EP1301699B1 - Method for adapting a crude nox concentration - Google Patents

Description

The invention relates to a method for adapting a NOx raw concentration of a lean and rich phase Internal combustion engine equipped with a NOx storage reduction catalyst is provided in an exhaust duct the, internal combustion engine arranged during the lean phase NOx adsorbed from the exhaust gas and adsorbed during the fatty phase NOx can implement.

To fuel consumption in motor vehicles with ottomotorischem drive to reduce, more and more often internal combustion engines used in selected operating areas be operated with a lean mixture.

In order to meet exhaust emission limits, special internal exhaust aftertreatment is used in such internal combustion engines. For this purpose, NOx storage reduction catalysts, hereinafter also referred to as NOx storage catalysts used. Due to their coating, these NOx storage catalytic converters are able to adsorb NOx compounds from the exhaust gas during a storage phase. The storage phase of the NOx storage catalyst is also referred to as its loading phase. During a regeneration phase following the loading phase, the adsorbed or stored NO x compounds are catalytically converted into harmless compounds. As a reducing agent for the conversion is used in lean-burn gasoline engines CO, H ₂ and HC (hydrocarbons). The reducing agents are generated by the short-term operation of the internal combustion engine with a rich mixture and the NOx storage catalyst provided in the form of exhaust gas components, whereby the stored NOx compounds are degraded in the catalyst.

The adsorption efficiency of NOx storage catalysts drops with higher NOx loading level. The degree of loading is the quotient of instantaneous NOx loading and maximum NOx storage capacity. The calculated degree of loading can be used for Control of the lean and rich cycles of the internal combustion engine be used. To determine the degree of loading a precise knowledge of both the current load as well as the maximum storage capacity needed.

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. Indeed this storage capacity is subject to an aging process, which requires it during operation to adapt.

Methods are known which have maximum storage capacity in the Adapt driving operation. However, these procedures require the knowledge of either the current load and / or a corrected NOx raw concentration. With corrected NOx raw concentration is the order of a stationary conversion concentration denoted reduced NOx raw concentration. The most accurate knowledge of the corrected NOx raw concentration is next to the age adaptation of the storage capacity also for the catalyst control via the calculation of the Degree of loading required.

A method for adapting the corrected NOx concentration is described in international application WO 00/28201. The method stores operating point dependent Values for the raw NOx concentration of the internal combustion engine read a map and an adaptation of the concentration fluctuations on the basis of a downstream of the NOx storage catalyst arranged NOx sensor made. This method gives satisfactory results for the adaptation, however, is mandatory on the use of a Instructed NOx sensor.

The invention has for its object to provide a method with the NOx raw concentration of an internal combustion engine adapted as precisely as possible with simple means can be.

The object is solved by the features of patent claim 1. Advantageous developments of the invention are in the Subclaims specified.

The above method leads during an adaptation process for the raw NOx concentration, the following four process steps out. In a first step, the duration of a first lean phase so shortened that no NOx emission occurs behind the catalyst during the first lean phase. The NOx emission during a lean phase is qualitative known: takes place in a first section of the lean phase no or essentially no NOx emission behind the catalyst, which rises sharply from one point in time. The Duration of the first lean phase is in the first step chosen so that the lean phase is completed before it to an increase in the NOx concentration after the catalyst comes. In the second step of the method according to the invention is the during the lean phase in the NOx storage catalyst stored storage amount calculated. The Storage amount corresponds to the corrected NOx supply, since here no breakthrough share occurs in the first lean phase. Because the first lean phase is over before it becomes one Breakthrough is coming. In a further step, also at the same time to the second step, the calculated Amount of storage with one for the first lean phase with Help of a map modeled depending on the operating conditions NOx loading of the NOx storage catalyst compared. For the first lean phase should be neglected of the breakthrough modeled NOx loading with the amount of storage because there is no NOx emission after the catalyst during the first lean phase.

The deviation of these two sizes from each other is in one fourth step used for the adaptation. After adaptation of the NOx raw concentration, the internal combustion engine again after operated methods known. Advantageous to the present Procedure is that by shortening the first Lean phase with simple means an accurate determination of NOx loading is possible.

To conclude that in the first step a sufficient short lean phase of consideration is based in the second step additionally the amount of memory in a second Lean phase determined, whose duration compared to the first lean phase is further shortened. These are essentially the process steps from the adaptation cycle with the first Lean phase repeated. In this continuation of the invention Procedure is the whole process as the repetition of two adaptation cycles with different long lean phases, wherein in the second cycle the first and the second method step for the second Undergo lean phase. For the first and the second Lean phase, the average storage amounts per time, i. calculated amount of storage divided by the duration of the lean phase, compared to each other in the case of an approximate Match a lack of NOx emission in the first lean phase determine. In case of mismatch loading is not proportional to time, i.e. during the lean phase is, for example, the NOx concentration after the catalyst already increased and the breakthrough quantity thus not negligible. If missing Consistency becomes the first and second lean phases further shortened, wherein preferably the second adaptation cycle it takes the place of the first as the basic cycle.

In an expedient continuation of the method is at a shortening of the lean phases to below a predetermined Minimum duration of a signal that is missing Indicates the suitability of the NOx catalyst for lean operation. In a not suitable for lean operation NOx storage catalytic converter takes place even with a sufficiently short Lean phase no NOx loading proportional to the duration the lean phase is.

To the amount of storage of the NOx storage catalyst sufficient To be able to determine exactly, this is in a fat phase for determines the past lean phase. It will be so omitted, the amount of storage directly during the lean phase Therefore, it is based on the use of a NOx sensor waived.

To the amount of storage for the previous lean phase sufficient to be able to calculate exactly, this becomes dependent on the amount of oxygen stored, from the period between Beginning of the fat phase and a recognition of a complete NOx regeneration, from the fuel mass flow and the Substance ratio of the reaction fuel and NOx determined. It is assumed that the additional, for stoichiometric combustion unused fuel mass flow for the reduction of the stored NOx mass as well as for Exploitation of the stored oxygen is used. is the amount of stored oxygen, the time between onset the fat phase until recognizing a complete NOx regeneration of the storage catalyst, the additional Fuel mass flow and the molar ratio of the reaction Fuel plus NOx known, the stored NOx mass can be calculated.

In order to detect the complete NOx regeneration, a lambda probe is preferably arranged downstream of the NOx storage catalytic converter. The lambda probe indicates the air ratio in the exhaust gas flow downstream of the NOx storage catalytic converter and thus makes it possible to detect the completion of the regeneration phase. In this method, it is preferably also taken into consideration that both NOx and O ₂ , which are released from the reservoir with different characteristics, are stored in the NOx storage catalytic converter. The NOx / O ₂ ratio can be taken into account by means of characteristic curves.

As an alternative to using an O ₂ sensor, it is also possible to use a NOx sensor downstream of the NOx storage catalyst.

Appropriately, the adaptation of the NOx raw concentration in the fourth step via a correction factor for a reduction factor of the raw NOx concentration or for a correction factor directly for the raw NOx concentration.

Preferably, the change is proportional to the difference between the storage amount and the modeled NOx load. It is also possible to make the change proportional to the difference of 1 and the quotient of the modeled NOx loading and the amount of storage.

Fig. 1

die NOx-Konzentration stromabwärts eines NOx-Speicherkatalysators abhängig von der Zeit,

Fig. 2

die Berechnung eines Korrekturfaktors für die NOx-Rohkonzentration und

Fig. 3

die Berechnung eines Korrekturfaktors für einen Reduktionsfaktor der NOx-Rohkonzentration.

A preferred embodiment of the method is described in more detail below using an exemplary embodiment. It shows:

Fig. 1

the NOx concentration downstream of a NOx storage catalyst depending on the time

Fig. 2

the calculation of a correction factor for the NOx raw concentration and

Fig. 3

the calculation of a correction factor for a reduction factor of the raw NOx concentration.

Fig. 1 shows the time evolution of the NOx concentration in a NOx storage catalyst. The curve marked 10 indicates the NOx concentration after the catalyst. At the time t ₀ , which is marked with 12, begins in the normal storage / regeneration operation, the regeneration of the NOx storage catalyst. The area marked 14 indicates the NOx storage amount (SM) stored up to t ₀ . The area fraction lying below the curve 10 indicates the breakthrough quantity DB, that is to say the quantity which has exited until the time t ₀ . If an adaptation of the raw emission now takes place, the threshold 12 is offset at the beginning to 18. For example, for this purpose, the duration of the lean phase can be halved.

To check if at the duration 18 of the lean phase one negligible breakthrough amount DB is present in one another adaptation cycle, the lean phase to a point in time 20 shortened. If the amount of memory in the shortened Lean phase in the same proportion to the amount of storage in the longer lean phase 14 is, as the duration of the shorter Lean phase at the time of the longer lean phase, so has no breakthrough occurred and the storage catalyst has stored in proportion to the duration of the lean phase NOx.

• ein erster Teil wird auch im Magerbetrieb von der Abgasreinigungsanlage in unschädliche Substanzen umgewandelt,
• ein zweiter Teil wird im NOx-Speicherkatalysator gespeichert (SM) und
• ein dritter Teil wird an die Umgebung abgegeben (DB)(Durchbruch).

In general, the amount of NOx emitted during a lean phase of an internal combustion engine can be split into the following parts:

• a first part is converted into harmless substances even in lean operation by the emission control system,
• a second part is stored in the NOx storage catalyst (SM) and
• a third part is delivered to the environment (DB) (breakthrough).

Regardless of the method used according to the invention Calculation of the storage amount SM is based on the in Maps stored NOx raw concentration and the reduction factor the integral of the corrected NOx concentration over the lean phase (IKK) is calculated. The value of the integral is the sum of modeled NOx loading and (modeled) Post-emission. For the lean phases in which no Breakthrough, SM should be equal to IKK if the modeled, corrected raw NOx concentration of the actual, reduced by the actual stationary reduction factor, NOx raw concentration corresponds.

In the flow chart shown in Fig. 2, a correction factor for the raw NOx concentration (RK) is calculated. The correction factor (RKKF) is determined as a function of the modeled NOx load (IKK) and the storage amount (SM). In the flowchart shown in Fig. 2, the factor becomes: 1-IKK / SM amplified with an amplifier 22 and added with a corresponding correction factor RKKF (N-1) to determine RKKF for the subsequent correction of the NOx raw concentration. The adaptation takes place iteratively, whereby the correction factor of the (n-1) -th adaptation is changed at an n-th adaptation step. The raw NOx concentration is multiplied by the factor (1-RF), where RF is the reduction factor for the raw NOx concentration RK. The reduction factor, for example, takes into account the steady-state conversion in the catalyst, depending on the catalyst temperature. The product is referred to as the corrected raw NOx concentration.

Fig. 3 shows a flow chart for an alternative determination the corrected NOx raw concentration. In this process For example, the size 1-SM / IKK is amplified by an amplifier 24 and added with a correction factor for the reduction factor. The correction factor for the reduction factor RFKF becomes multiplied by the reduction factor RF, so that a corrected Reduction factor is present. With the factor (1-RFKFxRF) From the raw NOx concentration (RK), the corrected raw NOx concentration calculated.

In both methods, as an alternative to the quotient of SM and IKK also used the difference of the values.

Claims (12)

1. Method for adapting a crude NOx concentration (RK) in an internal combustion engine operating with lean or rich phases, which is provided with a NOx storage reduction catalyser, which absorbs the NOx arranged in an exhaust-gas duct of the internal combustion engine from the exhaust gas during the lean phase, and can convert the absorbed NOx during the rich phase,
   characterised in that
   during an adaptation process for the crude NOx concentration, the following steps are executed;

   in a first step the duration of a first lean phase is reduced such that no NOx emission occurs behind the catalyser during the first lean phase,

   in a second step the quantity stored during the first lean phase (SM) is calculated,

   in a third step, a comparison value is calculated from the quantity stored (SM) and from a NOx loading (IKK) for the lean phase, modelled with the aid of characteristic fields,

   in a fourth step an adaptation of the crude Nox concentration (RK) is executed as a function of the comparison value
2. Method according to Claim 1
   characterised in that
   in the second step, the quantity stored (SM) in the second lean phase is additionally determined, the duration of which is reduced in comparison with the duration of the first lean phase, whereby the average stored quantities are compared with one another each time in the first and second lean phases, in order to determine an absence of NOx emission in the first lean phase in the case of approximate correspondence, and in order to repeat the method with a shorter duration for the first and second lean phases in the case of a lack of correspondence.
3. Method according to Claim 2
   characterised in that
   a signal is generated with a reduction in the lean phases to below a predetermined minimal duration, said signal indicating a lack of suitability of the NOx storage catalyser for the lean operation.
4. Method according to one of the Claims 1 to 3
   characterised in that
   in the second step, the stored quantity of the Nox storage reduction catalyser is determined in a rich phase for the previous lean phase.
5. Method according to Claim 4,
   characterised in that
   in the second step, the stored quantity for the preceding lean phase is calculated as a function of the length of time taken between the start of the rich phase and a detection of a complete NOX regeneration, the stored oxygen quantity, the fuel mass flow and the ratio of substances from the fuel and NOx reaction.
6. Method according to Claim 5
   characterised in that
   the complete NOx regeneration is detected by means of an O ₂ sensor arranged downstream from the NOx storage catalyser.
7. Method according to Claim 5,
   characterised in that
   the complete NOx regeneration is recognised by means of a NOx sensor arranged downstream from the NOx storage reduction catalyser.
8. Method according to one of Claims 1 to 5
   characterised in that
   in the fourth step, a correction factor (RFKR) is determined for a reduction factor (RF) of the NOx crude concentration.
9. Method according to one of Claims 1 to 7,
   characterised in that
   in the fourth step, a correction factor (RKKF) is determined for the crude NOx concentration (RK).
10. Method according to one of the Claims 1 to 9,
    characterised in that
    in the fourth step, the difference between the stored quantity (SM) and the modelled NOx loading functions as a comparison value.
11. Method according to one of Claims 1 to 9,
    characterised in that
    in the fourth step, the difference between the stored quantity (SM) and the modelled NOx loading divided by the stored quantity (SM) functions as a comparison value.
12. Method according to Claim 8,
    characterised in that
    in the fourth step, the difference between the modelled NOx loading and the stored quantity (SM) divided by the modelled NOx loading functions as a comparison value.

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