WO2010060503A1

WO2010060503A1 - Method for operating a diesel engine having an exhaust gas cleaning system comprising a nitrogen oxide storage catalytic converter

Info

Publication number: WO2010060503A1
Application number: PCT/EP2009/007163
Authority: WO
Inventors: Michael Lenz; Bernd Lindemann; Ullrich Merten
Original assignee: Daimler Ag
Priority date: 2008-11-29
Filing date: 2009-10-06
Publication date: 2010-06-03
Also published as: JP2012510025A; EP2358985A1; JP5311082B2; DE102008059698A1

Abstract

The invention relates to a method wherein an air-fuel mixture having a lambda value is combusted in a combustion chamber of the diesel engine (1) and exhaust gas arising therefrom is fed into the nitrogen oxide storage catalytic converter (6). Starting from operation of the diesel engine (1) in a first operating mode, wherein the air-fuel mixture comprises a first lambda value greater than one, operation of the diesel engine (1) in a second operating mode is selected for regenerating the nitrogen oxide storage catalytic converter (6), wherein the air-fuel mixture comprises a second lambda value of less than one. Directly before selecting the second operating mode, a transition phase is inserted, in which the diesel engine (1) is operated in a third operating mode, wherein a third lambda value less than that of the first operating mode, and slightly greater than one, is set for the air-fuel mixture. According to the invention, operation of the diesel engine (1) takes place in the third operating mode and is controlled relative to the lambda value of the air-fuel mixture such that an exhaust gas lambda value is captured by means of a lambda sensor (9) disposed downstream of the nitrogen oxide storage catalytic converter (6) in the exhaust gas cleaning system (2), and said value is used as a control parameter for controlled adjustment of a prescribable target value for the third lambda value.

Description

A method for operating a diesel engine with a nitrogen oxide storage catalyst having emission control system

The invention relates to a method for operating a diesel engine with a nitrogen oxide storage catalytic converter having exhaust gas purification system according to the preamble of claim 1 and a diesel engine with a control device for carrying out the method.

From DE 103 49 876 A1 a generic method for operating a diesel engine with a nitrogen oxide storage catalyst having emission control system is known. In the method, in connection with a nitrate regeneration starting from a lean air-fuel mixture immediately before setting a rich air-fuel mixture with a lambda value below one, an operating mode transition phase is inserted at which a lambda value slightly above one is set. As a result, the formation of ammonia is improved, which is sought in the subsequent operating phase with a rich air-fuel mixture in the reduction of nitrogen oxides stored in the nitrogen oxide storage catalyst. The ammonia formed is used to further increase nitrogen oxide reduction in a downstream SCR catalyst. For the efficient achievement of a good regeneration result, a reliable and reproducible adjustment of the lambda value is required, in particular in the rich operating phase in which the actual regeneration of the nitrogen oxide storage catalytic converter takes place.

The object of the invention is to provide a method for operating a diesel engine with a nitrogen oxide storage catalytic converter having emission control system, which allows a reliable and reproducible adjustment of the lambda value, especially in carrying out a regeneration of the nitrogen oxide storage catalytic converter. It is another object of the invention to provide a diesel engine with a Specify nitrogen oxide storage catalytic converter having exhaust gas purification system, which allows the apparatus to perform a simple regeneration of the nitrogen oxide storage catalytic converter in a simple manner.

These objects are achieved by a method having the features of claim 1 and by a diesel engine having the features of claim 16.

The inventive method works with a diesel engine, in whose single or multiple combustion chambers a lambda value exhibiting air-fuel mixture is at least partially burned and thereby produced exhaust gas is fed to the nitrogen oxide storage catalyst. Starting from an operation of the diesel engine with a first operating mode, in which the air-fuel mixture has a first lambda value of greater than one, an operation with a second operating mode is set for a regeneration of the nitrogen oxide storage catalytic converter for the diesel engine, in which the air Fuel mixture has a second lambda value of less than one. Immediately prior to setting the second mode of operation, an operating mode transition phase is entered in which the diesel engine is operated in a third mode of operation in which the air-fuel mixture is set to a third lambda value lower than in the first mode of operation and slightly above one , According to the invention, in the third operating mode, a diesel engine controlled in relation to the lambda value of the air-fuel mixture is detected such that an exhaust lambda value is detected by means of a lambda sensor arranged downstream of the nitrogen oxide storage catalyst in the exhaust gas purification system and used as control variable for the regulated setting of a predefinable desired value for the lambda sensor third lambda value is used.

The setpoint value for the third lambda value in the operating mode transition phase provided according to the invention is typically in a range from 1.01 to 1.10, preferably 1.02 to 1.10, and more preferably at about 1. 03, and thus relatively close to that the actual regeneration set second lambda value of about 0.95. Thus, in the operating mode transition phase, it is possible to set engine operating variables which determine the operation of the diesel engine to values which are at least approximately required in the immediately following operating phase in the second operating mode for a rich-air-fuel-ratio diesel engine. The operating mode transition phase carried out in accordance with the invention thus serves to stably set engine operating parameters required for rich engine operation, but with weak engine operation still occurring. Thus, it is advantageously possible to approximate the conditions that are inherently difficult to set in a diesel engine for rich engine operation. The subsequent transition to the second operating mode requires only slight changes of one or more engine operating variables and can thus be simplified. Preferably, the operating mode transition phase is maintained with a lambda value only slightly above one, only as long as it is necessary to set stable conditions. Typically, this time is in the low single-digit second range. Preferably, after about two to five seconds, the operation of the diesel engine is switched from the third operating mode to the second operating mode.

In particular, due to the lambda-controlled engine operation provided according to the invention in the weakly lean operating mode transition phase in the third operating mode, a particularly reliable and accurate adjustment of the engine operation is made possible. In this case, the knowledge is exploited that in the operating mode transition phase of the lambda control used, arranged downstream of the nitrogen oxide storage catalytic converter lambda sensor provides the lambda value of the burned in diesel engine air-fuel mixture very accurately corresponding measured value, since in the previous first operating mode also a lean air Fuel mixture was set. Since the first operating mode was set for a long time, typically in the range from 10 seconds to several minutes, effects of the nitrogen oxide storage catalytic converter influencing the exhaust gas lambda value have subsided.

For the purposes of the invention is to be understood as a nitrogen oxide storage catalyst, an exhaust gas purification element having on an inert, preferably executed in honeycomb body support a catalytic coating with the ability to store nitric oxides. The corresponding storage component may be an alkali or alkaline earth compound such as barium carbonate. This removes oxidizing exhaust gas with a lambda value of greater than one nitrogen oxides (NOx) and sulfur oxides (SOx) to form solid barium nitrate or barium sulfate. Due to the associated material exhaustion regenerations of the nitrogen oxide storage catalyst are necessary from time to time, in which stored NOx or SOx are removed again and the storage capacity is restored. A regeneration happens in that for a certain time reducing exhaust gas is supplied. In this case, nitrates or sulfates can decompose to release the corresponding oxides. Re-released NOx are from the present in the exhaust reducing agents (H ₂ , CO and HC) at the on the nitrogen oxide storage Catalyst existing catalytically active coating component to harmless nitrogen (N ₂ ) and reduced to ammonia (NH ₃ ).

Here, as usual, a lambda value is understood as meaning the stoichiometric ratio of the content of the oxygen and the content of fuel or of reducing constituents in the air-fuel mixture or the exhaust gas supplied to the engine. With a lambda value of greater than one, there is a lean air-fuel mixture or exhaust gas with an excess of oxygen, while with a lambda value of less than one, there is a rich air-fuel mixture or exhaust gas with an excess of reducing agents.

Typically, air and fuel are supplied to the combustion chambers of the multi-cylinder diesel engine, which is preferably four-stroke, on separate paths and combusted in the combustion chambers to release mechanical work. The combustion can be more or less complete depending on the combustion process. In order to remove pollutants from the exhaust gas, the proposed exhaust gas purification system may have further filter-active and / or catalytically active components in addition to the nitrogen oxide storage catalyst. Furthermore, the emission control system has sensors for detecting exhaust gas parameters such as temperature and composition.

The lambda value of the combustion exhaust gas is equal to that of the air-fuel mixture immediately after discharge from the combustion chamber or combustion chambers. However, by the action of an exhaust gas purification component, in particular by conversion, storage and / or release of exhaust gas constituents, a change in the lambda value may occur. Furthermore, a change in the lambda value may be provided by the supply of air or fuel from the engine external sources to the exhaust. If necessary for the sake of clarity, the following is explicitly spoken of an exhaust lambda value. The lambda value of the air-fuel mixture supplied to the combustion chambers of the engine, where appropriate for clarity, is also referred to below as engine lambda value. Although not necessarily limited thereto, it is assumed below that in the method according to the invention, a change in the lambda value of the exhaust gas supplied to the nitrogen oxide storage catalyst is exclusively or almost exclusively brought about by a change in the engine lambda value. Since the nitrogen oxide storage catalytic converter typically has a storage effect with respect to oxygen and / or reducing agents, in particular when the engine lambda value changes from greater than one to less than one (or vice versa), then deviations from the engine lambda value occur temporarily downstream of the nitrogen oxide storage catalytic converter Exhaust lambda values before. For their detection, a so-called lambda sensor is provided, which can be designed in a familiar to the expert form, such as a binary or continuous lambda probe or as a NOx sensor with lambda sensitivity.

According to the invention, a closed loop is provided, in which especially during operation of the diesel engine in the third operating mode by means of the lambda sensor downstream of the nitrogen oxide storage catalytic converter, exhaust lambda values are sampled continuously or sampled in a short sequence, and fed back as a control variable. In the control loop, a comparison is made with a predefinable desired value and a controller of the control loop adjusts the engine lambda value in such a way that the deviation of the lambda value detected by the lambda sensor from the desired value for the third lambda value becomes at least approximately zero. The controller can be designed in any known to those skilled execution, such as a PI or PID controller. The controller may be hardware and / or software implemented.

In an embodiment of the method takes place in the second operating mode with respect to the lambda value of the air-fuel ratio, an unregulated operation of the diesel engine. This takes into account the fact that, during the actual regeneration of the nitrogen oxide storage catalyst during the second operating mode, this reducing agent used in the exhaust gas is used for NOx or SOx reduction and thus removed from the exhaust gas. For this reason, an exhaust gas lambda value is detected by the downstream arranged lambda sensor, which does not coincide with the engine lambda value at least as long as a noticeable consumption of the reducing exhaust gas components takes place. As a result, the exhaust lambda value remains approximately at the stoichiometric value of one as long as the removal of, in particular, stored nitrogen oxides is not yet complete, even though the set engine lambda value is lower. The exhaust lambda value measured downstream of the nitrogen oxide storage catalytic converter is not used in this case as a controlled variable for setting the engine lambda value.

In a further embodiment of the method, a desired value is specified for the second lambda value, and in the second and in the third operating mode, a precontrol is performed the lambda value of the air-fuel mixture influencing engine operating variable as a manipulated variable such that by the pilot control of the second and third lambda value their respective intended target value at least approximately reach.

Preferably, in the second and in the third operating mode, a plurality of engine operating variables are adjusted in a pilot-controlled manner, wherein the pilot control values are preferably kept retrievable in a memory. The pilot-set engine operating variables do not necessarily have to be effective as manipulated variables in the control sense for the lambda control performed in the third operating mode.

The retrieved and adjusted precontrol values are preferably assigned to the respective operating point of the diesel engine with regard to load and rotational speed. In particular, it is provided that even in the third operating mode with a weakly lean air-fuel ratio essential engine operating variables determining fuel combustion in the combustion chamber be set to values as required for rich operation in the second operating mode. In this way, the combustion process is already set in the operation mode transition phase according to the requirements for the at least partial combustion of a rich air-fuel mixture in the subsequent second operating mode. The transition to the second mode of operation accordingly requires only minor changes and thus can be done reliably and accurately.

In a further embodiment of the method, the precontrol is designed as an adaptive feedforward control such that an adaptively variable correction value influencing the manipulated variable is provided. The correction value can be embodied as a multiplication value or as an additive to the manipulated variable for setting the second and / or the third lambda value. The correction value is thus designed as an adaptively variable reference value, which is adapted on the basis of detected control deviations if necessary so that the precontrol can compensate the control deviation. As a result of the adaptively executed feedforward disturbances can be effectively compensated in particular temporally small variable disturbances, since a regulator intervention to compensate for disturbances minimized and thus a balancing can be done very quickly and with minimal transients.

It is envisaged that the possibly newly learned correction value in the case of a transition from a lambda-controlled operation in the third operating mode of the operating Mode transition phase is taken on the immediately following engine operation in the second operating mode with pure pilot operation. As a result of the adaptive pilot control, the comparatively small lambda change from approximately 1. 03 to 0.95 can be carried out very precisely. On the other hand, a direct jump, dispensing with the operating mode transition phase according to the invention, running from the typically comparatively high first lambda value to the rich second lambda value would be unreliable and imprecise.

In a further refinement of the method, in the second and in the third operating mode, a pilot injection of a total injection quantity of fuel injected into the combustion chamber of the diesel engine in a working cycle is carried out in such a way that the diesel engine is supplied with at least partial combustion of the air-fuel mixture in accordance with an air mass measuring device Air mass flow of the second and third lambda value their respective intended target value at least approximately reach. In this case, it is particularly preferred if, in a further embodiment of the method according to the invention, the air mass flow determined by the air mass measuring device is used as a controlled variable for the controlled setting of a predefinable air mass flow setpoint. Preferably, a separate control loop is provided for controlling the air mass flow. In this way, the settings of air mass flow and total injection quantity as the air-fuel ratio determining quantities are decoupled control technology. The air mass measuring device typically delivers a highly accurate measured value for the actual air mass flow, so that the engine lambda value can also be set very precisely with the correspondingly set total injection quantity.

In a further refinement of the method, the total injection quantity comprises a main injection quantity injected in a main injection and a post-injection quantity injected in a post-injection following the main injection. The main injection amount is preferably injected into the combustion chamber in a crank angle range of about 10 degrees before top dead center to about 10 degrees after top dead center, while the post injection quantity is preferably in a crank angle range of about 15 degrees to about 45 degrees after top dead center in the power stroke in FIG the combustion chamber is injected. Due to the post-injection, an enrichment or enrichment of the air-fuel mixture that has little or no influence on the power output or torque output of the diesel engine is effectively enabled. In order to improve the combustion process, a pilot injection upstream of the main injection is preferably provided in the compression stroke. Especially preferred two pilot injections are carried out at short intervals. The corresponding pilot injection quantity is preferably injected in a crank angle range of 25 degrees to 15 degrees before top dead center.

In connection with the distribution of the total injection quantity to at least one main injection and a post-injection, it is particularly preferred if, in a further embodiment of the method, the post-injection quantity is used as a manipulated variable for setting the nominal values for the second and / or third lambda value. With the exception of an increased post-injection quantity, all or at least most of the other engine operating variables remain unchanged during the transition from the third operating mode to the second operating mode. The mixture enrichment during the transition from the third lambda value to the second lambda value is thus preferably accomplished exclusively by an increase in the post-injection quantity.

In a further refinement of the method, in the third operating mode a deviation from the exhaust gas lambda value resulting from the precontrol and the setpoint value for the third lambda value is determined and, if necessary, the adaptively variable correction value is modified such that the deviation assumes an at least approximately negligible extent. A learning or an adaptation of the correction value thus takes place during the operating mode transition phase during operation of the diesel engine in the third operating mode, wherein a respectively newly learned correction value is written to a readable memory and is read out again at the next setting of the third operating mode. Preference is given to predetermined release conditions, such as a falling below a predefinable maximum load and / or a maximum value for speed fluctuations and an absence of a push operation, provided for the implementation of an adaptation. If the release conditions are not present, the adaptation or learning of the correction value is not carried out or aborted. In this case, the third lambda value is adjusted unregulated, but piloted on the basis of the since then valid correction value. The assumption of a newly learned correction value is preferably omitted if the deviation from the correction value valid since then falls below a specifiable minimum dimension or exceeds a predefinable maximum. These measures prevent too frequent or erroneous learning of the correction value.

In a further refinement of the method, a motor operating map is provided which has characteristic map regions of predeterminable size, to each of which a correction value is assigned. The engine operating map is preferably a load Speed map. A reliable regeneration of the nitrogen oxide storage catalytic converter with an accurate lambda value setting in at least the predominant part of the engine operating map is made possible in particular by the fact that in a further embodiment of the method the pilot control for setting the second and / or the third lambda value in a given engine operation Map range falls back to a correction value, which was associated with this map area in connection with a previous regeneration of the nitrogen oxide storage catalytic converter. Preferably, a division of the engine operating map into 10 to 20 identically sized map areas. However, it may also be provided a finer or coarser map grid. Particularly in the case of a coarse rasterization, it is preferable to perform an interpolation between adjacently stored correction values and to use the interpolation value.

In a further refinement of the method, in the second operating mode, at least one of the engine operating variables exhaust gas recirculation rate and intake air throttle rate are set as in the third operating mode set immediately before. In this way, a particularly reliable and smooth transition from the third operating mode to the second operating mode is made possible. Preferably, further engine operating parameters, such as injection timing and injection quantity of main and / or pilot injection are adopted unchanged.

In a further embodiment of the method, the exhaust lambda value detected by means of the lambda sensor arranged downstream of the nitrogen oxide storage catalytic converter is monitored for falling below a predeterminable limit value during execution of a nitrate regeneration to remove stored nitrogen oxide from the nitrogen oxide storage catalytic converter in the second operating mode Falling below the predetermined limit, the operation of the diesel engine is switched back to the first operating mode. The lambda sensor arranged downstream of the nitrogen oxide storage catalytic converter thus serves for the end detection of the nitrate regeneration, the lambda value preferably being selected in the range from 1.00 to 0.98 as the authoritative limit value. This can be avoided or at least minimized with sufficient certainty unwanted break through of reducing exhaust gas components such as carbon monoxide or hydrocarbon.

In a further embodiment of the method, in the implementation of a sulfate regeneration for the removal of stored sulfur oxide from the nitrogen oxide storage catalyst in the second operating mode of the by means of the downstream of the nitrogen oxide Storage catalytic converter arranged lambda sensor detected exhaust lambda value monitored for falling below a predetermined limit and switched to below the predetermined limit under at least approximately maintaining the second lambda value of an unregulated with respect to the lambda value of the air-fuel mixture operation of the diesel engine to a regulated operation.

As is stored in the nitrogen oxide storage catalyst of sulfur oxides are typically bound significantly more than is stored nitrogen oxides are required in comparison to the nitrate-regeneration in a sulphate regeneration both higher temperatures of more than 550 ⁰ C as well as a prolonged rich operation. The second mode of operation is therefore preferably maintained unchanged for a sulfate regeneration over a period of 10 seconds to 30 seconds. However, after a fraction of this period of time, the consumption of reducing exhaust gas components in the nitrogen oxide storage catalytic converter has dropped sharply and the exhaust gas lambda value detected by the lambda sensor is at least approximately equal to the engine lambda value. If the approach has taken place up to a predefinable level, lambda-controlled operation of the diesel engine can therefore be carried out again using the measured value supplied by the lambda sensor. This improves the accuracy of setting the rich exhaust lambda value required for efficient sulfate regeneration.

The problem underlying the invention is also solved by a diesel engine with a nitrogen oxide storage catalytic converter having emission control system and with a control device for carrying out the method according to the invention, wherein the downstream of the nitrogen oxide storage catalytic converter arranged in the exhaust gas purification system lambda sensor is the only one for setting the lambda value of in the lambda sensor provided in the exhaust system is at least partially burned air-fuel mixture the combustion chamber of the diesel engine. Since a lambda adjustment is made possible solely by means of the lambda sensor arranged downstream of the nitrogen oxide storage catalytic converter in the exhaust gas purification system, a further lambda sensor, in particular arranged upstream of the nitrogen oxide storage catalytic converter, is unnecessary. Thus, a considerable cost saving can be achieved.

In an embodiment of the invention, a particle filter is arranged in the exhaust gas purification system between the nitrogen oxide storage catalytic converter and the lambda sensor. Thus, the lambda sensor is disposed downstream of the particulate filter, which additionally allows control or monitoring of a particulate filter regeneration by Rußabbrand. moreover the risk of carbon fouling of the lambda sensor is avoided and thus improves the reliability and accuracy of Lambdamessung.

Advantageous embodiments of the invention are illustrated in the drawings and described below. In this case, the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination of features, but also in other combinations or alone, without departing from the scope of the present invention.

Showing:

Fig. 1 is a schematic representation of an advantageous embodiment of a

Systems of diesel engine and emission control system for carrying out the method according to the invention,

Fig. 2 is a diagram for the time course of the lambda value λ _M for in the

Diesel engine burned air-fuel mixture and measured in the exhaust downstream of the nitrogen oxide storage catalyst lambda value λ _Am in connection with the implementation of a nitrate regeneration and

Fig. 3 is a diagram for the time course of the lambda value λ _M for in the

Diesel engine burned air-fuel mixture and measured in the exhaust downstream of the nitrogen oxide storage catalyst lambda value λ _Am in connection with the implementation of a sulfate regeneration

Fig. 1 shows schematically an advantageous embodiment of a system of internal combustion engine 1 and exhaust gas purification system 2 for a motor vehicle, not shown, for carrying out the method according to the invention. The internal combustion engine 1 is preferably embodied as a direct-injection lean-running engine, in particular as an air-compressing internal combustion engine according to the reciprocating piston principle, hereinafter referred to simply as a diesel engine. An associated not shown fuel injection system is preferably designed as a so-called common rail system with adjustable rail pressure or fuel injection pressure or in the form of an injection system according to the pump-nozzle or pump-line-nozzle principle.

The cylinders of the internal combustion engine are each associated with a combustion chamber with one or two intake and exhaust valves, a glow plug and a fuel injector and one or more inlet channels for the combustion air, which is not shown in detail. The fuel injectors are capable of performing multiple injections. The diesel engine 1 receives its combustion air via an air supply line 3, in which an unillustrated air mass meter is arranged. The air mass meter is preferably designed as a so-called hot-film air mass meter or as a hot-wire air mass meter. Air density fluctuations can be detected by this and compensated for when adjusting the air mass flow. By means of an adjustable throttle element, also not shown, the air mass flow supplied to the diesel engine 1 can be throttled to an adjustable level. The combustion air is compressed by means of an exhaust gas turbocharger 15 and fed to a charge air cooler 16 for cooling. The exhaust gas turbocharger is preferably designed as a so-called VTG loader or as a wastegate loader with adjustable boost pressure. Exhaust gas generated in the combustion chambers of the cylinders of the diesel engine 1 is discharged via an exhaust pipe 4. In this case, the combustion air can be added via an exhaust gas recirculation line 13 exhaust gas and thus returned to the diesel engine 1. The proportion of recirculated exhaust gas (EGR rate) can be adjusted via an EGR valve 14. Preferably, the recirculated exhaust gas to the diesel engine 1 is cooled by means of an EGR cooler, not shown, wherein for the EGR cooler an optionally adjustable bypass may be provided. As a result, the combustion air can be optionally mixed with cooled or hot exhaust gas. Non-recirculated exhaust gas is supplied via the exhaust gas turbocharger 15 of the exhaust gas purification system 2. With the described embodiment, different values for the essential engine operating parameters such as, for example, air mass flow, injection time quantity, pressure and time point of a plurality of fuel injections, EGR rate, charge air pressure and thus different combustion processes can be displayed. In particular, the diesel engine 1 can be operated with an air-fuel mixture with varying lambda values, hereinafter referred to as engine lambda value λ _M. Engine lambda values λ _M greater than one correspond to a lean and engine lambda values λ _M less than one rich air-fuel mixture or operation of the diesel engine 1. Accordingly, results from lean engine operation, a lean exhaust gas with an excess of oxidizing components such as in particular Oxygen and in a rich engine operation, a rich exhaust gas with an excess of reducing constituents such as carbon monoxide, hydrogen and hydrocarbons. The exhaust gas composition is subsequently characterized analogously to this definition by the exhaust gas lambda value λA.

A preferred embodiment of the exhaust gas cleaning system 2 associated with the diesel engine 1 comprises an oxidation catalytic converter 5, a nitrogen oxide storage catalytic converter 6, a particle filter 7 and an SCR catalytic converter 8 in this sequence called Wallflow filter on SiC- Cordiererit- or Aluminiumtitanatbasis used. However, the particle filter 7 can also be designed as a sintered metal filter or as a filter unit with an open filter structure. The arranged downstream of the nitrogen oxide storage catalytic converter 6 SCR catalyst 8 has the property of being able to storing under reducing conditions NH ₃ and is-stored in oxidizing conditions and ev. Fed NH ₃ as a reactant in a selective catalytic reduction reaction to form nitrogen for chemical reduction of NOx use to be able to.

The latter property is used in particular to neutralize NOx supplied to the SCR catalyst 8. The SCR catalytic converter 8 receives NOx in the arrangement according to FIG. 1, for example by increasing NOx slippage as a result of the decreasing NOx absorption capacity of the nitrogen oxide storage catalytic converter 6 during lean operation of the diesel engine 1 in the course of the NOx storage. Catalyst 8 is preferably formed as a full catalyst based on V ₂ O ₅ -WO ₃ or zeolite or as a coated catalyst with noble metal-containing coating. Particularly preferred is an embodiment as a supported catalyst with a copper or iron-containing zeolite coating. The catalysts 5, 7, 8 are preferably designed as honeycomb monoliths which are crossed by catalytically coated channels through which the supplied waste gas can flow.

On the input side of the oxidation catalyst 5, a fuel addition unit may be provided, via which, for example, fuel can be supplied as fuel to the exhaust gas. This allows due to exothermic oxidation of the exhaust demand supplied fuel targeted heating of the exhaust gas. If present, the fuel adding unit is activated primarily in the context of active regeneration of the particulate filter 7 by thermal soot burnup or for heating a downstream exhaust gas purifying component. However, it is preferable to dispense with the fuel adding unit and make an enrichment of the exhaust gas with oxidizable constituents by engine operation by a rich air-fuel mixture operation. Below is assumed from the latter variant.

In the exhaust gas aftertreatment device 2, various temperature and exhaust gas sensors are provided for detecting exhaust gas and component temperatures as well as concentrations of important exhaust gas constituents. By way of example, in FIG. 1 on the input side of the nitrogen oxide storage catalytic converter 6 and on the output side of the particle filter 7, a temperature sensor 10, 11 is arranged in the exhaust gas purification system 2. On the output side of the SCR catalyst 8 is a sensitive to NOx and / or NH ₃ gas sensor 12 provided. To determine the loading of the particulate filter 7 with soot and / or ash, it is also preferred to provide inlet and outlet side of the particulate filter 7 pressure sensors or a differential pressure sensor, which is not shown separately in Fig. 1. Furthermore, downstream of the nitrogen oxide storage catalytic converter 6, a lambda sensor 9 for detecting the exhaust gas lambda value λ _{A present there is} arranged. For precise characterization, the measured value for the exhaust gas lambda value, determined via the lambda sensor 9, downstream of the nitrogen oxide storage catalytic converter is referred to below as the exhaust gas lambda value λ _A m. As shown, the lambda sensor 9 can be arranged on the output side of the nitrogen oxide storage catalytic converter 6, but also on the output side of the particle filter 7, ie between the particle filter 7 and the SCR catalytic converter 8. By means of these and optionally other sensors, the operating state of the exhaust gas purification system 2 can be comprehensively determined and the operation of the diesel engine 1 optionally adjusted. In this case, it is preferred that, apart from the lambda sensor 9, no further lambda sensor is present in the exhaust gas purification system 2. In particular, it is provided according to the invention that the lambda sensor 9 is the only lambda sensor of the emission control system 2 which is used to set the lambda value of the air-fuel mixture at least partially combusted in the diesel engine 1.

For setting or detecting the engine operation, an electronic engine control unit 17 is provided. On the one hand, the engine control unit 17 receives information about relevant engine operating variables, such as, for example, Speed, engine load, temperatures, pressures from the respective sensors or probes and on the other hand, control signals as adjustment variables to actuators such. to the EGR valve 14, the exhaust gas turbocharger 15 or the throttle element in the air supply line 3 output. There is provided an adjustability of state variables of the gas supply side and the fuel supply side. In particular, the engine control unit 17 is able to control the fuel injectors to perform multiple injections and optionally adjust the fuel injection pressure as needed. Further, the engine control unit 17 is arranged to perform control and regulating operations, with which engine operating variables are adjusted or controlled. For this purpose, the engine control unit 17 can resort to stored maps or calculation or control or control routines. Subsystems provided for this purpose, such as computers, memories or input / output units and the like, are not shown separately.

In an analogous manner, a second control unit 18 is provided for the detection and adjustment of operating and state variables of the exhaust gas aftertreatment device 2. The engine control unit 17 and the second control unit 18 are by means of a bidirectional Data line 19 connected to each other. In this way, a mutual exchange of data available to a particular control device is made possible. It is understood that the control units 17, 18 can also be combined in a single integral measured value acquisition and control unit.

The nitrogen oxide storage catalyst 6 has the ability to store NOx and SOx present in the exhaust gas under oxidizing conditions, mainly by chemical bonding as nitrate or sulfate to the coating material. In the usual mode of operation of the diesel engine 1 with excess air, hereinafter referred to as the first mode of operation, this is thus generally the case. While the storage of NOx is desirable because of the desired nitrogen oxide removal per se, the incorporation of the SOx is disadvantageous because they block storage spaces for NOx. In order to maintain the NO x removal function of the nitrogen oxide storage catalytic converter, recurrent regenerations are required in which the stored NO x or SO x are removed again. The removal of the stored NOx takes place in a so-called nitrate regeneration, the removal of SOx in a so-called sulfate regeneration. Because of the significantly higher concentration of NOx in the exhaust gas compared to SOx, nitrate regeneration is required at much shorter intervals than sulphate regeneration. Typically, nitrate regenerations are carried out at intervals of 30 seconds to a few minutes, while sulfate regenerations are preferably carried out in terms of specific driving distances after covering approximately 1000 km. In both cases it is necessary, at least temporarily, to provide a reducing exhaust gas, ie an exhaust gas with an exhaust lambda value λ _A of less than one. For this purpose, according to the invention, the diesel engine 1 is supplied with a rich air-fuel mixture and operated in an operating mode with an engine lambda value XM of less than one. This mode of operation will be referred to as a second mode of operation hereinafter. Under the then prevailing reducing conditions, NOx stored in a nitrate regeneration is released again and converted for the most part into N ₂ and NH ₃ . In sulfate regeneration, sulfur stored as sulfate is reduced to volatile sulfur compounds such as SO ₂ or H ₂ S.

For reasons of fuel consumption, a high proportion of lean engine operation time in the first operating mode with an engine lambda value λ _M greater than one is desirable. Accordingly, a comparatively low time fraction is desirable for the second mode of operation. The first operating mode is set in the normal lean operation of the diesel engine 1 anyway. The setting of the second operating mode with an engine lambda value XM of less than one to supply the nitrogen oxide However, storage catalytic converter 6 with reducing exhaust gas with an exhaust gas lambda value λA of less than one requires special measures, in particular with regard to a reliable and precise adjustment of the engine lambda value λ _M , which will be explained in more detail below. In the first place, with additional reference to FIG. 2, the procedure according to the invention for carrying out a nitrate regeneration will be discussed.

In the diagram of FIG. 2, a preferred time profile of the engine lambda value λ _M and the exhaust gas lambda value λ _Am detected by the lambda sensor 9 arranged downstream of the nitrogen oxide storage catalytic converter 6 are shown schematically in the various operating modes of the diesel engine 1. The course of the engine lambda value λ _M is represented by the solid line, the exhaust lambda value λ _Am detected by means of the lambda sensor 9 by the dotted line. It is assumed that upstream of the nitrogen oxide storage catalytic converter 6 no components influencing the exhaust gas lambda value are arranged in the exhaust gas purification system 2 and therefore the exhaust gas supplied to the nitrogen oxide storage catalytic converter has an exhaust gas lambda value λ _A corresponding to the engine lambda value λ _M.

In a first method step, the first operating mode in FIG. 2 is initially set. The period of time with the first operating mode active is indicated in FIG. 2 by the reference symbol I. When the first operating mode is active, the nitrogen oxide storage catalytic converter 6 is supplied with a lean exhaust gas having a high oxygen content. This is supplied by the diesel engine 1 operated with an engine lambda value λ _M of, for example, λ _M = 3. The diesel engine 1 is operated here in relation to the engine lambda value λ _M unregulated. The engine operating variables such as EGR rate, boost pressure, rail pressure, injection parameters of pre-injection and main injection, etc. are set according to the required power and the operating point in the load-speed map map-controlled.

Most of the NOx emitted by the diesel engine 1 and contained in the exhaust gas are stored in the catalyst material of the nitrogen oxide storage catalyst 6, preferably in the form of nitrates, and thus removed from the exhaust gas. Slippage of NOx passing through the nitrogen oxide storage catalytic converter 6 is at least partially rendered harmless by reduction in the downstream SCR catalytic converter 8. If, with increasing saturation of the nitrogen oxide storage catalytic converter 6, a nitrogen oxide slip increased to unacceptable levels, for example, sensor-based or model-based, or if a predefinable nitrogen oxide saturation threshold value is reached, nitrate regeneration is initiated, if predetermined release conditions are met. As a release condition, for example, the presence of a motor operation in a predefinable load-speed map area with an engine load of a predetermined fraction of the full load can be used. If the release conditions are met, the operation of the diesel engine 1 is initially switched over to the third operating mode with a motor lambda value λ _M , approximately λ _M = 1, 03, which is slightly above 1.0. The time span with active third operating mode is indicated in FIG. 2 by the reference symbol IM. The conversion preferably takes place almost abruptly, at least very rapidly with a steep gradient. To change from the first operating mode to the third operating mode, the following measures are taken in detail.

The air mass flow supplied to the diesel engine 1 is throttled to a nominal value specified in the map. For this purpose, an independent control loop in the engine control unit 17 is implemented such that the signal supplied by the air mass meter for the air mass flow is used as a control variable and a manipulated variable generated by the corresponding controller acts on the throttle element in the air supply line 3. Furthermore, essential engine operating parameters such as EGR rate, boost pressure, rail pressure, injection parameters of pre-injection and main injection, center of gravity of combustion, etc. are set to the values intended for rich engine operation. In addition, a post-fuel injection is activated. According to the invention, apart from the total injection quantity determined by pre-main injection and post-injection, the engine operating parameters mentioned are set to values which are likewise provided in the subsequent operating phase in the second operating mode. The period of time with active second operating mode is indicated in Fig. 2 by indicating the reference symbol Il.

The nitrogen oxide storage catalytic converter 6, which is saturated with oxygen during operation in the previous first operating mode, allows the exhaust gases to pass substantially unchanged in the third operating mode with respect to the components determining the exhaust gas lambda value λ _A. The exhaust lambda value λ _Am delivered by the lambda sensor 9 therefore corresponds, apart from a slight time delay and a certain degree of slippage the lambda transition, as shown quite accurately the upstream of the nitrogen oxide storage catalytic converter 6 existing exhaust lambda value λ _A and thus the engine lambda value λ _M. This is inventively exploited to the effect that is transferred from an unregulated engine operation to a regulated in relation to the engine lambda λ _M operation of the diesel engine 1. The control in active third operating mode is preferably designed as an adaptive pilot control, which will be explained in more detail below.

In the present case, the measurement signal provided by the lambda sensor 9 is converted by the second control unit 18 into a lambda value (exhaust lambda value λ _Am ) in accordance with a stored characteristic curve and transmitted to the engine control unit 17. From a lambda controller implemented in the engine control unit 17, the exhaust lambda value λ _Am measured in this way is used as the controlled variable and compared with the desired value of the engine lambda value λ _M which is decisive for the third operating mode. On the basis of the comparison result, a manipulated variable is output which acts on the fuel injectors and determines the total injection quantity. For pre-controlled adjustment of the total injection quantity as a manipulated variable, a correction value influencing this is provided, which is read from a read-write memory. Overall, therefore, the total injection quantity serving as a manipulated variable results from a component output by the lambda controller and a component determined by the correction value, which component can be linked to the controller component in an additive or multiplicative manner. A multicompanying link is preferred.

According to the invention, it is provided that ascertained deviations between the measured exhaust lambda value λ _A m and the desired value for the engine lambda value λ _M relevant in the third operating mode are optionally taken into account by a change in the correction value such that the deviations become at least approximately zero due to the changed correction value , For this purpose, the value provided by the air mass meter for the air mass flow is evaluated. The total injection amount is adjusted so that, on the basis of the value for the air mass flow, the nominal value of the engine lambda value λ _M is calculated, the total injection quantity being determined by the correspondingly determined correction value. The old correction value is then replaced by the possibly changed newly learned correction value, ie overwritten in memory. The controller therefore only needs additional correct occurring disturbances. The controller interventions are therefore correspondingly low. An override of the correction value can be omitted if the changes are small or strong changes in engine operation, for example, due to a load requests requested by the driver occur.

In this context, it is particularly preferred if only the post-injection quantity is readjusted if necessary, and the pre-controlled values of the pilot and main injection quantities are kept constant. Therefore, in this particularly preferred embodiment, only the proportion of the total injection quantity attributable to the post-injection quantity is used as a manipulated variable for setting the engine lambda value λ _M precisely.

If the Einregelvorgang for the lambda value of the third operating mode has been carried out, which is considered, for example, when the control deviations have fallen below a minimum value, then the third operating mode is terminated at time t1 and the engine operation is switched to the second operating mode. The transients of the third mode of operation are typically decayed after a short time, such as one to three seconds, and therefore, in the third mode of operation, engine operation may be referred to as an operational mode transient phase interposed between the first mode of operation and the second mode of operation.

In the second operating mode, a rich engine lambda value λ _M of about 0.95 is set for the diesel engine 1 and the diesel engine 1 is changed over to an operation uncontrolled with respect to the engine lambda value λ _M. For this purpose, the controller output is frozen to the value present at the end of the preceding third operating mode and the total injection quantity is increased, ie the corresponding precontrol value is increased. In order to determine the extent of the increase, the air mass flow value provided by the air mass meter is preferably again evaluated and the total injection quantity is set so that, on the basis of the value for the air mass flow, the nominal value of the reduced new engine lambda value λ _M is calculated. In this case, it is again particularly preferred if only the post-injection quantity is adjusted and the pre-control values for the pilot and main injection quantities are kept constant. As a manipulated variable for the pilot-controlled adjustment of the engine lambda value λ _M , therefore, only the proportion of the total injection quantity attributable to the post-injection quantity is used. The other engine operating parameters remain unchanged since they already have the values that are required for the rich operation of the second operating mode and were already set in the previous third operating mode.

With the reducing exhaust gas supplied to the nitrogen oxide storage catalytic converter 6 in the second operating mode, the actual nitrate regeneration of the nitrogen oxide storage catalytic converter 6 takes place. The NOx stored in the nitrogen oxide storage catalytic converter 6 is reduced to N ₂ and NH ₃ . Released NH ₃ is fed to the subsequent SCR catalyst 8 and stored there. As a result of the reduction processes in the nitrogen oxide storage catalytic converter 6 with consumption of reducing agent, the exhaust gas downstream of the nitrogen oxide storage catalytic converter 6 initially has no reducing components and the lambda sensor 9 first measures an exhaust lambda value λ _Am of 1.0. If stored NOx are largely reduced, then reducing agents contained in the rich exhaust gas increasingly break through and the exhaust lambda value λ _Am decreases and approaches the engine lambda value λ _M present upstream of the nitrogen oxide storage catalytic converter 6. Thus, an end of the regeneration processes can be detected by evaluating the measured value provided by the lambda sensor 9. Preferably, the second operating mode and thus the nitrate regeneration of the nitrogen oxide storage catalytic converter 6 is terminated at time t2 and the conditions of the first operating mode are set again when the exhaust gas lambda value λ _Am detected by means of the lambda sensor 9 falls below a predefinable limit value.

The method for the adaptive precontrol of the engine lambda values λ _M in the second and in the third operating mode is preferably refined in such a way that the correction values learned in the third operating mode are assigned to a map area of the load-rotating field characteristic map in which the current operating point of the diesel engine 1 is located. For this purpose, it is advantageous if the load rotary field map is divided into characteristic areas of predetermined or predefinable size. A fine screening of the load-rotating field characteristic improves the accuracy of the precontrol, but increases with increasing detail of the effort. A division into 10 to 40 map areas is preferred.

To further increase the accuracy can be provided to take into account gas transit times in the air path and / or in the exhaust gas purification system 2 in the evaluation of the measurement signals of the air mass meter and / or the lambda probe 9. Through a dead Time compensation, a lead time-related lead of the measurement signal of the air mass meter with respect to the measurement signal of the lambda probe 9 can be compensated. For this purpose, a model can be provided which simulates the time differences between the measurement signal of the air mass meter, the injection time of the respective total injection quantity or Nacheinspritzmenge and the time of the associated resulting Lambda nals engine model to dynamically correct the pilot control of the total injection quantity or Nacheinspritzmenge.

The following deals with preferred procedures for carrying out a sulfate regeneration of the nitrogen oxide storage catalyst 6. Here, with reference to the time chart shown in Fig. 3, the differences in comparison with the above-described procedure when performing a nitrate regeneration are discussed specifically. 3 shows time profiles of the engine lambda value λw and of the exhaust gas lambda value λ _Am measured in the exhaust gas downstream of the nitrogen oxide storage catalyst, analogously to the diagram of FIG. 2.

A sulfate regeneration of the nitrogen oxide storage catalyst 6 is carried out when it is determined that an unacceptably high amount of sulfur oxides is stored. This can be done, for example, model-based or based on the amount of fuel consumed and the fuel sulfur content. Sulfate regeneration is performed in a manner similar to nitrate regeneration. The main difference is a temperature of the exhaust gas or of the nitrogen oxide storage catalytic converter 6 which has been increased to approximately 650 ° C., and a preferably set enrichment to engine lambda values _λω of approximately 0.8 to 0.9 In addition, the duration of the enrichment is compared A further difference consists in that, preferably at elevated temperature, a successive change of operating phases takes place with a rich and a lean engine lambda value λ _M. This enables a decomposition of the comparatively stable sulphates Sulfur regeneration in conjunction with a thermal particle filter regeneration by Rußabbrand performed. This reduces the frequency of heating processes and thus the fuel consumption is reduced.

The elevated temperature is achieved by adjusting an early post-injection post-injection and / or late post-injection non-co-incineration. Due to the early post-injection in a crank angle range From about 10 degrees to about 40 degrees after top dead center in the power stroke, the outlet temperature of the exhaust gas can be increased immediately. Due to the late post-injection in a crank angle range from about 45 degrees to about 120 degrees after top dead center in the power stroke enrichment of the exhaust gas with unburned components, which burn by oxidation with residual oxygen contained in the exhaust gas in the oxidation catalyst 5 and / or in the nitrogen oxide storage catalyst 6 , whereby a Abgasaufheizung or Katalysatoraufheizung is effected.

With the pilot-operated engine operating parameters predetermined for the execution of a sulfate regeneration, a changeover from the first operating mode to the third operating mode is carried out analogously to the procedure explained above in connection with a nitrate regeneration. Likewise, an adaptation of the correction value takes place in the set third operating mode of the operating mode transition phase. However, different sets of correction values may be provided for performing nitrate regeneration and for performing sulfate regeneration.

Analogous to nitrate regeneration has in a sulfate regeneration after setting a rich engine lambda value λ _M in the second mode of operation, the exhaust gas downstream of the nitrogen oxide storage 6 initially no reducing components and the lambda sensor 9 is first an exhaust lambda value λ _Am of 1 , 0 measured. If stored NOx and SOx are largely reduced, reducing agents contained in the rich exhaust gas increasingly break through and the exhaust lambda value λ _Am decreases and approaches the engine lambda value λ _M present upstream of the nitrogen oxide storage catalytic converter 6. Unlike a nitrate regeneration but is now at a very close approximation of the exhaust gas lambda value λ _at λ to the engine lambda value _M of the rich engine lambda value inventively λ _M still maintained some time and at time t2 by a relative to the Lambda value of the air-fuel mixture uncontrolled operation of the diesel engine switched to a regulated operation. After expiration of a predefinable total duration of, for example, about 20 seconds for the second operating mode with a rich engine lambda value λ _M , the engine operation is switched back to the uncontrolled with respect to the air-fuel ratio first operating mode I at time t3. The operating phase of the second operating mode with a rich engine lambda value X _M is thus divided into two subsections. In the first, in Fig. 3 marked with the reference numeral IIa section, the diesel engine 1 is operated in a pre-controlled operating mode with respect to the rich engine lambda value λ _M unregulated. In the second subsection labeled Il b, the diesel engine 1 is operated in an operating mode regulated with respect to the rich engine lambda value λ _M , the pre-control values for the engine operating parameters being taken from the first subsection IIa or the third operating mode.

For the most complete removal of stored SOx, it is provided, after a comparatively short period of about 5 to 15 seconds in the first operating mode, the procedure with setting the operating mode transition phase and subsequent second operating mode with an unregulated first section IIa and a regulated second section IIb unchanged to repeat increased temperature. In particular, a 5 to 20 times repetition is provided.

After completion of the preferably predetermined number of repetitions, the measures to achieve an increased exhaust gas or catalyst temperature are terminated and transferred to the normal operation of the diesel engine 1 with recurrent nitrate regeneration.

To increase the accuracy of the lambda control in the second subsection IIb of the operation in the second operating mode, it is preferably provided to adapt the stored characteristic curve of the lambda sensor 9 with respect to a cross-sensitivity to H ₂ . This takes into account the fact that, as a result of side reactions such as, for example, a water gas shift reaction, the measurement signal of the lambda sensor 9 can be falsified during prolonged rich operation. In this way, a regulation of a wrong engine lambda value λ _{M is} reliably avoided.

Overall, owing to the lambda control provided according to the invention when a nitrate or sulfate regeneration is carried out using the lambda sensor 9 arranged downstream of the nitrogen oxide storage catalytic converter 6, a reliable and accurate lambda adjustment is possible. As a result of the further preferably provided in particular adaptive feedforward control, however, if necessary at any time be resorted to a sole pre-control operation. This improves the system security when a control mode, for example, due to unfavorable driving conditions or due to a failure of the lambda sensor 9 is not possible.

Claims

claims

1. A method for operating a diesel engine (1) with a nitrogen oxide storage catalytic converter (6) having exhaust gas purification system (2), wherein a lambda value exhibiting air-fuel mixture in a combustion chamber of the diesel engine (1) is at least partially burned and thereby resulting exhaust the nitrogen oxide storage catalyst (6) is supplied, starting from an operation of the diesel engine (1) with a first operating mode in which the air-fuel mixture has a first lambda value of greater than one, for a regeneration of the nitrogen oxide storage catalyst (6) for the diesel engine (1) an operation is set with a second operating mode, in which the air-fuel mixture has a second lambda value of less than one, wherein immediately before setting the second operating mode, an operating mode transition phase is inserted, in which the diesel engine ( 1) is operated in a third operating mode, wel chem for the air-fuel mixture, a third lambda value is set, which is lower than in the first operating mode and slightly above one, characterized in that in the third operating mode with respect to the lambda value of the air-fuel mixture controlled operation of the diesel engine (1) such in that an exhaust gas lambda value (λ _Am ) is detected by means of a lambda sensor (9) arranged downstream of the nitrogen oxide storage catalytic converter (6) in the exhaust gas purification system (2) and used as a control variable for the regulated setting of a predefinable setpoint value for the third lambda value.

2. The method according to claim 1, characterized in that in the second operating mode with respect to the lambda value of the air-fuel ratio unregulated operation of the diesel engine (1).

3. The method of claim 1 or 2, characterized in that for the second lambda value, a desired value is set and in the second and in the third operating mode, a pilot control of the lambda value of the air fuel mixture influencing engine operating variable as a manipulated variable is such that by the pilot control of the second and the third lambda value at least approximately reach their respective intended setpoint.

4. The method according to claim 3, characterized in that the feedforward control is designed as an adaptive pilot control such that an adaptively variable, the manipulated variable influencing correction value is provided.

5. The method according to any one of claims 1 to 4, characterized in that in the second and in the third operating mode, a pilot control of a total injection amount of in a working cycle in the combustion chamber of the diesel engine (1) injected fuel is made such that in accordance with one of an air mass meter determined, at least partial combustion of the air-fuel mixture to the diesel engine (1) supplied air mass flow of the second and third lambda value their respective intended target value at least approximately reach.

6. The method according to any one of claims 5, characterized in that the air mass flow determined by the air mass measuring device is used as a controlled variable for the controlled setting of a predeterminable air mass flow setpoint.

7. The method according to claim 5 or 6, characterized in that the total injection quantity comprises a injected in a main injection main injection amount and injected in a post-injection following the main injection after injection quantity.

8. The method according to claim 7, characterized in that the post-injection quantity is used as a manipulated variable for setting the setpoint values for the second and / or the third lambda value.

9. The method according to any one of claims 4 to 8, characterized in that determined in the third operating mode, a deviation from the resulting as a result of pilot control exhaust lambda (λ _A m) and the desired value for the third lambda value and, if necessary, the adaptively variable correction value such is changed that the deviation assumes an at least approximately negligible extent.

10. The method according to claim 4 to 9, characterized in that a motor operating map is provided which has characteristic map areas of predeterminable size, each of which is assigned a correction value.

11. The method according to claim 10, characterized in that the feedforward control for setting the second and / or the third lambda value in an engine operation in a predetermined map range to a correction value, which in connection with a previous regeneration of the nitrogen oxide storage catalyst (6) this Map area has been assigned.

12. The method according to any one of claims 1 to 11, characterized in that in the second operating mode, at least one of the engine operating variables exhaust gas recirculation rate and intake air throttle rate are set as in the immediately preceding third operating mode.

13. The method according to any one of claims 7 to 12, characterized in that in the second operating mode, the main injection amount is set as in the immediately previously set third operating mode.

14. The method according to any one of claims 1 to 13, characterized in that when performing a nitrate regeneration to remove stored nitrogen oxide from the nitrogen oxide storage catalyst (6) in the second operating mode by means of the downstream of the nitrogen oxide storage catalyst (6) Lambda sensor (9) detected exhaust lambda value (λ _Am ) is monitored for falling below a predeterminable limit value out and when falling below the predetermined limit, the operation of the diesel engine (1) is switched back to the first operating mode.

15. The method according to any one of claims 1 to 14, characterized in that when performing a sulfate regeneration to remove stored sulfur oxide from the nitrogen oxide storage catalyst (6) in the second mode of operation by means of the downstream of the nitrogen oxide storage catalyst (6) Lambda sensor (9) detected exhaust lambda value (λ _Am ) is monitored for falling below a predetermined limit and after falling below the predetermined limit under at least approximately maintaining the second lambda value of an uncontrolled with respect to the lambda value of the air-fuel mixture operation of the diesel engine (1 ) is switched to a regulated operation.

16. Diesel engine with a nitrogen oxide storage catalytic converter (6) having exhaust gas purification system (2) and with a control device (17, 18) for carrying out a method according to one of claims 1 to 15, wherein the downstream of the nitrogen oxide storage catalyst (6) in the Emission control system (2) arranged lambda sensor (9) is the only for adjusting the lambda value of the combustion chamber of the diesel engine (1) at least partially burned air-fuel mixture in the exhaust gas purification system (2) provided lambda sensor.

17. Diesel engine according to claim 16, characterized in that in the exhaust gas purification system (2) between the nitrogen oxide storage catalyst (6) and the lambda sensor (9) a particle filter (7) is arranged.