EP1131549A1 - METHOD FOR ADAPTING THE NOx CONCENTRATION OF AN INTERNAL COMBUSTION ENGINE OPERATED WITH AN EXCESS OF AIR - Google Patents

METHOD FOR ADAPTING THE NOx CONCENTRATION OF AN INTERNAL COMBUSTION ENGINE OPERATED WITH AN EXCESS OF AIR

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Publication number
EP1131549A1
EP1131549A1 EP99962044A EP99962044A EP1131549A1 EP 1131549 A1 EP1131549 A1 EP 1131549A1 EP 99962044 A EP99962044 A EP 99962044A EP 99962044 A EP99962044 A EP 99962044A EP 1131549 A1 EP1131549 A1 EP 1131549A1
Authority
EP
European Patent Office
Prior art keywords
nox
nox concentration
raw
concentration
internal combustion
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP99962044A
Other languages
German (de)
French (fr)
Other versions
EP1131549B1 (en
Inventor
Hong Zhang
Corinna Pfleger
Wolfgang Ludwig
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
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Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP1131549A1 publication Critical patent/EP1131549A1/en
Application granted granted Critical
Publication of EP1131549B1 publication Critical patent/EP1131549B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • 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
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • 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
    • F02D41/1401—Introducing closed-loop corrections characterised by the control or regulation method
    • F02D41/1402—Adaptive control
    • 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
    • F02D41/146—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 NOx content or concentration
    • F02D41/1461—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 NOx content or concentration of the exhaust gases emitted by the engine
    • F02D41/1462—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 NOx content or concentration of the exhaust gases emitted by the engine with determination means using an estimation
    • 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
    • F02D41/146—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 NOx content or concentration
    • F02D41/1463—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 NOx content or concentration of the exhaust gases downstream of exhaust gas treatment apparatus

Definitions

  • the invention relates to a method for adapting the raw NOx concentration of an internal combustion engine working with excess air according to the preamble of patent claim 1.
  • NOx storage reduction catalysts hereinafter simply referred to as NOX storage catalysts. Due to their coating, these NOx storage catalytic converters are able to adsorb NOx compounds from the exhaust gas during a storage phase, also referred to as the loading phase, which arise during lean combustion. During a regeneration phase, the adsorbed or stored NOx compounds are converted into harmless compounds with the addition of a reducing agent. CO, H 2 and HC (hydrocarbons) can be used as reducing agents for lean-burn gasoline internal combustion engines. These are generated by briefly operating the internal combustion engine with a rich mixture and made available to the NOx storage catalytic converter as exhaust gas components, as a result of which the stored NOx compounds in the catalytic converter are broken down.
  • the adsorption efficiency of such a NOx storage catalyst drops with a higher NOx loading level.
  • the degree of loading is the quotient of the current, absolute NOx loading and the maximum NOx storage capacity.
  • the calculated degree of loading can be used to control the lean and rich cycles of the internal combustion engine. It can be seen that in order to determine the degree of loading it is necessary to have as precise a knowledge as possible of both the current loading and the maximum storage capacity.
  • the maximum storage capacity can be determined on the engine test bench by measuring the amount of NOx stored per unit of time until a saturation state is reached, while saturation of the NOx storage catalytic converter in the motor vehicle is not possible for emission reasons.
  • this storage capability is subject to an aging process, so that it is necessary to adapt it over the vehicle running route. For this you need either the value for the current loading and / or a very precise value for the raw NOx emission of the internal combustion engine.
  • One way of determining the raw NOx concentration is to measure a reference internal combustion engine on a test bench and to store the data in suitable maps. However, reading these maps only provides meaningful results if the raw NOx concentration of various internal combustion engines in a series does not fluctuate too much. If the fluctuations in the raw NOx concentrations exceed a certain level, an adaptation of the raw NOx concentration of the internal combustion engine in the motor vehicle is necessary.
  • the invention is based on the object of specifying a method with which the raw NOx concentration of an internal combustion engine of the type mentioned at the outset can be adapted in a simple manner.
  • the operating point-dependent values for the raw NOx concentration of the internal combustion engine are read from a map and the concentration fluctuations are adapted on the basis of the output signal of a NOx sensor arranged downstream of the NOx storage catalytic converter either by modifying a reduction factor which is used to calculate the corrected raw NOx concentration from the raw NOx concentration, or by directly correcting the values read from the map for the raw NOx concentration with a raw concentration correction factor.
  • FIG. 1 shows a schematic illustration of a lean-burn internal combustion engine with a NOx storage catalytic converter
  • FIG. 2 shows a diagram which shows the amount of NOx and NOx emitted during a lean phase of the internal combustion engine.
  • FIG. 3 shows a block diagram for adapting the raw NOx concentration by means of a correction factor for the reduction factor
  • FIG. 4 shows a block diagram for adapting the raw NOx concentration by means of a correction factor for the raw NOx concentration
  • Figure 5 is a diagram showing the integrals of the NOx concentrations.
  • FIG. 1 shows a lean-burn internal combustion engine with a NOx exhaust gas aftertreatment system in the form of a block diagram, in which the method according to the invention is applied becomes. Only the components that are necessary to understand the invention are shown.
  • the lean-burn internal combustion engine 10 is supplied with an air / fuel mixture via an intake duct 11.
  • a load sensor in the form of an air mass meter 12 a throttle valve block 13 with a throttle valve 14 and a throttle valve sensor (not shown) for detecting the opening angle of the throttle valve 14 and a number of cylinders corresponding to the number of cylinders are provided, one after the other, a set of injection valves 15, of which only one is shown.
  • the method according to the invention can also be used in a system in which the fuel is injected directly into the respective cylinder (direct injection).
  • an exhaust gas aftertreatment system for lean exhaust gas is provided in this exhaust gas duct 16. It consists of a pre-catalytic converter 17 (3-way catalytic converter) arranged near the internal combustion engine 10 and a NOx storage catalytic converter 18 arranged downstream of the pre-catalytic converter 17 in the flow direction of the exhaust gas.
  • a pre-catalytic converter 17 (3-way catalytic converter) arranged near the internal combustion engine 10
  • a NOx storage catalytic converter 18 arranged downstream of the pre-catalytic converter 17 in the flow direction of the exhaust gas.
  • the sensor system for the exhaust gas aftertreatment system includes an oxygen sensor 19 upstream of the pre-catalytic converter 17, a temperature sensor 20 in the connecting pipe between the pre-catalytic converter 17 and the NOx storage catalytic converter 18 close to the inlet area thereof, and a further exhaust gas sensor 21 downstream of the NOx storage catalytic converter 18.
  • temperature sensor 20 which detects the exhaust gas temperature and from whose signal the temperature of the NOx storage catalytic converter 18 can be calculated using a temperature model
  • temperature sensor 201 is shown in FIG. records that directly measures the monolith temperature of the NOx storage catalyst 18.
  • a further possibility is to calculate the monolith temperature of the NOx storage catalytic converter 18 using an exhaust gas temperature model, some or all of the following parameters, such as speed, load, ignition angle, air ratio, exhaust gas recirculation rate, intake air temperature, coolant temperature, being used as input variables for this model .
  • the use of a temperature sensor 20 can be dispensed with.
  • the calculation or measurement of the temperature of the NOx storage catalytic converter 18 is necessary for controlling the system in terms of consumption and emissions. Based on this measured, calculated or modeled temperature signal, catalyst heating or catalyst protection measures are also initiated.
  • a broadband lambda probe is preferably used as the oxygen sensor 19, which, depending on the oxygen content in the exhaust gas, has a constant, e.g. outputs linear output signal.
  • the signal from this broadband lambda probe is used to regulate the air ratio during lean operation and during the regeneration phase with a rich mixture in accordance with the setpoint values.
  • This function is performed by a lambda control device 22 known per se, which is preferably integrated in a control device 23 which controls the operation of the internal combustion engine 10.
  • Electronic control devices of this type which generally contain a microprocessor and which, in addition to fuel injection and ignition, also perform a large number of other control and regulating tasks, including the control of the exhaust gas aftertreatment system, are known per se, so that in the following only the in connection with the invention relevant structure and its functioning becomes.
  • the control device 23 is connected to a memory device 24, in which various characteristic curves or maps KF1, KF2, and correction factors RFKF and RKKF, among other things, are stored, the respective meaning of which is explained in more detail with reference to the description of the following figures.
  • a temperature sensor 29 detects a signal corresponding to the temperature of the internal combustion engine, for example by measuring the coolant temperature.
  • the speed of the internal combustion engine is detected with the help of a markings on the crankshaft or a sensor 30 which is connected to the sensor wheel.
  • the output signal of the air mass meter 12 and the signals of the throttle valve sensor, the oxygen sensor 19, the exhaust gas probe 21, the temperature sensors 20, 29 and the speed sensor 30 are supplied to the control device 23 via corresponding connecting lines.
  • control device 23 is connected, in addition to an ignition device 27 for the air-fuel mixture, to further sensors and actuators (not explicitly shown) via a data and control line 28, which is only shown schematically.
  • an exhaust gas sensor in the form of a NOx sensor 21 Downstream of the NOx storage catalytic converter 18, an exhaust gas sensor in the form of a NOx sensor 21 is arranged in the exhaust gas duct, the output signal thereof for controlling the storage regeneration and for adapting model variables such as the oxygen or NOx storage capacity, the NOx storage catalytic converter 18 and Detection of the aging state of the NOx storage catalytic converter is used.
  • the raw NOx emission of the internal combustion engine is adapted with the output signal of the NOx sensor 21 if necessary.
  • a bout the already mentioned parameter is detected in the controller 21 filed by executing control routines, inter alia, the load state of the internal combustion engine, determines the NO x raw emission of the internal combustion engine and adapted, and determines the degree of loading of the NOx storage catalyst.
  • the total amount of NOx emitted by the internal combustion engine during a lean phase can be broken down into the following parts:
  • the above-mentioned NOx quantities SU, SM and DB can be formed from the respective concentrations by integration over time.
  • Corrected raw NOx concentration KK is understood below to mean the raw NOx concentration minus the stationary turnover concentration SK.
  • the stationary turnover concentration SK is recorded via a reduction factor RF.
  • the most accurate knowledge of the corrected raw NOx concentration KK is necessary for catalyst control by calculating the degree of loading and for adapting the storage capacity to aging.
  • FIG. 2 shows a diagram in which the above-mentioned proportions of the raw NOx emission emitted by the internal combustion engine during the lean phase are entered.
  • the lean phase has ended and a regeneration phase for the NOx storage catalytic converter 18 is requested.
  • the hatched areas indicate the individual NOx quantities of stationary sales quantity SU, storage quantity SM and breakthrough quantity DB.
  • KK (nl) is the corrected raw NOx concentration before the current adaptation process, with KK (n) the corrected raw NOx concentration after the current one A daption called.
  • the associated values for the stationary turnover concentration SK (nl) with an uncorrected reduction factor and with a corrected reduction factor SK (n) are also shown.
  • FIG. 3 shows in the form of a block diagram a first exemplary embodiment for adapting the NOx concentration fluctuations by modifying the reduction factor RF, which is used to calculate the corrected raw NOx concentration from the raw NOx concentration.
  • the corrected raw NOx concentration KK is determined with the aid of the signal from the NOx sensor 21 arranged downstream of the NOx storage catalytic converter and adapted if necessary.
  • the adaptation is carried out as follows during a cycle consisting of a lean and fat phase.
  • breakthrough amount DB and the amount of memory SM are determined.
  • the breakthrough quantity DB is detected in the lean phase by measuring the post-cat NOx concentration with the NOx sensor 21 and integrating it over the lean phase duration.
  • the storage quantity SM in the lean phase can be calculated in the fat phase following the lean phase. For this it is assumed that the additional fuel mass flow, which is not required for stoichiometric combustion, is used to reduce the stored NOx mass and to use up the stored oxygen.
  • the stored amount of oxygen the length of time from the beginning of the rich phase until a complete NOx regeneration of the NOx storage catalytic converter is recognized, the additional fuel mass flow and the molar ratio of the fuel + NOx reaction, it is possible to draw conclusions about the stored NOx amount.
  • the integral of the corrected NOx concentration over the lean phase IKK is calculated.
  • the raw NOx concentration RK is, for example, dependent on ger or all of the following parameters determined: speed, load, ignition angle, air ratio, exhaust gas recirculation rate, intake air temperature, coolant temperature.
  • the correction factor RFKF for the reduction factor RF is reduced or increased in a suitable manner. It is reduced if IKK ⁇ DB + SM and it is increased if IKK> DB + SM applies.
  • the reduction factor RF read out from the map KF2 for example as a function of the temperature of the NOx storage catalytic converter 18, is multiplied by the correction factor RFKF which has remained unchanged or has been adapted in the manner described above.
  • the value obtained in this way is subtracted from 1 and this value is multiplied by the raw NOx concentration RK, which is read out from the map KF1 for this purpose.
  • FIG. 4 Another possibility of adaptation is the adaptation of a correction factor RKKF for the raw NOx concentration RK.
  • RKKF correction factor
  • the reduction factor RF is not modified in the method presented here, but the raw NOx concentration RK is multiplied by a correction factor RKKF that can be calculated according to the above-described adaptation method (ratio or difference formation of IKK and (DB + SM)).
  • This pre-corrected raw NOx concentration RKK is then multiplied by the value 1-RF, RF again denoting the reduction factor that is read from the map KF2.
  • FIG. 5 shows the integrals of the corrected NOx concentration IKK over the lean phase, the storage amount SM and the breakthrough amount DB.
  • the corrected raw NOx concentration KK and the sum of storage concentration SPK and post-catalyst concentration NK are shown.
  • the integral values IKK and SM + DB are the same and no adaptation needs to be carried out, otherwise an adaptation is carried out according to the method explained with reference to FIGS. 3 or 4.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

The operating point dependent values for the crude NOx concentration (RK) of the internal combustion engine are read out from an engine characteristics map. The variations in concentration are adapted on the basis of the starting signal of an NOx sensor which is arranged down-stream of the NOx storage catalyst either by modification of a reduction factor (RF) which serves to calculate the corrected crude NOx concentration (KK) from the crude NOx concentration (RK) or by direct correction of the values read out from the engine characteristics map for the crude NOx concentration (RK) with a crude concentration correction factor.

Description

Beschreibung description
Verfahren zum Adaptieren der NOx-Rohkonzentration einer mit Luftüberschύß arbeitenden BrennkraftmaschineMethod for adapting the raw NOx concentration of an internal combustion engine working with excess air
Die Erfindung betrifft ein Verfahren zum Adaptieren der NOx- Rohkonzentration einer mit Luftüberschuß arbeitenden Brennkraftmaschine gemäß dem Oberbegriff des Patentanspruches 1.The invention relates to a method for adapting the raw NOx concentration of an internal combustion engine working with excess air according to the preamble of patent claim 1.
Um den Kraftstoffverbrauch von Kraftfahrzeugen mit ottomotorischem Antrieb weiter zu reduzieren, kommen immer häufiger Brennkraftmaschinen zum Einsatz, die zumindest in ausgewählten Betriebsbereichen mit magerem Gemisch betrieben werden.In order to further reduce the fuel consumption of motor vehicles with an petrol engine, internal combustion engines are being used more and more, which are operated with a lean mixture at least in selected operating areas.
Zur Erfüllung der geforderten Abgasemissionsgrenzwerte ist bei solchen Brennkraftmaschinen eine spezielle Abgasnachbehandlung notwendig. Dazu werden NOx-Speicherreduktions- katalysatoren, im folgenden vereinfacht als NOX-Speicher- katalysatoren bezeichnet, verwendet. Diese NOx-Speicher- katalysatoren sind aufgrund ihrer Beschichtung in der Lage, während einer Speicherphase, auch als Beladungsphase bezeichnet, NOx-Verbindungen aus dem Abgas zu adsorbieren, die bei magerer Verbrennung entstehen. Während einer Regenerationsphase werden die adsorbierten bzw. gespeicherten NOx- Verbindungen unter Zugabe eines Reduktionsmittels in unschädliche Verbindungen umgewandelt. Als Reduktionsmittel für magerbetriebene Otto-Brennkraftmaschinen können CO, H2 und HC (Kohlenwasserstoffe) verwendet werden. Diese werden durch kurzzeitigen Betrieb der Brennkraftmaschine mit einem fetten Gemisch erzeugt und dem NOx-Speicherkataly-sator als Abgaskomponenten zur Verfügung gestellt, wodurch die gespeicherten NOx-Verbindungen im Katalysator abgebaut werden.In order to meet the required exhaust emission limit values, special exhaust gas aftertreatment is necessary in such internal combustion engines. For this purpose, NOx storage reduction catalysts, hereinafter simply referred to as NOX storage catalysts, are used. Due to their coating, these NOx storage catalytic converters are able to adsorb NOx compounds from the exhaust gas during a storage phase, also referred to as the loading phase, which arise during lean combustion. During a regeneration phase, the adsorbed or stored NOx compounds are converted into harmless compounds with the addition of a reducing agent. CO, H 2 and HC (hydrocarbons) can be used as reducing agents for lean-burn gasoline internal combustion engines. These are generated by briefly operating the internal combustion engine with a rich mixture and made available to the NOx storage catalytic converter as exhaust gas components, as a result of which the stored NOx compounds in the catalytic converter are broken down.
Der Adsorptions-Wirkungsgrad eines solchen NOx-Speicherkata- lysators fällt mit höherem NOx-Beladungsgrad ab. Als Beladungsgrad ist der Quotient aus der momentanen, absoluten NOx- Beladung und der maximalen NOx-Speicherkapazität bezeichnet. Der errechnete Beladungsgrad kann zur Steuerung der Magerund Fettzyklen der Brennkraftmaschine herangezogen werden. Es ist ersichtlich, daß zur Ermittlung des Beladungsgrades eine möglichst genaue Kenntnis sowohl der momentanen Beladung als auch der maximalen Speicherkapazität nötig ist.The adsorption efficiency of such a NOx storage catalyst drops with a higher NOx loading level. The degree of loading is the quotient of the current, absolute NOx loading and the maximum NOx storage capacity. The calculated degree of loading can be used to control the lean and rich cycles of the internal combustion engine. It can be seen that in order to determine the degree of loading it is necessary to have as precise a knowledge as possible of both the current loading and the maximum storage capacity.
Die maximale Speicherkapazität kann auf dem Motorprüfstand durch Messung der eingelagerten NOx-Menge pro Zeiteinheit bis zum Erreichen eines Sättigungszustandes ermittelt werden, während das Sättigen des NOx-Speicherkatalysators im Kraftfahrzeug aus Emissionsgründen nicht möglich ist. Allerdings unterliegt diese Speicherfähigkeit einem Alterungsprozeß, so daß es nötig ist, sie über der Fahrzeuglaufstrecke zu adaptieren. Hierzu benötigt man entweder den Wert für die momen- tane Beladung und/oder einen sehr genauen Wert für die NOx- Rohemission der Brennkraftmaschine.The maximum storage capacity can be determined on the engine test bench by measuring the amount of NOx stored per unit of time until a saturation state is reached, while saturation of the NOx storage catalytic converter in the motor vehicle is not possible for emission reasons. However, this storage capability is subject to an aging process, so that it is necessary to adapt it over the vehicle running route. For this you need either the value for the current loading and / or a very precise value for the raw NOx emission of the internal combustion engine.
Eine Möglichkeit der Ermittlung der NOx-Rohkonzentration ist das Vermessen einer Referenz-Brennkraftmaschine auf einem Prüfstand und die Ablage der Daten in geeigneten Kennfeldern. Das Auslesen dieser Kennfelder liefert allerdings nur dann sinnvolle Ergebnisse, wenn die NOx-Rohkonzentration verschiedener Brennkraftmaschinen einer Serie nicht allzu stark schwanken. Überschreiten die Schwankungen der NOx- Rohkonzentrationen ein gewisses Maß, ist eine Adaption der NOx-Rohkonzentration der Brennkraftmaschine im Kraftfahrzeug nötig.One way of determining the raw NOx concentration is to measure a reference internal combustion engine on a test bench and to store the data in suitable maps. However, reading these maps only provides meaningful results if the raw NOx concentration of various internal combustion engines in a series does not fluctuate too much. If the fluctuations in the raw NOx concentrations exceed a certain level, an adaptation of the raw NOx concentration of the internal combustion engine in the motor vehicle is necessary.
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren anzu- geben, mit dem die NOx-Rohkonzentration einer Brennkraftmaschine der eingangs genannten Art auf einfache Weise adaptiert werden kann.The invention is based on the object of specifying a method with which the raw NOx concentration of an internal combustion engine of the type mentioned at the outset can be adapted in a simple manner.
Diese Aufgabe wird durch die Merkmale des Patentanspruchs 1 gelöst. Vorteilhafte Weiterbildungen der Erfindung sind in den Unteransprüchen angegeben. Gemäß dem erfindungsgemäßen Verfahren werden die betriebspunktabhängigen Werte für die NOx-Rohkonzentration der Brennkraftmaschine aus einem Kennfeld ausgelesen und die Adaption der Konzentrationsschwankungen erfolgt auf der Basis des Ausgangssignals eines stromabwärts des NOx-Speicherkatalysators angeordneten NOx-Sensors entweder durch Modifikation eines Reduktionsfaktors, der zur Berechnung der korrigierten NOx-Rohkonzentration aus der NOx-Rohkonzentration dient, oder durch direkte Korrektur der aus dem Kennfeld ausgelesenen Werte für die NOx-Rohkonzentration mit einem Rohkonzentrati- onskorrekturfaktor.This object is achieved by the features of patent claim 1. Advantageous developments of the invention are specified in the subclaims. According to the method according to the invention, the operating point-dependent values for the raw NOx concentration of the internal combustion engine are read from a map and the concentration fluctuations are adapted on the basis of the output signal of a NOx sensor arranged downstream of the NOx storage catalytic converter either by modifying a reduction factor which is used to calculate the corrected raw NOx concentration from the raw NOx concentration, or by directly correcting the values read from the map for the raw NOx concentration with a raw concentration correction factor.
Die Erfindung wird nachfolgend unter Bezugnahme auf die Zeichnung näher erläutert. Es zeigen:The invention is explained in more detail below with reference to the drawing. Show it:
Figur 1 eine schematische Darstellung einer Mager-Brennkraft- aschine mit einem NOx-Speicherkatalysator,FIG. 1 shows a schematic illustration of a lean-burn internal combustion engine with a NOx storage catalytic converter,
Figur 2 ein Diagramm, das die während einer Magerphase der Brennkraftmaschine emitierte NOx-Menge und NOx-FIG. 2 shows a diagram which shows the amount of NOx and NOx emitted during a lean phase of the internal combustion engine.
Konzentration zeigt,Concentration shows
Figur 3 eine Blockdarstellung zur Adaption der NOx- Rohkonzentration mittels eines Korrekturfaktors für den Reduktionsfaktor,FIG. 3 shows a block diagram for adapting the raw NOx concentration by means of a correction factor for the reduction factor,
Figur 4 eine Blockdarstellung zur Adaption der NOx- Rohkonzentration mittels eines Korrekturfaktors für die NOx-Rohkonzentration undFIG. 4 shows a block diagram for adapting the raw NOx concentration by means of a correction factor for the raw NOx concentration and
Figur 5 ein Diagramm, das die Integrale der NOx- Konzentrationen zeigt.Figure 5 is a diagram showing the integrals of the NOx concentrations.
In Fig. 1 ist in Form eines Blockschaltbildes eine Mager- Brennkraftmaschine mit einer NOx-Abgasnachbehandlungsanlage gezeigt, bei der das erfindungsgemäße Verfahren angewendet wird. Dabei sind nur die Komponenten dargestellt, die zum Verständnis der Erfindung nötig sind.1 shows a lean-burn internal combustion engine with a NOx exhaust gas aftertreatment system in the form of a block diagram, in which the method according to the invention is applied becomes. Only the components that are necessary to understand the invention are shown.
Der Mager-Brennkraftmaschine 10 wird über einen Ansaugkanal 11 ein Luft-/Kraftstoffgemisch zugeführt. Im Ansaugkanal 11 sind in Strömungsrichtung der angesaugten Luft gesehen nacheinander ein Lastsensor in Form eines Luftmassenmessers 12, ein Drosselklappenblock 13 mit einer Drosselklappe 14 und einem nicht dargestellten Drosselklappensensor zur Erfassung des Öffnungswinkels der Drosselklappe 14 und entsprechend der Zylinderanzahl ein Satz Einspritzventile 15 vorgesehen, von denen nur eines gezeigt ist. Das erfindungsgemäße Verfahren ist aber auch bei einem System anwendbar, bei der der Kraftstoff direkt in die jeweiligen Zylinder eingespritzt wird (Direkteinspritzung) .The lean-burn internal combustion engine 10 is supplied with an air / fuel mixture via an intake duct 11. In the intake duct 11, a load sensor in the form of an air mass meter 12, a throttle valve block 13 with a throttle valve 14 and a throttle valve sensor (not shown) for detecting the opening angle of the throttle valve 14 and a number of cylinders corresponding to the number of cylinders are provided, one after the other, a set of injection valves 15, of which only one is shown. However, the method according to the invention can also be used in a system in which the fuel is injected directly into the respective cylinder (direct injection).
Ausgangsseitig ist die Brennkraftmaschine 10 mit einem Abgaskanal 16 verbunden. In diesem Abgaskanal 16 ist eine Abgasnachbehandlungsanlage für mageres Abgas vorgesehen. Sie be- steht aus einem nahe der Brennkraftmaschine 10 angeordneten Vorkatalysator 17 (3-Wege-Katalysator) und einem in Strömungsrichtung des Abgases dem Vorkatalysator 17 nachgeschalteten NOx-Speicherkatalysator 18.On the output side, the internal combustion engine 10 is connected to an exhaust gas duct 16. An exhaust gas aftertreatment system for lean exhaust gas is provided in this exhaust gas duct 16. It consists of a pre-catalytic converter 17 (3-way catalytic converter) arranged near the internal combustion engine 10 and a NOx storage catalytic converter 18 arranged downstream of the pre-catalytic converter 17 in the flow direction of the exhaust gas.
Die Sensorik für die Abgasnachbehandlungsanlage beinhaltet einen Sauerstoffmeßaufnehmer 19 stromaufwärts des Vorkatalysators 17, einen Temperatursensor 20 im Verbindungsrohr zwischen Vorkatalysator 17 und NOx-Speicherkatalysator 18 nahe am Eintrittsbereich desselben und einen weiteren Abgassensor 21 stromabwärts des NOx-Speicherkatalysators 18.The sensor system for the exhaust gas aftertreatment system includes an oxygen sensor 19 upstream of the pre-catalytic converter 17, a temperature sensor 20 in the connecting pipe between the pre-catalytic converter 17 and the NOx storage catalytic converter 18 close to the inlet area thereof, and a further exhaust gas sensor 21 downstream of the NOx storage catalytic converter 18.
Anstelle des Temperatursensors 20, der die Abgastemperatur erfasst und aus dessen Signal mittels eines Temperaturmodells die Temperatur des NOx-Speicherkatalysators 18 berechnet werden kann, ist es auch möglich, die NOx-Speicherkatalysator- temperatur unmittelbar zu messen. In der Figur 1 ist mit strichlinierter Linie ein solcher Temperatursensor 201 einge- zeichnet, der die Monolithtemperatur des NOx-Speicherkatalysators 18 direkt mißt.Instead of the temperature sensor 20, which detects the exhaust gas temperature and from whose signal the temperature of the NOx storage catalytic converter 18 can be calculated using a temperature model, it is also possible to measure the NOx storage catalytic converter temperature directly. Such a temperature sensor 201 is shown in FIG. records that directly measures the monolith temperature of the NOx storage catalyst 18.
Eine weitere Möglichkeit besteht darin, die Monolithtempera- tur des NOx-Speicherkatalysators 18 mittels eines Abgastemperaturmodells zu berechnen, wobei als Eingangsgrößen für dieses Modell einige oder alle der folgenden Parameter, wie Drehzahl, Last, Zündwinkel, Luftzahl, Abgasrückführrate, Ansauglufttemperatur, Kühlmitteltemperatur herangezogen werden. Dadurch kann auf den Einsatz eines Temperatursensors 20 verzichtet werden.A further possibility is to calculate the monolith temperature of the NOx storage catalytic converter 18 using an exhaust gas temperature model, some or all of the following parameters, such as speed, load, ignition angle, air ratio, exhaust gas recirculation rate, intake air temperature, coolant temperature, being used as input variables for this model . As a result, the use of a temperature sensor 20 can be dispensed with.
Die Berechnung bzw. die Messung der Temperatur des NOx- Speicherkatalysators 18 ist zur Verbrauchs- und emissionsop- timalen Steuerung des Systems erforderlich. Basierend auf diesem gemessenen, berechneten oder modellierten Temperatursignal werden auch Katalysatorheiz- bzw. Katalysatorschutzmaßnahmen eingeleitet.The calculation or measurement of the temperature of the NOx storage catalytic converter 18 is necessary for controlling the system in terms of consumption and emissions. Based on this measured, calculated or modeled temperature signal, catalyst heating or catalyst protection measures are also initiated.
Als Sauerstoffmeßaufnehmer 19 wird vorzugsweise eine Breit- band-Lambdasonde eingesetzt, welche in Abhängigkeit des Sau- erstoffgehaltes im Abgas ein stetiges, z.B. lineares Ausgangssignal abgibt. Mit dem Signal dieser Breitband-Lambda- sonde wird die Luftzahl während des Magerbetriebes und wäh- rend der Regenerationsphase mit fettem Gemisch entsprechend der Sollwertvorgaben eingeregelt. Diese Funktion übernimmt eine an sich bekannte Lambdaregelungseinrichtung 22, die vorzugsweise in eine den Betrieb der Brennkraftmaschine 10 steuernde Steuerungseinrichtung 23 integriert ist.A broadband lambda probe is preferably used as the oxygen sensor 19, which, depending on the oxygen content in the exhaust gas, has a constant, e.g. outputs linear output signal. The signal from this broadband lambda probe is used to regulate the air ratio during lean operation and during the regeneration phase with a rich mixture in accordance with the setpoint values. This function is performed by a lambda control device 22 known per se, which is preferably integrated in a control device 23 which controls the operation of the internal combustion engine 10.
Solche elektronischen Steuerungseinrichtungen, die in der Regel einen Mikroprozessor beinhalten und die neben der Kraftstoffeinspritzung und der Zündung noch eine Vielzahl weiterer Steuer- und Regelaufgaben, u.a. auch die Steuerung der Abgas- nachbehandlungsanlage übernehmen, sind an sich bekannt, so daß im folgenden nur auf den im Zusammenhang mit der Erfindung relevanten Aufbau und dessen Funktionsweise eingegangen wird. Insbesondere ist die Steuerungseinrichtung 23 mit einer Speichereinrichtung 24 verbunden, in dem u.a. verschiedene Kennlinien bzw. Kennfelder KF1, KF2, sowie Korrekturfaktoren RFKF und RKKF gespeichert sind, deren jeweilige Bedeutung an- hand der Beschreibung der nachfolgenden Figuren noch näher erläutert wird.Electronic control devices of this type, which generally contain a microprocessor and which, in addition to fuel injection and ignition, also perform a large number of other control and regulating tasks, including the control of the exhaust gas aftertreatment system, are known per se, so that in the following only the in connection with the invention relevant structure and its functioning becomes. In particular, the control device 23 is connected to a memory device 24, in which various characteristic curves or maps KF1, KF2, and correction factors RFKF and RKKF, among other things, are stored, the respective meaning of which is explained in more detail with reference to the description of the following figures.
Ein Temperatursensor 29 erfaßt ein der Temperatur der Brennkraftmaschine entsprechendes Signal, beispielsweise über eine Messung der Kühlmitteltemperatur. Die Drehzahl der Brennkraftmaschine wird mit Hilfe eines Markierungen der Kurbelwelle oder eines mit ihr verbundenen Geberrades abtastenden Sensors 30 erfaßt.A temperature sensor 29 detects a signal corresponding to the temperature of the internal combustion engine, for example by measuring the coolant temperature. The speed of the internal combustion engine is detected with the help of a markings on the crankshaft or a sensor 30 which is connected to the sensor wheel.
Das Ausgangssignal des Luftmassenmessers 12 und die Signale des Drosselklappensensors, des Sauerstoffmeßaufnehmers 19, der Abgassonde 21, der Temperatursensoren 20, 29, und des Drehzahlsensors 30 werden über entsprechende Verbindungsleitungen der Steuerungseinrichtung 23 zugeführt.The output signal of the air mass meter 12 and the signals of the throttle valve sensor, the oxygen sensor 19, the exhaust gas probe 21, the temperature sensors 20, 29 and the speed sensor 30 are supplied to the control device 23 via corresponding connecting lines.
Zur Steuerung und Regelung der Brennkraftmaschine 10 ist die Steuerungseinrichtung 23 außer mit einer Zündeinrichtung 27 für das Luft-Kraftstoffgemisch über eine nur schematisch dargestellte Daten - und Steuerleitung 28 noch mit weiteren, nicht explizit dargestellten Sensoren und Aktoren verbunden.To control and regulate the internal combustion engine 10, the control device 23 is connected, in addition to an ignition device 27 for the air-fuel mixture, to further sensors and actuators (not explicitly shown) via a data and control line 28, which is only shown schematically.
Stromabwärts des NOx-Speicherkatalysators 18 ist im Abgaskanal ein Abgassensor in Form eines NOx-Sensors 21 angeordnet, dessen Ausgangssignal zur Steuerung der Speicherregeneration und zur Adaption von Modellgrößen wie z.B. der Sauerstoff- bzw. NOx-Speicherkapazität, des NOx-Speicherkatalysators 18, sowie zum Erfassen des Alterungszustandes des NOx-Speicherkatalysators herangezogen wird. Außerdem wird mit dem Ausgangssignal des NOx-Sensors 21 im Bedarfsfall die NOx-Rohemission der Brennkraftmaschine adaptiert. Über die bereits erwähnten Parameter wird in der Steuerungseinrichtung 21 durch Abarbeiten abgelegter Steuerungsroutinen u.a. der Lastzustand der Brennkraftmaschine erkannt, die NOx- Rohemission der Brennkraftmaschine bestimmt und adaptiert, sowie der Beladungsgrad des NOx-Speicherkatalysators bestimmt .Downstream of the NOx storage catalytic converter 18, an exhaust gas sensor in the form of a NOx sensor 21 is arranged in the exhaust gas duct, the output signal thereof for controlling the storage regeneration and for adapting model variables such as the oxygen or NOx storage capacity, the NOx storage catalytic converter 18 and Detection of the aging state of the NOx storage catalytic converter is used. In addition, the raw NOx emission of the internal combustion engine is adapted with the output signal of the NOx sensor 21 if necessary. A bout the already mentioned parameter is detected in the controller 21 filed by executing control routines, inter alia, the load state of the internal combustion engine, determines the NO x raw emission of the internal combustion engine and adapted, and determines the degree of loading of the NOx storage catalyst.
Die während einer Magerphase von der Brennkraftmaschine emi- tierte NOx-Gesamtmenge kann in folgende Teile aufgespalten werden:The total amount of NOx emitted by the internal combustion engine during a lean phase can be broken down into the following parts:
- Ein Teil wird auch im Magerbetrieb von der Abgasreinigungsanlage in unschädlichere Substanzen umgewandelt. Dieser Anteil wird im folgenden als stationäre Umsatzmenge SU be zeichnet.- A part is also converted into harmless substances by the exhaust gas cleaning system in lean operation. This share is referred to below as stationary sales volume SU.
- Ein weiterer Teil wird im NOx-Speicherkatalysator gespeichert, der im folgenden als Speichermenge SM bezeichnet wird.- Another part is stored in the NOx storage catalytic converter, which is referred to below as the storage amount SM.
- Ein dritter Teil wird an die Umgebung abgegeben. Dieser An- teil wird im folgenden als Durchbruchsmenge DB bezeichnet.- A third part is released into the environment. This proportion is referred to below as the breakthrough quantity DB.
Wird nicht das Integral dieser gesamten NOx-Menge über den Zeitraum einer Magerphase betrachtet, sondern die momentane NOx-Rohkonzentration, kann auch diese analog nach der oben beschriebenen Vorgehensweise aufgespalten werden inIf it is not the integral of this total amount of NOx over the period of a lean phase that is considered, but the current raw NOx concentration, this can also be split into analogously using the procedure described above
- eine den stationären Umsatz SU hervorrufende Stationärumsatz-Konzentration SK,a stationary turnover concentration SK which causes the stationary turnover SU,
- eine die Speichermenge SM hervorrufende Speicher- konzentration SPK unda storage concentration SPK and the storage amount SM
-eine weder umgesetzte noch gespeicherte Nach-Kat- Konzentration NK.-A post-cat concentration NK neither implemented nor saved.
Aus den jeweiligen Konzentrationen können durch Integration über der Zeit die oben genannten NOx-Mengen SU, SM und DB gebildet werden. Unter korrigierter NOx-Rohkonzentration KK wird im folgenden die NOx-Rohkonzentration abzüglich der Stationärumsatz- Konzentration SK verstanden. Die Stationärumsatz- Konzentration SK wird über einen Reduktionsfaktor RF erfaßt. Die korrigierte NOx-Rohkonzentration KK ist als Produkt von der Differenz von Eins und dem Reduktionsfaktor RF und der NOx- Rohkonzentration RK der Brennkraftmaschine definiert: KK=(1-RF) * RK.The above-mentioned NOx quantities SU, SM and DB can be formed from the respective concentrations by integration over time. Corrected raw NOx concentration KK is understood below to mean the raw NOx concentration minus the stationary turnover concentration SK. The stationary turnover concentration SK is recorded via a reduction factor RF. The corrected raw NOx concentration KK is defined as the product of the difference between one and the reduction factor RF and the raw NOx concentration RK of the internal combustion engine: KK = (1-RF) * RK.
Die möglichst genaue Kenntnis der korrigierten NOx-Rohkonzentration KK ist zur Katalysatorsteuerung über die Berechnung des Beladungsgrades sowie zur Alterungsadaption der Speicherkapazität nötig.The most accurate knowledge of the corrected raw NOx concentration KK is necessary for catalyst control by calculating the degree of loading and for adapting the storage capacity to aging.
Die Figur 2 zeigt ein Diagramm, in das die oben genannten Anteile der von der Brennkraftmaschine während der Magerphase emitierte NOx-Rohemission eingetragen sind. Zum Zeitpunkt tO ist die Magerphase beendet und eine Regenerationsphase für den NOx-Speicherkatalysator 18 wird angefordert. Die schraf- fierten Bereiche kennzeichnen die einzelnen NOx-Mengen stationäre Umsatzmenge SU, Speichermenge SM und Durchbruchsmenge DB.FIG. 2 shows a diagram in which the above-mentioned proportions of the raw NOx emission emitted by the internal combustion engine during the lean phase are entered. At the time tO, the lean phase has ended and a regeneration phase for the NOx storage catalytic converter 18 is requested. The hatched areas indicate the individual NOx quantities of stationary sales quantity SU, storage quantity SM and breakthrough quantity DB.
Außerdem sind in das Diagramm bestimmte Anteile der NOx- Konzentration eingetragen. Neben der weder umgesetzten, noch gespeicherten Nach-Kat-Konzentration NK, die gegen Ende der Magerphase rasch ansteigt, sind als Ordinatenabschnitte die aus dem Kennfeld KF1 ausgelesene NOx-Rohkonzentration RK und die tatsächliche, aber nicht ermittelbare NOx- Rohkonzentration RKT dargestellt. Der zusätzlich eingezeichnete Kurvenverlauf von NK nach dem Zeitpunkt tO würde sich einstellen, wenn zum Zeitpunkt tO keine Regeneration eingeleitet werden würde.In addition, certain portions of the NOx concentration are entered in the diagram. In addition to the post-catalyst concentration NK, which has not been converted or stored, and which rises rapidly towards the end of the lean phase, the crude NOx concentration RK read from the map KF1 and the actual, but not ascertainable, raw NOx concentration RKT are shown as ordinate sections. The additionally drawn curve profile of NK after the time tO would occur if no regeneration were initiated at the time tO.
Mit dem Bezugszeichen KK(n-l) ist die korrigierte NOx- Rohkonzentration vor dem aktuellen Adaptionsvorgang, mit KK(n) die korrigierte NOx-Rohkonzentration nach der aktuellen Adaption bezeichnet. Die zugehörigen Werte für die Stationärumsatz-Konzentration SK(n-l) bei einem unkorrigierten Reduk- tionsfator und bei einem korrigierten Reduktionsfaktor SK(n) sind ebenfalls eingezeichnet.With the reference symbol KK (nl) is the corrected raw NOx concentration before the current adaptation process, with KK (n) the corrected raw NOx concentration after the current one A daption called. The associated values for the stationary turnover concentration SK (nl) with an uncorrected reduction factor and with a corrected reduction factor SK (n) are also shown.
In der Figur 3 ist in Form einer Blockdarstellung ein erstes Ausführungsbeispiel zur Adaption der NOx-Konzentrations- schwankungen durch Modifikation des Reduktionsfaktors RF, der zur Berechnung der korrigierten NOx-Rohkonzentration aus der NOx-Rohkonzentration dient, dargestellt. Die korrigierte NOx- Rohkonzentration KK wird dabei mit Hilfe des Signales der stromabwärts des NOx-Speicherkatalysators angeordneten NOx- Sensors 21 ermittelt und falls nötig adaptiert.FIG. 3 shows in the form of a block diagram a first exemplary embodiment for adapting the NOx concentration fluctuations by modifying the reduction factor RF, which is used to calculate the corrected raw NOx concentration from the raw NOx concentration. The corrected raw NOx concentration KK is determined with the aid of the signal from the NOx sensor 21 arranged downstream of the NOx storage catalytic converter and adapted if necessary.
Die Adaption wird während eines Zyklus, bestehend aus Magerund Fettphase folgendermaßen durchgeführt. Als erstes werden Durchbruchsmenge DB und die Speichermenge SM ermittelt. Die Durchbruchsmenge DB wird in der Magerphase durch Messen der Nach-Kat-NOx-Konzentration mit dem NOx-Sensor 21 und deren Integration über der Magerphasendauer erfaßt. Die Speichermenge SM in der Magerphase kann in der an die Magerphase anschließenden Fettphase berechnet werden. Hierzu wird angenommen, der zusätzliche, zur stöchiometrischen Verbrennung nicht benötigte Kraftstoffmassenstrom wird zur Reduktion der ge- speicherten NOx-Masse sowie zum Aufbrauchen des eingelagerten Sauerstoffs verwendet. Ist die gespeicherte Sauerstoffmenge, die Zeitdauer vom Beginn der Fettphase bis zum Erkennen einer vollständigen NOx-Regeneration des NOx-Speicherkatalysators, der zusätzliche Kraftstoffmassenstrom sowie das Stoffmengen- Verhältnis der Reaktion Kraftstoff + NOx bekannt, kann so auf die eingespeicherte NOx-Menge zurückgeschlossen werden.The adaptation is carried out as follows during a cycle consisting of a lean and fat phase. First, breakthrough amount DB and the amount of memory SM are determined. The breakthrough quantity DB is detected in the lean phase by measuring the post-cat NOx concentration with the NOx sensor 21 and integrating it over the lean phase duration. The storage quantity SM in the lean phase can be calculated in the fat phase following the lean phase. For this it is assumed that the additional fuel mass flow, which is not required for stoichiometric combustion, is used to reduce the stored NOx mass and to use up the stored oxygen. If the stored amount of oxygen, the length of time from the beginning of the rich phase until a complete NOx regeneration of the NOx storage catalytic converter is recognized, the additional fuel mass flow and the molar ratio of the fuel + NOx reaction, it is possible to draw conclusions about the stored NOx amount.
Basierend auf der in dem Kennfeld KF1 abgelegten NOx- Rohkonzentration RK und des in einem Kennfeld KF2 abgelegten Reduktionsfaktors RF wird das Integral der korrigierten NOx- Konzentration über der Magerphase IKK berechnet. Die NOx- Rohkonzentration RK wird beispielsweise in Abhängigkeit eini- ger oder aller folgender Parameter ermittelt: Drehzahl, Last, Zündwinkel, Luftzahl, Abgasrückführrate, Ansauglufttemperatur, Kühlmitteltemperatur.Based on the raw NOx concentration RK stored in the map KF1 and the reduction factor RF stored in a map KF2, the integral of the corrected NOx concentration over the lean phase IKK is calculated. The raw NOx concentration RK is, for example, dependent on ger or all of the following parameters determined: speed, load, ignition angle, air ratio, exhaust gas recirculation rate, intake air temperature, coolant temperature.
Die Summe aus der Durchbruchsmenge DB und der Speichermenge SM, sowie der Integralwert der korrigierten NOx-Konzentration über der Magerphase IKK werden zu einer Divisionsstufe Dl geführt und dort das Verhältnis (DB+SM) /IKK gebildet. Anschließend wird die Differenz 1- (DB+SM) /IKK gebildet und dieser Wert zu einem Verstärkerelement V geführt. Stimmt die Berechnung der korrigierten NOx-Konzentration mit der aus den Sondensignalen ermittelten, nicht direkt reduzierten NOx- Konzentration überein, so gilt: IKK=DB + SM. In diesem Fall liegt am Summationspunkt Sl der Wert Null an und der Korrek- turfaktor RFKF für den Reduktionsfaktor RF wird nicht adaptiert (RFKF(n-l) = RFKF(n).The sum of the breakthrough quantity DB and the storage quantity SM, as well as the integral value of the corrected NOx concentration over the lean phase IKK are led to a division level D1 and the ratio (DB + SM) / IKK is formed there. Then the difference 1- (DB + SM) / IKK is formed and this value leads to an amplifier element V. If the calculation of the corrected NOx concentration matches the NOx concentration determined from the probe signals, which is not directly reduced, the following applies: IKK = DB + SM. In this case, the value zero is present at the summation point S1 and the correction factor RFKF for the reduction factor RF is not adapted (RFKF (n-l) = RFKF (n).
Wird festgestellt, das eine nicht hinnehmbare Abweichung zwischen dem Wert IKK und dem Summenwert DB+SM besteht, wird der Korrekturfaktor RFKF für den Reduktionsfaktor RF, mit dem der Reduktionsfaktor RF multipliziert wird, in geeigneter Weise verkleinert oder vergrößert. Er wird verkleinert, wenn IKK<DB+SM ist und er wird vergrößert, wenn IKK>DB+SM gilt.If it is determined that there is an unacceptable deviation between the value IKK and the total value DB + SM, the correction factor RFKF for the reduction factor RF, by which the reduction factor RF is multiplied, is reduced or increased in a suitable manner. It is reduced if IKK <DB + SM and it is increased if IKK> DB + SM applies.
Es ist auch möglich, anstelle der Verhältnisbildung von IKK und (DB+SM) die Differenz von IKK und (DB+SM) zur Bestimmung des Inkrements bzw. Dekrements heranzuziehen, mit dem der Korrekturfaktor RFKF verändert wird.Instead of forming the ratio of IKK and (DB + SM), it is also possible to use the difference between IKK and (DB + SM) to determine the increment or decrement with which the correction factor RFKF is changed.
Der aus dem Kennfeld KF2 beispielsweise als Funktion der Temperatur des NOx-Speicherkatalysators 18 ausgelesene Reduktionsfaktor RF wird mit dem unverändert gebliebenen oder mit dem in der oben beschriebenen Weise adaptierten Korrekturfaktor RFKF multipliziert. Der so erhaltene Wert wird von 1 ab- gezogen und dieser Wert mit der NOx-Rohkonzentration RK multipliziert, der hierzu aus dem Kennfeld KF1 ausgelesen wird. Als Ergebnis erhält man einen Wert für die korrigierte NOX- Rohkonzentration KK = (1-RF)*RK.The reduction factor RF read out from the map KF2, for example as a function of the temperature of the NOx storage catalytic converter 18, is multiplied by the correction factor RFKF which has remained unchanged or has been adapted in the manner described above. The value obtained in this way is subtracted from 1 and this value is multiplied by the raw NOx concentration RK, which is read out from the map KF1 for this purpose. The result is a value for the corrected raw NOX concentration KK = (1-RF) * RK.
Eine weitere Möglichkeit der Adaption stellt die Adaption ei- nes Korrekturfaktors RKKF für die NOx-Rohkonzentration RK dar. Das Verfahren ist in Figur 4 ebenfalls in Form einer Blockdarstellung gezeigt und ist ähnlich dem anhand der Figur 3 erläuterten Verfahren.Another possibility of adaptation is the adaptation of a correction factor RKKF for the raw NOx concentration RK. The method is also shown in FIG. 4 in the form of a block diagram and is similar to the method explained with reference to FIG.
Allerdings wird beim hier vorgestellten Verfahren nicht der Reduktionsfaktor RF modifiziert, sondern die NOx- Rohkonzentration RK wird mit einem nach dem oben erläuterten Adaptionsverfahren (Verhältnis- bzw. Differenzbildung von IKK und (DB+SM) ) berechenbaren Korrekturfaktor RKKF multipli- ziert. Anschließend wird diese vorkorrigierte NOx- Rohkonzentration RKK mit dem Wert 1-RF multipliziert, wobei mit RF wieder der Reduktionsfaktor bezeichnet ist, der aus dem Kennfeld KF2 ausgelesen wird. Als Ergebnis erhält man einen Wert für die korrigierte NOX-Rohkonzentration KK = (1- RF) *RKK.However, the reduction factor RF is not modified in the method presented here, but the raw NOx concentration RK is multiplied by a correction factor RKKF that can be calculated according to the above-described adaptation method (ratio or difference formation of IKK and (DB + SM)). This pre-corrected raw NOx concentration RKK is then multiplied by the value 1-RF, RF again denoting the reduction factor that is read from the map KF2. The result is a value for the corrected raw NOX concentration KK = (1- RF) * RKK.
In Figur 5 sind die Integrale der korrigierten NOx-Konzentration IKK über der Magerphase, der Speichermenge SM und der Durchbruchsmenge DB dargestellt. Außerdem sind die korrigier- te NOx-Rohkonzentration KK und die Summe aus Speicherkonzentration SPK und Nach-Kat-Konzentration NK eingezeichnet. Im Idealfall sind die Integralwerte IKK und SM+DB gleich und es brauchen keine Adaption durchgeführt werden, andernfalls wird eine Adaption nach den anhand der Figuren 3 oder 4 erläuter- ten Verfahren durchgeführt. FIG. 5 shows the integrals of the corrected NOx concentration IKK over the lean phase, the storage amount SM and the breakthrough amount DB. In addition, the corrected raw NOx concentration KK and the sum of storage concentration SPK and post-catalyst concentration NK are shown. In the ideal case, the integral values IKK and SM + DB are the same and no adaptation needs to be carried out, otherwise an adaptation is carried out according to the method explained with reference to FIGS. 3 or 4.

Claims

Patentansprüche claims
1. Verfahren zum Adaptieren der NOx-Rohkonzentration (RK) einer zumindest in bestimmten Betriebsbereichen mit Luftüber- schuß arbeitenden Brennkraftmaschine (10) , wobei1. Method for adapting the raw NOx concentration (RK) of an internal combustion engine (10) operating at least in certain operating areas with excess air, wherein
- in einem Abgaskanal (16) der Brennkraftmaschine (10) ein NOx-Speicherreduktionskatalysator (18) angeordnet ist,- An NOx storage reduction catalyst (18) is arranged in an exhaust gas duct (16) of the internal combustion engine (10),
—der NOx während einer Speicherphase adsorbiert, wenn die Brennkraftmaschine (10) mit einem mageren Luft- Kraftstoffgemisch betrieben wird,—The NOx adsorbs during a storage phase when the internal combustion engine (10) is operated with a lean air / fuel mixture,
—der in einer Regenerationsphase unter Zugabe von Regenerationsmittel das gespeicherte NOx katalytisch umsetzt,—Which converts the stored NOx in a regeneration phase with the addition of regeneration agent,
- stromabwärts des NOx-Speicherreduktionskatalysators (18) ein NOx-Sensor (21) angeordnet ist, - die NOx-Rohkonzentration (RK) abhängig von Betriebsparametern der Brennkraftmaschine (10) in einem Kennfeld (KF1) einer Speichereinrichtung (24) einer die Brennkraftmaschine (10) steuernden Steuereinrichtung (23) abgelegt ist, dadurch gekennzeichnet, daß die im Betrieb der Brennkraftmaschine (10) aus dem Kennfeld- A NOx sensor (21) is arranged downstream of the NOx storage reduction catalytic converter (18), - The raw NOx concentration (RK) depends on the operating parameters of the internal combustion engine (10) in a map (KF1) of a storage device (24) of the internal combustion engine ( 10) controlling control device (23) is stored, characterized in that the operation of the internal combustion engine (10) from the map
(KF1) ausgelesene NOx-Rohkonzentration (RK) während eines Zyklus, bestehend aus der Speicherphase und der Regenerationsphase auf der Grundlage des Ausgangssignals des NOx- Sensors (21) adaptiert wird.(KF1) read out raw NOx concentration (RK) during a cycle consisting of the storage phase and the regeneration phase is adapted on the basis of the output signal of the NOx sensor (21).
2.Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Adaption der NOx-Rohkonzentration (RK) durch Verändern eines Reduktionsfaktors (RF) erfolgt, mit dem die NOx- Rohkonzentration (RK) beaufschlagt wird und der eine Statio- närumsatz-Konzentration (SK) berücksichtigt, die im Magerbetrieb der Brennkraftmaschine (10) vom NOx-Speicherreduktions- katalysators (18) umgewandelt wird.2. The method according to claim 1, characterized in that the adaptation of the raw NOx concentration (RK) is carried out by changing a reduction factor (RF) with which the raw NOx concentration (RK) is applied and which is a steady-state concentration (SK ) is taken into account, which is converted by the NOx storage reduction catalytic converter (18) during lean operation of the internal combustion engine (10).
3.Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß -eine Durchbruchsmenge (DB) in der Magerphase durch Messen der Nach-Kat-NOx-Konzentration (NK) mittels des NOx-Sensors (21) und deren Integration über der Magerphasendauer erfaßt wird, -eine Speichermenge (SM) in der Magerphase in der an die Magerphase anschließenden Fettphase berechnet wird, -basierend auf der NOx-Rohkonzentration (RK) und des Reduktionsfaktors (RF) das Integral der korrigierten NOx- Konzentration über der Magerphase (IKK) berechnet wird, -die Summe aus der Durchbruchsmenge (DB) und der Speichermenge (SM) , sowie der Integralwert der korrigierten NOx- Konzentration über der Magerphase (IKK) in ein Verhältnis ( (DB+SM) /IKK) gesetzt werden, -abhängig von dem Wert des Verhältnisses ein Korrekturfaktor (RFKF) für den Reduktionsfaktor (RF) verändert wird oder unverändert bleibt, -der Reduktionsfaktor (RF) mit dem Korrekturfaktor (RFKF) multipliziert wird.3. The method according to claim 2, characterized in that a breakthrough amount (DB) in the lean phase by measuring the post-cat NOx concentration (NK) by means of the NOx sensor (21) and their integration is recorded over the lean phase duration, -a storage quantity (SM) is calculated in the lean phase in the fat phase following the lean phase, -based on the raw NOx concentration (RK) and the reduction factor (RF) the integral of corrected NOx concentration over the lean phase (IKK) is calculated, - the sum of the breakthrough amount (DB) and the storage amount (SM), as well as the integral value of the corrected NOx concentration over the lean phase (IKK) in a ratio ((DB + SM) / IKK), - depending on the value of the ratio, a correction factor (RFKF) for the reduction factor (RF) is changed or remains unchanged, - the reduction factor (RF) is multiplied by the correction factor (RFKF).
4.Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß aus dem adaptierten Reduktionsfaktors (RF) die korrigierte NOx- Rohkonzentration (KK) berechnet wird als Produkt von der Differenz von 1 und dem adaptierten Reduktionsfaktors (RF) und der aus dem Kennfeld (KF1) ausgelesenen NOx-Rohkonzentration (RK) .4. The method according to claim 3, characterized in that from the adapted reduction factor (RF) the corrected raw NOx concentration (KK) is calculated as the product of the difference of 1 and the adapted reduction factor (RF) and from the map (KF1) read NOx raw concentration (RK).
5.Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Adaption der NOx-Rohkonzentration (RK) durch Verändern eines Korrekturfaktors (RKKF) erfolgt, mit dem die aus dem Kennfeld (KF1) ausgelesene NOx-Rohkonzentration (RK) unmittelbar multipliziert wird und dabei ein vorkorrigierter Wert für die NOx-Rohkonzentration (RKK) erhalten wird.5.The method according to claim 1, characterized in that the adaptation of the raw NOx concentration (RK) is carried out by changing a correction factor (RKKF) with which the raw NOx concentration (RK) read out from the map (KF1) is directly multiplied and thereby a pre-corrected value for the raw NOx concentration (RKK) is obtained.
6.Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß -eine Durchbruchsmenge (DB) in der Magerphase durch Messen der Nach-Kat-NOx-Konzentration (NK) mittels des NOx-Sensors (21) und deren Integration über der Magerphasendauer erfaßt wird, -eine Speichermenge (SM) in der Magerphase in der an die Magerphase anschließenden Fettphase berechnet wird, -basierend auf der NOx-Rohkonzentration (RK) und des Reduktionsfaktors (RF) das Integral der korrigierten NOx- Konzentration über der Magerphase (IKK) berechnet wird,6.The method according to claim 5, characterized in that a breakthrough amount (DB) in the lean phase is measured by measuring the post-cat NOx concentration (NK) by means of the NOx sensor (21) and its integration over the lean phase duration, a storage quantity (SM) in the lean phase is calculated in the fat phase following the lean phase, -based on the raw NOx concentration (RK) and the reduction factor (RF) the integral of the corrected NOx concentration over the lean phase (IKK) is calculated ,
-die Summe aus der Durchbruchsmenge (DB) und der Speichermenge (SM) , sowie der Integralwert der korrigierten NOx- Konzentration über der Magerphase (IKK) in ein Verhältnis ( (DB+SM) /IKK) gesetzt werden, -abhängig von dem Wert des Verhältnisses der Korrekturfaktor (RKKF) für die NOx-Rohkonzentration (RK) verändert wird oder unverändert bleibt.-The sum of the breakthrough amount (DB) and the storage amount (SM), as well as the integral value of the corrected NOx concentration over the lean phase (IKK) are set in a ratio ((DB + SM) / IKK), depending on the value the ratio of the correction factor (RKKF) for the raw NOx concentration (RK) is changed or remains unchanged.
7. Verfahren nach Anspruch 6, dadurch gekennzeichnet, daß aus dem vorkorrigierten Wert für die NOx-Rohkonzentration (RKK) die korrigierte NOx-Rohkonzentration (KK) berechnet wird als Produkt von der Differenz von 1 und dem Reduktionsfaktor (RF) und der vorkorrigierten NOx-Rohkonzentration (RKK) .7. The method according to claim 6, characterized in that from the pre-corrected value for the raw NOx concentration (RKK) the corrected raw NOx concentration (KK) is calculated as the product of the difference of 1 and the reduction factor (RF) and the pre-corrected NOx - Raw concentration (RKK).
8.Verfahren nach einem der Ansprüche 2,3 oder 7, dadurch gekennzeichnet, daß der Reduktionsfaktor (RF) in einem Kennfeld (KF2) abhängig von der Temperatur des NOx-Speicherreduktions- katalysators (18) abgelegt ist. 8. The method according to one of claims 2, 3 or 7, characterized in that the reduction factor (RF) is stored in a characteristic diagram (KF2) as a function of the temperature of the NOx storage reduction catalyst (18).
EP99962044A 1998-11-09 1999-11-03 METHOD FOR ADAPTING THE NOx CONCENTRATION OF AN INTERNAL COMBUSTION ENGINE OPERATED WITH AN EXCESS OF AIR Expired - Lifetime EP1131549B1 (en)

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