem Einregeln auf eine Restwelligkeit von 350 mV Amplitude der Schwingung der Sondenausgangsspannung. Aufgrund der abflachenden Sondenkennlinie erfolgt ein Pendeln mit geringerer Amplitude der Schwingung der Sondenausgangsspannung. Erfindungsgemäß wird der Schaltpunkt soweit verschoben, bis die gewünschte Amplitude der Schwingung der Sondenausgangsspannung (beispielsweise 350 mV) erreicht ist. Dieser Wert ist einem Lambdawert zuordenbar. Der Zusammenhang zwischen Lambdawert und Amplitude der Schwingung der Sondenausgangsspannung muss vorher für einen im Regelalgorithmus definierten Regelhub bestimmt werden. Im praktischen Betrieb des Lambdareglers erfolgt weiterhin in Betriebsbereichen bei Lambda nahe 1 eine Regelung mittels des Zweipunktreglers auf einen definierten Schaltpunkt, beispielsweise 450 mV Sondenausgangsspannung für die beispielhaft vorliegende Sprungsonde mit einer Sondenkennlinie gemäß Figur 1. In Sonderbetriebsbereichen, z. B. Aufheizen des Katalysators oder in Betriebsbereichen, in denen hohe Abgastemperaturen unerwünscht sind (sog. Bauteilschutz), werden Lambdawerte abweichend von Lambda = 1 eingestellt. Hier wird der Schaltpunkt in Richtung "fett" oder "mager" (Sondenausgangsspannung kleiner oder größer 450 mV) verschoben. Gleichzeitig wird die Amplitude der Sondenausgangsspannung gemessen und bei einem gleichbleibenden Regelhub (Variation der einzuspritzenden Kraftstoffmenge bei Unter- bzw. Überschreiten des sich verändernden Schaltpunktes um jeweils 2% der Basiseinspritzmenge) erfolgt ein Einregeln auf eine vorgegebene Amplitude der Sondenausgangsspannung. Die Sondenausgangsspannung schwingt dabei um einen neuen Schaltpunkt, welcher über die Amplitude der Schwingung der Sondenausgangsspannung definiert ist. Es erfolgt damit ein Einregeln der "fetten" bzw. "mageren" Betriebszustände bei Beibehaltung der Reglerstruktur.In FIG. 2 the probe signal with adapted switching point is shown. There is a shift of the switching point in the direction of higher probe output voltage, wherein the control stroke is maintained. The subarea of the shift of the switching point is hidden. Shown is the Probe output voltage after adjusting to a residual ripple of 350 mV amplitude of the oscillation of the probe output voltage. Due to the flattening probe characteristic, oscillation occurs with a lower amplitude of the oscillation of the probe output voltage. According to the switching point is shifted so far until the desired amplitude of the vibration of the probe output voltage (for example, 350 mV) is reached. This value can be assigned to a lambda value. The relationship between the lambda value and the amplitude of the oscillation of the probe output voltage must first be determined for a control stroke defined in the control algorithm. In practical operation of the lambda controller continues to be in operating ranges at lambda near 1 a control by means of the two-point controller to a defined switching point, for example, 450 mV probe output voltage for the example present jump probe with a probe characteristic according to FIG. 1 , In special operating areas, eg B. heating of the catalyst or in operating areas where high exhaust gas temperatures are undesirable (so-called. Component protection), lambda values are set differently from lambda = 1. Here, the switching point is shifted in the direction of "rich" or "lean" (probe output voltage less than or greater than 450 mV). At the same time, the amplitude of the probe output voltage is measured and, with a constant control stroke (variation of the fuel quantity to be injected when the changing switching point is undershot or exceeded by 2% of the basic injection quantity), a regulation takes place to a predetermined amplitude of the probe output voltage. The probe output voltage oscillates by a new switching point, which is defined by the amplitude of the oscillation of the probe output voltage. There is thus an adjustment of the "rich" or "lean" operating states while maintaining the controller structure.

Durch die beschriebene Regelung auf die Amplitude der Schwingung der Sondenausgangsspannung stellt sich ein Schaltpunkt in Abhängigkeit von der realen Sondenkennlinie ein. Die für bestimmte Betriebspunkte im "mageren" oder "fetten" Bereich ermittelten Schaltpunkte können zu Diagnosezwecken herangezogen werden. Auf Basis des Vergleichs der sich einstellenden Schaltpunkte mit vordefinierten, für ideale Sondenkennlinien ermittelten Schaltpunkten wird durch die ermittelte Abweichung zu den Schaltpunkten der realen Sonde eine Diagnoseinformation gewonnen. Weichen die ermittelten Schaltpunkte um einen vorher definierten Betrag von den für eine ideale Sonde ermittelten Werten ab, wird die Sonde als fehlerhaft bewertet.The described control on the amplitude of the oscillation of the probe output voltage sets a switching point as a function of the real sonic characteristic. The switching points determined for certain operating points in the "lean" or "rich" range can be used for diagnostic purposes. Based on the comparison of the set switching points with predefined switching points determined for ideal probe characteristics, the determined deviation from the switching points of the real probe gained diagnostic information. If the determined switching points deviate by a predefined amount from the values determined for an ideal probe, the probe is rated as defective.

In Figur 3 wird anhand eines weiteren Beispiels die Zweipunktregelung mit Schaltpunktadaption näher dargestellt. Es wird hier eine Ausführungsform der Erfindung beschrieben, bei welcher die Oszillation des Messsignals der Lambdasonde anhand der Unsymmetrie der Schwingung um den Schaltpunkt bewertet wird. Es ist in Figur 3 die Sondenausgangsspannung über der Zeit für einen Einregelvorgang eines vom stöchiometrischen Verhältnis abweichenden fetten Gemisches dargestellt. Im Teilbereich A erfolgt die an sich bekannte Zweipunktregelung mittels einer Sprungsonde, welche eine charakteristische Sondenkennlinie der Sondenausgangsspannung zum Lambdawert - wie in Figur 1 dargestellt - aufweist.In FIG. 3 is further illustrated by another example, the two-step control with switching point adaptation. An embodiment of the invention is described in which the oscillation of the measuring signal of the lambda probe is evaluated on the basis of the asymmetry of the oscillation about the switching point. It is in FIG. 3 the probe output voltage over time for a Einregelvorgang a deviating from the stoichiometric ratio rich mixture shown. In the subarea A, the known two-step control by means of a jump probe, which a characteristic probe characteristic of the probe output voltage to the lambda value - as in FIG. 1 shown - has.

Die Sondenausgangsspannung schwingt im Teilbereich A um einen Schaltpunkt bei 450 mV, welcher einem stöchiometrischen Gemisch entspricht. Soll nun für Sonderbetriebspunkte, wie Beschleunigungsanfettung oder Bauteilschutz, ein kraftstoffreicheres Gemisch eingestellt werden, erfolgt dies weiterhin geregelt. Als Führungsgröße wird hierbei die Unsymmetrie der Schwingung des Sondenausgangssignals genutzt. Es erfolgt eine Verschiebung des Schaltpunktes des Zweipunktreglers (Teilbereich B), bis die vordefinierte, zu dem jeweiligen Lambdawert gehörige Unsymmetrie erreicht ist. Dies kann beispielsweise als Verhältnis der Amplitude der Halbwellen obere Halbwelle Ao / untere Halbwelle Au gebildet werden. Weiterhin kann das Verhältnis der Flächen der oberen zur unteren Halbwelle in Bezug zu einer Geraden durch den Schaltpunkt zur Auswertung genutzt werden.The probe output voltage oscillates in subarea A by a switching point at 450 mV, which corresponds to a stoichiometric mixture. If a fuel-rich mixture is now to be set for special operating points, such as acceleration lubrication or component protection, this will continue to be regulated. The reference variable used here is the asymmetry of the oscillation of the probe output signal. There is a shift of the switching point of the two-point controller (sub-area B) until the predefined, to the respective lambda value associated asymmetry is reached. This can be formed, for example, as a ratio of the amplitude of the half-waves upper half-wave Ao / lower half-wave Au. Furthermore, the ratio of the areas of the upper to the lower half-wave with respect to a straight line through the switching point can be used for evaluation.

In einer weiteren Ausbildung der Erfindung erfolgt eine kombinierte Zweipunktregelung mit Schaltpunktadaption derart, dass der Schaltpunkt auf Basis der Restwelligkeit und der Unsymmetrie adaptiert wird. Die Regelung kann dabei als Kaskadenregelung aufgebaut sein, wobei der innere Regelkreis die Restwelligkeitsregelung enthält und der äußere Regelkreis die Regelung auf einen Wert der Krümmung der Sondenkennlinie, welcher durch die Asymmetrie der Schwingung der Sondenspannung um die Schaltschwelle, ausgedrückt wird.In a further embodiment of the invention, a combined two-point control with switching point adaptation takes place such that the switching point is adapted on the basis of the residual ripple and the imbalance. The control can be constructed as a cascade control, wherein the inner loop contains the ripple control and the outer loop control to a value of the curvature of the probe characteristic, which is expressed by the asymmetry of the vibration of the probe voltage to the switching threshold.

Claims (14)

  1. Method for adjusting a fuel/air mixture by means of a two-point regulator, in which method a desired fuel/air mixture is regulated as a function of a measurement signal of a lambda sensor configured as a bistable sensor, whereby the switching point of the two-point regulator is adapted, comprising the following method steps:
    - the switching point of the two-point regulator is displaced in the direction of the desired lambda value, which deviates from the stoichiometric ratio,
    - the oscillation of the measurement signal of the lambda sensor around the switching point is recorded, whereby a regulation stroke that remains the same is assured,
    - a reference value of the oscillation of the measurement signal of the lambda sensor around the switching point, in each instance, is predetermined,
    - the switching point of the two-point regulator is displaced in such a manner that the reference value of the oscillation of the measurement signal of the lambda sensor occurs.
  2. Method according to claim 1,
    wherein
    for a desired lambda value that deviates from the stoichiometric ratio, in each instance, a related amplitude of the oscillation (residual ripple) of the measurement signal of the lambda sensor is predetermined, and regulated by means of displacing the switching point of the two-point regulator.
  3. Method according to claim 1,
    wherein
    the switching point of the two-point regulator is displaced as a function of the identified curvature of the sensor characteristic curve, in the direction of the desired lambda value that deviates from the stoichiometric ratio, whereby a value of the non-symmetry of the oscillation of the sensor output voltage around the switching point generated from the two-point regulation, with the regulation stroke remaining the same, is determined as the equivalent of the curvature of the sensor characteristic curve, in that the amplitude and/or the area of the half-waves of the oscillation of the sensor output voltage around the switching point are evaluated.
  4. Method according to claim 3,
    wherein
    for a desired lambda value that deviates from the stoichiometric ratio, in each instance, a related value of the non-symmetry of the oscillation of the measurement signal of the lambda sensor is predetermined, and regulated by means of displacing the switching point of the two-point regulator.
  5. Method according to claim 3 and 4,
    wherein
    in addition, the amplitude of the oscillation of the measurement signal of the lambda sensor around the switching point, in each instance, (residual ripple) is considered for the adaptation of the switching point.
  6. Method according to claim 1 to 5,
    wherein
    for setting a "rich" air/fuel mixture, the switching point of the two-point regulator is displaced in the direction of a higher sensor output voltage than the sensor output voltage at the turning point of the sensor characteristic curve, and that for setting a "lean" air/fuel mixture, the switching point of the two-point regulator is displaced in the direction of a lower sensor output voltage than the sensor output voltage at the turning point of the sensor characteristic curve.
  7. Method according to one of the preceding claims,
    wherein
    the signal of the sensor output voltage of the lambda sensor ahead of the catalytic converter is used as the measurement signal.
  8. Method according to one of claim 1, 3, 4 and 6 - 8,
    wherein
    a switching point that occurs for a predetermined non-symmetry of the oscillation of the measurement signal of the lambda sensor is determined, and a diagnosis of the lambda sensor takes place on the basis of the deviation from a predefined switching point.
  9. Method according to one of the preceding claims 1, 2 and 6 to 8,
    wherein
    a switching point that occurs for a predetermined amplitude of the oscillation of the measurement signal of the lambda sensor is determined, and a diagnosis of the lambda sensor takes place on the basis of the deviation from a predefined switching point.
  10. Method according to one of the preceding claims,
    wherein
    an evaluation of the lambda sensor signal takes place in the case of an adaptation of the switching point of the two-point regulator, and the lambda sensor signal is analyzed at a displaced switching point, and an evaluation of the lambda sensor with regard to its ability to function takes place on the basis of the deviation from previously set standards of a lambda sensor.
  11. Method according to one of the preceding claims,
    wherein
    in the case of a defined displacement of the switching point of the two-point regulator, an analysis of the output signal of the lambda sensor takes place, and the residual ripple and/or non-symmetry of the oscillation of the output signal around the switching point that occurs at a predetermined regulation stroke that is kept constant during the displacement of the switching point is recorded, and an evaluation of the lambda sensor with regard to its ability to function takes place on the basis of the deviation from the previous standard values determined for a lambda sensor.
  12. Method according to claim 1,
    wherein
    in the case of a displacement of the switching point of the two-point regulator, while the regulation stroke is kept constant, an analysis of the output signal of the lambda sensor takes place, and adjustment of a desired lambda value that deviates from the stoichiometric ratio takes place, in such a manner that a related value of the non-symmetry of the oscillation of the measurement signal of the lambda sensor and/or the residual ripple is predetermined and regulated by means of displacement of the switching point of the two-point regulator, and the switching point of the two-point regulator that results from the predetermination of the non-symmetry and/or the residual ripple in this way is determined, and an evaluation of the lambda sensor with regard to its ability to function takes place on the basis of the deviation from the previous standard values of the switching point determined for a lambda sensor.
  13. Method according to one of claims 9 - 11,
    wherein
    the switching point of the two-point regulator is displaced in the direction of the desired lambda value that deviates from the stoichiometric ratio, whereby a value of the non-symmetry of the oscillation of the sensor output voltage around the switching point generated from the two-point regulation, with the regulation stroke remaining the same, is determined, in that the amplitude and/or the area of the half-waves of the oscillation of the sensor output voltage around the switching point are evaluated.
  14. Method according to one of the preceding claims 9 - 13,
    wherein
    a switching point that occurs for a predetermined non-symmetry of the oscillation of the measurement signal of the lambda sensor is determined, and from this, the real progression of the sensor characteristic curve is reproduced, with regard to its curvature, and an evaluation of the lambda sensor as being defective takes place on the basis of the deviation of the curvature from an ideal characteristic curve.
EP07722105A 2006-04-18 2007-03-24 Method for adjusting the air/fuel ratio of an internal combustion engine Not-in-force EP2013464B1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE200610017863 DE102006017863B3 (en) 2006-04-18 2006-04-18 Internal combustion engine fuel/air mixture adjusting method, involves shifting switching point of two lever controller such that reference value of oscillation of measuring signal of lambda probe is adjusted
DE200610049348 DE102006049348A1 (en) 2006-10-19 2006-10-19 Fuel/air ratio adjusting method for internal combustion engine, involves displacing switching point of on-off controller while oscillation of test signal of lambda probe is analyzed, so that desired value of oscillation is reached
DE200610049350 DE102006049350A1 (en) 2006-10-19 2006-10-19 Fuel/air ratio adjusting method for internal combustion engine, involves displacing switching point of on-off controller while oscillation of test signal of lambda probe is analyzed, so that desired value of oscillation is reached
PCT/DE2007/000546 WO2007118444A1 (en) 2006-04-18 2007-03-24 Method for adjusting the air/fuel ratio of an internal combustion engine

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EP2013464A1 EP2013464A1 (en) 2009-01-14
EP2013464B1 true EP2013464B1 (en) 2009-12-23

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DE102012211683B4 (en) * 2012-07-05 2024-03-21 Robert Bosch Gmbh Method and device for correcting a characteristic curve of a two-point lambda sensor
US9506415B2 (en) * 2013-12-31 2016-11-29 Stephen Mullen Controller for modifying the voltage signal of an exhaust gas oxygen sensor

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EP2013464A1 (en) 2009-01-14
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US20090138182A1 (en) 2009-05-28
US7706959B2 (en) 2010-04-27

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