DE102006007122A1 - Operating process for internal combustion engine involves reporting suitable combinations of engine operating values for preset nitrogen oxide emission value - Google Patents

Abstract

The operating process is for an internal combustion engine (1) with air induction line (3) and exhaust line (4) and its exhaust gas treatment device (2) with an oxidation catalytic converter (5). Suitable combinations of engine operating values for a preset nitrogen oxide initial emission target value, of which those are selected for which an extreme value for a preset state value of the engine exists.

Description

The Invention relates to a method for operating an internal combustion engine, in particular a motor vehicle and one to the internal combustion engine connected exhaust gas aftertreatment device, wherein the internal combustion engine an exhaust gas with an adjustable NOx and particulate emissions level generates and the exhaust gas aftertreatment device, the NOx content of the exhaust gas reduced to a NOx tailpipe emission value.

From the DE 196 29 163 C1 A method is known for operating an automotive internal combustion engine with an exhaust aftertreatment device connected thereto for reducing nitrogen oxides (NOx), in which the internal combustion engine is operated with a late fuel injection start, if the temperature of the exhaust gas after-treatment device is outside a predeterminable range, in which the exhaust aftertreatment device is a low NOx -Umsatzvermögen has. Since at a late fuel injection start the engine generates exhaust gas with a low NOx emission level, for example when the engine is warming up, if the efficiency of the exhaust aftertreatment device is not or only to a limited extent due to temperature, the corresponding motor vehicle can still have low NOx tailpipe emission values operate. However, the operation of the late-injection-fuel internal combustion engine is disadvantageous in other respects, for example, in terms of fuel consumption.

In contrast, is It is an object of the invention to provide a method for operating an internal combustion engine and to indicate an exhaust aftertreatment device connected thereto, which low exhaust emissions and at the same time as possible advantageous engine operation allows.

These The object is achieved by a method having the features of the claim 1 solved.

According to the invention is for a predeterminable NOx raw emission target value an amount of this NOx raw emission target value associated n-tuples with values for n predetermined, adjustable and the NOx raw emission value and / or the particulate matter emission value determining influencing engine operating variables. For one respective n-tuple is used in a further process step associated Value for at least one predetermined, of the n engine operating variables of n-tuple dependent State variable of the internal combustion engine determines and from the set of determined n-tuples that n-tuple selected, which is for the at least one predetermined state variable gives an extreme value. In In a further method step, the values for the n Motor operating variables of the selected n-tuple set. In this way, the operation of the internal combustion engine and the Exhaust after-treatment device optimally matched.

As usual will under a raw emission value, the content of a given component of the exhaust gas, For example, NOx, in the combustion exhaust gas emitted from the engine before the implementation an exhaust aftertreatment measure or before supplying the Exhaust gas for exhaust aftertreatment device understood. In contrast, there the tailpipe emission value is the content of the relevant pollutant in the exhaust after execution the exhaust aftertreatment measure or after leaving the exhaust aftertreatment device. the Accordingly, a target value to be aimed at is under the NOx raw emission target value for the NOx raw emissions to understand. The emission values can thereby can be specified arbitrarily. Common are on the route or the work done by the engine related pollutant masses. For particles also comes their number into consideration.

The Raw emissions can in an internal combustion engine with a given configuration in general influenced, at least to a certain extent, by changing adjustable engine operating variables become. These are among those adjustable engine operating variables to understand the engine operating state determining quantities, which at least can be set freely selectable within certain limits. The Setting limits can be conditioned or predetermined in various ways. Usually Smooth running, driveability, noise, wear and the like these limits. However, it can also be physically predetermined Limits, for example due to component properties like a Pump performance, heat dissipation and the like act. After all can the setting limits of adjustable motor operating variables also through Requirements of the driver of the corresponding motor vehicle specified be. As an example, here the amount of injected into the internal combustion engine Called fuel, which are indeed changed within certain limits can, without the driver's desired Power development of the engine undesirable to affect however, it can not be arbitrarily reduced.

According to the invention, such adjustable engine operating variables are selectively selected which influence the NOx and / or the particulate matter emission value of the internal combustion engine. The corresponding dependence of the raw emission values of The values of the selected adjustable engine operating variables are preferably stored in the form of tables, characteristic diagrams or functional dependencies in a memory or are available in another way. Therefore, at least a single combination of values, but usually several value combinations of these engine operating variables can be assigned to a specific, predetermined NOx raw emission target value. In this sense, an n-tuple is understood here as meaning precisely such a combination of n values for the n selected engine operating variables. In the simplest case, n may also be given by the integer one, so that a corresponding tuple contains only a single value for a single selected adjustable engine operating variable. Preferably, however, more than just an adjustable engine operating variable is selected. In particular, n such engine operating variables are selected, which have a marked influence on the NOx and / or particulate emissions of the internal combustion engine and combined to form an n-tuple.

It is provided, at least a predetermined state variable of the internal combustion engine in terms of an advantageous engine operating condition and taking into account the predetermined or currently specified NOx emission target value to optimize. Here is under a state variable of the engine here a size understood, which itself can only be influenced indirectly. As an an example can be called here the engine temperature. According to the invention is a such state variable is selected, which depends on the above-mentioned engine operating variables combined into n-tuples, or influenced by them.

to Optimization of the engine operation according to the invention any determined n-tuple of motor operating variables defined value for the at least one selected State variable assigned. This is preferably carried out analogously to the assignment of the raw emission value to an n-tuple also about characteristics or fields, tables or the like. The optimization itself takes place according to the invention by that one n-tuple selected will, for which for the at least one selected state variable is an extreme value results. The values for the n Motor operating variables of the selected in such a way n-tuples are then discontinued.

On This way is thus achieved on the one hand, that the internal combustion engine generates an exhaust gas with the predetermined NOx raw emission target value. On the other hand, it is achieved that the selected state variable of the internal combustion engine takes an extreme value, which is a maximum value or can be a minimum value. Thus, an overall system is included an internal combustion engine and an exhaust aftertreatment device optimized for its operation. This results in benefits across from an independent one Optimization of the operation of the individual system components, since their reciprocal Be better taken into account can.

In Embodiment of the method include the NOx raw emission value and / or the n motor operating variables influencing the particulate matter emission value Exhaust gas recirculation rate of Internal combustion engine and / or an injection parameter of a fuel injection in a combustion chamber of the internal combustion engine. It is under the Exhaust gas recirculation rate as usual the proportion the recirculated to the fresh air side of the engine exhaust gas in the total amount of the internal combustion engine for fuel combustion supplied Understood combustion gas. In the injection parameter as an alternative according to the invention or additionally taken into account Motor operating size is it is preferably the time of the start of injection one Main fuel injection. Further injection parameters such as injection pressure and / or injection duration, injection quantity of the main injection and / or optionally a pre- or post-injection can also be considered become. The dependence NOx and / or particulate matter emission values from said engine operating variables preferably filed in a map. By reversing the respective dependence can in turn, one or more of a particular target emission value Combinations for these engine operating parameters are assigned.

In Another embodiment of the method is dependent on the n engine operating variables state variable of the engine through a cooling capacity and / or represented by fuel consumption. It is under the cooling capacity the heat flow transported away from the combustion engine with the exhaust gas Understood. As a result of the assignment according to the invention to the NOx raw emission target value oriented selection of engine operating variables to an extreme value of a State variable of the internal combustion engine, in particular to a minimum value for the cooling capacity and / or the fuel consumption, becomes a particularly advantageous engine operation with simultaneously low tailpipe emission values reached.

In a further refinement of the method, a current value of an operating variable of the exhaust gas aftertreatment device is determined and the size of a NOx conversion capacity of the exhaust gas aftertreatment device and / or an achievable minimum value for the NOx tailpipe emission determined on the basis of the determined value of the operating variable of the exhaust gas aftertreatment device. In the Operating variable of the exhaust aftertreatment device may be one or more of the following variables: exhaust gas mass flow through the exhaust aftertreatment device, temperature of the exhaust gas or a component of the exhaust aftertreatment device, amount of a reducing agent stored in a catalyst of the exhaust aftertreatment device for NOx reduction, aging state of a catalytic converter, supply amount of Additive or an exhaust gas component such as NOx, hydrocarbon (HC) or oxygen (O2) and optionally other operating variables. The corresponding operating variables can be detected directly by means of suitable sensors and / or determined indirectly by calculation from sensor measured values or from values stored in characteristic diagrams. By determined in advance and stored, for example, in a control unit dependencies of one, but preferably of several of these sizes, the NOx conversion capacity of the exhaust aftertreatment device and / or the achievable minimum value for the NOx tailpipe emission is determined. In addition, it may be provided to determine a value for an optionally occurring particle reduction. In this way, comprehensive information about the current performance of the exhaust aftertreatment device is obtained.

In Another embodiment of the method is provided that the size of the NOx conversion capacity of the Exhaust gas aftertreatment device and / or the achievable minimum value for the NOx tailpipe emission within of a predefinable to the current values of the operating variables of Exhaust gas aftertreatment device determined interval determined become. This allows over the Determining the current performance of the exhaust aftertreatment device addition in addition a determination of a performance potential according to the specification of the Interval size changed values for the Operating variables of Exhaust treatment device. In this way, if necessary not exhausted Performance potential of the exhaust aftertreatment device are detected. By taking appropriate measures, such as heating the exhaust gas is an improvement of the capacity allows the exhaust aftertreatment device.

In Another embodiment of the method is a NOx raw emission target value on the basis of the determined NOx turnover capacity and / or on the basis the determined achievable minimum value of the tailpipe NOx emission specified so that the achievable minimum value of the NOx tailpipe emission a specified limit value is reached or fallen below. Regarding If the limit value is undershot, a certain tolerance range can also be provided be. The NOx raw emission target value is thus set that current sales the exhaust aftertreatment device while maintaining compliance the limit for the NOx tailpipe emission possible Completely exhausted becomes. this leads to for the internal combustion engine to operate at one operating point in which it is an exhaust gas with a comparatively high NOx emission level generated, but of the exhaust aftertreatment device safely on reduces the tailpipe emission level determined by the limit can be. On the one hand, this results in low NOx tailpipe emissions achieved, on the other hand avoids that the internal combustion engine for example, at the expense of fuel consumption at an operating point with unnecessary low NOx raw emissions is operated.

In Another embodiment of the method are used to determine and if necessary setting of the motor operating variables and / or the state variables of the Internal combustion engine, an engine control unit and to determine and optionally adjustment the current size of the company Exhaust after-treatment device used a second control unit and the engine control unit and the second controller are operated with bidirectional data exchange such that a mutual data access is enabled. This allows for easy Way a shortcut the operating and state variables of the Internal combustion engine with those of the exhaust aftertreatment device and vice versa. Engine control unit and second controller can physically be separate from each other or in a common control unit be integrated.

In Further embodiment of the invention, the exhaust aftertreatment device an SCR catalyst, which is used for NOx reduction. As SCR catalyst is preferably a precious metal-containing and / or a vanadium pentoxide catalyst used, which in is able, by means of a in the exhaust aftertreatment device generated or the exhaust from the outside added reducing agent NOx even in the presence of an excess of oxygen to reduce nitrogen (N2). Preferably, ammonia is provided (NH3) or to use an NH3 releasing reducing agent. Especially the use of urea as reducing agent is preferred.

In a further embodiment of the invention, the exhaust aftertreatment device comprises a particulate filter with upstream oxidation catalyst, wherein the particulate filter filtered oxidizable particles are removed by oxidation with oxygen contained in the exhaust gas (O2) and / or nitrogen dioxide (NO2). Preferably, a so-called wall-flow filter or an open filter or a depth filter is used as a particle filter. The use of a sintered metal filter is also possible. Fiction According to the particulate filter is regenerable, wherein the regeneration can actively take place by burning accumulated particles with O2 contained in the exhaust gas at exhaust gas temperatures of 500 ° C or above and / or passively with NO2 contained in the exhaust gas at lower temperatures. Generation of the NO2 required for passive regeneration can be achieved by oxidation of nitrogen monoxide (NO) present in the exhaust gas in the oxidation catalytic converter. The exhaust aftertreatment device is thus able to remove both NOx and particulates from the exhaust gas and convert them into harmless substances.

In Another embodiment of the invention comprises the exhaust aftertreatment device Means for supplying fuel into the exhaust gas of the internal combustion engine upstream of the oxidation catalyst and a supply of the fuel is made such that due to oxidation of the fuel on the oxidation catalyst, the exhaust gas heated by a predetermined amount becomes. This allows one hand the setting of a for the NOx conversion optimum temperature range of the exhaust aftertreatment device, on the other hand, an optionally present particulate filter brought to a temperature required for active regeneration become.

advantageous embodiments The invention is illustrated and illustrated in the drawings described below. Here are the 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 internal combustion engine and exhaust aftertreatment device for carrying out the method according to the invention,

2 a diagram with a schematically illustrated dependence of the NOx raw emission value of the EGR rate and the time of the main fuel injection and

3 a further diagram with a schematically illustrated dependence of the NOx raw emission value of the EGR rate and the time of the main fuel injection.

1 schematically shows an advantageous embodiment of a system of internal combustion engine 1 and exhaust aftertreatment device 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, air-compressing internal combustion 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 a combustion chamber with one or two inlet and outlet valves, a glow plug and a fuel injector and one or more inlet channels for the combustion air assigned, which is not shown in detail. The fuel injectors are doing so to carry enabled by multiple injections.

The internal combustion engine 1 receives its combustion air via an air supply line 3 in which an unillustrated air mass meter is arranged. 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 internal combustion 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 internal combustion 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 internal combustion 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 exhaust aftertreatment device 2 fed.

A preferred embodiment of the internal combustion engine 1 associated exhaust aftertreatment system 2 includes in the flow direction of the exhaust gas seen in this order a first oxidation catalyst 5 , a particle filter 6 , a second oxidation catalyst 7 and an SCR catalyst 8th , First and second oxidation catalyst 5 . 7 can be carried out in a known manner as a honeycomb body with a conventional oxidation catalyst coating with or without oxygen storage function. As a particle filter 6 For example, a so-called wallflow filter based on SiC-cordierite or aluminum titanate is preferred sentence. The particle filter 6 However, it can also be designed as a sintered metal filter or as a filter unit with an open filter structure. The SCR catalyst 8th is preferably a catalyst suitable for carrying out a selective catalytic NOx reduction reaction by means of ammonia. It may, for example, be a V2O5-WO3-based or zeolite-based full catalyst or a coated catalyst with a noble metal-containing coating.

Input side of the first oxidation catalyst 5 is a fuel addition unit 9 provided, via which, for example, fuel can be supplied as fuel to the exhaust gas. As a result of exothermic oxidation of the exhaust demand supplied fuel is a targeted heating of the exhaust gas allows. The fuel addition unit is actuated 9 mainly in the context of an active regeneration of the particulate filter 6 by thermal Rußabbrand or for heating a downstream exhaust gas purification component. For the addition of ammonia or another preferably for the release of ammonia-capable reducing agent for NOx reduction is the input side of the SCR catalyst 8th a reductant addition unit 11 intended. Preferably, aqueous urea solution is used as the reducing agent. The fuel addition unit 9 and the reducing agent addition unit 11 are preferably connected to dosing systems not shown in detail.

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 particle filter 6 a temperature sensor 10 and on the output side of the SCR catalyst 8th a sensitive to NOx and / or NH3 gas sensor 12 intended. By means of these and possibly other sensors, the operating state of the exhaust gas aftertreatment device 2 be determined.

For controlling or detecting the engine operation is an electronic engine control unit 17 intended. The engine control unit 17 On the one hand receives information about relevant state variables such as speed, temperatures, pressures from the corresponding sensors or sensors and on the other hand, control signals as parameters to actuators such as, to the EGR valve 14 or to the turbocharger 15 output. This relates to state variables on the gas supply side as well as on 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. For this purpose, the engine control unit 17 resort to stored maps or calculation routines.

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.

The inventive method for operating the internal combustion engine 1 and the connected exhaust gas aftertreatment device preferably operates as follows.

The engine control unit 17 determined on the basis of information available to him about the engine operating state from the maps provided for this purpose, a current value of the NOx raw emissions. The authoritative information may relate to intake air mass flow, fuel injection pressure, fuel injector timing, EGR rate, boost pressure, intake air temperature, and optionally other quantities. The quantities mentioned can be directly from sensor signals or indirectly from characteristic curves or maps or through in the engine control unit 17 stored calculation routines are determined. Preferably, the assignment of NOx raw emission values to the relevant quantities is also stored in characteristic curves or characteristic diagrams. The determined actual NOx emission value is then the second control unit 18 over the data line 19 transmitted.

Parallel determines the second control unit 18 on the basis of information available about the operating state of the exhaust aftertreatment device 2 From this maps provided a current value of the NOx conversion capacity of the SCR catalyst 8th , Hereinafter, it is assumed that the supply of reducing agent for NOx reduction into the exhaust gas via the reducing agent addition unit 11 such that the catalyst under the given conditions develops a maximum or approximately maximum effect. This can be done in a conventional manner by means of regulation via the gas sensor 12 or by ongoing balancing of supplied and reacted reducing agent. In the case of an SCR catalyst 8th With reducing agent storage capability, this can also be done on the reducing agent loading of the SCR catalyst 8th oriented reducing agent addition and / or a loading sensor may be provided.

The figures used to determine the NOx sales volume gens authoritative quantities can directly from sensor signals or indirectly from characteristic curves or maps or by in the second control unit 18 stored calculation routines are determined. Typically, information is given regarding the temperature of the SCR catalyst 8th , the exhaust gas mass flow, the amount of in the SCR catalyst 8th stored reductant, if available aging ratios for the SCR catalyst 8th and, where appropriate, other available information relevant to the determination of NOx conversion.

With knowledge of the engine control unit 17 determined NOx raw emission value and the determined NOx-reactivity determines the second controller 18 an achievable NOx tailpipe emission value. Alternatively or additionally, the NOx tailpipe emission value can be determined directly by sensors. In this case, a data comparison between the indirectly determined and the directly sensory determined NOx tailpipe emission value can be provided and a Plausibiltätsprüfung be performed. In this way, a computational model for the reducing agent dosage can be matched with sensor data or, conversely, a sensor can be checked for functionality by means of modeled data.

Of the NOx tailpipe emission value will now be at a predeterminable limit for the NOx tailpipe emissions compared. Preferably, the limit becomes as on a driving route, a motor work or a time related NOx mass specified. Further, it is preferable for the limit one in particular predominantly to provide a tolerance range extending to smaller values.

The following cases are distinguished. If, in the first case, the NOx tailpipe emission value lies within the intended tolerance range or approximately corresponds to the limit value, then preferably no changes are made to engine operating variables or operating variables of the exhaust gas aftertreatment device 2 performed. In this case, it is assumed that both the internal combustion engine 1 as well as the exhaust aftertreatment device 2 to work as desired.

If, in the second case, the NOx tailpipe emission value is greater than the limit value or is above the intended tolerance range, this means that the exhaust gas aftertreatment device 2 more NOx is supplied, as this can implement to comply with the limit. To counter this, it is provided, operating variables of the internal combustion engine 1 in the sense of reducing the NOx raw emission value. Alternatively or additionally, it may be provided, operating variables of the exhaust gas aftertreatment device 2 in the sense of increasing their NOx conversion. For example, the second control device 18 the fuel addition unit 9 or activate the associated dosing system for adding fuel to the exhaust gas. The added fuel heated by exothermic oxidation of the subsequent first oxidation catalyst 5 the exhaust gas flowing through it, whereby the downstream SCR catalyst 8th is heated to a temperature at which an increased NOx conversion is possible.

In order to reduce the NOx raw emission value, the second control unit transmits 18 a NOx raw emission target value to the engine control unit 17 , The NOx raw emission target value is provided by the second controller 18 on the basis of the previously determined NOx conversion capacity of the exhaust aftertreatment device 2 chosen so that with a correspondingly reduced NOx raw emissions, the limit for the NOx tailpipe emission can be reached or exceeded or the NOx tailpipe emission value can reach the tolerance range.

In order to achieve a modified raw NOx emission, which corresponds to the thus specified NOx raw emission target value, engine operating variables must be changed. The corresponding procedure for this is explained below by way of example with reference to the determination for a change in the engine operating variables EGR rate and injection time for the main fuel injection. A change of other, for the NOx raw emissions relevant operating variables can also be provided, which is done in a similar manner. For explanation, reference will be made to the in 2 taken diagram shown.

In 2 is schematically the dependence of the NOx raw emission value NOx, roh the internal combustion engine 1 from the EGR rate EGR and the time of the main fuel injection ABHE (ABHE = start of main injection start) with DOWN as a parameter. As can be seen, different combinations of the two engine operating variables "EGR rate" and "time of the main fuel injection" result for a given target value ZW for the raw NOx emission NOx, crude. In the exemplary case shown, these are the three combinations or 2-tuples (AGR1, ABHE1), (AGR2, ABHE2) and (AGR3, ABHE3). There are thus available for EGR and ABHE in the example selected three settings for achieving an engine operation with a NOx raw emission according to the predetermined target value ZW available. From the engine control unit 17 Now one or more state variables of the internal combustion engine 1 assigned in value to the determined 2-tuples. In particular, the fuel consumption resulting for a respective 2-tuple of EGR and ABHE is determined as an important state quantity. For a cheap Mo door operation is now that 2-tuple selected, for which results in the lowest fuel consumption. The corresponding values for the EGR rate AGR and the time of the main fuel injection ABHE are then from the engine control unit 17 set. For this purpose, appropriate control signals to the fuel injection device and an adjusting device for the EGR valve 14 output. The procedure according to the invention makes it possible, on the one hand, to maintain low NOx tailpipe emission values and, on the other hand, to enable low-consumption engine operation.

Finally, the third case may result in a NOx tailpipe emission value which is below the limit value or below the tolerance range for the latter. In this case, it can be assumed that comparatively low NO x raw emission values are present at the expense of an advantageous engine operation. Analogously to the second case explained above, one of the NOx conversion capacities of the exhaust gas aftertreatment device is also used here 2 oriented target value for the raw NOx emission. This is greater than the current NOx raw emission value, but is selected such that, in the correspondingly increased NOx raw emission, the limit value for the tailpipe NOx emission remains below or the NOx tailpipe emission value comes within the tolerance range.

The NOx raw emission target value thus specified is allocated, as explained, an amount of associated n-tuples for n predetermined adjustable engine operating variables such as EGR rate, boost pressure, start of main fuel injection, intake air temperature or others. Thereafter, that n-tuple is selected, which is a minimum value for the fuel consumption or the cooling capacity of the internal combustion engine 1 is assigned and the values for the operating variables of this n-tuple are set.

In the cases mentioned are for the internal combustion engine 1 Thus, operating variables are set such that, taking into account a NOx tailpipe emission limit value to be observed, the greatest possible NOx emission value results. As a result of the opposite dependence on raw NOx emission and particulate matter emissions, the latter result in low values. Thus, by the procedure according to the invention also a low load of the particulate filter 6 reached. This in turn reduces the frequency of active particulate filter regeneration with thermal soot burnup. This trend is reinforced by the fact that with the consideration of the conditions mentioned above maximum NOx raw emissions that the particulate filter 6 supplied exhaust gas due to oxidation processes at the upstream first oxidation catalyst 5 has a comparatively high NO 2 content. Due to the high NO2 content results in an increased passive regeneration of the particulate filter 6 with oxidation of the deposited soot particles by NO2, a process which proceeds even at comparatively low temperatures (350 ° C and below). This reduces the frequency of energy-intensive active regeneration.

In connection with the explained procedure, it is advantageous if setting limits are specified for the engine operating variables assigned to a NOx raw emission target value, within which a change is provided. In this way it is avoided that an n-tuple of engine operating variables is selected, for which, despite optimization of an associated state variable in other respects disadvantageous properties of the engine operation would result. The corresponding procedure here is based on the in 3 illustrated diagram explained below.

In the in 3 represented diagram, which is essentially the the 2 corresponds, specify AGR4 and AGR5 specifiable setting limits within which a change in the EGR rate is allowed. These setting limits preferably result from other engine operating variables or

State variables of the internal combustion engine 1 , For example, a current engine speed or torque fluctuations can be decisive for determining the setting limits. In an analogous manner, setting limits can also be specified for other engine operating variables grouped into n-tuples.

Further it is advantageous to state variables of engine operation to connect with each other and an optimization of such a linked state variable To make extreme value. For example, the state variables can be efficient of engine operation and noise multiplicatively or additively or otherwise linked together. In this case, an n-tuple of engine operating variables is selected for which for the linked one Size gives an extreme value. That way you can Target conflicts in the optimization of state variables of the internal combustion engine be avoided.

It is understood that the described procedure is not limited to exhaust aftertreatment devices, which the in 1 represented correspond. However, the method according to the invention is particularly advantageous in exhaust aftertreatment devices with a combined NOx and particulate reduction function.

Claims (10)

Method for operating an internal combustion engine, in particular of a motor vehicle, and of an internal combustion engine ( 1 ) connected exhaust gas aftertreatment device ( 2 ), wherein the internal combustion engine ( 1 ) generates an exhaust gas with an adjustable NOx and particulate matter emission value and the exhaust aftertreatment device ( 2 ) reduces the NOx content of the exhaust gas to a NOx tailpipe emission value, at which - for a predeterminable NOx raw emission target value (ZW), an amount of n-tuples associated with that NOx raw emission target value (ZW) with values for n predetermined adjustable and the NOx For a respective n-tuple, an associated value for at least one predetermined state variable of the internal combustion engine that depends on the n engine operating variables of the n-tuple is determined (Roemissionswert and / or the Partikelrohemissionswert 1 ), the n-tuple is selected from the set of the determined n-tuples in which an extreme value results for the at least one predetermined state variable and - the values for the n motor operating variables of the selected n-tuple are set. Method according to Claim 1, characterized in that the n engine operating variables influencing the NOx raw emission value and / or the particulate oxygen emission value have an exhaust gas recirculation rate (EGR) of the internal combustion engine ( 1 ) and / or an injection parameter of a fuel injection into a combustion chamber of the internal combustion engine ( 1 ). A method according to claim 1 or 2, characterized in that the dependent of the n engine operating variables state variable of the internal combustion engine ( 1 ) is represented by a cooling capacity and / or fuel consumption. Method according to one of claims 1 to 3, characterized in that a current values of an operating variable of the exhaust gas aftertreatment device ( 2 ) is determined and on the basis of the determined value of the operating variable of the exhaust aftertreatment device ( 2 ) the size of a NOx conversion capacity of the exhaust aftertreatment device ( 2 ) and / or an achievable minimum value for the NOx tailpipe emission. A method according to claim 4, characterized in that the size of the NOx conversion capacity of the exhaust aftertreatment device ( 2 ) and / or the achievable minimum value for the tailpipe NOx emission within a respectively predefinable interval around the current values of the operating variables of the exhaust aftertreatment device ( 2 ) be determined. Method according to claim 4 or 5, characterized that on the basis of the determined NOx-convertibility and / or the achievable minimum value of the tailpipe NOx emission of the NOx raw emission target value (ZW) is set so that the achievable Minimum NOx tailpipe emissions reaches or falls below a predefinable limit. Method according to one of claim 4 or 5, characterized in that for determining and optionally setting the engine operating variables and / or the state variables of the internal combustion engine ( 1 ) an engine control unit ( 17 ) and for determining and optionally setting the current operating variables of the exhaust aftertreatment device ( 2 ) a second control device ( 18 ) and the engine control unit ( 17 ) and the second control device ( 18 ) are operated with bidirectional data exchange such that a mutual data access is enabled. Method according to one of claims 1 to 7, characterized in that the exhaust gas aftertreatment device ( 2 ) an SCR catalyst ( 8th ), which is used for NOx reduction. Method according to one of claims 1 to 8, characterized in that the exhaust gas aftertreatment device ( 2 ) a particle filter ( 6 ) with upstream oxidation catalyst ( 5 ), wherein the particle filter ( 6 ) filtered out oxidizable particles by oxidation with oxygen and / or nitrogen dioxide contained in the exhaust gas. A method according to claim 9, characterized in that the exhaust aftertreatment device ( 2 ) Means for supplying fuel into the exhaust gas of the internal combustion engine ( 1 ) upstream of the oxidation catalyst ( 5 ) and a supply of the fuel is carried out such that due to oxidation of the fuel on the oxidation catalyst ( 5 ) the exhaust gas is heated by a predetermined amount.