EP1131549B1 - METHOD FOR ADAPTING THE NOx CONCENTRATION OF AN INTERNAL COMBUSTION ENGINE OPERATED WITH AN EXCESS OF AIR - Google Patents

Description

Method for adapting a NOx raw concentration value a working with excess air internal combustion engine

The invention relates to a method for adapting a NOx raw concentration value of an excess air Internal combustion engine according to the preamble of claim 1.

To the fuel consumption of motor vehicles with Otto engine Drive to reduce further, come more often Internal combustion engines are used, at least in selected Operating areas are operated with a lean mixture.

In order to meet the required exhaust emission limit values, a special exhaust aftertreatment is necessary in such internal combustion engines. For this purpose, NOx storage reduction catalysts, hereinafter referred to simply as NOX storage catalysts, are used. Due to their coating, these NOx storage catalysts are able, during a storage phase, also referred to as a loading phase, to adsorb NOx compounds from the exhaust gas which are produced during lean combustion. During a regeneration phase, the adsorbed or stored NOx compounds are converted into harmless compounds with the addition of a reducing agent. As a reducing agent for lean-burn gasoline engines CO, H ₂ and HC (hydrocarbons) can be used. These are generated by short-term operation of the internal combustion engine with a rich mixture and provided to the NOx storage catalytic converter as exhaust gas components, whereby the stored NOx compounds are degraded in the catalyst.

The adsorption efficiency of such a NOx storage catalyst drops with higher NOx loading level. As degree of loading is the quotient of the current, absolute NOx load and the maximum NOx storage capacity. The calculated degree of loading can be used to control the lean and Grease cycles of the internal combustion engine are used. It It can be seen that to determine the degree of loading a as accurate as possible knowledge of both the current load and also the maximum storage capacity is necessary.

The maximum storage capacity can be on the engine test bench by measuring the amount of NOx stored per unit time until to reach a saturation state, while saturating the NOx storage catalyst in the motor vehicle for emission reasons is not possible. Indeed subject to this storage capacity an aging process, so that it is necessary to adapt them over the vehicle running distance. For this one needs either the value for the momentary Loading and / or a very accurate value for the NOx raw emissions the internal combustion engine. As raw emissions are generally referred to the emission without exhaust aftertreatment.

One way of determining the NOx raw concentration values is the measurement of a reference internal combustion engine on a test bench and the filing of the data in suitable maps. The reading out of these maps provides only meaningful results, if the NOx raw concentration values of various internal combustion engines a series does not fluctuate too much. Exceed the Fluctuations in NOx raw concentration levels to a certain extent, is an adaptation of the NOx raw concentration values of the internal combustion engine necessary in the vehicle.

The invention has for its object to provide a method with the NOx raw concentration values of an internal combustion engine of the type mentioned in a simple way can be adapted.

This object is achieved by the features of patent claim 1 solved. Advantageous developments of the invention are in specified in the dependent claims.

According to the method of the invention, the operating point dependent Values for the raw NOx concentration of the internal combustion engine read out of a map and the adaptation the concentration variations are based on the output signal one downstream of the NOx storage catalyst arranged NOx sensor either by modification of a Reduction factor used to calculate the corrected NOx raw concentration from the NOx raw concentration values, or by direct correction of the read out of the map Values for the NOx raw concentration with a raw concentration correction factor.

Figur 1

eine schematische Darstellung einer Mager-Brennkraftmaschine mit einem NOx-Speicherkatalysator,

Figur 2

ein Diagramm, das die während einer Magerphase der Brennkraftmaschine emitierte NOx-Menge und NOx-Konzentration zeigt,

Figur 3

eine Blockdarstellung zur Adaption der NOx-Rohkonzentrationswerte mittels eines Korrekturfaktors für den Reduktionsfaktor,

Figur 4

eine Blockdarstellung zur Adaption der NOx-Rohkonzentrationswerte mittels eines Korrekturfaktors für die NOx-Rohkonzentrationswerte und

Figur 5

ein Diagramm, das die Integrale der NOx-Konzentrationen zeigt.

The invention will be explained in more detail with reference to the drawing. Show it:

FIG. 1

a schematic representation of a lean-burn engine with a NOx storage catalyst,

FIG. 2

a diagram showing the amount of NOx and NOx concentration emitted during a lean phase of the internal combustion engine,

FIG. 3

a block diagram for the adaptation of the NOx raw concentration values by means of a correction factor for the reduction factor,

FIG. 4

a block diagram for the adaptation of the NOx raw concentration values by means of a correction factor for the NOx Rohkonzentrationswerte and

FIG. 5

a diagram showing the integrals of the NOx concentrations.

At the same time, the expression NOx raw concentration value becomes simplistic the term NOx concentration is used.

In Fig. 1 is a lean-burn engine in the form of a block diagram with a NOx exhaust aftertreatment system shown used in the inventive method becomes. Only the components are shown, which are for Understanding the invention are necessary.

The lean-burn engine 10 is via an intake passage 11 supplied an air / fuel mixture. In the intake passage 11th are seen in the flow direction of the sucked air in succession a load sensor in the form of an air mass meter 12, a throttle block 13 with a throttle valve 14 and a not shown throttle valve sensor for detection the opening angle of the throttle valve 14 and according to the Number of cylinders a set injectors 15 provided by which only one is shown. The inventive method but is also applicable to a system in which the fuel injected directly into the respective cylinder (Direct injection).

On the output side, the internal combustion engine 10 with an exhaust passage 16 connected. In this exhaust passage 16 is an exhaust aftertreatment system intended for lean exhaust gas. she consists arranged from a near the internal combustion engine 10 Pre-catalyst 17 (3-way catalyst) and one in the flow direction of the exhaust gas downstream of the primary catalytic converter 17 NOx storage catalyst 18.

The sensor system for the exhaust aftertreatment system includes a Sauerstoffmeßaufnehmer 19 upstream of the pre-catalyst 17, a temperature sensor 20 in the connecting pipe between the pre-catalyst 17 and NOx storage catalyst 18 near the inlet region thereof and a further exhaust gas sensor 21 downstream of the NOx storage catalyst 18th
Instead of the temperature sensor 20, which detects the exhaust gas temperature and from whose signal the temperature of the NOx storage catalytic converter 18 can be calculated by means of a temperature model, it is also possible to measure the NOx storage catalytic converter temperature directly. In the figure 1, such a temperature sensor 201 is shown with a dashed line, which measures the monolith temperature of the NOx storage catalyst 18 directly.

Another possibility is the monolith temperature the NOx storage catalyst 18 by means of an exhaust gas temperature model to calculate, taking as input to this Model some or all of the following parameters, like Speed, load, ignition angle, air ratio, exhaust gas recirculation rate, intake air temperature, Coolant temperature can be used. As a result, the use of a temperature sensor 20 is dispensed with become.

The calculation or measurement of the temperature of the NOx storage catalytic converter 18 is optimized for consumption and emissions Control of the system required. Based on this measured, calculated or modeled temperature signal also become Katalysatorheiz- or catalyst protection measures initiated.

As Sauerstoffmeßaufnehmer 19 is preferably a broadband lambda probe used, which depends on the oxygen content in the exhaust a steady, e.g. linear output signal emits. With the signal of this broadband lambda probe is the air ratio during lean operation and during the regeneration phase with a rich mixture accordingly adjusted the setpoint specifications. This function takes over a known lambda control device 22, preferably in a the operation of the internal combustion engine 10 controlling Control device 23 is integrated.

Such electronic control devices, as a rule include a microprocessor and in addition to the fuel injection and the ignition a lot more Control tasks, i.a. also the control of the exhaust aftertreatment system take over, are known per se, so that in the following only on the in connection with the invention relevant structure and its functioning received becomes. In particular, the control device 23 is provided with a Memory device 24 is connected, in the u.a. various Characteristic curves or maps KF1, KF2, as well as correction factors RFKF and RKKF are stored, their respective meaning the description of the following figures even closer is explained.

A temperature sensor 29 detects a temperature of the internal combustion engine corresponding signal, for example via a Measurement of the coolant temperature. The speed of the internal combustion engine is using a mark the crankshaft or a sensor wheel connected to it Detected sensors 30.

The output of the air mass meter 12 and the signals the throttle position sensor, the Sauerstoffmeßaufnehmers 19, the exhaust gas probe 21, the temperature sensors 20, 29, and the Speed sensor 30 are via corresponding connecting lines the control device 23 is supplied.

For controlling and regulating the internal combustion engine 10 is the Control device 23 except with an ignition device 27th for the air-fuel mixture over a only schematically illustrated Data and control line 28 with additional, not explicitly shown sensors and actuators connected.

Downstream of the NOx storage catalyst 18 is in the exhaust passage an exhaust gas sensor arranged in the form of a NOx sensor 21, its output signal for controlling memory regeneration and for adapting model sizes, e.g. the oxygen- or NOx storage capacity of the NOx storage catalyst 18, and for detecting the aging state of the NOx storage catalyst is used. It also comes with the output signal of the NOx sensor 21, if necessary, the raw NOx emission adapted to the internal combustion engine.

About the already mentioned parameters is in the control device 23 by processing stored control routines et al the load state of the internal combustion engine detected, the NOx raw emissions determined and adapted the internal combustion engine, and determines the degree of loading of the NOx storage catalytic converter.

• Ein Teil wird auch im Magerbetrieb von der Abgasreinigungsanlage in unschädlichere Substanzen umgewandelt. Dieser Anteil wird im folgenden als stationäre Umsatzmenge SU be zeichnet.
• Ein weiterer Teil wird im NOx-Speicherkatalysator gespeichert, der im folgenden als Speichermenge SM bezeichnet wird.
• Ein dritter Teil wird an die Umgebung abgegeben. Dieser Anteil wird im folgenden als Durchbruchsmenge DB bezeichnet.

The total amount of NOx emitted by the internal combustion engine during a lean phase can be split into the following parts:

• A part is also converted in lean operation of the emission control system into harmless substances. This proportion is hereinafter referred to as stationary sales volume SU be.
• Another part is stored in the NOx storage catalyst, which will be referred to as storage amount SM hereinafter.
• A third part is given to the environment. This proportion is referred to below as the breakthrough amount DB.

• eine den stationären Umsatz SU hervorrufende Stationärumsatz-Konzentration SK,
• eine die Speichermenge SM hervorrufende Speicherkonzentration SPK und
• eine weder umgesetzte noch gespeicherte Nach-Kat-Konzentration NK.

If the integral of this total amount of NOx over the period of a lean phase is not considered, but the instantaneous NOx raw concentration, this can also be split analogously in accordance with the procedure described above

• a steady-state conversion concentration SK causing the steady-state turnover SU,
• a storage amount SM causing memory concentration SPK and
• an unreacted or stored post-catalyst concentration NK.

From the respective concentrations can by integration over time, the above NOx levels SU, SM and DB formed become.

Under corrected raw NOx concentration KK will be described below the NOx raw concentration less the stationary conversion concentration SK understood. The stationary sales concentration SK is detected via a reduction factor RF. The corrected raw NOx concentration KK is a product of the difference of one and the reduction factor RF and the NOx raw concentration RK of the internal combustion engine defines: KK = (1-RF) * RK.

The most accurate knowledge of the corrected NOx raw concentration KK is for catalyst control via the calculation the degree of loading and the aging adaptation of Storage capacity needed.

FIG. 2 shows a diagram in which the abovementioned proportions that of the internal combustion engine during the lean phase emitted raw NOx emission are registered. At the time t0 the lean phase is over and a regeneration phase for the NOx storage catalyst 18 is requested. The hatched Areas characterize the individual quantities of NOx stationary Sales volume SU, storage volume SM and breakthrough volume DB.

In addition, certain parts of the NOx concentration are in the diagram entered. In addition to neither implemented, nor stored after-cat concentration NK, which towards the end of the Lean phase rises rapidly, are as Ordinatenabschnitte the from the map KF1 read NOx raw concentration RK and the actual, but not determinable raw NOx concentration RKT shown. The additionally drawn Curve of NK after the time t0 would be if regeneration is not initiated at time t0 would become.

Numeral KK (n-1) is the corrected raw NOx concentration before the current adaptation process, with KK (n) is the corrected NOx raw concentration after the current one Termed adaptation. The associated values for the stationary sales concentration SK (n-1) for an uncorrected reduction fier and at a corrected reduction factor SK (n) are also drawn.

FIG. 3 is a first block diagram Embodiment for the adaptation of the NOx concentration fluctuations by modification of the reduction factor RF, the for calculating the corrected raw NOx concentration from the NOx raw concentration is shown. The corrected NOx raw concentration KK is doing with the help of the signal of downstream of the NOx storage catalyst arranged NOx sensor 21 determined and adapted if necessary.

The adaptation is during a cycle consisting of lean and Fat phase performed as follows. Be first Breakthrough amount DB and the storage amount SM determined. The Breakthrough amount DB is measured in the lean phase by measuring the After-Kat-NOx concentration with the NOx sensor 21 and its Integration detected over the lean phase duration. The amount of memory SM in the lean phase may be in the lean phase following Fat phase can be calculated. For this purpose it is assumed the additional, not to stoichiometric combustion required fuel mass flow is used to reduce the stored NOx mass and to exhaust the stored Used oxygen. Is the stored amount of oxygen, the time from the beginning of the fat phase to the detection of a complete NOx regeneration of the NOx storage catalyst, the additional fuel mass flow and the molar ratio the reaction fuel + known NOx, so on the stored amount of NOx are closed back.

Based on the NOx raw concentration stored in the map KF1 RK and the filed in a map KF2 Reduction factor RF becomes the integral of the corrected NOx concentration calculated over the lean phase IKK. The NOx raw concentration For example, RK is dependent on some or all the following parameters: speed, load, Ignition angle, air ratio, exhaust gas recirculation rate, intake air temperature, Coolant temperature.

The sum of the breakthrough amount DB and the amount of memory SM, as well as the integral value of the corrected NOx concentration over the lean phase IKK are led to a division stage D1 and there formed the ratio (DB + SM) / IKK. Subsequently the difference 1- (DB + SM) / IKK is formed and this Value to an amplifier element V out. Fits the calculation the corrected NOx concentration with that from the probe signals determined, not directly reduced NOx concentration match, then: IKK = DB + SM. In this case is at the summation point S1 to the value zero and the correction factor RFKF for the reduction factor RF is not adapted (RFKF (n-1) = RFKF (n).

Is found to be an unacceptable deviation between is the value IKK and the sum value DB + SM, the Correction factor RFKF for the reduction factor RF, with which the Reduction factor RF is multiplied, in a suitable manner reduced or enlarged. He is downsized, though IKK <DB + SM is and it is increased if IKK> DB + SM.

It is also possible, instead of the ratio formation of IKK and (DB + SM) the difference of IKK and (DB + SM) for determination of the increment or decrement with which the Correction factor RFKF is changed.

The from the map KF2 example, as a function of temperature of the NOx storage catalyst 18 read reduction factor RF is with the unchanged or with the adapted in the manner described above correction factor RFKF multiplied. The value thus obtained is subtracted from 1 and this value is multiplied by the raw NOx concentration RK, this is read from the map KF1.

The result is a value for the corrected NOX raw concentration KK = (1-RF) * RK.

Another possibility of adaptation is the adaptation of a Correction factor RKKF for the raw NOx concentration RK The method is in Figure 4 also in the form of a Block diagram shown and is similar to the reference to the figure 3 explained method.

However, in the process presented here is not the Reduction factor RF modified, but the NOx raw concentration RK is using a after explained above Adaptation method (ratio or difference formation of IKK and (DB + SM)) computable correction factor RKKF multiplied. Subsequently, this pre-corrected NOx raw concentration RKK multiplied by the value 1-RF, where with RF again the reduction factor is designated, the off the map KF2 is read out. The result is one Value for the corrected NOX raw concentration KK = (1-RF) * RKK.

In Figure 5, the integrals of the corrected NOx concentration IKK over the lean phase, the amount of memory SM and the Breakthrough amount DB shown. Besides, the corrected ones NOx raw concentration KK and the sum of storage concentration SPK and post-catalyst concentration NK marked. Ideally the integral values IKK and SM + DB are the same and it is no adaptation needs to be done, otherwise it will an adaptation according to the explained with reference to the figures 3 or 4 Procedure performed.

Claims (8)

1. Method for adapting a NOx concentration value (RK) of an internal combustion engine (10) operated, at least in certain operating ranges, with an excess of air, whereby

   located in an exhaust gas duct (16) of the internal combustion engine (10) is a NOx-storage reducing catalytic converter (18),

   which adsorbs NOx during a storage phase if the internal combustion engine (10) is operated using a lean burn air-fuel mixture,

   and which in a regeneration phase with the addition of regeneration agents converts the stored NOx by means of a catalytic process,

   located downstream of the NOx-storage reducing catalytic converter (18) is a NOx sensor (21),

   the NOx concentration value (RK), which is dependent on operating parameters of the internal combustion engine (10), is stored in an identification field (KF1) in a memory device (24) within a control device (23) which controls an internal combustion engine (10),

   characterized in that the NOx concentration value (RK) which is read out from the identification field (KF1) while the internal combustion engine (10) is operating is adapted during a cycle consisting of the storage phase and the regeneration phase on the basis of the output signal from the NOx sensor (21).
2. Method according to Claim 1, characterized in that the adaptation of the NOx concentration value (RK) is carried out by changing a reduction factor (RF) which affects the NOx concentration value (RK) and takes into consideration a stationary conversion concentration (SK) which is converted in the lean burn operation of the internal combustion engine (10) by the NOx-storage reducing catalytic converter (18).
3. Method according to Claim 2, characterized in that

   a break-out quantity (DB) in the lean burn phase is detected by measuring the NOx concentration (NK) downstream of the NOx-storage reducing catalytic converter (18) with the aid of the NOx sensor (21) and integrating it over the period of the lean burn phase,

   a storage quantity (SM) in the lean burn phase is calculated in the rich burn phase which follows the lean burn phase,

   based on the NOx concentration value (RK) and the reduction factor (RF) the integral of the corrected NOx concentration is calculated for the lean burn phase (IKK),

   the sum of the break-out quantity (DB) and the storage quantity (SM), as well as the integral value of the corrected NOx concentration for the lean burn phase (IKK) are placed in a ratio ((DB+SM) / IKK),

   depending on the value of the ratio a correction factor (RFKF) for the reduction factor (RF) is changed or left unchanged,

   the reduction factor (RF) is multiplied by the correction factor (RFKF).
4. Method according to Claim 3, characterized in that the adapted reduction factor (RF) is used to calculate the corrected NOx concentration (KK) as a product of the difference between 1 and the adapted reduction factor (RF), and the gross NOx concentration (RK) read out from the identification field (KF1).
5. Method according to Claim 1, characterized in that the adaptation of the NOx concentration value (RK) is carried out by changing a correction factor (RKKF) with which the NOx concentration value (RK) imported from the identification field (KF1) is immediately multiplied, thereby obtaining a pre-corrected value for the NOx concentration (RKK).
6. Method according to Claim 5, characterized in that

   a break-out quantity (DB) in the lean burn phase is detected by measuring the NOx concentration (NK) downstream of the NOx catalyzer (18) with the aid of the NOx sensor (21) and integrating it over the period of the lean burn phase,

   a storage quantity (SM) in the lean burn phase is calculated in the rich burn phase which follows the lean burn phase,

   based on the NOx concentration (RK) and the reduction factor (RF) the integral of the corrected NOx concentration is calculated for the lean burn phase (IKK),

   the sum of the break-out quantity (DB) and the storage quantity (SM), as well as the integral value of the corrected NOx concentration for the lean burn phase (IKK) are placed in a ratio ((DB+SM) / IKK),

   depending on the value of the ratio the correction factor (RFKF) for the reduction factor (RF) is changed or left unchanged.
7. Method according to Claim 6, characterized in that the pre-corrected value for the NOx concentration (RKK) is used to calculate the corrected NOx concentration (KK) as a product of the difference between 1 and the reduction factor (RF), and the pre-corrected NOx concentration (RKK).
8. Method according to one of the Claims 2, 3 or 7, characterized in that the reduction factor (RF) is stored in an identification field (KF2) depending on the temperature of the NOx-storage reducing catalytic converter (18).

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