WO2000028200A1 - METHOD FOR DETERMINING THE NOx CRUDE EMISSION OF AN INTERNAL COMBUSTION ENGINE OPERATED WITH AN EXCESS OF AIR - Google Patents

METHOD FOR DETERMINING THE NOx CRUDE EMISSION OF AN INTERNAL COMBUSTION ENGINE OPERATED WITH AN EXCESS OF AIR Download PDF

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Publication number
WO2000028200A1
WO2000028200A1 PCT/DE1999/003515 DE9903515W WO0028200A1 WO 2000028200 A1 WO2000028200 A1 WO 2000028200A1 DE 9903515 W DE9903515 W DE 9903515W WO 0028200 A1 WO0028200 A1 WO 0028200A1
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Prior art keywords
internal combustion
combustion engine
nox
fac
exhaust gas
Prior art date
Application number
PCT/DE1999/003515
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German (de)
French (fr)
Inventor
Hong Zhang
Corinna Pfleger
Wolfgang Ludwig
Original Assignee
Siemens Aktiengesellschaft
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Publication of WO2000028200A1 publication Critical patent/WO2000028200A1/en

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Classifications

    • 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
    • F02D41/30—Controlling fuel injection
    • F02D41/3011—Controlling fuel injection according to or using specific or several modes of combustion
    • F02D41/3017—Controlling fuel injection according to or using specific or several modes of combustion characterised by the mode(s) being used
    • F02D41/3023—Controlling 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
    • 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
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • 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
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • 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
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B75/00—Other engines
    • F02B75/12—Other methods of operation
    • F02B2075/125—Direct injection in the combustion chamber for spark ignition engines, i.e. not in pre-combustion chamber
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
    • F02B23/08—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition
    • F02B23/10—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder
    • F02B23/101—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder the injector being placed on or close to the cylinder centre axis, e.g. with mixture formation using spray guided concepts
    • 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
    • F02D41/30—Controlling fuel injection
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D2041/389—Controlling fuel injection of the high pressure type for injecting directly into the cylinder
    • 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
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0065—Specific aspects of external EGR control
    • F02D41/0072—Estimating, calculating or determining the EGR rate, amount or flow
    • 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
    • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
    • F02D41/1441—Plural sensors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
    • F02D41/1456—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio with sensor output signal being linear or quasi-linear with the concentration of oxygen
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M2026/001—Arrangements; Control features; Details
    • F02M2026/004—EGR valve controlled by a temperature signal or an air/fuel ratio (lambda) signal
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the invention relates to a method for determining the raw NOx emission of an internal combustion engine that can be operated with excess air, according to the preamble of patent claim 1.
  • the internal combustion engine In the upper load range, the internal combustion engine is operated with a homogeneous cylinder charge. The injection takes place during the intake process in order to obtain a good mixture of fuel and air. The intake air mass is adjusted according to the driver's torque request via a throttle valve. The required injection quantity is calculated from the air mass and the speed and corrected via the lambda control.
  • NOx storage catalytic converters are used for this. Due to their coating, these NOx storage catalytic converters are able to remove NOx compounds from the storage during a storage phase, also known as the loading phase Adsorb exhaust gas that arises from lean combustion. During a regeneration phase, the adsorbed or stored NOx compounds are converted into harmless compounds with the addition of a reducing agent. CO, H 2 and HC (hydrocarbons) can be used as reducing agents for lean-burn gasoline internal combustion engines. These are generated by briefly operating the internal combustion engine with a rich mixture and made available to the NOx storage catalytic converter as exhaust gas components, as a result of which the stored NOx compounds in the catalytic converter are broken down.
  • the storage efficiency of such a NOx storage catalytic converter depends on numerous influencing variables described in the literature.
  • the degree of catalyst loading is a primary influencing variable. With increasing lean phase duration and the resulting storage of NOx, the storage efficiency decreases continuously, so that, taking into account the exhaust gas limit values or other operating conditions, a switchover to the rich - i.e. in the regeneration mode is necessary.
  • the NOx storage catalytic converter is preferably loaded up to a specified loading quantity. This amount can be calculated from the raw NOx emission in the raw exhaust gas. To do this, it is necessary to determine this raw NOx emission as precisely as possible.
  • the raw NOx emission can be determined using a calculation model.
  • EP 0 597 106 AI discloses a method for regenerating a NOx storage catalytic converter, in which the amount of NOx compounds adsorbed by the NOx storage catalytic converter is calculated as a function of operating data of the internal combustion engine. When a predetermined limit of NOx stored in the NOx storage catalytic converter is exceeded, a regeneration phase is initiated. In this way, however, reliable compliance with the exhaust gas emission limit values is not always guaranteed.
  • the invention is based on the object of specifying a method with which the raw NOx emission of an internal combustion engine which can be operated with excess air can be determined in a stratified charge mode in a simple manner.
  • the throttle valve is fully open in stratified charge mode.
  • the intake air must be tightened. This change in the throttle valve angle affects the cylinder charge and the raw NOx emission.
  • the intake air temperature also influences the raw NOx emission due to its temperature-dependent density by changing the cylinder charge.
  • the throttling and the intake air temperature are taken into account quantitatively within a calculation model for determining the raw NOx emission.
  • the basic raw NOx emission in stratified charge mode of the internal combustion engine is obtained from a map as a function of the fuel mass and the engine speed. This basic value is corrected with a correction value which is determined as a function of the intake air temperature. The value thus obtained is in turn corrected with a correction value as a function of the engine speed and the exhaust gas recirculation rate.
  • the throttling in stratified charge mode is taken into account by a further correction factor which is determined as a function of the relationship between the actual intake air mass and a reference intake air mass. The actual intake air mass is measured, the reference intake air mass corresponds to the intake air mass, which can be measured under defined environmental conditions and with the throttle valve fully open. It is still dependent on the engine speed.
  • the value for the raw NOx emission can be determined with high accuracy, which in turn e.g. enables an exact determination of the degree of loading of the NOx storage catalytic converter.
  • FIG. 1 shows a schematic illustration of an internal combustion engine with a NOx storage catalytic converter
  • FIG. 2 shows a block diagram for determining the raw NOx emission in stratified charge operation of the internal combustion engine
  • Internal combustion engine with gasoline direct injection depending on operating parameters with both a homogeneous mixture can also be operated with stratified charge and has a device for exhaust gas recirculation. For reasons of clarity, only those parts are drawn which are necessary for understanding the invention. In particular, only one cylinder of a multi-cylinder internal combustion engine is shown.
  • Reference number 10 denotes a piston which delimits a combustion chamber 12 in a cylinder 11.
  • An intake duct 13 opens into the combustion chamber 12, through which the combustion air flows into the cylinder 11, controlled by an inlet valve 14.
  • an exhaust duct 16 branches off from the combustion chamber 12, in the further course of which an oxygen sensor in the form of a broadband (linear) lambda probe 17 and a NOx storage catalytic converter 18 are arranged.
  • the air ratio is regulated in accordance with the setpoint values in the various operating ranges of the internal combustion engine.
  • This function is performed by a lambda control device known per se, which is preferably integrated in a control device 21 of the internal combustion engine.
  • the signal from an oxygen sensor 32 arranged after the NOx storage catalytic converter 18 is required as a guide probe.
  • a binary lambda probe (2-point sensor) is preferably used as the oxygen sensor 32.
  • This probe signal from the lambda probe 32 arranged after the NOx storage catalytic converter 18 is also used to control the storage regeneration and to adapt model variables such as the oxygen or NOx storage capacity.
  • Alternative to that as a leadership probe NOx sensor 32 can also be used a NOx sensor.
  • the temperature of the NOx storage catalytic converter 18, which is required for the consumption and emission-optimal control of the exhaust gas aftertreatment system, is calculated using a temperature model from the sensor signal of a temperature sensor 33. Based on this measurement signal, catalyst heating or catalyst protection measures are also initiated. Alternatively, the temperature of the NOx storage catalytic converter 15 can also be measured directly by arranging a temperature sensor directly in the housing thereof.
  • the NOx storage catalytic converter is used to comply with the required exhaust gas limit values in operating areas with lean combustion. Due to its coating, it adsorbs the NOx compounds generated in the exhaust gas during lean combustion.
  • An exhaust gas recirculation device is provided in order to reduce the NOx emissions of the internal combustion engine that occur especially in internal combustion engines with direct injection and stratified charge operation. By adding exhaust gas to the fresh air drawn in, the peak combustion temperature is reduced, which reduces the temperature-dependent nitrogen oxide emission.
  • an exhaust gas recirculation line 19 branches off from the exhaust gas duct 16 in the flow direction of the exhaust gas, in front of the NOx storage catalytic converter 18
  • Throttle valve 20 opens into the intake duct 13.
  • the amount of the recirculated exhaust gas is set by changing the duty cycle EGR_RATIO of a signal output by the electronic control device 21 for a controllable valve 22, generally referred to as an exhaust gas recirculation valve.
  • the fresh air necessary for combustion in the cylinder 11 flows through an air filter (not shown) and an air mass meter 23 into the intake tract 13 to the throttle valve 20.
  • This throttle valve 20 is an electric motor-controlled throttle element (E-gas system), the opening cross section of which in addition to being actuated by the driver (driver request), it can also be set independently of this via signals from the electronic control device 21.
  • E-gas system electric motor-controlled throttle element
  • this can reduce disturbing load change reactions of the vehicle when accelerating and decelerating, as well as torque jumps during the transition from operation with a homogeneous mixture to operation with stratified cargo and unrestricted air flow.
  • a signal for the position of the throttle valve 20 is output to the control device 21 for monitoring.
  • a temperature sensor 24 detects the temperature of the intake air in the intake duct 13 of the internal combustion engine and outputs a corresponding signal TIA to the control device 21.
  • the temperature sensor 24 can be integrated in the air mass meter 23.
  • a spark plug 25 and an injection valve 26 protrude into the combustion chamber 12 and can be used to inject fuel against the compression pressure in the combustion chamber 12.
  • the delivery and provision of the fuel for this injection valve 26 is carried out by a known fuel supply system for gasoline direct injection, with only one high-pressure reservoir 27 from the associated fuel circuit being shown, to which the individual injection valves are connected.
  • a temperature sensor 28 detects a signal corresponding to the temperature of the internal combustion engine, for example by measuring the coolant temperature.
  • the speed N of the internal combustion engine is scanned with the aid of markings on the crankshaft or a sensor wheel connected to it Sensor 29 detected. Both signals are fed to the control device 21 for further processing, inter alia for controlling the internal combustion engine with regard to the control strategy to be selected — homogeneous mixture or stratified mixture.
  • control parameters that are required for operating the internal combustion engine such as, for example, accelerator pedal position, throttle valve position, signals from knock sensors, battery voltage, driving dynamics requirements, etc., are likewise supplied to the control device 21 and are generally identified in the figure by the reference symbol 30.
  • the above-mentioned parameters are used in the control device 21 by processing stored control routines, among other things.
  • the load state of the internal combustion engine is recognized, the raw NOx emission of the internal combustion engine and the degree of loading of the NOx storage catalytic converter are determined.
  • the parameters are also processed and processed in such a way that, in certain operating states of the internal combustion engine, i.a. a switch from operation with a homogeneous mixture to operation with
  • control device 21 is connected to a storage device 31, in which, among other things, Various maps KF1-KF4, as well as values for a reference intake air mass LMM are stored, the respective meaning of which is explained in more detail with reference to the description of the following figure.
  • FIG. 2 uses a block diagram to illustrate the structure for determining the raw NOx emission of the internal combustion engine in stratified charge mode.
  • the fuel mass MFF and the speed N of the internal combustion engine characterize the current operating point of the internal combustion engine and are therefore input variables Map KF1. Depending on the values of these input variables, a base value for the raw NOx emission NOX_B, for example in the unit mg / s, is read out from the map KF1.
  • the fuel mass MFF can be derived from the values for the opening duration, the throughput and / or the pressure at the injection valve.
  • the speed N of the internal combustion engine is detected with the aid of the speed sensor 29.
  • the temperature level at which the combustion takes place in the cylinder of the internal combustion engine is essentially influenced by the intake air temperature, the exhaust gas recirculation rate and the air mass flow.
  • the basic value of the raw NOX emission NOX_B obtained from the map KF1 is therefore corrected with a first correction factor FAC_TIA, which is determined as a function of the intake air temperature TIA.
  • FAC_TIA a corresponding value for the correction factor FAC TIA is read from a map KF2 for the respective value of the intake air temperature TIA.
  • the intake air temperature TIA is detected by means of the temperature sensor 24 or derived from the value of the ambient temperature, for example via a model.
  • the corrected base value for the raw NOx emission obtained in this way is multiplied by a further correction factor FAC_EGR, which is read out from a map KF3.
  • FAC_EGR further correction factor
  • the influence of the exhaust gas recirculation rate for a given value for the exhaust gas recirculation rate EGR_RATIO is not constant above the speed N. For this reason, the influence of the speed is taken into account when reading from the map KF3.
  • the value for the exhaust gas recirculation rate EGR_RATIO can be derived from the position of the opening element of the exhaust gas recirculation valve 22.
  • the throttling in stratified charge mode is taken into account by means of a further correction factor FAC_LM which, depending on the ratio between the actual intake air mass LM and a reference intake air mass LMM is communicated.
  • the actual intake air mass LM is measured by means of the air mass meter 23, the reference intake air mass LMM corresponds to the intake air mass which is determined under defined ambient conditions and with the throttle valve 20 fully open.
  • the values for the reference intake air mass LMM, which are dependent in particular on the speed N, are also stored in the storage device 31.
  • the relationship between the actual intake air mass LM and the reference intake air mass LMM is determined as follows:
  • This ratio FAC is the input variable for a map KF4, in which the relationship between this ratio FAC and the correction factor FAC_LM is stored.
  • This correction factor FAC_LM is also taken into account multiplicatively when modeling the raw NOx emission.
  • FAC_GES FAC_TIA * FAC_EGR * FAC_LM.
  • NOX_COR is available for the NOX_ raw emission, which can be used, for example, to determine the degree of loading of the NOx storage catalytic converter 18 precisely.

Abstract

According to the inventive method, an internal combustion engine is operated in the stratified charge operation and a base value for the NOx crude emission is determined which depends on the amount of fuel (MFF) injected into the cylinders of the internal combustion engine and the speed (N) of the internal combustion engine. A correction factor is added to the base value. Said correction factor takes into consideration the exhaust gas recirculation ratio (EGR_RATIO), the temperature of the intake air (TIA) and the position of the throttle device (20) in the stratified charge operation.

Description

Beschreibung description
Verfahren zum Bestimmen der NOx-Rohemission einer mit Luftüberschuß betreibbaren BrennkraftmaschineMethod for determining the raw NOx emission of an internal combustion engine that can be operated with excess air
Die Erfindung betrifft ein Verfahren zum Bestimmen der NOx- Rohemission einer mit Luftüberschuß betreibbaren Brennkraftmaschine gemäß dem Oberbegriff des Patentanspruches 1.The invention relates to a method for determining the raw NOx emission of an internal combustion engine that can be operated with excess air, according to the preamble of patent claim 1.
Um den Kraftstoffverbrauch von Kraftfahrzeugen mit ottomotorischem Antrieb weiter zu reduzieren, kommen immer häufiger Brennkraftmaschinen zum Einsatz, die mit magerem Gemisch betrieben werden. Dabei wird zwischen zwei grundlegenden Betriebsarten unterschieden. Im unteren Lastbereich wird die Brennkraftmaschine mit einer stark geschichteten Zylinderladung und hohem Luftüberschuß betrieben (Schichtladebetrieb) . Dies wird durch eine späte Einspritzung kurz vor dem Zündzeitpunkt erreicht. Die Brennkraftmaschine wird dabei unter Vermeidung von Drosselverlusten weitgehend ungedrosselt be- trieben. Zur Absenkung der NOx-Rohemission wird eine hohe Ab- gasrückführrate angestrebt.In order to further reduce the fuel consumption of motor vehicles with an petrol engine, internal combustion engines that are operated with a lean mixture are increasingly being used. A distinction is made between two basic operating modes. In the lower load range, the internal combustion engine is operated with a strongly stratified cylinder charge and a large excess of air (stratified charge mode). This is achieved by late injection shortly before the ignition point. The internal combustion engine is operated largely without throttling while avoiding throttle losses. A high exhaust gas recirculation rate is aimed at to reduce the raw NOx emission.
Im oberen Lastbereich wird die Brennkraftmaschine mit homogener Zylinderladung betrieben. Die Einspritzung erfolgt be- reits während des Ansaugvorganges, um eine gute Durchmischung von Kraftstoff und Luft zu erhalten. Die angesaugte Luftmasse wird entsprechend dem Drehmoment ünsch des Fahrers über eine Drosselklappe eingestellt. Die benötigte Einspritzmenge wird aus der Luftmasse und der Drehzahl berechnet und über die Lambdaregelung korrigiert.In the upper load range, the internal combustion engine is operated with a homogeneous cylinder charge. The injection takes place during the intake process in order to obtain a good mixture of fuel and air. The intake air mass is adjusted according to the driver's torque request via a throttle valve. The required injection quantity is calculated from the air mass and the speed and corrected via the lambda control.
Zur Erfüllung der geforderten Abgasemissionsgrenzwerte ist bei solchen Brennkraftmaschinen eine spezielle Abgasnachbehandlung notwendig. Dazu werden NOx-Speicherkatalysatoren verwendet. Diese NOx-Speicherkatalysatoren sind aufgrund ihrer Beschichtung in der Lage, während einer Speicherphase, auch als Beladungsphase bezeichnet, NOx-Verbindungen aus dem Abgas zu adsorbieren, die bei magerer Verbrennung entstehen. Während einer Regenerationsphase werden die adsorbierten bzw. gespeicherten NOx-Verbindungen unter Zugabe eines Reduktionsmittels in unschädliche Verbindungen umgewandelt. Als Reduk- tionsmittel für magerbetriebene Otto-Brennkraftmaschinen können CO, H2 und HC (Kohlenwasserstoffe) verwendet werden. Diese werden durch kurzzeitigen Betrieb der Brennkraftmaschine mit einem fetten Gemisch erzeugt und dem NOx- Speicherkatalysator als Abgaskomponenten zur Verfügung ge- stellt, wodurch die gespeicherten NOx-Verbindungen im Katalysator abgebaut werden.In order to meet the required exhaust emission limit values, special exhaust gas aftertreatment is necessary in such internal combustion engines. NOx storage catalytic converters are used for this. Due to their coating, these NOx storage catalytic converters are able to remove NOx compounds from the storage during a storage phase, also known as the loading phase Adsorb exhaust gas that arises from lean combustion. During a regeneration phase, the adsorbed or stored NOx compounds are converted into harmless compounds with the addition of a reducing agent. CO, H 2 and HC (hydrocarbons) can be used as reducing agents for lean-burn gasoline internal combustion engines. These are generated by briefly operating the internal combustion engine with a rich mixture and made available to the NOx storage catalytic converter as exhaust gas components, as a result of which the stored NOx compounds in the catalytic converter are broken down.
Der Speicherwirkungsgrad eines solchen NOx- Speicherkatalysators hängt von zahlreichen, in der Literatur beschriebenen Einflußgrößen ab. Eine primäre Einflußgröße stellt der Katalysatorbeladungsgrad dar. Mit zunehmender Dauer der Magerphase und daraus resultierenden Speicherung von NOx nimmt der Speicherwirkungsgrad kontinuierlich ab, so daß unter Berücksichtigung der Abgasgrenzwerte oder weiterer Be- triebsbedingungen eine Umschaltung in den Fett- d.h. in den Regenerationsbetrieb notwendig wird.The storage efficiency of such a NOx storage catalytic converter depends on numerous influencing variables described in the literature. The degree of catalyst loading is a primary influencing variable. With increasing lean phase duration and the resulting storage of NOx, the storage efficiency decreases continuously, so that, taking into account the exhaust gas limit values or other operating conditions, a switchover to the rich - i.e. in the regeneration mode is necessary.
Die Beladung des NOx-Speicherkatalysators erfolgt vorzugsweise bis zu einer festgelegten Beladungsmenge. Diese Menge kann aus der NOx-Rohemission im Rohabgas berechnet werden. Dazu ist es nötig, diese NOx-Rohemission möglichst genau zu bestimmen. Die NOx-Rohemission kann dabei mittels eines Rechenmodells bestimmt werden.The NOx storage catalytic converter is preferably loaded up to a specified loading quantity. This amount can be calculated from the raw NOx emission in the raw exhaust gas. To do this, it is necessary to determine this raw NOx emission as precisely as possible. The raw NOx emission can be determined using a calculation model.
Bekannte Lösungen dieses Problems basieren auf einer in ihrer Art variierenden Modellrechnung zur Ermittlung der aktuellen Beladung und des Regenerationsmittelbedarfs bzw. der Regenerationsdauer, wobei die Güte des Modells (Struktur und Kalibration) die Güte der Lösung des oben beschriebenen Problems vorgibt (z.B. DE 195 17 168 AI). Aus der EP 0 597 106 AI ist ein Verfahren zur Regeneration eines NOx-Speicherkatalysators bekannt, bei dem die vom NOx- Speicherkatalysator adsorbierte Menge an NOx-Verbindungen in Abhängigkeit von Betriebsdaten der Brennkraftmaschine berechnet wird. Bei Überschreiten einer vorbestimmten Grenzmenge von im NOx-Speicherkatalysator gespeichertem NOx wird eine Regenerationsphase eingeleitet. Auf diese Weise ist jedoch ein zuverlässiges Einhalten der Abgasemissionsgrenzwerte nicht immer gewährleistet.Known solutions to this problem are based on a model calculation that varies in its nature to determine the current load and the regeneration agent requirement or the regeneration duration, the quality of the model (structure and calibration) specifying the quality of the solution to the problem described above (for example DE 195 17 168 AI). EP 0 597 106 AI discloses a method for regenerating a NOx storage catalytic converter, in which the amount of NOx compounds adsorbed by the NOx storage catalytic converter is calculated as a function of operating data of the internal combustion engine. When a predetermined limit of NOx stored in the NOx storage catalytic converter is exceeded, a regeneration phase is initiated. In this way, however, reliable compliance with the exhaust gas emission limit values is not always guaranteed.
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren anzugeben, mit dem auf einfache Weise die NOx-Rohemission einer mit Luftüberschuß betreibbaren Brennkraftmaschine im Schichtladebetrieb bestimmt werden kann.The invention is based on the object of specifying a method with which the raw NOx emission of an internal combustion engine which can be operated with excess air can be determined in a stratified charge mode in a simple manner.
Diese Aufgabe wird durch die Merkmale des Patentanspruchs 1 gelöst. Vorteilhafte Ausgestaltungen der Erfindung sind in den Unteransprüchen angegeben.This object is achieved by the features of patent claim 1. Advantageous embodiments of the invention are specified in the subclaims.
Theoretisch ist die Drosselklappe im Schichtladebetrieb vollständig geöffnet. Um anderen Fahrzeugkomponenten, wie z.B. der Tankentlüftungsanlage, Unterdruck im Ansaugsystem zur Verfügung zu stellen oder um die Verbrennung zu stabilisieren und die Laufunruhe zu minimieren, ist allerdings eine Andros- seiung der Ansaugluft nötig. Diese Änderung des Drosselklappenwinkels beeinflußt die Zylinderfüllung und die NOx- Rohemission. Auch die Ansauglufttemperatur beeinflußt durch ihre von der Temperatur abhängige Dichte über eine Veränderung der Zylinderfüllung die NOx-Rohemission.Theoretically, the throttle valve is fully open in stratified charge mode. To other vehicle components, such as of the tank ventilation system to provide negative pressure in the intake system or in order to stabilize the combustion and to minimize uneven running, the intake air must be tightened. This change in the throttle valve angle affects the cylinder charge and the raw NOx emission. The intake air temperature also influences the raw NOx emission due to its temperature-dependent density by changing the cylinder charge.
Um eine möglichst genaue Annäherung der modellierten NOx- Rohemission an die tatsächliche NOx-Rohemission zu erreichen, wird die Androsselung sowie die Ansauglufttemperatur innerhalb eines Rechenmodells zur Bestimmung der NOx-Rohemission quantitativ berücksichtigt. Die Basis-NOx-Rohemission im Schichtladebetrieb der Brennkraftmaschine wird aus einem Kennfeld in Abhängigkeit von der Kraftstoffmasse und der Motordrehzahl gewonnen. Dieser Basiswert wird mit einem Korrekturwert, der in Abhängigkeit von der Ansauglufttemperatur bestimmt wird, korrigiert. Der so erhaltene Wert wird wiederum mit einem Korrekturwert in Abhängigkeit von der Motordrehzahl und der Abgasrückführrate korrigiert. Die Berücksichtigung der Androsselung im Schichtladebetrieb erfolgt durch einen weiteren Korrekturfaktor, der in Abhängigkeit des Verhältnisses zwischen der tatsächlichen Ansaugluftmasse und einer Referenzansaugluftmasse ermittelt wird. Die tatsächliche Ansaugluftmasse wird gemessen, die Referenzansaugluftmasse entspricht der Ansaugluftmasse, die bei definierten Umgebungsbedingungen und vollständig geöffneter Drosselklappe meßbar ist. Sie ist weiterhin von der Motordrehzahl abhängig.In order to achieve the most accurate approximation of the modeled raw NOx emission to the actual raw NOx emission, the throttling and the intake air temperature are taken into account quantitatively within a calculation model for determining the raw NOx emission. The basic raw NOx emission in stratified charge mode of the internal combustion engine is obtained from a map as a function of the fuel mass and the engine speed. This basic value is corrected with a correction value which is determined as a function of the intake air temperature. The value thus obtained is in turn corrected with a correction value as a function of the engine speed and the exhaust gas recirculation rate. The throttling in stratified charge mode is taken into account by a further correction factor which is determined as a function of the relationship between the actual intake air mass and a reference intake air mass. The actual intake air mass is measured, the reference intake air mass corresponds to the intake air mass, which can be measured under defined environmental conditions and with the throttle valve fully open. It is still dependent on the engine speed.
Durch zusätzliche Berücksichtigung der Drosselklappenstellung und der Ansauglufttemperatur bei der Modellierung der NOx- Rohemission im Schichtladebetrieb der Brennkraftmaschine kann der Wert für die NOx-Rohemission mit hoher Genauigkeit ermittelt werden, was wiederum z.B. eine genaue Bestimmung des Beladungsgrades des NOx-Speicherkatalysators ermöglicht.Through additional consideration of the throttle valve position and the intake air temperature when modeling the raw NOx emission in stratified charge mode of the internal combustion engine, the value for the raw NOx emission can be determined with high accuracy, which in turn e.g. enables an exact determination of the degree of loading of the NOx storage catalytic converter.
Die Erfindung wird nachfolgend unter Bezugnahme auf die Zeichnung näher erläutert. Es zeigen:The invention is explained in more detail below with reference to the drawing. Show it:
Figur 1 eine schematische Darstellung einer Brennkraftmaschine mit einem NOx-Speicherkatalysator,FIG. 1 shows a schematic illustration of an internal combustion engine with a NOx storage catalytic converter,
Figur 2 eine Blockdarstellung zur Ermittlung der NOx- Rohemission im Schichtladebetrieb der BrennkraftmaschineFIG. 2 shows a block diagram for determining the raw NOx emission in stratified charge operation of the internal combustion engine
Die Figur 1 zeigt in grob schematischer Darstellung eine1 shows a roughly schematic representation of a
Brennkraftmaschine mit Benzin-Direkteinspritzung, die abhängig von Betriebsparametern sowohl mit homogenem Gemisch als auch mit geschichteter Ladung betreibbar ist und eine Vorrichtung zur Abgasrückführung aufweist. Aus Gründen der Übersichtlichkeit sind dabei nur diejenigen Teile gezeichnet, die für das Verständnis der Erfindung notwendig sind. Insbesonde- re ist nur ein Zylinder einer mehrzylindrigen Brennkraftmaschine dargestellt.Internal combustion engine with gasoline direct injection, depending on operating parameters with both a homogeneous mixture can also be operated with stratified charge and has a device for exhaust gas recirculation. For reasons of clarity, only those parts are drawn which are necessary for understanding the invention. In particular, only one cylinder of a multi-cylinder internal combustion engine is shown.
Mit dem Bezugszeichen 10 ist ein Kolben bezeichnet, der in einem Zylinder 11 einen Verbrennungsraum 12 begrenzt. In den Verbrennungsraum 12 mündet ein Ansaugkanal 13, durch den gesteuert durch ein Einlaßventil 14 die Verbrennungsluft in den Zylinder 11 strömt. Gesteuert durch ein Auslaßventil 15 zweigt vom Verbrennungsraum 12 ein Abgaskanal 16 ab, in dessen weiterer Verlauf ein Sauerstoffsensor in Form einer breitbandigen (linearen) Lambdasonde 17 und ein NOx- Speicherkatalysator 18 angeordnet ist.Reference number 10 denotes a piston which delimits a combustion chamber 12 in a cylinder 11. An intake duct 13 opens into the combustion chamber 12, through which the combustion air flows into the cylinder 11, controlled by an inlet valve 14. Controlled by an exhaust valve 15, an exhaust duct 16 branches off from the combustion chamber 12, in the further course of which an oxygen sensor in the form of a broadband (linear) lambda probe 17 and a NOx storage catalytic converter 18 are arranged.
Mit dem Signal der Lambdasonde 17 wird die Luftzahl entsprechend den Sollwertvorgaben in den verschiedenen Betriebsbe- reichen der Brennkraftmaschine geregelt. Diese Funktion übernimmt eine an sich bekannte Lambdaregelungseinrichtung, die vorzugsweise in eine Steuerungseinrichtung 21 der Brennkraftmaschine integriert ist.With the signal from the lambda probe 17, the air ratio is regulated in accordance with the setpoint values in the various operating ranges of the internal combustion engine. This function is performed by a lambda control device known per se, which is preferably integrated in a control device 21 of the internal combustion engine.
Zur Regelung des Kraftstoff-/Luftgemisches der Brennkraftmaschine im optimalen Lambda-Fenster während des stöchiometri- schen Betriebs ist das Signal eines nach dem NOx- Speicherkatalysator 18 angeordneten Sauerstoffmeßaufnehmers 32 als Führungssonde erforderlich. Als Sauerstoffmeßaufnehmer 32 dient vorzugsweise eine binäre Lambdasonde (2-Punkt-To control the fuel / air mixture of the internal combustion engine in the optimal lambda window during stoichiometric operation, the signal from an oxygen sensor 32 arranged after the NOx storage catalytic converter 18 is required as a guide probe. A binary lambda probe (2-point sensor) is preferably used as the oxygen sensor 32.
Lambdasonde) auf der Basis von Zirkonoxid Zr02, die bei einem Lambdawert λ=l bezüglich ihres Ausgangssignales eine Sprungcharakteristik aufweist. Dieses Sondensignal der nach dem NOx-Speicherkatalysator 18 angeordneten Lambdasonde 32 wird auch zur Steuerung der Speicherregeneration und zur Adaption von Modellgrößen wie z.B. der Sauerstoff- bzw. NOx- Speicherkapazität eingesetzt. Alternativ zu dem als Führungs- sonde dienenden Sauerstoffmeßaufnehmer 32 kann auch ein NOx- Sensor verwendet werden.Lambda probe) based on zirconium oxide Zr02, which has a step characteristic with regard to its output signal at a lambda value λ = 1. This probe signal from the lambda probe 32 arranged after the NOx storage catalytic converter 18 is also used to control the storage regeneration and to adapt model variables such as the oxygen or NOx storage capacity. Alternative to that as a leadership probe NOx sensor 32 can also be used a NOx sensor.
Die Temperatur des NOx-Speicherkatalysators 18, die zur ver- brauchs- und emissionsoptimalen Steuerung des Abgasnachbehandlungssystems erforderlich ist, wird mittels eines Temperaturmodells aus dem Sensorsignal eines Temperatursensors 33 errechnet. Basierend auf diesem Meßsignal werden auch Katalysatorheiz- bzw. Katalysatorschutzmaßnahmen eingeleitet. Al- ternativ hierzu kann die Temperatur des NOx- Speicherkatalysators 15 auch direkt gemessen werden, indem ein Temperatursensor unmittelbar im Gehäuse desselben angeordnet wird.The temperature of the NOx storage catalytic converter 18, which is required for the consumption and emission-optimal control of the exhaust gas aftertreatment system, is calculated using a temperature model from the sensor signal of a temperature sensor 33. Based on this measurement signal, catalyst heating or catalyst protection measures are also initiated. Alternatively, the temperature of the NOx storage catalytic converter 15 can also be measured directly by arranging a temperature sensor directly in the housing thereof.
Der NOx-Speicherkatalysator dient dazu, um in Betriebsbereichen mit magerer Verbrennung die geforderten Abgasgrenzwerte einhalten zu können. Er adsorbiert aufgrund seiner Beschichtung die bei magerer Verbrennung erzeugten NOx-Verbindungen im Abgas .The NOx storage catalytic converter is used to comply with the required exhaust gas limit values in operating areas with lean combustion. Due to its coating, it adsorbs the NOx compounds generated in the exhaust gas during lean combustion.
Um die speziell bei Brennkraftmaschinen mit Direkteinspritzung und Schichtladebetrieb auftretenden NOx-Emissionen der Brennkraftmaschine zu verringern, ist eine Abgasrückführvor- richtung vorgesehen. Durch Zumischen von Abgas zur angesaug- ten Frischluft wird die Verbrennungs-Spitzentemperatur gesenkt, wodurch die temperaturabhängige Stickoxidemission reduziert wird. Zum Rückführen eines definierten Teilstromes des Abgases zweigt deshalb vom Abgaskanal 16 in Strömungsrichtung des Abgases gesehen vor dem NOx-Speicherkatalysator 18 eine Abgasrückführleitung 19 ab, die stromabwärts einerAn exhaust gas recirculation device is provided in order to reduce the NOx emissions of the internal combustion engine that occur especially in internal combustion engines with direct injection and stratified charge operation. By adding exhaust gas to the fresh air drawn in, the peak combustion temperature is reduced, which reduces the temperature-dependent nitrogen oxide emission. To return a defined partial flow of the exhaust gas, an exhaust gas recirculation line 19 branches off from the exhaust gas duct 16 in the flow direction of the exhaust gas, in front of the NOx storage catalytic converter 18
Drosselklappe 20 in den Ansaugkanal 13 mündet. Die Menge des rückgeführten Abgases wird durch das Verändern des Tastverhältnisses EGR_RATIO eines von der elektronischen Steuerungseinrichtung 21 ausgegebenen Signales für ein ansteuerbares Ventil 22, in der Regel als Abgasrückführventil bezeichnet, eingestellt . Die zur Verbrennung im Zylinder 11 notwendige Frischluft strömt über ein nichtdargestelltes Luftfilter und einen Luftmassenmesser 23 in den Ansaugtrakt 13 zu der Drosselklappe 20. Bei dieser Drosselklappe 20 handelt es sich um ein elek- tromotorisch angesteuertes Drosselorgan (E-Gas-System) , dessen Öffnungsquerschnitt neben der Betätigung durch den Fahrer (Fahrerwunsch) auch unabhängig davon über Signale der elektronischen Steuerungseinrichtung 21 einstellbar ist. Damit lassen sich beispielsweise störende Lastwechselreaktionen des Fahrzeugs beim Gasgeben und -wegnehmen genauso reduzieren wie Drehmomentsprünge beim Übergang vom Betrieb mit homogenem Gemisch zum Betrieb mit geschichteter Ladung und ungedrosseltem Luftweg. Zugleich wird zur Überwachung ein Signal für die Stellung der Drosselklappe 20 an die Steuerungseinrichtung 21 abgegeben.Throttle valve 20 opens into the intake duct 13. The amount of the recirculated exhaust gas is set by changing the duty cycle EGR_RATIO of a signal output by the electronic control device 21 for a controllable valve 22, generally referred to as an exhaust gas recirculation valve. The fresh air necessary for combustion in the cylinder 11 flows through an air filter (not shown) and an air mass meter 23 into the intake tract 13 to the throttle valve 20. This throttle valve 20 is an electric motor-controlled throttle element (E-gas system), the opening cross section of which in addition to being actuated by the driver (driver request), it can also be set independently of this via signals from the electronic control device 21. For example, this can reduce disturbing load change reactions of the vehicle when accelerating and decelerating, as well as torque jumps during the transition from operation with a homogeneous mixture to operation with stratified cargo and unrestricted air flow. At the same time, a signal for the position of the throttle valve 20 is output to the control device 21 for monitoring.
Ein Temperatursensor 24 erfaßt die Temperatur der Ansaugluft im Ansaugkanal 13 der Brennkraftmaschine und gibt ein entsprechendes Signal TIA an die Steuerungseinrichtung 21 ab. Der Temperatursensor 24 kann in einer bevorzugten Ausfüh- rungsform in den Luftmassenmesser 23 integriert sein.A temperature sensor 24 detects the temperature of the intake air in the intake duct 13 of the internal combustion engine and outputs a corresponding signal TIA to the control device 21. In a preferred embodiment, the temperature sensor 24 can be integrated in the air mass meter 23.
In den Verbrennungsraum 12 ragt eine Zündkerze 25 und ein Einspritzventil 26, durch das entgegen den Kompressionsdruck im Verbrennungsraum 12 Kraftstoff eingespritzt werden kann. Die Förderung und Bereitstellung des Kraftstoffes für dieses Einspritzventil 26 erfolgt durch ein bekanntes Kraftstoffversorgungssystem für Benzin-Direkteinspritzung, wobei von dem zugehörigen Kraftstoffkreislauf lediglich ein Hochdruckspei- eher 27 dargestellt ist, an den die einzelnen Einspritzventile angeschlossen sind.A spark plug 25 and an injection valve 26 protrude into the combustion chamber 12 and can be used to inject fuel against the compression pressure in the combustion chamber 12. The delivery and provision of the fuel for this injection valve 26 is carried out by a known fuel supply system for gasoline direct injection, with only one high-pressure reservoir 27 from the associated fuel circuit being shown, to which the individual injection valves are connected.
Ein Temperatursensor 28 erfaßt ein der Temperatur der Brennkraftmaschine entsprechendes Signal, beispielsweise über eine Messung der Kühlmitteltemperatur. Die Drehzahl N der Brennkraftmaschine wird mit Hilfe eines Markierungen der Kurbelwelle oder eines mit ihr verbundenen Geberrades abtastenden Sensors 29 erfaßt. Beide Signale werden der Steuerungseinrichtung 21 zur weiteren Verarbeitung, u.a. zur Steuerung der Brennkraftmaschine hinsichtlich der zu wählenden Steuerstrategie -homogenes Gemisch oder geschichtetes Gemisch- zuge- führt .A temperature sensor 28 detects a signal corresponding to the temperature of the internal combustion engine, for example by measuring the coolant temperature. The speed N of the internal combustion engine is scanned with the aid of markings on the crankshaft or a sensor wheel connected to it Sensor 29 detected. Both signals are fed to the control device 21 for further processing, inter alia for controlling the internal combustion engine with regard to the control strategy to be selected — homogeneous mixture or stratified mixture.
Weitere Steuerparameter, die zum Betrieb der Brennkraftmaschine benötigt werden, wie beispielsweise Gaspedalstellung, Drosselklappenstellung, Signale von Klopfsensoren, Batterie- Spannung, Fahrdynamik-Anforderungen usw. sind ebenfalls der Steuerungseinrichtung 21 zugeführt und sind allgemein in der Figur mit dem Bezugszeichen 30 gekennzeichnet. Über die bereits erwähnten Parameter wird in der Steuerungseinrichtung 21 durch Abarbeiten abgelegter Steuerungsroutinen u.a. der Lastzustand der Brennkraftmaschine erkannt, die NOx- Rohemission der Brennkraftmaschine und der Beladungsgrad des NOx-Speicherkatalysators bestimmt. Auch werden die Parameter derart aufbereitet und weiterverarbeitet, daß bei bestimmten Betriebszuständen der Brennkraftmaschine u.a. eine Umschal- tung vom Betrieb mit homogenem Gemisch auf Betrieb mitFurther control parameters that are required for operating the internal combustion engine, such as, for example, accelerator pedal position, throttle valve position, signals from knock sensors, battery voltage, driving dynamics requirements, etc., are likewise supplied to the control device 21 and are generally identified in the figure by the reference symbol 30. The above-mentioned parameters are used in the control device 21 by processing stored control routines, among other things. the load state of the internal combustion engine is recognized, the raw NOx emission of the internal combustion engine and the degree of loading of the NOx storage catalytic converter are determined. The parameters are also processed and processed in such a way that, in certain operating states of the internal combustion engine, i.a. a switch from operation with a homogeneous mixture to operation with
Schichtladung und umgekehrt durchgeführt und/oder eine Rückführung von Abgas eingeleitet werden kann.Stratified charging and vice versa and / or a recirculation of exhaust gas can be initiated.
Ferner ist die Steuerungseinrichtung 21 mit einer Spei- chereinrichtung 31 verbunden, in dem u.a. verschiedene Kennfelder KF1-KF4, sowie Werte für eine Referenzansaugluftmasse LMM gespeichert sind, deren jeweilige Bedeutung anhand der Beschreibung der nachfolgenden Figur noch näher erläutert wird.Furthermore, the control device 21 is connected to a storage device 31, in which, among other things, Various maps KF1-KF4, as well as values for a reference intake air mass LMM are stored, the respective meaning of which is explained in more detail with reference to the description of the following figure.
Die Figur 2 veranschaulicht anhand einer Blockdarstellung die Struktur zur Ermittlung der NOx-Rohemission der Brennkraftmaschine im Schichtladebetrieb.FIG. 2 uses a block diagram to illustrate the structure for determining the raw NOx emission of the internal combustion engine in stratified charge mode.
Die Kraftstoffmasse MFF und die Drehzahl N der Brennkraftmaschine charakterisieren den momentanen Betriebspunkt der Brennkraftmaschine und sind deshalb Eingangsgrößen eines Kennfeldes KF1. Abhängig von den Werten dieser Eingangsgrößen wird aus dem Kennfeld KF1 ein Basiswert für die NOx- Rohemission NOX_B, beispielsweise in der Einheit mg/s ausgelesen. Die Kraftstoffmasse MFF kann dabei aus den Werten für die Öffnungsdauer, des Durchsatzes und/oder des Druckes am Einspritzventil abgeleitet werden. Die Drehzahl N der Brennkraftmaschine wird mit Hilfe des Drehzahlsensors 29 erfaßt.The fuel mass MFF and the speed N of the internal combustion engine characterize the current operating point of the internal combustion engine and are therefore input variables Map KF1. Depending on the values of these input variables, a base value for the raw NOx emission NOX_B, for example in the unit mg / s, is read out from the map KF1. The fuel mass MFF can be derived from the values for the opening duration, the throughput and / or the pressure at the injection valve. The speed N of the internal combustion engine is detected with the aid of the speed sensor 29.
Das Temperaturniveau, bei dem die Verbrennung im Zylinder der Brennkraftmaschine abläuft, wird im wesentlichen von der Ansauglufttemperatur, der Abgasrückführrate und dem Luftmassenstrom beeinflußt.The temperature level at which the combustion takes place in the cylinder of the internal combustion engine is essentially influenced by the intake air temperature, the exhaust gas recirculation rate and the air mass flow.
Der aus dem Kennfeld KF1 erhaltene Basiswert der NOX- Rohemission NOX_B wird deshalb mit einem ersten Korrekturfaktor FAC_TIA, der in Abhängigkeit von der Ansauglufttemperatur TIA bestimmt wird, korrigiert. Hierzu wird zu dem jeweiligen Wert der Ansauglufttemperatur TIA ein entsprechender Wert für den Korrekturfaktor FAC TIA aus einem Kennfeld KF2 ausgele- sen. Die Ansauglufttemperatur TIA wird mittels des Temperatursensors 24 erfaßt oder aus dem Wert der Umgebungstemperatur abgeleitet, beispielsweise über eine Modellbildung.The basic value of the raw NOX emission NOX_B obtained from the map KF1 is therefore corrected with a first correction factor FAC_TIA, which is determined as a function of the intake air temperature TIA. For this purpose, a corresponding value for the correction factor FAC TIA is read from a map KF2 for the respective value of the intake air temperature TIA. The intake air temperature TIA is detected by means of the temperature sensor 24 or derived from the value of the ambient temperature, for example via a model.
Der so erhaltene korrigierte Basiswert für die NOx- Rohemission wird mit einem weiteren Korrekturfaktor FAC_EGR multipliziert, der aus einem Kennfeld KF3 ausgelesen wird. Der Einfluß der Abgasrückführrate ist bei gegebenem Wert für die Abgasrückführrate EGR_RATIO nicht konstant über der Drehzahl N. Aus diesem Grund wird der Drehzahleinfluß beim Ausle- sen aus dem Kennfeld KF3 berücksichtigt. Der Wert für die Abgasrückführrate EGR_RATIO kann dabei aus der Stellung des Öffnungsorgans des Abgasrückführventils 22 abgeleitet werden.The corrected base value for the raw NOx emission obtained in this way is multiplied by a further correction factor FAC_EGR, which is read out from a map KF3. The influence of the exhaust gas recirculation rate for a given value for the exhaust gas recirculation rate EGR_RATIO is not constant above the speed N. For this reason, the influence of the speed is taken into account when reading from the map KF3. The value for the exhaust gas recirculation rate EGR_RATIO can be derived from the position of the opening element of the exhaust gas recirculation valve 22.
Die Berücksichtigung der Androsselung im Schichtladebetrieb erfolgt durch einen weiteren Korrekturfaktor FAC_LM, der in Abhängigkeit des Verhältnisses zwischen der tatsächlichen Ansaugluftmasse LM und einer Referenzansaugluftmasse LMM ermit- telt wird. Die tatsächliche Ansaugluftmasse LM wird mittels des Luftmassenmessers 23 gemessen, die Referenzansaugluftmasse LMM entspricht der Ansaugluftmasse, die bei definierten Umgebungsbedingungen und vollständig geöffneter Drosselklappe 20 ermittelt wird. Die, insbesondere von der Drehzahl N abhängigen Werte für die Referenzansaugluftmasse LMM sind ebenfalls in der Speichereinrichtung 31 abgelegt. Das Verhältnis zwischen der tatsächlichen Ansaugluftmasse LM und der Refe- renzansaugluftmasse LMM wird bestimmt zu:The throttling in stratified charge mode is taken into account by means of a further correction factor FAC_LM which, depending on the ratio between the actual intake air mass LM and a reference intake air mass LMM is communicated. The actual intake air mass LM is measured by means of the air mass meter 23, the reference intake air mass LMM corresponds to the intake air mass which is determined under defined ambient conditions and with the throttle valve 20 fully open. The values for the reference intake air mass LMM, which are dependent in particular on the speed N, are also stored in the storage device 31. The relationship between the actual intake air mass LM and the reference intake air mass LMM is determined as follows:
LM FAC =LM FAC =
LMMLMM
Dieses Verhältnis FAC ist Eingangsgröße für ein Kennfeld KF4, in dem der Zusammenhang zwischen diesem Verhältnis FAC und dem Korrekturfaktor FAC_LM abgelegt ist. Auch dieser Korrekturfaktor FAC_LM wird multiplikativ bei der Modellierung des der NOx-Rohemission eingerechnet.This ratio FAC is the input variable for a map KF4, in which the relationship between this ratio FAC and the correction factor FAC_LM is stored. This correction factor FAC_LM is also taken into account multiplicatively when modeling the raw NOx emission.
Die einzelnen Korrekturfaktoren lassen sich zu einem gesamten Korrekturfaktor FAC_GES zusammenfassen, wobei gilt: FAC_GES = FAC_TIA * FAC_EGR * FAC_LM.The individual correction factors can be combined into an overall correction factor FAC_GES, whereby the following applies: FAC_GES = FAC_TIA * FAC_EGR * FAC_LM.
A Ende dieser Korrekturkette steht ein Wert NOX_COR für die NOX_Rohemission zur Verfügung, der beispielsweise zur genauen Ermittlung des Beladungsgrades des NOx-Speicherkatalysators 18 verwendet werden kann. At the end of this correction chain, a value NOX_COR is available for the NOX_ raw emission, which can be used, for example, to determine the degree of loading of the NOx storage catalytic converter 18 precisely.

Claims

Patentansprüche claims
1. Verfahren zum Bestimmen der NOx-Rohemission einer wahlweise mit homogener Zylinderladung oder geschichteter Zylin- derladung mit Luftüberschuß betreibbaren Brennkraftmaschine, -wobei die Brennkraftmaschine einen im Abgaskanal (16) angeordneten NOx-Speicherkatalysator (18), eine Abgasrückführ- vorrichtung (19,22) zum Rückführen von Abgas in einen An- saugkanal (13) und eine Drosseleinrichtung (20) zum gedrosselten Betrieb der Brennkraftmaschine aufweist und -die NOx-Rohemission aus Betriebsparametern der Brennkraftmaschine ermittelt wird, dadurch gekennzeichnet, daß -im Schichtladebetrieb der Brennkraftmaschine ein Basiswert für die NOx-Rohemission (NOX_B) abhängig von der in die Zylinder der Brennkraftmaschine eingespritzten Kraftstoffmasse (MFF) und der Drehzahl (N) der Brennkraftmaschine bestimmt wird, -der Basiswert für die NOx-Rohemission (NOX_B) mit einem Korrekturfaktor (FAC_GES) beaufschlagt wird, der den Einfluß der Abgasrückführrate (EGR_RATIO) , der Ansauglufttemperatur (TIA) und die Stellung (FAC) der Drosseleinrichtung (20) im Schichtladebetrieb berücksichtigt .1. A method for determining the raw NOx emission of an internal combustion engine which can be operated optionally with a homogeneous cylinder charge or stratified cylinder charge with excess air, the internal combustion engine comprising an NOx storage catalytic converter (18) arranged in the exhaust gas duct (16) and an exhaust gas recirculation device (19, 22) ) for returning exhaust gas into an intake duct (13) and a throttle device (20) for throttled operation of the internal combustion engine and - the raw NOx emission is determined from operating parameters of the internal combustion engine, characterized in that - in stratified charge operation of the internal combustion engine a base value for the raw NOx emission (NOX_B) is determined as a function of the fuel mass (MFF) injected into the cylinders of the internal combustion engine and the speed (N) of the internal combustion engine, - a correction factor (FAC_GES) is applied to the base value for the raw NOx emission (NOX_B) , the influence of the exhaust gas recirculation rate (EGR_RATIO), the intake air temperature (TIA) and the position (FAC) of the throttle device (20) in stratified charge mode are taken into account.
2.Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß sich der Korrekturfaktor (FAC_GES) multiplikativ zusammensetzt aus -einem Korrekturfaktor (FAC_TIA) , der die Temperatur der An- saugluft (TIA) beinhaltet,2.The method according to claim 1, characterized in that the correction factor (FAC_GES) is composed of a multiplicative correction factor (FAC_TIA) which contains the temperature of the intake air (TIA),
-einem Korrekturfaktor (FAC_EGR) , der die Abgasrückführrate-a correction factor (FAC_EGR) that determines the exhaust gas recirculation rate
(EGR_RATIO) der Brennkraftmaschine beinhaltet, -einem Korrekturfaktor (FAC_LM) , der das Verhältnis zwischen der tatsächlichen Ansaugluftmasse (LM) und einer Referenzan- saugluftmasse (LMM) durch die Drosselvorrichtung (20) beinhaltet. (EGR_RATIO) of the internal combustion engine includes a correction factor (FAC_LM) which contains the ratio between the actual intake air mass (LM) and a reference intake air mass (LMM) by the throttle device (20).
3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß der Basiswert für die NOx-Rohemission (NOX_B) und die Korrekturfaktoren (FAC_TIA,FAC_EGR,FAC_LM) in Kennfelder (KF1,KF2,KF3,KF4) einer Speichereinrichtung (31) einer zur Steuerung der Brennkraftmaschine dienenden Steuerungseinrichtung (21) abgelegt sind.3. The method according to claim 2, characterized in that the base value for the raw NOx emission (NOX_B) and the correction factors (FAC_TIA, FAC_EGR, FAC_LM) in maps (KF1, KF2, KF3, KF4) of a memory device (31) for control the control device (21) serving the internal combustion engine.
4. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß als Referenzansaugluftmasse (LMM) diejenige Luftmasse verwendet wird, die bei vorgegebenen Umgebungsbedingungen bei vollständig geöffneter Drosseleinrichtung (20) im Ansaugkanal (13) vorliegt .4. The method according to claim 2, characterized in that that air mass is used as the reference intake air mass (LMM), which is present at predetermined ambient conditions when the throttle device (20) is completely open in the intake duct (13).
5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der korrigierte Basiswert für die NOx-Rohemission (NOX_COR) als Eingangsgröße für ein Modell zur Berechnung der NOx-Beladung des NOx-Speicherkatalysators (18) verwendet wird. 5. The method according to claim 1, characterized in that the corrected base value for the raw NOx emission (NOX_COR) is used as an input variable for a model for calculating the NOx loading of the NOx storage catalytic converter (18).
PCT/DE1999/003515 1998-11-06 1999-11-03 METHOD FOR DETERMINING THE NOx CRUDE EMISSION OF AN INTERNAL COMBUSTION ENGINE OPERATED WITH AN EXCESS OF AIR WO2000028200A1 (en)

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