EP0822856A1 - PROCESS FOR REGENERATING AN NOx STORAGE CATALYTIC CONVERTER - Google Patents

PROCESS FOR REGENERATING AN NOx STORAGE CATALYTIC CONVERTER

Info

Publication number
EP0822856A1
EP0822856A1 EP97914147A EP97914147A EP0822856A1 EP 0822856 A1 EP0822856 A1 EP 0822856A1 EP 97914147 A EP97914147 A EP 97914147A EP 97914147 A EP97914147 A EP 97914147A EP 0822856 A1 EP0822856 A1 EP 0822856A1
Authority
EP
European Patent Office
Prior art keywords
catalytic converter
nox
storage catalytic
nox storage
storage
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.)
Ceased
Application number
EP97914147A
Other languages
German (de)
French (fr)
Inventor
Willibald SCHÜRZ
Erwin Achleitner
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
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP0822856A1 publication Critical patent/EP0822856A1/en
Ceased legal-status Critical Current

Links

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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9495—Controlling the catalytic process
    • 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
    • F02D41/1438—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
    • F02D41/1465—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 with determination means using an estimation
    • 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
    • F01N2250/00—Combinations of different methods of purification
    • F01N2250/12—Combinations of different methods of purification absorption or adsorption, and catalytic conversion
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/08—Exhaust gas treatment apparatus parameters
    • F02D2200/0806—NOx storage amount, i.e. amount of NOx stored on NOx trap
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/08—Exhaust gas treatment apparatus parameters
    • F02D2200/0811—NOx storage efficiency

Definitions

  • the invention relates to a method for regenerating a NOx storage catalytic converter according to the preamble of the claim
  • NOx storage catalytic converters are used in order to be able to comply with the required exhaust gas limit values in engine concepts with lean combustion.
  • the NOx storage catalytic converters absorb the NOx compounds generated during lean combustion.
  • a method for the regeneration of a NOx storage catalytic converter is already known from EP 0 597 106 A1, in which the amount of NOx compounds absorbed by the storage catalytic converter is calculated as a function of the intake air and the engine load.
  • the internal combustion engine is supplied with a rich mixture for regeneration of the storage catalytic converter. In this way, however, reliable compliance with the exhaust gas limit values is not guaranteed.
  • the object of the invention is to provide a method for the regeneration of a NOx storage catalytic converter which ensures reliable compliance with the exhaust gas limit values and enables improved, needs-based regeneration of the NOx storage catalytic converter.
  • the object of the invention is achieved by the features of claim 1.
  • An essential advantage of the invention resides in the fact that the regeneration of the NOx storage catalytic converter is started as a function of the NOx emissions. In this way, reliable compliance with the exhaust gas limit values is ensured.
  • FIG. 1 shows a schematic arrangement of an internal combustion engine with a NOx storage catalytic converter
  • FIG. 2 is a schematic representation of the invention
  • Figure 3 shows a method for determining NOx emissions
  • FIG. 4 shows a method for determining the loading of the storage catalytic converter.
  • FIG. 1 shows an arrangement in which the inventive method is applied.
  • An internal combustion engine 2 is connected to an intake tract 1 and an exhaust tract 3.
  • the internal combustion engine 2 comprises an injection system with a valve arrangement and a cooling circuit.
  • the exhaust tract 3 leads to a NOx storage catalytic converter 4 to which a temperature sensor 13 is connected.
  • the NOx storage catalytic converter 4 is referred to as storage catalytic converter 4 in the following.
  • a control device 5 with a memory 6 is shown, the control device 5 via a load measurement line 12 with the load measurement device 11, via a temperature measurement line 10 with the temperature sensor 9, via a data and control line 8 with the internal combustion engine 2 and over a measuring line 7 with the temperature sensor 13 is connected.
  • a lambda probe 14 is introduced into the exhaust tract 3 in front of the storage catalytic converter 4 and connected to the control unit 5 via a second measuring line 15.
  • FIG. 2 schematically shows a method for determining the raw NOx emission NR.
  • the control unit 5 preferably checks one or more starting conditions at program point 20 before further calculations are carried out. It is first checked whether the internal combustion engine is in the “start” operating state. If this is the case, no further calculation is carried out, but is waited until the internal combustion engine 2 has left the "start” operating state. It is also checked whether there is a post-start control of the internal combustion engine 2. If this is the case, further calculations are waited until the post-start control has ended. In addition, a check is carried out to determine whether the catalyst temperature KT is greater than a predetermined minimum value. If this is the case, then it is checked whether the air ratio in the exhaust gas upstream of the catalytic converter has a value greater than 1. If the conditions mentioned are met, the program branches to program item 21. In a simple embodiment, the conditions queried at program point 20 can also be dispensed with.
  • program point 22 is followed by a query as to whether the NOx emission NA that leaves the storage catalytic converter 4 is greater than a predetermined limit value NE. If this is the case, the program branches to program item 23.
  • the NOx emission NA is calculated using the following formula:
  • NA (n) NRK (n) • TA • (l-KEK (n)) • (1-NO)
  • NRK is the corrected raw emission
  • TA is the predetermined time interval between the times n and n + 1
  • KEK is the corrected storage efficiency
  • NO is a correction factor that takes into account the proportion of NOx emissions that is chemically reduced by the storage catalytic converter 4 becomes.
  • the raw NOx emission NR is used instead of the corrected raw NOx emission NRK.
  • the question is asked whether the NOx emission NA (n) exceeds the limit value NG. If this is not the case, the program branches back to program item 20. However, if the NOx emission NA (n) exceeds the limit value NG, the regeneration of the storage catalytic converter 4 is initiated at program point 23, in which a fuel / air mixture is supplied to the internal combustion engine 2, which mixture in the exhaust tract 3 in front of the storage catalytic converter 4 Air number less than 1 leads. The program then branches back to program point 20.
  • FIG. 3 shows individual steps of program point 21 for calculating the raw NOx emission NR.
  • program point 30 there is a query as to whether the air ratio ⁇ measured in the exhaust tract 3 upstream of the storage catalyst 4 is greater than a predetermined starting value LS, for example 1.0. If not
  • the program branches back to program item 20. If, however, the query at program point 30 reveals that the air ratio ⁇ is greater than the predetermined starting value LS, then the crude NOx emission mass NR is read out from a load and speed-dependent first map at program point 31.
  • the first map is stored in memory 6.
  • an improvement of the method according to the invention is achieved by carrying out at least one of the program steps 32, 33, 34 or 35.
  • an ignition angle correction factor KZ is calculated for a correction of the raw NOx emission mass NR, taking into account the parameter ignition angle.
  • the predetermined target ignition angle is first read from the memory 6 from a second characteristic diagram, which contains a target ignition angle ZS as a function of the load and the speed, in accordance with the load and the speed of the internal combustion engine 2, and the current ignition angle ZG is measured .
  • a correction factor KF is read out of the memory 6 from a third map depending on the load and the speed of the internal combustion engine 2.
  • the ignition angle correction factor KZ is then calculated using the following formula:
  • KZ 1 + KF • (ZG - ZS) calculated.
  • the program then branches to program point 36 or to program point 33.
  • an air ratio correction factor KL is determined for a correction of the raw NOx emission NR, in which the air ratio ⁇ is taken into account.
  • a target air number LS specified in accordance with the load and the speed of the internal combustion engine 2 is read out from a fourth characteristic diagram as a function of the load and the speed.
  • the actual air ratio LG is measured.
  • a differential air ratio LD is then calculated using the following formula:
  • an air ratio correction factor KL is read from a fifth map in the memory 6.
  • the program then branches to either item 36 or item 34.
  • a temperature correction factor FT is calculated, in which the cooling water temperature TL and the suction air temperature TA are taken into account.
  • a temperature correction factor FT is read from a sixth map, which is stored in the memory 6. The program then branches to program point 36 or to program point 35.
  • a correction factor for the valve overlap is calculated for a correction of the raw NOx emission NR, taking into account the valve overlap during the injection.
  • a setpoint VS as a function of the load and the speed for the valve overlap is read out from a seventh characteristic diagram, which is stored in the memory 6, and the difference to a measured value VG for the valve overlap is calculated.
  • the program then branches to point 36.
  • NRK NR • KZ • KL • FT • KV.
  • NRK NR • KT.
  • FIG. 4 schematically shows the calculation of the loading state of the storage catalytic converter 4, which is preferably used as the starting condition for a regeneration phase for the storage catalytic converter 4.
  • the control unit 5 calculates the storage efficiency KE of the storage catalytic converter 4.
  • the storage efficiency KE is read out from a ninth characteristic map in the storage 6 as a function of the intake air mass LM and the loading efficiency KB of the storage catalytic converter.
  • the storage capacity KS is read from a tenth map in the memory 6, which depends on the catalyst temperature! KT and the number of regeneration phases SZ that have already taken place.
  • the regeneration phases in which a rich mixture is fed to the storage catalytic converter 4 in order to reduce the NOx storage are counted by the control unit 5 and stored in the storage 6 as a regeneration number.
  • the storage efficiency KE is preferably corrected as a function of the catalyst temperature KT and as a function of the charging cycles SZ which have already taken place, a correction value KS being read out from an eleventh characteristic diagram which depends on the charging cycles SZ which have already taken place and the catalyst temperature KT, and the storage efficiency KE thus is multiplied:
  • KA (n) KA (n-l) + NRK (n) • TA • KEK (n) • 1 (1-N0),
  • the query is made as to whether the current load KA is greater than a predetermined minimum load KAM. If this is the case, a regeneration phase for the NOx storage catalytic converter 4 is started at program point 43. If this is not the case, the program branches back to program item 40. After the regeneration phase has been carried out, the program branches back from program point 43 to program point 40.
  • An advantageous development of the invention is based on carrying out a load determination of the storage catalytic converter 4 during a regeneration phase in order to terminate the regeneration phase in good time.
  • the loading of the storage catalytic converter 4 is decremented by a value KD and the regeneration phase is ended when the catalytic converter loading KA falls below a predetermined threshold value.
  • the decrement is read from a twelfth characteristic diagram, which depends on the intake air mass LM and the air ratio LG measured in front of the storage catalytic converter 4 in the exhaust tract 3.
  • a memory field is provided in the memory 6, in which the number of regeneration phases that have elapsed so far are counted and stored as a non-volatile regeneration number.
  • a bit is provided in the memory 6 which can be assigned zero or one, with a zero setting the regeneration number being set to zero and the regeneration phases starting from zero being counted up again .
  • a more precise counting of the regeneration phases is achieved by also counting the regeneration phases which are caused by a rich fuel mixture during unsteady operation, i.e. e.g. at acceleration.
  • the regeneration phases are detected ( ⁇ ⁇ 1) with the lambda probe 14 in the exhaust tract 3 in front of the storage catalytic converter 4 and counted by the control unit 5 and stored in the storage 6 as a regeneration number.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Health & Medical Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Exhaust Gas After Treatment (AREA)

Abstract

In the process for regenerating an NOx storage catalytic converter, a regeneration phase is initiated when the converter emits more than a predetermined threshold quantity of NOx compounds. NOx emission is calculated on the basis of load, engine speed and other operating conditions in the internal combustion engine.

Description

Beschreibungdescription
Verfahren zur Regeneration eines NOx-SpeicherkatalysatorsProcess for the regeneration of a NOx storage catalytic converter
Die Erfindung betrifft ein Verfahren zur Regeneration eines NOx-Speicherkatalysators gemäß dem Oberbegriff des AnspruchsThe invention relates to a method for regenerating a NOx storage catalytic converter according to the preamble of the claim
1.1.
NOx-Speicherkatalysatoren werden verwendet, um bei Motorkon- zepten mit magerer Verbrennung die geforderten Abgasgrenzwer¬ te einhalten zu können. Die NOx-Speicherkatalysatoren absor¬ bieren die bei magerer Verbrennung erzeugten NOx-Verbin- dungen. Da jedoch die Speicherkapazität eines NOx-Speicher¬ katalysators begrenzt ist, ist es notwendig eine bedarfsge- rechte Regeneration des Speicherkatalysators durchzuführen. Dies erfolgt durch kurzzeitiges Betreiben des Motors mit ei¬ nem fetten Gemisch, wodurch die gespeicherten NOx-Verbin- dungen im Katalysator abgebaut werden.NOx storage catalytic converters are used in order to be able to comply with the required exhaust gas limit values in engine concepts with lean combustion. The NOx storage catalytic converters absorb the NOx compounds generated during lean combustion. However, since the storage capacity of a NOx storage catalytic converter is limited, it is necessary to regenerate the storage catalytic converter as required. This is done by briefly operating the engine with a rich mixture, as a result of which the stored NOx compounds in the catalytic converter are broken down.
Aus der EP 0 597 106 AI ist bereits ein Verfahren zur Regene¬ ration eines NOx-Speicherkatalysators bekannt, bei dem die vom Speicherkatalysator absorbierte Menge an NOx-Verbindungen in Abhängigkeit von der angesaugten Luft und der Motorlast berechnet wird. Bei Überschreiten einer vorgegebenen Grenz- menge von im NOx-Speicherkatalysator gespeicherten NOx-Ver¬ bindungen wird der Brennkraftmaschine ein fettes Gemisch zur Regeneration des Speicherkatalysators zugeführt. Auf diese Weise ist jedoch ein zuverlässiges Einhalten der Abgasgrenz¬ werte nicht gewährleistet.A method for the regeneration of a NOx storage catalytic converter is already known from EP 0 597 106 A1, in which the amount of NOx compounds absorbed by the storage catalytic converter is calculated as a function of the intake air and the engine load. When a predetermined limit quantity of NOx compounds stored in the NOx storage catalytic converter is exceeded, the internal combustion engine is supplied with a rich mixture for regeneration of the storage catalytic converter. In this way, however, reliable compliance with the exhaust gas limit values is not guaranteed.
Die Aufgabe der Erfindung beruht darin, ein Verfahren zur Re¬ generation eines NOx-Speicherkatalysators zur Verfügung zu stellen, das eine sichere Einhaltung der Abgasgrenzwerte ge¬ währleistet und eine verbesserte, bedarfsgerechte Regenerati- on des NOx-Speicherkatalysators ermöglicht. Die Aufgabe der Erfindung wird durch die Merkmale des An¬ spruchs 1 gelöst. Ein wesentlicher Vorteil der Erfindung be¬ ruht darin, daß die Regeneration des NOx-Speicherkatalysators in Abhängigkeit vom NOx-Ausstoß gestartet wird. Auf diese Weise ist eine sichere Einhaltung der Abgasgrenzwerte gewähr¬ leistet .The object of the invention is to provide a method for the regeneration of a NOx storage catalytic converter which ensures reliable compliance with the exhaust gas limit values and enables improved, needs-based regeneration of the NOx storage catalytic converter. The object of the invention is achieved by the features of claim 1. An essential advantage of the invention resides in the fact that the regeneration of the NOx storage catalytic converter is started as a function of the NOx emissions. In this way, reliable compliance with the exhaust gas limit values is ensured.
Vorteilhafte Ausbildungen und Verbesserungen der Erfindung sind in den Unteransprüchen angegeben.Advantageous developments and improvements of the invention are specified in the subclaims.
Die Erfindung wird anhand der Figuren näher erläutert; es zeigen:The invention is illustrated by the figures; show it:
Figur 1 eine schematische Anordnung einer Brennkraftmaschine mit einem NOx-Speicherkatalysator,FIG. 1 shows a schematic arrangement of an internal combustion engine with a NOx storage catalytic converter,
Figur 2 eine schematische Darstellung des erfindungsgemäßenFigure 2 is a schematic representation of the invention
Verfahrens,Process,
Figur 3 ein Verfahren zur Bestimmung des NOx-Ausstoßes undFigure 3 shows a method for determining NOx emissions and
Figur 4 ein Verfahren zur Bestimmung der Beladung des Spei- cherkatalysators.FIG. 4 shows a method for determining the loading of the storage catalytic converter.
Figur 1 zeigt eine Anordnung, bei der das erfindungsgemäße Verfahren angewendet wird. Eine Brennkraftmaschine 2 ist mit einem Ansaugtrakt 1 und einem Abgastrakt 3 verbunden. Im An- saugtrakt 1 ist ein Temperaturfühler 9 und eine Lastmeßein¬ richtung 11, beispielsweise ein Luftmassenmesser oder ein Druckmesser, angeordnet. Die Brennkraftmaschine 2 umfaßt eine Einspritzanlage mit einer Ventilanordnung und einen Kühl- kreislauf . Der Abgastrakt 3 führt zu einem NOx-Speicher- katalysator 4, an dem ein Temperatursensor 13 angeschlossen ist. Der NOx-Speicherkatalysator 4 wird im folgenden kurz als Speicherkatalysator 4 bezeichnet. Weiterhin ist ein Steuerge¬ rät 5 mit einem Speicher 6 dargestellt, wobei das Steuergerät 5 über eine Lastmeßleitung 12 mit der Lastmeßeinrichtung 11, über eine Temperaturmeßleitung 10 mit dem Temperaturfühler 9, über eine Daten- und Steuerleitung 8 mit der Brennkraftma¬ schine 2 und über eine Meßleitung 7 mit dem Temperatursensor 13 verbunden ist . Zudem ist eine Lambdasonde 14 in den Ab¬ gastrakt 3 vor dem Speicherkatalysator 4 eingebracht und über eine zweite Meßleitung 15 mit dem Steuergerät 5 verbunden.Figure 1 shows an arrangement in which the inventive method is applied. An internal combustion engine 2 is connected to an intake tract 1 and an exhaust tract 3. A temperature sensor 9 and a load measuring device 11, for example an air mass meter or a pressure meter, are arranged in the intake tract 1. The internal combustion engine 2 comprises an injection system with a valve arrangement and a cooling circuit. The exhaust tract 3 leads to a NOx storage catalytic converter 4 to which a temperature sensor 13 is connected. The NOx storage catalytic converter 4 is referred to as storage catalytic converter 4 in the following. Furthermore, a control device 5 with a memory 6 is shown, the control device 5 via a load measurement line 12 with the load measurement device 11, via a temperature measurement line 10 with the temperature sensor 9, via a data and control line 8 with the internal combustion engine 2 and over a measuring line 7 with the temperature sensor 13 is connected. In addition, a lambda probe 14 is introduced into the exhaust tract 3 in front of the storage catalytic converter 4 and connected to the control unit 5 via a second measuring line 15.
Figur 2 zeigt schematisch ein Verfahren zur Bestimmung der NOx-Rohemission NR. Das Steuergerät 5 überprüft bei Programm¬ punkt 20 vorzugsweise eine oder mehrere Startbedingungen, be¬ vor weitere Berechnungen erfolgen. Dabei wird zuerst über¬ prüft, ob sich die Brennkraftmaschine im Betriebszustand "Start" befindet. Ist dies der Fall, so wird keine weitere Berechnung durchgeführt, sondern abgewartet, bis die Brenn¬ kraftmaschine 2 den Betriebszustand "Start" verlassen hat. Weiterhin wird überprüft, ob eine Nachstartsteuerung der Brennkraftmaschine 2 vorliegt. Ist dies der Fall, wird mit weiteren Berechnungen so lange gewartet, bis die Nachstart¬ steuerung beendet ist. Zudem wird noch überprüft, ob die Ka¬ talysatortemperatur KT größer als ein vorgegebener Mindest- wert ist. Ist dies der Fall, so wird noch überprüft, ob die Luftzahl im Abgas vor dem Katalysator einen Wert größer als 1 aufweist. Sind die genannten Bedingungen erfüllt, so wird nach Programmpunkt 21 verzweigt. In einer einfachen Ausfüh¬ rung kann auch auf die bei Programmpunkt 20 abgefragten Be¬ dingungen verzichtet werden.FIG. 2 schematically shows a method for determining the raw NOx emission NR. The control unit 5 preferably checks one or more starting conditions at program point 20 before further calculations are carried out. It is first checked whether the internal combustion engine is in the “start” operating state. If this is the case, no further calculation is carried out, but is waited until the internal combustion engine 2 has left the "start" operating state. It is also checked whether there is a post-start control of the internal combustion engine 2. If this is the case, further calculations are waited until the post-start control has ended. In addition, a check is carried out to determine whether the catalyst temperature KT is greater than a predetermined minimum value. If this is the case, then it is checked whether the air ratio in the exhaust gas upstream of the catalytic converter has a value greater than 1. If the conditions mentioned are met, the program branches to program item 21. In a simple embodiment, the conditions queried at program point 20 can also be dispensed with.
Bei Programmpunkt 21 wird die Berechnung der NOx-Rohemission NR oder der korrigierten NOx-Rohemission NRK durchgeführt . Dies wird anhand eines Unterprogrammes, das in Figur 3 darge¬ stellt ist, ausgeführt.At program point 21, the calculation of the raw NOx emission NR or the corrected raw NOx emission NRK is carried out. This is carried out using a subroutine which is shown in FIG. 3.
Nach Programmpunkt 21 folgt bei Programmpunkt 22 die Abfrage, ob die NOx-Emission NA, die den Speicherkatalysator 4 ver¬ läßt, größer als ein vorgegebener Grenzwert NE ist. Ist dies der Fall, so wird nach Programmpunkt 23 verzweigt. Die NOx- Emission NA wird nach folgender Formel berechnet :After program point 21, program point 22 is followed by a query as to whether the NOx emission NA that leaves the storage catalytic converter 4 is greater than a predetermined limit value NE. If this is the case, the program branches to program item 23. The NOx emission NA is calculated using the following formula:
NA (n) = NRK (n) • TA • (l-KEK(n)) • (1-NO) wobei NRK die korrigierte Rohemission, TA das vorgegebene Zeitintervall zwischen den Zeitpunkten n und n+1, KEK den korrigierten Speicherwirkungsgrad, und NO einen Korrekturfak¬ tor darstellt, der den Anteil der NOx-Emissionen berücksich- tigt, der durch den Speicherkatalysator 4 chemisch reduziert wird. In einer einfachen Ausbildung der Erfindung wird an¬ stelle der korrigierten NOx-Rohemission NRK die NOx-Roh- emission NR verwendet werden.NA (n) = NRK (n) • TA • (l-KEK (n)) • (1-NO) where NRK is the corrected raw emission, TA is the predetermined time interval between the times n and n + 1, KEK is the corrected storage efficiency, and NO is a correction factor that takes into account the proportion of NOx emissions that is chemically reduced by the storage catalytic converter 4 becomes. In a simple embodiment of the invention, the raw NOx emission NR is used instead of the corrected raw NOx emission NRK.
Nach Berechnung der NOx-Emission NA(n) erfolgt die Abfrage, ob die NOx-Emission NA(n) den Grenzwert NG überschreitet. Ist dies nicht der Fall, so wird nach Programmpunkt 20 zurückver¬ zweigt. Überschreitet jedoch die NOx-Emission NA(n) den Grenzwert NG, so wird bei Programmpunkt 23 die Regeneration des Speicherkatalysators 4 eingeleitet, in der der Brenn¬ kraftmaschine 2 ein Kraftstoff/Luftgemisch zugeführt wird, das im Abgastrakt 3 vor dem Speicherkatalysator 4 zu einer Luftzahl kleiner als 1 führt. Anschließend wird zu Programm¬ punkt 20 zurückverzweigt.After calculating the NOx emission NA (n), the question is asked whether the NOx emission NA (n) exceeds the limit value NG. If this is not the case, the program branches back to program item 20. However, if the NOx emission NA (n) exceeds the limit value NG, the regeneration of the storage catalytic converter 4 is initiated at program point 23, in which a fuel / air mixture is supplied to the internal combustion engine 2, which mixture in the exhaust tract 3 in front of the storage catalytic converter 4 Air number less than 1 leads. The program then branches back to program point 20.
Figur 3 zeigt einzelne Schritte des Programmpunktes 21 zur Berechnung der NOx-Rohemission NR. Bei Programmpunkt 30 er¬ folgt die Abfrage, ob die im Abgastrakt 3 vor dem Speicherka¬ talysator 4 gemessene Luftzahl λ größer als ein vorgegebener Startwert LS, beispielsweise 1,0 ist. Ist dies nicht derFIG. 3 shows individual steps of program point 21 for calculating the raw NOx emission NR. At program point 30 there is a query as to whether the air ratio λ measured in the exhaust tract 3 upstream of the storage catalyst 4 is greater than a predetermined starting value LS, for example 1.0. If not
Fall, so wird nach Programmpunkt 20 zurückverzweigt. Ergibt jedoch die Abfrage bei Programmpunkt 30, daß die Luftzahl λ größer als der vorgegebene Startwert LS ist, so wird bei Pro¬ grammpunkt 31 aus einem last- und drehzahlabhängigen ersten Kennfeld die NOx-Rohemissionsmasse NR ausgelesen. Das erste Kennfeld ist im Speicher 6 abgelegt. In einer einfachen Aus¬ führung der Erfindung kann nach der Abarbeitung des Programm¬ punktes 31 zu Programmpunkt 22 zurückverzweigt werden. Eine Verbesserung des erfindungsgemäßen Verfahrens wird jedoch da- durch erreicht, daß mindestens einer der Programmschritte 32, 33, 34 oder 35 durchgeführt wird. Bei Programmpunkt 32 wird ein Zündwinkelkorrekturfaktor KZ für eine Korrektur der NOx-Rohemissionsmasse NR, unter Be¬ rücksichtigung des Parameters Zündwinkel berechnet. Dazu wird zuerst aus dem Speicher 6 aus einem zweiten Kennfeld, das in Abhängikeit von der Last und der Drehzahl einen Sollzündwin¬ kel ZS enthält, entsprechend der Last und der Drehzahl der Brennkraftmaschine 2 der vorgegebene Sollzündwinkel ausgele¬ sen und der aktuelle Zündwinkel ZG wird gemessen. Zudem wird aus einem dritten Kennfeld in Abhängikeit von der Last und der Drehzahl der Brennkraftmaschine 2 ein Korrekturfaktor KF aus dem Speicher 6 ausgelesen. Anschließend wird der Zündwin¬ kelkorrekturfaktor KZ nach folgender Formel berechnet :If so, the program branches back to program item 20. If, however, the query at program point 30 reveals that the air ratio λ is greater than the predetermined starting value LS, then the crude NOx emission mass NR is read out from a load and speed-dependent first map at program point 31. The first map is stored in memory 6. In a simple embodiment of the invention, after program point 31 has been processed, it is possible to branch back to program point 22. However, an improvement of the method according to the invention is achieved by carrying out at least one of the program steps 32, 33, 34 or 35. At program point 32, an ignition angle correction factor KZ is calculated for a correction of the raw NOx emission mass NR, taking into account the parameter ignition angle. For this purpose, the predetermined target ignition angle is first read from the memory 6 from a second characteristic diagram, which contains a target ignition angle ZS as a function of the load and the speed, in accordance with the load and the speed of the internal combustion engine 2, and the current ignition angle ZG is measured . In addition, a correction factor KF is read out of the memory 6 from a third map depending on the load and the speed of the internal combustion engine 2. The ignition angle correction factor KZ is then calculated using the following formula:
KZ = 1+KF • (ZG - ZS) berechnet.KZ = 1 + KF • (ZG - ZS) calculated.
Anschließend wird nach Programmpunkt 36 oder nach Programm¬ punkt 33 verzweigt.The program then branches to program point 36 or to program point 33.
Bei Programmpunkt 33 wird ein Luftzahlkorrekturfaktor KL für eine Korrkektur der NOx-Rohemission NR ermittelt, bei dem die Luftzahl λ berücksichtigt wird. Dazu wird aus einem vierten Kennfeld in Abhängikeit von der Last und der Drehzahl eine entsprechend der Last und der Drehzahl der Brennkraftmaschine 2 vorgegebe Solluftzahl LS ausgelesen. Zudem wird die tat- sächliche Luftzahl LG gemessen. Anschließend wird eine Diffe- renzluftzahl LD nach folgender Formel berechnet:At program point 33, an air ratio correction factor KL is determined for a correction of the raw NOx emission NR, in which the air ratio λ is taken into account. For this purpose, a target air number LS specified in accordance with the load and the speed of the internal combustion engine 2 is read out from a fourth characteristic diagram as a function of the load and the speed. In addition, the actual air ratio LG is measured. A differential air ratio LD is then calculated using the following formula:
LD = LS - LG berechnet.LD = LS - LG calculated.
Anhand der Differenzluftzahl LD und der Motorlast ML wird aus einem fünften Kennfeld im Speicher 6 ein Luftzahlkorrektur¬ faktor KL ausgelesen.On the basis of the differential air ratio LD and the engine load ML, an air ratio correction factor KL is read from a fifth map in the memory 6.
Anschließend wird entweder nach Programmpunkt 36 oder nach Programmpunkt 34 verzweigt.The program then branches to either item 36 or item 34.
Bei Programmpunkt 34 wird ein Temperaturkorrekturfaktor FT berechnet, bei dem die Kühlwassertemperatur TL und die An- sauglufttemperatur TA berücksichtigt werden. Anhand der Kühl- wassertemperatur TL und der Ansauglufttemperatur TA wird aus einem sechsten Kennfeld, das im Speicher 6 abgelegt ist, ein Temperaturkorrekturfaktor FT ausgelesen. Anschließend wird nach Programmpunkt 36 oder nach Programmpunkt 35 verzweigt.At program point 34, a temperature correction factor FT is calculated, in which the cooling water temperature TL and the suction air temperature TA are taken into account. On the basis of the cooling water temperature TL and the intake air temperature TA, a temperature correction factor FT is read from a sixth map, which is stored in the memory 6. The program then branches to program point 36 or to program point 35.
Bei Programmpunkt 35 wird ein Korrekturfaktor für die Ventil- Überschneidung für eine Korrektur der NOx-Rohemission NR un¬ ter Berücksichtigung der Ventilüberschneidung bei der Ein- spritzung berechnet. Dazu wird aus einem siebten Kennfeld, das im Speicher 6 abgelegt ist, ein Sollwert VS in Abhängig¬ keit von der Last und der Drehzahl für die Ventilüberschnei¬ dung ausgelesen und die Differenz zu einem gemessenen Wert VG für die Ventilüberschneidung berechnet. Aus der Differenz VD = VS - VG wird aus einem achten Kennfeld in Abhängigkeit von der Motorlast ML und der Differenz VD der Ventilüberschnei¬ dung eine Korrekturfaktor KV für die Ventilüberschneidung ausgelesen. Anschließend wird nach Programmpunkt 36 ver¬ zweigt .At program point 35, a correction factor for the valve overlap is calculated for a correction of the raw NOx emission NR, taking into account the valve overlap during the injection. For this purpose, a setpoint VS as a function of the load and the speed for the valve overlap is read out from a seventh characteristic diagram, which is stored in the memory 6, and the difference to a measured value VG for the valve overlap is calculated. A correction factor KV for the valve overlap is read out from the difference VD = VS-VG from an eighth characteristic diagram as a function of the engine load ML and the difference VD of the valve overlap. The program then branches to point 36.
Bei Programmpunkt 36 wird die Korrektur der NOx-Rohemission NR durchgeführt. In Abhängigkeit von den durchgeführten Pro¬ grammpunkten 32 - 35 werden die darin berechneten Korrektur¬ faktoren berücksichtigt.At program point 36, the correction of the raw NOx emission NR is carried out. Depending on the program points 32-35 carried out, the correction factors calculated therein are taken into account.
Werden alle in Figur 3 dargestellten Programmpunkte durchge¬ führt, so ergibt sich für die korrigierte NOx-Rohemission NRK folgender Wert :If all the program points shown in FIG. 3 are carried out, the following value results for the corrected raw NOx emission NRK:
NRK = NR • KZ • KL • FT • KV.NRK = NR • KZ • KL • FT • KV.
Ein Fachmann wird bei der Berechnung der korrigierten NOx- Rohemission NRK die Anzahl der zu berücksichtigenden Korrek¬ turfaktoren entsprechend den Gegebenheiten wählen, so daß in einfachen Verfahren die NOx-Rohemission z.B. nur mit Tempera¬ turkorrekturfaktor KT korrigiert wird, so daß sich für die korrigierte NOx-Rohemission NRK folgende Berechnung ergibt: NRK = NR • KT.When calculating the corrected raw NOx emission NRK, a person skilled in the art will choose the number of correction factors to be taken into account in accordance with the circumstances, so that in simple processes the raw NOx emission is corrected, for example, only with a temperature correction factor KT, so that the corrected raw NOx emission NRK results in the following calculation: NRK = NR • KT.
Nach der Berechnung der korrigierten NOx-Rohemission NRK wird nach Programmpunkt 22 zurückverzweigt.After calculating the corrected raw NOx emission NRK, the program branches back to item 22.
In Figur 4 ist schematisch die Berechnung des Beladungszu¬ standes des Speicherkatalysators 4 dargestellt, der vorzugs¬ weise als Startbedingung für eine Regenerationsphase für den Speicherkatalysator 4 verwendet wird. Bei Programmpunkt 40 berechnet das Steuergerät 5 den Speicherwirkungsgrad KE des Speicherkatalysators 4. Der Speicherwirkungsgrad KE wird in Abhängigkeit von der angesaugten Luftmasse LM und dem Bela¬ dungsgrad KB des Speicherkatalysators aus einem neunten Kenn¬ feld im Speicher 6 ausgelesen. Der Beladungsgrad KB des Spei- cherkatalysators berechnet sich aus der aktuellen Beladung KA bezogen auf die Speicherkapazität KS des Speicherkatalysators 4 durch folgende Formel: KB = KA/KS.FIG. 4 schematically shows the calculation of the loading state of the storage catalytic converter 4, which is preferably used as the starting condition for a regeneration phase for the storage catalytic converter 4. At program point 40, the control unit 5 calculates the storage efficiency KE of the storage catalytic converter 4. The storage efficiency KE is read out from a ninth characteristic map in the storage 6 as a function of the intake air mass LM and the loading efficiency KB of the storage catalytic converter. The degree of loading KB of the storage catalytic converter is calculated from the current loading KA based on the storage capacity KS of the storage catalytic converter 4 using the following formula: KB = KA / KS.
Die Speicherkapazität KS wird aus einem zehnten Kennfeld im Speicher 6 ausgelesen, das von der Katalysatortemperatur !KT und der bereits erfolgten Anzahl von Regenerationsphasen SZ abhängt. Die Regenerationsphasen, bei denen dem Speicherkata¬ lysators 4 fettes Gemisch zugeführt wird, um die NOx-Spei- cherung abzubauen, werden vom Steuergerät 5 gezählt und im Speicher 6 als Regenerationszahl abgelegt.The storage capacity KS is read from a tenth map in the memory 6, which depends on the catalyst temperature! KT and the number of regeneration phases SZ that have already taken place. The regeneration phases in which a rich mixture is fed to the storage catalytic converter 4 in order to reduce the NOx storage are counted by the control unit 5 and stored in the storage 6 as a regeneration number.
Der Speicherwirkungsgrad KE wird vorzugsweise in Abhängigkeit von der Katalysatortemperatur KT und in Abhängigkeit von den bereits erfolgten Ladezyklen SZ korrigiert, wobei aus einem elften Kennfeld, das von den bereits erfolgten Ladezyklen SZ und der Katalysatortemperatur KT abhängt, ein Korrekturwert KS ausgelesen und der Speicherwirkungsgrad KE damit multipli¬ ziert wird:The storage efficiency KE is preferably corrected as a function of the catalyst temperature KT and as a function of the charging cycles SZ which have already taken place, a correction value KS being read out from an eleventh characteristic diagram which depends on the charging cycles SZ which have already taken place and the catalyst temperature KT, and the storage efficiency KE thus is multiplied:
KEK = KE • KS,KEK = KE • KS,
wobei KEK den korrigierten Speicherwirkungsgrad darstellt. Anschließend wird bei Programmpunkt 41 die aktuelle Beladung KA des Speicherkatalysators 4 nach folgender Formel berech¬ net:where KEK represents the corrected storage efficiency. The current load KA of the storage catalytic converter 4 is then calculated at program point 41 using the following formula:
KA (n) = KA (n-l) + NRK (n) • TA • KEK (n) • 1(1-N0),KA (n) = KA (n-l) + NRK (n) • TA • KEK (n) • 1 (1-N0),
wobei mit KA (n) die Beladung zum Zeitpunkt n, mit KA (n-l) die Beladung zu dem Zeitpunkt n-l, mit NRK die korrigierte NOx-Rohemission, mit TA der Zeitabstand zwischen zwei Berech¬ nungszeitpunkten n und n-l, mit KEK der korrigierte Speicher¬ wirkungsgrad und mit NO ein Korrekturfaktor bezeichnet ist, der den Anteil der NOx-Emissionen, die durch den Speicherka¬ talysator 4 chemisch reduziert werden, berücksichtigt.whereby with KA (n) the loading at time n, with KA (nl) the loading at time nl, with NRK the corrected raw NOx emission, with TA the time interval between two calculation times n and nl, with KEK the corrected memory ¬ efficiency and with NO is a correction factor that takes into account the proportion of NOx emissions that are chemically reduced by the storage catalyst 4.
Anschließend erfolgt bei Programmpunkt 42 die Abfrage, ob die aktuelle Beladung KA größer als eine vorgegebene Mindestbela¬ dung KAM ist. Ist dies der Fall, so wird bei Programmpunkt 43 eine Regenerationsphase für den NOx-Speicherkatalysator 4 ge- startet. Ist dies nicht der Fall, so wird nach Programmpunkt 40 zurückverzweigt. Nach Durchführung der Regenerationsphase wird von Programmpunkt 43 nach Programmpunkt 40 zurückver¬ zweigt.Subsequently, at program point 42, the query is made as to whether the current load KA is greater than a predetermined minimum load KAM. If this is the case, a regeneration phase for the NOx storage catalytic converter 4 is started at program point 43. If this is not the case, the program branches back to program item 40. After the regeneration phase has been carried out, the program branches back from program point 43 to program point 40.
Eine vorteilhafte Weiterbildung der Erfindung beruht darin, eine Beladungsermittlung des Speicherkatalysators 4 während einer Regenerationsphase durchzuführen, um die Regenerati¬ onsphase rechtzeitig abzubrechen. Während der Regenerati¬ onsphase wird die Beladung des Speicherkatalysators 4 um ei- nen Wert KD dekrementiert und die Regenerationsphase wird be¬ endet, wenn die Katalysatorbeladung KA unter einen vorgegebe¬ nen Schwellwert fällt. Das Dekrement wird aus einem zwölften Kennfeld ausgelesen, das von der Ansaugluftmasse LM und der vor dem Speicherkatalysator 4 im Abgastrakt 3 gemessenen Luftzahl LG abhängt. Die aktuelle Katalysatorbeladung wird in festgelegten Zeitabständen wie folgt berechnet: KA (n) = KA (n-l) - KD, wobei KD das aus dem Kennfeld ausgelesene Dekrement, KA (n) die Beladung zum Zeitpunkt n und KA(n-l) die Beladung zum Zeitpunkt n-l darstellt.An advantageous development of the invention is based on carrying out a load determination of the storage catalytic converter 4 during a regeneration phase in order to terminate the regeneration phase in good time. During the regeneration phase, the loading of the storage catalytic converter 4 is decremented by a value KD and the regeneration phase is ended when the catalytic converter loading KA falls below a predetermined threshold value. The decrement is read from a twelfth characteristic diagram, which depends on the intake air mass LM and the air ratio LG measured in front of the storage catalytic converter 4 in the exhaust tract 3. The current catalyst loading is calculated at specified time intervals as follows: KA (n) = KA (nl) - KD, where KD represents the decrement read from the map, KA (n) the load at time n and KA (nl) the load at time nl.
In dem Speicher 6 ist ein Speicherfeld vorgesehen, in dem die Anzahl der bisher abgelaufenen Regenerationsphasen gezählt und nichtflüchtig als Regenerationszahl abgespeichert werden. Um jedoch den Austausch eines Speicherkatalysators 4 zu be¬ rücksichtigen, ist im Speicher 6 ein Bit vorgesehen, das mit Null oder Eins belegt werden kann, wobei bei einer Belegung mit Null die Regenerationszahl auf Null festgelegt wird und die Regenerationsphasen von Null ausgehend wieder hochgezählt werden.A memory field is provided in the memory 6, in which the number of regeneration phases that have elapsed so far are counted and stored as a non-volatile regeneration number. However, in order to take into account the replacement of a storage catalytic converter 4, a bit is provided in the memory 6 which can be assigned zero or one, with a zero setting the regeneration number being set to zero and the regeneration phases starting from zero being counted up again .
Eine genauere Zählung der Regenerationsphasen wird dadurch erreicht, daß auch die Regenerationsphasen mitgezählt werden, die durch ein fettes Kraftstoffgemisch bei Instationärbe- trieb, d.h. z.B. bei Beschleunigung, durchgeführt werden.A more precise counting of the regeneration phases is achieved by also counting the regeneration phases which are caused by a rich fuel mixture during unsteady operation, i.e. e.g. at acceleration.
Die Regenerationsphasen werden beispielsweise mit der Lam- dasonde 14 im Abgastrakt 3 vor dem Speicherkatalysator 4 de¬ tektiert (λ<l) und von dem Steuergerät 5 gezählt und als Re¬ generationszahl im Speicher 6 abgespeichert. The regeneration phases are detected (λ <1) with the lambda probe 14 in the exhaust tract 3 in front of the storage catalytic converter 4 and counted by the control unit 5 and stored in the storage 6 as a regeneration number.

Claims

Patentansprüche claims
1. Verfahren zur Regeneration eines NOx-Speicherkatalysators (4) , wobei abhängig von einem Betriebszustand des NOx- Speicherkatalysators (4) eine Regenerationsphase gestartet wird, bei der ein Kraftstoffgemisch der Brennkraftmaschine zugeführt wird, das einer Luftzahl kleiner als 1 vor dem NOx- Speicherkatalysator (4) entspricht, dadurch gekennzeichnet, daß der Betriebszustand mindestens einer Grenzmenge von NOx- Verbindungen entspricht, die vom NOx-Speicherkatalysator (4) ausgegeben wird.1. A method for the regeneration of a NOx storage catalytic converter (4), a regeneration phase being started depending on an operating state of the NOx storage catalytic converter (4), in which a fuel mixture is supplied to the internal combustion engine which has an air ratio less than 1 in front of the NOx storage catalytic converter (4), characterized in that the operating state corresponds to at least a limit quantity of NOx compounds, which is output by the NOx storage catalytic converter (4).
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Betriebszustand mindestens einer Grenzspeicherung von NOx-Verbindungen im NOx-Speicherkatalysator (4) entspricht.2. The method according to claim 1, characterized in that the operating state corresponds to at least one limit storage of NOx compounds in the NOx storage catalyst (4).
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die vom NOx-Speicherkatalysator (4) abgegebene Menge an NOx-Verbindungen aus mindestens einem Kennfeld ermittelt wird, das von der Last und/oder der Drehzahl der Brennkraftmaschine (1) abhängt.3. The method according to claim 1, characterized in that the amount of NOx compounds emitted by the NOx storage catalyst (4) is determined from at least one map, which depends on the load and / or the speed of the internal combustion engine (1).
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß die abgegebene Menge an NOx-Verbindungen in Abhängigkeit vom Zündwinkel und oder von der Luftzahl und/oder von der Kühlwassertemperatur und/oder von der Ansauglufttemperatur und/oder von einer Ventilüberschneidung korrigiert wird.4. The method according to claim 3, characterized in that the amount of NOx compounds released as a function of the ignition angle and or of the air ratio and / or of the Cooling water temperature and / or from the intake air temperature and / or from a valve overlap is corrected.
5. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß als Wert für die Grenzspeicherung der Beladungszustand des NOx-Speicherkatalysators (4) in Abhängigkeit vom Speicherwirkungsgrad des NOx-Speicherkatalysators (4) berechnet wird, wobei der Speicherwirkungsgrad abhängig von der Anzahl der bereits durchgeführten Regenerationsphasen korrigiert wird.5. The method according to claim 2, characterized in that the loading state of the NOx storage catalytic converter (4) is calculated as a value for the limit storage as a function of the storage efficiency of the NOx storage catalytic converter (4), the storage efficiency depending on the number of regeneration phases already carried out is corrected.
6. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Beladungszustand des NOx-Speicherkatalysators (4) während der Regenerationsphase überprüft wird und die Regenerationsphase unterbrochen wird, wenn der6. The method according to claim 1, characterized in that the loading state of the NOx storage catalyst (4) is checked during the regeneration phase and the regeneration phase is interrupted when the
Beladungszustand unter eine vorgegebene Mindestbeladung fällt. Load condition falls below a specified minimum load.
EP97914147A 1996-02-26 1997-02-13 PROCESS FOR REGENERATING AN NOx STORAGE CATALYTIC CONVERTER Ceased EP0822856A1 (en)

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DE1996107151 DE19607151C1 (en) 1996-02-26 1996-02-26 Regeneration of nitrogen oxide storage catalyst
DE19607151 1996-02-26
PCT/DE1997/000278 WO1997031704A1 (en) 1996-02-26 1997-02-13 PROCESS FOR REGENERATING AN NOx STORAGE CATALYTIC CONVERTER

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