EP2151554B1 - Alterungsbestimmungsvorrichtung und Verfahren für Abgasreinigungsvorrichtung - Google Patents

Alterungsbestimmungsvorrichtung und Verfahren für Abgasreinigungsvorrichtung Download PDF

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Publication number
EP2151554B1
EP2151554B1 EP09166320A EP09166320A EP2151554B1 EP 2151554 B1 EP2151554 B1 EP 2151554B1 EP 09166320 A EP09166320 A EP 09166320A EP 09166320 A EP09166320 A EP 09166320A EP 2151554 B1 EP2151554 B1 EP 2151554B1
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EP
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Prior art keywords
nox
purifying catalyst
deterioration determination
amount
oxidation atmosphere
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EP09166320A
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English (en)
French (fr)
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EP2151554A1 (de
Inventor
Jun Iida
Kojiro Tsutsumi
Hidetaka Maki
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Honda Motor Co Ltd
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Honda Motor Co Ltd
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    • 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
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
    • 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
    • F01N13/0093—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 the purifying devices are of the same type
    • 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
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • 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

Definitions

  • the present invention relates to a deterioration determination device and method for an exhaust emission reduction device including a NOx purifying catalyst for purifying NOx in exhaust gases, which is configured to determine deterioration of the NOx purifying catalyst.
  • This exhaust emission reduction device includes a NOx purifying catalyst disposed in an exhaust passage of a lean-burn engine, and the NOx purifying catalyst is of a type which purifies NOx in exhaust gases by reduction reaction in the presence of HC. Further, the deterioration determination device determines deterioration of the NOx purifying catalyst, and includes a NOx concentration sensor. This NOx concentration sensor is disposed in the exhaust passage at a location downstream of the NOx purifying catalyst, for detecting NOx concentration NOxconc in the exhaust gases that have flowed through the NOx purifying catalyst.
  • a standard concentration SNOxconc of NOx is calculated by searching a map according to the engine speed and the amount of intake air, and a standard amount Sg of NOx is calculated based on the calculated standard concentration SNOxconc, the intake air amount, and the specific gravity of NOx. Then, a standard value SG is calculated by integrating the standard amount Sg (steps 3 to 5). Further, an emission amount g of NOx is calculated based on the NOx concentration NOxconc detected by the NOx concentration sensor, the intake air amount, and the gravity of NOx, and an integrated emission amount g is calculated by integrating the emission amount g (steps 7 to 9).
  • the integrated emission amount G and the standard value SG are compared with each other, and if G > GS is satisfied, it is determined that the NOx purifying catalyst has been deteriorated (steps 6, 10, and 11).
  • the emission amount g of NOx is calculated based on the NOx concentration NOxconc in exhaust gases that have flowed through the NOx purifying catalyst and the intake air amount, and by integrating the emission amount g until the predetermined execution time elapses, the integrated emission amount g used for the deterioration determination is calculated. Therefore, if the predetermined execution time is set to be short, when the engine is in an operating condition in which the flow rate of exhaust gases is decreasing or in which the NOx concentration in exhaust gases is decreasing, the computation result of the integrated emission amount g sometimes becomes so small to lower the accuracy of degradation determination. On the other hand, if the predetermined execution time is set to be long, although the determination accuracy can be improved in comparison with the case of the short predetermined execution time, it takes a longer time before obtaining the determination result.
  • US 2003/140622 A1 on which the preamble of claims 1 and 8 is based, discloses a deterioration determination device in which a NOx purifying catalyst is determined to be deteriorated (need to be regenerated) when the amount of NOx stored diminishes to (below) a predetermined level.
  • a deterioration determination device for an exhaust emission reduction device in accordance with claim 1.
  • the exhaust emission reduction device includes a NOx purifying catalyst that is provided in an exhaust passage of an internal combustion engine, for trapping, when exhaust gases forming an oxidation atmosphere flow therein, NOx in the exhaust gases, the deterioration determination device determining deterioration of the NOx purifying catalyst, comprising upstream NOx concentration parameter-detecting means for detecting a parameter indicative of a NOx concentration in exhaust gases upstream of the NOx purifying catalyst, as an upstream NOx concentration parameter, downstream NOx concentration parameter-detecting means for detecting a parameter indicative of a NOx concentration in exhaust gases downstream of the NOx purifying catalyst, as a downstream NOx concentration parameter, control means for performing oxidation atmosphere control for controlling the exhaust gases flowing into the NOx purifying catalyst to an oxidation atmosphere, NOx supply amount-calculating means for calculating an integrated value of an amount of NOx having flowed into the NOx purifying catalyst, as a NOx supply amount, using the upstream NOx concentration parameter detected during execution of the oxidation atmosphere control, NOx slip amount-calculating means
  • the oxidation atmosphere control for controlling exhaust gases flowing into the NOx purifying catalyst to the oxidation atmosphere is executed, and the integrated value of the amount of NOx flowing into the NOx purifying catalyst is calculated as the NOx supply amount, using the upstream NOx concentration parameter detected during the execution of the oxidation atmosphere control.
  • the NOx supply amount is calculated such that it accurately represents the amount of NOx having actually flowed into the NOx purifying catalyst.
  • the integrated value of the amount of NOx having flowed through the NOx purifying catalyst is calculated as the NOx slip amount.
  • the downstream NOx concentration parameter is a parameter indicative of NOx concentration in exhaust gases on the downstream side of the NOx purifying catalyst
  • the NOx slip amount is calculated such that it accurately represents the total amount of NOx having actually flowed through the NOx purifying catalyst.
  • the deterioration of the NOx purifying catalyst is determined by comparing the calculated NOx slip amount with the predetermined reference value, and hence by properly setting these predetermined threshold and predetermined reference value, when the amount of NOx having actually flowed into the NOx purifying catalyst reaches a sufficiently large value, it is possible to determine the deterioration of the NOx purifying catalyst depending on whether the total amount of NOx having actually flowed through the NOx purifying catalyst till then is large or small. This makes it possible to accurately determine the deterioration of the NOx purifying catalyst.
  • the deterioration determination device further comprises execution condition-determining means for determining whether or not conditions for executing the deterioration determination of the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and zero point-correcting means for correcting a zero point of the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination, and the NOx slip amount-calculating means calculates the NOx slip amount, using the downstream NOx concentration parameter of which the zero point has been corrected.
  • the detecting means such as the downstream NOx concentration parameter-detecting means, for detecting a parameter indicative of NOx concentration in the exhaust gases on the downstream side of the NOx purifying catalyst, has characteristics that the output thereof is liable to an aging-caused change, such as zero point drift, and hence the output characteristics thereof are prone to change, and if the exhaust gas composition is changed due to the activated state or the like of the NOx purifying catalyst, this causes an output fluctuation. For this reason, when the deterioration of the NOx purifying catalyst is determined using the downstream NOx concentration parameter-detecting means, there is a fear that the accuracy of the deterioration determination is lowered due to the aforementioned change in the output characteristics or the output fluctuation.
  • the zero point-correcting means corrects the zero point of the downstream NOx concentration parameter, and using the corrected downstream NOx concentration parameter, the NOx slip amount is calculated. Therefore, even when the downstream NOx concentration parameter-detecting means is suffering from the above-mentioned change in the output characteristics or the output fluctuation, it is possible to determine the deterioration of the NOx purifying catalyst while preventing the determination from being adversely affected by the change in the output characteristics or the output fluctuation, thereby making it possible to improve the accuracy of the deterioration determination.
  • the zero point-correcting means corrects the zero point of the downstream NOx concentration parameter based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination.
  • the zero point of the downstream NOx concentration parameter is corrected based on the average value of a plurality of values of the downstream NOx concentration parameter detected during the predetermined time period after satisfaction of the conditions for executing the deterioration determination. Therefore, even if the detection result from the downstream NOx concentration parameter-detecting means suffers from a temporary fluctuation or a relatively large temporary error during the predetermined time period, it is possible to correct the zero point of the downstream NOx concentration parameter while preventing the correction from being adversely affected by the temporary fluctuation or error, thereby making it possible to further improve the accuracy of the deterioration determination.
  • the deterioration determination device further comprises execution condition-determining means for determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and reference value-calculating means for calculating the predetermined reference value based on the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination.
  • the detecting means such as the downstream NOx concentration parameter-detecting means, for detecting a parameter indicative of the NOx concentration in the exhaust gases on the downstream side of the NOx purifying catalyst has characteristics that it is liable to a change in the output characteristics or output fluctuation, if the determination of the deterioration of the NOx purifying catalyst is carried out using the above-mentioned downstream NOx concentration parameter-detecting means, there is a fear that the accuracy of the deterioration determination is lowered.
  • the predetermined reference value is calculated by the reference value-calculating means based on the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination, and hence even when the downstream NOx concentration parameter-detecting means is suffering from the above-mentioned change in the output characteristics or output fluctuation, it is possible to calculate the predetermined reference value while causing the change in the output characteristics or output fluctuation to be reflected thereon, and determine the deterioration of the NOx purifying catalyst using the reference value calculated as above. This makes it possible to improve the accuracy of the deterioration determination.
  • the reference value-calculating means calculates the predetermined reference value based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination.
  • the predetermined reference value is calculated based on the average value of the plurality of values of the downstream NOx concentration parameter detected during the predetermined time period after satisfaction of the conditions for executing the deterioration determination, and hence even when the fluctuation or relatively-large error temporarily occurs in the detection result from the downstream NOx concentration parameter-detecting means during the predetermined time period, it is possible to calculate the predetermined reference value while preventing the calculation from being adversely affected by the temporary fluctuation or errors, thereby making it possible to further improve the accuracy of the deterioration determination.
  • the deterioration determination device further comprises execution condition-determining means for determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and the control means controls, during execution of the oxidation atmosphere control, the NOx concentration in the exhaust gases to a higher value when the conditions for executing the deterioration determination are satisfied than when the conditions for executing the deterioration determination are not satisfied.
  • the NOx concentration in the exhaust gases is controlled to be higher than when the conditions for executing the deterioration determination are not satisfied, and hence it is possible to reduce a time period required for the NOx supply amount to exceed the predetermined threshold, thereby making it possible to rapidly carry out the deterioration determination.
  • the NOx purifying catalyst has characteristics of reducing the trapped NOx when the exhaust gases flow therein form a reduction atmosphere
  • the deterioration determination device further comprising NOx trapping amount-calculating means for calculating an amount of NOx trapped by the NOx purifying catalyst during execution of the oxidation atmosphere control, as a NOx trapping amount, and the control means terminates the oxidation atmosphere control when the NOx trapping amount calculated during execution of the oxidation atmosphere control exceeds a predetermined trapping reference value, and controls the exhaust gases flowing into the NOx purifying catalyst to the reduction atmosphere
  • the deterioration determination device further comprising trapping reference value-setting means for setting the predetermined trapping reference value to a larger value when the conditions for executing the deterioration determination are satisfied during execution of the oxidation atmosphere control than when the conditions for executing the deterioration determination are not satisfied.
  • the oxidation atmosphere control when the NOx-trapping amount calculated during the execution of the oxidation atmosphere control exceeds the predetermined trapping reference value, the oxidation atmosphere control is terminated, and the exhaust gases flowing into the NOx purifying catalyst is controlled to the reduction atmosphere.
  • This causes the NOx trapped by the NOx purifying catalyst to be reduced since the NOx purifying catalyst has a characteristic that it reduces the trapped NOx when the exhaust gases forming the reduction atmosphere flow into the NOx purifying catalyst.
  • the NOx concentration in the exhaust gases is controlled to be higher than when the conditions for executing the deterioration determination are not satisfied.
  • the increasing degree of the NOx trapped by the NOx purifying catalyst becomes larger than when the conditions for executing the deterioration determination are not satisfied. Therefore, the NOx trapping amount more readily exceeds the predetermined trapping reference value, causing interruption of the oxidation atmosphere control, and hence there is a fear that it is impossible to properly determine the deterioration of the NOx purifying catalyst.
  • the predetermined NOx trapping reference value is set to a larger value than when the conditions for executing the deterioration determination are not satisfied, and hence it is possible to properly carry out the deterioration determination for the NOx purifying catalyst, while continuing the oxidation atmosphere control of the exhaust gases.
  • the deterioration determination means executes determining the deterioration of the NOx purifying catalyst when the NOx slip amount exceeds a predetermined value in a case where the NOx supply amount is not more than the predetermined threshold.
  • the determination of the deterioration of the NOx purifying catalyst is carried out, even when the amount of NOx having actually flowed into the NOx purifying catalyst does not reach a sufficiently large value, if the total amount of NOx having actually flowed through the NOx purifying catalyst is large, it is possible to carry out the determination of the deterioration of the NOx purifying catalyst by properly setting the predetermined value. This makes it possible to rapidly carry out the determination of the deterioration of the NOx purifying catalyst.
  • this deterioration determination device for the exhaust emission reduction device it is possible to reduce the time required to control the NOx in the exhaust gases to the state of high NOx concentration, thereby making it possible to suppress degradation of the exhaust emission characteristics.
  • a downstream NOx purifying catalyst is provided downstream of the NOx purifying catalyst in the exhaust passage of the engine, for trapping, when exhaust gases forming the oxidation atmosphere flow therein, NOx in the exhaust gases.
  • the downstream NOx purifying catalyst is provided in the exhaust passage at a location downstream of the NOx purifying catalyst, and hence it is possible to purify the NOx having flowed through the NOx purifying catalyst by the downstream NOx purifying catalyst during the determination of the deterioration of the NOx purifying catalyst. This makes it possible to positively prevent the degradation of the exhaust emission characteristics during the determination of the deterioration of the NOx purifying catalyst.
  • the exhaust emission reduction device includes a NOx purifying catalyst that is provided in an exhaust passage of an internal combustion engine, for trapping, when exhaust gases forming an oxidation atmosphere flow therein, NOx in the exhaust gases, the deterioration determination method determining deterioration of the NOx purifying catalyst, characterized by detecting a parameter indicative of a NOx concentration in exhaust gases upstream of the NOx purifying catalyst, as an upstream NOx concentration parameter, detecting a parameter indicative of a NOx concentration in exhaust gases downstream of the NOx purifying catalyst, as a downstream NOx concentration parameter, performing oxidation atmosphere control for controlling the exhaust gases flowing into the NOx purifying catalyst to an oxidation atmosphere, calculating an integrated value of an amount of NOx having flowed into the NOx purifying catalyst, as a NOx supply amount, using the upstream NOx concentration parameter detected during execution of the oxidation atmosphere control, calculating an integrated value of an amount of NOx having flowed through the NOx purifying catalyst, as a NOx slip amount, using the downstream NOx
  • the deterioration determination method further comprises determining whether or not conditions for executing the deterioration determination of the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and correcting a zero point of the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination, wherein the calculating the NOx slip amount includes calculating the NOx slip amount, using the downstream NOx concentration parameter of which the zero point has been corrected.
  • the correcting a zero point includes correcting the zero point of the downstream NOx concentration parameter based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination.
  • the deterioration determination method further comprises determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and calculating the predetermined reference value based on the downstream NOx concentration parameter detected after satisfaction of the conditions for executing the deterioration determination.
  • the calculating the predetermined reference value includes calculating the predetermined reference value based on an average value of a plurality of values of the downstream NOx concentration parameter detected during a predetermined time period after satisfaction of the conditions for executing the deterioration determination.
  • the deterioration determination method further comprises determining whether or not the conditions for executing the deterioration determination for the NOx purifying catalyst are satisfied during execution of the oxidation atmosphere control, and wherein the performing oxidation atmosphere control includes controlling, during execution of the oxidation atmosphere control, the NOx concentration in the exhaust gases to a higher value when the conditions for executing the deterioration determination are satisfied than when the conditions for executing the deterioration determination are not satisfied.
  • the NOx purifying catalyst has characteristics of reducing the trapped NOx when the exhaust gases flow therein form a reduction atmosphere
  • the deterioration determination method further comprising calculating an amount of NOx trapped by the NOx purifying catalyst during execution of the oxidation atmosphere control, as a NOx trapping amount, wherein the performing oxidation atmosphere control includes terminating the oxidation atmosphere control when the NOx trapping amount calculated during execution of the oxidation atmosphere control exceeds a predetermined trapping reference value, and controls the exhaust gases flowing into the NOx purifying catalyst to the reduction atmosphere
  • the deterioration determination method further comprising trapping reference value-setting means for setting the predetermined trapping reference value to a larger value when the conditions for executing the deterioration determination are satisfied during execution of the oxidation atmosphere control than when the conditions for executing the deterioration determination are not satisfied.
  • the determining deterioration includes executing determining the deterioration of the NOx purifying catalyst when the NOx slip amount exceeds a predetermined value in a case where the NOx supply amount is not more than the predetermined threshold.
  • a downstream NOx purifying catalyst is provided downstream of the NOx purifying catalyst in the exhaust passage of the engine, for trapping, when exhaust gases forming the oxidation atmosphere flow therein, NOx in the exhaust gases.
  • the deterioration determination device 1 includes an ECU 2, and the ECU 2 performs various control processes, including an air-fuel ratio control process for an internal combustion engine (hereinafter simply referred to as "the engine") 3, and performs a deterioration determination process for an exhaust emission reduction device 10.
  • the engine an air-fuel ratio control process for an internal combustion engine (hereinafter simply referred to as "the engine") 3, and performs a deterioration determination process for an exhaust emission reduction device 10.
  • the engine 3 is a diesel engine that is installed on a vehicle, not shown, and includes a plurality of pairs (only one pair is shown) of cylinders 3a and pistons 3b.
  • the engine 3 has a cylinder head 3c having fuel injection valves 4 inserted into the cylinders 3a thereof in a manner facing respective associated combustion chambers.
  • the fuel injection valves 4 are connected to a high-pressure pump and a fuel tank via a common rail, none of which are shown. Fuel pressurized by the high-pressure pump is supplied to each fuel injection valves 4 via the common rail to be injected therefrom into the cylinders 3a.
  • the ECU 2 controls a valve opening time period and valve opening timing of each fuel injection valve 4, thereby executing fuel injection control.
  • the engine 3 is provided with a crank angle sensor 20.
  • the crank angle sensor 20 is formed by a magnet rotor and an MRE pickup, and delivers a CRK signal and a TDC signal, which are both pulse signals, to the ECU 2 in accordance with rotation of a crankshaft 3d.
  • One pulse of the CRK signal is delivered whenever the crankshaft 3d rotates through a predetermined angle (e.g. 10 ° ).
  • the ECU 2 calculates the rotational speed NE of the engine 3 (hereinafter referred to as "the engine speed NE") based on the CRK signal.
  • the TDC signal indicates that each piston 3b in an associated one of the cylinders 3a is in a predetermined crank angle position slightly before the TDC position at the start of the intake stroke thereof, and one pulse thereof is delivered whenever the crankshaft 3d rotates through a predetermined crank angle.
  • the engine 3 has an intake passage 5 having an air flow sensor 21 inserted therein, which detects an amount (intake air amount) GAIR of air sucked into the cylinders 3a, to deliver a signal indicative of the sensed intake air amount GAIR to the ECU 2.
  • the engine 3 has an exhaust passage 7 provided with the exhaust emission reduction device 10 which includes a NOx purifying catalyst 11, a downstream NOx purifying catalyst 12 and so forth.
  • the NOx purifying catalyst 11 has a capability of trapping (storing) NOx in exhaust gases flowing therein, provided that the exhaust gases form an oxidation atmosphere.
  • the NOx trapped by the NOx purifying catalyst 11 is reduced by reacting with a reducing agent when exhaust gases forming a reduction atmosphere flow into the NOx purifying -catalyst 11.
  • downstream NOx purifying catalyst 12 similarly to the NOx purifying catalyst 11, the downstream NOx purifying catalyst 12 also has a capability of trapping NOx in exhaust gases flowing therein when the exhaust gases forming the oxidation atmosphere flow therein.
  • the NOx trapped by the downstream NOx purifying catalyst 12 is reduced by reacting with the reducing agent when the exhaust gases forming the reduction atmosphere flow into the downstream NOx purifying catalyst 12.
  • the exhaust passage 7 has an upstream NOx sensor 22 disposed upstream of the NOx purifying catalyst 11, and a downstream NOx sensor 23 disposed downstream of the NOx purifying catalyst 11.
  • the upstream NOx sensor 22 detects NOx concentration in the exhaust gases flowing in the exhaust passage 7 to deliver a signal indicative of the detected NOx concentration to the ECU 2.
  • the ECU 2 calculates NOx concentration (hereinafter referred to as "the upstream NOx concentration") CNOx_Pre in exhaust gases on the upstream side of the NOx purifying catalyst 11, based on the detection signal from the upstream NOx sensor 22.
  • the upstream NOx sensor 22 corresponds to upstream NOx concentration parameter-detecting means
  • the upstream NOx concentration CNOx_Pre corresponds to a upstream NOx concentration parameter.
  • downstream NOx sensor 23 similarly to the upstream NOx sensor 22, the downstream NOx sensor 23 also detects NOX concentration in exhaust gases that flowing in the exhaust passage 7 to deliver a signal indicative of the detected NOx concentration to the ECU 2.
  • the ECU 2 calculates NOx concentration (hereinafter referred to as "the downstream NOx concentration") CNOx_Post in the exhaust gases that have flowed through the NOx purifying catalyst 11, based on the detection signal from the downstream NOx sensor 23.
  • the downstream NOx sensor 23 corresponds to downstream NOx concentration parameter-detecting means
  • the downstream NOx concentration CNOx_Post corresponds to a downstream NOx concentration parameter.
  • the NOx purifying catalyst 11 has a catalyst temperature sensor 24 mounted thereon, for detecting temperature (hereinafter referred to as "the catalyst temperature") TCAT of the NOx purifying catalyst 11 to deliver a signal indicative of the detected catalyst temperature to the ECU 2.
  • the catalyst temperature detecting temperature (hereinafter referred to as "the catalyst temperature") TCAT of the NOx purifying catalyst 11 to deliver a signal indicative of the detected catalyst temperature to the ECU 2.
  • the engine 3 is provided with an exhaust recirculation mechanism 8.
  • This exhaust recirculation mechanism 8 recirculates part of exhaust gases in the exhaust passage 7 to the intake passage 5, and is comprised of an EGR passage 8a connecting between the intake passage 5 and the exhaust passage 7, and an EGR control valve 8b which opens and closes the EGR passage 8a.
  • One end of the EGR passage 8a opens into a portion of the exhaust passage 7 upstream of the NOx purifying catalyst 11, and the other end of EGR passage 8a opens into a portion of the intake passage 5 downstream of the air flow sensor 21.
  • the EGR control valve 8b is formed by a linear solenoid valve of which the opening is linearly changed between a maximum value and a minimum value, and is electrically connected to the ECU 2.
  • the ECU 2 controls a recirculation amount of exhaust gases, i.e. an EGR amount by changing the opening of the EGR passage 8a via the EGR control valve 8b.
  • the ECU 2 controls the air-fuel ratio, as described hereinafter, by performing the EGR amount control and the above-mentioned fuel injection control.
  • the engine 3 is normally operated in a lean combustion state in which a mixture leaner than the stoichiometric air-fuel ratio is burned, and during rich spike control, referred to hereinafter, it is operated in a rich combustion state in which a mixture richer than the stoichiometric air-fuel ratio is burned.
  • the ECU 2 has an accelerator opening sensor 25 electrically connected thereto.
  • the accelerator opening sensor 25 detects a stepped-on amount (hereinafter referred to as "accelerator opening") AP of an accelerator pedal, not shown, and delivers a detection signal indicative of the detected accelerator opening AP to the ECU 2.
  • the ECU 2 is implemented by a microcomputer comprised of a CPU, a RAM, a ROM, and an I/O interface (none of which is shown).
  • the ECU 2 determines operating conditions of the engine 3 according to the detection signals from the aforementioned sensors 20 to 25 and carries out various control processes. Specifically, as described hereinafter, the ECU 2 carries out an air-fuel ratio control process, and a deterioration determination process for determining deterioration of the NOx purifying catalyst 11 of the exhaust emission reduction device 10.
  • the ECU 2 corresponds to the upstream NOx concentration parameter-detecting means, the downstream NOx concentration parameter-detecting means, control means, NOx supply amount-calculating means, NOx slip amount-calculating means, deterioration determination means, execution condition-determining means, zero point-correcting means, NOx trapping amount-calculating means, and trapping reference value-setting means, in the present invention.
  • This process calculates a fuel injection amount QINJ indicative of the amount of fuel injected by each fuel injection valve 4 and fuel injection timing ⁇ INJ, and controls the EGR amount through the EGR control valve 8b.
  • the process is executed at a control period synchronized with occurrence of the TDC signal pulse.
  • step 1 it is determined whether or not a rich condition flag F_RICH is equal to 1.
  • the rich condition flag F_RICH is set in a process for setting the rich condition flag F_RICH, as described hereinafter.
  • step 2 If the answer to the question of the step 1 is negative (NO), the process proceeds to a step 2, wherein it is determined whether or not a high NOx condition flag F_NOxUP is equal to 1.
  • the value of the high NOx condition flag F_NOxUP is set in the deterioration determination process, referred to hereinafter.
  • step 3 a lean control process is executed.
  • demanded torque PMCMD for lean control is calculated by searching a map, not shown, according to the accelerator pedal opening AP and the engine speed NE, and a map, not shown, is searched according to the demanded torque PMCMD for lean control and the engine speed NE, to thereby calculate a fuel injection amount QINJ for lean control. Further, a map, not shown, is searched according to the fuel injection amount QINJ for lean control and the engine speed NE, to thereby calculate fuel injection timing ⁇ INJ for lean control.
  • a map is searched according to the demanded torque PMCMD for lean control and the engine speed NE, to thereby calculate a target intake air amount GAIR_CMD for lean control, and the EGR control valve 8b is feedback-controlled such that the intake air amount GAIR converges to the target intake air amount GAIR_CMD.
  • the present process is terminated.
  • This controls the air-fuel ratio of the engine 3 to a value leaner than the stoichiometric air-fuel ratio.
  • the exhaust gases forming the oxidation atmosphere are exhausted from the engine 3 into the exhaust passage 7.
  • step 4 a rich spike control process is executed.
  • demanded torque PMCMD for rich spike control is calculated by searching a map, not shown, according to the accelerator pedal opening AP and the engine speed NE, and a map, not shown, is searched according to the demanded torque PMCMD for rich spike control and the engine speed NE, to thereby calculate the fuel injection amount QINJ for rich spike control.
  • a map, not shown is searched according to the fuel injection amount QINJ for rich spike control and the engine speed NE, to thereby calculate fuel injection timing ⁇ INJ for rich spike control.
  • a map is searched according to the demanded torque PMCMD for rich spike control and the engine speed NE, to thereby calculate a target intake air amount GAIR_CMD for rich spike control, and the EGR control valve 8b is feedback-controlled such that the intake air amount GAIR converges to the target intake air amount GAIR_CMD.
  • the present process is terminated.
  • This controls the air-fuel ratio of the engine 3 to a value richer than the stoichiometric air-fuel ratio.
  • the exhaust gases forming the reduction atmosphere are exhausted from the engine 3 into the exhaust passage 7, whereby the NOx trapped by the NOx purifying catalyst 11 is reduced.
  • step 5 the high NOx concentration control process is executed. Specifically, the high NOx concentration control process is executed as shown in FIG. 3 .
  • the fuel injection amount QINJ and the fuel injection timing ⁇ INJ for high NOx concentration control are calculated in a manner similar to the above-described lean control process and the rich spike control process. That is, demanded torque PMCMD for high NOx concentration control is calculated by searching a map, not shown, according to the accelerator pedal opening AP and the engine speed NE, and a map, not shown, is searched according to the demanded torque PMCMD for high NOx concentration control and the engine speed NE, to thereby calculate the fuel injection amount QINJ and the fuel injection timing ⁇ INJ for high NOx concentration control.
  • a map, not shown, is searched according to the demanded torque PMCMD for high NOx concentration control and the engine speed NE, to thereby calculate the target intake air amount GAIR_CMD for high NOx concentration control.
  • the process proceeds to a step 12, wherein the EGR control process is executed, followed by terminating the present process.
  • the EGR control value 8b is feedback-controlled such that the intake air amount GAIR converges to the target intake air amount GAIR_CMD, to thereby control the EGR amount to be less than that during the lean control.
  • the exhaust gases exhausted from the engine 3 into the exhaust passage 7 are controlled to the same oxidation atmosphere as during the lean control, and the NOx concentration is controlled to a higher value than that during the lean control.
  • the upstream NOx concentration CNOx_Pre is controlled to a predetermined upper limit CNOx_H, referred to hereafter.
  • the air-fuel ratio control process is terminated.
  • This process determines deterioration of the NOx purifying catalyst 11 based on the upstream NOx concentration CNOx_Pre and the downstream NOx concentration CNOx_Post, and is executed at a predetermined control period ⁇ T (e.g. 10 msec).
  • a judgment condition satisfaction flag F_JUD is set in a setting process shown in FIG. 5 .
  • the judgment condition satisfaction flag F_JUD is set in a setting process shown in FIG. 5 .
  • the judgment condition satisfaction flag F_JUD is set to 1, whereas if not, the judgment condition satisfaction flag F_JUD is set to 0. In the step 40, the judgment condition satisfaction flag F_JUD is set as above, followed by terminating the present process.
  • step 20 if the answer to the question of the step 20 is negative (NO), i.e. the conditions for the deterioration determination of the NOx purifying catalyst 11 are not satisfied, it is determined that the deterioration determination of the NOx purifying catalyst 11 should not be executed, so that the process proceeds to a step 21, wherein both of two flags F_ZERO and F_CAL, referred to hereinafter, are set to 0, followed by terminating the present process.
  • step 22 it is determined whether or not the zero point correction completion flag F_ZERO is equal to 1. If the answer to the question of the step 22 is negative (NO), the zero point correction of the downstream NOx concentration CNOx_Post should be executed, so that the process proceeds to a step 23, wherein the zero point correction process is executed as described hereinafter, followed by terminating the present process.
  • the downstream NOx concentration CNOx_Post calculated based on the detection signals from the downstream NOx sensor 23 is sampled at each control period ⁇ T, and when a predetermined number of (e.g. 100) calculated values of the downstream NOx concentration CNOx_Post have been sampled, the predetermined number of the sampled values of the downstream NOx concentration CNOx_Post are averaged (the arithmetic mean thereof is calculated) to thereby calculate an average value. Then, after calculating the average value, the average value is subtracted from an actual value of the downstream NOx concentration CNOx_Post calculated based on the detection signal from the downstream NOx sensor 23 to thereby calculate the zero point-corrected downstream NOx concentration CNOx_Post.
  • a predetermined number of (e.g. 100) calculated values of the downstream NOx concentration CNOx_Post are averaged (the arithmetic mean thereof is calculated) to thereby calculate an average value.
  • the zero point correction completion flag F_ZERO is set to 1. It should be noted that in the present embodiment, a time period required for the predetermined number of calculated values of the downstream NOx concentration CNOx_Post to be sampled corresponds to the predetermined time period.
  • the process proceeds to a step 24, wherein it is determined whether or not the reference value calculation completion flag F_CAL is equal to 1.
  • NOx trapping capability NOxS is calculated by searching a map in FIG. 6 according to the NOx trapping amount S_QNOx.
  • the NOx trapping amount S_QNOx is the amount of NOx estimated to have been trapped by the NOx purifying catalyst 11, and is calculated in a rich condition flag F_RICH setting process, as described hereinafter.
  • the NOx trapping capability NoxS indicates the amount of NOx which can be trapped by the NOx purifying catalyst 11, and in the map in FIG. 6 , as the NOx trapping amount S_QNOx is larger, the NOx trapping capability NoxS is set to a smaller value. This is because the NOx trapping amount S_QNOx is the amount of NOx estimated to have been trapped by the NOx purifying catalyst 11, and hence as the NOx trapping amount S_QNOx is larger, the amount of NOx which can be trapped by the NOx purifying catalyst 11 becomes smaller.
  • a catalyst temperature-dependent correction coefficient CorTCAT is calculated by searching a map in FIG. 7 according to the catalyst temperature TCAT.
  • TREFa to TREFd are predetermined values of the catalyst temperature TCAT set such that TREFa ⁇ TREFb ⁇ TREFc ⁇ TREFd holds.
  • the catalyst temperature-dependent correction coefficient CorTCAT is set to a smaller value as the catalyst temperature TCAT is lower.
  • the catalyst temperature-dependent correction coefficient CorTCAT is set to a fixed value. This is because when the catalyst temperature TCAT is in the range of TREFb ⁇ TCAT ⁇ TREFc, the activity of the NOx purifying catalyst 11 does not change. Further, in a range of TREFc ⁇ TCAT ⁇ TREFd, the catalyst temperature-dependent correction coefficient CorTCAT is set to a smaller value as the catalyst temperature TCAT is higher.
  • an exhaust gas flow rate-dependent correction coefficient CorQGAS is calculated by searching a map shown in FIG. 8 according to the exhaust gas flow rate QGAS. In this map, the exhaust gas flow rate-dependent correction coefficient CorQGAS is set to a smaller value as the exhaust gas flow rate QGAS is larger.
  • the process proceeds to a step 29, wherein the reference value calculation completion flag F_CAL is set to 1, followed by terminating the present process.
  • the process proceeds to a step 30, wherein it is determined whether or not the high NOx condition flag F_NOxUP is equal to 1. If the answer to the question of the step 30 is negative (NO), the process proceeds to a step 31, wherein, to indicate the fact that the high NOx concentration control should be executed, the high NOx condition flag F_NOxUP is set to 1, followed by terminating the present process.
  • sumPreNOxZ represents the immediately preceding value of the NOx supply amount.
  • the second term of the right side of the equation (2) is the product CNOx_Pre ⁇ QGAS ⁇ ⁇ T of the upstream NOx concentration, the flow rate of exhaust gases, and the control period, and hence represents the amount of NOx supplied to the NOx purifying catalyst 11 during the time period between the immediately preceding control timing and the present control timing.
  • sumPostNOxZ represents the immediately preceding value of the NOx slip amount.
  • the second term of the right side of the equation (3) is the product CNOx_Post ⁇ QGAS ⁇ ⁇ T of the downstream NOx concentration, the flow rate of exhaust gases, and the control period, and hence represents the amount of NOx having flowed through the NOx purifying catalyst 11 without being trapped by the NOx purifying catalyst 11 during the time period between the start timing of the high NOx concentration control process and the present control timing.
  • the NOx slip amount sumPostNOx is calculated by integrating the above-mentioned value CNOx_Post ⁇ QGAS ⁇ ⁇ T, the NOx slip amount sumPostNOx represents the total amount of NOx which is estimated to have flowed through the NOx purifying catalyst 11 during the time period between the start timing of the high NOx concentration control process and the present control timing.
  • a step 34 it is determined whether or not sumPreNOx > NOxREF holds. If the answer to the question of the step 34 is affirmative (YES), i.e. sumPreNOx > NOxREF holds, it is determined that the amount of NOx enough to carry out the deterioration determination of the NOx purifying catalyst 11 has been supplied to the NOx purifying catalyst 11, so that the process proceeds to a step 36, referred to hereinafter.
  • NOxREF2 is a predetermined reference value (predetermined value) of the NOx slip amount sumPostNOx, and is set to a fixed value.
  • step 35 If the answer to the question of the step 35 is negative (NO), the process is immediately terminated. On the other hand, if the answer to the question of the step 35 is affirmative (YES), i.e. sumPostNOx > NOxREF2 holds, the amount of NOx having flowed through the NOx purifying catalyst 11 is large, and hence it is determined that the deterioration determination of the NOx purifying catalyst 11 should be carried out, so that the process proceeds to the step 36.
  • a catalyst deterioration flag F_CATNG setting process is executed. Specifically, the catalyst deterioration flag F_CATNG setting process is executed as shown in FIG. 9 .
  • a step 50 it is determined whether or not the NOx slip amount sumPostNOx is larger than a predetermined reference value NOxJUD.
  • the reference value NOxJUD is set to a fixed value. If the answer to the question of the step 50 is negative (NO), i.e. sumPostNox ⁇ NOxJUD holds, it is determined that the NOx purifying catalyst 11 has not been deteriorated, so that the process proceeds to a step 51, wherein to indicate this fact, the catalyst deterioration flag F_CATNG is set to 0.
  • step 53 the high NOx condition flag F_NOxUP is set to 0.
  • step 54 both of the NOx supply amount sumPreNOx and the NOx slip amount sumPostNOx are set to 0, followed by terminating the present process.
  • the catalyst deterioration flag F_CATNG setting process is executed as described above, followed by terminating the present deterioration determination process.
  • the process may be configured to compare the NOx slip amount sumPostNOx with the reference value NOxJUD used in the above-mentioned step 50 in place of the reference value NOxREF2.
  • step 60 it is determined whether or not the rich condition flag F_RICH is equal to 1. If the answer to the question of the step 60 is negative (NO), the process proceeds to a step 61, wherein the NOx trapping amount S_QNOx is calculated.
  • the NOx trapping amount S_QNOx is the amount of NOx estimated to have been trapped by the NOx purifying catalyst 11, as mentioned hereinabove, and is specifically calculated as follows: A NOx exhaust amount QNOx exhausted from the combustion chamber of the engine 3 into the exhaust passage 7 is calculated by searching a map, now shown, according to parameters, such as the demanded torque PMCMD, the engine speed NE, the intake air amount GAIR, and the opening of the EGR control valve 8b (i.e. EGR amount), and the NOx trapping amount S_QNOx is calculated by integrating the calculated NOx exhaust amount QNOx.
  • step 62 it is determined whether or not the above-mentioned high NOx condition flag F_NOxUP is equal to 1. If the answer to the question of the step 62 is negative (NO), i.e. if the lean control is being executed, the process proceeds to a step 63, wherein a trapping reference value SREF is set to a first predetermined value SREF1.
  • the process proceeds to a step 64, wherein the trapping reference value SREF is set to a second predetermined value SREF2.
  • the first and second predetermined values SREF1 and SREF2 are set to fixed values such that SREF1 ⁇ SREF2 holds. This is because during execution of the high NOx concentration control, the operation of the engine 3. is controlled such that the NOx concentration in exhaust gases becomes higher than that during the lean control, so that the increasing degree of the NOx trapping amount S_QNOx becomes larger than that during the lean control.
  • a step 65 following the step 63 or 64 it is determined whether or not the NOx trapping amount S_QNOx is larger than the trapping reference value SREF. If the answer to the question of the step 65 is negative (NO), it is determined that the lean control or the high NOx concentration control should be continued, and hence the process is immediately terminated, whereas if the answer to the question of the step 65 is affirmative (YES), it is determined that the rich spike control should be executed, so that the process proceeds to a step 66, wherein to indicate this fact, the rich condition flag F_RICH is set to 1, followed by terminating the present process.
  • a subtraction value DEC is calculated.
  • the subtraction value DEC is an amount of NOx estimated to have been reduced by the NOx purifying catalyst 11 during a time period between the immediately preceding control timing and the present control timing by execution of the rich spike control.
  • the subtraction value DEC is calculated by searching a map, not shown, according to the parameters indicative of the operating conditions (e.g. the demanded torque PMCMD, the engine speed NE, the intake air amount GAIR, and the opening of the EGR control valve 8b).
  • step 68 the NOx trapping amount S_QNOx is set to a value (S_QNOxZ - DEC) obtained by subtracting the subtraction value DEC from the immediately preceding value S_QNOxZ of the NOx trapping amount S_QNOx.
  • step 69 it is determined whether or not the NOx trapping amount S_QNOx is not more than a predetermined termination reference value SDEC. If the answer to the question of the step 69 is negative (NO), it is determined that the rich spike control should be continued, so that the present process is immediately terminated.
  • the downstream NOx concentration CNOx_Post also rises with the lapse of time after the NOx supply amount sumPreNOx starts to rise, and the NOx slip amount sumPostNOx also rises with the lapse of time. Then, when the condition of sumPreNOx > NOxREF is satisfied (at a time point t4), the condition of sumPostNOx > NOxJUD is satisfied, whereby it is determined that the NOx purifying catalyst 11 has been deteriorated.
  • the zero point-corrected downstream NOx concentration CNOx_Post is calculated based on the detection signal values from the downstream NOx sensor 23, and the NOx slip amount sumPostNOx is calculated based on the calculated zero point-corrected downstream NOx concentration CNOx_Post.
  • the upstream NOx concentration CNOx_Pre is calculated based on the detection signal values from the upstream NOx sensor 22, and the NOx supply amount sumPreNOx is calculated based on the calculated upstream NOx concentration CNOx_Pre.
  • the deterioration determination of the NOx purifying catalyst 11 is carried out by comparing the NOx slip amount sumPostNOx with the predetermined reference value NOxJUD. That is, the deterioration of the NOx purifying catalyst 11 is determined depending on whether the total amount of NOx estimated to have flowed through the NOx purifying catalyst 11 is large or small at the time point at which the amount of NOx having actually flowed into the NOx purifying catalyst 11 has reached a sufficiently large value.
  • a sensor such as the downstream NOx sensor 23, which detects a parameter indicative of NOx concentration in exhaust gases downstream of the NOx purifying catalyst 11 has characteristics that the output thereof is liable to an aging-caused change, such as zero point drift, and hence the output characteristics thereof are prone to change, and if the exhaust gas composition is changed due to the activated state of the NOx purifying catalyst 11, this causes an output fluctuation. For this reason, when the deterioration of the NOx purifying catalyst 11 is determined using the downstream NOx sensor 23, there is a fear that the accuracy of calculation of the downstream NOx concentration CNOx_Post is lowered, and hence the accuracy of the deterioration determination is lowered.
  • the zero point-corrected downstream NOx concentration CNOx_Post is used, and hence even if the downstream NOx sensor 23 is suffering from the above-mentioned change in the output characteristics or the output fluctuation immediately before starting the deterioration determination, it is possible to determine the deterioration of the NOx purifying catalyst 11 while preventing the determination from being adversely affected by the change in the output characteristics or the output fluctuation, thereby making it possible to improve the accuracy of the deterioration determination.
  • the predetermined number of the downstream NOx concentration CNOx_Post calculated based on the detection signal from the downstream NOx sensor 23 after the conditions for the deterioration determination of the NOx purifying catalyst 11 are satisfied are sampled, and by using the average value of these sampled values as the correction term, the zero point-corrected downstream NOx concentration CNOx_Post is calculated.
  • the high NOx concentration control process of the step 5 is executed in the air-fuel ratio control process in FIG. 2 .
  • This controls the exhaust gases exhausted from the engine 3 into the exhaust passage 7 to the same oxidation atmosphere as during in the lean control, and controls the NOx concentration in the exhaust gases to be higher than that during the lean control, whereby it is possible to reduce a time period required for the answer to the question of the step 34 or 35 in FIG. 4 to become affirmative (YES). As a result, it is possible to rapidly execute the deterioration determination of the NOx purifying catalyst 11.
  • the deterioration determination of the NOx purifying catalyst 11 is executed by comparing the NOx slip amount sumPostNOx with the predetermined reference value NOxJUD in the steps 50 to 52. That is, even when the amount of NOx having actually flowed into the NOx purifying catalyst 11 is small, if the total amount of NOx having actually flowed through the NOx purifying catalyst 11 is large, which means that there is a high possibility that the NOx purifying. catalyst 11 has been deteriorated, the high NOx concentration control is interrupted by executing the deterioration determination of the NOx purifying catalyst 11.
  • the trapping reference value SREF for comparison with the NOx trapping amount S_QNOx is set to the second predetermined value SREF2 which is larger than the first predetermined value SREF1 during the lean control.
  • downstream NOx purifying catalyst 12 is disposed downstream of the NOx purifying catalyst 11 in the exhaust passage 7, and therefore during the deterioration determination of the NOx purifying catalyst 11, it is possible to purify the NOx having flowed through the NOx purifying catalyst 11 by the downstream NOx purifying catalyst 12. This makes it possible to positively prevent the exhaust emission characteristics from being degraded during the deterioration determination of the NOx purifying catalyst 11.
  • the first embodiment is an example in which the upstream NOx sensor 22 is employed as the upstream NOx concentration parameter-detecting means, this is not limitative, but any suitable upstream NOx concentration parameter-detecting means may be employed insofar as it is capable of detecting a parameter indicative of NOx concentration on the upstream side of the NOx purifying catalyst.
  • the first embodiment is an example in which the downstream NOx sensor 23 is employed as the downstream NOx concentration parameter-detecting means, this is not limitative, but any suitable downstream NOx concentration parameter-detecting means may be employed insofar as it is capable of detecting a parameter indicative of NOx concentration on the downstream side of the NOx purifying catalyst.
  • the zero point correction process may be executed as follows: The detection signal value from the downstream NOx sensor 23 is sampled at each control period ⁇ T, and when a predetermined number of (e.g. 100) detection signal values have been sampled, the predetermined number of the sampled values are averaged (arithmetic mean thereof is calculated) to thereby calculate the correction term. Then, after the calculation of the correction term, the downstream NOx concentration CNOx_Post is calculated based on a value obtained by subtracting the correction term from the actual detection signal value from the downstream NOx sensor 23. Even when the zero point correction process is executed as above in the step 23 in FIG. 4 , it is possible to obtain the same advantageous effects as provided by the first embodiment.
  • a predetermined number of (e.g. 100) detection signal values have been sampled
  • the predetermined number of the sampled values are averaged (arithmetic mean thereof is calculated) to thereby calculate the correction term.
  • the downstream NOx concentration CNOx_Post is calculated based on a value obtained by subtracting the correction term
  • the first embodiment is an example in which the high NOx concentration control process is executed as shown in FIG. 3 , this is not limitative, but any suitable high NOx concentration control process may be executed insofar as it controls the exhaust gases flowing into the NOx purifying catalyst 11 to the same oxidation atmosphere as during the lean control, and controls the NOx concentration in the exhaust gases to a higher value than that during the lean control.
  • the high NOx concentration control process may be executed as shown in FIG. 12 .
  • the fuel injection amount QINJ for high NOx concentration control and the fuel injection timing ⁇ INJ for high NOx concentration control are calculated in a manner similar to the step 10.
  • a target value CNOx_PreCMD of the upstream NOx concentration CNOx_Pre is calculated by searching a map, not shown, according to the demanded torque PMCMD for high NOx concentration control and the engine speed NE.
  • This target value CNOx_PreCMD is set to a higher value than the upstream NOx concentration CNOx_Pre in the lean control.
  • a step 73 following the step 72 the EGR control process is executed. Specifically, the EGR control valve 8b is feedback-controlled such that the upstream NOx concentration CNOx_Pre converges to the above-mentioned target value CNOx_PreCMD. Then, the present process is terminated.
  • the exhaust gases exhausted from the engine 3 into the exhaust passage 7 are controlled to form the same oxidation atmosphere as during the lean control, and the upstream NOx concentration CNOx_Pre is controlled to a higher value than that during the lean control. This makes it possible to accurately and rapidly execute the deterioration determination of the NOx purifying catalyst 11.
  • a deterioration determination device for an exhaust emission reduction device is different from the deterioration determination device 1 according to the first embodiment only in that a deterioration determination process shown in FIG. 13 is executed by the ECU 2 in place of the deterioration determination process shown in FIG. 4 in the first embodiment, so that only the deterioration determination process shown in FIG. 13 will be explained.
  • the ECU 2 corresponds to upstream NOx concentration parameter-detecting means, downstream NOx concentration parameter-detecting means, control means, NOx supply amount-calculating means, NOx slip amount-calculating means, deterioration determination means, execution condition-determining means, reference value-calculating means, NOx trapping amount-calculating means, and trapping reference value-setting means.
  • the.deterioration determination of the NOx purifying catalyst 11 is carried out based on the upstream NOx concentration CNOx_Pre and the downstream NOx concentration CNOx_Post, and is executed at the predetermined control period ⁇ T (e.g. 10 msec).
  • a step 80 it is determined whether or not the above-mentioned judgment condition satisfaction flag F_JUD is equal to 1. If the answer to the question of the step 80 is negative (NO), i.e. if the conditions for the deterioration determination of the NOx purifying catalyst 11 are not satisfied, it is determined that the deterioration determination of the NOx purifying catalyst 11 should not be executed, and the process proceeds to a step 81, wherein both of an averaged value calculation completion flag F_AVE, referred to hereinafter and the above-mentioned reference value calculation completion flag F_CAL are set to 0, followed by terminating the present process.
  • the process proceeds to a step 82, wherein it is determined whether or not the average value calculation completion flag F_AVE is equal to 1. If the answer to the question of the step 82 is negative (NO), it is determined that an average value aveCNOx of the downstream NOx concentration CNOx_Post should be calculated, so that the process proceeds to a step 83, wherein a process of calculating the average value aveCNOx is executed, followed by terminating the present process. It should be noted that in the present embodiment, the average value aveCNOx corresponds to the average value of the downstream NOx concentration parameters.
  • the average value aveCNOx is calculated as follows: First, the downstream NOx concentration CNOx_Post is calculated at each control period ⁇ T based on the detection signal from the downstream NOx sensor 23, and the calculated value is sampled. Then, when a predetermined number of (e.g. 100) calculated values of the downstream NOx concentration CNOx_Post are sampled, the predetermined number of sampled values of the downstream NOx concentration CNOx_Post are averaged (arithmetic mean thereof is calculated) to thereby calculate the average value aveCNOx. It should be noted that in the present embodiment, a time period required for the predetermined number of downstream NOx concentration CNOx_Post to be sampled corresponds to the predetermined time period. Then, when the average value aveCNOx is calculated, to indicate that the average value has been calculated, the averaged value calculation completion flag F_AVE is set to 1.
  • step 83 If the averaged value calculation completion flag F_AVE is set to 1 in the step 83 as described above, the answer to the question of the step 82 becomes affirmative (YES), and in this case, the process proceeds to a step 84, wherein it is determined whether or not the reference value calculation completion flag F_CAL is equal to 1.
  • step 84 If the answer to the question of the step 84 is negative (NO), it is determined that the NOx supply amount reference value NOxREF should be calculated, so that steps 85 to 89 are executed similarly to the above described steps 25 to 29, followed by terminating the present process.
  • step 89 If the step 89 is executed as above, the answer to the question of the step 84 becomes affirmative (YES), and in this case, the process proceeds to a step 90, wherein it is determined whether or not the above-mentioned high NOx concentration condition flag F_NOxUP is equal to 1. If the answer to the question of the step 90 is negative (NO), it is determined that the high NOx concentration control should be executed, so that the process proceeds to a step 91, wherein to indicate this fact, the high NOx concentration condition flag F_NOxUP is set to 1, followed by terminating the present process.
  • step 91 If the high NOx concentration condition flag F_NOxUP is set to 1 in the step 91 as described above, the answer to the question of the step 90 becomes affirmative (YES), and in this case, the process proceeds to a step 92, wherein the NOx supply amount sumPreNOx is calculated by the above-mentioned equation (2).
  • step 93 wherein the NOx slip amount sumPostNOx is calculated by the above-mentioned equation (3).
  • sumQGAS represents the immediately preceding value of the exhaust supply amount.
  • the second term of the right side of the equation (4) is the product QGAS ⁇ T of the exhaust flow rate and the control period, and hence indicates the amount of exhaust gases estimated to have been supplied to the NOx purifying catalyst 11 during the time period between the immediately preceding control timing and the present control timing.
  • the exhaust gas supply amount sumQGAS is calculated by integrating the above-mentioned value QGAS ⁇ T, and hence represents the total amount of exhaust gases estimated to have been supplied to the NOx purifying catalyst 11 during the time period between the start timing of the high NOx concentration control process and the present control timing.
  • step 95 wherein similarly to the above-mentioned step 34, it is determined whether or not the condition of sumPreNOx > NOxREF is satisfied. If the answer to the question of the step 95 is affirmative (YES), i.e. if the condition of sumPreNOx > NOxREF is satisfied, it is determined that the enough amount of NOx for executing the deterioration determination of the NOx purifying catalyst 11 has been supplied to the NOx purifying catalyst 11, so that the process proceeds to a step 97.
  • step 95 determines whether or not the condition of sumPostNOx > NOxREF2 is satisfied. If the answer to the question of the step 96 is negative (NO), the present process is immediately terminated. On the other hand, if the answer to the question of the step 96 is affirmative (YES), the process proceeds to the step 97.
  • C1 represents a predetermined constant.
  • the reference value NOxJUD2 is calculated by adding the product sumQGAS ⁇ aveCNOx of the exhaust supply amount and the average value to the constant C1, and hence is calculated such that it represents the total amount of NOx estimated to have been supplied to the NOx purifying catalyst 11 during the time period between the start timing of the high NOx concentration control process and the present control timing.
  • step 101 it is determined whether or not the NOx slip amount sumPostNOx is larger than the reference value NOxJUD2. If the answer to the question of the step 101 is negative (NO), i.e. if sumPostNOx NOxJUD2 holds, it is determined that the NOx purifying catalyst 11 has not been deteriorated, so that the process proceeds to a step 102, wherein to indicate this fact, the catalyst deterioration flag F_CATNG is set to 0.
  • step 101 determines whether the NOx purifying catalyst 11 has been deteriorated. If the answer to the question of the step 101 is affirmative (YES), i.e. if sumPostNOx > NOxJUD2 holds, it is determined that the NOx purifying catalyst 11 has been deteriorated, so that the process proceeds to a step 103, wherein to indicate this fact, the catalyst deterioration flag F_CATNG is set to 1.
  • the high NOx condition flag F_NOxUP is set to 0.
  • step 105 wherein all of the NOx supply amount sumPreNOx, the NOx slip amount sumPostNOx, and the exhaust gas supply amount sumQGAS are set to 0, followed by terminating the present process.
  • the process may be configured to compare the Nox slip amount sumPostNOx with the reference value NOxJUD2 calculated in the above-mentioned step 100 in place of the reference value NOxREF2.
  • the downstream NOx concentration CNOx_Post is calculated based on the detection signal values from the downstream NOx sensor 23, and the NOx slip amount sumPostNOx is calculated based on the calculated downstream NOx concentration CNOx_Post.
  • the upstream NOx concentration CNOx_Pre is calculated based on the detection signal values from the upstream NOx sensor 22, and the NOx supply amount sumPreNOx is calculated based on the calculated upstream NOx concentration CNOx_Pre. Then, when the condition of sumPreNOx > NOxREF is satisfied, the deterioration determination of the NOx purifying catalyst 11 is executed by comparing the NOx slip amount sumPostNOx with the reference value NOxJUD2. That is, the deterioration of the NOx purifying catalyst 11 is determined depending on whether the total amount of NOx estimated to have flowed through the NOx purifying catalyst 11 is large or small at the time point at which the amount of NOx having actually flowed into the NOx purifying catalyst 11 has reached a sufficiently large value.
  • the average value aveCNOx of the downstream NOx concentration CNOx_Post is calculated, and the reference value NOxJUD2 for comparison with the NOx slip amount sumPostNOx is calculated based on the calculated average value aveCNOx. Therefore, even when the downstream NOx sensor 23 is suffering from the above-mentioned change in the output characteristics, it is possible to calculate the reference value NOxJUD2 while causing the change in the output characteristics to be reflected thereon, and determine the deterioration of the NOx purifying catalyst 11 using the reference value calculated as above, thereby making it possible to improve the accuracy of the deterioration determination.
  • the predetermined number of values of the downstream NOx concentration CNOx_Post are sampled which are calculated based on the detection signal from the downstream NOx sensor 23 detected after the conditions for the deterioration determination of the NOx purifying catalyst 11 are satisfied, and the predetermined number of the sampled values are averaged (arithmetic mean thereof is calculated) to thereby calculate the average value aveCNOx.

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  • General Engineering & Computer Science (AREA)
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Claims (14)

  1. Verschlechterungsbestimmungsvorrichtung für eine Abgasemissionsreduktionsvorrichtung, die einen NOx-Reinigungskatalysator (11) enthält, der in einem Auslasskanal (7) eines Verbrennungsmotors (3) vorgesehen ist, um dann, wenn darin eine Oxidationsatmosphäre bildende Abgase fließen, NOx in den Abgasen aufzufangen, wobei die Verschlechterungsbestimmungsvorrichtung die Verschlechterung des NOx-Reinigungskatalysators bestimmt, umfassend:
    ein Stromaufwärtiger-NOx-Konzentrationsparameter-Erfassungsmittel (22) zum Erfassen eines Parameters, der eine NOx-Konzentration in Abgasen stromauf des NOx-Reinigungskatalysators angibt, als stromaufwärtigen NOx-Konzentrationsparameter (CNOx_Pre);
    ein Stromabwärtiger-NOx-Konzentrationsparameter-Erfassungsmittel (23) zum Erfassen eines Parameters, der eine NOx-Konzentration in Abgasen stromab des NOx-Reinigungskatalysators angibt, als stromabwärtigen NOx-Konzentrationsparameter (CNOx_Post);
    ein Steuermittel zur Durchführung einer
    Oxidationsatmosphärensteuerung zum Steuern/Regeln der in den NOx-Reinigungskatalysator fließenden Abgase zu einer Oxidationsatmosphäre;
    ein NOx-Zufuhrmengenberechnungsmittel (2) zum Berechnen eines integrierten Werts einer NOx-Menge, die in den NOx-Reinigungskatalysator geflossen ist, als NOx-Zufuhrmenge (sumPreNOx) unter Verwendung des während der Ausführung der Oxidationsatmosphärensteuerung erfassten stromaufwärtigen NOx-Konzentrationsparameters; und
    ein NOx-Schlupfmengenberechnungsmittel zum Berechnen eines integrierten Werts einer NOx-Menge, die durch den NOx-Reinigungskatalysator geflossen ist, als NOx-Schlupfmenge (sumPostNOx) unter Verwendung des während der Ausführung der Oxidationsatmosphärensteuerung erfassten stromabwärtigen NOx-Konzentrationsparameters;
    gekennzeichnet durch ein Verschlechterungsbestimmungsmittel zum Bestimmen einer Verschlechterung des NOx-Reinigungskatalysators durch Vergleich der berechneten NOx-Schlupfmenge mit einem vorbestimmten NOx-Referenzwert (NOxJUD; NOxJUD2), wenn die berechnete NOx-Zufuhrmenge einen vorbestimmten Schwellenwert (NOxREF) überschreitet, der die NOx-Fangfähigkeit (NOxS) des NOx-Reinigungskatalysators (11) angibt.
  2. Verschlechterungsbestimmungsvorrichtung nach Anspruch 1, ferner umfassend:
    ein Ausführungsbedingungsbestimmungsmittel zum Bestimmen, ob Bedingungen zur Ausführung der Verschlechterungsbestimmung des NOx-Reinigungskatalysators während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind oder nicht; und
    einen Nullpunktkorrekturparameter, der nach Erfüllung der Bedingungen zur Ausführung der Verschlechterungsbestimmung erfasst wird, und
    worin das NOx-Schlupfmengenberechnungsmittel die NOx-Schlupfmenge unter Verwendung des stromabwärtigen NOx-Konzentrationsparameters, dessen Nullpunkt korrigiert worden ist,
    berechnet.
  3. Verschlechterungsbestimmungsvorrichtung nach Anspruch 1, ferner umfassend:
    ein Ausführungsbedingungsbestimmungsmittel zum Bestimmen, ob die Bedingungen zur Ausführung der Verschlechterungsbestimmung für den NOx-Katalysator während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind oder nicht; und
    ein Referenzwertberechnungsmittel zum Berechnen des vorbestimmten Referenzwerts (NOxJUD2) basierend auf dem stromabwärtigen NOx-Konzentrationsparameter, der nach der Erfüllung der Bedingungen zur Ausführung der Verschlechterungsbestimmung erfasst ist.
  4. Verschlechterungsbestimmungsvorrichtung nach Anspruch 1, die ferner ein Ausführungsbedingungsbestimmungsmittel umfasst, um zu bestimmen, ob die Bedingungen zur Ausführung der Verschlechterungsbestimmung für den NOx-Reinigungskatalysator während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind oder nicht, und
    worin das Steuermittel während der Ausführung der Oxidationsatmosphärensteuerung die NOx-Konzentration in den Abgasen auf einen höheren Wert steuert/regelt, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung erfüllt sind, als dann, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung nicht erfüllt sind.
  5. Verschlechterungsbestimmungsvorrichtung nach Anspruch 4, worin der NOx-Reinigungskatalysator Charakteristiken hat, das aufgefangene NOx zu reduzieren, wenn die darin fließenden Abgase eine Reduktionsatmosphäre bilden,
    wobei die Verschlechterungsbestimmungsvorrichtung ferner ein NOx-Auffangmengenberechnungsmittel aufweist, um eine von dem NOx-Reinigungskatalysator aufgefangene NOx-Menge während der Ausführung der Oxidationsatmosphärensteuerung als NOx-Auffangmenge zu berechnen,
    worin das Steuermittel die Oxidationsatmosphärensteuerung beendet, wenn die während der Ausführung der Oxidationsatmosphärensteuerung berechnete NOx-Auffangmenge einen vorbestimmten Auffangreferenzwert überschreitet, und die in den NOx-Reinigungskatalysator fließenden Abgase zu der Reduktionsatmosphäre steuert,
    wobei die Verschlechterungsbestimmungsvorrichtung ferner ein Auffangreferenzwertsetzmittel aufweist, um den vorbestimmten Auffangreferenzwert auf einen größeren Wert zu setzen, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind, als dann, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung nicht erfüllt sind.
  6. Verschlechterungsbestimmungsvorrichtung nach Anspruch 1, worin in einem Fall, wo die NOx-Zufuhrmenge nicht größer als der vorbestimmte Stellenwert ist, das Verschlechterungsbestimmungsmittel die Bestimmung der Verschlechterung des NOx-Reinigungskatalysators ausführt, wenn die NOx-Schlupfmenge einen vorbestimmten Wert überschreitet.
  7. Verschlechterungsbestimmungsvorrichtung nach Anspruch 1, worin ein stromabwärtiger NOx-Reinigungskatalysator stromab des NOx-Reinigungskatalysators in dem Auslasskanal des Motors vorgesehen ist, um dann, wenn darin die die Oxidationsatmosphäre bildenden Abgase fließen, NOx in den Abgasen aufzufangen.
  8. Verschlechterungsbestimmungsverfahren für eine Abgasemissionsvorrichtung, die einen NOx-Reinigungskatalysator (11) enthält, der in einem Auslasskanal (7) eines Verbrennungsmotors (3) vorgesehen ist, um dann, wenn darin eine Oxidationsatmosphäre bildende Abgase fließen, NOx in den Abgasen aufzufangen, wobei das Verschlechterungsbestimmungsverfahren die Verschlechterung des NOx-Reinigungskatalysators bestimmt,
    umfassend:
    Erfassen eines Parameters, der eine NOx-Konzentration in Abgasen stromauf des NOx-Reinigungskatalysators angibt, als stromaufwärtigen NOx-Konzentrationsparameter (CNOx_Pre);
    Erfassen eines Parameters, der eine NOx-Konzentration in Abgasen stromab des NOx-Reinigungskatalysators angibt, als stromabwärtigen NOx-Konzentrationsparameter (CNOx_Post);
    Durchführen einer Oxidationsatmosphärensteuerung zum Steuern/Regeln der in den NOx-Reinigungskatalysator fließenden Abgase zu einer Oxidationsatmosphäre;
    Berechnen eines integrierten Werts einer NOx-Menge, die in den NOx-Reinigungskatalysator geflossen ist, als NOx-Zufuhrmenge (sumPreNOx) unter Verwendung des während der Ausführung der Oxidationsatmosphärensteuerung erfassten stromaufwärtigen NOx-Konzentrationsparameters;
    Berechnen eines integrierten Werts einer NOx-Menge, die durch den NOx-Reinigungskatalysator geflossen ist, als NOx-Schlupfmenge (sumPostNOx) unter Verwendung des während der Ausführung der Oxidationsatmosphärensteuerung erfassten stromabwärtigen NOx-Konzentrationsparameters; und
    Bestimmen einer Verschlechterung des NOx-Reinigungskatalysators durch Vergleich der berechneten NOx-Schlupfmenge mit einem vorbestimmten NOx-Referenzwert (NOxJUD; NOxJUD2), wenn die berechnete NOx-Zufuhrmenge einen vorbestimmten Schwellenwert (NOxREF) überschreitet, der die NOx-Fangfähigkeit (NOxS) des NOx-Reinigungskatalysators (11) angibt.
  9. Verschlechterungsbestimmungsverfahren nach Anspruch 8, ferner umfassend:
    Bestimmen, ob Bedingungen zur Ausführung der Verschlechterungsbestimmung des NOx-Reinigungskatalysators während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind oder nicht; und
    Korrigieren eines Nullpunkts des stromabwärtigen NOx-Konzentrationsparameters, der nach Erfüllung der Bedingungen zur Ausführung der Verschlechterungsbestimmung erfasst wird, und
    worin die Berechnung der Nox-Schlupfmenge enthält, die NOx-Schlupfmenge unter Verwendung des stromabwärtigen NOx-Konzentrationsparameters, dessen Nullpunkt korrigiert worden ist, zu berechnen.
  10. Verschlechterungsbestimmungsverfahren nach Anspruch 8, ferner umfassend:
    Bestimmen, ob die Bedingungen zur Ausführung der Verschlechterungsbestimmung für den NOx-Katalysator während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind oder nicht; und
    Berechnen des vorbestimmten Referenzwerts (NOxJUD2) basierend auf dem stromabwärtigen NOx-Konzentrationsparameter, der nach der Erfüllung der Bedingungen zur Ausführung der Verschlechterungsbestimmung erfasst worden ist.
  11. Verschlechterungsbestimmungsverfahren nach Anspruch 8, ferner umfassend:
    Bestimmen, ob die Bedingungen zur Ausführung der Verschlechterungsbestimmung für den NOx-Reinigungskatalysator während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind oder nicht, und
    worin die Ausführung der Oxidationsatmosphärensteuerung enthält, die NOx-Konzentration in den Abgasen auf einen höheren Wert zu steuern/regeln, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung erfüllt sind, als dann, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung nicht erfüllt sind.
  12. Verschlechterungsbestimmungsverfahren nach Anspruch 11, worin der NOx-Reinigungskatalysator Charakteristiken hat, das aufgefangene NOx zu reduzieren, wenn die darin fließenden Abgase eine Reduktionsatmosphäre bilden,
    wobei das Verschlechterungsbestimmungsverfahren ferner umfasst, eine von dem NOx-Reinigungskatalysator aufgefangene NOx-Menge während der Ausführung der Oxidationsatmosphärensteuerung als NOx-Auffangmenge zu berechnen,
    worin die Durchführung der Oxidationsatmosphärensteuerung enthält, die Oxidationsatmosphärensteuerung zu beenden, wenn die während der Ausführung der Oxidationsatmosphärensteuerung berechnete NOx-Auffangmenge einen vorbestimmten Auffangreferenzwert überschreitet, und die in den NOx-Reinigungskatalysator fließenden Abgase zu der Reduktionsatmosphäre steuert,
    wobei das Verschlechterungsbestimmungsverfahren ferner ein Auffangreferenzwertsetzmittel aufweist, um den vorbestimmten Auffangreferenzwert auf einen größeren Wert zu setzen, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung während der Ausführung der Oxidationsatmosphärensteuerung erfüllt sind, als dann, wenn die Bedingungen zur Ausführung der Verschlechterungsbestimmung nicht erfüllt sind.
  13. Verschlechterungsbestimmungsverfahren nach Anspruch 8, worin die Verschlechterungsbestimmung enthält, die Bestimmung der Verschlechterung des NOx-Reinigungskatalysators auszuführen, wenn die NOx-Schlupfmenge einen vorbestimmten Wert überschreitet, in einem Fall, wo die NOx-Zufuhrmenge nicht größer als der vorbestimmte Stellenwert ist.
  14. Verschlechterungsbestimmungsverfahren nach Anspruch 8, worin ein stromabwärtiger NOx-Reinigungskatalysator stromab des NOx-Reinigungskatalysators in dem Auslasskanal des Motors vorgesehen ist, um dann, wenn die die Oxidationsatmosphäre bildenden Abgase darin fließen, NOx in den Abgasen aufzufangen.
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