DE102016200155A1 - Method for monitoring an exhaust aftertreatment system of an internal combustion engine and control device for an exhaust aftertreatment system - Google Patents

Abstract

In a method according to the invention for monitoring an exhaust aftertreatment system (3) of an internal combustion engine (1) designed for lean operation, which comprises a NOx storage catalytic converter (5), nitrogen oxides stored in a regeneration phase (12) in the NOx storage catalytic converter (5) are supplied by supplying a Reduces reducing means, after the end of the regeneration phase (12) in the lean operation of the internal combustion engine (1) an oxygen uptake of the NOx storage catalyst (5) is detected, and from the detected oxygen uptake is concluded on the functioning of the NOx storage catalyst (5). The invention also relates to a corresponding control device for an exhaust aftertreatment system (3) of an internal combustion engine (1) designed for a lean operation (11, 13).

Description

The invention relates to a method for monitoring an exhaust aftertreatment system of an internal combustion engine according to the preamble of claim 1 and to a corresponding control device for an exhaust aftertreatment system.

Internal combustion engines often generate considerable amounts of nitrogen oxides (NO _x ) during operation. In particular, in diesel and gasoline engines used in motor vehicles, the amounts of nitrogen oxides in the exhaust gas are generally above the permissible limits, so that an exhaust aftertreatment to reduce NO _x emissions is necessary. In many engines, the reduction of nitrogen oxides by the non-oxidized constituents contained in the exhaust gas, namely by carbon monoxide (CO) and unburned hydrocarbons (HC), using a three-way catalyst. However, this method is not available in particular in the case of diesel and Otto lean-burn engines, since the reduction of NO _x does not or hardly occurs due to the high proportion of oxygen in the exhaust gas. For lean-burn engines, therefore, according to a widespread method, an NO _x storage catalytic converter (Lean NO _x trap, LNT) is used, which receives and stores the nitrogen oxides contained in the exhaust gas of the internal combustion engine. From time to time, there is a regeneration of the NO _x storage catalytic converter, for which a fuel excess is generated in the exhaust gas conducted through the NO _x storage catalytic converter.

However, the functionality of the NO _x storage catalyst decreases with increasing operating time, which is due, inter alia, to contamination of the storage catalyst with the sulfur contained in the exhaust gas, as well as thermal aging as a result of high temperatures, such as occur in a regular to be carried out desulfurization. It is therefore necessary to monitor the functioning of a provided in the exhaust system NO _x storage.

From the European patent application EP 1 936 140 A1 a method for monitoring an exhaust aftertreatment system of an internal combustion engine is known, upstream and downstream of the exhaust aftertreatment system is arranged in each case a lambda probe and to check the functioning of the exhaust aftertreatment system, the internal combustion engine is converted into an operation in which the exhaust gases have a high concentration of unburned hydrocarbons. It is assumed that the exhaust aftertreatment system is inoperable if the air conditions detected by the two lambda probes and due to the high HC concentration are substantially the same.

According to DE 10 2012 218 728 A1 For checking the functionality of a NO _x storage catalytic converter of an internal combustion engine, the internal combustion engine is converted into a substoichiometric operation (λ <1) and the air ratio is detected by a respective lambda probe arranged upstream or upstream of the storage catalytic converter. In this case, the enrichment, ie the enrichment of the exhaust gas with unburned hydrocarbons, limited so that the probes operate error-free. In a fully functional storage catalyst unburned hydrocarbons located in the exhaust due to the enrichment upstream of the catalyst are completely oxidized as it flows through the catalyst, so that there are no unburned hydrocarbons in the exhaust gas downstream of the catalyst. If the functionality of the NO _x storage catalytic converter is limited, no or less unburned hydrocarbons in the exhaust gas are oxidized by release of stored nitrogen oxides. From the time course of the detected by the downstream of the storage cylinder lambda probe air ratio during the phase of enrichment and in particular from the time course of the determined from the signals of the probes, integrated over a short time interval mass flows of unburned hydrocarbons in the exhaust gas can be statements regarding the functionality of the storage catalytic converter.

Out KR 10 2011 006 3140 A It is known that from the signals of two lambda probes, one of which is arranged upstream and the other downstream of a NO _x storage catalyst, the amount of the reducing agent, which is supplied to the storage catalyst, and the amount of the reducing agent after passing is present in the exhaust gas through the storage catalyst. From the thus determined through or slip ratio (slip ratio), the aging of the NO _x storage catalytic converter is determined.

According to US 2004/0182068 A1 For example, the oxygen storage capability of an NO _x storage catalyst (LNT) is estimated based on the signal from a sensor located downstream of the storage catalyst. As a result, the end of a regeneration phase can be predicted more accurately in order to reduce pollutant emissions.

In US 2007/0084195 A1 is a method for determining an _NOx storage capacity of a catalytic device, such as a NO _x storage catalytic converter disclosed exhaust gas treating an internal combustion engine, said internal combustion engine is operated in a first interval with a rich air-fuel ratio, a temperature of the catalyst device to a diagnostic temperature for measuring an oxygen uptake the catalytic device is adjusted, the internal combustion engine is operated in a second interval with a lean air-fuel ratio, and the temperature of the catalyst device is set to an operating temperature. The oxygen storage capacity of the NO _x storage catalyst is determined by comparing the signals of an upstream and downstream of the catalyst arranged UEGO sensor during a transition from rich to lean mixture with each other. For this purpose, after the end of a regeneration cycle, a diagnostic air-fuel ratio is maintained which is closer to a stoichiometric ratio than in normal lean operation.

Since the behavior of an NO _x storage catalyst depends to a large extent on the temperature of the storage catalytic converter, the known monitoring methods provide reliable information about the functionality of the NO _x storage catalytic converter only in a relatively narrow temperature range. This is particularly problematic because to monitor the functionality of the NO _x storage catalytic converter and to comply with the prescribed monitoring procedures (In-Use Performance Requirements, IUPR) the appropriate monitoring measures during operation of a equipped with the NO _x storage vehicle motor vehicle at least with a predetermined Frequency must be performed so that compliance with the narrow temperature range can not always be guaranteed.

It is an object of the present invention to provide an alternative or improved method for monitoring an exhaust aftertreatment system of an internal combustion engine, in particular an engine designed for lean operation, and a corresponding control device for such an exhaust aftertreatment system.

This object is achieved by a method and by a control device as indicated in the independent claims.

An inventive method for monitoring an exhaust aftertreatment system of an internal combustion engine relates in particular to an engine designed for lean operation, for example, a diesel engine or a gasoline lean-burn engine, in particular a diesel or gasoline engine with direct injection. Preferably, it is the internal combustion engine and the exhaust aftertreatment system of a motor vehicle. The term "lean operation" means that the internal combustion engine is operated with excess air, ie that the lambda value (air ratio) assumes a value λ> 1. The exhaust aftertreatment system comprises a NO _x storage catalytic converter for reducing the nitrogen oxides (NO _x ) contained in the exhaust gas of the internal combustion engine. The inventive method is used in particular for monitoring the functionality of the NO _x storage catalytic converter.

In normal operation of the internal combustion engine, which is the lean operation, the NO _x storage catalytic converter stores the nitrogen oxides contained in the exhaust gas stream. For regeneration, ie for renewal of the storage capacity of the NO _x storage catalytic converter, occasional regeneration phases are necessary in which the nitrogen oxides stored in the NO _x storage catalytic converter are reduced by means of a reducing agent supplied to the exhaust gas flow and released in the form of harmless gases. In particular, fuel can serve as a reducing agent, for which purpose the exhaust gas stream conducted through the NO _x storage catalyst is enriched with unburnt fuel in the regeneration phase, for example by fuel injection into the exhaust aftertreatment system upstream of the NO _x storage catalytic converter or by appropriate control of the internal combustion engine, in particular an injection system of the internal combustion engine , This means that there is a substoichiometric oxygen concentration in the regeneration phase, ie that the lambda value is less than 1, λ <1. Such regeneration is also referred to as "rich purge".

According to the invention, after the end of the regeneration phase, in particular immediately after the end of the regeneration phase, in lean operation of the internal combustion engine, an oxygen uptake of the NO _x storage catalytic converter, ie in particular the absorbed oxygen amount or mass, detected and concluded on the functioning of the NO _x storage catalytic converter. It is exploited that during the regeneration of the stored oxygen in the NO _x storage catalyst is consumed. After the end of the regeneration phase, ie when the exhaust gas stream which is fed to the NO _x storage catalytic converter again has an excess of oxygen (λ> 1), oxygen is available for storage in the NO _x storage catalytic converter. According to the invention, it has been recognized that the oxygen uptake of the NO _x storage catalyst taking place after the transition to operation with excess oxygen permits a conclusion as to its functionality. In particular, the aging state of the NO _x storage catalytic converter can be concluded by comparison with reference values of the aging-dependent oxygen uptake of NO _x storage catalysts and, for example, an aging parameter can be determined which represents a measure of the aging or of the functionality of the NO _x storage catalytic converter. It can be provided be that of operating parameters of the exhaust aftertreatment system depends, such as a temperature of the NO _x storage catalytic converter, whether the method described above carried out and detects the oxygen uptake and it is concluded that the functionality of the NO _x storage catalytic converter.

The fact that after the end of the regeneration phase, an oxygen uptake of the NO _x storage catalytic converter is detected and closed from the detected oxygen uptake on the functioning of the NO _x storage catalytic converter, a possibility for monitoring the functionality of the NO _x storage catalyst is provided, which is independent of during the regeneration phase is performed measurements. Surprisingly, it has been found that in this way a reliable determination of the aging state of the NO _x storage catalytic converter is possible, so that the method according to the invention can enable the functionality of the NO _x storage catalytic converter to be monitored under such operating conditions of the internal combustion engine known methods no longer deliver a reliable result. The fact that the oxygen uptake is detected in lean operation, ie in particular during normal operation of the internal combustion engine, it is possible to operate the engine again in normal operation immediately after the end of the regeneration phase, so that avoided by the monitoring restriction of the operation of the engine or at least can be minimized, for example, a diagnostic phase can be avoided, during which the engine is operated even after the end of the regeneration phase in a manner deviating from normal operation. As a result, an improved and in particular the requirements of the frequency of the monitoring measures sufficient monitoring of the exhaust aftertreatment system of the internal combustion engine with minimal impact on the operation of the internal combustion engine allows.

The oxygen uptake of the NO _x storage catalytic converter is preferably determined by comparing an oxygen content of the exhaust gas determined upstream of the NO _x storage catalytic converter with a downstream of the NO _x storage catalytic converter. For this purpose, the exhaust aftertreatment system comprises at least one first oxygen sensor which is arranged downstream of the NO _x storage catalytic converter, ie in particular in the exhaust gas stream downstream of the NO _x storage catalytic converter, wherein the oxygen content of the exhaust gas downstream of the NO _x storage catalytic converter is determined from the signal of the first oxygen sensor. Since the oxygen uptake of the NO _x storage catalyst, which takes place after the end of the regeneration phase and the transition to an operation in which the exhaust gas stream has an excess of oxygen, is shown by a reduction in the oxygen content of the exhaust gas as it flows through the NO _x storage catalytic converter is This enables a simple determination of the oxygen uptake of the NO _x storage catalytic converter in a simple manner.

Advantageously, the exhaust aftertreatment system comprises at least one second oxygen sensor which is arranged upstream of the NO _x storage catalytic converter, ie in the exhaust gas flow upstream of the NO _x storage catalytic converter, and from whose signal the oxygen content of the exhaust gas upstream of the NO _x storage catalytic converter is determined. As a result, the accuracy of the monitoring of the functionality of the NO _x storage catalytic converter can be further improved. Alternatively, it can be provided that the oxygen content of the exhaust gas present upstream of the NO _x storage catalytic converter is determined from an air mass flow and data from the engine control, in particular from the injection parameters; As a result, a particularly cost-effective solution can be achieved.

The at least one first and / or the at least one second oxygen sensor may be designed as lambda probes, in particular as broadband lambda probes or UEGO (Universal Exhaust Gas Oxygen) sensors.

Preferably, the oxygen storage, ie the amount of oxygen stored or mass and thus the oxygen absorption capacity of the NO _x storage catalytic converter is determined and from this infer the functionality of the NO _x storage catalytic converter. The oxygen storage or the oxygen uptake capacity can be determined, for example, by determining an oxygen uptake or a reduction in the oxygen content of the exhaust gas as it flows through the NO _x storage catalytic converter from the end of the regeneration phase until a time when there is no significant reduction in the oxygen content can be determined or the detected reduction has fallen below a threshold value. In particular, the absorbed oxygen mass can be determined by integrating the difference between the oxygen mass flow determined upstream and downstream of the NO _x storage catalytic converter over the stated period of time. The relevant mass flows can be determined, for example, from the signals of the at least one second or the at least one first oxygen sensor and / or data of the engine control and an air mass flow. It can be assumed that the amount of oxygen that can be absorbed by the storage catalytic converter during this period of time has been recorded, so that from this the stored oxygen mass and thus the absorption capacity of the NO _x storage catalyst can be determined.

Further, with respect to the detection of the oxygen storage of the NO _x storage catalyst after the end of the regeneration phase to the patent application DE 10 2015 200 0752.9 referred to in the present application by reference. As a result, a particularly reliable conclusion on the aging state of the NO _x storage catalytic converter is possible.

According to a preferred embodiment of the invention, an outlet of reducing agent from the NO _x storage catalytic converter is detected during the regeneration phase and closed from the determined reducing agent outlet on the functionality of the NO _x storage catalytic converter. During a regeneration phase, the exhaust gas stream conducted through the NO _x storage catalyst is enriched with reducing agent, in particular with fuel, wherein the reducing agent reduces the nitrogen oxides stored in the NO _x storage catalyst and thereby releases it in harmless form. As a result of this, as well as by reaction with oxygen stored in the NO _x storage catalytic converter, the reducing agent with which the exhaust gas stream is enriched before it enters the NO _x storage catalytic converter is consumed, so that, if the NO _x storage catalytic converter is functional, the exhaust gas flow is lower Contains proportion of the reducing agent. On the other hand, if the NO _x storage catalytic converter is not functional or has only limited functionality, a smaller amount of nitrogen oxides is stored therein, and the reducing agent contained in the exhaust gas flow passes through the NO _x storage catalytic converter to a greater extent and exits from it again in unconsumed form , Such reductant exit is also referred to as reductant slip. From the reducing agent outlet can thus be concluded that the NO _x storage catalytic converter is functional. Such methods are for example in EP 1 936 140 A1 and DE 10 2012 218 728 A1 and DE 10 2015 200 0751.0 described in this regard by reference in the present application. In particular, the ratio of the reducing agent content in the exhaust gas stream after leaving the NO _x storage catalytic converter to the proportion before entering the NO _x storage catalytic converter can be determined (reducing agent slip ratio, slip ratio), which can be used as an indication of the functioning or an aging state of the NO _x storage catalyst allows. In this way, an additional possibility for monitoring the functionality or for determining an aging parameter of the NO _x storage catalytic converter is provided and thus enables monitoring of the functionality of the NO _x storage catalytic converter with increased reliability. It may be provided that it depends on operating parameters of the exhaust aftertreatment system, for example, a temperature of the NO _x storage catalytic converter, whether the leakage of reducing agent from the NO _x storage recorded during the regeneration phase and concluded on the functionality of the NO _x storage catalytic converter becomes.

In accordance with a particularly preferred embodiment of the invention, the temperature of the NO _x storage catalytic converter is determined, in particular by means of at least one temperature sensor assigned to the NO _x storage catalytic converter or also from other exhaust gas flow measurement data and / or motor control data calculated on the basis of a model. The temperature may be, for example, the current temperature of the NO _x storage catalyst at the beginning, at the end of a regeneration phase or at another time before, during or after the regeneration phase. The functionality or the aging parameter of the NO _x storage catalyst is according to this embodiment of the invention in a lower temperature range from the reducing agent outlet from the NO _x storage in the regeneration phase, in particular from the Reduktionsmittelschlupfverhältnis, and in a higher temperature range from the oxygen uptake of NO _x Storage catalyst determined after the end of the regeneration phase. In particular, in each case in the manner described above from the reducing agent outlet or from the oxygen uptake on the functionality of the NO _x storage catalytic converter can be concluded. It may be provided, for example, that the temperature of the NO _x storage catalytic converter is determined and only when the temperature is in a lower temperature range, in the manner described above, the reducing agent outlet in the regeneration phase detected and from there on the functioning of NO _x - Storage catalytic converter is closed, and that only when the temperature is in a higher temperature range, in the manner described above, the oxygen uptake of the NO _x storage catalytic converter after the end of the regeneration phase detected and from this on the functioning of the NO _x storage catalytic converter is concluded. For example, the lower temperature range may range up to about 250-350 ° C and the higher temperature range may begin at the temperature of interest. It can also be provided that the two temperature ranges overlap one another or that both methods are used together to determine the operability or the aging parameter of the NO _x storage catalytic converter, the respectively determined aging parameters being weighted as a function of the temperature. This is one in a wider temperature range especially Reliable monitoring of the functionality of the NO _x storage catalytic converter allows.

Preferably, the exhaust aftertreatment system comprises a first NO _x sensor, which downstream of the NO _x storage catalytic converter, that is, in particular in the exhaust gas flow after this, is arranged and a second NO _x sensor upstream of the NO _x storage catalytic converter, ie in the exhaust gas flow upstream of this, is arranged. The NO _x sensors can be designed, for example, as broadband lambda probes or comprise broadband lambda probes which can simultaneously serve as oxygen sensors for detecting the oxygen uptake of the NO _x storage catalytic converter. The values supplied by the NO _x sensors are evaluated to determine the nitrogen oxide content in the exhaust gas before and after flowing through the NO _x storage catalytic converter. In this way, monitoring of the NO _x intake of the NO _x storage catalytic converter can be made possible in order to initiate a regeneration phase when the maximum intake capacity is reached, and / or additional monitoring of the functionality of the NO _x storage catalytic converter can be made possible, which combines with the monitoring method described above can be. As a result, the effectiveness and monitoring of the exhaust aftertreatment system can be further improved.

According to a preferred embodiment of the invention, the internal combustion engine has a low-pressure exhaust gas recirculation, and the at least one first oxygen or NO _x sensor arranged downstream of the NO _x storage catalytic converter is arranged in an intake tract of the internal combustion engine. As a result, the possibility is created to use such existing in the intake system sensor to monitor the operation of the NO _x storage catalytic converter. This is particularly possible in an advantageous manner when a regeneration takes place in an operating state of the internal combustion engine, in which a high proportion of the exhaust gas or even the entire exhaust gas flow is recycled, such as in a braking or deceleration phase of the motor vehicle. As a result, monitoring of the exhaust aftertreatment system or of the NO _x storage catalytic converter is made possible in a particularly simple and cost-effective manner.

A control device according to the invention for an exhaust aftertreatment system of an internal combustion engine, which is designed for a lean operation, is set up for carrying out the above-described method for monitoring the exhaust aftertreatment system. The control device may comprise storage means for storing reference values of the oxygen uptake of a NO _x storage catalytic converter of the exhaust gas aftertreatment system as a function of an aging state of the NO _x storage catalytic converter and processor means for determining the oxygen uptake of the NO _x storage catalytic converter and, for example, an aging parameter of the storage catalytic converter. In particular, the control device is configured to control the at least one first and / or second oxygen sensor and possibly the at least one first and / or second NO _x sensor or the lambda probes serving as such sensors in order to process the respective sensor signals and, for example, values for determine the oxygen content of the exhaust stream, the proportion of unburned fuel and / or the NO _x -Anteil in the exhaust stream and further evaluate them in the manner described above. Such a determined result of the monitoring of the functionality of the NO _x storage catalytic converter or a determined aging parameter can be provided, for example, for a display for a driver of a motor vehicle equipped with the internal combustion engine and / or stored in an error memory. The controller may be further configured to control an injection of a reducing agent, in particular fuel, into the exhaust line upstream of the NO _x storage catalytic converter in order to cause the regeneration of the NO _x storage catalytic converter. Alternatively or additionally, the control device may be designed for communication with an engine control device of the internal combustion engine in order to effect an enrichment of the exhaust gas flow with fuel for the regeneration of the NO _x storage catalytic converter by driving the internal combustion engine or the injection system of the internal combustion engine. The control device may be part of an electronic engine control of the internal combustion engine.

The invention will be explained in more detail by way of example with reference to the drawings. Show it:

1 symbolically an internal combustion engine having an exhaust aftertreatment system comprising a NO _x storage catalyst;

2 exemplifies the time profile of the air ratio λ upstream or downstream of the NO _x storage catalyst before, during and after a regeneration phase;

3 for example, the reducing agent slip ratio during the regeneration phase as a function of the prevailing temperature of the NO _x storage catalytic converter for different aging states of the storage catalytic converter, and

4 For example, the oxygen storage by the NO _x storage catalyst immediately after the end of the regeneration phase also depending on the case prevailing Temperature for different aging states of the storage catalyst.

As in 1 exemplified symbolically, the exhaust gases of an internal combustion engine 1 via an exhaust manifold 2 to an exhaust aftertreatment system 3 directed. The exhaust aftertreatment system 3 points in the exhaust system 4 comprising a plurality of pipe sections, a NO _x storage catalyst 5 through which the exhaust stream is passed. Downstream of the NO _x storage catalytic converter 5 is a first lambda probe 7 and upstream of the NO _x storage catalyst 5 a second lambda probe 6 arranged. The lambda probes 6 . 7 each detect an oxygen content of the exhaust gas stream before entering and leaving the NO _x storage catalytic converter 5 , From the signals of the lambda probes 6 . 7 can be determined by means of a control device, not shown, in each case an air ratio λ. The exhaust aftertreatment system 3 may include other components, also not shown. In particular, further filters or catalysts may be present as well as further sensors, for example, instead of the first lambda probe 7 two first lambda probes 7 downstream of the NO _x storage catalytic converter 5 be provided. In general, however, is a first lambda probe 7 sufficient.

In 2 are from the signal upstream of the NO _x storage catalytic converter 5 the exhaust aftertreatment system 3 arranged second lambda probe 6 determined λ value (curve 8th ) and the signals from two downstream of the NO _x storage catalytic converter 5 arranged first lambda probes 7 determined λ values (curves 9 . 10 ) over time t, with time t given in units of 100 ms. In normal operation of the exhaust aftertreatment system 3 or the internal combustion engine 1 is in the exhaust stream, an excess of oxygen present, ie λ> 1. This area, the lean operation of the internal combustion engine 1 corresponds and already well before the in 2 Period shown is in 2 with the reference number 11 characterized. For the regeneration of the NO _x storage catalytic converter 5 the exhaust gas is enriched by, for example, an injection system of the internal combustion engine 1 is controlled so that the exhaust gas stream is enriched with unburned fuel, or by in the exhaust manifold 2 or in the exhaust system 4 upstream of the NO _x storage catalytic converter 5 Fuel is injected. This is shown by the fact that due to the signal upstream of the NO _x storage catalytic converter 5 arranged second lambda probe 6 determined λ value falls to values below 1. The regeneration phase, which is characterized by values λ <1 of the upstream second lambda probe 6 (Curve 8th ) is in 2 with the reference number 12 marked. Typically, the regeneration phase lasts 12 a few seconds, for example about 2 to 6 seconds. After the end of the regeneration phase 12 the λ value of the second lambda probe increases 6 (Curve 8th ) back to values above 1, ie the internal combustion engine 1 and the exhaust aftertreatment system 3 are again in lean operation. This area, which is well into the end of the in 2 lasts in the period shown is in 2 with the reference number 13 indicated.

The signals from the first lambda probes 7 determined λ values (curves 9 . 10 ) are in the initial lean operation 11 also above λ = 1, ie the exhaust gas flow is also after passing through the NO _x storage catalytic converter 5 an excess of oxygen. At the beginning of the regeneration phase 12 and during the majority of the duration of the regeneration phase 12 is the λ value of the first lambda probes 7 (curves 9 . 10 ) above the λ value of the second lambda probe 6 (Curve 8th ), ideally at about λ = 1, ie during the regeneration phase 12 into the NO _x storage catalytic converter 5 Existing exhaust gas flow existing unburned fuel is used to reduce the NO _x storage catalytic converter 5 stored nitrogen oxides and consumed by reaction with the oxygen also stored therein. However, they are near the end of the regeneration phase 12 in the NO _x storage catalytic converter 5 stored nitrogen oxides completely or substantially reduced, so fuel passes through it, and the signals downstream of the NO _x storage catalytic converter 5 arranged first lambda probes 7 also result in a fuel surplus (λ <1). The λ values of the first lambda probes 7 (curves 9 . 10 ) then approach that of the second lambda probe 6 (Curve 8th ) or even under the second lambda probe 6 lie.

gibt die Sauerstoffaufnahme des NO_x-Speicherkatalysators 5 an, wobei die Integration zu dem Zeitpunkt t₁ beginnt, wenn der λ-Wert der zweiten Lambdasonde 6 (Kurve 8) den Wert λ = 1 überschreitet (zu Beginn des Magerbetriebs 13, s. 2), und die Integration zu dem Zeitpunkt t₂ endet, wenn die λ-Werte der ersten Lambdasonden 7 (Kurven 9, 10) den λ-Wert der zweiten Lambdasonde 6 (Kurve 8) erreichen oder nahezu erreichen (am rechten Rand der 2). Aus der derart ermittelten Sauerstoffaufnahme M_O2 lässt sich ein Rückschluss auf die Funktionsfähigkeit des NO_x-Speicherkatalysators 5 bzw. auf dessen Alterungszustand ziehen.After the end of the regeneration phase 12 increases the λ value, which results from the signal of the upstream of the NO _x storage catalytic converter 5 arranged second lambda probe 6 is determined (curve 8th ) quickly returns to levels above 1, indicating an excess of oxygen. In contrast, the λ values of the first lambda probes remain 7 (curves 9 . 10 ) initially at λ ≤ 1. Only at a later time, typically a few seconds after the end of the regeneration phase 12 , also prevails in that by the NO _x storage catalytic converter 5 passing through exhaust gas flow again an excess of oxygen, as by the steep increase in the λ values of the two first lambda probes 7 (curves 9 . 10 ) is displayed at values λ> 1 in the further course. The delayed increase due to the signals of the first lambda probes 7 determined λ values is due to the fact that during the regeneration phase 12 in the NO _x storage catalytic converter 5 stored oxygen has been consumed and at the beginning of lean operation 13 when in the Exhaust gas flow again oxygen is available, resumed. From the delay of the increase in the λ values of the first lambda probes 7 or from the beginning of the lean operation 13 initially low λ values of the first lambda probes 7 , compared with the λ value of the second lambda probe 6 , The oxygen uptake and from it the oxygen storage or the oxygen uptake capacity of the NO _x storage catalytic converter 5 be determined. In particular, from the λ value of the second lambda probe 6 an oxygen mass flow m _O2u upstream and from the λ values of the first lambda _probes 7 an oxygen mass flow m _O2d downstream of the NO _x storage _catalyst 5 be determined. The temporal integral of the difference between the two mass flows

gives the oxygen uptake of the NO _x storage catalyst 5 , wherein the integration begins at the time t ₁ , when the λ value of the second lambda probe 6 (Curve 8th ) exceeds the value λ = 1 (at the beginning of the lean operation 13 , s. 2 ), and the integration ends at the time t ₂ when the λ values of the first lambda probes 7 (curves 9 . 10 ) the λ value of the second lambda probe 6 (Curve 8th ) or almost reach (on the right edge of the 2 ). From the thus determined oxygen uptake M _O2 , a conclusion can be drawn on the functionality of the NO _x storage catalytic converter 5 or on its aging state.

In the in 2 Example shown are two sensors, namely two lambda probes 7 , downstream of the NO _x storage catalytic converter 5 arranged to redundant or a more accurate determination of the oxygen content of the exhaust stream after passing through the NO _x storage catalytic converter 5 or a corresponding λ value. For determining the oxygen uptake or storage, for example, an average value of the signals of the two first lambda probes 7 or the λ values determined therefrom (curves 9 . 10 ) be used. In a correspondingly simpler form, the method can also be used with only a first lambda probe 7 be performed.

Furthermore, the outlet of reducing agent from the NO _x storage catalyst 5 in the regeneration phase resulting from the course of the λ values of the lambda probes 6 . 7 (curves 8th . 9 . 10 ), to determine the operability of the NO _x storage catalytic converter 5 be used. In particular, this may be the ratio of the reducing agent content in the exhaust gas stream after leaving the NO _x storage catalytic converter 5 to the proportion before entering the NO _x storage catalyst 5 which is referred to as the slip ratio (SR).

In 3 is the reducing agent slip ratio (SR) during the regeneration phase 12 shown as a function of the prevailing temperature for NO _x storage catalysts with different aging states. The different aging states are, as in the upper right in 3 have been produced by a prior heating of the NO _x storage catalyst for each of a period of ten hours to different high temperatures. The measured values for the reducing agent slip ratio SR, which are each represented by dots, are grouped around the curves 14 . 15 . 16 . 17 , where the lower curve 14 NO _x storage catalyst with the least aging (at 650 ° C) corresponds to the mean curves 15 . 16 a medium aging state (aging at 750 ° C and 850 ° C respectively) and the upper curve 17 refers to the measured values at the highest aging (at 950 ºC). How out 3 can be seen, the different aging conditions in the temperature range below about 300 ° C by the during the regeneration phase 12 The reductant slip ratio SR determined relatively well, while above 300-350 ° C, especially above 350 ° C, the curves 14 . 15 . 16 . 17 converge, ie, the reducing agent slip ratios SR approach each other regardless of the aging state. Therefore, the reducing agent slip ratio SR allows reliable detection of the aging state of an NO _x storage catalyst only in a temperature range below about 300-350 ° C. The specified temperature of the NO _x storage catalytic converter is the temperature in an inlet section of the NO _x storage catalytic converter, which can be detected by a temperature sensor arranged there or upstream thereof.

In 4 is the oxygen storage M _O2 , ie the absorbed oxygen mass, immediately after the end of the regeneration phase 12 and the transition to lean operation 13 is also shown for NO _x storage catalysts with different aging states. The aging conditions are as if 3 described been generated. While oxygen uptake at temperatures below about 250 ° C is largely independent of the aging state of the NO _x storage catalyst 5 is, at temperatures above 250 ° C, a differentiation of the different aging states based on the oxygen storage M _O2 readily possible.

Like from the 3 and 4 is apparent, is thus by detecting the Reducing agent slip ratio SR during the regeneration phase 12 and by detecting oxygen uptake after the end of the regeneration phase 12 in an extended temperature range, a conclusion on the aging state of the NO _x storage catalytic converter 5 possible. In particular, at temperatures below about 300-350 ° C, the reductant slip ratio SR can be used for this, while at higher temperatures, or even at temperatures above about 250 ° C, oxygen storage M _{O2 can} serve as the basis for detecting the aging condition. As a result, in a wide range of operating conditions, reliable monitoring of the functionality of the NO _x storage catalytic converter can always be ensured 5 respectively.

LIST OF REFERENCE NUMBERS

1

 internal combustion engine

2

 exhaust

3

 aftertreatment system

4

 exhaust gas line

5

NO _x storage catalyst

6

 lambda probe

7

 lambda probe

8th

 Curve

9

 Curve

10

 Curve

11

 lean operation

12

 regeneration phase

13

 lean operation

14

 Curve

15

 Curve

16

 Curve

17

 Curve

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1936140 A1 [0004, 0021]
• DE 102012218728 A1 [0005, 0021]
• KR 1020110063140 A [0006]
• US 2004/0182068 A1 [0007]
• US 2007/0084195 A1 [0008]
• DE 1020152000752 [0020]
• DE 1020152000751 [0021]

Claims (10)

Method for monitoring an exhaust aftertreatment system ( 3 ) of a combustion engine designed for lean operation ( 1 ) containing a NO _x storage catalyst ( 5 ), wherein in a regeneration phase ( 12 ) in the NO _x storage catalytic converter ( 5 ) are reduced by supplying a reducing agent, characterized in that after the end of the regeneration phase ( 12 ) in lean operation of the internal combustion engine ( 1 ) an oxygen uptake of the NO _x storage catalytic converter ( 5 ) and from the recorded oxygen uptake on the functionality of the NO _x storage catalytic converter ( 5 ) is closed. A method according to claim 1, characterized in that an oxygen content of the exhaust gas stream downstream of the NO _x storage catalytic converter ( 5 ) by means of at least one first oxygen sensor downstream of the NO _x storage catalytic converter ( 5 ) is detected, and that the oxygen uptake of the NO _x storage catalytic converter ( 5 ) by comparing an oxygen content of the exhaust gas stream upstream of the NO _x storage catalytic converter ( 5 ) is determined with the oxygen content of the exhaust gas flow detected by the at least one first oxygen sensor. A method according to claim 2, characterized in that the oxygen content of the exhaust gas stream upstream of the NO _x storage catalytic converter ( 5 ) by means of at least one second oxygen sensor upstream of the NO _x storage catalytic converter ( 5 ) is detected is detected. A method according to claim 2, characterized in that the oxygen content of the exhaust gas stream upstream of the NO _x storage catalytic converter ( 5 ) is determined from an air mass flow and data of the engine control. Method according to one of the preceding claims, characterized in that an oxygen absorption capacity of the NO _x storage catalytic converter ( 5 ) is determined. Method according to one of the preceding claims, characterized in that an outlet of reducing agent from the NO _x storage catalytic converter ( 5 ) during the regeneration phase ( 12 ) and from the detected reducing agent outlet on the functionality of the NO _x storage catalytic converter ( 5 ) is closed. Method according to claim 6, characterized in that the temperature of the NO _x storage catalytic converter ( 5 ) is determined and that in a lower temperature range from the reducing agent outlet from the NO _x storage catalytic converter ( 5 ) and in a higher temperature range from the oxygen uptake of the NO _x storage catalytic converter ( 5 ) on the functionality of the NO _x storage catalytic converter ( 5 ) is closed. Method according to one of the preceding claims, characterized in that a first NO _x sensor downstream of the NO _x storage catalytic converter ( 5 ) and a second NO _x sensor upstream of the NO _x storage catalytic converter ( 5 ) is arranged and that from the determined by the first and the second NO _x sensor NO _x -Anteilen in the exhaust gas flow on the functionality of the NO _x storage catalytic converter ( 5 ) is closed. Method according to one of the preceding claims, back to claim 2, or claim 8, characterized in that the internal combustion engine ( 1 ) has a low-pressure exhaust gas recirculation and that the at least one first oxygen sensor and / or the at least one first NO _x sensor in an intake tract of the internal combustion engine ( 1 ) is arranged. Control device for an exhaust aftertreatment system ( 3 ) one for a lean operation ( 11 . 13 ) designed internal combustion engine ( 1 ), the exhaust aftertreatment system ( 3 ) an NO _x storage catalyst ( 5 ), characterized in that the control device for carrying out the method for monitoring the exhaust aftertreatment system ( 3 ) is set up according to one of the preceding claims.

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