DE10028882A1 - Carrying out nitrogen oxides regeneration of nitrogen oxides storage catalyst in IC engine comprises using nitrogen oxides storage activity values of storage catalyst during all or one part of rich phases - Google Patents

Abstract

Carrying out nitrogen oxide (NOx) regeneration of at least one NOx storage catalyst arranged in an exhaust gas stream of an alternately rich and lean burn IC engine comprises determining NOx storage activity values (A) of the storage catalyst during all or one part of the rich phases by comparing the measured and/or calculated first NOx emission values (E1) in the exhaust gas stream before the catalyst with measured second NOx emission values (E2) in the exhaust gas stream after the catalyst. The termination lambda value ( lambda A) is changed in certain distances, where the direction of the change is dependent on a NOx storage activity difference value ( DELTA A) which is the difference between a NOx storage activity value (A(x)) determined before the change and a NOx storage activity value before the determination of the NOx storage activity value. An Independent claim is also included for a device for determining the termination lambda value. Preferred Features: The process is a closed-loop regulated process. The termination lambda value is shifted in the region of rich burn when the NOx storage activity difference value is positive or a negative boundary value is not exceeded.

Description

The invention relates to a method for performing the NO _x regeneration of a NO _x storage catalytic converter according to the preamble of claim 1 and a device for determining an abort lambda value according to the preamble of claim 9.

From EP 580 389 A1 and EP 0585 900 A1, so-called NO _x storage catalysts for use in the exhaust gas flow of lean-burn internal combustion engines are known. The lean operation of internal combustion engines has the advantage that fuel consumption can be significantly reduced, but the disadvantage is that a relatively large amount of nitrogen oxides (NO _x ) is present in the raw exhaust gas during lean operation. In order to solve this problem, it is known to arrange a NO _x storage catalytic converter in the exhaust gas flow of the internal combustion engine, on the surface of which the nitrogen oxides are deposited and chemically bound, for example according to the following reaction:

2BaO + O ₂ + 4NO ₂ → 2Ba (NO ₃ ) ₂

This significantly reduces the amount of nitrogen oxides in the exhaust gas flow from the catalyst. Such a storage catalytic converter must be regenerated at certain intervals since its storage capacity is exhausted. This happens because the internal combustion engine is operated rich for a certain period of time, so that there are unburned hydrocarbons and carbon monoxide in the raw exhaust gas stream, that is between the internal combustion engine and the NO _x catalyst. The storage catalytic converter is regenerated by means of these reducing agents, the nitrogen oxides or the corresponding nitrates being reduced to nitrogen by the reducing agents present, for example with the following reaction:

Ba (NO ₃ ) ₂ + 5CO → BaO + N ₂ + 5CO ₂

Ideally, these reducing agents are fully implemented, so that in the Final exhaust gas neither nitrogen oxides nor unburned during the regeneration phase Hydrocarbons or carbon monoxide.

So far, the regeneration of the NO _x storage catalytic converter has been carried out as follows: At a certain point in time, the combustion in the internal combustion engine is switched to rich, and the lambda value in the raw exhaust gas flow is thereby reduced to a predetermined value which is at or below 1. Efforts are made to keep this value as small as possible, that is to make the reducing agent flow as large as possible during the regeneration phase in order to achieve the shortest possible regeneration times. During the regeneration phase, the lambda value in the final exhaust gas flow is measured. The regeneration is stopped as soon as the lambda value in the final exhaust gas flow falls below a predetermined termination lambda value, which is less than 1, that is to say when reducing agents pass through the NO _x storage cat to a certain extent. This is called a breakthrough of reducing agents.

When using NO _x storage catalytic converters on diesel engines and in the case of strongly aged NO _x storage catalytic converters on gasoline engines, however, it has been observed that the actual end of regeneration, i.e. the at least almost complete clearing of the storage catalytic converter, does not necessarily correlate with the lambda jump in the exhaust gas flow of the storage catalytic converter , Deviations in both directions have been observed, ie an actual end of regeneration with significantly richer or leaner lambda values than 1. However, this means that the regeneration is often terminated at the wrong time, ie either too early or too late. However, this is disadvantageous for the emission behavior, since either the NO _x storage catalytic converter is not emptied, or significant amounts of nitrogen oxides are released into the atmosphere due to the late termination of the regeneration.

Starting from this prior art, it is an object of the invention to further develop the NO _x regeneration of NO _x storage catalysts in such a way that the NO _x regeneration is always terminated at the right time.

This object is achieved with a method having the features of claim 1 and solved a device with the features of claim 9.

The basic idea of the invention is that NO _x -Speicheraktivität the NO _x - to determine storage catalyst in the lean continuously or at least in a more or less regular intervals, and use the therefrom information obtained a permanent or at least periodic adjustment of the demolition lambda value. This creates a feedback system. In each case the NO _x storage activity values are compared with one another during chronologically successive lean phases and, depending on the resulting NO _x storage activity difference value, the termination lambda value is either increased or decreased. To a certain extent, the system works with a constant "trial and error" process, ie by continually trying it out, a continuously optimized demolition lambda value is achieved, thus improving the vehicle's emission behavior.

Advantageous refinements of the method according to the invention result from the Dependent claims. The inventive method and the inventive Device will now be described using exemplary embodiments with reference to the accompanying Figures explained in more detail. Show it:

Fig. 1 shows a schematic representation of the device according to the invention,

Fig. 2 is a schematic flowchart of the method according to the invention,

Fig. 3 schematic curves of the NO _x -Speicheraktivitätsdifferenzwertes and the abort-lambda value.

In Fig. 1, an apparatus according to the invention, which is also suitable for performing the method according to the invention, is shown schematically. The raw exhaust gases originating from an internal combustion engine 10 flow to at least one NO _x storage catalytic converter 20 via a raw exhaust gas line 12 . The processed exhaust gases leave the NO _x storage catalytic converter 20 via the end exhaust gas lines 22 . In the Rohabgasleitung 12, a first _NOx sensor 14 is disposed, which the first NO _x value E1, that is, the NO _x value in the raw, measures. A second NO _x sensor 24 and a lambda probe 26 are arranged behind the NO _x storage catalytic converter 20 . Components 24 and 26 can also be integrated in a sensor.

The lambda value λ measured by the lambda probe 26 is used to monitor the end of regeneration of the NO _x storage catalytic converter. As described above, the regeneration, ie the rich phase, is terminated when the lambda value measured in the final exhaust gas falls below a certain termination value. In contrast to previous methods, however, a fixed termination value is not used here, but the termination lambda value λ _A is constantly adapted to the actual conditions. This is done as follows:

The first and the second NO _x sensors 14 , 24 are connected to the calculation unit 30 . This generated from the first and the second NO _x -Emissionswert, so by comparing the NOx concentration before and after the NO _x storage catalyst 20, a NO _x -Speicheraktivitätswert A. This NO _x -Speicheraktivitätswert A is only required during the lean phase, so that it is only generated during these lean phases. Basically, it is sufficient to generate only one NO _x storage activity value A per lean phase, so that in each case one NO _x storage activity value A, for example averaged, is generated per lean phase and is supplied to the difference image 40 . If necessary, however, several NO _x storage activity values A z. B. formed at the beginning and end of the lean phase and stored, for. B. also monitor the function and mode of operation of the NO _x storage catalytic converter 20 .

The difference image 40 forms the difference between the two last received NO _x storage activity values A (x) and A (x - 1), that is: ΔA (x) = A (x) - A (x - 1). The NO _x storage activity difference value ΔA is a measure of the change over time in the storage behavior of the NO _x storage catalytic converter 20 . In principle, it is also possible to determine the NO _x storage activity difference value ΔA less frequently, for example only in a 10-phase interval. The following would then apply: ΔA (x) = A (x) - A (x - 10).

The NO _x storage activity difference value ΔA is now fed to the limit value generator 50 . This changes the termination lambda value λ _A as a function of ΔA. As long as ΔA is positive or does not fall below a certain first limit value, the limit value generator 50 shifts the current termination lambda value λ _A towards lean, forming a new termination lambda value λ _A. However, if ΔA is below a certain second limit value, then the abort lambda value λ _A is shifted in the bold direction by a certain amount. Here, however, minimum and maximum values for the termination lambda value λ _{A are} provided.

The abort lambda value λ _A generated in this way is supplied to the engine control 60 . Furthermore, the engine control unit 60 is supplied with the current lambda value λ present at the output of the NO _x storage catalytic converter 20 , so that the end of the regeneration phase is initiated by the engine control unit 60 in the usual manner when the current lambda value λ is the currently current termination lambda value λ _A below. This creates a feedback control loop.

The electronic signal processing elements described above Of course, the device according to the invention does not have to be discrete as shown here Components are designed, but can also be an integral part of the engine Control. They can also be implemented using appropriate software solutions be, the software then z. B. also specify the amounts of change can. Additional engine status data can also be used for general support the calculation.

Instead of measuring the first NO _x emission value by means of the first NO _x sensor 14 , this can also be calculated from the current engine status data. A combination of calculation and measurement is also conceivable.

The method according to the invention will now be explained again with reference to the flow diagram shown in FIG. 2:

At the beginning of the method, for example when the internal combustion engine is freshly started, a predetermined abort lambda value λ _{A is first} generated in a first step S1. In the next step S2, as shown above, a first NO _x storage activity value A (1) is determined in a first lean phase. In step S3, the termination lambda value λ _A is shifted towards a lean direction by a predetermined or predeterminable amount. In step S4 it is checked whether the shift of the abort lambda value λ _{A has left} a certain predetermined permitted range. If this is the case, the abort lambda value Lambda A is set to its minimum or maximum value.

In step S5, the NO _x storage activity value A (2) is determined during the next lean phase. In step S6, the NO _x storage activity difference value ΔA is formed between the two last NO _x storage activity values A. The penultimate NO _x storage activity value A (1), or generally: A (x - 1), is subtracted from the last NO _x storage activity value A (2), generally: A (x). If the NO _x storage activity difference value ΔA is positive, or if it does not fall below a predeterminable, preferably negative limit value, the method is continued in step S3, ie the abort lambda value λ _A is again shifted towards lean by a predetermined amount. However, if ΔA falls below the predefinable negative limit value G, the abort lambda value λ _A is shifted in the direction of bold in a step S7 and the method is continued in step S4.

In Fig. 3 the dependence of the termination lambda value λ _A of NO _x is - storage activity difference value .DELTA.A exemplified over a period of 6 cycles. As long as the NO _x storage activity difference value is greater than the negative limit value G, the abort lambda value λ _{A is} shifted toward a lean direction by a predetermined value for the next cycle. However, if the memory activity difference value ΔA is below the limit value G, the abort lambda value for the next cycle is shifted by a certain value in the direction of bold.

LIST OF REFERENCE NUMBERS

10

Internal combustion engine

12

Rohabgasleitung

14

first NO _x

-Sensor

20

NO _x

storage catalyst

22

Endabgasleitung

24

second NO _x

-Sensor

26

lambda probe

30

calculation unit

40

difference images

50

threshold generator

60

motor control
A NO _x

-Speicheraktivitätswert
ΔA NO _x

-Speicheraktivitätsdifferenzwert
λ lambda value
λ _A

Demolition lambda value
E ₁

first NO _x

-Emissionswert
E ₂

second NO _x

-Emissionswert
G limit

Claims (13)

1. A method for carrying out the NO _x regeneration of at least one NO _x storage catalytic converter ( 20 ) arranged in the exhaust gas flow of an alternately lean and richly operated internal combustion engine ( 10 ), the NO _x regeneration being terminated when the value falls below an abort lambda value (λ _A ) and the internal combustion engine ( 10 ) changes to lean operation, characterized in that in a cyclic process NO _x storage activity values (A) of the NO _x storage catalytic converter ( 20 ) during all or part of the lean phases by comparison of measured and / or calculated first NO _x -Emissionswerten (E1) in the exhaust stream upstream of the NO _x storage catalytic converter (20) with measured second NO _x -Emissionswerten (E2) in the exhaust stream downstream of the NO _x - storage catalytic converter (20) are determined, and that the cancellation lambda value (λ _A ) is changed at certain intervals, the direction of the change in the abort lambda value (λ _A ) being active by a NO _x store difference value (ΔA), this NOx storage activity difference value (ΔA) being the difference between an xth NO _x storage activity value (A (x)) determined before the change in the abort lambda value (λA) and one before the determination of the x th NO _x -Speicheraktivitätswertes particular (x - n) th NO _x -Speicheraktivitätswert, wherein x and n are natural numbers, and x is greater than n. 2. The method according to claim 1, characterized in that the cyclic Process is a closed-loop regulated process, which is based on a fixed natural one Number n is done at regular intervals. 3. The method according to claim 1 or 2, characterized in that the abort lambda value (λ _A ) is shifted towards lean if the NO _x - storage activity difference value (ΔA) is positive or a certain first predefinable, preferably negative limit value (G) not less. 4. The method according to claim 3, characterized in that the abort lambda value (λ _A ) is shifted towards a lean by a predetermined first amount. 5. The method according to any one of the preceding claims, characterized in that the termination lambda value (λ _A ) is shifted in the bold direction when the NO _x storage activity difference value (ΔA) is below a specific second limit value (G). 6. The method according to claim 5, characterized in that the abort lambda value (λ _A ) is shifted in the bold direction by a predetermined second amount. 7. The method according to claims 3 and 5, characterized in that the the first and the second limit are identical. 8. The method according to any one of the preceding claims, characterized in that the termination lambda value (λ _A ) is limited to predeterminable minimum and / or maximum values. 9. The method according to any one of the preceding claims, characterized in that when the method is started, the first change in the termination lambda value (λ _A ) takes place in the lean direction. 10. Device for determining an abort lambda value (λ _A ), the drop below which leads to the abort of the regeneration phase of at least one NO _x storage catalytic converter ( 20 ) in an alternately lean and rich-operated internal combustion engine ( 10 ), characterized by:
first means for determining a first NO _x emission value (E1) between the internal combustion engine ( 10 ) and a NO _x storage catalytic converter ( 20 ) arranged in the exhaust gas flow of the internal combustion engine,
a second NO _x sensor ( 14 ) arranged in the exhaust gas flow of the NO _x storage catalytic converter ( 20 ) for determining a second NO _x emission value (E2),
a calculation unit ( 30 ) which forms a NO _x storage activity value (A) by comparing the first with the second emission value for at least some of the lean phases,
a difference image ( 40 ) which, by subtracting the (x - n) th NO _x storage activity value (A (x - n)) from the x th NO _x storage activity value (A (x)), produces a NO _x storage activity difference value (ΔA ) forms, where x and n are natural numbers and x is greater than n,
a limit value generator ( 50 ), which shifts the abort lambda value (λ _A ) in the lean direction if the NO _x storage activity difference value (ΔA) is positive or does not fall below a predeterminable first limit value (G) and the abort lambda value (λ _A ) shifts towards bold if the NO _x storage activity difference value (ΔA) is below a certain second limit value (G). 11. The device according to claim 10, characterized in that first means for determining a first NOX emission value (E1) is a first NOX sensor ( 14 ). 12. The apparatus of claim 10 or 11, characterized in that the second NO _x sensor ( 24 ) additionally determines a lambda signal. 13. Device according to one of claims 10 to 12, characterized in that the second NO _x emission value (E2) on the basis of the values of the NO _x sensor ( 24 ) arranged downstream of the NO _x storage catalytic converter ( 20 ) and / or the other engine status data is determined.