DE102008059698A1 - A method for operating a diesel engine with a nitrogen oxide storage catalyst having emission control system - Google Patents

Abstract

The invention relates to a method for operating a diesel engine (1) with an exhaust gas purification system (2) having a nitrogen oxide storage catalytic converter (6). In the method, a lambda value-containing air-fuel mixture in a combustion chamber of the diesel engine (1) is at least partially burned and thereby resulting exhaust gas to the nitrogen oxide storage catalyst (6). 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) is operated with a set second operating mode in which the air-fuel mixture has a second lambda value of less than one. Immediately before setting the second mode of operation, an operating mode transition phase is entered, in which the diesel engine (1) is operated in a third operating mode, in which a third lambda value is set for the air-fuel mixture, which is lower than in the first operating mode and slightly is above one. According to the invention, in the third operating mode, a controlled operation with respect to the lambda value of the air-fuel mixture of the diesel engine (1) takes place in such a way that by means of a lambda sensor (9) arranged downstream of the nitrogen oxide storage catalytic converter (6) in the exhaust gas purification system (2). an exhaust lambda value ...

Description

The The invention relates to a method for operating a diesel engine with a nitrogen oxide storage catalyst having emission control system according to the preamble of claim 1 and a Diesel engine with a control device for implementation of the procedure.

From the DE 103 49 876 A1 is a generic method for operating a diesel engine with a nitrogen oxide storage catalyst having emission control system 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.

task The invention is a method for operating a diesel engine with a nitrogen oxide storage catalyst having emission control system indicate which is a reliable and reproducible Adjustment of lambda value, especially during execution a regeneration of the nitrogen oxide storage catalyst allows. It is another object of the invention to provide a diesel engine with a a nitrogen oxide storage catalyst having emission control system specify which, in a simple manner, the efficient implementation a regeneration of the nitrogen oxide storage catalyst allows.

These Tasks are performed by a method having the features of the claim 1 and solved by a diesel engine with the features of claim 16.

The inventive method works with a Diesel engine, in its single or multiple combustion chambers a lambda value having air-fuel mixture at least Partially burned and thereby resulting exhaust gas to the nitrogen oxide storage catalyst is supplied. Starting from an operation of the diesel engine with a first mode of operation in which the air-fuel mixture has a first lambda value greater than one, is for a regeneration of the nitrogen oxide storage catalyst set for the diesel engine an operation with a second operating mode, in which the air-fuel mixture has a second lambda value of less than one. Immediately before setting the second mode of operation becomes an operation mode transition phase inserted, in which the diesel engine in a third mode of operation is operated, wherein for the air-fuel mixture a third lambda value is set, which is lower than in the first operating mode is and is slightly above one. According to the invention in the third operating mode with respect to the lambda value of the air-fuel mixture controlled operation of the diesel engine such that by means of a downstream arranged by the nitrogen oxide storage catalyst in the emission control system Lambda sensor detected an exhaust gas lambda value and as a controlled variable for the regulated setting of a predefinable setpoint for the third lambda value is used.

Of the Reference value for the third lambda value in the inventively provided Operating mode transition phase is typically within a range from 1.01 to 1.10, preferably 1.02 to 1.06, and more preferably at about 1.03, and thus relatively close to that at the actual Regeneration set second lambda value of about 0.95. In order to is a setting in the operation mode transition phase from the operation of the diesel engine determining engine operating variables values possible, as at least approximate also in the immediately following operating phase in the second operating mode for one with a rich air-fuel ratio operated diesel engine needed. The inventively carried out Operating mode transition phase thus serves a stable Adjustment of engine operating parameters required for rich engine operation, however, still a weak lean engine operation takes place.

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 from the third mode of operation to the second mode of operation switched.

Especially is due to in the weak lean operating mode transition phase in third operating mode provided according to the invention lambda-controlled engine operation a particularly reliable and allows accurate adjustment of engine operation. there the insight is exploited that in the operating mode transition phase the used for lambda control, downstream of the nitrogen oxide storage catalyst arranged lambda sensor a the lambda value of the diesel engine burned air-fuel mixture very accurately corresponding reading supplies, since in the previous first operating mode also a lean Air-fuel mixture was set. Because the first operating mode over longer time, typically in the range of 10 seconds was set to several minutes, are the exhaust lambda value influencing Decayed effects of the nitrogen oxide storage catalyst.

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 reduced by the present in the exhaust reducing agents (H ₂ , CO and HC) on the catalytic converter on the nitrogen oxide storage catalytically active coating component to harmless nitrogen (N ₂ ) and ammonia (NH ₃ ).

Under a lambda value is here as usual the stoichiometric ratio from the content of the oxygen and the content of fuel or at reducing components in the engine supplied Air-fuel mixture or in the exhaust gas understood. At a lambda value greater than one is a lean air-fuel mixture or exhaust gas with an excess of oxygen before, while at a lambda value of less than one, a rich air-fuel mixture Exhaust gas is present with an excess of reducing agents.

typically, Air and fuel are the combustion chambers of the preferably operating on the 4-stroke process, multi-cylinder running Diesel engines supplied on separate ways and burn in the combustion chambers with release of mechanical work. The combustion can be more or less complete depending on the combustion process run. To remove pollutants from the exhaust gas, the planned emission control system next to the nitrogen oxide storage catalyst further filter-effective and / or catalytically active components exhibit. Furthermore, the emission control system has sensors for detection of exhaust gas parameters such as temperature and composition on.

Of the Lambda value of the combustion exhaust gas is off immediately after discharge the combustion chamber or combustion chambers equal to the air-fuel mixture. By the action of an exhaust gas purification component, in particular by Conversion, storage and / or release of exhaust components, However, a change in the lambda value can occur. Furthermore, a change in the lambda value by Supply of air or fuel from off-engine sources to the exhaust be provided. If necessary for the sake of clarity, will be described below explicitly spoken by an exhaust lambda value. The lambda value of the Combustion chambers of the engine supplied air-fuel mixture is, where the clarity is useful, hereinafter also as engine lambda value designated. Although not necessarily limited to is assumed below that in the inventive Method is a change in the lambda value of the nitrogen oxide storage catalyst supplied exhaust exclusively or almost exclusively caused by a change in the engine lambda value becomes.

There the nitrogen oxide storage catalyst typically has a storage effect with respect to oxygen and / or reducing agents are in particular when changing the engine lambda value of greater as one to less than one (or vice versa) temporarily downstream of the nitrogen oxide storage catalytic converter deviating from the engine lambda value Exhaust lambda values before. For their detection is a so-called lambda sensor provided in a familiar to the expert Shape, as a binary or continuous lambda probe or Also designed as a NOx sensor with lambda sensitivity can be.

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 sticko xid storage catalytic converter Exhaust gas lambda values recorded continuously or in quick succession, and fed back as a controlled 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 Embodiment of the method takes place in the second operating mode in Reference to the lambda value of the air-fuel ratio an unregulated operation of the diesel engine. This takes into account the fact worn that during the actual regeneration of the Nitrogen oxide storage catalyst during the second operating mode from this reducing element contained in the exhaust gas to the NOx or SOx reduction and thus removed from the exhaust gas. For this reason, from the downstream arranged lambda sensor detected an exhaust gas lambda value, at least as long as not with the Engine lambda value coincides as a noticeable consumption the reducing exhaust gas components takes place. As a result of this persists the exhaust gas lambda value is approximately at the stoichiometric Value of one as long as the distance is stored in particular Nitrogen oxides is not complete, although the set Engine lambda value is lower. The downstream of the nitrogen oxide storage catalyst Measured exhaust lambda value in this case is not considered a controlled variable used for setting the engine lambda value.

In Another embodiment of the method is for the second Lambda value a setpoint given and in the second and in the third Operating mode is a pilot control of the lambda value of the air-fuel mixture influencing engine operating variable as manipulated variable in such a way that the pilot control activates the second and third lambda values their respective intended setpoint at least approximately to reach.

Preferably In the second and third operating modes, a plurality of Motor operating variables pre-set, wherein the pre-control values preferably held retrievable in a memory are. The pilot-operated motor operating variables not necessarily have all as manipulated variables in the regulatory sense of the third operating mode performed lambda control be effective.

The retrieved and adjusted pre-control values are preferred to respective operating point of the diesel engine with respect to load and Assigned speed. In particular, it is provided already in the third Operating mode with low lean air-fuel ratio essential determining fuel combustion in the combustion chamber Set engine operating variables to values such as they are required for rich operation in the second operating mode are. In this way, the combustion process is already in the operation mode transition phase according to the requirements for the at least partially Combustion of a rich air-fuel mixture in the following second operating mode set. The transition to the second mode of operation accordingly only requires minor changes and thus can be reliable and done precisely.

In Another embodiment of the method is the feedforward control as adaptive Pilot control designed such that an adaptively changeable, the manipulated variable influencing correction value provided is. The correction value may be multiplicative or additive to the Manipulated variable for setting the second and / or be formed of the third lambda value acting correction value. The correction value is thus as an adaptively changeable learning value trained on the basis of established control deviations as needed is adjusted so that the feedforward offset the control deviation can. Due to the adaptive feedforward control can especially temporally small variable disturbances be effectively balanced, as a regulator intervention to compensate minimizes the interference and thus a Balancing very quickly and with the least transients can be done.

It is provided that the possibly previously learned correction value at a transition from a lambda controlled operation in third mode of operation mode transition phase on the immediately following engine operation in the second operating mode is taken over with pure pre-tax operation. As a result of adaptive pilot control can the relatively small lambda change from about 1.03 to 0.95 can be performed very precisely. On the other hand would be a direct jump waiving the inventively executed Operating mode transition phase of typically comparatively high first lambda value on the fat second lambda value unequal more susceptible to errors and inaccurate.

In a further embodiment 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 one working cycle is carried out in such a way that the diesel engine is supplied to 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 values at least approximately reach their respective intended setpoint. 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 Another embodiment of the method comprises the total injection quantity a main injection amount injected in a main injection, and one in a post-injection following the main injection injected post injection quantity. The main injection amount is preferably in a crank angle range of about 10 degrees before top dead center sprayed into the combustion chamber to about 10 degrees after top dead center, while the post-injection amount is preferably in a crank angle range from about 15 degrees to about 45 degrees after top dead center in the power stroke is injected into the combustion chamber. Due to the post-injection is on Effectively a the output or torque output of the Diesel engines little or no influence enrichment or Enrichment of the air-fuel mixture allows. Prefers is one of the main injection to improve the combustion process temporally upstream pilot injection provided in the compression stroke. Particularly preferred are two pilot injections at a short distance carried out. The corresponding pilot injection quantity is preferably in a crank angle range of 25 degrees to 15 degrees injected at top dead center.

in the Related to the distribution of the total injection quantity to at least a main injection and a post-injection is special preferred, if in a further embodiment of the method, the Nacheinspritzmenge as manipulated variable for setting the setpoints for the second and / or third lambda value is used. Prefers remain, except for an increased post injection quantity, in the transition from the third mode of operation to the second Operating mode all or at least most other engine operating variables unchanged. The mixture enrichment at the transition from the third lambda value to the second lambda value is thus preferred exclusively by an increase in the post-injection quantity accomplished.

In Further embodiment of the method is in the third mode of operation a deviation from that resulting from the pilot control Exhaust lambda value and the setpoint for the third lambda value determined and, if necessary, the adaptively changeable Correction value changed such that the deviation at least approximately negligible extent. Learning or adaptation of the correction value thus takes place during the operation mode transition phase during operation of the diesel engine in the third mode of operation, with a newly learned correction value is written in a readable memory and at the next Setting the third operating mode is read out again. Prefers are predetermined release conditions, such as falling below a predefinable maximum load and / or a maximum value for Speed fluctuations and an absence of a pushing operation, intended for carrying out an adaptation. If the release conditions are not available, then the adaptation or the learning of the correction value is not performed or aborted. In this case, the third lambda value is unregulated, but pre-controlled adjusted on the basis of the since then valid correction value. The takeover a newly learned correction value is preferably omitted when the deviation from the correction value valid since then can be specified Minimum value or exceeds a predefinable maximum. These measures will be too frequent or erroneous learning of the correction value prevented.

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. Preferably, the engine operating map is 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 during engine operation in a predetermined map range 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. In particular, in the case of coarse rasterization, it is preferable to perform an interpolation between adjacently stored correction values and the interpolation value use.

In Further embodiment of the method are in the second mode of operation at least one of the engine operating variables exhaust gas recirculation rate and intake throttle rate as set immediately before third operating mode set. This way is a special one reliable and smooth transition from the third Operating mode to the second operating mode allows. Preference is given to other engine operating parameters, such as Injection time and injection quantity of main and / or pilot injection unchanged.

In Further embodiment of the method is in a implementation a nitrate regeneration to remove stored nitric oxide from the nitrogen oxide storage catalyst in the second operating mode of arranged by means of the downstream of the nitrogen oxide storage catalyst Lambda sensor detected exhaust lambda value to fall below one Predefined limit value out and undershot the predetermined limit, the operation of the diesel engine on the switched back first operating mode. The downstream of the Nitrogen storage catalytic converter arranged lambda sensor is thus used for end-detection of nitrate regeneration, being the authoritative limit preferably selected a lambda value in the range of 1.00 to 0.98 becomes. This can with sufficient certainty an undesirable Breaks off reducing exhaust gas constituents such as carbon monoxide or hydrocarbon avoided or at least minimized.

In Further embodiment of the method is in the implementation Sulfate regeneration to remove stored sulfur oxide from the nitrogen oxide storage catalyst in the second operating mode of arranged by means of the downstream of the nitrogen oxide storage catalyst Lambda sensor detected exhaust lambda value to fall below one Predefined limit and monitored after falling below the predeterminable limit under at least approximate Maintaining the second lambda value of one in relation to the Lambda value of the air-fuel mixture uncontrolled operation of the Diesel engine switched to a regulated operation.

There typically stored in the nitrogen oxide storage catalyst sulfur oxides are significantly more strongly bound than stored nitrogen oxides, are compared to nitrate regeneration in a sulfate regeneration both higher temperatures of more than 550 ° C as well as a longer-lasting rich operation required. The second mode of operation is therefore in sulfate regeneration preferably over a period of 10 seconds to 30 seconds maintained unchanged. Already after a fraction However, this period is the consumption of reducing exhaust gas components dropped sharply in the nitrogen oxide storage catalytic converter and that of the lambda sensor detected exhaust lambda value is at least approximately equal to Motor lambda value. Is the approach to a predefinable Measured, can therefore again using the of Lambda sensor delivered a lambda-controlled operation be made of the diesel engine. This improves the accuracy the setting of the for efficient sulfate regeneration required rich exhaust lambda value.

The The problem underlying the invention is also solved by a diesel engine with a nitrogen oxide storage catalyst 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 catalyst in the emission control system arranged lambda sensor is the only one to adjust the lambda value of at least partially burned in the combustion chamber of the diesel engine Air-fuel mixture provided in the exhaust system lambda sensor is. Since a lambda adjustment solely by means of the downstream of the nitrogen oxide storage catalyst allows arranged in the emission control system lambda sensor is, there is no need for another, especially upstream the nitrogen oxide storage catalytic converter arranged lambda sensor. Thus, can a considerable cost saving can be achieved.

In Embodiment of the invention is between the nitrogen oxide storage catalyst and the lambda sensor a particulate filter in the emission control system arranged. Thus, the lambda sensor is downstream of the particulate filter arranged, what additional control or monitoring a particulate filter regeneration by Rußabbrand allows. In addition, the risk of fouling of the lambda sensor is avoided and thus the reliability and accuracy the lambda measurement improved.

advantageous Embodiments of the invention are in the drawings illustrated and described below. Here are the mentioned above and to be explained below Features not only in the specified feature combination, but also usable in other combinations or in isolation, without to leave the scope of the present invention.

there demonstrate:

1 a schematic representation of an advantageous embodiment of a system of Diesel engine and emission control system for carrying out the method according to the invention,

2 a diagram for the time course of the lambda value λ _M for the burned in the diesel engine air-fuel mixture and the exhaust gas downstream of the nitrogen oxide storage catalyst measured lambda value λ _Am in connection with the implementation of a nitrate regeneration and

3 a diagram for the time course of the lambda value λ _M for the burned in the diesel engine air-fuel mixture and the exhaust gas downstream of the nitrogen oxide storage catalyst measured lambda value λ _Am in connection with the implementation of a sulfate regeneration

1 schematically shows an advantageous embodiment of a system of internal combustion engine 1 and emission control system 2 for a motor vehicle, not shown, for carrying out the method according to the invention. The internal combustion engine 1 is preferably designed as a direct injection lean running, in particular as air-compressing internal combustion engine according to the reciprocating principle, hereinafter referred to simplified as a diesel engine executed. 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 a combustion chamber with one or two intake and exhaust valves, one glow plug and a fuel injector and one or more intake ports for the combustion air assigned, which in detail not is shown in more detail. The fuel injectors are included 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, of the diesel engine 1 supplied air mass flow can be throttled to an adjustable level. The combustion air is by means of an exhaust gas turbocharger 15 compressed and a charge air cooler 16 supplied for cooling. The exhaust gas turbocharger is preferably designed as a so-called VTG loader or as a wastegate loader with adjustable boost pressure. In the combustion chambers of the cylinders of the diesel engine 1 generated exhaust gas is via an exhaust pipe 4 derived. In this case, the combustion air via an exhaust gas recirculation line 13 Adds exhaust gas and thus to the diesel engine 1 to be led back. The proportion of recirculated exhaust gas (EGR rate) can via an EGR valve 14 be set. Preferably, this becomes the diesel engine 1 recycled exhaust gas cooled by means of an EGR cooler, not shown, with an optionally adjustable bypass can be provided for the EGR cooler. As a result, the combustion air can be optionally mixed with cooled or hot exhaust gas. Non-recirculated exhaust gas is passed through the exhaust gas turbocharger 15 the emission control system 2 fed. With the described embodiment, different values for the essential engine operating parameters such. As air mass flow, injection time, pressure and time point of multiple fuel injections, EGR rate, charge air pressure and thus different combustion processes are shown. In particular, the diesel engine 1 with an air-fuel mixture with varying lambda values, hereinafter referred to as engine lambda λ _M , operated. Engine lambda values λ _M greater than one correspond to a lean and engine lambda values λ _M less than one for a rich air-fuel mixture or operation of the diesel engine 1 , Accordingly, a lean engine operation results in a lean exhaust gas with an excess of oxidizing constituents such as, in particular, oxygen and in 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 λ _A.

A preferred embodiment of the diesel engine 1 associated emission control system 2 includes in the flow direction of the exhaust gas seen in this order an oxidation catalyst 5 , a nitrogen oxide storage catalyst 6 , a particle filter 7 and an SCR catalyst 8th , As a particle filter 7 For example, a so-called wallflow filter based on SiC-cordierite or aluminum titanate is preferably used. The particle filter 7 However, it can also be designed as a sintered metal filter or as a filter unit with an open filter structure. The downstream of the nitrogen oxide storage catalyst 6 arranged SCR catalyst 8th has the property of being able to store NH ₃ at reducing conditions and to be able to use NH ₃ fed in oxidizing conditions and possibly supplied NH ₃ as a reaction partner in a selective catalytic reduction reaction under nitrogen formation for the chemical reduction of NO x.

The latter property is used in particular to the SCR catalyst 8th Trains led NOx to harm. The SCR catalyst 8th gets NOx in the arrangement 1 for example due to increasing NOx slip as a result of the decreasing NOx absorption capacity of the nitrogen oxide storage catalytic converter in the course of the NOx storage 6 in lean operation of the diesel engine 1 , The SCR catalyst 8th is preferably designed 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 are preferred 5 . 7 . 8th designed as honeycomb monoliths, which are crossed by catalytically coated channels through which the supplied exhaust gas can flow.

Input side of the oxidation catalyst 5 For example, a fuel addition unit can 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 addition unit is primarily associated with active regeneration of the particulate filter 7 activated by thermal Rußabbrand or for heating a downstream exhaust gas purification component. However, it is preferable to dispense with the fuel adding unit and make an enrichment of the oxidizable component exhaust gas by a rich air-fuel mixture operation. Below is assumed from the latter variant.

In the exhaust aftertreatment device 2 Various temperature and exhaust gas sensors are provided to detect exhaust gas and component temperatures as well as concentrations of important exhaust gas constituents. Exemplary are in 1 on the input side of the nitrogen oxide storage catalytic converter 6 as well as the output side of the particulate filter 7 one temperature sensor each 10 . 11 in the emission control system 2 arranged. On the output side of the SCR catalytic converter 8th is a sensitive to NOx and / or NH ₃ gas sensor 12 intended. To determine the loading of the particulate filter 7 with soot and / or ash, it is also preferred, inlet and outlet side of the particulate filter 7 Provide pressure sensors or a differential pressure sensor, which in 1 not shown separately. Furthermore, downstream of the nitrogen oxide storage catalyst 6 a lambda sensor 9 arranged to detect the exhaust gas lambda value λ _A present there. For precise characterization, the following about the lambda sensor 9 determined measured value for the exhaust gas lambda value downstream of the nitrogen oxide storage catalyst as exhaust lambda value λ _Am denoted. The lambda sensor 9 can, as shown on the output side of the nitrogen oxide storage catalyst 6 , but also on the output side of the particulate filter 7 ie between the particle filter 7 and the SCR catalyst 8th be arranged. By means of these and possibly other sensors, the operating state of the emission control system 2 comprehensively detected and the operation of the diesel engine 1 be adjusted if necessary. It is presently preferred that except the lambda sensor 9 no further lambda sensor in the emission control system 2 is available. In particular, it is provided according to the invention that the lambda sensor 9 the only lambda sensor of the emission control system 2 is to adjust the lambda value of the diesel engine 1 at least partially burned air-fuel mixture is used.

For setting or detecting the engine operation is an electronic engine control unit 17 intended. The engine control unit 17 receives on the one hand information about significant engine operating variables such. As speed, engine load, temperatures, pressures from the corresponding sensors or sensors and on the other hand control signals as adjustment variables to actuators such. B. to the EGR valve 14 , the 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 being able to control the fuel injectors to perform multiple injections and optionally adjust the fuel injection pressure as needed. Furthermore, the engine control unit 17 set up for carrying out control and regulating operations, with which motor operating variables are regulated or controlled. For this purpose, the engine control unit 17 rely on stored maps or calculation or control or control routines. For this purpose provided subsystems, such as computers, memory or input-output units and the like are not shown separately.

In an analogous manner is for the detection and adjustment of operating and state variables of the exhaust gas aftertreatment device 2 a second controller 18 intended. The engine control unit 17 and the second controller 18 are by means of a bidirectional data line 19 connected with 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 devices 17 . 18 can also be combined in a single integral Meßwerterfassungs- and control unit.

The nitrogen oxide storage catalyst 6 has the ability to produce NOx and SOx present in the exhaust gas under oxidizing conditions, mainly by chemical bonding as nitrate or sulfate the coating material to be stored. In the usual 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 NOx removal function of the nitrogen oxide storage catalytic converter, recurring regenerations are required in which the stored NOx or SOx 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 occur at intervals of 30 seconds to a few minutes, while sulphate regenerations are preferably carried out in relation to a specific journey after traveling about 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, the diesel engine according to the invention 1 supplied with a rich air-fuel mixture and operated in an operating mode with an engine lambda value λ _M 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 mode of operation is the normal lean operation of the diesel engine 1 set anyway. The setting of the second operating mode with an engine lambda value λ _M of less than one for the supply of the nitrogen oxide storage catalytic converter 6 However, with reducing exhaust gas with an exhaust lambda value λ _A of less than one requires special measures, in particular with respect to a reliable and precise adjustment of the engine lambda value λ _M , which will be explained in more detail below. It is initially under additional reference to 2 on the procedure according to the invention in the implementation of a nitrate regeneration received.

In the diagram of 2 schematically is a preferred time course of the engine lambda value λ _M and from the downstream of the nitrogen oxide storage catalytic converter 6 arranged lambda sensor 9 detected exhaust lambda value λ _Am in the various operating modes of the diesel engine 1 shown. The course of the engine lambda value λ _M is indicated by the solid line, which by means of the lambda sensor 9 detected exhaust lambda value λ _{Am represented} by the dotted line. It is assumed that upstream of the nitrogen oxide storage catalyst 6 no components in the exhaust gas purification system that significantly influence the exhaust gas lambda value 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, first in 2 first operating mode set. The time span with active first operating mode is in 2 denoted by reference numeral I. When the first operating mode is active, the nitrogen oxide storage catalytic converter becomes 6 a lean exhaust gas supplied with a high oxygen content. This is provided by the diesel engine operated with an engine lambda value λ _M of, for example, λ _M = 3 1 delivered. The diesel engine 1 is operated in this case with respect 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 requested power and the operating point in the load-speed map map-controlled.

From the diesel engine 1 emitted and contained in the exhaust NOx are largely in the catalyst material of the nitrogen oxide storage catalyst 6 , Preferably in the form of nitrates, stored and so removed from the exhaust. Optionally by the nitrogen oxide storage catalyst 6 Occurring slip of NOx is due to reduction in the downstream SCR catalyst 8th at least partially harmless.

Will with increasing saturation of the nitrogen oxide storage catalyst 6 For example, if a nitrogen oxide slip increased to an unacceptable level on the basis of sensors or models, or if a predefinable nitrogen oxide saturation threshold has been 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, then at the time t0 the operation of the diesel engine 1 first to the third operating mode with a slightly above 1.0 Mo Tor lambda λ _M , about λ _M = 1.03, converted. The time span with active third operating mode is in 2 designated by the reference III. 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 diesel engine 1 supplied air mass flow is throttled to a nominal setpoint. This is an independent control circuit in the engine control unit 17 implemented such that the signal supplied by the air mass meter for the air mass flow is used as a controlled variable and a control variable generated by the corresponding controller to the throttle element in the air supply line 3 acts. 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 the combustion, etc. set to the values provided for a rich engine operation maps controlled. 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 time span with active second operating mode is in 2 denoted by reference number II.

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

That of the lambda sensor 9 provided measuring signal is present according to a stored characteristic of the second control unit 18 converted into a lambda value (exhaust lambda value λ _Am ) and to the engine control unit 17 transmitted. From one in the engine control unit 17 lambda controller implemented the so measured exhaust gas lambda value is used _Am λ as controlled variable and compared with the desired value of λ for the facts in the third operating mode, engine lambda value _M. 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 _Am 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 to compensate for additional disturbances that occur. 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 optionally readjusted 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.

Is the Einregelvorgang for the lambda value of the third mode of operation has occurred, which is considered, for example, considered given when the Re gelabweichungen 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 is for the diesel engine 1 a rich engine lambda λ _M of about 0.95 set and the diesel engine 1 switched to one with respect to the engine lambda value λ _M unregulated operation. 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 required for rich operation of the second operating mode and already set in the previous third operating mode.

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

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 lies. 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, gas running times in the air path and / or in the emission control system 2 in the evaluation of the measuring signals of the air mass meter and / or the lambda probe 9 to take into account. By 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 be compensated. For this purpose, a model may be provided which simulates 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 signal model to dynamically correct the feedforward control of the total injection quantity or Nacheinspritzmenge.

The following will discuss preferred approaches to performing sulfate regeneration of the nitrogen oxide storage catalyst 6 received. In doing so, with reference to the in 3 illustrated timing diagram specifically discusses the differences compared to the above-described approach in the implementation of nitrate regeneration. In the time diagram of 3 are time profiles of the engine lambda value λ _M and the measured in the exhaust gas downstream of the nitrogen oxide storage catalyst exhaust lambda value λ _Am analogous to the diagram of 2 shown.

A sulfate regeneration of the nitrogen oxide storage catalyst 6 is carried out when committed is set that an impermissibly 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 an elevated temperature of about 650 ° C of the exhaust gas and the nitrogen oxide storage catalyst 6 and a preferably set higher enrichment for engine lambda values λ _M of about 0.8 to 0.9. In addition, the duration of enrichment is increased compared to a nitrate regeneration. Another difference is that preferably at elevated temperature successively a multiple change of operating phases with a rich and a lean engine lambda values λ _M occurs. As a result, a decomposition of the relatively stable sulfates is possible. Preferably, a sulfate regeneration is performed in temporal relation with a thermal particle filter regeneration by Rußabbrand. As a result, 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. By the early post-injection in a crank angle range of about 10 degrees to about 40 degrees after the top dead center in the power stroke, the exhaust 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 by oxidation contained in the exhaust residual oxygen in the oxidation catalyst 5 and / or in the nitrogen oxide storage catalyst 6 burn, causing a Abgasaufheizung or Katalysatoraufheizung is effected.

With for performing a sulphate regeneration characteristic predetermined pre-controlled engine operating parameters a change from the first operating mode takes place to the third mode of operation analogous to that in connection with a Nitrate regeneration explained above. Also analogously, an adaptation of the correction value takes place at the set third operating mode of the operating mode transition phase. However, there may be different sets of correction values for the implementation of nitrate regeneration and for the implementation of sulfate regeneration be provided.

Analogous to nitrate regeneration has in a sulfate regeneration after setting a rich engine lambda value λ _M in the second operating mode, the exhaust gas downstream of the nitrogen oxide storage catalyst 6 initially no reducing components on and off the lambda sensor 9 First, an exhaust lambda value λ _Am of 1.0 is measured. If stored NOx and SOx are largely reduced, so reducing agents contained in the rich exhaust gas break through increasingly and the exhaust lambda value λ _Am decreases and approaches the upstream of the nitrogen oxide storage catalytic converter 6 existing engine lambda value λ _M. 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 λ _M is thus divided into two subsections. In the first, in 3 designated by the reference numeral IIa subsection is the diesel engine 1 operated in a pre-controlled operating mode with respect to the rich engine lambda value λ _M unregulated. In IIb designated second subsection is the diesel engine 1 operated in a regulated with respect to the rich engine lambda value λ _M operating mode, wherein the pilot control values for the engine operating parameters from the first subsection IIa, and the third operating mode are adopted.

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

After completion of the preferably predetermined number of repetitions, the measures for achieving an increased exhaust gas or catalyst temperature are terminated and in the normal operation of the diesel engine 1 with repeated nitrate regeneration.

To increase the accuracy of the lambda control in the second section IIb of the operation in the second operating mode, it is preferably provided that the stored characteristic of the Lamb dasensors 9 with respect to 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 becomes more pronounced during extended periods of rich operation 9 can be falsified. In this way, a regulation of a wrong engine lambda value λ _{M is} reliably avoided.

Overall, due to the inventively provided in the implementation of a nitrate or sulfate regeneration lambda control using the downstream of the nitrogen oxide storage catalyst 6 arranged lambda sensor 9 a reliable and accurate lambda adjustment 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 operation, for example, due to unfavorable driving conditions or due to a failure of the lambda sensor 9 not possible.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 10349876 A1 [0002]

Claims (17)

Method for operating a diesel engine ( 1 ) with a nitrogen oxide storage catalyst ( 6 ) having exhaust gas purification system ( 2 ), in which a lambda value having air-fuel mixture in a combustion chamber of the diesel engine ( 1 ) is at least partially burned while resulting exhaust gas 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 regeneration of the nitrogen oxide storage catalytic converter ( 6 ) for the diesel engine ( 1 ) an operation is set with a second operating mode, wherein 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 in which a third lambda value is set for the air-fuel mixture, which is lower than in the first operating mode and slightly above one, characterized in that in the third operating mode, a lambda value of the air Fuel-mixture controlled operation of the diesel engine ( 1 ) is carried out in such a way that by means of a downstream of the nitrogen oxide storage catalyst ( 6 ) in the emission control system ( 2 ) arranged lambda sensor ( 9 ) an exhaust gas lambda value (λ _Am ) is detected and used as a controlled variable for the regulated setting of a predefinable setpoint value for the third lambda value. A method according to claim 1, characterized in that in the second operating mode with respect to the lambda value of the air-fuel ratio, an unregulated operation of the diesel engine ( 1 ) he follows. Method according to claim 1 or 2, characterized that a setpoint is specified for the second lambda value is and in the second and in the third operating mode, a feedforward control a the lambda value of the air-fuel mixture influencing Motor operating variable as manipulated variable such that by the pilot control of the second and the third Lambda value their respective intended target value at least approximately to reach. Method according to claim 3, characterized that the feedforward control designed as an adaptive feedforward control is that an adaptively changeable, the manipulated variable is provided influencing correction value. Method according to 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 ) fuel to be injected is carried out in such a way that, in accordance with a determination of an air mass measuring device, for the at least partial combustion of the air-fuel mixture, the diesel engine ( 1 ) supplied air mass flow of the second and the third lambda value their respective intended target value at least approximately reach. Method according to one of claims 5, characterized characterized in that the determined by the air mass measuring device Air mass flow as a controlled variable to the regulated Setting a predeterminable air mass flow setpoint used becomes. Method according to claim 5 or 6, characterized the total injection amount is a main injection amount injected in a main injection and one in a post-injection following the main injection includes injected injection quantity. Method according to claim 7, characterized in that that the Nacheinspritzmenge as a manipulated variable for Setting the setpoints for the second and / or the third lambda value is used. Method according to one of Claims 4 to 8, characterized in that, in the third operating mode, a deviation from the exhaust gas lambda value (λ _Am ) resulting from the precontrol and the setpoint value for the third lambda value is determined and, if necessary, the adaptively variable correction value is changed in such a way, that the deviation assumes an at least approximately negligible extent. Method according to Claims 4 to 9, characterized a motor operating map is provided, which map areas predeterminable size, each having a Correction value is assigned. A 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 ) has been assigned to this map area. Method according to 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 throttle rate as set immediately before third operating mode can be set. Method according to one of claims 7 to 12, characterized in that in the second operating mode, the main injection quantity as set in the immediately before set third operating mode becomes. Method according to 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 catalytic converter ( 6 ) arranged lambda sensor ( 9 ) detected exhaust gas lambda value (λ _Am ) is monitored to below a predefinable limit value out and falls below the predetermined limit, the operation of the diesel engine ( 1 ) is switched back to the first operating mode. Method according to one of claims 1 to 14, characterized in that when performing a sulfate regeneration for the removal of stored sulfur oxide from the nitrogen oxide storage catalyst ( 6 ) in the second operating mode by means of the downstream of the nitrogen oxide storage catalytic converter ( 6 ) arranged lambda sensor ( 9 ) Detected exhaust gas lambda value (λ _Am) is monitored for falling short of a predeterminable limit value, and (of an uncontrolled with respect to the lambda value of the air-fuel mixture operation of the diesel engine falls below the predeterminable threshold value while at least approximately maintaining the second lambda value 1 ) is switched to a regulated operation. 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 ) the only one for adjusting the lambda value of the in 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 is. 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.