DE102006021303A1 - Exhaust gas treatment system monitoring and/or controlling method for e.g. direct injection diesel engine, involves determining axial temperature distribution in one of exhaust gas treatment systems by dynamic heat model - Google Patents

Abstract

The invention relates to a method for monitoring and / or controlling at least one exhaust gas aftertreatment system of an internal combustion engine having at least one cylinder and at least one exhaust pipe for discharging the exhaust gas containing various exhaust components from said at least one cylinder, wherein the axial temperature distribution in the at least one exhaust aftertreatment system by means of a dynamic heat model (1) is determined and the during the exhaust aftertreatment in the at least one exhaust aftertreatment system generated reaction heat .DELTA.H resulting from the conversion of at least one exhaust gas constituent in the exhaust gas is determined by means of a kinetic model (2).
It is a method of the above type are shown, with which the determination of the temperature distribution in the at least one exhaust aftertreatment system and the determination of the generated during the exhaust aftertreatment in the at least one exhaust aftertreatment system reaction heat ΔH online is enabled, and this with a greater accuracy than in use conventional methods.
This is achieved by a process in which
- For the dynamic heat model (1) the at least one exhaust aftertreatment system by at least two discrete cells (n ≧ 2), which are arranged one behind the other in the axial direction, is shown, and
- for the kinetic model (2) the at least one exhaust aftertreatment system by ...

Description

The The invention relates to a method for monitoring and / or control at least one exhaust aftertreatment system of an internal combustion engine, the at least one cylinder and at least one exhaust pipe to lead away of the different exhaust gas components having exhaust gas from this having at least one cylinder, wherein the axial temperature distribution in the at least one exhaust aftertreatment system by means of a dynamic heat model is determined and during the the exhaust aftertreatment in the at least one exhaust aftertreatment system generated reaction heat ΔH, from the Conversion of at least one exhaust component located in the exhaust gas is determined by means of a kinetic model.

To The prior art are internal combustion engines for reduction Pollutant emissions with various exhaust aftertreatment systems fitted. Although finds without additional measures during the expansion and the Pushing out the cylinder filling at a sufficiently high temperature level and the presence enough greater Oxygen levels an oxidation of the unburned hydrocarbons (HC) and carbon monoxide (CO) instead. These reactions are due to the downstream rapidly decreasing exhaust gas temperature and consequently rapidly sinking reaction rate quickly stops. any Lack of oxygen can be compensated by a secondary air injection become. However, you have to usually special reactors and / or filters provided in the exhaust system be to pollutant emissions under all operating conditions noticeable to reduce.

thermal Reactors try to achieve extensive post-oxidation of HC and CO in the exhaust system, by providing a thermal insulation and sufficient great Volume be provided in the exhaust pipe of the exhaust system. The heat insulation should one possible ensure a high temperature level by minimizing heat losses whereas a big one Exhaust pipe volume ensures a long residence time of the exhaust gases. Both the long residence time and the high temperature level support the desired post-oxidation. Disadvantages are the poor efficiency in substoichiometric combustion and the high costs. For Diesel engines are thermal reactors due to the generally lower temperature level not effective.

Out the reasons mentioned come after the state of the art in gasoline engines catalytic reactors used, using catalytic materials, the increase the speed of certain reactions, an oxidation of HC and ensure CO even at low temperatures. Should also nitrogen oxides This can be reduced by using a three-way catalyst be achieved, but to a running within narrow limits stoichiometric Operation (λ ≈ 1) of the gasoline engine requires.

In this case, the nitrogen oxides NO _{x are} reduced by means of the existing unoxidized exhaust gas components, namely the carbon monoxides and the unburned hydrocarbons, wherein at the same time these exhaust gas components are oxidized.

at Internal combustion engines operated with excess air So, for example, working in lean-burn gasoline engines, in particular but direct injection diesel engines and direct injection gasoline engines, can the nitrogen oxides in the exhaust gas are inherent in the principle - d. H. due to the lack of reducing agents - can not be reduced. to Oxidation of unburned hydrocarbons (HC) and carbon monoxide (CO), therefore, an oxidation catalyst is provided in the exhaust system. For one noticeable i. sufficient conversion is a minimum temperature - the so-called Light-off temperature - required, for example between 120 ° C up to 250 ° C can amount.

to Reduction of nitrogen oxides become selective catalysts - so-called SCR catalysts - used, in which reducing agents are introduced into the exhaust gas in a targeted manner, to selectively reduce the nitrogen oxides. Come as a reducing agent In addition to ammonia and urea also unburned hydrocarbons for use. The latter is also referred to as HC enrichment, where the unburned hydrocarbons go directly into the exhaust tract be introduced or by internal engine measures, namely by a post-injection of additional fuel in the Combustion chamber after the actual combustion, to be supplied. The nacheingespritzte fuel should not in the combustion chamber through the still running main combustion or by the - even after completion the main combustion - high Combustion gas temperatures ignited be, but during the charge change into the exhaust tract be initiated.

Internal combustion engines, who make use of a post-injection, but are from home from very vulnerable for one dilution or contamination of the oil by unburned hydrocarbons. Depending on the quantity of post-injection Fuel and the injection timing, arrives more or less greater Share of post-injected fuel on the cylinder inner wall and mixes there with the adhering oil film. Then arrives the fuel together with the oil and the blow-by gas in the crankcase and thus contributes significantly to the oil dilution. The oil dilution decreases with increasing fuel quantity and shifting the post-injection after late to. By the change the lubricant properties of the oil, the oil dilution has a significant influence on the wear and the Durability i. the life of the internal combustion engine.

Basically, the nitrogen oxide emissions can also use so-called nitrogen oxide storage catalysts (LNT - Lean _NOx Trap) are reduced. The nitrogen oxides are first - during lean operation of the internal combustion engine - absorbed in the catalyst, ie collected and stored to then during a regeneration phase, for example by means of a substoichiometric operation (for example, λ <0.95) of the engine to be reduced in oxygen deficiency. Further internal engine options for realizing a rich ie a stoichiometric operation of the internal combustion engine provides the exhaust gas recirculation (EGR) and - in diesel engines - the throttling in the intake system. In-engine measures can be dispensed with if the reducing agent is introduced directly into the exhaust tract, for example by injecting additional fuel. During the regeneration phase, the nitrogen oxides are released and converted essentially into nitrogen dioxide (N ₂ ), carbon dioxide (CO ₂ ) and water (H ₂ O). The frequency of the regeneration phases is determined by the total emission of nitrogen oxides and the storage capacity of the LNT. The temperature of the storage catalyst (LNT) should preferably be in a temperature window between 200 ° C and 450 ° C, so that on the one hand a rapid reduction is ensured and on the other hand no desorption takes place without conversion of the released nitrogen oxides, which can be triggered by excessive temperatures ,

Difficulty in the use and in particular in the arrangement of the LNT in the exhaust system results from the sulfur contained in the exhaust gas, which is also absorbed in the LNT and must be removed regularly in a so-called desulfurization (deSO _x ) ie a desulfurization. For this purpose, the LNT to high temperatures, usually between 600 ° C and 700 ° C, heated and supplied with a reducing agent, which in turn can be achieved by the transition to a rich operation of the internal combustion engine. The desulfurization of the LNT can contribute to the thermal aging of the catalyst and adversely affect the desired conversion of nitrogen oxides towards the end of its life.

to Minimizing the emission of soot particles According to the prior art so-called regenerative particle filters used the soot particles Filter out and store the exhaust, these soot particles burned intermittently during the regeneration of the filter become. The intervals of regeneration will be among others by the exhaust back pressure, which is due to the increasing flow resistance of the filter due to the increasing particle mass in the filter, certainly.

The for the regeneration of the particulate filter high temperatures - about 550 ° C at not existing catalytic support - are only included in the operation high loads and high speeds achieved. Therefore, on additional activities resorted be a regeneration of the filter under all operating conditions to ensure.

The Combustion of the particles can thereby by provided in the exhaust system Additional burner done or by a post-injection of additional Fuel in the combustion chamber, with the nacheingespritzte fuel already ignited in the combustion chamber What is caused by the expiring main combustion or the against End of combustion in the combustion chamber present high temperatures can happen so that the exhaust gas temperature in the exhaust tract pushed out exhaust gases inside engine is raised. Disadvantageous This procedure is especially in the exhaust system on the Way to the filter to be feared heat losses and the associated temperature reduction of the hot exhaust gases. The filter can easily be a meter and more from the outlet of the Combustor be located away in the exhaust tract.

Of the Compensation of heat losses by generating correspondingly high exhaust gas temperatures by the temperature resistance of others provided in the exhaust system Components limits, in particular the temperature resistance a arranged in the exhaust turbine of an exhaust gas turbocharger, a Three-way catalyst or a storage catalyst. Usually becomes the turbine with the highest temperatures charged as they are closest at the outlet of Combustion chamber is arranged.

Of the Post-injected fuel may also be unburned and possibly already prepared to be pushed out into the exhaust tract and then targeted locally oxidized there in the exhaust system, where high exhaust gas temperatures necessary, namely in the particle filter or in its immediate vicinity. The Combustion of post-injected fuel may be catalytic initiated by means of a catalyst positioned in front of the filter which gives the regeneration temperature exemplified above lowered from about 550 ° C can be. But it can also be an electric ignition in or on the soot filter be provided. The post-injection of fuel for the purpose The filter regeneration has the disadvantages already described above.

Similar to already for The reduction of nitrogen oxides suggested may also be fuel be introduced directly into the exhaust system. The further procedure corresponds to the previously described, in which the additionally injected Unburned fuel enters the exhaust system and targeted in the neighborhood of the particulate filter is oxidized.

It must be considered be that the use of additional Fuel, whether due to a transition to a rich engine operation or due to the enrichment of the exhaust gas with fuel, in principle the fuel consumption of the internal combustion engine adversely affected. In particular, the frequency, with which the particle filter is regenerated or the LNT is cleaned, has authoritative and directly affect the amount of fuel used for these purposes and thus on the total consumption.

Since both the exhaust gases of gasoline engines and the exhaust gases of diesel engines - albeit in different quantities and qualities - unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO _x ) and soot particles, come in the prior art in the Typically, combined exhaust aftertreatment systems employing one or more of the catalysts, reactors, and / or filters described above are employed.

Investigations have shown that in-engine measures for realizing a richer operation of the internal combustion engine - whether to increase the exhaust gas temperature with the aim of filter regeneration or for enrichment for the regeneration of LNT - basically lead to increased methane emissions (CH ₄ ), in diesel engines almost all of the methane passes through the exhaust pipe and the intended exhaust aftertreatment systems and exits into the environment without being oxidized. The present in the exhaust system or oxidation catalyst during normal operation of the internal combustion engine temperatures are not high enough to convert the methane contained in the exhaust or oxidize. For this temperatures of about 500 ° C are required.

consequently HC emissions, which include methane emissions, are noticeably increasing when a planned in the exhaust system storage catalyst cleaned or a particle filter is to be regenerated and on this occasion the internal combustion engine by means of internal engine measures into the fat operation is transferred. The methane can be up to 90% of the unburned hydrocarbons make out during the of the rich operation emitted by the internal combustion engine and in the exhaust tract be initiated.

On the other hand, the NO _x and particulate emissions increase when it is less frequently switched to rich operation of the internal combustion engine with regard to the HC emissions and thus a planned in the exhaust system storage catalyst and / or particulate filter is not cleaned or regenerated with the necessary frequency. When the storage capacity of the LNT is exhausted, the nitrogen oxides pass unhindered into the environment. Too high a loaded particulate filter leads to an unfavorably high exhaust back pressure, which also the quality of the combustion, in particular by a deteriorated gas exchange, suffers.

In summary, it can be stated that the intended simultaneous reduction of the relevant pollutants, namely HC and CO on the one hand and NO _x and particles on the other hand, leads to a conflict; as previously shown. In addition, further conflicts arise in the arrangement of the individual exhaust aftertreatment systems - the oxidation catalyst, the LNT and the particulate filter - in the exhaust system. The simultaneous operation and control of said exhaust aftertreatment systems leads to further difficulties, especially in the coordination of the systems, because the different exhaust aftertreatment systems require different and partially conflicting boundary conditions. In particular, the requirements for the preferred temperature level and the air ratio λ diverge greatly.

The above-discussed conflict of objectives is discussed below with reference to a so-called four-way catalyst. This is a combined exhaust aftertreatment system, which is a Spei catalyser (LNT), a particulate filter and an oxidation catalyst as exhaust aftertreatment systems.

The individual exhaust aftertreatment systems of the four-way catalyst are connected in series, with the oxidation catalyst upstream of the Storage catalyst or the particulate filter is arranged. Of the Storage catalyst and the particulate filter can be integrated as structural Unit be formed. This means for the purposes of the present For example, registration for both the storage catalyst and for the Particle filter own carrier substrate can be provided, wherein the two carrier substrates adjacent to each other be arranged and thus form a structural unit or be formed from home as a continuous carrier substrate. Alternatively it can serve as a particle filter, a honeycomb filter, the same time as a carrier substrate is used to form a storage catalyst.

Thereby, the oxidation catalyst is upstream of the other two components is provided, the oxidation catalyst is the exhaust aftertreatment component, the closest is arranged at the outlet of the internal combustion engine and first of the hot ones Exhaust gases flowed through becomes. Consequently, the heat losses and the associated temperature reduction of the hot exhaust gases comparatively low. Accordingly, the oxidation catalyst reaches its so-called light-off temperature even after a cold start within a relatively short one Period of time. Both for Diesel engines used oxidation catalysts as well Gasoline engines used three-way catalysts require a certain operating temperature, to convert the pollutants sufficiently and the Pollutant emissions noticeable to reduce. The three-way catalysts are intended as part of the of the present invention are counted among the oxidation catalysts.

The effect in the oxidation catalyst expired exothermic reactions a warming of the flowing through Exhaust gas and thus a warming the downstream i. arranged downstream of the catalyst Exhaust aftertreatment systems, what for these exhaust aftertreatment systems assigned tasks is advantageous.

The Temperature of the storage catalyst (LNT) should preferably be in a temperature window between 200 ° C and 450 ° C, so that on the one hand a quick reduction is ensured and on the other hand no Desorption without conversion of the released nitrogen oxides takes place. Also the reactions taking place in the storage catalytic converter are with a heat output connected and lead in this way to an increase the exhaust gas temperature and the downstream exhaust aftertreatment systems, but also to a warming the storage catalyst itself.

The particulate filter usually does not reach its regeneration temperature of 550 ° C during normal lean engine operation. However, even at lower temperatures, passive regeneration of the filter takes place, where the nitrogen oxides (NO _x ) present in the exhaust gas supply the oxygen for the oxidation, ie the combustion of the soot particles stored in the filter, essentially nitrogen monoxide (NO) and carbon monoxide (CO) is formed.

One Target in the development of combined exhaust aftertreatment systems is it the upstream of the particulate filter located exhaust aftertreatment systems in the To operate type or control that the particulate filter easily Action i. solely due to the operation of the upstream oxidation catalyst and the storage catalyst reaches its regeneration temperature. Such a synergy effect would the operation of the combined exhaust aftertreatment system in question simplify and also help save fuel. targeted Filter regeneration would be no more or less often required than by the state the technique usual.

According to one Method for operating such a combined exhaust aftertreatment system the oxidation catalyst is at a vorgebare minimum temperature heated and the exhaust gas when reaching this minimum temperature with reducing agents enriched.

at Accumulation of the exhaust gas by injection of fuel in the exhaust pipe can be sufficient for a minimum temperature T ≈ 200 ° C-250 ° C. This temperature the oxidation catalyst together with those in the oxidation catalyst ongoing exothermic reactions that the downstream Storage catalyst in his for the cleaning preferred temperature window from 200 ° C to 450 ° C works.

Becomes the enrichment of the exhaust gas with reducing agent by contrast internal engine measures realized, it becomes necessary to oxidize large quantities of methane, which is why the specification of a higher minimum temperature is required, for example, T ≈ 500 ° C-550 ° C. The warming of the oxidation catalyst to such high temperatures can a time delayed Regeneration of the downstream used particulate filter, if after heating of the Oxidation catalyst and the enrichment of the exhaust gas, the internal combustion engine is again transferred to the lean operation and in the exhaust of the for the soot combustion required oxygen excess is present.

Becomes the combined exhaust aftertreatment system as described above operated, planted starting from the oxidation catalyst one Temperature wave in the exhaust pipe continues, leaving the downstream Exhaust aftertreatment systems, in particular the particulate filter, its maximum temperature only reached after a time delay. investigations have shown that 20 to 200 seconds after finishing the cleaning process the LNT of the particulate filter has its maximum temperature reached.

As from the comments it is clear that it is for the effective operation of exhaust aftertreatment systems, in particular of combined exhaust aftertreatment systems, required Temperatures or the local and temporal temperature distribution in the exhaust aftertreatment systems used, wherein the metrological detection of these temperatures difficult and often even not possible. Therefore, according to the prior art in different places in the at least one exhaust pipe, the temperatures by means of sensors recorded and as a basis for the estimate the temperatures in the at least one exhaust aftertreatment system used. But this procedure proves just in view on the surveillance and controlling combined exhaust aftertreatment systems as insufficient.

The previously made statements show about it In addition, it further requires the conversion to monitor the pollutants and for example information about the loading of a particulate filter or the saturation to provide a storage catalyst, since on the one hand these operating parameters Have an influence on the operation of the exhaust aftertreatment system and on the other hand, the conversion of pollutants i. the chemical Reactions in the context of exhaust aftertreatment release heat and influence on the temperatures and the temperature distribution.

Out The prior art also includes methods for monitoring and / or control an exhaust aftertreatment system known in which the temperature in the exhaust aftertreatment system by means of a dynamic heat model is determined and during the the exhaust aftertreatment in the at least one exhaust aftertreatment system generated reaction heat ΔH by means of a kinetic model is determined, with which, if appropriate the operating state of the exhaust aftertreatment system, for example the conversion rate in an oxidation catalyst and / or the Loading or conversion rate in a particle filter or the saturation or conversion rate in a storage catalytic converter, calculated can be.

conventional Models subdivide the exhaust aftertreatment system into discrete ones Cells or consider the exhaust aftertreatment system as a single linear i. one-dimensional element. But this results in a Conflict between the dynamic heat model and the kinetic Model. To the temperature or temperature distribution in the exhaust aftertreatment system with the help of the dynamic heat model be able to determine with sufficient accuracy For example, a sufficiently high number n of cells is required n> 20. Such a thing high number of cells leads but when using the comparatively complex kinetic model too long computing times, which is the traditional model for online operation or make onboard use unsuitable.

Therefore The number of cells in the prior art is limited by the exhaust aftertreatment system as a single linear i. dimensional Cell is considered, causing the axial temperature distribution a concrete temperature value is reduced. A larger number Cells require sufficient computing power, which is why such models only for Simulations and theoretical calculation in the development phase be used.

Against this background, it is the object of the present invention to provide a method for monitoring and / or controlling at least one exhaust aftertreatment system of an internal combustion engine, with which the determination of the temperature distribution in the at least one exhaust aftertreatment system and the determination of generated during the exhaust aftertreatment in the at least one exhaust aftertreatment system Reaction heat ΔH online allows, and with a larger Accuracy than when using a conventional method.

• • für das dynamische Wärmemodell das mindestens eine Abgasnachbehandlungssystem durch mindestens zwei diskrete Zellen (n ≥ 2), die in axialer Richtung hintereinander angeordnet sind, dargestellt wird,
• • für das kinetische Modell das mindestens eine Abgasnachbehandlungssystem durch mindestens eine diskrete Zelle (N ≥ 1) dargestellt wird, wobei
• • die mittels des kinetischen Modells bestimmte Reaktionswärme ΔH als Eingangsgröße für das Wärmemodell verwendet wird.

This object is achieved by a method for monitoring and / or controlling at least one exhaust aftertreatment system of an internal combustion engine, the at least one cylinder and at least one exhaust pipe for discharging the exhaust components comprising different exhaust gas from this at least one cylinder, wherein the axial temperature distribution in the at least one exhaust aftertreatment system is determined by means of a dynamic heat model and the heat of reaction .DELTA.H generated during the exhaust aftertreatment in the at least one exhaust aftertreatment system, resulting from the conversion of at least one exhaust gas constituent in the exhaust gas, is determined by means of a kinetic model;

• For the dynamic heat model, the at least one exhaust aftertreatment system is represented by at least two discrete cells (n ≥ 2) arranged one behind the other in the axial direction,
• For the kinetic model, the at least one exhaust aftertreatment system is represented by at least one discrete cell (N ≥ 1), wherein
• • the heat of reaction ΔH determined by the kinetic model is used as input to the heat model.

in the Compared to conventional The method will not be the at least one exhaust aftertreatment system considered as a single cell, but at least for the dynamic one thermal model divided into at least two discrete cells, so that the axial Temperature distribution in online operation with greater accuracy can be determined as this is possible according to the prior art.

Advantageous are embodiments of the method in which the number n of discrete cells for the heat model is chosen larger as the number N of discrete cells for the kinetic model d. H. the following applies: n> N.

According to the method of the invention can the number of cells of the two models used, namely the dynamic heat model on the one hand and the kinetic model on the other.

In order to becomes the possibility created the number n of cells for the dynamic heat model to choose comparatively high, about the axial temperature distribution in the at least one exhaust aftertreatment system preferably to determine exactly, whereas the number of cells N for the essential more complex kinetic model is chosen smaller to get the needed computation time or to limit the necessary computer power and thus the process for one To make online operation usable. Unlike from the state The method known in the art is used in the method according to the invention the quality the determined temperature distribution is not due to the complexity of the kinetic Limited model i.e. reduced.

Thereby the problem underlying the invention is solved, namely a Procedure for monitoring and / or controlling at least one exhaust aftertreatment system an internal combustion engine show, which can be used online is and at the same time determining the temperature distribution in the at least one exhaust aftertreatment system with greater accuracy permitted as this by means of conventional Procedure possible is.

Of the Term "axial Temperature distribution "characterizes while the temperature distribution along the main flow direction the exhaust gas i. along an imaginary path that the exhaust when flowing through the at least one exhaust aftertreatment system follows. The thought Distance is usually obtained by connecting the flow direction the exhaust gas at the entrance to the at least one exhaust aftertreatment system and the flow direction the exhaust gas at the exit from the at least one exhaust aftertreatment system out.

The Temperature distribution perpendicular to the main flow direction is - at least if it concerns the considered exhaust aftertreatment system an oxidation catalyst or an LNT is - of minor importance Meaning, so that the temperature change in the radial direction is neglected according to the invention, which greatly simplifies the models and further the online use favored. If, however, a particle filter is considered, it may be necessary become the temperature distribution in the radial direction in the consideration i.e. into the models. In the further description However, for the sake of simplicity, the temperature change will be made to the present invention in the radial direction in principle neglected.

Out This is why embodiments are advantageous in the method in which linear, i.e. dimensional Elements are used.

Further advantageous method variants according to the subclaims explained below.

Advantageous are embodiments of the method in which the number n of discrete cells for the heat model bigger or equal to a multiple of the number N of discrete cells for the kinetic model is i. e. it holds: n> x · N, where x a natural one Number is.

These Process variant offers advantages in the calculation, because it must considered be that the two models used, namely the dynamic heat model on the one hand and the kinetic model, on the other hand, interrelated and each model input values for the other model supplies.

The reaction heat ΔH determined by means of the kinetic model serves, for example, as an input variable for the heat model for determining the temperature distribution in the at least one exhaust aftertreatment system. On the other hand, the dynamic heat model supplies the cell temperature T ^i, ie the temperature of the cell i of the at least one exhaust aftertreatment system, as an input to the kinetic model.

If, according to the embodiment in question, five times as many cells are used for the dynamic heat model as for the kinetic model (x = 5), for example with n = 20 and N = 4, then the temperatures T _i determined by the heat model become the first five Averaged (that is, added and divided by five) cells (i = 1 to 5) and provided this average temperature of the first cell (j = 1) of the kinetic model as a cell temperature.

On the other hand, the kinetic model heat of reaction ΔH ^{j = 1 of} the first cell (j = 1) of the kinetic model is divided among the five first cells of the heat model and the proportion thus determined is assigned to each of the first five cells of the heat model, for simplicity's sake in that in each of the first five cells (i = 1 .. 5) of the heat model an equal amount of heat of reaction is released. In the context of this assignment, a transformation of the kinetic model heat of reaction ΔH ^{j = 1} into a temperature increase ΔT caused by this heat of reaction is required, expressing the following equation. .DELTA.T AH i = 1..5 = 0.2 · ΔT (ΔH j = 1 )

Of the Temperature increase ΔT is a function of the heat of reaction.

Advantageous embodiments of the method are those in which the temperature T ^{i-1 of} the adjacent, upstream cell i-1 is used as an input variable in the context of the determination of the temperature distribution by means of heat model for each cell i, wherein i = 1 for the first upstream cell the temperature at the inlet of the at least one exhaust aftertreatment system is used as input.

The temperature T ^{i of} the cell i can be determined by means of the following differential equation.

In this equation, k is a correction factor which is usually close to 1. ΔT _ΔH ⁱ denotes the kinetic model determined heat of reaction in the cell i. M stands for the mass of the carrier substrate of the at least one exhaust aftertreatment system and m _exh for the exhaust gas mass flow, while n represents the total number of cells of the heat model.

According to the above equation, the temperature in the exhaust pipe is also detected by measuring technology (Tsen _out ) by means of a temperature sensor at the outlet of the exhaust aftertreatment system. This temperature Tsen _out is provided to the heat model in the context of a feedback for adaptation of the model, so that in the present case a so-called monitoring structure is provided. In this case, K ⁰ stands for the sensitivity or amplification of this monitoring structure or feedback and Tmod _out for the temperature determined by means of the heat model at the outlet of the exhaust gas aftertreatment system.

The following applies: Tmod out = T n

In this case, T ^{n represents} the temperature of the last cell n.

The Provide a monitoring structure improves the quality i.e. the accuracy of the temperature distribution determined by the heat model, as an adaptation of the model to the actual temperatures present This is done without measuring a temperature Tsen and recycling this Temperature not possible would.

With the term L (Tamb - T i ) the heat loss to the environment is taken into account, where Tamb stands for the ambient temperature and L represents a heat loss factor. If the heat transfer to the environment is not included in the consideration, this term can basically be omitted.

Advantageous are for the reasons mentioned embodiments the process in which at least one temperature in the at least an exhaust pipe metrologically and in the context of a return to the dynamic heat model provided as an input becomes.

Also advantageous are embodiments of the method in which the kinetic model is used to determine the conversion of at least one of the following exhaust constituents in the at least one exhaust aftertreatment system: nitrogen oxides (NO _x ), soot particles, carbon monoxide (CO), unburned hydrocarbons (HC) and / or oxygen (O ₂ ).

If the at least one exhaust aftertreatment system comprises a storage catalytic converter, embodiments of the method are advantageous in which the kinetic model is used to determine the saturation φ _{LNT, right of} the storage catalytic converter.

If the at least one exhaust aftertreatment system comprises a particulate filter, embodiments of the method are advantageous in which the kinetic model is used to determine the _charge φ _{DPF, right of} the particulate filter.

The two aforementioned embodiments provide additional information about the operating state of the at least one exhaust aftertreatment system and can be used to monitor and / or control the at least one exhaust aftertreatment system. If the _{degree of} saturation φ _LNT determined by the kinetic model _reaches a predefinable saturation _limit , this can be regarded as a signal for initiating the cleaning of the storage catalytic converter by enriching the exhaust gas and used to prevent the degree of saturation from exceeding a maximum permissible saturation, for example can lead that located in the exhaust gas nitrogen oxides pass through the storage catalyst unhindered and get into the environment.

In a similar manner, a filter _regeneration can be initiated if the filter loading φ _{DPF, rech reaches} a predetermined maximum allowable value for the load.

In the following the invention with reference to a method variant according to the 1 described in more detail. Hereby shows:

1 schematically a first embodiment of the method in the form of a block diagram.

1 schematically shows a first embodiment of the method in the form of a block diagram.

The number n of cells of the heat model 1 is greater than the number N of cells for the kinetic model 2 , The following applies: n> N.

This results in the possibility of the axial temperature distribution in the at least one exhaust gas To determine the treatment system with the help of a high number n of cells as accurately as possible and at the same time the computing time for the complex kinetic model 2 to limit N by a small number of cells selected. This enables online use of the process.

By means of the kinetic model 2 is the heat of reaction ΔH ^j for each cell (j = 1 ... N) of the kinetic model 2 certainly. Depending on the exhaust aftertreatment system to be considered, the heat of reaction may be the heat released as a result of oxidation in an oxidation catalyst, reduction of nitrogen oxides in a storage catalyst, or heat released in the regeneration of a particulate filter or, if a combined exhaust aftertreatment system Subject of the method is - to a combination of said reaction heats. The mentioned reaction heats are only exemplary in character.

Because the number of cells of the two models 1 . 2 may differ for a cell j of the kinetic model 2 determined reaction heat ΔH ^j not directly a single cell i of the dynamic heat model 1 be assigned. Therefore, the determined heat of reaction ΔH ^{j of} the cell j only proportionally of a cell i of the dynamic heat model 1 assigned.

For the temperature increase ΔT _ΔH ^{i = 1,} for example, of the first cell (i = 1) of the heat model 1 owing to the kinetic model of the heat of reaction ΔH ^{j = 1 of} the first cell (j = 1) of the kinetic model, the following applies: .DELTA.T AH i = 1 = N / n · ΔT (ΔH j = 1 )

Analogously, the dynamic heat model delivers 1 the cell temperature T ⁱ ie the temperature of cell i to the kinetic model 2 (not shown). Due to the different number of cells i, j of the two models 1 . 2 need to determine the temperature T ^{j of} the cell j of the kinetic model 2 at least two cells of the heat model 1 are used, the temperatures T ⁱ proportionately added and averaged.

When determining the temperature distribution by means of a heat model 1 For each cell i, the temperature T ^{i-1 of} the adjacent upstream cell i-1 is used as input.

For the first upstream cell i = 1, the inlet temperature T ^{in of} the at least one exhaust aftertreatment system is used as the input variable. The temperature T ^{n of} the last cell (i = n) is also the outlet temperature of the exhaust aftertreatment system.

The abbreviations for the pollutants contained in the exhaust gas, namely CO, HC, NO _x and soot, and the abbreviation for oxygen O ₂ are intended to illustrate that with the kinetic model, if appropriate, the saturation φ _LNT, the storage catalytic converter and / or the _charge φ _{DPF , Rech} the particulate filter can be determined, as far as they are the subject of the process.

Furthermore, the kinetic model 2 be used to determine the conversion of one or more of these exhaust gas constituents.

1

dynamic thermal model

2

kinetic model

AGR

Exhaust gas recirculation

CO

Carbon monoxide

deNO _x

cleaning of the storage catalyst

deSoot

regeneration of the particulate filter

deSO _x

Desulfurisation, desulphurization

AH

heat of reaction

ΔH ^j

Reaction heat of Cell j of the kinetic model

HC

unburned hydrocarbons

i

cell of the dynamic heat model

j

cell of the kinetic model

k

correction factor

K ⁰

sensitivity or reinforcement the surveillance structure

M

Dimensions of the carrier substrate the exhaust aftertreatment system

m _exh ,

Exhaust gas mass flow

n

number the cells of the dynamic heat model

N

number the cells of the kinetic model

NO _x

Nitrogen oxides

L

Heat loss factor

LNT

Lean NO _x trap, storage catalyst

φ _{DPF, right}

by means of kinetic model determined loading of the particulate filter

φ _{LNT, right}

by means of kinetic model determined saturation level of

storage catalyst

SCR

Selective Catalytic Reduction

soot

soot

SO _x

sulfur oxides

tamb

ambient temperature

T ⁱ

temperature the cell i of the heat model

T ⁿ

temperature the cell n of the heat model

ΔT _ΔH ⁱ

temperature rise the cell i of the heat model as a result of

Reaction heat ΔH ^{j = 1 of} the cell j of the kinetic model

Tsen _out

by means of Temperature sensor at the output of the

aftertreatment system detected temperature

Tmod _out

by means of thermal model certain temperature at the outlet of the exhaust gas

aftertreatment system

T ⁱⁿ

inlet temperature the at least one exhaust aftertreatment system

T ⁿ

temperature the last cell n of the heat model

x

natural number

Claims (9)

Method for monitoring and / or controlling at least one exhaust gas aftertreatment system of an internal combustion engine having at least one cylinder and at least one exhaust pipe for discharging the exhaust gas comprising different exhaust gas components from said at least one cylinder, wherein the axial temperature distribution in the at least one exhaust aftertreatment system by means of a dynamic heat model ( 1 ) and the reaction heat .DELTA.H generated during the exhaust aftertreatment in the at least one exhaust aftertreatment system, which results from the conversion of at least one exhaust gas constituent in the exhaust gas, by means of a kinetic model ( 2 ) and where • for the dynamic heat model ( 1 ) the at least one exhaust aftertreatment system is represented by at least two discrete cells (n ≥ 2) arranged one behind the other in the axial direction, and • for the kinetic model ( 2 ) the at least one exhaust gas aftertreatment system is represented by at least one discrete cell (N ≥ 1), whereby • by means of the kinetic model ( 2 ) determined heat of reaction ΔH as an input variable for the heat model ( 1 ) is used. Method according to claim 1, characterized in that the number n of discrete cells for the heat model ( 1 ) is greater than the number N of discrete cells for the kinetic model ( 2 ) ie: n> N. Method according to claim 1 or 2, characterized that as cells linear d. H. used one-dimensional elements become. Method according to one of the preceding claims, characterized in that the number n of discrete cells for the heat model ( 1 ) is greater than or equal to a multiple of the number N of discrete cells for the kinetic model ( 2 ), ie n> x · N, where x is a natural number. Method according to one of the preceding claims, characterized in that in the context of the determination of the temperature distribution by means of heat model ( 1 ) for each cell i the temperature T ^{i-1 of} the adjacent upstream cell i-1 is used as an input, wherein for the first upstream cell i = 1 the temperature at the inlet of the at least one exhaust aftertreatment system is used as an input. Method according to one of the preceding claims, characterized in that at least one temperature Tsen in the at least one exhaust gas line is detected by measurement and in the context of a feedback the dynamic heat model ( 1 ) is provided as input. Method according to one of the preceding claims, characterized in that the kinetic model ( 2 ) is used to determine the conversion of at least one of the following exhaust constituents in the at least one exhaust aftertreatment system: nitrogen oxides (NO _x ), soot particles, carbon monoxide (CO), unburned hydrocarbons (HC), and / or oxygen (O ₂ ). Method according to one of the preceding claims, wherein the at least one exhaust aftertreatment system comprises a storage catalyst, characterized in that the kinetic model ( 2 ) is used to determine the saturation φ _{LNT, right of} the storage _catalyst . Method according to one of the preceding claims, wherein the at least one exhaust aftertreatment system comprises a particulate filter, characterized in that the kinetic model ( 2 ) is used to determine the loading φ _{DPF, right of} the particulate filter.