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EP1307639B1 - Method and controller for operating a nitrogen oxide (nox) storage catalyst - Google Patents

Method and controller for operating a nitrogen oxide (nox) storage catalyst Download PDF

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Publication number
EP1307639B1
EP1307639B1 EP01956310A EP01956310A EP1307639B1 EP 1307639 B1 EP1307639 B1 EP 1307639B1 EP 01956310 A EP01956310 A EP 01956310A EP 01956310 A EP01956310 A EP 01956310A EP 1307639 B1 EP1307639 B1 EP 1307639B1
Authority
EP
European Patent Office
Prior art keywords
nox
msnonk
catalytic converter
storage catalytic
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.)
Expired - Lifetime
Application number
EP01956310A
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German (de)
French (fr)
Other versions
EP1307639A1 (en
Inventor
Eberhard Schnaibel
Klaus Winkler
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Robert Bosch GmbH
Original Assignee
Robert Bosch GmbH
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Publication of EP1307639A1 publication Critical patent/EP1307639A1/en
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Publication of EP1307639B1 publication Critical patent/EP1307639B1/en
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1438Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/146Introducing 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
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828Exhaust 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
    • F01N3/0842Nitrogen oxides
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828Exhaust 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
    • F01N3/0864Oxygen
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0871Regulation of absorbents or adsorbents, e.g. purging
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/021Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027Introducing 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
    • F02D41/0275Introducing 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
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1438Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/146Introducing 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
    • F02D41/1463Introducing 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
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1438Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/146Introducing 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
    • F02D41/1463Introducing 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
    • F02D41/1465Introducing 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
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D2200/00Input parameters for engine control
    • F02D2200/02Input parameters for engine control the parameters being related to the engine
    • F02D2200/08Exhaust gas treatment apparatus parameters
    • F02D2200/0806NOx storage amount, i.e. amount of NOx stored on NOx trap
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1401Introducing closed-loop corrections characterised by the control or regulation method
    • F02D41/1402Adaptive control
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/30Controlling fuel injection
    • F02D41/3011Controlling fuel injection according to or using specific or several modes of combustion
    • F02D41/3017Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used
    • F02D41/3023Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used a mode being the stratified charge spark-ignited mode
    • F02D41/3029Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used a mode being the stratified charge spark-ignited mode further comprising a homogeneous charge spark-ignited mode

Definitions

  • the present invention relates to a method for operating a nitrogen oxide (NOx) storage catalytic converter of an internal combustion engine, in particular of a motor vehicle, according to claim 1, part 1.
  • nitrogen oxides generated by the internal combustion engine are stored in the storage catalytic converter in a first operating phase and nitrogen oxides stored in the storage catalytic converter are stored out of the storage catalytic converter in a second operating phase.
  • the beginning of the second operating phase is determined on the basis of a nitrogen oxide (NOx) level of the NOx storage catalytic converter wherein the NOx level is modeled using a nitrogen oxide (NOx) storage model.
  • the invention also relates to a control device for an internal combustion engine, in particular of a motor vehicle, according to claim 7, part 1.
  • the internal combustion engine can be switched back and forth by the control unit between a first operating phase, in which nitrogen oxides produced by the internal combustion engine are stored in the nitrogen oxide (NOx) storage catalytic converter, and a second operating phase, in which stored nitrogen oxides are expelled from the NOx storage catalytic converter become.
  • the control unit has first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) level modeled by means of a nitrogen oxide (NOx) storage model of the NOx storage catalyst on.
  • the present invention relates to a control, in particular a read-only memory or a flash memory, for such a control device.
  • the present invention relates to an internal combustion engine, in particular a motor vehicle according to the first part of claim 8.
  • the internal combustion engine has a control unit and a nitrogen oxide (NOx) storage catalytic converter.
  • the internal combustion engine can be switched back and forth by the control unit between a first operating phase, in which nitrogen oxides generated by the internal combustion engine are stored in the NOx storage catalytic converter, and a second operating phase, in which stored nitrogen oxides are expelled from the NOx storage catalytic converter.
  • the internal combustion engine has first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) level of the NOx storage catalytic converter modeled by means of a nitrogen oxide (NOx) storage model.
  • the invention relates to a control according to claim 6.
  • nitrogen oxide (NOx) storage catalysts are used to store the nitrogen oxide (NOx) emissions emitted by the internal combustion engine during a first operating phase (lean operation) .
  • This first operating phase of the NOx storage catalyst is also referred to as Ein untilphase.
  • Ein Grandephase With increasing duration of Ein Grandephase the efficiency of the NOx storage catalyst decreases, which leads to an increase in NOx emissions downstream of the NOx storage catalyst.
  • the cause of the decrease in efficiency is the increase in the nitrogen oxide (NOx) level of the NOx storage catalyst.
  • the NOx level can be monitored and after exceeding a predetermined threshold, the second phase of operation of the NOx storage catalyst (Aus Grande Listephase) are initiated.
  • a nitrogen oxide (NOx) storage model can be used for determining the NOx level of the NOx storage catalytic converter.
  • a reducing agent is added to the exhaust gas of the internal combustion engine, which reduces stored nitrogen oxides to nitrogen and oxygen.
  • the reducing agent for example, hydrocarbon (HC) and / or carbon monoxide (CO) can be used, which can be generated by a rich adjustment of the fuel / air mixture in the exhaust gas.
  • urea may also be added to the exhaust gas as the reducing agent. It is used to reduce the nitrogen oxide to oxygen and nitrogen ammonia from the urea. The ammonia can be obtained by hydrolysis from a urea solution.
  • the NOx level of the NOx storage catalyst depending on, inter alia, the NOx mass flow upstream of the NOx storage catalytic converter, the NOx mass flow downstream of the NOx storage catalytic converter and the temperature of the NOx storage catalytic converter. From these quantities, an efficiency of the NOx storage catalytic converter is determined, which multiplied by the NOx mass flow upstream of the NOx storage catalytic converter integrally supplies the current NOx level. As soon as the NOx level exceeds the predefinable threshold value, the second operating phase is initiated. The efficiency of the NOx storage catalyst decreases at constant boundary conditions with increasing NOx level.
  • the amount of stored NOx is regulated in a storage catalytic converter 5 of an internal combustion engine, wherein a storage model is provided with a controlled parameter Alpha.
  • This parameter alpha is integrally changed with a controller when the measured (oxygen) sensor voltage V downstream of the memory 5 during the emptying of the memory 5 at a time t ⁇ t3 (not) reaches the threshold for a rich mixture.
  • the present invention has for its object to be able to determine the NOx level of a NOx storage catalytic converter with the help of a NOx Ein headingmodells and thus the beginning and end of the second phase of operation (Aus emergephase) as accurately and reliably as possible to ensure optimum exhaust quality.
  • This object is achieved with the features according to the independent claims.
  • the invention it is therefore proposed to correct the NOx injection model by a measured value. From the measured value, a correction factor for the NOx injection model can be obtained, which can be used for diagnostic purposes. Due to the measured value of the NOx level, the with
  • the NOx injection model modeled NOx level corrected and thus the beginning and the end of the second phase of operation can be determined with a much higher accuracy. This in turn allows to go to the limit of the storage capacity of the NOx storage catalyst, d. H. make full use of the storage capacity of the NOx storage tank without exceeding it, which leads to a significantly improved exhaust gas quality.
  • the NOx storage model or the start and the end of the second operating phase are adapted to the actual emissions of the internal combustion engine.
  • the first value of the NOx mass flow downstream of the NOx storage catalytic converter be measured by means of a NOx sensor.
  • a second value of the NOx mass flow downstream of the NOx storage catalytic converter is taken from the NOx storage model and the NOx storage model is corrected as a function of the two values of the NOx mass flow.
  • a difference between the two values of the NOx mass flows is formed and the NOx injection model is corrected as a function of the difference.
  • the NOx level is determined by integrating the product of the NOx mass flow upstream of the NOx storage catalyst and an efficiency of the NOx storage catalyst in the NOx storage model.
  • the efficiency of the NOx storage catalytic converter becomes, for example, dependent on the NOx mass flow upstream of the NOx storage catalytic converter and on the temperature of the NOx storage catalytic converter determined.
  • the difference between the two values of the NOx mass flow downstream of the NOx storage catalytic converter is supplied to a controller and the NOx storage model is corrected as a function of a control variable of the controller.
  • the controller is preferably designed as an integrating (I) controller.
  • the output signal of the NOx sensor arranged downstream of the NOx storage catalytic converter is therefore not evaluated directly, for example via the absolute value, the gradient or the like, but serves to regulate the NOx injection model by means of the I controller.
  • the NOx injection model is corrected as a function of the efficiency of the NOx storage catalytic converter as the manipulated variable of the controller.
  • control element which is provided for a control unit of an internal combustion engine, in particular of a motor vehicle.
  • a program is stored on the control, which is executable on a computing device, in particular on a microprocessor, and suitable for carrying out the method according to the invention.
  • the invention is realized by a program stored on the control program, so that this provided with the program control in the same way is the invention as the method to whose execution the program is suitable.
  • an electrical storage medium can be used as the control, for example a read-only memory or a flash memory.
  • control unit proposes second means for detecting a first value of the nitrogen oxide (NOx) mass flow downstream of the NOx storage catalytic converter and third means for correcting the NOx storage model as a function of the detected first value having.
  • NOx nitrogen oxide
  • the internal combustion engine second means for detecting a first value of the nitrogen oxide (NOx) mass flow behind the NOx storage catalyst and third means for correcting the NOx Ein headingmodells in response to the detected first value.
  • NOx nitrogen oxide
  • FIG. 1 shows a direct-injection internal combustion engine 1 of a motor vehicle is shown, in which a piston 2 in a cylinder 3 back and forth.
  • the cylinder 3 is provided with a combustion chamber 4, which u.a. is limited by the piston 2, an inlet valve 5 and an outlet valve 6.
  • an intake valve 5 With the intake valve 5, an intake pipe 7 and the exhaust valve 6, an exhaust pipe 8 is coupled.
  • a fuel injection valve 9 and a spark plug 10 protrude in the combustion chamber 4. Via the injection valve 9, fuel can be injected into the combustion chamber 4. With the spark plug 10, the fuel in the combustion chamber 4 can be ignited.
  • a rotatable throttle valve 11 is housed, via which the intake pipe 7 air can be supplied.
  • the amount of air supplied is dependent on the angular position of the throttle valve 11.
  • a catalyst 12 is housed, which cleans the exhaust gases resulting from the combustion of the fuel.
  • the catalyst 12 is a nitrogen oxide (NOx) storage catalyst 12 'coupled to a 3-way catalyst 12 "as an oxygen storage.
  • NOx nitrogen oxide
  • a control unit 18 is acted upon by input signals 19, which represent operating variables of the internal combustion engine 1 measured by means of sensors.
  • the control unit 18 generates output signals 20 with which the behavior of the internal combustion engine 1 can be influenced via actuators or actuators.
  • the controller 18 is to intended to control the operating variables of the internal combustion engine 1 and / or to regulate.
  • the control unit 18 is provided with a microprocessor which has stored in a storage medium, in particular in a flash memory, a program which is adapted to perform said control and / or regulation.
  • a so-called homogeneous operation of the internal combustion engine 1 the throttle valve 11 is partially opened or closed depending on the desired torque.
  • the fuel is injected from the injection valve 9 during a suction phase caused by the piston 2 into the combustion chamber 4.
  • the throttle valve 11 air By simultaneously sucked on the throttle valve 11 air, the injected fuel is swirled and thus substantially uniformly distributed in the combustion chamber 4.
  • the fuel-air mixture is compressed during the compression phase to be ignited by the spark plug 10. Due to the expansion of the ignited fuel, the piston 2 is driven.
  • the resulting torque depends in homogeneous operation u.a. from the position of the throttle valve 11 from.
  • a so-called shift operation of the internal combustion engine 1 the throttle valve 11 is opened wide.
  • the fuel is injected from the injection valve 9 during a caused by the piston 2 compression phase in the combustion chamber 4, locally in the immediate vicinity of the spark plug 10 and in time at a suitable distance before the ignition.
  • we ignited with the help of the spark plug 10 of the fuel so that the piston 2 in the now following working phase by the expansion of the inflamed Fuel is driven.
  • the resulting torque largely depends on the injected fuel mass during shift operation.
  • the stratified operation is provided for the idle operation and the partial load operation of the internal combustion engine 1.
  • lambda is usually> 1.
  • a first operating phase the internal combustion engine 1 is operated in stratified operation and the storage catalytic converter 12 'is charged with nitrogen oxides and the 3-way catalyst 12 "with oxygen (injection phase)
  • a second operating phase the storage catalytic converter 12' and the third Pathway catalyst 12 "discharged again so that they can again absorb nitrogen oxides or oxygen in a subsequent shift operation (Aus shallphase).
  • a reducing agent is added to the exhaust gas upstream of the catalyst 12.
  • the reducing agent for example, hydrocarbons (HC), carbon monoxide (CO) or urea can be used. Hydrocarbons and carbon monoxide are generated in the exhaust gas by a rich mixture adjustment (operation of the internal combustion engine in homogeneous operation).
  • Urea can be metered controlled from a reservoir to the exhaust gas.
  • the reducing agent reduces the stored nitrogen oxides to nitrogen and oxygen. These substances exit from the catalyst 12, so that there is an excess of oxygen behind the catalyst 12 during the regeneration phase, although the internal combustion engine 1 is operated with a rich fuel / air mixture (lack of oxygen).
  • an oxygen (02) sensor 13 and after the catalyst 12 a nitrogen (NOx) sensor 14 in the exhaust pipe 8 is arranged.
  • the O2 sensor 13 reacts virtually instantaneously. Due to the prevailing excess oxygen during the shift operation in the exhaust gas, the oxygen storage locations of the catalytic converter 12 are initially almost all occupied. After switching to lack of oxygen at the beginning of the regeneration phase, the oxygen storage sites are successively freed of oxygen, which then emerges from the catalyst 12. After the catalyst 12 therefore prevails after switching to the Regeneratonsphase initially further excess oxygen.
  • FIG. 2 schematically shows a NOx storage model 30.
  • the NOx mass flow msnovk upstream of the catalytic converter 12 and an efficiency eta_sp of the NOx storage catalytic converter 12 ' are applied to the NOx injection model 30.
  • the efficiency eta_sp is dependent on u.a. the NOx mass flow msnovk before the NOx storage catalytic converter 12 ', a NOx mass flow msnonk behind the NOx storage catalytic converter 12' and the temperature of the NOx storage catalytic converter 12 'determined.
  • the efficiency eta_sp is a non-linear function of the NOx filling level mnosp of the NOx storage catalytic converter 12 'and decreases as the NOx level increases.
  • a product mnsospe of the NOx mass flow msnovk and the efficiency eta_sp is formed.
  • the product mnsospe is stored in an integrator 32 integrated.
  • the integrator 32 supplies the NOx filling level mnosp of the NOx storage catalytic converter 12 '. This is compared in a comparator 33 with a predefinable threshold schw. If the NOx level mnosp exceeds the threshold value schw, the regeneration phase of the NOx storage catalytic converter 12 'is initiated by means of a regeneration signal B_denox.
  • FIG. 3 schematically shows a method according to the invention.
  • an output signal msnonk_s of the arranged behind the catalyst 12 NOx sensor 14 is used to control the NOx injection model 30.
  • the beginning and end of the second phase of operation (regeneration phase) of the NOx storage catalyst 12 ' can be determined much more accurate and reliable , which leads to a significantly improved exhaust quality.
  • a modeled NOx mass flow msnonk_m after the catalyst 12 is modeled.
  • the modeled NOx mass flow msnonk_m results from the difference of the NOx mass flow msnovk before the catalyst 12 and the product of the NOx mass flow msnovk and the efficiency eta_sp, d. H. from msnovk ⁇ (1 - eta_sp).
  • the NOx mass flow msnovk upstream of the catalyst 12 may be measured by a NOx sensor (not shown) or taken from the NOx model.
  • control difference 34 of the control circuit shown in Figure 3 is formed.
  • the control difference 34 is supplied to an integrating I-controller 35.
  • I-controller 35 any other suitable regulators can also be used.
  • a manipulated variable 36 of the I-controller 35 is passed to an actuator 37, which varies a manipulated variable 38 in order to act in a controlled manner on the NOx injection model 30.
  • the manipulated variable 38 is the efficiency eta_sp of the NOx storage catalytic converter 12 '.

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

Abstract

The invention relates to a method for operating a nitrogen oxide (NOx) storage catalyst (12') on an internal combustion engine (1), in particular in a motor vehicle (1). The nitrogen oxides (NOx) generated by the internal combustion engine (1) are stored in the storage catalyst (12') during a first operating phase and the nitrogen oxides stored in the storage catalyst (12') are released during a second operating phase. The beginning of the second operating phase is determined by means of a nitrogen oxide (NOx) level (mnosp) of the NOx storage catalyst (12'), which is modelled by means of a nitrogen oxide (NOx) storing model (30). According to the invention, in order to be able to determine the beginning and the end of the second operating phase as exactly and reliably as possible, a first value for nitrogen oxide (NOx) mass flow (msnonk s) behind the NOx storage catalyst (12') is determined and the NOx storing model (30) is corrected based on the determined first value (msnonk s).

Description

Die vorliegende Erfindung betrifft ein Verfahren zum Betreiben eines Stickoxid (NOx)-Speicherkatalysators einer Brennkraftmaschine insbesondere eines Kraftfahrzeugs, gemäß Anspruch 1, 1.Teil. Dabei werden von der Brennkraftmaschine erzeugte Stickoxide in einer ersten Betriebsphase in den Speicherkatalysator eingespeichert und in den Speicherkatalysator eingespeicherte Stickoxide in einer zweiten Betriebsphase aus dem Speicherkatalysator ausgespeichert..Der Beginn der zweiten Betriebsphase wird anhand eines Stickoxid (NOx)-Füllstandes des NOx-Speicherkatalysators bestimmt, wobei der NOx-Füllstand anhand eines Stickoxid (NOx)-Einspeichermodells modelliert wird.The present invention relates to a method for operating a nitrogen oxide (NOx) storage catalytic converter of an internal combustion engine, in particular of a motor vehicle, according to claim 1, part 1. In this process, nitrogen oxides generated by the internal combustion engine are stored in the storage catalytic converter in a first operating phase and nitrogen oxides stored in the storage catalytic converter are stored out of the storage catalytic converter in a second operating phase. The beginning of the second operating phase is determined on the basis of a nitrogen oxide (NOx) level of the NOx storage catalytic converter wherein the NOx level is modeled using a nitrogen oxide (NOx) storage model.

Die Erfindung betrifft außerdem ein Steuergerät für eine Brennkraftmaschine insbesondere eines Kraftfahrzeugs, gemäß Anspruch 7, 1.Teil. Die Brennkraftmaschine kann von dem Steuergerät zwischen einer ersten Betriebsphase, in der von der Brennkraftmaschine erzeugte Stickoxide in den Stickoxid (NOx)-Speicherkatalysator eingespeichert werden, und einer zweiten Betriebsphase, in der eingespeicherte Stickoxide aus dem NOx-Speicherkatalysator ausgespeichert werden, hin- und hergeschaltet werden. Das Steuergerät weist erste Mittel zum Bestimmen des Beginns der zweiten Betriebsphase anhand eines mittels eines Stickoxid (NOx)-Einspeichermodells modellierten Stickoxid (NOx)-Füllstandes des NOx-Speicherkatalysators auf. Des Weiteren betrifft die vorliegende Erfindung ein Steuerelement, insbesondere ein Read-Only-Memory oder ein Flash-Memory, für ein derartiges Steuergerät.The invention also relates to a control device for an internal combustion engine, in particular of a motor vehicle, according to claim 7, part 1. The internal combustion engine can be switched back and forth by the control unit between a first operating phase, in which nitrogen oxides produced by the internal combustion engine are stored in the nitrogen oxide (NOx) storage catalytic converter, and a second operating phase, in which stored nitrogen oxides are expelled from the NOx storage catalytic converter become. The control unit has first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) level modeled by means of a nitrogen oxide (NOx) storage model of the NOx storage catalyst on. Furthermore, the present invention relates to a control, in particular a read-only memory or a flash memory, for such a control device.

Schließlich betrifft die vorliegende Erfindung eine Brennkraftmaschine, insbesondere eines Kraftfahrzeugs gemäß dem ersten Teil nach Anspruch 8. Die Brennkraftmaschine weist ein Steuergerät und einen Stickoxid (NOx)-Speicherkatalysator auf. Die Brennkraftmaschine kann zwischen einer ersten Betriebsphase, in der von der Brennkraftmaschine erzeugte Stickoxide in den NOx-Speicherkatalysator eingespeichert werden, und einer zweiten Betriebsphase, in der eingespeicherte Stickoxide aus dem NOx-Speicherkatalysator ausgespeichert werden, von dem Steuergerät hin- und hergeschaltet werden. Die Brennkraftmaschine weist erste Mittel zum Bestimmen des Beginns der zweiten Betriebsphase anhand eines mittels eines Stickoxid (NOx)-Einspeichermodells modellierten Stickoxid (NOx)-Füllstandes des NOx-Speicherkatalysators auf.Finally, the present invention relates to an internal combustion engine, in particular a motor vehicle according to the first part of claim 8. The internal combustion engine has a control unit and a nitrogen oxide (NOx) storage catalytic converter. The internal combustion engine can be switched back and forth by the control unit between a first operating phase, in which nitrogen oxides generated by the internal combustion engine are stored in the NOx storage catalytic converter, and a second operating phase, in which stored nitrogen oxides are expelled from the NOx storage catalytic converter. The internal combustion engine has first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) level of the NOx storage catalytic converter modeled by means of a nitrogen oxide (NOx) storage model.

Außerdem betrifft die Erfindung ein Steuerelement gemäß Anspruch 6.Moreover, the invention relates to a control according to claim 6.

Stand der TechnikState of the art

Bei Brennkraftmaschinen, die mit einem mageren Kraftstoff/Luft-Gemisch (Lambda > 1) betrieben werden können, werden Stickoxid (NOx)-Speicherkatalysatoren eingesetzt, um die von der Brennkraftmaschine während einer ersten Betriebsphase (Magerbetrieb) ausgestoßenen Stickoxid (NOx)-Emissionen einzuspeichern. Diese erste Betriebsphase des NOx-Speicherkatalysators wird auch als Einspeicherphase bezeichnet. Mit zunehmender Dauer der Einspeicherphase nimmt der Wirkungsgrad des NOx-Speicherkatalysators ab, was zu einem Anstieg der NOx-Emissionen hinter dem NOx-Speicherkatalysator führt. Die Ursache für die Abnahme des Wirkungsgrads liegt in der Zunahme des Stickoxid (NOx)-Füllstands des NOx-Speicherkatalysators. Der NOx-Füllstand kann überwacht und nach Überschreiten eines vorgebbaren Schwellenwertes die zweite Betriebsphase des NOx-Speicherkatalysators (Ausspeicherphase) eingeleitet werden. Zum Ermitteln des NOx-Füllstands des NOx-Speicherkatalysators kann ein Stickoxid (NOx)-Einspeichermodell eingesetzt werden.In internal combustion engines which can be operated with a lean fuel / air mixture (lambda> 1), nitrogen oxide (NOx) storage catalysts are used to store the nitrogen oxide (NOx) emissions emitted by the internal combustion engine during a first operating phase (lean operation) , This first operating phase of the NOx storage catalyst is also referred to as Einspeicherphase. With increasing duration of Einspeicherphase the efficiency of the NOx storage catalyst decreases, which leads to an increase in NOx emissions downstream of the NOx storage catalyst. The cause of the decrease in efficiency is the increase in the nitrogen oxide (NOx) level of the NOx storage catalyst. The NOx level can be monitored and after exceeding a predetermined threshold, the second phase of operation of the NOx storage catalyst (Ausspeicherphase) are initiated. For determining the NOx level of the NOx storage catalytic converter, a nitrogen oxide (NOx) storage model can be used.

Während der zweiten Betriebsphase wird dem Abgas der Brennkraftmaschine ein Reduktionsmittel hinzugegeben, das eingespeicherte stickoxide zu Stickstoff und Sauerstoff reduziert. Als Reduktionsmittel können bspw. Kohlenwasserstoff (HC) und/oder Kohlenmonoxid (CO) verwendet werden, die durch eine fette Einstellung des Kraftstoff/Luft-Gemisches in dem Abgas erzeugt werden können. Alternativ kann als Reduktionsmittel auch Harnstoff zu dem Abgas hinzugegeben werden. Dabei wird zur Reduktion des Stickoxids zu Sauerstoff und Stickstoff Ammoniak aus dem Harnstoff verwendet. Der Ammoniak kann per Hydrolyse aus einer Harnstofflösung gewonnen werden.During the second operating phase, a reducing agent is added to the exhaust gas of the internal combustion engine, which reduces stored nitrogen oxides to nitrogen and oxygen. As the reducing agent, for example, hydrocarbon (HC) and / or carbon monoxide (CO) can be used, which can be generated by a rich adjustment of the fuel / air mixture in the exhaust gas. Alternatively, urea may also be added to the exhaust gas as the reducing agent. It is used to reduce the nitrogen oxide to oxygen and nitrogen ammonia from the urea. The ammonia can be obtained by hydrolysis from a urea solution.

Gegen Ende der Ausspeicherphase ist ein Großteil des eingespeicherten Stickoxids reduziert und immer weniger des Reduktionsmittels trifft auf Stickoxid, das es zu Sauerstoff und Stickstoff reduzieren kann. In der Folge steigt gegen Ende der Ausspeicherphase der Anteil an Reduktionsmittel in dem Abgas hinter dem NOx-Speicherkatalysator an, der Anteil an Sauerstoff in dem Abgas hinter dem NOx-Speicherkatalysator nimmt ab. Durch eine Analyse des Abgases hinter dem NOx-Speicherkatalysator durch geeignete Abgassensoren kann das Ende der Ausspeicherphase dann eingeleitet werden, wenn der Großteil des Stickoxids aus dem NOx-Speicherkatalysator ausgespeichert worden ist.Towards the end of the Ausspeicherphase a large part of the stored nitrogen oxide is reduced and less and less of the reducing agent meets nitric oxide, which can reduce it to oxygen and nitrogen. As a result, toward the end of the Ausspeicherphase increases the proportion of reducing agent in the exhaust gas behind the NOx storage catalyst, the proportion of oxygen in the exhaust gas downstream of the NOx storage catalyst decreases. By analyzing the exhaust gas behind the NOx storage catalyst by means of suitable exhaust gas sensors, the end of the Ausspeicherphase can then be initiated when the majority of the nitrogen oxide has been stored out of the NOx storage catalyst.

Bei einem aus dem Stand der Technik bekannten NOx-Einspeichermodell wird der NOx-Füllstand des NOx-Speicherkatalysators in Abhängigkeit von u.a. dem NOx-Massenstrom vor dem NOx-Speicherkatalysator, dem NOx-Massenstrom hinter dem NOx-Speicherkatalysator und der Temperatur des NOx-Speicherkatalysators bestimmt. Aus diesen Größen wird ein Wirkungsgrad des NOx-Speicherkatalysators bestimmt, der multipliziert mit dem NOx-Massenstrom vor dem NOx-Speicherkatalysator aufintegriert den aktuellen NOx-Füllstand liefert. Sobald der NOx-Füllstand den vorgebbaren Schwellenwert überschreitet, wird die zweite Betriebsphase eingeleitet. Der Wirkungsgrad des NOx-Speicherkatalysators nimmt bei konstanten Randbedingungen mit zunehmendem NOx-Füllstand ab.In one known from the prior art NOx injection model, the NOx level of the NOx storage catalyst depending on, inter alia, the NOx mass flow upstream of the NOx storage catalytic converter, the NOx mass flow downstream of the NOx storage catalytic converter and the temperature of the NOx storage catalytic converter. From these quantities, an efficiency of the NOx storage catalytic converter is determined, which multiplied by the NOx mass flow upstream of the NOx storage catalytic converter integrally supplies the current NOx level. As soon as the NOx level exceeds the predefinable threshold value, the second operating phase is initiated. The efficiency of the NOx storage catalyst decreases at constant boundary conditions with increasing NOx level.

Nach der EP-A-0 997 626 wird die Menge des gespeicherten NOx in einem Speicherkatalysator 5 einer Brennkraftmaschine geregelt, wobei ein Einspeichermodell mit einem geregelten Parmeter Alpha vorgesehen ist. Dieser Parameter Alpha wird mit einem Regler integrierend verändert wenn die gemessen (Sauerstoff -) Sensor- Spannung V stromab des Speichers 5 während der Entleerung des Speichers 5 zu einem Zeitpunkt t < t3 (nicht) den Schwellwert für ein fettegt Gemisch erreicht.According to EP-A-0 997 626, the amount of stored NOx is regulated in a storage catalytic converter 5 of an internal combustion engine, wherein a storage model is provided with a controlled parameter Alpha. This parameter alpha is integrally changed with a controller when the measured (oxygen) sensor voltage V downstream of the memory 5 during the emptying of the memory 5 at a time t <t3 (not) reaches the threshold for a rich mixture.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, den NOx-Füllstand eines NOx-Speicherkatalysators mit Hilfe eines NOx-Einspeichermodells und damit Anfang und Ende der zweiten Betriebsphase (Ausspeicherphase) möglichst genau und zuverlässig bestimmen zu können, um eine optimale Abgasqualität zu gewährleisten. Diese Aufgabe wird gelöst mit den Merkmalen gemäß den unabängigen Ansprüchen.The present invention has for its object to be able to determine the NOx level of a NOx storage catalytic converter with the help of a NOx Einspeichermodells and thus the beginning and end of the second phase of operation (Ausspeicherphase) as accurately and reliably as possible to ensure optimum exhaust quality. This object is achieved with the features according to the independent claims.

Vorteile der ErfindungAdvantages of the invention

Erfindungsgemäß wird also vorgeschlagen, das NOx-Einspeichermodell durch einen gemessenen Wert zu korrigieren. Aus dem gemessenen Wert kann ein Korrekturfaktor für das NOx-Einspeichermodell gewonnen werden, der zu Diagnosezwecken herangezogen werden kann. Durch den gemessenen Wert des NOx-Füllstands kann der mitAccording to the invention, it is therefore proposed to correct the NOx injection model by a measured value. From the measured value, a correction factor for the NOx injection model can be obtained, which can be used for diagnostic purposes. Due to the measured value of the NOx level, the with

Hilfe des NOx-Einspeichermodells modellierte NOx-Füllstand korrigiert und damit auch der Anfang und das Ende der zweiten Betriebsphase mit einer wesentlich höheren Genauigkeit bestimmt werden. Das wiederum erlaubt es, an die Grenze der Speicherfähigkeit des NOx-Speicherkatalysators zu gehen, d. h. die Speicherfähigkeit des NOx-Speichers voll auszunutzen ohne sie zu überschreiten, was zu einer deutlich verbesserten Abgasqualität führt. Mit Hilfe des erfindungsgemäßen Verfahrens wird das NOx-Einspeichermodell bzw. der Anfang und das Ende der zweiten Betriebsphase den tatsächlichen Emissionen der Brennkraftmaschine angepaßt.Help the NOx injection model modeled NOx level corrected and thus the beginning and the end of the second phase of operation can be determined with a much higher accuracy. This in turn allows to go to the limit of the storage capacity of the NOx storage catalyst, d. H. make full use of the storage capacity of the NOx storage tank without exceeding it, which leads to a significantly improved exhaust gas quality. With the aid of the method according to the invention, the NOx storage model or the start and the end of the second operating phase are adapted to the actual emissions of the internal combustion engine.

Gemäß einer vorteilhaften Weiterbildung der vorliegenden Erfindung wird vorgeschlagen, dass der erste Wert des NOx-Massenstroms hinter dem NOx-Speicherkatalysator mittels eines NOx-Sensors gemessen wird.According to an advantageous development of the present invention, it is proposed that the first value of the NOx mass flow downstream of the NOx storage catalytic converter be measured by means of a NOx sensor.

Gemäß einer bevorzugten Ausführungsform der vorliegenden Erfindung wird vorgeschlagen, dass ein zweiter Wert des NOx-Massenstroms hinter dem NOx-Speicherkatalysator dem NOx-Einspeichermodell entnommen wird und das NOx-Einspeichermodell in Abhängigkeit der beiden Werte des NOx-Massenstroms korrigiert wird.According to a preferred embodiment of the present invention, it is proposed that a second value of the NOx mass flow downstream of the NOx storage catalytic converter is taken from the NOx storage model and the NOx storage model is corrected as a function of the two values of the NOx mass flow.

Vorteilhafterweise wird eine Differenz der beiden Werte der NOx-Massenströme gebildet und das NOx-Einspeichermodell in Abhängigkeit der Differenz korrigiert.Advantageously, a difference between the two values of the NOx mass flows is formed and the NOx injection model is corrected as a function of the difference.

Vorteilhafterweise wird der NOx-Füllstand durch Integration des Produkts aus dem NOx-Massenstrom vor dem NOx-Speicherkatalysator und einem Wirkungsgrad des NOx-Speicherkatalysators in dem NOx-Einspeichermodell, ermittelt. Der Wirkungsgrad des NOx-Speicherkatalysators wird bspw. in Abhängigkeit des NOx-Massenstroms vor dem NOx-Speicherkatalysator und von der Temperatur des NOx-Speicherkatalysators ermittelt.Advantageously, the NOx level is determined by integrating the product of the NOx mass flow upstream of the NOx storage catalyst and an efficiency of the NOx storage catalyst in the NOx storage model. The efficiency of the NOx storage catalytic converter becomes, for example, dependent on the NOx mass flow upstream of the NOx storage catalytic converter and on the temperature of the NOx storage catalytic converter determined.

Gemäß einer weiteren bevorzugten Ausführungsform der vorliegenden Erfindung wird vorgeschlagen, dass die Differenz der beiden Werte des NOx-Massenstroms hinter dem NOx-Speicherkatalysator einem Regler zugeführt wird und das NOx-Einspeichermodell in Abhängigkeit einer Stellgröße des Reglers korrigiert wird. Der Regler ist vorzugsweise als integrierender (I)-Regler ausgebildet. Das Ausgangssignal des nach dem NOx-Speicherkatalysator angeordneten NOx-Sensors wird also nicht direkt, bspw. über den Absolutwert, die Steigung o.ä., ausgewertet, sondern dient zur Regelung des NOx-Einspeichermodells mittels des I-Reglers.According to a further preferred embodiment of the present invention, it is proposed that the difference between the two values of the NOx mass flow downstream of the NOx storage catalytic converter is supplied to a controller and the NOx storage model is corrected as a function of a control variable of the controller. The controller is preferably designed as an integrating (I) controller. The output signal of the NOx sensor arranged downstream of the NOx storage catalytic converter is therefore not evaluated directly, for example via the absolute value, the gradient or the like, but serves to regulate the NOx injection model by means of the I controller.

Schließlich wird vorgeschlagen, dass das NOx-Einspeichermodell in Abhängigkeit von dem Wirkungsgrad des NOx-Speicherkatalysators als der Stellgröße des Reglers korrigiert wird.Finally, it is proposed that the NOx injection model is corrected as a function of the efficiency of the NOx storage catalytic converter as the manipulated variable of the controller.

Von besonderer Bedeutung ist die Realisierung des erfindungsgemäßen Verfahrens in Form eines Steuerelements, das für ein Steuergerät einer Brennkraftmaschine insbesondere eines Kraftfahrzeugs vorgesehen ist. Dabei ist auf dem Steuerelement ein Programm abgespeichert, das auf einem Rechengerät, insbesondere auf einem Mikroprozessor, ablauffähig und zur Ausführung des erfindungsgemäßen Verfahrens geeignet ist. In diesem Fall wird also die Erfindung durch ein auf dem Steuerelement abgespeichertes Programm realisiert, so dass dieses mit dem Programm versehene Steuerelement in gleicher Weise die Erfindung darstellt wie das Verfahren, zu dessen Ausführung das Programm geeignet ist. Als Steuerelement kann insbesondere ein elektrisches Speichermedium zur Anwendung kommen, bspw. ein Read-Only-Memory oder ein Flash-Memory.Of particular importance is the realization of the method according to the invention in the form of a control element which is provided for a control unit of an internal combustion engine, in particular of a motor vehicle. In this case, a program is stored on the control, which is executable on a computing device, in particular on a microprocessor, and suitable for carrying out the method according to the invention. In this case, therefore, the invention is realized by a program stored on the control program, so that this provided with the program control in the same way is the invention as the method to whose execution the program is suitable. In particular, an electrical storage medium can be used as the control, for example a read-only memory or a flash memory.

Als eine weitere Lösung der Aufgabe der vorliegenden Erfindung wird ausgehend von dem Steuergerät der eingangs genannten Art vorgeschlagen, dass das Steuergerät zweite Mittel zum Erfassen eines ersten Werts des Stickoxid (NOx)-Massenstroms hinter dem NOx-Speicherkatalysator und dritte Mittel zur Korrektur des NOx-Einspeichermodells in Abhängigkeit von dem erfassten ersten Wert aufweist.As a further solution to the problem of the present According to the invention, the control unit proposes second means for detecting a first value of the nitrogen oxide (NOx) mass flow downstream of the NOx storage catalytic converter and third means for correcting the NOx storage model as a function of the detected first value having.

Schließlich wird zur Lösung der Aufgabe der vorliegenden Erfindung ausgehend von der Brenrikraftmaschine der eingangs genannten Art vorgeschlagen, dass die Brennkraftmaschine zweite Mittel zum Erfassen eines ersten Werts des Stickoxid (NOx)-Massenstroms hinter dem NOx-Speicherkatalysator und dritte Mittel zur Korrektur des NOx-Einspeichermodells in Abhängigkeit von dem erfassten ersten Wert aufweist.Finally, to solve the object of the present invention, starting from the Brenrikraftmaschine of the type mentioned above, it is proposed that the internal combustion engine second means for detecting a first value of the nitrogen oxide (NOx) mass flow behind the NOx storage catalyst and third means for correcting the NOx Einspeichermodells in response to the detected first value.

Zeichnungendrawings

Weitere Merkmale, Anwendungsmöglichkeiten und Vorteile der Erfindung ergeben sich aus der nachfolgenden Beschreibung von Ausführungsbeispielen der Erfindung, die in der Zeichnung dargestellt sind. Dabei bilden alle beschriebenen oder dargestellten Merkmale für sich oder in beliebiger Kombination den Gegenstand der Erfindung, unabhängig von ihrer Zusammenfassung in den Patentansprüchen oder deren Rückbeziehung sowie unabhängig von ihrer Formulierung bzw. Darstellung in der Beschreibung bzw. in der Zeichnung. Es zeigen:

Figur 1
ein schematisches Blockschaltbild einer erfindungsgemäßen Brennkraftmaschine gemäß einer bevorzugten Ausführungsform;
Figur 2
einen schematischen Signallaufplan eines NOx-Einspeichermodells; und
Figur 3
einen schematischen Signallaufplan eines erfindungsgemäßen Verfahrens gemäß einer bevorzugten Ausführungsform.
Other features, applications and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, which are illustrated in the drawing. All described or illustrated features, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing. Show it:
FIG. 1
a schematic block diagram of an internal combustion engine according to the invention according to a preferred embodiment;
FIG. 2
a schematic signal diagram of a NOx injection model; and
FIG. 3
a schematic signal plan of a inventive method according to a preferred embodiment.

Beschreibung der AusführungsbeispieleDescription of the embodiments

In Figur 1 ist eine direkteinspritzende Brennkraftmaschine 1 eines Kraftfahrzeugs dargestellt, bei der ein Kolben 2 in einem Zylinder 3 hin- und herbewegbar ist. Der Zylinder 3 ist mit einem Brennraum 4 versehen, der u.a. durch den Kolben 2, ein Einlassventil 5 und ein Auslassventil 6 begrenzt ist. Mit dem Einlassventil 5 ist ein Ansaugrohr 7 und mit dem Auslassventil 6 ein Abgasrohr 8 gekoppelt.1 shows a direct-injection internal combustion engine 1 of a motor vehicle is shown, in which a piston 2 in a cylinder 3 back and forth. The cylinder 3 is provided with a combustion chamber 4, which u.a. is limited by the piston 2, an inlet valve 5 and an outlet valve 6. With the intake valve 5, an intake pipe 7 and the exhaust valve 6, an exhaust pipe 8 is coupled.

Im Bereich des Einlassventils 5 und des Auslassventils 6 ragen ein Kraftstoffeinspritzventil 9 und eine Zündkerze 10 in dem Brennraum 4. Über das Einspritzventil 9 kann Kraftstoff in dem Brennraum 4 eingespritzt werden. Mit der Zündkerze 10 kann der Kraftstoff in dem Brennraum 4 entzündet werden.In the region of the inlet valve 5 and the outlet valve 6, a fuel injection valve 9 and a spark plug 10 protrude in the combustion chamber 4. Via the injection valve 9, fuel can be injected into the combustion chamber 4. With the spark plug 10, the fuel in the combustion chamber 4 can be ignited.

In dem Ansaugrohr 7 ist eine drehbare Drosselklappe 11 untergebracht, über die dem Ansaugrohr 7 Luft zuführbar ist. Die Menge der zugeführten Luft ist abhängig von der Winkelstellung der Drosselklappe 11. In dem Abgasrohr 8 ist ein Katalysator 12 untergebracht, der die durch die Verbrennung des Kraftstoffs entstehenden Abgase reinigt. Bei dem Katalysator 12 handelt es sich um einen Stickoxid (NOx)-Speicherkatalysator 12', der mit einem 3-Wege-Katalysator 12" als Sauerstoffspeicher gekoppelt ist.In the intake pipe 7, a rotatable throttle valve 11 is housed, via which the intake pipe 7 air can be supplied. The amount of air supplied is dependent on the angular position of the throttle valve 11. In the exhaust pipe 8, a catalyst 12 is housed, which cleans the exhaust gases resulting from the combustion of the fuel. The catalyst 12 is a nitrogen oxide (NOx) storage catalyst 12 'coupled to a 3-way catalyst 12 "as an oxygen storage.

Ein Steuergerät 18 ist von Eingangssignalen 19 beaufschlagt, die mittels Sensoren gemessene Betriebsgrößen der Brennkraftmaschine 1 darstellen. Das Steuergerät 18 erzeugt Ausgangssignale 20, mit denen über Aktoren bzw. Steller das Verhalten der Brennkraftmaschine 1 beeinflusst werden kann. Unter anderem ist das Steuergerät 18 dazu vorgesehen, die Betriebsgrößen der Brennkraftmaschine 1 zu steuern und/oder zu regeln. Zu diesem Zweck ist das Steuergerät 18 mit einem Mikroprozessor versehen, der in einem Speichermedium, insbesondere in einem Flash-Memory, ein Programm abgespeichert hat, das dazu geeignet ist, die genannte Steuerung und/oder Regelung durchzuführen.A control unit 18 is acted upon by input signals 19, which represent operating variables of the internal combustion engine 1 measured by means of sensors. The control unit 18 generates output signals 20 with which the behavior of the internal combustion engine 1 can be influenced via actuators or actuators. Among other things, the controller 18 is to intended to control the operating variables of the internal combustion engine 1 and / or to regulate. For this purpose, the control unit 18 is provided with a microprocessor which has stored in a storage medium, in particular in a flash memory, a program which is adapted to perform said control and / or regulation.

In einer ersten Betriebsart, einem sogenannten Homogenbetrieb der Brennkraftmaschine 1, wird die Drosselklappe 11 in Abhängigkeit von dem erwünschten Drehmoment teilweise geöffnet bzw. geschlossen. Der Kraftstoff wird von dem Einspritzventil 9 während einer durch den Kolben 2 hervorgerufenen Ansaugphase in den Brennraum 4 eingespritzt. Durch die gleichzeitig über die Drosselklappe 11 angesaugte Luft wird der eingespritzte Kraftstoff verwirbelt und damit in dem Brennraum 4 im Wesentlichen gleichmäßig verteilt. Danach wird das Kraftstoff Luft-Gemisch während der Verdichtungsphase verdichtet, um dann von der Zündkerze 10 entzündet zu werden. Durch die Ausdehnung des entzündeten Kraftstoffs wird der Kolben 2 angetrieben. Das entstehende Drehmoment hängt im Homogenbetrieb u.a. von der Stellung der Drosselklappe 11 ab. Im Hinblick auf eine geringe Schadstofentwicklung wird das Kraftstoff Luft-Gemisch möglichst auf Lambda=1 eingestellt.In a first operating mode, a so-called homogeneous operation of the internal combustion engine 1, the throttle valve 11 is partially opened or closed depending on the desired torque. The fuel is injected from the injection valve 9 during a suction phase caused by the piston 2 into the combustion chamber 4. By simultaneously sucked on the throttle valve 11 air, the injected fuel is swirled and thus substantially uniformly distributed in the combustion chamber 4. Thereafter, the fuel-air mixture is compressed during the compression phase to be ignited by the spark plug 10. Due to the expansion of the ignited fuel, the piston 2 is driven. The resulting torque depends in homogeneous operation u.a. from the position of the throttle valve 11 from. In view of a low pollutant development, the fuel air mixture is adjusted as possible to lambda = 1.

In einer zweiten Betriebsart, einem sogenannten Schichtbetrieb der Brennkraftmaschine 1, wird die Drosselklappe 11 weit geöffnet. Der Kraftstoff wird von dem Einspritzventil 9 während einer durch den Kolben 2 hervorgerufenen Verdichtungsphase in den Brennraum 4 eingespritzt, und zwar örtlich in die unmittelbare Umgebung der Zündkerze 10 sowie zeitlich in geeignetem Abstand vor dem Zündzeitpunkt. Dann wir mit Hilfe der Zündkerze 10 der Kraftstoff entzündet, so dass der Kolben 2 in der nunmehr folgenden Arbeitsphase durch die Ausdehnung des entzündeten Kraftstoffs angetrieben wird. Das entstehende Drehmoment hängt im Schichtbetrieb weitgehend von der eingespritzten Kraftstoffmasse ab. Im Wesentlichen ist der Schichtbetrieb für den Leerlaufbetrieb und den Teillastbetrieb der Brennkraftmaschine 1 vorgesehen. Im Schichtbetrieb ist Lambda üblicherweise > 1.In a second mode, a so-called shift operation of the internal combustion engine 1, the throttle valve 11 is opened wide. The fuel is injected from the injection valve 9 during a caused by the piston 2 compression phase in the combustion chamber 4, locally in the immediate vicinity of the spark plug 10 and in time at a suitable distance before the ignition. Then we ignited with the help of the spark plug 10 of the fuel, so that the piston 2 in the now following working phase by the expansion of the inflamed Fuel is driven. The resulting torque largely depends on the injected fuel mass during shift operation. Essentially, the stratified operation is provided for the idle operation and the partial load operation of the internal combustion engine 1. In stratified operation lambda is usually> 1.

Während einer ersten Betriebsphase wird die Brennkraftmaschine 1 im Schichtbetrieb betrieben und der Speicherkatalysator 12' wird mit Stickoxiden und der 3-Wege-Katalysator 12" mit Sauerstoff beladen (Einspeicherphase). In einer zweiten Betriebsphase (Regenerationsphase) werden der Speicherkatalysator 12' und der 3-Wege-Katalysator 12" wieder entladen, so dass sie in einem nachfolgenden Schichtbetrieb erneut Stickoxide bzw. Sauerstoff aufnehmen können (Ausspeicherphase). Während der Regenerationsphase wird vor dem Katalysator 12 ein Reduktionsmittel in das Abgas gegeben. Als Reduktionsmittel können bspw. Kohlenwasserstoffe (HC), Kohlenmonoxid (CO) oder Harnstoff verwendet werden. Kohlenwasserstoffe und Kohlenmonoxid werden im Abgas durch eine fette Gemischeinstellung (Betrieb der Brennkraftmaschine im Homogenbetrieb) erzeugt. Harnstoff kann aus einem Vorratsbehälter dem Abgas gesteuert zudosiert werden. Während der Regenerationsphase des Katalysators 12 laufen folgende Prozesse ab: Das Reduktionsmittel reduziert die gespeicherten Stickoxide zu Stickstoff und Sauerstoff. Diese Stoffe treten aus dem Katalysator 12 heraus, so dass sich hinter dem Katalysator 12 während der Regenerationsphase ein Sauerstoffüberschuss ergibt, obwohl die Brennkraftmaschine 1 mit einem fetten Kraftstoff/Luft-Gemisch (Sauerstoffmangel) betrieben wird.During a first operating phase, the internal combustion engine 1 is operated in stratified operation and the storage catalytic converter 12 'is charged with nitrogen oxides and the 3-way catalyst 12 "with oxygen (injection phase) In a second operating phase (regeneration phase), the storage catalytic converter 12' and the third Pathway catalyst 12 "discharged again so that they can again absorb nitrogen oxides or oxygen in a subsequent shift operation (Ausspeicherphase). During the regeneration phase, a reducing agent is added to the exhaust gas upstream of the catalyst 12. As the reducing agent, for example, hydrocarbons (HC), carbon monoxide (CO) or urea can be used. Hydrocarbons and carbon monoxide are generated in the exhaust gas by a rich mixture adjustment (operation of the internal combustion engine in homogeneous operation). Urea can be metered controlled from a reservoir to the exhaust gas. During the regeneration phase of the catalyst 12, the following processes take place: The reducing agent reduces the stored nitrogen oxides to nitrogen and oxygen. These substances exit from the catalyst 12, so that there is an excess of oxygen behind the catalyst 12 during the regeneration phase, although the internal combustion engine 1 is operated with a rich fuel / air mixture (lack of oxygen).

Vor dem Katalysator 12 ist ein Sauerstoff (02)-Sensor 13 und nach dem Katalysator 12 ein Stickstoff (NOx)-Sensor 14 in dem Abgasrohr 8 angeordnet. Nach dem Umschalten auf Sauerstoffmangel (Betrieb der Brennkraftmaschine 1 mit fettem Gemisch) vor dem Katalysator 12 zu Beginn der Regenerationsphase reagiert der O2-Sensor 13 praktisch verzögerungslos. Aufgrund des während des Schichtbetriebs vorherrschenden Sauerstoffüberschusses in dem Abgas sind die.Sauerstoffspeicherplätze des Katalysators 12 zunächst nahezu alle besetzt. Nach dem Umschalten auf Sauerstoffmangel zu Beginn der Regenerationsphase werden die Sauerstoffspeicherplätze sukzessive von Sauerstoff befreit, der dann aus dem Katalysator 12 heraustritt. Hinter dem Katalysator 12 herrscht daher nach dem Umschalten in die Regeneratonsphase zunächst weiter Sauerstoffüberschuss. Nach einer von der Sauerstoffspeicherfähigkeit des Katalysators 12 abhängigen Zeitspanne ist das gesamte in dem Speicherkatalysator 12' eingespeicherte Stickoxid reduziert und der gesamte in dem Sauerstoffspeicher 12" eingespeicherte Sauerstoff entfernt, so dass auch hinter dem Katalysator 12 Sauerstoffmangel auftritt.Before the catalyst 12, an oxygen (02) sensor 13 and after the catalyst 12, a nitrogen (NOx) sensor 14 in the exhaust pipe 8 is arranged. After switching to Lack of oxygen (operation of the internal combustion engine 1 with a rich mixture) before the catalyst 12 at the beginning of the regeneration phase, the O2 sensor 13 reacts virtually instantaneously. Due to the prevailing excess oxygen during the shift operation in the exhaust gas, the oxygen storage locations of the catalytic converter 12 are initially almost all occupied. After switching to lack of oxygen at the beginning of the regeneration phase, the oxygen storage sites are successively freed of oxygen, which then emerges from the catalyst 12. After the catalyst 12 therefore prevails after switching to the Regeneratonsphase initially further excess oxygen. After a period of time dependent on the oxygen storage capacity of the catalytic converter 12, the entire nitrogen oxide stored in the catalytic converter 12 'is reduced and the total oxygen stored in the oxygen storage 12 "is removed, so that oxygen deficiency also occurs behind the catalytic converter 12.

In Figur 2 ist ein NOx-Einspeichermodell 30 schematisch dargestellt. Als Eingangsgrößen liegen an dem NOx-Einspeichermodell 30 der NOx-Massenstrom msnovk vor dem Katalysator 12 und ein Wirkungsgrad eta_sp des NOx-Speicherkatalysators 12' an. Der Wirkungsgrad eta_sp wird in Abhängigkeit von u.a. dem NOx-Massenstrom msnovk vor dem NOx-Speicherkatalysator 12', einem NOx-Massenstrom msnonk hinter dem NOx-Speicherkatalysator 12' und der Temperatur des NOx-Speicherkatalysators 12' bestimmt. Der Wirkungsgrad eta_sp ist eine nichtlineare Funktion des NOx-Füllstands mnosp des NOx-Speicherkatalysators 12' und nimmt mit zunehmendem NOx-Füllstand ab.FIG. 2 schematically shows a NOx storage model 30. As input variables, the NOx mass flow msnovk upstream of the catalytic converter 12 and an efficiency eta_sp of the NOx storage catalytic converter 12 'are applied to the NOx injection model 30. The efficiency eta_sp is dependent on u.a. the NOx mass flow msnovk before the NOx storage catalytic converter 12 ', a NOx mass flow msnonk behind the NOx storage catalytic converter 12' and the temperature of the NOx storage catalytic converter 12 'determined. The efficiency eta_sp is a non-linear function of the NOx filling level mnosp of the NOx storage catalytic converter 12 'and decreases as the NOx level increases.

In einem Multiplikator 31 wird ein Produkt mnsospe des NOx-Massenstroms msnovk und des Wirkungsgrads eta_sp gebildet. Das Produkt mnsospe wird in einem Integrator 32 aufintegriert. Als Ausgangssignal liefert der Integrator 32 den NOx-Füllstand mnosp des NOx-Speicherkatalysators 12'. Dieser wird in einem Vergleicher 33 mit einem vorgebbaren Schwellwert schw verglichen. Übersteigt der NOx-Füllstand mnosp den Schwellwert schw, wird mittels eines Regenerationssignals B_denox die Regenerationsphase des NOx-Speicherkatalysators 12' eingeleitet.In a multiplier 31, a product mnsospe of the NOx mass flow msnovk and the efficiency eta_sp is formed. The product mnsospe is stored in an integrator 32 integrated. As an output signal, the integrator 32 supplies the NOx filling level mnosp of the NOx storage catalytic converter 12 '. This is compared in a comparator 33 with a predefinable threshold schw. If the NOx level mnosp exceeds the threshold value schw, the regeneration phase of the NOx storage catalytic converter 12 'is initiated by means of a regeneration signal B_denox.

In Figur 3 ist ein erfindungsgemäßes Verfahren schematisch dargestellt. Bei dem Verfahren dient ein Ausgangsignal msnonk_s des hinter dem Katalysator 12 angeordneten NOx-Sensors 14 zur Regelung des NOx-Einspeichermodells 30. Dadurch kann der Anfang und das Ende der zweiten Betriebsphase (Regenerationsphase) des NOx-Speicherkatalysators 12' wesentlich genauer und zuverlässiger bestimmt werden, was zu einer deutlich verbesserten Abgasqualität führt.FIG. 3 schematically shows a method according to the invention. In the method, an output signal msnonk_s of the arranged behind the catalyst 12 NOx sensor 14 is used to control the NOx injection model 30. Thus, the beginning and end of the second phase of operation (regeneration phase) of the NOx storage catalyst 12 'can be determined much more accurate and reliable , which leads to a significantly improved exhaust quality.

Es wird ein modellierter NOx-Massenstrom msnonk_m nach dem Katalysator 12 modelliert. Der modellierte NOx-Massenstrom msnonk_m ergibt sich aus der Differenz des NOx-Massenstroms msnovk vor dem Katalysator 12 und dem Produkt des NOx-Massenstroms msnovk und dem Wirkungsgrad eta_sp, d. h. aus msnovk · (1 - eta_sp). Der NOx-Massenstrom msnovk vor dem Katalysator 12 kann durch einen NOx-Sensor (nicht dargestellt) gemessen oder dem NOx-Modell entnommen werden.A modeled NOx mass flow msnonk_m after the catalyst 12 is modeled. The modeled NOx mass flow msnonk_m results from the difference of the NOx mass flow msnovk before the catalyst 12 and the product of the NOx mass flow msnovk and the efficiency eta_sp, d. H. from msnovk · (1 - eta_sp). The NOx mass flow msnovk upstream of the catalyst 12 may be measured by a NOx sensor (not shown) or taken from the NOx model.

Aus einer Differenz des modellierten NOx-Massenstroms msnonk_m nach dem Katalysator 12 und des durch den NOx-Sensor 14 gemessenen NOx-Massenstroms msnonk_s nach dem Katalysator 12 wird eine Regeldifferenz 34 des in Figur 3 dargestellten Regelkreises gebildet. Die Regeldifferenz 34 wird einem integrierenden I-Regler 35 zugeführt. Statt eines I-Reglers 35 können auch beliebig andere geeignete Regeler eingesetzt werden.From a difference of the modeled NOx mass flow msnonk_m after the catalyst 12 and the measured by the NOx sensor 14 NOx mass flow msnonk_s after the catalyst 12, a control difference 34 of the control circuit shown in Figure 3 is formed. The control difference 34 is supplied to an integrating I-controller 35. Instead of an I-controller 35, any other suitable regulators can also be used.

Eine Stellgröße 36 des I-Reglers 35 wird an ein Stellglied 37 geleitet, das eine Stellgröße 38 variiert, um auf das NOx-Einspeichermodell 30 gezielt regelnd einzuwirken. Als Stellgröße 38 wird der Wirkungsgrad eta_sp des NOx-Speicherkatalysators 12' herangezogen.A manipulated variable 36 of the I-controller 35 is passed to an actuator 37, which varies a manipulated variable 38 in order to act in a controlled manner on the NOx injection model 30. The manipulated variable 38 is the efficiency eta_sp of the NOx storage catalytic converter 12 '.

Claims (8)

  1. Method for operating a nitrogen oxide (NOx) storage catalytic converter (12') of an internal combustion engine (1) in particular of a motor vehicle, in which nitrogen oxides (NOx) generated by the internal combustion engine (1) are accumulated in the NOx storage catalytic converter (12') during a first operating phase and nitrogen oxides which have accumulated in the NOx catalytic converter (12') are discharged from the NOx storage catalytic converter (12') in a second operating phase, the start of the second operating phase is determined on the basis of a nitrogen oxide (NOx) filling level (mnosp) of the NOx storage catalytic converter (12'), the NOx filling level (mnosp) is modelled on the basis of a nitrogen oxide (NOx) accumulation model (30), and a first value of a nitrogen oxide (NOx) mass flow (msnonk_s) downstream of the NOx storage catalytic converter (12') is recorded, and the NOx accumulation model (30) is corrected as a function of the recorded first value, characterized in that a second value of the NOx mass flow (msnonk_m) downstream of the NOx storage catalytic converter (12') is removed from the NOx accumulation model (30), and a difference between the two values of the NOx mass flows (msnonk_m - msnonk_s) is formed and the NOx accumulation model (30) is corrected as a function of the difference (msnonk_m - msnonk_s).
  2. Method according to Claim 1, characterized in that the difference (msnonk_m - msnonk_s) between the two values (msnonk_m, msnonk_s) is fed to a controller (35), and the NOx accumulation model (30) is corrected as a function of a control variable (38) of the controller (35).
  3. Method according to Claim 1 or 2, characterized in that the NOx filling level (mnosp) is determined by integrating the product of the NOx mass flow (msnovk) upstream of the NOx storage catalytic converter (12') and an efficiency (eta_sp) of the NOx storage catalytic converter (12') in the NOx accumulation model (30).
  4. Method according to Claim 2 or 3, characterized in that the NOx accumulation model (30) is corrected as a function of the efficiency (eta_sp) of the NOx storage catalytic converter (12') as the control variable (38) of the controller (35).
  5. Method according to one of Claims 1 to 4, characterized in that the first value of the NOx mass flow (msnonk_s) downstream of the NOx storage catalytic converter (12') is measured by means of an NOx sensor (14).
  6. Control element, in particular read only memory or flash memory, for a control unit (18) of an internal combustion engine (1) in particular of a motor vehicle, on which is stored a program which can run on a computer unit, in particular on a microprocessor, and is suitable for executing a method according to one of Claims 1 to 5.
  7. Control unit (18) for an internal combustion engine (1) in particular of a motor vehicle, it being possible for the internal combustion engine (1) to be switched by the control unit (18) between a first operating phase, in which nitrogen oxides (NOx) generated by the internal combustion engine (1) are accumulated in the nitrogen oxide (NOx) storage catalytic converter (12'), and a second operating phase, in which accumulated nitrogen oxides are discharged from the NOx storage catalytic converter (12'), and the control unit (18) having first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) filling level (mnosp) of the storage catalytic converter (12'), which has been modelled by means of a nitrogen oxide (NOx) accumulation model (30), second means (14) for recording a first value of the nitrogen oxide (NOx) mass flow (msnonk_s) downstream of the NOx storage catalytic converter (12'), and third means for correcting the NOx accumulation model (30) as a function of the recorded first value (msnonk_s), characterized in that the control unit (18) has fourth means for removing a second value of the NOx mass flow (msnonk_m) downstream of the NOx storage catalytic converter (12') from the NOx accumulation model (30) and fifth means for forming a difference between the two values of the NOx mass flows (msnonk_m - msnonk_s), and the third means correct the NOx accumulation model (30) as a function of the difference (msnonk_m - msnonk_s).
  8. Internal combustion engine (1) in particular of a motor vehicle, the internal combustion engine (1) having a control unit (18) and a nitrogen oxide (NOx) storage catalytic converter (12'), and it being possible for the internal combustion engine (1) to be switched by the control unit (18) between a first operating phase, in which nitrogen oxides (NOx) generated by the internal combustion engine (1) are accumulated in the NOx storage catalytic converter (12'), and a second operating phase, in which accumulated nitrogen oxides are discharged from the NOx storage catalytic converter (12'), and the internal combustion engine (1) having first means for determining the start of the second operating phase on the basis of a nitrogen oxide (NOx) filling level (mnosp) of the NOx storage catalytic converter (12'), which has been modelled by means of a nitrogen oxide (NOx) accumulation model (30), second means (14) for recording a first value of the nitrogen oxide (NOx) mass flow (msnonk_s) downstream of the NOx storage catalytic converter (12') and third means for correcting the NOx accumulation model (30) as a function of the recorded first value (msnonk_s), characterized in that the internal combustion engine (1) has fourth means for removing a second value of the NOx mass flow (msnonk_m) downstream of the NOx storage catalytic converter (12') from the NOx accumulation model (30) and fifth means for forming a difference between the two values of the NOx mass flows (msnonk_m - msnonk_s), and the third means correct the NOx accumulation model (30) as a function of the difference (msnonk_m - msnonk_s).
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DE10036453A DE10036453A1 (en) 2000-07-26 2000-07-26 Operating a nitrogen oxide storage catalyst on vehicle IC engine comprises storing nitrogen oxides generated from the engine in first phase in storage catalyst
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