DE102016204216B4 - Method and device for determining the loading condition of a NOx storage catalytic converter - Google Patents

Abstract

Method for determining the loading state of a NOx storage catalytic converter (16) in the exhaust line (12) of an internal combustion engine (10) comprising the following steps: - Operating the internal combustion engine (10) with a super-stoichiometric, lean combustion air ratio λE> 1 in a storage phase of the NOx storage catalytic converter ( 16), - determining the NOx mass stored in the NOx storage catalytic converter (16) from the NOx mass flow in the storage phase, - operating the internal combustion engine (10) with a sub-stoichiometric, rich combustion air ratio λE<1 in a regeneration phase of the NOx storage catalytic converter (16), - determining the NOx mass stored out of the NOx storage catalytic converter (16) from the NOx mass flow in the regeneration phase of the NOx storage catalytic converter (16), - calculating the current loading status of the NOx storage catalytic converter (16), - ending the storage phase when a defined, maximum degree of loading of the NOx storage catalytic converter (16) is reached, - ending the regeneration of the NOx storage catalyst (16) when a defined, minimum degree of loading of the NOx storage catalyst (16) is undershot, with - a NOx concentration in the exhaust system (12) at a first NOx Sensor (18) upstream of the NOx storage catalytic converter (16) and at a second NOx sensor (20) downstream of the NOx storage catalytic converter (16) is measured, and the stored NOx mass flow is measured by the NOx sensors (18, 20) measured NOx concentrations are determined and the NOx mass stored in the NOx storage catalytic converter (16) is calculated, with the calculation model of the stored NOx mass flow being adapted if the second NOx sensor (20) downstream of the NOx Storage catalytic converter (16) exceeds a specified threshold value for NOx slip or a reducing agent breakthrough is measured at a lambda probe (22) or the NOx sensor (20) downstream of the NOx storage catalytic converter (16).

Description

The invention relates to a method for determining the loading condition of a NOx storage catalytic converter in an exhaust system of an internal combustion engine.

The current exhaust gas legislation and one that will become increasingly strict in the future place high demands on engine raw emissions and the exhaust gas aftertreatment of combustion engines. Vehicle and engine manufacturers are also required to reduce the consumption of combustion engines and the associated CO2 emissions. Among other things, this means that consumption-optimized combustion processes are being developed for internal combustion engines. One way of reducing the consumption of a gasoline engine is a lean burn process, i.e. a combustion process in which the internal combustion engine is operated with a super-stoichiometric combustion air ratio as far as possible. Since the NOx emissions can no longer be converted from the exhaust gas with a conventional three-way catalytic converter in a lean-burn process, additional catalytic converters such as NOx storage catalytic converters are required. The NOx emissions are stored as nitrates in the NOx storage catalytic converter. These NOx storage catalytic converters have to be regenerated periodically with the help of an engine rich phase. Each regeneration of the NOx storage catalytic converter means a consumption disadvantage, since the internal combustion engine is operated with a rich, sub-stoichiometric combustion mixture to regenerate the NOx storage catalytic converter.

Methods are known from the prior art in which the NOx storage catalytic converter is regenerated by means of a rich phase in the engine. A complete regeneration of the NOx storage catalytic converter is assumed when the exhaust gas is rich, that is to say the exhaust gas is sub-stoichiometric, downstream of the NOx storage catalytic converter. This fat breakthrough can be diagnosed, for example, by a lambda probe arranged downstream of the NOx storage catalytic converter in the exhaust gas duct. The disadvantage of such a method, however, is that increased secondary emissions occur when fat breaks through.

In addition to these methods, other methods are known in which the loading state of the NOx storage catalytic converter is modeled by means of modeling. For example, from the DE 102 49 609 B4 a method for determining the loading state of the NOx storage catalytic converter is known, in which the stored NOx mass in the NOx storage catalytic converter and the cumulative NOx mass broken through the NOx storage catalytic converter downstream of the NOx storage catalytic converter by a NOx sensor downstream of the NOx storage catalytic converter is determined, the NOx mass flow upstream of the NOx storage catalytic converter is calculated using a model stored in the engine control unit and, depending on the loading state of the NOx storage catalytic converter, the internal combustion engine switches between different lean combustion processes.

From the DE 103 18 116 A1 a method for modeling the loading state of a NOx storage catalytic converter is known, in which a lean combustion mixture is supplied to an internal combustion engine and the nitrogen oxides produced during combustion are stored in a NOx storage catalytic converter. The NOx storage catalytic converter is periodically regenerated, with a signal curve over time of a NOx mass flow being determined downstream of the NOx storage catalytic converter and the regeneration of the NOx storage catalytic converter being initiated as a function of the signal curve over time.

From the EP 1 798 392 A1 a method for assessing the functionality of a NOx storage catalytic converter is known, in which a first exhaust gas parameter for loading is formed with a calculation model using a first value for the storage capacity of the NOx storage catalytic converter and a second exhaust gas parameter is measured downstream of the NOx storage catalytic converter. The calculation model is adjusted by adapting the first calculated exhaust gas parameter to the second measured exhaust gas parameter. The functionality of the NOx storage catalytic converter is assessed as a function of an adaptation value. The method is characterized in that an actual loading of the NOx storage catalytic converter is determined and the adaptation value for the diagnosis is corrected as a function of the actual loading.

the DE 10 2006 005 546 A1 discloses a method for controlling a NOx storage catalyst in the exhaust system of an internal combustion engine. Here, during an operating point in which the catalyst temperature is in a low temperature range, the catalyst is allowed to store NOx until it is saturated. The saturated catalyst is heated to a temperature exceeding the low temperature range. The heated catalyst is regenerated. Through this procedure, the performance of the NOx storage catalyst at low temperatures can be improved without a significant increase in fuel consumption.

In addition, from the DE 102 49 609 B4 a method for controlling a NOx storage catalyst in the exhaust system of an internal combustion engine is known. For this purpose, a NOx sensor is arranged in the exhaust system downstream of the NOx storage catalytic converter, which is connected to an engine control unit of the internal combustion engine. In this case, in a lean operating phase of the internal combustion engine, an operating mode changeover to another lean operating phase is made dependent on the NOx storage capacity to be expected in the NOx storage catalytic converter. In this case, premature regeneration of the NOx storage catalytic converter is suppressed if regeneration of the NOx storage catalytic converter is to be expected within a specified period of time.
A disadvantage of the known methods, however, is that they generally propose complete regeneration of the NOx storage catalytic converter. Undesirable secondary emissions occur at the end of the regeneration process. The modeling is only used to identify an upper load limit of the NOx storage.

From the DE 10 2008 029 877 A1 a method for determining a quantity of nitrogen oxide stored in a nitrogen oxide storage catalytic converter is known. A nitrogen oxide mass throughput through the nitrogen oxide storage catalytic converter and an efficiency of the nitrogen oxide storage catalytic converter are determined and the nitrogen oxide mass is calculated on the basis of the determined mass throughput and the efficiency.

The invention is now based on the object of enabling improved regeneration of the NOx storage catalytic converter and of avoiding the secondary emissions occurring in the known methods.

• - Betreiben des Verbrennungsmotors mit einem überstöchiometrischen, mageren Verbrennungsgemisch in einer Einspeicherungsphase des NOx-Speicherkatalysators,
• - Ermitteln der in den NOx-Speicherkatalysator eingespeicherten NOx-Masse aus dem NOx-Massenstrom in der Einspeicherungsphase,
• - Betreiben des Verbrennungsmotors mit einem unterstöchiometrischen, fetten Verbrennungsgemisch in einer Regenerationsphase des NOx-Speicherkatalysators,
• - Ermitteln der aus dem NOx-Speicherkatalysator ausgespeicherten NOx-Masse aus dem NOx-Massenstrom in der Regenerationsphase,
• - Berechnen des aktuellen Beladungszustands des NOx-Speicherkatalysators,
• - Beenden der Einspeicherungsphase, wenn ein definierter, maximaler Beladungsgrad des NOx-Speicherkatalysators erreicht ist, und
• - Beenden der Regeneration des NOx-Speicherkatalysators, wenn ein definierter, minimaler Beladungsgrad des NOx-Speicherkatalysators unterschritten wird.

The object is achieved by a method for determining the loading state of a NOx storage catalytic converter, which is arranged in an exhaust system of an internal combustion engine, the method comprising the following steps:

• - Operation of the internal combustion engine with a hyper-stoichiometric, lean combustion mixture in a storage phase of the NOx storage catalyst,
• - Determining the NOx mass stored in the NOx storage catalytic converter from the NOx mass flow in the storage phase,
• - Operation of the internal combustion engine with a sub-stoichiometric, rich combustion mixture in a regeneration phase of the NOx storage catalytic converter,
• - Determining the NOx mass stored out of the NOx storage catalytic converter from the NOx mass flow in the regeneration phase,
• - Calculation of the current loading status of the NOx storage catalyst,
• - Ending the storage phase when a defined, maximum degree of loading of the NOx storage catalytic converter is reached, and
• - Termination of the regeneration of the NOx storage catalytic converter if the loading level of the NOx storage catalytic converter falls below a defined, minimum level.

By ending the storage phase when the maximum permissible degree of loading of the NOx storage catalytic converter is reached below the loading limit of the NOx storage catalytic converter, it can be prevented that an increased NOx slip occurs in the storage phase when the NOx storage catalytic converter is almost completely loaded by the loading phase is terminated in good time before such a NOx slip occurs. The proposed method also makes it possible to predictively control the regeneration of the NOx storage catalytic converter during regeneration. When regenerating the NOx storage catalytic converter, ending the regeneration phase in good time prevents the occurrence of secondary emissions, which occur when the NOx storage catalytic converter is completely regenerated. If the NOx storage catalytic converter falls below a defined residual loading level, a new loading phase can start when the NOx storage catalytic converter is essentially regenerated, without undesirable secondary emissions occurring. This avoids fat breakthrough during regeneration and the associated increased emissions of unburned hydrocarbons, carbon monoxide and ammonia.

According to the invention, it is provided that a NOx concentration in the exhaust line is measured at a first NOx sensor upstream of the NOx storage catalytic converter and at a second NOx sensor downstream of the NOx storage catalytic converter. This makes it possible to measure the NOx mass flows in the exhaust gas duct, whereby the proposed method can be supported by measured values and the balancing model can be adjusted when it occurs between the NOx mass flows calculated by the balancing model and the actual, measured NOx mass flows. It is provided that the stored NOx mass flow and the stored NOx mass flow are determined by the NOx concentrations measured at the NOx sensors and the NOx mass stored in the NOx storage catalytic converter is calculated.

According to a preferred embodiment of the method, it is provided that the storage phase is terminated as a function of the current state of the NOx storage catalytic converter if a loading level of the NOx storage catalytic converter is a distance from a maximum loading level of the NOx storage catalytic converter of 10% provided at this operating point, in particular of 5% falls below. By keeping the loading of the NOx storage catalytic converter at a distance of 5 - 10% from the maximum permissible loading at this operating point, the storage phase can be ended before there is increased NOx slip, which can be detected, for example, by a NOx sensor downstream of the NOx storage catalytic converter can be detected. However, a gap of 5 - 10% does not unnecessarily shorten the storage phase, so that the number of regeneration phases does not increase significantly.

According to a further preferred embodiment of the method, it is provided that the regeneration phase is terminated as a function of the ambient conditions of the NOx storage catalytic converter when a degree of loading of the NOx storage catalytic converter is at a distance from a minimum loading of 10%, in particular 5%, provided at this operating point. falls below As a result, a sufficiently large distance can be maintained from an operating point of the NOx storage catalytic converter at which undesirable secondary emissions occur. In particular, in this way a rich breakthrough through the NOx storage catalytic converter is avoided, which would otherwise lead to an increase in the emissions of unburned hydrocarbons (HC) and ammonia (NH ₃ ). In addition, an increase in carbon monoxide emissions (CO) can be avoided by predictively ending the regeneration of the NOx storage catalytic converter in good time at a residual loading level of 5-10%.

In a further preferred embodiment of the invention, it is provided that the stored NOx mass is modeled on the basis of a chemical reaction mechanism of the NO ₂ release and the NO ₂ reduction. Since the chemical reactions that take place during the regeneration of the NOx storage catalytic converter are essentially known, the chemical reaction mechanisms are particularly suitable for modeling the NOx mass in the NOx storage catalytic converter. In addition, an adjustment is possible by calculating the difference in the NOx concentration at the two NOx sensors upstream and downstream of the NOx storage catalytic converter, so that the modeling can be supported by the measured values for the NOx emissions introduced into the NOx storage catalytic converter.

In another advantageous further development of the method, a reducing agent mass flow required for the regeneration of the NOx storage catalytic converter is calculated using the fuel quantity metered into the internal combustion engine and the combustion air ratio of the internal combustion engine. Using the combustion air ratio, it is easy to calculate how much fuel is completely converted during combustion and how much reducing agent is present in the exhaust gas duct due to the sub-stoichiometric combustion air ratio. A reducing agent mass flow can thus be calculated in a simple and cost-effective manner using existing sensors.

According to the invention, the calculation model for the stored NOx mass flow is adapted if a specified threshold value for NOx slip is exceeded at the second NOx sensor downstream of the NOx storage catalytic converter or if a reducing agent breakthrough is measured at a lambda probe downstream of the NOx storage catalytic converter . It is particularly preferred if an adaptation factor takes place based on a comparison of the loading state determined by measurement when the regeneration was aborted with the modeled loading level of the NOx storage catalytic converter. In this way, a simple comparison between the results determined by measurement and the modeled degree of loading of the NOx storage catalytic converter is possible. In the event of a rich breakthrough through the NOx storage catalytic converter, a complete regeneration of the NOx storage catalytic converter is assumed, which corresponds to a residual loading of 0%. This value can easily be modeled with the Comparing the remaining load, whereby an adaptation factor for the calculation model can be determined in a simple way and the model can be adapted if a deviation is found.

Further preferred configurations of the invention result from the remaining features mentioned in the dependent claims.

Unless stated otherwise in the individual case, the various embodiments of the invention mentioned in this application can advantageously be combined with one another.

• 1 ein Ablaufschema zum funktionalen Zusammenhang eines erfindungsgemäßen Speichermodells zur Ermittlung des Beladungszustands eines NOx-Speicherkatalysators,
• 2 ein Ablaufschema zur Regeneration eines NOx-Speicherkatalysators bei einem erfindungsgemäßen Verfahren,
• 3 ein Ablaufschema zur Vorgehensweise des Speichermodells während einer Adaption,
• 4 eine Darstellung einer prädiktiven Steuerung der Regeneration eines NOx-Speicherkatalysators anhand des erfindungsgemäßen Verfahrens, und
• 5 einen vereinfachten Aufbau eines Verbrennungsmotors mit Abgasstrang, in dem ein erfindungsgemäßes Verfahren durchführbar ist.

The invention is explained below in exemplary embodiments with reference to the associated drawings. Show it:

• 1 a flowchart for the functional relationship of a storage model according to the invention for determining the loading state of a NOx storage catalyst,
• 2 a flow chart for the regeneration of a NOx storage catalyst in a method according to the invention,
• 3 a flow chart for the procedure of the memory model during an adaptation,
• 4 a representation of a predictive control of the regeneration of a NOx storage catalytic converter using the method according to the invention, and
• 5 a simplified structure of an internal combustion engine with an exhaust line, in which a method according to the invention can be carried out.

5 shows an internal combustion engine 10 with an exhaust system 12. A three-way catalytic converter 14 and downstream of the three-way catalytic converter 14 a NOx storage catalytic converter 16 are arranged in the exhaust gas flow direction of an exhaust gas of the internal combustion engine 10 in the exhaust gas system 12. A first NOx sensor 18 is arranged downstream of the three-way catalytic converter 14 and upstream of the NOx storage catalytic converter 16 . A second NOx sensor 20 and optionally an additional lambda probe 22 are arranged downstream of the NOx storage catalytic converter 16 . The NOx sensors 18 , 20 and the lambda probe 22 are connected to a control unit 24 of the internal combustion engine 10 via signal lines 26 . Other embodiments of the exhaust system 12 can in principle be used since the storage model only relates to the NOx storage catalytic converter 16 and the NOx sensors 18, 20 and the lambda probe 22 assigned to the NOx storage catalytic converter 16 and can be operated independently of the rest of the exhaust system. In particular, the use of further exhaust gas aftertreatment components such as a particle filter, further three-way catalytic converters and/or a catalytic converter for the selective reduction of nitrogen oxides is conceivable.

1 shows a flowchart for the functional relationship of a storage model according to the invention for determining the loading state of the NOx storage catalytic converter 16. The storage model takes into account both operating phases of the NOx storage catalytic converter 16, i.e. both a storage phase in which the internal combustion engine 10 with a superstoichiometric, lean combustion air ratio λ _E > 1 is operated, as well as the regeneration phase, in which the internal combustion engine 10 is operated with a sub-stoichiometric, rich combustion air ratio λ _E <1. After a start S of the method, a distinction is made in a first method step <100> as to whether the NOx storage catalytic converter 16 is in a storage phase X or a regeneration phase Y. In the storage phase X, the stored NOx mass is calculated using a NOx mass flow. For this purpose, the NOx concentration in the exhaust system 12 upstream and downstream of the NOx storage catalytic converter 16 is measured by the NOx sensors 18, 20 in a method step <110>. In a method step <120>, the stored NOx mass is calculated from the change in the NOx concentration via the NOx storage catalytic converter 16 . In a regeneration Y, a reducing agent mass flow is calculated in a method step <130>. The reducing agent mass flow is calculated, for example, using the fuel quantity injected into the cylinders of internal combustion engine 10 and using combustion air ratio λ _E of internal combustion engine 10. In a method step <140>, a NOx mass flow stored from NOx storage catalytic converter 16 is calculated. A continuous balancing of the two mass flows results in the current loading of the NOx storage catalytic converter 16.

The total loading of the NOx storage catalytic converter 16 is calculated using the following formula: $${\dot{m}}_{NSC}\left(t\right)={\displaystyle \int {\dot{m}}_{NOxein}}\left(t\right)-\left({\dot{m}}_{NOxa\mathrm{and}s}\left(t\right)\times faktO{\mathrm{right}}_{A\mathrm{i.e}aptiOn}\right)\mathrm{i.e}t$$

The balancing of the total loading is carried out independently of the operating states, so that the loading of the NOx storage catalytic converter 16 can be output at any time.

The nitrogen oxides (NOx) are stored during a lean operating phase of the internal combustion engine 10. Nitrogen monoxide (NO) present in the exhaust system 12 is oxidized on the catalytic material of the NOx storage catalytic converter 16 to form nitrogen dioxide (NO ₂ ). Platinum is preferably used as the catalytic material. Only NO ₂ is stored in the storage material of the NOx storage catalytic converter 16, which is preferably barium oxide, as a result of nitrate formation. The method uses the signals from the first NOx sensor 18 upstream of the NOx storage catalytic converter 16 and the second NOx sensor 20 downstream of the NOx storage catalytic converter 16 to balance the stored NOx mass in the storage material. Alternatively or additionally, the loading of the NOx storage catalytic converter 16 can be mapped by an untreated emissions model stored in the control unit 24 of the internal combustion engine 10 . Storage takes place until a defined, maximum degree of loading of the NOx storage catalytic converter 16, which is stored in the control unit 24, is reached.

The release and chemical conversion of the nitrates takes place with a rich exhaust gas composition, which is set by a sub-stoichiometric combustion air ratio λ _E of the internal combustion engine 10 of, for example, λ _E =0.92. In regeneration phase Y, the storage model calculates the stored NOx mass flow. In 2 the procedure of the storage model during regeneration is illustrated.

In a first method step <200> the reducing agent mass flow is calculated. As described in the previous section, this is done, for example, from the injected fuel quantity and the combustion air ratio. On the basis of the reducing agent mass flow, a NOx mass flow stored out of the NOx storage catalytic converter 16 is calculated in a method step <210>. In a further method step <220>, the calculated loading of the NOx storage catalytic converter 16 is compared with a defined, minimum loading of the NOx storage catalytic converter 16 and the regeneration ends <E> if this defined minimum loading is reached or not reached.

The modeling is based on the chemical reaction mechanism $$Ba{\left({\text{NO}}_3\right)}_2+{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">H</figure-callout>}}_2\rightleftharpoons )BaO+2\mathrm{<figure-callout\; id="2"\; label="N\; O"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">N</figure-callout>}{O}_{}{}_2+H_{2}O$$

A release of the nitrogen dioxide from the barium nitrate thus requires one mole of molecular hydrogen.

The reduction of nitrogen dioxide takes place according to the following chemical reaction mechanism $$N{O}_{}$$$${}_2+2{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">H</figure-callout>}}_2\rightleftharpoons \frac{1}{2}{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">N</figure-callout>}}_2+2H_{2}O$$

Thus, the reduction of the nitrogen dioxide consumes an additional two moles of molecular hydrogen. The required amount of molecular hydrogen can be calculated using these two reaction equations: $$\frac{1m\mathrm{<figure-callout\; id="2"\; label="O\; l\; H"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">O</figure-callout>}l{H}_{}{}_2}{2mO\mathrm{<figure-callout\; id="2"\; label="l\; N\; O"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">l</figure-callout>}N{O}_{}{}_2}+\frac{2m\mathrm{<figure-callout\; id="2"\; label="O\; l\; H"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">O</figure-callout>}l{H}_{}{}_2}{1mO\mathrm{<figure-callout\; id="2"\; label="l\; N\; O"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">l</figure-callout>}N{O}_{}{}_2}\leftrightharpoons 2.5\frac{mOl{H}_2}{mO\mathrm{<figure-callout\; id="2"\; label="l\; N\; O"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">l</figure-callout>}N{O}_{}{}_2}$$

The two parts for the NO ₂ release and for the NO ₂ reduction are combined. Converting one mole of NO ₂ to molecular nitrogen requires 2.5 moles of molecular hydrogen.

The available reducing agent mass flow is determined via the fuel mass flow and the combustion air ratio λ _E . The calculation is illustrated with the following formula: $${\dot{m}}_{\mathrm{right}e\mathrm{i.e}}={\dot{m}}_{K\mathrm{right}}\times \left(1-{\lambda }_E\right)$$

The fuel mass flow is calculated using the air ratio, the stoichiometric air requirement and the exhaust gas mass flow. With the available reducing agent mass flow and the required reducing agents, a NO _x mass flow discharged from the NOx storage catalytic converter 16 can be calculated. For the calculation, the reducing agent mass flow is divided into three components, namely unburned hydrocarbons (HC), carbon monoxide (CO) and molecular hydrogen (H ₂ ). $${\dot{m}}_{N{O}_{x}a\mathrm{and}s}=\left({\dot{m}}_{\mathrm{right}e\mathrm{i.e}}*x_{CO}*\frac{1}{1.5221}\right)+\left({\dot{m}}_{\mathrm{right}e\mathrm{i.e}}*x_{HC}*\frac{1}{0.1525}\right)+\left({\dot{m}}_{\mathrm{right}e\mathrm{i.e}}*{\mathrm{<figure-callout\; id="2"\; label="x\; H"\; filenames="DE102016204216B4\_0010.png"\; state="\{\{state\}\}">x</figure-callout>}}_{H_{}}*\frac{1}{0.1096}\right)$$

An adaptation of the calculation of the stored NOx mass flow compensates for inaccuracies in the simulation of the chemical reaction mechanisms. If a defined NOx slip downstream of the NOx storage catalytic converter 16 is exceeded or if the reducing agent breaks through, which can be measured by the lambda probe 22 downstream of the NOx storage catalytic converter 16, the model calculation is adapted. This ensures continuous monitoring of the storage model. In 3 the procedure for calculating the adaptation factor is illustrated.

In a first method step <300>, at the time when the regeneration is aborted, which is detected by a rich breakthrough downstream of the NOx storage catalytic converter 16 at the lambda probe 22 or the NOx sensor 20, i.e. when the NOx storage catalytic converter 16 is completely regenerated, the modeled residual loading of the NOx storage catalytic converter 16 read out. An adaptation factor is calculated in a subsequent method step <310> on the basis of the residual loading and the maximum loading of the NOx storage catalytic converter 16 . The calculation of the adaptation factor is illustrated using the following formula: $$faktO{\mathrm{right}}_{A\mathrm{i.e}aptiOn}=\frac{m_{ma{x}_{NSC}}}{m_{ma{x}_{NSC}}-m_{Res{t}_{NSC}}}-1$$

The adaptation factor determined in this way is stored in a matrix in a method step <320> and output in a method step <330>. In addition, the memory model is automatically adapted by monitoring the input and output. The sub-stoichiometric, rich combustion air ratio λ _E < 1 is maintained until the storage model has reached a defined residual load. The procedure for the predictive control of a regeneration phase of the NOx storage catalytic converter 16 is shown schematically in 4 clarified. A predictive control of the regeneration of the NOx storage catalytic converter 16 according to the proposed method is represented by the dot-dash line and a conservative regeneration, which is only initiated or ended when there are corresponding breakthroughs through the NOx storage catalytic converter 16, is represented by the solid line. Likewise is in 4 to see a history of the emissions. Number 1 indicates the start of the regeneration of the NOx storage catalytic converter 16. If the regeneration is already terminated when a defined residual load is reached (number 2) and not only when the reducing agent breaks through (number 3), then the details under X and Y do not apply recognized increase in secondary emissions.

Reference List

10

combustion engine

12

exhaust line

14

Three-way catalytic converter

16

NOx storage catalyst

18

first NOx sensor

20

second NOx sensor

22

lambda probe

24

control unit

26

signal line

λE

combustion air ratio

CO

carbon monoxide

NH3

ammonia

NOx

nitric oxide

NPC

NOx storage catalyst

TWC

Three-way catalytic converter

mg

milligram

s

second

Claims (7)

Method for determining the loading condition of a NOx storage catalytic converter (16) in the exhaust line (12) of an internal combustion engine (10), comprising the following steps: - Operating the internal combustion engine (10) with a super-stoichiometric, lean combustion air ratio λ _E > 1 in a storage phase of the NOx storage catalytic converter (16), - determining the NOx mass stored in the NOx storage catalytic converter (16) from the NOx mass flow in the storage phase, - operating the internal combustion engine (10) with a substoichiometric, rich combustion air ratio λ _E <1 in a regeneration phase of the NOx - storage catalytic converter (16), - determining the NOx mass removed from the NOx storage catalytic converter (16) from the NOx mass flow in the regeneration phase of the NOx storage catalytic converter (16), - calculating the current loading status of the NOx storage catalytic converter (16), - End of the storage phase when a defined, maximum degree of loading of the NOx storage cat analyzer (16) is reached, - ending the regeneration of the NOx storage catalytic converter (16) when a defined, minimum degree of loading of the NOx storage catalytic converter (16) is undershot, with - a NOx concentration in the exhaust system (12) at a first NOx sensor (18) upstream of the NOx storage catalytic converter (16) and at a second NOx sensor (20) downstream of the NOx storage catalytic converter (16), and the stored NOx mass flow is measured by the NOx sensors (18 , 20) measured NOx concentrations are determined and the NOx mass stored in the NOx storage catalytic converter (16) is calculated, with - the calculation model of the stored NOx mass flow being adapted if the second NOx sensor (20) downstream of the NOx -storage catalytic converter (16) exceeds a specified threshold value for NOx slip or a reducing agent breakthrough is measured at a lambda probe (22) or the NOx sensor (20) downstream of the NOx storage catalytic converter (16). n will. procedure after claim 1 , characterized in that the storage phase is ended when a degree of loading of the NOx storage catalytic converter (16) falls below a distance from a maximum loading degree of the NOx storage catalytic converter (16) of 10%, in particular 5%, provided at this operating point. procedure after claim 1 or 2 , characterized in that the regeneration phase is terminated when a degree of loading of the NOx storage catalytic converter (16) falls below a distance from a minimum loading of 10%, in particular 5%, provided at this operating point. Procedure according to one of Claims 1 until 3 , characterized in that the stored NOx mass is modeled on the basis of a chemical reaction mechanism of NO ₂ release and NO ₂ reduction. Procedure according to one of Claims 1 until 4 , characterized in that a for the regeneration of the NOx storage catalyst (16) necessary reducing agent mass flow based on the in the internal combustion engine (10) metered fuel quantity and the combustion air ratio of the internal combustion engine (10) is calculated. procedure after claim 1 , characterized in that an adaptation factor takes place based on a comparison of the loading condition determined when the regeneration was aborted with the modeled loading level of the NOx storage catalytic converter (16). Device for determining a loading condition of a NOx storage catalytic converter (16) in an exhaust line (12) of an internal combustion engine (10), comprising a arranged first NOx sensor (18) and a second NOx sensor (20) arranged downstream of the NOx storage catalytic converter (16), the sensors being connected to a control unit (22) of the internal combustion engine (10) via signal lines (24), thereby characterized in that the control unit (22) is set up, a method according to one of Claims 1 until 6 to perform.

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