Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
  • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
  • F01N3/2066—Selective catalytic reduction [SCR]
  • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
  • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
  • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
  • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
  • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
  • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
  • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
  • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
  • F01N3/2006—Periodically heating or cooling catalytic reactors, e.g. at cold starting or overheating
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/021—Introducing corrections for particular conditions exterior to the engine
  • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
  • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
  • F01N2240/40—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being a hydrolysis catalyst
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2390/00—Arrangements for controlling or regulating exhaust apparatus
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
  • F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
  • F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
  • F01N2560/14—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics having more than one sensor of one kind
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
  • F01N2900/06—Parameters used for exhaust control or diagnosing
  • F01N2900/14—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust gas
  • F01N2900/1402—Exhaust gas composition
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
  • F01N2900/06—Parameters used for exhaust control or diagnosing
  • F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
  • F01N2900/1621—Catalyst conversion efficiency
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
  • F01N2900/06—Parameters used for exhaust control or diagnosing
  • F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
  • F01N2900/1622—Catalyst reducing agent absorption capacity or consumption amount
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/021—Introducing corrections for particular conditions exterior to the engine
  • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
  • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
  • F02D41/029—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a particulate filter
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
  • F02D41/146—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• SCR selective catalytic reduction
• nitrogen oxides (NO ⁇ ) contained in the exhaust gas of the internal combustion engine are reduced by involving a chemical reducing agent stored by the reduction catalyst.
• nitrogen oxides (NO ⁇ ) in particular are among the environmentally hazardous, directly emitted primary pollutants which are produced during operation of internal combustion engines, in particular diesel engines.
• CO carbon monoxide
• HC hydrocarbons
• NO ⁇ nitrogen oxides
• a use of three-way catalysts, as used in ⁇ 1 controlled gasoline engines, is not possible due to the excess of oxygen in the very lean diesel engine exhaust. For this reason, a selective SCR catalyst was developed to reduce nitrogen oxide emissions in diesel engines, with an added reducing agent
• the reducing agent is added directly to the exhaust gas or it is added a chemical precursor of the reducing agent, which releases the reducing agent only in the exhaust system.
• Ammonia (NH 3 ) which is supplied to the exhaust gas as a gas or as an aqueous solution, serves in particular as a reducing agent. Due to the non-hazardous handling of NH 3 , urea is usually used today as a chemical precursor, which is present either in the form of an aqueous solution or as a solid.
• the thermohydrolytic decomposition of urea with the release of NH 3 is carried out by the heat of the exhaust gas stream or the catalyst or in an evaporator.
• SCR catalysts have a temperature-dependent storage capacity for the
• Reducing agent (NH 3 ), wherein the temperature dependence at low catalyst temperatures is particularly pronounced.
• NO x conversion rate of SCR catalysts increases with the NH 3 loading level.
• the compliance a safety distance to the maximum load level usual to minimize the risk of reducing agent slip.
• the object of the present invention is therefore to provide a method for operating an SCR catalyst, in which an uncontrolled release of the stored reducing agent is avoided.
• the loading level of the SCR catalytic converter can be adapted to the external conditions such that a Uncontrolled release of reducing agents, in particular of NH 3 , is largely avoided.
• the (active or passive) lowering of the loading level of the SCR catalyst in such operating conditions of Internal combustion engine and / or the components of the exhaust system which would lead to the desorption of the reducing agent (eg NH 3 ) from the SCR catalyst without the procedure according to the invention.
• This is preferably a current or requested increased exhaust-gas temperature, in particular a current or requested exhaust-gas temperature increase.
• a threshold value can be preset for the exhaust-gas temperature or the exhaust-gas temperature difference, the exceeding of which triggers the load reduction according to the invention.
• Operating state in which the influence on the loading state of the SCR catalytic converter is advantageous is a strong load requirement in predeterminable minimum height by the driver by appropriate operation of the accelerator pedal, for example during acceleration. Furthermore, temperature increases can occur through strongly exothermic processes on the particle filter during its regeneration and / or on a catalyst, which lead to an influence on the loading level. In all these cases, the loading level of the SCR catalyst is expediently lowered, in particular to a predetermined minimum loading level.
• the desired level of loading in particular the desired minimum level of loading, can be predetermined for the different operating states to varying degrees. For example, when requesting a particulate filter regeneration, which requires particularly high exhaust gas temperatures, can be lowered to a lower loading level than required catalyst heating measures.
• the reducing agent supply to the exhaust system is prevented as the first measure to reduce the loading level, that is, the reducing agent metering is deactivated.
• the critical operating situation is a requirement of a particulate filter regeneration and / or a catalyst heating measure, according to a preferred embodiment of the invention, additionally, the beginning of the requested exhaust gas temperature increase is delayed, preferably until a desired loading level of the SCR catalytic converter is reached.
• the lowering of the loading level of the SCR catalyst can also be done by increasing the NO x -remission of the internal combustion engine.
• the reducing agent (NH 3 ) and NO x is ensured, so that no environmentally relevant pollutant emissions arise.
• the increase in the NO x raw emissions can be effected, for example, by changing the exhaust gas recirculation rate, the amount of fresh air supplied to the internal combustion engine, and / or by changing fuel injection parameters, such as injection timing and fuel quantity.
• fuel injection parameters such as injection timing and fuel quantity.
• gasoline engines also comes a change in the ignition in question.
• the type of mixture preparation can be influenced, for example, by switching a stratified charge mode, in which a highly concentrated fuel cloud is present only in a part of the combustion chamber, to a homogeneous operation with a uniform mixture distribution.
• the increase in the raw NO ⁇ emission of the internal combustion engine is preferably carried out when the operating situation can not be actively influenced, but is conditioned by an individual driving behavior, such as under heavy load requirements. It may also be used as a secondary measure to assist or accelerate the lowering of the loading level by the above measures.
• the current loading level of the SCR catalyst is determined with reducing agents. This is preferably done by determining the cumulative amount of reducing agent stored in the SCR catalyst and subtracting the amount of reducing agent consumed by the NO ⁇ conversion of the SCR catalyst.
• the requisite balancing of the NO x conversion of the SCR catalytic converter ie the comparison of the NO.sub.x content of the exhaust gas present upstream and downstream of the catalytic converter, can be modeled mathematically or using in particular temperature-dependent characteristic diagrams or by means of upstream and / or downstream of the SCR Catalyst arranged NO x sensors are measured.
• the sole FIGURE shows an internal combustion engine 10, which is in particular a diesel engine here.
• a coming from the internal combustion engine 10 exhaust gas is in a directed in total with 12 designated exhaust system.
• the exhaust system 12 includes an exhaust passage 14 containing various components for exhaust aftertreatment.
• the exhaust gas channel 14 accommodates an SCR catalytic converter 16.
• This is a reduction catalytic converter which converts nitrogen oxides (NO x ) of the exhaust gas into N 2 and H 2 O with the participation of a reducing agent, here ammonia (NH 3 ).
• the reducing agent NH 3 is injected into the exhaust gas channel 14 in the form of an aqueous urea solution as a chemical precursor for ammonia via a metering unit 18, which is connected to a reservoir for the aqueous urea solution, not shown here.
• the urea solution enters a heatable evaporator 20, where the NH 3 is released by hydrolysis and thermolysis.
• the optional evaporator 20 is advantageous because the kinetics of the urea decomposition reaction at low exhaust gas temperatures is very slow and must be expected to form undesirable polymerization.
• the NH 3 thus generated is stored in the SCR catalyst 16.
• urea solution instead of a urea solution, it is also possible to use solid urea (for example in the form of pellets or prills), which is processed mechanically or thermally.
• a reactor In thermal treatment, a reactor is required, which may be arranged outside or inside the exhaust system 12.
• gaseous NH 3 or an aqueous ammonia solution can also be injected into the exhaust system 12.
• the use of a NH 3 releasing precursor is preferred.
• an oxidation catalyst 22 is arranged in the exhaust passage 14, which performs a conversion of carbon monoxide (CO) and hydrocarbons (HC).
• the arrangement of the oxidation catalytic converter 22 upstream of the SCR catalytic converter 16 is particularly advantageous since, in particular, in the low temperature range, the activity of the SCR catalytic converter 16 is markedly improved.
• an NO 2 content of about 50% based on the total nitrogen oxides NO x behind the oxidation catalyst 22 is generated.
• a deactivation of the SCR catalyst 16 due to increased HC emissions is avoided, which is particularly pronounced at low temperatures.
• a particle filter 24 may be arranged downstream of the SCR catalytic converter 16, which filters soot particles of the exhaust gas and is thermally regenerated from time to time.
• the order and configuration of the various components of the exhaust system 12 may differ from that shown here.
• the particulate filter 24 may be placed before the SCR Catalyst 16 may be arranged or a particulate filter with integrated oxidation catalyst upstream of the SCR catalyst 16.
• a further oxidation catalytic converter can be provided downstream of the SCR catalytic converter which effects an oxidation of exiting NH 3 .
• the exhaust duct 14 also houses a series of sensors.
• a lambda probe 26 can be arranged, which in a known manner serves for the lambda control of the internal combustion engine 10.
• the SCR catalytic converter 16 is followed by an NO x sensor 28, which measures the NO 2 content of the exhaust gas downstream of the catalytic converter 16.
• another NO x sensor 30 may be provided upstream of the reduction catalyst 16.
• the engine controller 36 has a control unit 38 which controls the operation of the SCR catalyst 16 in the manner described below.
• the control unit 38 includes for this purpose a program algorithm for carrying out the method according to the invention as well as necessary maps.
• the stored in the control unit 38 program algorithm controls the SCR catalyst 16 in particular so that its loading level with the reducing agent NH 3 as a function of a current or requested operating condition of the internal combustion engine 10 and / or of the components of the exhaust system 12, in particular the Oxidationskata- lysator 22nd or the particulate filter 24, is lowered.
• the lowering takes place preferably at present or requested temperature changes of the exhaust gas exceeding a predetermined threshold.
• An operating state in which the method is used is present, for instance, when the oxidation catalytic converter 22 has not yet reached its necessary operating temperature during an engine cold start or when regeneration of the particulate filter 24 is requested due to an exhausted storage capacity.
• highly exothermic processes on the oxidation catalyst 22 or on the particulate filter 24 due to its regeneration cause a high temperature rise or a very high load requirement of the internal combustion engine 10 by the driver.
• Catalyst 16 to a predetermined loading level, which can be predetermined differently for the different operating situations.
• the loading level of the SCR catalyst 16 is lowered to a minimum level of loading.
• the loading level can be predetermined in the form of a loading level, which is the percentage ratio of the current loading amount to the maximum loading amount, or as the specific loading amount, which is the ratio of the current loading amount and catalyst volume.
• the supply of the reducing agent via the metering unit 18 is interrupted as a first measure. Further, in the case of requesting a particulate filter regeneration or a Katalysatorwortinchdging the required increase in the exhaust gas temperature is delayed as far as possible. For this purpose, a plausibility check is provided, which checks before initiating exhaust-gas-raising measures as to whether predetermined boundary conditions exist, in this case a correspondingly low loading level of the SCR catalytic converter 16.
• the internal combustion engine 10 is changed over to the requested operating condition.
• a motor action is taken, which leads to an increase in the exhaust gas temperature. This may be, for example, an operation of the internal combustion engine 10 with reduced engine efficiency.
• the control unit 38 additionally influences at least one parameter of the internal combustion engine 10 such that an increase in the NO x raw emissions results.
• the exhaust gas recirculation rate is preferably changed and / or the injection time and / or the fuel quantity. The increased engine NO x raw emission is maintained until the desired level of loading, in particular the minimum load level, is reached.
• An advantageous embodiment of the invention provides in this context, such operating situations that lead to an undesirable increase in temperature to forecast in advance.
• the course of the pedal value can be tracked and extrapolated for a certain future duration.
• Corresponding prediction methods are familiar to the person skilled in the art and are not explained in detail at this point. It is also possible to track and extrapolate the temperature of the oxidation catalyst 22. If the extrapolation results in an expected critical increase in temperature, then the reduction agent supply is interrupted again and, if this measure is not sufficient, the increase in NO x raw emissions by the measures described above.
• the NH 3 loading level of the SCR catalyst 16 is monitored continuously.
• the cumulative NH 3 feed is determined by integration over time and a quantitative storage in the SCR catalyst 16 is assumed.
• the stored supplied NH 3 mass can be determined by taking the NH 3 storage capability of the SCR catalyst 16 from temperature-dependent maps or characteristics and taken into account. In this case, aging effects of the SCR catalyst 16 can also be taken into account with the aid of correction variables.
• the consumption of the stored NH 3 mass is determined via the NO 2 conversion in the SCR catalytic converter 16. The loading level then results from the difference of the cumulated NH 3 feed and the NH 3 mass consumed by NO x conversion in the catalyst 16.
• the balancing of the NO ⁇ conversion in the SCR catalytic converter 16 takes place by comparing the NO x content upstream and downstream of the catalytic converter 16, which can be measured or modeled in each case with NO ⁇ sensors.
• the NO x content upstream of the catalytic converter 16 can be determined as NO x raw emissions as a function of a current operating point of the internal combustion engine 10 from stored characteristic maps or detected by direct measurement with the NO x sensor 30 and the NO x content downstream of Catalyst 16 are measured with the NO x sensor.
• An improvement in the accuracy of the sales accounting is achieved if possible NO x adsorption and NO x desorption processes in the SCR catalyst 16 are taken into account.
• the loading level of the SCR catalytic converter 16 is determined until the system readiness of the NO ⁇ sensor is reached. Sensors 28, 30 by modeling, using a temperature-dependent conversion characteristic. The thus determined current NH 3 -loading level of the SCR catalytic converter 16 is stored in the control unit 38 even after switching off the internal combustion engine 10 and serves as an input variable at the next engine start.
• the inventive method thus an undesirable NH 3 -slip can be effectively prevented. Furthermore, the method allows to avoid inadmissible or undefined NH 3 loading levels of the SCR catalyst 16.

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• 2006
  • 2006-05-31 DE DE102006025257.8A patent/DE102006025257B4/de active Active
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