DE102015200762A1 - 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 in the NOx storage catalytic converter (5) are reduced by supplying a reducing agent, In the regeneration phase, a first air ratio (λ1) is detected by means of at least one first oxygen sensor which is arranged downstream of the NOx storage catalytic converter (5) and is designed as a narrow-band oxygen sensor, a breakthrough time point (t2) at which the first air ratio ( λ1) falls below a predeterminable threshold value (λS) is determined, and from at least one of the breakthrough time (t2) dependent characteristic size is closed on the functionality 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 lean operation.

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. In particular, in diesel and gasoline lean-burn engines, however, this method is not available due to the small amounts of non-oxidized exhaust gas constituents. 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 catalyst is limited, no or less in the exhaust gas located unburned hydrocarbons 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.

From the KR 10 2011 00 63 140 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.

The known monitoring methods do not provide reliable information about its functionality under all operating conditions of the NO _x storage catalytic converter; for example, the known methods are highly temperature-dependent. 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, for example, compliance with a narrow temperature range can not always be guaranteed. Furthermore, the known methods with associated with a considerable effort, which is particularly due to the necessary sensors.

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 a designed for lean operation internal combustion engine, and a corresponding control device for such an exhaust aftertreatment system, in particular such a method or such a control device, wherein the above-mentioned disadvantages can be avoided as possible.

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 fuel surplus or 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, a first air ratio is detected during the regeneration phase 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 at least one first oxygen sensor becomes. The at least one first oxygen sensor is designed as a narrow-band oxygen sensor, in particular, the at least one first oxygen sensor is a narrow-band lambda probe. Further, a breakthrough time is determined at which the detected air ratio falls below a predeterminable threshold value, and at least one of the breakthrough time dependent characteristic size is closed on the functionality of the NO _x storage catalytic converter. According to the invention, use is made of the fact that during regeneration the reducing agent supplied in high concentration is consumed for reducing the nitrogen oxides stored in the NO _x storage catalytic converter and by reaction with the oxygen also stored therein and the exhaust gas flow after passing through the NO _x storage catalytic converter is no or a smaller proportion of the reducing agent. In the course of regeneration, therefore, the amount of nitrogen oxides stored in the NO _x storage catalyst, as well as the amount of stored oxygen, also decreases. In the course of regeneration, therefore, a point in time is reached at which the supplied reducing agent is no longer completely consumed for the reduction of the nitrogen oxides or the reaction with the stored oxygen and begins to emerge again in unconsumed form from the NO _x storage catalytic converter. Such reductant exit is also referred to as reductant slip. The time within a regeneration phase when the reductant exit begins is referred to herein as "breakthrough time".

The breakthrough time is detected by the fact that the first air ratio detected downstream of the NO _x storage catalytic converter falls below a predeterminable threshold value. The first air ratio is thus detected at least from the beginning of the regeneration phase, which may be defined by a start time, to below the threshold value. The threshold value for the air ratio is predetermined to a value λ <1, which is an excess of fuel or on Indicates reducing agent and thereby enables the detection of the breakthrough.

According to the invention, the functionality of the NO _x storage catalytic converter is concluded from a characteristic variable dependent on the breakthrough time. Such a characteristic variable can be, for example, the time elapsed from the start of the regeneration phase to the breakthrough time, the amount of reducing agent or fuel quantity or gas flow quantity supplied to the exhaust gas flow during the regeneration phase or another characteristic variable dependent on the breakthrough time, which is detected during the regeneration phase. The invention is based on the finding that the breakthrough time with increasing aging of the NO _x storage catalytic converter is always earlier and thus a characteristic value dependent on the breakthrough time permits a conclusion on the aging state or the functionality of the NO _x storage catalytic converter. In particular, by comparing the characteristic value dependent on the breakthrough time t ₂ with characteristic quantities of NO _x storage catalysts having known aging states, it is possible to determine the functionality of the NO _x storage catalytic converter ( 5 ) are closed and, for example, an aging parameter are determined, which is a measure of the aging or for the functionality of the NO _x storage catalytic converter.

Characterized in that during a regeneration phase downstream of the NO _x storage catalytic converter, a first air ratio is detected, a time of breakthrough of reducing agent by falling below a predeterminable threshold value of the first air ratio is determined and from at least one of the breakthrough time dependent characteristic variable on the functioning of the NO _x - Storage catalytic converter is closed, a possibility for reliable monitoring of the functionality of the NO _x storage catalyst is created. In particular, this makes it possible to monitor the functionality of the NO _x storage catalytic converter under such operating conditions of the internal combustion engine, under which the known methods do not provide a reliable result. Furthermore, it has been recognized according to the invention that, as a rule, a narrowband oxygen sensor which is arranged downstream of the NO _x storage catalytic converter for detecting the first air ratio is generally sufficient for determining the breakthrough time. As a result, a monitoring of the functionality of the NO _x storage catalytic converter is made possible in a particularly simple and cost-effective manner.

According to a preferred embodiment of the invention, the at least one characteristic variable is the time interval between a start time of the regeneration phase and the breakthrough time. The starting time indicates, for example, the beginning of the enrichment of the exhaust gas stream with reducing agent or the beginning of the entry of reducing agent in a high concentration in the NO _x storage catalytic converter and can be determined for example from a signal of the exhaust aftertreatment system associated sensor or by a signal of a controller , which initiates the regeneration phase or controls the enrichment of the exhaust gas stream with reducing agent, are given. The breakthrough time is in particular the earlier, the further the aging of the NO _x storage catalytic converter has progressed and the more its functionality is limited. As a result, a reliable monitoring of the functionality of the NO _x storage catalytic converter can be made possible in a particularly simple manner.

In accordance with a further preferred embodiment of the invention, the at least one characteristic variable is the amount of reducing agent supplied to the exhaust gas flow or the NO _x storage catalytic converter from the start time of the regeneration phase up to the breakthrough time. The amount of reducing agent supplied may be determined, for example, from a signal of a sensor associated with the exhaust aftertreatment system or may also be given by a signal from a controller which controls the supply of reducing agent into the exhaust gas flow. According to this aspect of the invention, it has been recognized that the amount of reducing agent supplied during the regeneration until the reducing agent exits again from the NO _x storage catalytic converter enables a particularly accurate inference to the aging state or the functionality of the NO _x storage catalytic converter. It can also be provided that both the time interval between the start time and the breakthrough time, as well as the amount of reducing agent supplied in this period serve as a basis for monitoring the functionality of the NO _x storage catalytic converter; As a result, a further improved reliability of the monitoring can be achieved.

Preferably, a second air ratio is detected upstream of the NO _x storage catalyst. Further, preferably, the amount of reducing agent supplied from the start time of the regeneration phase to the breakthrough time is multiplied by the integral of the difference between the second air ratio detected upstream of the NO _x storage catalyst and the downstream detected first air ratio multiplied by the air mass flow and divided by the stoichiometric fresh air / fuel ratio the integral is calculated from the start time of the regeneration phase to the breakthrough time. Out the difference between the upstream and downstream detected air ratio can be concluded on the amount of reducing agent supplied at the time, and from the integrated over the regeneration phase to the breakthrough time, in particular from the start time to the breakthrough time, the total difference during the regeneration phase the exhaust gas flow or determine the amount of reducing agent supplied to the NO _x storage catalytic converter. The amount of reducing agent supplied in particular is the lower, the further the aging of the NO _x storage catalytic converter has progressed and the more its functionality is limited. As a result, a particularly reliable monitoring of the functionality of the NO _x storage catalytic converter is made possible in a simple manner.

According to a preferred embodiment of the invention, a second air ratio is detected upstream of the NO _x storage catalyst and determined as the start time of the time at which the upstream of the NO _x storage catalytic converter detected second air ratio falls below the predeterminable threshold, which falls below the downstream of the NO _x - Storage catalytic converter detected first air ratio defined breakthrough time. The detected second air ratio can, as described above, also be used to determine the amount of reducing agent supplied from the start time of the regeneration phase to the breakthrough time. In this way, the accuracy of the determination of the start time and thus the reliability of the monitoring of the functionality of the NO _x storage catalytic converter can be further improved in a simple manner.

The exhaust aftertreatment system advantageously 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 the second air ratio is determined from the signal of the at least one second oxygen sensor. As a result, the accuracy of the monitoring of the functionality of the NO _x storage catalytic converter can be further improved.

The at least one second oxygen sensor is preferably designed as a broadband oxygen sensor, in particular as a broadband lambda probe or UEGO (Universal Exhaust Gas Oxygen) sensor. This makes it possible to achieve a further improvement in the reliability of the monitoring of the NO _x storage catalytic converter.

Alternatively, the second oxygen sensor may advantageously be designed as a narrow band oxygen sensor, in particular as a narrow band lambda probe. This allows a further simplified and particularly cost-effective design of the exhaust aftertreatment system.

Further alternatively, it may be provided that the second air ratio is determined from an air mass flow and data of the engine control, in particular from the injection parameters. As a result, a particularly cost-effective solution can be achieved.

According to a particularly preferred embodiment of the invention, the predeterminable threshold value is to a value less than or equal to 0.98, preferably to a value between about 0.96 and about 0.98, more preferably to a value between about 0.96 and about 0.97, more preferably predetermined to a value of 0.97. According to this aspect of the invention, it has been recognized that a particularly reliable differentiation between different aging states of the NO _x storage catalytic converter is possible if the threshold value, due to which the first air ratio undershoots the breakthrough time point, has a value in the stated range. Conventional narrow-band lambda probes have a steep characteristic approximately in the range between λ = 1.00 and λ = 0.97, ie the probe voltage changes relatively strongly even with small changes in the oxygen content. Characterized in that the threshold value is predetermined to a value which is in a range in which the first oxygen sensor has a steep characteristic, an accurate detection of the breakthrough time is made possible, at the same time by the use of a narrow-band oxygen sensor, a cost-effective and robust design of the Exhaust after-treatment system is made possible.

In the case that the internal combustion engine has a low-pressure exhaust gas recirculation, the at least one first oxygen sensor arranged downstream of the NO _x storage catalytic converter can be 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.

Advantageously, an additional statement about the functionality of the NO _x storage catalytic converter made possible by further methods be, for example, from the patent application DE 10 2015 20 00 752.9 are known, which is incorporated herein by reference in the present application.

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 breakthrough time and / or the amount of reductant supplied during a regeneration phase until the breakthrough of reductant and processor means for determining the breakthrough time and / or the amount of reductant supplied until the breakthrough time and determining the operability, in particular an aging parameter of storage catalyst. In particular, the control device is configured to control the at least one first and / or second oxygen sensor or the lambda probes serving as such sensors in order to process the respective sensor signals and to determine the respective air conditions 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 a NO _x storage catalyst in a regeneration for a new NO _x storage catalytic converter;

3 the same representation as in 2 but for an aged NO _x storage catalyst;

4a to 4d by way of example, the amount of reducing agent supplied during a regeneration until breakthrough for different aging states of an NO _x storage catalytic converter and for different predetermined threshold values, and

5 by way of example, the time elapsed during regeneration until breakthrough of the reducing agent for various aging states of an NO _x storage catalytic converter.

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 , which is a narrow-band lambda probe, and upstream of the NO _x storage catalytic converter 5 a second lambda probe 6 , which may be about a broadband lambda probe 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 2 are for a new, fully functional NO _x storage catalytic converter 5 for example, from the signal upstream of the NO _x storage catalytic converter 5 the exhaust aftertreatment system 3 arranged second lambda probe 6 determined second air ratio λ ₂ (curve 8th ) and that from the signal downstream of the NO _x storage catalytic converter 5 arranged first lambda probe 7 determined first air ratio λ ₁ (curve 9 ) over time t. Before the in 2 period shown is the internal combustion engine 1 in lean operation, the normal operation of the exhaust aftertreatment system 3 or the internal combustion engine 1 corresponds, wherein in the exhaust stream, an excess of oxygen is present, ie λ ₂ > 1. For the regeneration of the NO _x storage catalytic converter 5 will that Greased exhaust gas, for example, by 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 reflected in the fact that due to the signal of the second lambda probe 6 determined second air ratio λ ₂ (curve 8th ) falls to values below 1. Typically, the regeneration phase takes a few seconds, for example, about 2 to 6 seconds. After the end of the regeneration phase, this rises upstream of the NO _x storage catalytic converter 5 determined second air ratio λ ₂ (curve 8th ) back to values above 1, ie the internal combustion engine 1 and the exhaust aftertreatment system 3 go at the end of the in 2 back to normal or lean operation over.

That from the signal of the first lambda probe 7 determined first air ratio λ ₁ (curve 9 ) is in the initial lean operation also above 1, ie λ ₁ > 1, since the exhaust gas flow even after passing through the NO _x storage catalytic converter 5 has an excess of oxygen. At the beginning of the regeneration phase and during part of the duration of the regeneration phase, this is downstream of the NO _x storage catalyst 5 determined first air ratio λ ₁ close to 1 and falls further in the further course of the regeneration phase. This is due to the fact that the unburned fuel, with which in the NO _x storage catalytic converter 5 incoming exhaust gas stream is enriched during the regeneration phase, first to reduce the NO _x storage catalytic converter 5 stored nitrogen oxides and consumed by reaction with the oxygen also stored therein. With the progress of regeneration, an increasing proportion of the NO _x storage catalyst 5 stored nitrogen oxides and the stored oxygen is reduced, so that initially in small and in the course of the regeneration phase increasing amount of fuel passes through it and, accordingly, the downstream of the NO _x storage catalytic converter 5 determined first air ratio λ ₁ in the course of the regeneration phase drops, for example, from values λ ₁ > 0.98 to values λ ₁ <0.98 and finally even to values λ ₁ <λ ₂ .

The beginning of the exit of the fuel from the NO _x storage catalytic converter 5 to a significant extent, ie the breakthrough of the fuel through the NO _x storage catalytic converter 5 , is detected by the fact that the downstream determined air ratio λ ₁ falls below a threshold λ _S. In the in 2 As shown, this threshold value is λ _S = 0.98. The timing at which the downstream of the NO _x storage catalytic converter 5 determined first air ratio λ ₁ (curve 9 ) below the threshold λ _S , the breakthrough time is t ₂ . The beginning of the regeneration phase will be as in 2 shown detected by the upstream of the NO _x storage catalyst 5 determined second air ratio λ ₂ falls below the threshold λ _S = 0.98; this time is the start time t _{1 of} the regeneration phase. The time interval Δt = t ₂ -t ₁ thus indicates the duration of the regeneration phase until the fuel breaks through. In the example shown, this time interval is .DELTA.t for a new NO _x storage catalytic converter 5 just over two seconds.

In 3 are as in 2 also from the signal upstream of the NO _x storage catalytic converter 5 the exhaust aftertreatment system 3 arranged second lambda probe 6 determined second air ratio λ ₂ (curve 8th ) and that from the signal downstream of the NO _x storage catalytic converter 5 arranged first lambda probe 7 determined first air ratio λ ₁ (curve 9 ) during the regeneration phase over time t, but in the case of the NO _x storage catalyst 5 aged and only partially functional. As in 3 can be seen, the first air ratio in the example shown also falls from values λ ₁ > 0.98 to values λ ₁ <0.98 and finally even to values λ ₁ <λ ₂ , in comparison with 2 However, the breakthrough of fuel detected by falling below the threshold λ _S = 0.98 occurs earlier. The interval Δt = t ₂ -t ₁ between the start time t _{1 of} the regeneration phase and the breakthrough time t ₂ is therefore shorter than in FIG 2 illustrated case that the NO _x storage catalyst 5 is new or fully functional; In the example shown, Δt is for the aged NO _x storage catalyst 5 a little less than a second. From the time interval .DELTA.t = t ₂ - t ₁ can thus be a conclusion on the aging state or on the functionality of the NO _x storage catalytic converter 5 pull. In this case, the signal of the first lambda probes 7 needed alone to determine the time t ₂ . This allows the use of a low-cost narrow-band lambda probe as the first lambda probe 7 ,

multipliziert mit dem Luft Massenstrom und geteilt durch das stöchiometrische Frischluft/Kraftstoffverhältnis ist ein Maß für die in der Regenerationsphase bis zum Durchbruch insgesamt dem Abgasstrom zugeführte Kraftstoffmenge M_R, die besonders empfindlich vom Alterungszustand des NO_x-Speicherkatalysators 5 abhängt. Aus dem Wert des Integrals I kann somit besonders zuverlässig auf die Funktionsfähigkeit des NO_x-Speicherkatalysators 5 geschlossen werden. Auch hierbei ist eine Schmalband-Lambdasonde häufig ausreichend, um die Kraftstoffmenge M_R mit ausreichender Genauigkeit zu bestimmen.Similarly, from a comparison of 2 and 3 recognize that the difference between the first air ratio λ ₁ (curve 9 ) and the second air ratio λ ₂ (curve 8th ) in a new NO _x storage catalytic converter ( 2 ) is greater than an aged ( 3 ). The integral I over this difference from the start time t ₁ to the breakthrough time t ₂

multiplied by the air mass flow and divided by the stoichiometric fresh air / fuel ratio is a measure of the total in the regeneration phase to breakthrough the exhaust gas flow supplied amount of fuel M _R , which is particularly sensitive to the aging of the NO _x storage catalytic converter 5 depends. From the value of the integral I can thus particularly reliable on the functioning of the NO _x storage catalytic converter 5 getting closed. Again, a narrow-band lambda probe is often sufficient to determine the amount of fuel M _R with sufficient accuracy.

In the 4a to 4d is the amount of fuel M _R (supplied in a regeneration phase until breakthrough to the exhaust gas flow, determined from the integral I ( 4 ) each above the temperature T for different aging states of the NO _x storage catalyst 5 shown. The specified temperature T is the temperature in an inlet section of the NO _x storage catalytic converter 5 , which can be detected by a temperature sensor arranged there or upstream thereof. The different aging conditions are, as in the 4a to 4d each top right or left is indicated, by a previous heating of the NO _x storage catalyst 5 for a period of ten hours to different high temperatures, namely 650 ° C, 850 ° C or 950 ° C. In the 4a to 4d is in each case a different value for the threshold λ _S predetermined, namely λ _S = 0.99 ( 4a ), λ _S = 0.98 ( 4b ), λ _S = 0.97 ( 4c ) or λ _S = 0.96 ( 4d ).

Such as in 4b for λ _S = 0.98, the measured values for the fuel quantity M _R represented by dots, which cover a wide range of operating conditions, are grouped at temperatures above about 200 ° C, especially above about 250 ° C, for the different aging states in different areas. Thus, the values for a least aging NO _x storage catalyst (aging at 650 ° C) at a respective temperature T are each in an upper range, those for a middle aging condition (at 850 ° C) in a middle range, and the measured values at the highest aging (at 950 ºC) in a lower range. By detecting the integral I, from which it is possible to determine the quantity M _{R of} the reducing agent or of the fuel supplied until breakthrough, there is thus a conclusion as to the aging state of the NO _x storage catalytic converter 5 possible, especially at temperatures above about 200-250 ° C. Substantially the same applies if the threshold λ _S = 0.97 ( 4c ) or λ _S = 0.96 ( 4d ) is selected. From this it can be seen that in the illustrated example, at threshold values λ _S <0.98, a stable separation of the different aging states due to the amount M _R of the supplied until breakthrough reducing agent at a temperature T of the NO _x storage at least above about 250 ° C is possible. On the other hand shows 4a in that, when the threshold value λ _S = 0.99 is selected, the regions in which the measured values for the fuel quantity M _R supplied until breakthrough overlap to a considerable extent at each temperature T, so that there is no clear distinction between the different states of aging NO _x storage catalytic converter is possible.

Exemplary is in 5 the elapsed from the start time t ₁ to the breakthrough time t ₂ time .DELTA.t above the temperature T of the NO _x storage catalytic converter 5 for the same different aging states of the NO _x storage catalytic converter, wherein as a threshold value λ _S = 0.96 has been selected. As in the 4b to 4d also group according to 5 the measured values for fuel quantity M _R at temperatures above approximately 200 ° C., in particular above approximately 250 ° C., for the different aging states in different ranges, likewise the measured values for a NO _x storage catalyst having the least aging a respective temperature T in each case in an upper, which are for a middle aging state in a middle and the highest aging in a lower region. Also by detecting the time interval .DELTA.t between the start time t ₁ and the breakthrough time t ₂ is thus a conclusion on the aging state of the NO _x storage catalytic converter 5 possible, especially at temperatures above about 200-250 ° C.

This allows a reliable monitoring of the functionality of the NO _x storage catalytic converter 5 be made possible under operating conditions in which no such monitoring is possible with known methods.

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

I

 integral

t ₁

 Breakthrough time

t ₂

 Start time

.delta.t

 lag

λ ₁

 air ratio

λ ₂

 air ratio

λ _S

 threshold

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]
• DE 102012218728 A1 [0005]
• KR 1020110063140 A [0006]
• DE 1020152000752 [0026]

Claims (12)

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 in the NO _x storage catalytic converter ( 5 ) are reduced by supplying a reducing agent, characterized in that in the regeneration phase by means of at least one first oxygen sensor, the downstream of the NO _x storage catalytic converter ( 5 is arranged and is designed as a narrow-band oxygen sensor, a first air ratio (λ ₁ ) is detected, a breakthrough time (t ₂ ) to which the first air ratio (λ ₁ ) falls below a predeterminable threshold (λ _S ) is determined, and from at least one of the breakthrough time (t ₂ ) dependent characteristic size on the functionality of the NO _x storage catalytic converter ( 5 ) is closed. Method according to Claim 1, characterized in that the at least one characteristic variable is the time interval (Δt) between a start time (t ₁ ) of the regeneration phase and the breakthrough time (t ₂ ). Method according to Claim 1 or 2, characterized in that the at least one characteristic variable is the amount of reducing agent supplied from a starting time (t ₁ ) of the regeneration phase to the breakthrough time (t ₂ ). A method according to claim 3, characterized in that upstream of the NO _x storage catalytic converter ( 5 a second air ratio (λ ₂ ) is detected and that the amount of reducing agent supplied from the start time (t ₁ ) to the breakthrough time (t ₂ ) by means of the integral (I) of the difference (Δλ) between the second air ratio (λ ₂ ) and first air ratio (λ ₁ ) multiplied by the mass air flow divided by the stoichiometric fresh air / fuel ratio from the start time (t ₁ ) of the regeneration phase to the breakthrough time (t ₂ ) is determined. Method according to one of claims 2 to 4, characterized in that upstream of the NO _x storage catalytic converter ( 5 ) A second air ratio (λ ₂ ) is detected and that the starting time (t ₁ ) is the time at which the second air ratio (λ ₂ ) falls below the predeterminable threshold value (λ _S ). A method according to claim 4 or 5, characterized in that the second air ratio (λ ₂ ) 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 6, characterized in that the second oxygen sensor is designed as a broadband oxygen sensor. A method according to claim 6, characterized in that the second oxygen sensor is designed as a narrow-band oxygen sensor. A method according to claim 4 or 5, characterized in that the second air ratio (λ ₂ ) from an air mass flow and data of the engine control is determined. Method according to one of the preceding claims, characterized in that the threshold value (λ _S ) is less than or equal to about 0.98, and preferably between about 0.96 and about 0.98, more preferably between about 0.96 and about 0, 97, more preferably about 0.97. Method according to one of the preceding claims, characterized in that the internal combustion engine ( 1 ) has a low-pressure exhaust gas recirculation and that the at least one first oxygen sensor in an intake tract of the internal combustion engine ( 1 ) is arranged. Control device for an exhaust aftertreatment system ( 3 ) of a combustion engine designed for lean operation ( 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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