DE102015200751A1 - 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 downstream of the NOx storage catalytic converter (5), a breakthrough time (t2) at which the detected first air ratio (λ1) falls below a predeterminable threshold value (λS) is determined, and from at least one From the breakthrough time (t2) dependent characteristic size is closed 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 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. 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 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.

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.

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.

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 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, a breakthrough time is determined at which the detected air ratio falls below a predeterminable threshold value, and at least one characteristic value depending on the breakthrough time is concluded for 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 in particular to a value λ <1, which indicates an excess of fuel or of reducing agent and thereby enables the detection of the breakthrough. The threshold value may be predetermined, for example, to values in the range of about 0.96 to about 0.98.

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 NO _x - Storage catalyst is always earlier and thus dependent on the breakthrough time characteristic size allows a conclusion on the aging state or the functionality of the NO _x storage catalytic converter allows. 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. 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 is made possible.

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 determined by the integral of the difference between the second air ratio detected upstream of the NO _x storage catalyst and the first detected first air ratio, the integral being calculated from the start time of the regeneration phase to the breakthrough time. From the difference between the upstream and downstream detected air ratio can be concluded on the amount of reducing agent supplied at any time, and from the over the regeneration phase to the breakthrough time, in particular from the start time to the breakthrough time, integrated difference can therefore be the total during the regeneration phase Determine the exhaust stream or the NO _x storage catalyst supplied amount of reducing agent. 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 catalytic converter, and the start time is determined as the time at which the second air ratio detected upstream of the NO _x storage catalytic converter falls below the predeterminable threshold value whose undershooting of the first air ratio detected downstream of the NO _x storage catalytic converter defines the breakthrough time. The threshold value is predetermined in particular to a value λ <1, for example to values in the range from about 0.96 to about 0.98. 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.

Alternatively, it can 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.

Preferably, the exhaust gas aftertreatment system comprising at least a first oxygen sensor, the NO _x storage catalytic converter is disposed downstream of, ie for example in an exhaust gas tract of the internal combustion engine in the exhaust stream downstream of the NO _x storage catalytic converter, and from the signal of at least a first oxygen sensor, the first air ratio is detected. As a result, a precise determination of the air ratio downstream of the NO _x storage catalytic converter and thus monitoring of the functionality of the NO _x storage catalytic converter is made possible in a simple manner.

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.

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.

According to a preferred embodiment of the invention, a reducing agent slip ratio is detected in the regeneration phase and, in addition, from the detected reducing agent slip ratio, the functionality of the NO _x storage catalytic converter (FIG. 5 ) closed. For detecting the reducing agent slip ratio, in particular at least one oxygen sensor, for example a lambda probe, can be arranged upstream of the NO _x storage catalytic converter, ie in the exhaust gas flow upstream of the NO _x storage catalytic converter, and at least one oxygen sensor, for example a lambda probe, downstream of the NO _x storage catalytic converter; In particular, the previously mentioned first and second oxygen sensors can serve this purpose. The reducing agent slip ratio is determined by comparing the air conditions detected by the at least one upstream and the at least one downstream oxygen sensor. In this way, an additional statement about the functionality of the NO _x storage catalytic converter can be made possible. Furthermore, an additional statement about the functionality of the NO _x storage catalytic converter can be made possible by further methods, for example from the patent application DE 10 2012 218 728 A1 are known, which is incorporated herein by reference in the present application.

Preferably, the temperature of the NO _x storage catalyst is determined. In particular, the temperature is detected with the aid of at least one temperature sensor assigned to the NO _x storage catalytic converter or else determined with the aid of a model from other measured data of the exhaust gas flow and / or data of the engine control. The functionality or the aging parameter of the NO _x storage catalytic converter is determined according to this embodiment of the invention in a lower temperature range from the reducing agent slip ratio in the regeneration phase and in a higher temperature range from the at least one characteristic value dependent on the breakdown time. For example, the lower temperature range may range up to about 250-350 ° C, and the higher temperature range at that Start temperature. 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. As a result, a particularly reliable monitoring of the functionality of the NO _x storage catalytic converter is made possible in an extended temperature range.

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;

4 by way of example, the amount of reducing agent supplied during a regeneration until breakthrough for various aging states of a NO _x storage catalytic converter;

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 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 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 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 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, the second air ratio λ ₂ ascertained upstream of the NO _x storage catalytic converter 5 (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.

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.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

is a measure of the total in the regeneration phase until breakthrough the exhaust gas flow supplied amount of fuel M _R , which is particularly sensitive to the aging state 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.

This is also from the 4 and 5 in which the fuel quantity M _R (determined from the integral I in a regeneration phase until breakthrough is supplied to the exhaust gas flow 4 ) or the time Δt (from the start time t ₁ to the breakthrough time t ₂₎ 5 ) each above the temperature T for different aging states of the NO _x storage catalyst 5 is shown, in which case the threshold λ _S = 0.96. The specified temperature T 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. The different aging states are, as in the upper left in 4 and 5 indicated by a previous heating of the NO _x storage catalytic converter 5 for a period of ten hours to different high temperatures, namely 650 ° C, 850 ° C or 950 ° C. The measured values for the fuel quantity M _R and the time interval Δt, which comprise a wide range of operating conditions, are grouped at temperatures above about 200 ° C, in particular 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.

Like from the 4 and 5 can be seen, is thus by detecting the integral I, from which can be determined until breakthrough amount M _{R of} the reducing agent or the fuel, and by detecting the time interval .DELTA.t between the start time t ₁ and the breakthrough time t _{2 is} a conclusion 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 ₂

 air ratio

λ ₁

 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, 0025]
• KR 1020110063140 A [0006]

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 ) stored nitrogen oxides are reduced by supplying a reducing agent, characterized in that in the regeneration phase downstream of the NO _x storage catalytic converter ( 5 ) detects a first air ratio (λ ₁ ), a breakthrough time (t ₂ ) to which the first air ratio (λ ₁ ) falls below a predeterminable threshold value (λ _S ), and from at least one of the breakthrough time (t ₂ ) dependent characteristic size 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 ) 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 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 first air ratio (λ ₁ ) is detected by means of a first oxygen sensor which downstream of the NO _x storage catalytic converter ( 5 ) is arranged. Method according to 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 in an intake tract of the internal combustion engine ( 1 ) is arranged. Method according to one of the preceding claims, characterized in that a reducing agent slip ratio of the NO _x storage catalytic converter ( 5 ) and from the detected reducing agent slip ratio on the functionality of the NO _x storage catalytic converter ( 5 ) is closed. A method according to claim 10, characterized in that a temperature of the NO _x storage catalytic converter ( 5 ) and that in a lower temperature range from the Reduktionsmittelschlupfverhältnis and in a higher temperature range from the 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. 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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