EP1209332B1 - Method and device for regenerating a NOx catalytic converter - Google Patents

Description

The invention relates to methods for carrying out a regeneration of a NO _x storage catalytic converter in an exhaust line of an internal combustion engine and to devices for carrying out the regeneration with the features mentioned in the preambles of the independent claims 1 to 3 or 20 or 21.

Internal combustion engines, which are operated for reasons of consumption optimization at least temporarily in a lean operating mode, that is, with an oxygen-rich exhaust gas with λ> 1, produce nitrogen oxides NO _x in a stoichiometric excess. This has the consequence that in a catalytic oxidative conversion of unburned hydrocarbons HC and carbon monoxide CO nitrogen oxides NO _{x are} not completely converted to environmentally neutral nitrogen. As a remedy, it is known to arrange NO _x storage catalysts in the exhaust ducts of internal combustion engines, which store the NO _x as nitrate in lean phases of operation. To avoid NO _x breakthroughs due to a fully loaded NO _x storage catalytic converter, the NO _x storage catalytic converter must be regenerated at recurring intervals. For this purpose, the internal combustion engine is temporarily switched to a rich or stoichiometric working mode (λ ≦ 1). As a result, a reducing agent mass flow of the exhaust gas increases, the nitrate incorporated nitrogen oxides are desorbed and catalytically reacted on the NO _x storage catalyst with simultaneous oxidation of CO and HC.

In simple methods, a regeneration duration, during which the storage catalytic converter is exposed to the rich exhaust gas atmosphere, is fixed. The disadvantage of this is that an actual loading state of the NO _x storage catalytic converter and a current regeneration rate of the same is not taken into account. Such an approach involves the risk that the regeneration period is too short or too long, in the former case, an incomplete regeneration of the memory and in the second case an unnecessary fuel consumption and a Emission of environmentally harmful reducing agents (HC and CO) is accepted. Refined methods attempt to estimate an actual state of charge of the NO _x storage catalyst based on certain operating parameters during the last lean phase and deduce therefrom a required regeneration duration. However, this method is also subject to considerable inaccuracies, so that here too inappropriate NO _x regeneration periods can result with the mentioned consequences.

Furthermore, methods are known, such as in DE 198 44 082 described in which with the aid of a downstream of the NO _x storage catalytic converter arranged sensor system, which measures an oxygen content of the exhaust gas, the regeneration curve is monitored. In this case, a decreasing proportion of oxygen in the exhaust gas indicates a reduced reduction agent conversion at the NO _x reservoir and thus increasing proportions of the reducing agent in the exhaust gas. To avoid reducing agent breakthroughs, the NO _x regeneration is stopped, that is, the internal combustion engine is switched back to a lean operating mode as soon as the measured oxygen content falls below a predetermined limit value or a sensor voltage exceeds a corresponding limit voltage. This method has the disadvantage that the sensor can only react if a certain reductant breakthrough already occurs. Furthermore, at the time of the limit value achievement, the entire exhaust gas path between the internal combustion engine and the NO _x storage catalytic converter is still filled with rich, that is, with reducing agent, exhaust gas. These reducing agents (HC and CO) then pass largely unconverted as pollutants into the environment. In order to keep this pollutant emission low, the combustion lambda should not be regulated too rich during the regeneration according to this procedure. This leads in addition to the disadvantage of relatively long regeneration periods and unnecessary fuel consumption.

The invention is therefore based on the object to provide a method for NO _x regeneration of a NO _x storage catalyst available, which is optimized in terms of the lowest possible reducing agent emission and at the same time ensures complete regeneration of the storage catalyst. In a further aspect, the fastest possible procedure of the method, ie short regeneration periods, should be ensured. It is further intended to provide a device which is suitable and advantageous for carrying out the method.

This object is achieved by a method having the features mentioned in the independent claim 1. A suitable device is characterized by the features mentioned in independent claim 18.

1. (a) während der NO_X-Regeneration das sauerstoffabhängige Signal der stromab des NO_X-Speicherkatalysators angeordneten Messeinrichtung hochgerechnet wird,
2. (b) auf Basis des hochgerechneten Signals ein theoretischer Zeitpunkt bestimmt wird, an dem ein vorgegebener Signalschwellenwert voraussichtlich überschritten wird, und
3. (c) das Regenerationsende bestimmt wird, indem eine im Wesentlichen einer Abgaslaufzeit zwischen Verbrennungskraftmaschine und NO_X-Speicherkatalysator entsprechende Zeitspanne von dem theoretischen Zeitpunkt subtrahiert wird.

According to a first method according to the invention, it is provided that

1. (a) during the NO _x regeneration, the oxygen-dependent signal of the measuring device arranged downstream of the NO _x storage catalytic converter is extrapolated,
2. (b) determining, based on the extrapolated signal, a theoretical time at which a predetermined signal threshold is likely to be exceeded, and
3. (c) determining the regeneration end by subtracting an amount of time substantially corresponding to an exhaust running time between the internal combustion engine and the NO _x storage catalyst from the theoretical time.

Thus, by extrapolating the signal of the measuring device, the achievement of the predetermined signal threshold value can be determined in advance with sufficient reliability. This makes it possible to take into account the time span corresponding to the exhaust gas running time between the internal combustion engine and the NO _x storage catalytic converter - hereinafter referred to simply as the exhaust gas flow time - so that the NO _x regeneration can be stopped in good time, that is to say before the occurrence of a reductant breakthrough. Overall, the method thus allows a reduction of CO and HC emission and minimization of a need for NO _x regeneration additional fuel consumption.

The extrapolation of the oxygen-dependent signal of the measuring device is carried out according to an advantageous embodiment of the method based on current operating parameters of the internal combustion engine and / or the exhaust system. These may include, for example, a current air-fuel mixture (combustion lambda) supplied to the internal combustion engine and / or an exhaust gas mass flow and / or an exhaust gas temperature and / or a catalyst temperature. The accuracy of the extrapolation can be further increased by taking into account a behavioral model of the NO _x storage catalytic converter. Such a behavioral model can be, for example, the course of a regeneration rate as a function of the current reducing agent mass flow and / or the catalyst temperature include. The behavioral model can also take into account the waveform measured during the current regeneration. An advantageous further development of the method can also be achieved by extrapolating the signal taking into account a behavioral model of the oxygen-sensitive measuring device. In particular, an inertia, ie a time delay, with which the measuring device displays changed exhaust gas conditions, but also a current, measured about an internal resistance, temperature of the measuring device can be considered.

Although it is in principle possible to specify the exhaust gas flow time as a fixed value, it is preferably provided to calculate these using current operating parameters of the internal combustion engine. It can be used on known operating parameters such as engine load, speed or exhaust gas temperature or other suitable data.

Since the reliability of the extrapolation of the signal curve can be reduced under certain extreme boundary conditions, a preferred embodiment of the method provides for setting limits for different operating conditions of the internal combustion engine and / or the exhaust system and suppressing the extrapolation if these limits are not met. In particular, limit values for the exhaust gas mass flow and / or for the temperature of the NO _x storage catalytic converter are expedient, since the regeneration rates are too unstable if the exhaust gas mass flows are too high or the catalyst temperatures are too low to be able to be extrapolated with sufficient reliability. The signal extrapolation can advantageously also be suppressed if there are operating point-dependent disturbing influences which influence an irregular NO _x regeneration. This is the case, for example, with a fuel cut of the internal combustion engine.

According to a further advantageous embodiment of the method, the extrapolation is not carried out during the entire regeneration period of the storage catalytic converter, but only after elapse of a predetermined time after the beginning of the regeneration and / or flow rate of a given exhaust gas mass and / or after exceeding a predetermined minimum threshold of the signal of the measuring device. These measures ensure that the signal profile is already known for a certain minimum duration and thus extrapolated more reliably can be. After the start of extrapolation, the waveform should continue to be tracked, so that the extrapolation can be constantly updated.

1. (a) während der NO_X-Regeneration das sauerstoffabhängige Signal der stromab des NO_X-Speicherkatalysators angeordneten Messeinrichtung hochgerechnet wird und
2. (b) ein der Verbrennungskraftmaschine während der Regeneration zugeführtes Luft-Kraftstoff-Gemisch (Verbrennungslambda) in Abhängigkeit von dem hochgerechneten Signal unter Berücksichtigung einer im Wesentlichen der Abgaslaufzeit zwischen Verbrennungskraftmaschine und NO_X-Speicherkatalysator entsprechenden Zeitspanne variiert wird.

Another inventive method provides that

1. (A) during the NO _x regeneration, the oxygen-dependent signal of the arranged downstream of the NO _x storage catalytic converter measuring device is extrapolated, and
2. (b) an air-fuel mixture (combustion lambda) supplied to the internal combustion engine during the regeneration is varied as a function of the projected signal, taking into account a time span substantially corresponding to the exhaust gas running time between the internal combustion engine and the NO _x storage catalytic converter.

The extrapolation according to the invention makes it possible, in this aspect of the invention, to take into account the exhaust gas flow time during the change of the combustion lambda during the regeneration, so that it is possible to react to an expected signal height to a certain extent with foresight. Thus, for example, it is possible to raise the combustion lambda before an undesired reductant breakdown predicted by the projection occurs, and ultimately to reduce or even completely suppress this by this measure. Overall, the method thus allows a reduction in CO and HC emission and minimization of a need for the NO _x regeneration additional fuel consumption.

1. (a) während der NO_X-Regeneration das sauerstoffabhängige Signal der Messeinrichtung hochgerechnet wird,
2. (b) auf Basis des hochgerechneten Signals ein theoretischer Zeitpunkt bestimmt wird, an dem ein vorgegebener erster Signalschwellenwert überschritten wird, und
3. (c) ein der Verbrennungskraftmaschine während der Regeneration zugeführtes Luft-Kraftstoff-Gemisch in Abhängigkeit von dem hochgerechneten Signal und/oder dem Zeitpunkt unter Berücksichtigung einer im Wesentlichen einer Abgaslaufzeit zwischen Verbrennungskraftmaschine und NO_X-Speicherkatalysator entsprechenden Zeitspanne variiert wird, wobei insbesondere das Regenerationsende bestimmt wird, indem die im Wesentlichen der Abgaslaufzeit entsprechende Zeitspanne von dem theoretischen Zeitpunkt subtrahiert wird.

The above advantages are even more pronounced by a further process according to the invention, which essentially represents a combination of the two first-mentioned processes and according to which

1. (a) during the NO _x regeneration, the oxygen-dependent signal of the measuring device is extrapolated,
2. (b) determining on the basis of the extrapolated signal a theoretical time at which a predetermined first signal threshold is exceeded, and
3. (C) an air-fuel mixture supplied to the internal combustion engine during the regeneration as a function of the extrapolated signal and / or the time taking into account a substantially exhaust gas flow time between the internal combustion engine and NO _x storage catalytic converter corresponding time period is varied, in particular the regeneration end is determined by the time substantially corresponding to the exhaust gas time is subtracted from the theoretical time.

Accordingly, in addition to the measures of the aforementioned method, the (theoretical) achievement of the signal threshold value prescribed for a regeneration interruption is determined in advance. Thus, the regeneration can be stopped in time, that is, before the occurrence of a Reduktionsmitteldurchbruches.

According to a particularly advantageous embodiment of the method, the combustion lambda of the internal combustion engine is raised to the regeneration end to a value near λ = 1, which value is greater, that is leaner than a previous lambda value and at the same time <or = 1. According to the invention, there are several alternatives to determine a time of this increase. For example, the increase can take place after the expiry of a predefinable portion of a total regeneration duration determined by the extrapolation. It is even more advantageous to increase the combustion lambda on reaching a second predetermined signal threshold value by the projected sensor signal taking into account the exhaust gas flow time, the second signal threshold is usefully smaller than the first signal threshold, if it is a probe voltage. The increase of the combustion lambda before the regeneration end causes a reduction of a reducing agent mass flow at a time at which only small amounts of stored nitrogen oxides in the storage catalyst are available for the conversion of the reducing agent. By this measure, the risk of reducing agent breakthrough at the end of the regeneration is thus further reduced. It has proven particularly useful to increase the lambda Lambda values of 0.94 to 0.99, in particular 0.95 to 0.98.

According to a further advantageous embodiment, the combustion lambda of the internal combustion engine is lowered below a previous lambda value until the projected sensor signal, taking into account the exhaust gas running time, reaches a third predetermined signal threshold value. In this context, combustion lambda values of 0.6 to 0.9, in particular 0.7 to 0.8, have proven particularly useful. As a result of this embodiment of the method, the NO _x storage catalytic converter thus becomes with a comparatively very rich exhaust gas atmosphere acted as long as the memory still has a marked by the third signal threshold minimum loading of nitrogen oxides. As a result of this, at least temporarily, very powerful admission of the storage catalytic converter, an efficiency of the NO _x conversion is increased, the regeneration duration is shortened and, ultimately, the additional fuel consumption to be expended for the regeneration is minimized.

It is, of course, conceivable to specify further threshold values whose exceeding-triggered by the extrapolated sensor signal further variations of the combustion lambda. Additional threshold values may, for example, take into account an otherwise determined aging state of the storage catalytic converter. The various increases and / or reductions of the internal combustion engine to be supplied air-fuel mixture can also be done gradually or even continuously.

The devices according to the invention comprise means with which the described method steps can be carried out. The means comprise a control unit in which an algorithm for controlling the method steps is stored in digital form. This control unit can advantageously also be integrated in an engine control unit of the vehicle.

The oxygen-sensitive measuring device may be a lambda probe arranged downstream of the NO _x storage catalytic converter, in particular a broadband or a step response lambda probe, or an NO _x sensor having a lambda output signal.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

Figur 1

eine Prinzipdarstellung einer Verbrennungskraftmaschine mit einer Abgasanlage;

Figur 2

zeitliche Verläufe verschiedener Abgasparameter während einer herkömmlichen NO_x-Regeneration;

Figur 3

zeitliche Verläufe verschiedener Abgasparameter während einer NO_x Regeneration gemäß einer ersten Ausführung der vorliegenden Erfindung; und

Figur 4

zeitliche Verläufe verschiedener Abgasparameter während einer NO_x-Regeneration gemäß einer zweiten Ausführung der vorliegenden Erfindung.

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

FIG. 1

a schematic diagram of an internal combustion engine with an exhaust system;

FIG. 2

time histories of different exhaust gas parameters during a conventional NO _x regeneration;

FIG. 3

time histories of various exhaust parameters during NO _x regeneration according to a first embodiment of the present invention; and

FIG. 4

Timing of various emission parameters during a NO _x regeneration according to a second embodiment of the present invention.

The Indian FIG. 1 shown internal combustion engine 10 is associated with a generally designated 12 exhaust system. The exhaust system 12 includes an exhaust passage 14, in which a arranged in a near-engine position precatalyst 16 and a large-volume NO _x storage 18 is arranged. In addition to the catalyst system 16, 18, the exhaust duct 14 usually houses various gas and / or temperature sensors (not shown) for controlling the internal combustion engine 10. Shown here is merely an oxygen-sensitive measuring device 20, which is arranged downstream of the NO _x storage 18. The measuring device 20 may be, for example, a lambda probe or an NO _x sensor, which is equipped with a Lambdamessfunktion. In any case, the measuring device 20 provides a dependent of an oxygen content of the exhaust gas signal U _λ . This signal U _λ is transmitted to an engine control unit 22, in which it is digitized and further processed. Further, the operating state of the internal combustion engine 10 information concerning also found in the engine control unit 22. In the engine control unit 22, a control unit 24 is integrated, in which an algorithm for performing the method for NO _x regeneration of the NO _x storage 18 is stored. The engine control unit 22 and the control unit 24 are capable of influencing at least one operating parameter of the internal combustion engine 10, in particular an air-fuel mixture (combustion lambda) to be supplied, as a function of the signal U _{λ of} the measuring device in a manner to be explained.

FIG. 2 shows the time course of various parameters of the internal combustion engine 10 and the exhaust system 12 during a NO _x regeneration of the NO _x storage catalytic converter 18, which is carried out according to a conventional method. First, the internal combustion engine 10 is in a lean mode of operation in which it is supplied with an oxygen-rich air-fuel mixture with λ _M >> 1 (graph 100). In this phase, the exhaust gas contains an excess of nitrogen oxides NO _x , which is not complete by the precatalyst 16 can be converted. NO _x is therefore stored in the NO _x storage 18, the NO _x load continuously increases (Graph 102). Based on a suitable criterion, a NO _x regeneration need is recognized at a time t _A. This can be, for example, a NO _x breakthrough detected by the measuring device 20. The internal combustion engine Consequently, 10 is switched by influencing the engine control unit 22 in a rich operating mode with λ _F <1. As a result of the now increased mass flow of reducing agents CO and HC in the exhaust is - the _x desorbed NO _x storing catalyst 18 embedded NO and nitrogen reduced. However, a decrease in the NO _x charge (graph 102) of the storage catalytic converter 18 is only noticeable after a certain time delay after switching the internal combustion engine 10, since at the time t _A the exhaust duct 14 is still filled with lean exhaust gas, which initially still the storage catalytic converter 18 must happen before the reducing agents reach it. The course of the NO _x regeneration is meanwhile tracked with the aid of the signal U _λ provided by the measuring device 20, generally a voltage. The probe voltage U _λ (graph 104) behaves inversely proportional to an oxygen concentration of the exhaust gas downstream of the storage catalytic converter 18. Since the reducing agent is consumed to a lesser and greater extent as regeneration progresses, the signal U _{λ of} the measuring device 20 rises slowly. At a time t _E , the signal U _{λ reaches} a predetermined threshold value U _SE , whereupon the internal combustion engine 10 is generally switched back into a lean operating mode with λ _M >> 1. At the time of the regeneration end t _E , however, there is still exhaust gas with a high proportion of reducing agent in the exhaust gas duct 14 between the internal combustion engine 10 and the storage catalytic converter 18. This flows through the virtually NO _x -free storage catalytic converter 18 and enters the environment without being converted. The course of the measured downstream of the catalyst concentration of carbon monoxide CO and unburned hydrocarbons HC (graph 106) therefore shows after regeneration end t _E still an undesirably high increase.

In order to reduce the emission of pollutants, according to the present invention a different approach is followed to determine the regeneration end t _E. The time course of the same parameters as in FIG. 2 is in FIG. 3 shown - this time during regeneration according to a first typical embodiment of the method according to the invention. After the start of the regeneration at time t _A by switching the internal combustion engine 10 from a lean operating mode with λ _M >> 1 in a rich mode with λ _F1 <1, the signal U _{λ of} the measuring device 20 (graph 104) is first measured and recorded in a known manner. After elapse of a predetermined time period, the control unit 24 begins at a time t _AH with a projection of the signal U _λ . This is done on the basis of the previously measured course of U _λ and based on various operating parameters of the internal combustion engine 10 and the exhaust system 12. Furthermore, behavioral models of the storage catalytic converter 18 and the measuring device 20 can be taken into account in the extrapolation. On the basis of the projected signal curve, a time t _{S is} determined at which the predetermined signal threshold value U _{SE is} theoretically reached.

Based on selected operating parameters, the control unit 24 further calculates a period .DELTA.t, which corresponds to the current exhaust gas running time, which requires the exhaust gas until reaching the storage catalytic converter. According to a first aspect of the invention, the time of the actual regeneration end t _E is then determined by subtracting the exhaust gas flow time Δt from the time t _S. During the period T _H , the projection and thus the regeneration end t _{E is} constantly updated on the basis of current operating parameters and on the basis of the actual signal profile U _λ . Once the specific regeneration end t _{E has been} reached, the internal combustion engine 10 is switched back to the lean operating mode with λ _M. At this point in time, there is still a small amount of stored NO _x present in the storage catalytic converter 18 (graph 102), which is sufficient to convert the remaining reducing agent contained in the exhaust gas. Consequently, only very small amounts of pollutants are measured downstream of the storage catalytic converter 18 after the regeneration end t _E (graph 106).

The time profiles of the parameters according to an advantageous embodiment of a further inventive method in which a predetermined combustion lambda is varied taking into account the projected sensor signal U _λ and the exhaust gas flow time shows FIG. 4 , Here, the projection of the sensor signal U _λ (graph 104) and the determination of the exhaust gas flow time .DELTA.t is analogous to that in the context of FIG. 3 explained procedure.

Immediately after the start of the extrapolation of the sensor signal U _λ at the time t _AH , it is first checked whether the projected sensor signal U _λ is still below a predetermined first threshold value U _S1 at the current time and after expiry of the determined exhaust gas flow time Δt. Only if affirmative Verification can - as in the example shown - a the internal combustion engine 10 supplied air-fuel mixture to a deviating from an initially set lambda value λ _F1 lambda value λ _{F2 be} changed. (Graph 100). When the lambda value is reduced to a lambda value λ _{F2 which} is lower than the lambda value λ _F1 , the reducing agent mass flow of the exhaust gas continues to increase and thus the regeneration rate, which is reflected in a steeper drop in the NO _x charge of the storage catalytic converter 18 (graph 102). λ _F2 is maintained until the projected signal U _λ , taking into account Δt reaches the threshold value U _S1 . This is the case at time t ₁ at which the combustion lambda is raised again to a less rich lambda value λ _F3 (graph 100).

A short time later reached in the present example, the projected sensor signal U _λ a second, not shown for reasons of clarity signal threshold U _S2 , which is located between U _S1 and U _SE . The achievement of the signal threshold value U _S2 signals that the NO _x charge of the storage catalytic converter 18 is almost exhausted. In order to avoid an impending pollutant breakdown by the rich exhaust gas, the combustion lambda is further raised to a value of λ _F4 near 1. λ _F4 is then typically 0.95 to 0.98.

On the basis of the extrapolated signal curve is further according to the in FIG. 3 illustrated method, the time t _S determined at which the predetermined signal threshold U _{SE is achieved} theoretically. By subtracting the exhaust gas flow time At from the time t _S , the time of the (actual) regeneration end t _E is then determined. Once the particular regeneration end t _{E has been} reached, the internal combustion engine 10 is switched back to the lean operating mode with λ _{M in} order to prevent pollutant breakdown (graph 106). The small amount of NO _X (graph 102) still present in the storage catalytic converter 18 at this point in time ensures that the small amount of reducing agent still contained in the exhaust gas is largely converted.

The comparison of the graphs 106 in FIGS Figures 2 and 4 symbolized concentrations of carbon monoxide CO and unburned hydrocarbons HC downstream of the NO _x storage catalyst 18 shows a strong reduction of the regeneration-related pollutant emission. However, it also becomes clear that with a suitable choice of the lambda values λ _F1 to λ _F4, the total duration of the NO _x regeneration can be reduced by the method according to the invention, which results in a minimization of the additional fuel consumption necessary for the regeneration.

LIST OF REFERENCE NUMBERS

10

Internal combustion engine

12

exhaust system

14

exhaust duct

16

precatalyzer

18

NO _X storage catalyst

20

oxygen-sensitive measuring device

22

Engine control unit

24

control unit

100

combustion lambda

102

NO _x charge of the NO _x storage catalyst

104

Signal curve (U _λ ) of the measuring device

106

Reducing agent content in the exhaust gas

t _A

regeneration start

t _E

regeneration end

t _s

Time of exceeding of U _SE

t _AH

Extrapolation beginning

T _H

Extrapolation time

.delta.t

Exhaust maturity

U _λ

Signal of the measuring device

U _SE

Threshold to stop the NO _X regeneration

U _Si

Thresholds for raising or lowering the combustion lambda

λ _M

Lambda lean value

λ _F

Lambda fat value

Claims (21)

1. Method for the NO_X regeneration of an NO_X storage catalytic converter (18) which is arranged in an exhaust duct of an internal combustion engine (10) which is capable of lean running, wherein a rich to stoichiometric exhaust gas atmosphere with λ ≤ 1 is applied to the NO_X storage catalytic converter (18) until an end of the regeneration process is reached, and a regeneration course is pursued by means of an oxygen-dependent signal which is made available by an oxygen-sensitive measuring device (20) which is arranged downstream of the NO_X storage catalytic converter (18), characterized in that

   (a) the oxygen-dependent signal (U_λ) of the measuring device (20) is projected forward during the NO_X regeneration,
   and at least one of the following measures is carried out:

   (b) an air/fuel mixture (combustion lambda) which is supplied to the internal combustion engine (10) during the regeneration is varied as a function of the projected signal (U_λ) taking into account a time period (Δt) essentially corresponding to an exhaust gas transit time between the internal combustion engine (10) and NO_X storage catalytic converter (18), and

   (c) a theoretical time (t_S) at which a predefined signal threshold value (U_SE) is exceeded is determined on the basis of the projected signal (U_λ) and the end (t_E) of the regeneration is defined by subtracting the time period (Δt) from the theoretical time (t_S).
2. Method according to Claim 1, characterized in that the air/fuel mixture (combustion lambda) which is supplied to the internal combustion engine (10) during the regeneration is varied as a function of the projected signal (U_λ) and the time (t_S) taking into account the time period (Δt).
3. Method according to one of the preceding claims, characterized in that the oxygen-dependent signal (U_λ) is projected forward by means of current operating parameters of the internal combustion engine (10) and/or of the exhaust gas system (12).
4. Method according to Claim 3, characterized in that the oxygen-dependent signal (U_λ) is projected forward as a function of an air/fuel mixture which is supplied to the internal combustion engine (10) and/or an exhaust gas mass flow and/or an exhaust temperature and/or a catalytic converter temperature.
5. Method according to Claim 3 or 4, characterized in that the oxygen-dependent signal (U_λ) is projected forward taking into account a behaviour model of the NO_X storage catalytic converter (18).
6. Method according to one of Claims 3 to 5, characterized in that the oxygen-dependent signal (U_λ) is projected forward taking into account a behaviour model of the oxygen-sensitive measuring device (20), in particular an inertia of the measuring device (20).
7. Method according to one of the preceding claims, characterized in that the projection starts after the end of a predefined time after the start of the regeneration and/or after a predefined mass of exhaust gas has passed through and/or after a predefined threshold of the signal (U_λ) has been exceeded.
8. Method according to one of the preceding claims, characterized in that the exhaust gas transit time (Δt) is calculated by means of current operating parameters of the internal combustion engine (10) or is predefined.
9. Method according to one of the preceding claims, characterized in that the projection of the signal (U_λ) does not take place if predefined limiting values for operating conditions of the internal combustion engine (10) and/or of the exhaust gas system (12) are not complied with.
10. Method according to Claim 9, characterized in that limiting values are predefined for the exhaust gas mass flow and/or for the temperature of the NO_X storage catalytic converter (18).
11. Method according to Claim 9 or 10, characterized in that the projection of the signal (U_λ) does not take place in the event of an overrun shutoff during the NO_X regeneration.
12. Method according to one of the preceding claims, characterized in that the combustion lambda is raised if the projected sensor signal (U_λ) reaches a second predefined signal threshold value (U_S2) taking into account the exhaust gas transit time (Δt) or after the expiry of a predefinable portion of a regeneration period which is acquired by means of the projection.
13. Method according to Claim 12, characterized in that the combustion lambda of the internal combustion engine (10) is raised, in advance of the end (t_E) of the regeneration, to a value (λ_F4) which is higher than a preceding combustion lambda value and is ≤ 1.
14. Method according to Claim 13, characterized in that the combustion lambda is raised to λ_F4 = 0.94 to 0.99, in particular to 0.95 to 0.98.
15. Method according to one of the preceding claims, characterized in that the combustion lambda of the internal combustion engine (10) is lowered to a value (λ_F2) below a preceding lambda value ( (λ_F1) until the projected sensor signal (U_λ) reaches a third predefined signal threshold value (U_S1) taking into account the exhaust gas transit time (Δt).
16. Method according to Claim 15, characterized in that the combustion lambda is lowered to λ_F2 = 0.6 to 0.9, in particular to 0.7 to 0.8.
17. Method according to one of the preceding claims, characterized in that the raising and/or lowering of the combustion lambda is carried out incrementally.
18. Device for carrying out a regeneration of an NO_X storage catalytic converter (18) which is arranged in an exhaust duct of an internal combustion engine (10) which is capable of lean running, wherein a rich to stoichiometric exhaust gas atmosphere with λ ≤ 1 is applied to the NO_x storage catalytic converter (18) until an end of the regeneration process is reached, and a regeneration sequence is pursued by means of an oxygen-dependent signal which is made available by an oxygen-sensitive measuring device (20) which is arranged downstream of the NO_x storage catalytic converter (18), characterized by means with which the method steps

    (a) projecting forward of the oxygen-dependent signal (U_λ) of the measuring device (20) during the NO_X regeneration,
    and at least one of the following measures can be carried out:

    (b) an air/fuel mixture (combustion lambda) which is supplied to the internal combustion engine (10) during the regeneration is varied as a function of the projected signal (U_λ) taking into account a time period (Δt) essentially corresponding to an exhaust gas transit time between the internal combustion engine (10) and NO_X storage catalytic converter (18), and

    (c) a theoretical time (t_S) at which a predefined signal threshold value (U_SE) is exceeded is determined on the basis of the projected signal (U_λ) and the end (t_E) of the regeneration is defined by subtracting the time period (Δt) from the theoretical time (t_S).
19. Device according to Claim 18, characterized in that the means comprise a control unit (24) in which an algorithm for controlling the method steps is stored in a digital form.
20. Device according to Claim 19, characterized in that the control unit (24) is integrated into an engine control device (22).
21. Device according to one of Claims 18 to 20, characterized in that the oxygen-sensitive measuring device (20) comprises a broadband or step response lambda probe or an NO_X sensor.

Images