DE102016200207A1 - Emission control system for internal combustion engines - Google Patents

Abstract

OBJECT: The object of the present invention is to provide an exhaust gas purification system for internal combustion engines, comprising at least two catalysts with the task of reducing NOx in the exhaust gas, wherein at the same time the excess consumption is throttled and the overall NOx reduction rate is increased. Means for Solving the Problem: The present invention uses the means for solving the problem to arrange the following elements in the aforementioned exhaust gas purification system: a catalyst which traps NOx in an oxidizing atmosphere and reduces it in a reducing atmosphere; an SCR catalyst that allows NH3 to react with NOx to reduce NOx; and an FI-ECU which, when certain conditions are met, for reducing NOx accumulated in the LNT catalyst, performs DeNOx operation, and converts the LNT catalyst into reducing atmosphere. If the temperature of the SCR catalyst Scr_tmp exceeds the switching temperature SCR_LNT_MODE_TMP, which is regulated in the temperature range in which NOx can be reduced by means of the SCR catalyst, the FI-ECU prohibits the execution of the DeNOx operation (reduction of the LNT catalyst).

Description

Technical area

The present invention relates to an exhaust gas purification system for internal combustion engines. In particular, the present invention relates to an exhaust gas purification system for internal combustion engines, equipped with a plurality of catalysts with NOx reduction function.

General state of the art

Exhaust ports for internal combustion engines usually have catalysts that can reduce NOx in the exhaust gas. Widely used catalysts are three-way catalysts, lean NOx catalysts [hereinafter "LNT catalysts"] and selective reduction catalysts [hereinafter "SCR catalysts"]. Three-way catalysts reduce NOx in the exhaust gas by means of a reducing agent in the form of HC and CO. LNT catalysts capture NOx in an oxidizing atmosphere and reduce it in a reducing atmosphere. SCR catalysts remove NOx by means of a reducing agent in the form of, for example, NH ₃ . The aforementioned catalysts are their task, if different conditions are met. They are thus often combined, and achieve high NOx reduction rates under all operating conditions.

Patent Document 1 describes an exhaust gas purification system which is a combination of LNT and SCR catalyst. In the system, the LNT and SCR catalytic converters are arranged on different exhaust ducts. Depending on the engine load, it is possible to switch back and forth between the exhaust port of the LNT catalytic converter and the exhaust port of the SCR catalytic converter.

Patent Document 2 describes an exhaust gas purification system in which the LNT catalyst is disposed on the upstream side of the SCR catalyst. In the system, the decrease in the reduction rate of the SCR catalyst is compensated for by the reduction rate of the LNT catalyst by generating a reducing atmosphere in proportion to the decrease at shorter time intervals.

Patent Document 3 describes an exhaust gas purification system in which a urea / water mixture is sprayed from the upstream side of the LNT and SCR catalyst when the exhaust gas has a rich air ratio. The sprayed urea / water mixture preferably reacts with oxygen in the exhaust gas, which prevents the urea / water mixture from being used up before NH ₃ , which promotes NOx reduction, can form.

Documents of the prior art

patents

• Patent document 1: JP Patent Publication No. 2000-265828
• Patent document 2: Japanese Patent Laid-Open Publication No. 2010-116784
• Patent 3: Japanese Patent Laid-Open Publication No. 2009-85178

Brief description of the invention

Object of the present invention

However, a problem in the aforementioned LNT and SCR catalytic converter exhaust gas purification systems is that in addition to the regular fuel injection to the output of the vehicle, an additional fuel injection, which serves to meet the catalysts of their task to reduce NOx, is required. Thus, in LNT catalysts, the additional fuel injection converts the exhaust gas into a reducing atmosphere so that accumulated NOx can subsequently be reduced. In SCR catalysts, the SCR catalyst is heated by the additional fuel injection to a temperature suitable for NOx reduction. Due to the additional fuel injection, an increased cleaning effect of the exhaust gas is achieved, but the fuel balance on the entire vehicle deteriorates accordingly.

The deterioration of the fuel balance on the entire vehicle due to the additional fuel injection to purify the exhaust gas is referred to as "over-consumption". The extra consumption is that Relationship between a level of judgment (eg the amount of fuel consumed on the whole vehicle) and the consumption due to the additional fuel injection.

The above-mentioned multi-catalyst exhaust gas purification systems may bring the advantage of achieving excellent NOx reduction rates under all operating conditions because they perform their task under different conditions. Nevertheless, the strong focus on the catalysts threatens increased consumption. However, approaches to optimize the ratio of NOx reduction rate to fuel consumption have been heretofore researched as sufficiently limited.

• (1) Ein Abgasreinigungssystem (beispielsweise das im Folgenden beschriebene Abgasreinigungssystem 2) für eine Brennkraftmaschine (beispielsweise der im Folgenden beschriebene Motor 1), angeordnet in einem Abgaskanal (beispielsweise der im Folgenden beschriebene Abgaskanal 11) der Brennkraftmaschine, wobei das Abgasreinigungssystem die folgenden Elemente umfasst: einen LNT-Katalysator (beispielsweise der im Folgenden beschriebene stromaufwärtige Katalysatorwandler 31), womit NOx in oxidierender Atmosphäre angehäuft und in reduzierender Atmosphäre reduziert wird; eine Reduktionsvorrichtung für den LNT-Katalysator (beispielsweise die im Folgenden beschriebene FI-ECU 71), mittels derer, je nach dem Betriebszustand, eine zusätzliche Treibstoffeinspritzung vorgenommen, und der LNT-Katalysator zur reduzierenden Atmosphäre übergeführt wird; einen im Abgaskanal angeordneten SCR-Katalysator (beispielsweise der im Folgenden beschriebene stromabwärtige Katalysatorwandler 33) mit dem NOx dadurch reduziert wird, dass ein Reduktionsmittel mit NOx zur Reaktion gebracht wird; eine Zuführvorrichtung (beispielsweise die im Folgenden beschriebene Urea/Wasser-Zuführvorrichtung 4), mittel derer ein Reduktionsmittel oder dessen Vorläufer dem SCR-Katalysator zugeführt wird; und Temperaturerfassungselemente (beispielsweise die im Folgenden beschriebenen stromaufwärtiger Katalysatortemperatursensor 52, stromabwärtiger Katalysator-temperatursensor 53, und FI-ECU 71) womit die Temperatur des SCR-Katalysators erfasst wird.

The present invention therefore has for its object to provide an exhaust gas purification system for internal combustion engines, equipped with at least two different catalysts by means of which can reduce NOx, which can reduce the additional consumption and at the same time increase the overall NOx reduction rate. Means for solving the problem

• (1) An exhaust gas purification system (for example, the exhaust gas purification system described below 2 ) for an internal combustion engine (for example, the engine described below 1 ) disposed in an exhaust passage (for example, the exhaust passage described below 11 ) of the internal combustion engine, the exhaust gas purification system comprising the following elements: an LNT catalyst (for example, the upstream catalyst converter described below) 31 ), whereby NOx is accumulated in an oxidizing atmosphere and reduced in a reducing atmosphere; a reduction apparatus for the LNT catalyst (for example, the FI-ECU described below) 71 ), by means of which, depending on the operating condition, made an additional fuel injection, and the LNT catalyst is converted to the reducing atmosphere; an arranged in the exhaust passage SCR catalyst (for example, the downstream catalyst converter described below 33 ) is reduced with the NOx by reacting a reducing agent with NOx; a feeder (for example, the urea / water feeder described below) 4 ), by means of which a reducing agent or its precursor is supplied to the SCR catalyst; and temperature detecting elements (for example, the above-described upstream catalyst temperature sensor 52 , downstream catalyst temperature sensor 53 , and FI-ECU 71 ) with which the temperature of the SCR catalyst is detected.

By means of the reduction device of the LNT catalyst, the additional fuel injection is prohibited where the temperature detected by the temperature sensing elements exceeds a switching temperature, which in turn is in a temperature range in which NOx can be reduced by means of the SCR catalyst. The oxidizing atmosphere according to the present invention means the state wherein the oxygen concentration in the exhaust gas of the LNT catalyst is relatively higher than the concentration of the reduction ratio, for example.

• (2) Dabei bevorzugt ist das Abgasreinigungssystem zusätzlich ausgestattet mit einer Schalttemperatursteuereinheit (beispielsweise die im Folgenden beschriebene FI-ECU 71) womit die Schalttemperatur basierend auf der Fahrthistorie des Fahrzeugs gesteuert wird.
• (3) Dabei ferner bevorzugt ermitteln die Temperaturerfassungselemente die künftige Temperatur des SCR-Katalysators basierend auf der Fahrthistorie des Fahrzeugs.
• (4) Weiter ferner bevorzugt ist das Abgasreinigungssystem zusätzlich ausgestattet mit einer Katalysatorheizung (beispielsweise die im Folgenden beschriebene FI-ECU 71) womit der SCR-Katalysator auferhitzt wird wenn die mittels der Temperaturerfassungselemente erfasste Temperatur bei oder unter der Schalttemperatur und die NOx-Anhäufrate im LNT-Katalysator bei oder über einem bestimmten Wert liegt.
• (5) Noch weiter ferner bevorzugt sind der LNT-Katalysator und der SCR-Katalysator am Abgaskanal derart angeordnet sind, dass die Temperaturveränderung des SCR-Katalysators langsamer vonstattengeht als die Temperaturveränderung des LNT-Katalysators.
• (6) Dabei noch ferner bevorzugt ist der SCR-Katalysator ein NH₃-SCR-Katalysator, bei dem das Reduktionsmittel in Form von NH₃ vorliegt; die Zuführvorrichtung verfügt für das Reduktionsmittel über eine Urea/Wasser-Einspritzdüse (beispielsweise die im Folgenden beschriebene Urea/Wasser-Injektoren 42) womit im Abgaskanal ein Urea/Wasser-Gemisch, das ein Vorläufer von NH₃ ist, stromaufwärts vom NH₃-SCR-Katalysator gesprüht wird; und die Schalttemperatur ist höher eingestellt als die Temperatur die aufgrund der Ablagerungen des im Abgaskanal mittels der Urea/Wasser-Einspritzdüse gesprühten Urea/Wasser-Gemischs entsteht.

Hydrocarbon or carbon monoxide. Specifically, the oxidizing atmosphere is realized by, for example, generating a poor rather than stoichiometric air ratio in the internal combustion engine. The oxidizing atmosphere according to the present invention means the state wherein the oxygen concentration in the exhaust gas of the LNT catalyst is lower than the concentration of the reducing portion. Specifically, the reducing atmosphere is realized by supplying unburned fuel to the LNT catalyst, such as by generating an in-engine rich rather than stoichiometric air ratio by post-injection, or injecting fuel into the exhaust by means of injectors exhaust duct.

• (2) It is preferable that the exhaust gas purification system is additionally equipped with a switching temperature control unit (for example, the FI-ECU described below) 71 ) with which the switching temperature is controlled based on the driving history of the vehicle.
• (3) Further, preferably, the temperature detecting elements determine the future temperature of the SCR catalyst based on the driving history of the vehicle.
• (4) Further preferably, the exhaust gas purification system is additionally equipped with a catalyst heater (for example, the FI-ECU described below) 71 ) whereby the SCR catalyst is heated when the detected by the temperature detecting elements temperature at or below the switching temperature and the NOx accumulation rate in the LNT catalyst is at or above a certain value.
• (5) Still further preferably, the LNT catalyst and the SCR catalyst are disposed on the exhaust passage such that the temperature change of the SCR catalyst is slower than the temperature change of the LNT catalyst.
• (6) Still more preferably, the SCR catalyst is an NH ₃ -SCR catalyst in which the reducing agent is in the form of NH ₃ ; the supply device has a urea / water injection nozzle for the reducing agent (for example, the urea / water injectors described below 42 ) spraying a urea / water mixture, which is a precursor of NH ₃ , upstream of the NH ₃ -SCR catalyst in the exhaust duct; and the switching temperature is set higher than the temperature generated due to the deposits of urea / water mixture sprayed in the exhaust channel by means of the urea / water injection nozzle.

Effect of the invention

• (1) According to the present invention, an LNT catalyst and an SCR catalyst are disposed on a common exhaust passage. The task of the LNT catalyst is to collect NOx in an oxidizing atmosphere and to reduce it in a reducing atmosphere. However, in order to reduce NOx by means of the LNT catalyst, the amount of NOx accumulated in the catalyst should not exceed a certain limit. Therefore, in the LNT-cat reduction apparatus, by means of an additional, intermittent fuel injection, a reducing atmosphere is generated. The task of the SCR catalytic converter is to reduce NOx in the exhaust gas continuously, using a reducing agent supplied by the supply device. However, the temperature range in which NOx is effectively reduced by means of the SCR catalyst differs from the temperature range in which NOx is effectively reducible by the LNT catalyst (refer to FIG 2 ). Therefore, the vehicle operation is roughly divided into the areas of: operation in which the temperature in the exhaust passage is comparatively low (ie immediately after starting and in low-load operation), and operation in which the temperature in the exhaust passage is comparatively high (ie in high-load operation) , and in the former, the focus is on the LNT catalyst, and in the latter, the focus is on the SCR catalyst to achieve high NOx reduction rates in all operating ranges.

• (2) Die Schalttemperatur ist der Schwellwert, an dem entschieden wird, ob eine zusätzliche Treibstoffeinspritzung für den LNT-Katalysator erfolgen soll. Gemäß der vorliegenden Erfindung lässt sich die Schalttemperatur entsprechend der Fahrthistorie des Fahrzeugs ändern, und die zusätzliche Treibstoffeinspritzung zu einer Zeit tätigen bzw. unterdrücken, die angemessen angesichts der derzeitigen und unmittelbar künftigen Fahrtkonditionen erscheint. Da der LNT-Katalysator die Eigenschaft hat, mit zunehmender NOx-Menge weniger zusätzliches NOx aufzufangen (d. h. die NOx-Reduktionsrate des LNT-Katalysators in oxidierender Atmosphäre nimmt ab), wird mittels der vorgenannten zusätzlichen Treibstoffeinspritzung zu den angemessenen Zeiten zugleich dazu beigesteuert, dass die NOx-Reduktionsrate des LNT-Katalysators unverändert hoch bleibt, und die Gesamt-NOx-Reduktionsrate im System gesteigert wird. Ähnlich wird mittels des Unterdrückens der zusätzlichen Treibstoffeinspritzung wann angemessen zur Eindämmung des Mehrverbrauchs bei. Im Ergebnis wird der Mehrverbrauch gedrosselt bei nur minimaler Einbüße der NOx-Reduktionsrate.
• (3) Gemäß der vorliegenden Erfindung wird die Schalttemperatur mit der mittels den Temperaturerfassungselementen erfassten Temperatur des SCR-Katalysators verglichen, und bestimmt, ob die zusätzliche Treibstoffeinspritzung zu tätigen ist oder nicht. So lässt sich, wie bereits in (2) erwähnt, je nach dem Fahrtzustand des Fahrzeugs, die künftige Temperatur des SCR-Katalysators ermitteln und zur Schalttemperatur vergleichen, und so der Mehrverbrauch drosseln, während die Einbüße in der NOx-Reduktionsrate nur minimal ist.
• (4) Liegt die Temperatur des SCR-Katalysators über der Schalttemperatur, wird gemäß der vorliegenden Erfindung die zusätzliche Treibstoffeinspritzung im LNT-Katalysator unterdrückt. Ändert sich plötzlich der Fahrtzustand (etwa bei Parken des Fahrzeugs nach einer Autobahnstrecke und nach dem anschließenden Wieder-Losfahren) während die im LNT-Katalysator angehäufte Menge NOx sich nahe dem Maximum befindet, kann die Temperatur des SCR-Katalysators absinken. Dabei verringert sich vorübergehend die NOx-Reduktionsrate der beiden Katalysatoren. Die vorliegende Erfindung antizipiert ein solches Szenario, und erhitzt den SCR-Katalysator, wenn dessen Temperaturen unter die Schalttemperatur sinken obwohl die NOx-Anhäufrate des LNT-Katalysators bereits das Maximum überschritten hat, sodass sich prompt die NOx-Reduktionsrate des SCR-Katalysators wieder erholt und steigt, und der NOx-Ausstoß am Fahrzeug verringert wird.
• (5) Durch die vorliegende Erfindung lässt sich die Temperaturveränderung im SCR-Katalysator gegenüber der Temperaturveränderung im LNT-Katalysator verlangsamen. Dies wird dadurch erreicht, dass bspw. der SCR-Katalysator weiter stromabwärts als der LNT-Katalysator angeordnet wird, der SCR-Katalysator über eine höhere Wärmekapazität als der LNT-Katalysator verfügt, oder dadurch, einen Filter zwischen dem stromaufwärtigen LNT-Katalysator und dem stromabwärtigen SCR-Katalysator anzuordnen.

However, the temperature ranges of the two aforementioned catalysts which are suitable for NOx reduction are not entirely separate from each other, but have a common intersection. The reduction apparatus for the LNT catalyst according to the present invention recognizes when such an intersection of the catalysts comes, and prohibits, as soon as the temperature of the SCR catalyst, the switching temperature, which in turn is within the temperature range in which NOx by means of the SCR Catalyst reduces, exceeds, the additional fuel injection. In other words, according to the present invention, within this intersection range, the focus of NOx reduction is placed on the SCR rather than LNT catalyst. In this case, the aforementioned switching temperature regulates the maximum of the temperature range in which the additional fuel injection is carried out for the LNT catalyst, and thus represents the temperature threshold of the SCR catalyst. In that according to the present invention, the switching temperature not for the LNT but the Controlled SCR catalyst, the number of operations of the additional fuel injection with respect to the LNT catalyst can be reduced to a reasonable extent, and the additional consumption can be throttled accordingly. Now, since such suppression of the additional fuel injection takes place in the aforementioned intersection area (or redundant part) in which NOx is also reducible by means of the SR catalyst, it can not be said that the overall NOx reduction rate deteriorates around the part which was saved on additional consumption. As a result, the present invention thus enables a lower excess consumption while at the same time only minimally reducing the NOx reduction rate.

• (2) The switching temperature is the threshold at which it is decided whether additional fuel injection should be done for the LNT catalyst. According to the present invention, the switching temperature can be changed according to the driving history of the vehicle, and suppress the additional fuel injection at a time that appears appropriate in view of the current and immediately future driving conditions. Since the LNT catalyst has the property of absorbing less additional NOx as the amount of NOx increases (ie, the NOx reduction rate of the LNT catalyst in an oxidizing atmosphere decreases), by means of the aforementioned additional fuel injection at the appropriate times, it also contributes the NOx reduction rate of the LNT catalyst remains high and the total NOx reduction rate in the system is increased. Similarly, by suppressing the additional fuel injection when appropriate to curb the excess consumption. As a result, the excess consumption is throttled with only minimal decreases in the NOx reduction rate.
• (3) According to the present invention, the switching temperature is compared with the temperature of the SCR catalyst detected by the temperature detecting elements, and determines whether or not the additional fuel injection is to be made. Thus, as already mentioned in (2), depending on the running state of the vehicle, the future temperature of the SCR catalytic converter can be determined and compared with the switching temperature, thus throttling the excess consumption, while the losses in the NOx reduction rate are only minimal.
• (4) If the temperature of the SCR catalyst is above the switching temperature, according to the present invention, the additional fuel injection in the LNT catalyst is suppressed. If the driving state suddenly changes (for example, when the vehicle is parked after a motorway section and after the subsequent re-start), while the amount of NOx accumulated in the LNT catalytic converter is close to the maximum, the temperature of the SCR catalytic converter may drop. This temporarily reduces the NOx reduction rate of the two catalysts. The present invention anticipates such a scenario and heats the SCR catalyst as its temperatures drop below the switching temperature, even though the NOx accumulation rate of the LNT catalyst has already exceeded the maximum, promptly recovering the NOx reduction rate of the SCR catalyst and increases, and the NOx emissions on the vehicle is reduced.
• (5) By the present invention, the temperature change in the SCR catalyst can be slowed down from the temperature change in the LNT catalyst. This is accomplished by, for example, placing the SCR catalyst farther downstream than the LNT catalyst, the SCR catalyst having a higher heat capacity than the LNT catalyst, or by providing a filter between the upstream LNT catalyst and the LNT catalyst downstream SCR catalyst to arrange.

• (6) Im NH₃-SCR-Katalysator wird aus einer Urea/Wasser-Einspritzdüse ein Urea/Wasser-Gemisch ins Abgas gespritzt, das, bedingt durch die Wärme des Abgases bzw. Katalysators, hydrolysiert und so NH₃ erzeugt, das im NH₃-SCR-Katalysator die Funktion des Reduktionsmittels übernimmt. Bei niedrigen Temperaturen des Abgases bzw. Katalysators kann es jedoch dazu kommen, dass die während der Hydrolyse entstehenden Vorprodukte (Biuret, Cyanursäure etc.), selbst wenn die Temperaturen im NH₃-SCR-Katalysator hoch genug sind um NOx mittels NH₃ zu reduzieren, sich im Abgaskanal bzw. Katalysator ablagern. Gemäß der vorliegenden Erfindung wird deshalb die Schalttemperatur derart hoch geregelt, dass es zu keine solchen Ablagerungen kommt. Dabei wird unter den niedrigen Temperaturen im NH₃-SCR-Katalysator die es ermöglichen, dass besagte Ablagerungen nicht entstehen, zuverlässig verhindert, dass die Tätigung der zusätzlichen Treibstoffeinspritzung in Bezug auf den LNT-Katalysator untersagt wird. Da also selbst bei derart niedrigen Temperaturen, unter denen die vorgenannten Ablagerungen nicht entstehen können, die NOx-Reduktionsfunktion erfüllt wird, lässt sich ein Einspritzen des Urea/Wasser-Gemischs in den NH₃-SCR-Katalysator unterlassen, und besagte Ablagerungen vermeiden, ohne damit die NOx-Reduktionsrate des gesamten Systems zu verringern.

By means of the present invention, the reduction in the NOx reduction rate associated with the drop in temperature in the SCR catalyst can be slowed down. In the following, a scenario is described in which the temperatures of the SCR catalytic converter are below the switching temperature and a corresponding additional fuel injection is carried out for the LNT catalytic converter. The LNT catalyst can not achieve sufficient NOx reduction rates at a high NOx accumulation rate. Thus, if the NOx accumulated in the LNT catalyst was not sufficiently reduced immediately after allowing the additional fuel injection, it is not possible to immediately obtain sufficient NOx reduction rates by means of the LNT catalyst. In other words, after performing the additional fuel injection, the LNT catalyst can not achieve a sufficient NOx reduction rate as the NOx accumulated in the LNT catalyst is not sufficiently reduced. According to the present invention, by thus slowing down the temperature drop in the SCR catalyst, the NOx reduction rates throughout the system can be prevented from drastically decreasing in the LNT catalyst in the transition period from the addition of the additional fuel injection to the revival of the NOx reduction rates. In other words, by slowing the temperature drop in the SCR catalyst, the period of time during which additional fuel injection for the LNT catalyst occurs can be ensured.

• (6) In the NH ₃ -SCR catalyst from a urea / water injection nozzle, a urea / water mixture is injected into the exhaust gas, which, due to the heat of the exhaust gas or catalyst, hydrolyzed and thus generates NH ₃ , which in the NH ₃ -SCR catalyst takes over the function of the reducing agent. At low temperatures of the exhaust gas or catalyst, however, it may happen that the precursors (biuret, cyanuric acid, etc.) formed during the hydrolysis, even if the temperatures in the NH ₃ -SCR catalyst are high enough to reduce NOx by means of NH ₃ , Depositing in the exhaust duct or catalyst. Therefore, according to the present invention, the switching temperature is controlled so high that no such deposits occur. In doing so, under the low temperatures in the NH ₃ -SCR catalyst, which allows said deposits to not form, reliably prevents the prohibition of additional fuel injection from being prohibited with respect to the LNT catalyst. Thus, since even at such low temperatures, under which the aforementioned deposits can not occur, the NOx reduction function is met, injecting the urea / water mixture into the NH ₃ -SCR catalyst can be omitted, and said deposits avoid, without thus reducing the NOx reduction rate of the entire system.

Short description of

1 FIG. 14 is a view showing the structure of an engine and its exhaust gas purification system according to a first embodiment of the present invention. FIG.

2 FIG. 14 is a view showing the temperatures of the LNT and SCR catalysts at the respective NOx reduction degrees. FIG.

3 FIG. 13 is a view showing the progress of NOx reduction degree in the entire system of a vehicle equipped with a conventional exhaust gas purification system when driving for a certain driving pattern.

4 FIG. 15 is a view showing the relationship between excess consumption and amount of NOx emission in the vehicle with the driving pattern according to FIG 3 shows.

5 FIG. 11 is a flow chart showing the procedure for determining the operation mode of the engine. FIG.

6 Figure 11 is a graph showing the history of the base reduction rate of the LNT catalyst.

7 is a diagram showing the course of the compensation coefficient of the LNT catalyst.

8th is a diagram showing the course of the maximum amount of NOx that can be accumulated in the LNT catalyst.

9 FIG. 11 is a flow chart showing the detailed procedure for determining whether to heat.

10 FIG. 14 is a view showing the changes in the temperature of the SCR catalyst when driving for a certain driving pattern with a vehicle equipped with an exhaust gas purification system according to the aforementioned embodiment.

11 FIG. 15 is a view showing the relationship between the increased consumption and the total NOx discharge amount when driving according to the driving pattern according to FIG 10 shows.

12 FIG. 10 is a flowchart showing the procedure for determining the operation mode of the engine of the exhaust gas purification system according to a second embodiment of the present invention.

13 FIG. 13 is a view showing the principle behind the travel type recognition parameter.

14 Fig. 10 is a flowchart showing the detailed procedure for calculating the travel type recognition parameter.

15 FIG. 13 is a view showing the changes of the travel type recognition parameter when driving for a certain driving pattern with a vehicle equipped with an exhaust gas purification system according to the aforementioned embodiment.

16 FIG. 15 is a view showing the relationship between the increased consumption and the total NOx discharge amount when driving according to the driving pattern according to FIG 15 shows.

17 FIG. 14 is a view showing a comparison of the results of the exhaust gas purification system according to the first embodiment with the results of the exhaust gas purification system according to the second embodiment. FIG.

Embodiments of the invention

The following section deals, with reference to the figures, with a first embodiment of the present invention.

1 shows the structure of the internal combustion engine (hereinafter "engine") 1 and its exhaust gas purification system 2 according to the embodiment of the present invention. emission Control system 2 includes:
a catalyst device 3 , arranged on an exhaust duct 11 that extends from the exhaust port of the engine 1 extends; and
an electrical control unit 7 for controlling the engine 1 and the catalyst device 3 ,

The motor 1 belongs to the group of engines whose combustion is fundamentally "poor", ie whose air ratio is poor instead of stoichiometric. Specifically, these are diesel engines and gasoline lean-burn engines. At the engine 1 arranged are the fuel injectors 17 , by means of which the fuel is injected into the individual cylinders. The actuator for actuating the fuel injection nozzles 17 is electromagnetic to the electrical control unit 7 connected. By means of the electric control unit 7 let the operating mode of the motor 1 according to the procedure described below 5 determine, and the fuel injectors 17 operate such that the fuel is sprayed in quantities and at times, which depend on the respectively determined operating mode. Hereinafter, the name of such electric control unit for actuating the fuel injection to the engine 1 "FI-ECU 71 ".

The catalyst device 3 includes the following elements:
an upstream catalyst converter 31 ;
an exhaust gas purification filter 32 ;
a downstream catalyst converter 33 ;
a urea / water delivery device 4 ;
an air ratio sensor 51 ;
an upstream catalyst temperature sensor 52 ;
a downstream catalyst temperature sensor 53 ;
an NH ₃ sensor 54 ; and
an airflow sensor 55 ,

The upstream catalyst converter 31 is along the exhaust duct 11 in the section behind the engine 1 arranged. This refers to the section housed in the engine compartment or, if a compressor is located, the section in the engine compartment near the turbine. The downstream catalyst converter 33 is along the exhaust duct 11 downstream from the upstream catalyst converter 31 arranged. The exhaust gas purification filter 32 is along the exhaust duct 11 between the upstream catalyst converter 31 and the downstream catalyst converter 33 arranged. To the upstream catalyst converter 31 and the downstream catalyst converter 33 a catalyst is arranged to promote the reaction to remove the CC, HC, NOx etc. from the exhaust gas of the engine 1 responsible is.

The upstream catalyst converter 31 consists of a honeycomb body designed according to the "flow-through" principle, on which a lean NOx catalyst is supported. The LNT catalyst traps NOx in the exhaust gas in an oxidizing atmosphere and reduces it in a reducing atmosphere. However, the LNT catalyst can only capture a limited amount of NOx. As the accumulated NOx accumulation rate increases (actual NOx amount / maximum accumulable NOx amount), the NOx reduction rate of the LNT catalyst decreases. Therefore, the FI-ECU 71 as below with reference to 5 explains, depending on whether certain conditions are met, the engine 1 into a DeNOx operation in which the exhaust gas in the LNT catalyst is subjected to a reducing atmosphere, thus reducing NOx accumulated in the LNT catalyst.

The exhaust gas purification filter 32 comprises a honeycomb body according to the "wall-flow" principle, comprising cells which are divided by multi-porous walls, as well as closures, which are each arranged alternately on the upstream and the downstream side of the individual cells. Im from the engine 1 discharged exhaust gas is particulate matter (hereinafter "PM" for short) such as soot or SOF contained by the pores of the filter 32 oozes and gets in the filter 32 accumulates. Does an excessive amount of PM accumulate in the filter 32 on, the pressure decreases and more fuel has to be injected. A deterioration of the consumption balance threatens. The deposited amount of PM in the filter 32 is therefore measured, and it is determined that the amount exceeds a certain value, the filter 32 , initiated by the FI-ECU 71 , heated by means of a post-injection ("post-injection"), and made a strong regenerative combustion of the deposited PM.

The downstream catalyst converter 33 consists of a honeycomb body designed according to the "flow-through" principle, on which an NH ₃ -SCR catalyst (hereinafter "SCR catalyst") is supported. NOx in the exhaust gas is selectively reduced by means of the SCR catalyst in an NH ₃ -containing atmosphere. Specifically, NH _{3 will be} from a urea / water injector described below 42 and the supplied NH ₃ then selectively reduces NOx in the exhaust gas according to the following reaction formulas: NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O 4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O 6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O

On the one hand, the SCR catalytic converter has the abovementioned NOx reduction function and, on the other hand, a storage function of the specific amount NH ₃ . Below the amount obtained at NH _3, which accumulates in the SCR catalyst, the term storage amount ", and the maximum of the NH ₃ storage amount, the term" Max-NH ₃ storage amount ". If the NH ₃ storage amount of the SCR catalyst exceeds the maximum NH ₃ storage amount, the NH ₃ downstream shifts. The accumulated in the SCR catalyst NH ₃ is so together with that of the urea / water injectors 42 supplied NH ₃ consumed accordingly for the NO _x reduction. NOx reacts the better, the more NH ₃ enters the SCR catalyst, why the NOx reduction rate of the SCR catalyst sets higher with correspondingly large amounts of NH ₃ storage.

The downstream catalyst converter 33 with the SCR catalyst is located further downstream than the upstream catalyst converter 31 with the LNT catalyst. The exhaust gas purification filter 32 is located between the two catalyst transducers. By this arrangement, the temperature of the SCR catalyst changes more slowly than the temperature of the LNT catalyst.

The air ratio sensor 51 is, for example, along the exhaust duct 11 on the upstream side of the upstream catalyst converter 31 and determines the air ratio (ratio of fuel to oxygen in the exhaust gas) of the upstream catalyst converter 31 inflowing exhaust gas, and then sends a signal which is almost proportional to the detected value to the electric control unit 7 , The air flow sensor 55 Determines the amount of intake air that the intake manifold 12 of the motor 1 happens, and sends a signal that is almost proportional to the value determined to the electrical control unit 7 , The NH ₃ sensor 54 determines the NH ₃ concentration in the exhaust gas on the downstream side of the downstream catalyst converter 33 , and then sends a signal that is almost proportional to the value determined to the electrical control unit 7 ,

The upstream catalyst temperature sensor 52 is along the exhaust duct 11 on the upstream side of the upstream catalyst converter 31 arranged. The downstream catalyst temperature sensor 53 is along the exhaust duct 11 on the upstream side of the downstream catalyst converter 33 arranged. The temperature sensors 52 . 53 each determine the temperature of the upstream catalyst converter 31 and downstream catalyst converter 33 Incoming exhaust gases, and then send signals that are almost proportional to the detected values, to the electrical control unit 7 , The temperatures of the LNT catalyst of the upstream catalyst converter 31 and the SCR catalyst of the downstream catalyst converter 33 each based on the determinations of the temperature sensors 52 . 53 , based on the calculations by the electrical control unit 7 , calculated.

The urea / water delivery device 4 includes a urea / water tank 41 and the urea / water injectors 42 , The urea / water tank 41 accumulates a urea / water mixture, which is a precursor of NH ₃ , and is via a urea / water supply line 43 and an unillustrated urea / water pump with the urea / water injectors 42 connected. By actuating an actuator, not shown, the urea / water injectors open and close 42 and spray that from the urea / water tank 41 fed, as a reducing agent of the SCR catalyst fugierende urea / water mixture along the exhaust passage 11 to the upstream side of the downstream catalyst converter 33 , That of the urea / water injectors 42 sprayed urea / water mixture is in the exhaust gas, or in the downstream catalyst converter 33 , hydrolyzed to NH ₃ and utilized for NOx reduction.

The actuator for urea / water injectors 42 is electromagnetic with the electrical control unit 7 connected. The electric control unit 7 Determines the appropriate amount of urea / water to spray and controls the urea / water injectors 42 to inject the specified amount of urea / water mixture so as to provide optimum NOx reduction by means of NH ₃ in the SCR catalyst. The control of urea / water injection includes, for example, the "feed forward" control based on that of the catalyst converter 33 fed NOx, and the "Feed Backward" control based on the NH ₃ sensor 54 determined NH ₃ concentration. The exact explanation of the urea / water spray control should be waived. The electrical control unit, with which the aforementioned urea / water injection is carried out, carries the following description "DCU (Dosing Control Unit) 72 ".

The following section deals with the upstream catalyst converter 31 arranged LNT catalyst and the downstream catalyst converter 33 attached SCR catalyst, comparing their NOx purification rates. 2 FIG. 14 is a view showing the temperature characteristics of the respective NOx reduction rate [%] of the LNT and SCR catalysts.

The respective NOx reduction rate [%] of the aforementioned catalysts reaches, as in 2 can be seen at a certain temperature maximum, and describes an n-shaped parabola. The LNT catalyst already reduces NOx at low temperatures as the SCR catalyst. Specifically, the LNT catalyst achieves particularly high NOx reduction rates in the range of about 150 to 200 ° C. The LNT catalyst is therefore suitable for low temperatures, for example, in low-load operation or in the warm-up phase directly after starting the engine. The LNT catalyst is therefore, in the exhaust gas purification system 1 according to 1 located in the section behind the engine to achieve a maximum NOx reduction rate.

As already mentioned, the LNT catalyst may achieve a high NOx reduction rate at low temperatures, but does not achieve a sufficient NOx reduction rate in the high temperature range above 300 ° C or in high load operation in which the exhaust gas quantity increases significantly 2 ). Thus, the LNT catalyst does not achieve a sufficient NOx reduction rate, for example, when driving at high speed, uphill, or large acceleration over a long time. Also, at the proper time, DeNOx operation explained below is required to provide a rich, rather than stoichiometric, air ratio in the LNT catalyst, thus reducing the accumulated NOx and restoring the old NOx reduction rate of the catalyst. Ultimately, because of the numerous high load operating phases in which large amounts of NO x are expelled, the reduction process must be done more frequently and additional consumption is added. In the following, with extra consumption, the LNT catalyst means, in addition to the normal fuel consumption under poor air conditions, additional fuel consumption resulting from the reduction process.

The SCR catalyst achieves particularly high NOx reduction rates in the temperature range which is higher than the temperature range in which the SCR catalyst achieves particularly good NOx reduction rates (eg, between about 200 ° C and 300 ° C). Accordingly, with an SCR catalyst, unlike with an SCR catalyst, particularly high NOx reduction rates can be achieved in the high-temperature range and in the high-load range. 2 shows how the SCR catalyst begins at about 130 ° C to reduce NOx by means of accumulated until then NH ₃ . However, the temperature must rise above about 180 ° C in order for the hydrolysis of the urea / water mixture to proceed adequately and produce NH ₃ . If the temperatures remain below about 180 ° C, deposits form through the urea / water mixture. The DCU prohibits urea / water injection in the range below approx. 180 ° C. The temperature range in which NOx is continuously reducible by means of the SCR catalyst is therefore, as well 2 can be seen only in the range above the approximately 180 ° C mark, from where no deposits form by the urea / water mixture. For the reliable prevention of deposits by the urea / water mixture, temperatures of the SCR catalyst of over 200 ° C. are preferred.

If low load operation continues, the temperatures of the SCR catalyst may drop below approximately 180 ° C. In low-load operation, if the NOx reduction is to be continued by means of the SCR catalyst, the heating process requires increasing the temperature of the SCR catalyst, which, however, adds additional consumption. In the following, with additional consumption of the SCR catalyst in addition to the normal fuel consumption additional, by doing the heating process, resulting fuel consumption meant.

As mentioned earlier, the LNT catalyst typically achieves high NOx reduction rates in low load operation, while the SCR catalyst achieves high NOx reduction rates in high load operation. The two NOx reduction rates are therefore complementary. To deal with the emission control system 1 according to 1 To achieve high NOx reduction rates under all operating conditions, the LNT catalyst is combined with the SCR catalyst.

The following section deals with the problem of conventional exhaust gas purifying systems, in which "conventional exhaust gas purifying systems" a first exhaust gas purifying system that reduces NOx by means of an LNT catalyst, a second exhaust gas purifying system that reduces NOx by means of SCR catalyst, and a third exhaust gas purifying system in which the first and the second exhaust gas purification system are combined with each other.

The first emission control system initiates the reduction process by means of the LNT catalyst as soon as the amount of NOx accumulated in the LNT catalyst reaches a certain value. The second exhaust gas purification system initiates the NOx reduction process by means of the SCR catalyst and performs the urea / water injection when the temperature range is reached in which there is no deposits of the urea / water mixture. However, in the second exhaust gas purification system, no heating operation is performed even if the SCR catalyst is below the temperature range (approximately 180 ° C. in FIG 2 ), wherein there are no deposits of the urea / water mixture lies. Accordingly, the additional consumption in the second exhaust gas purification system is 0. The third exhaust gas purification system simply combines the first and second exhaust gas purification systems with each other, whereby reduction by the LNT catalyst and injection of the urea / water mixture in the SCR catalyst take place independently of each other Achieve optimum NOx reduction rates. In the third emission control system is similar to emission Control system 1 according to the embodiment of the present invention according to 1 , the LNT catalyst disposed on the upstream side of the SCR catalyst.

The respective NOx reduction rate [%] of the two aforementioned catalysts achieves the same as the 2 it can be seen at a certain temperature maximum, and describes an n-shaped parabola. 3 FIG. 14 is a view showing the history of NOx reduction rate [%] of the entire system when driving a vehicle with a conventional exhaust gas purification system after a certain drive pattern. Here are in 3 in turn, from top to bottom, the NOx reduction rates of the first exhaust gas purification system, the second exhaust gas purification system, and the third exhaust gas purification system are plotted. 4 , FIG. 15 is a view showing the excess consumption and the NOx discharge amount when driving according to the driving pattern according to FIG 3 shows. In the following, the peculiarities of the NOx reduction rates of the respective exhaust gas purification systems will be explained in order.

The juxtaposition in 3 of the first exhaust gas purification system and second exhaust gas purification system shows that in the first exhaust gas purification system in high load operation, the NOx reduction rate by means of only the LNT catalyst is insufficient. Ultimately, the total NOx emissions are as well 4 can be seen in the first emission control system highest. However, the first exhaust gas purification system achieves a comparatively high NOx reduction rate in low load operation.

The second exhaust gas purifying system, with only the SCR catalyst, achieved NOx reduction rates similar to those of three-way catalytic converters for gasoline engines under almost all operating conditions. As a result, the overall NOx emission rate undercuts, as well 4 it can be seen, the total NOx emission amount of the first emission control system. However, in the second exhaust gas purification system, no heating operation is performed so that it takes longer than the first exhaust gas purification system until the NOx reduction starts after the engine is started. In addition, with continuous low-load operation, the temperature of the catalyst decreases and the urea / water injection is suppressed, so that the accumulated NH _{3 is} exhausted and the NOx reduction rate is temporarily absent. In order to counteract this, it is possible to heat accordingly, but this would mean that the additional consumption would exceed the additional consumption of the first exhaust gas purification system.

In the third exhaust gas purification system in which the LNT catalyst and the SCR catalyst are combined, under all operating conditions such as engine start, low load operation, high load operation, etc., a NOx reduction rate higher than those of the first and second exhaust purification systems has been achieved. The total NOx emission was even lower than that of the second emission control system (see 4 ). Nevertheless, the second exhaust gas purification system also achieves a sufficient NOx reduction rate in high load operation. In contrast, in the third exhaust gas purification system, the NOx reduction rate of the second exhaust gas purification system was exceeded, and in particular, the NOx reduction rate in the high load operation was slightly excessive.

In the third exhaust gas purification system, under the operating conditions as in the first exhaust gas purifying system, that is, when the accumulated NOx amount in the LNT catalyst exceeded a certain level, the reduction process was made even if a high NOx purification rate was achieved with the SCR catalyst to the same additional consumption as in the first emission control system came. Thus, while simply combining LNT and SCR catalysts results in high overall NOx reduction rates in the system, it does not curb excess consumption, as is typical of the SCR catalyst.

It was shown how in the third exhaust gas purification system by means of the mere combination of LNT and SCR catalyst, no optimization of the combination of NOx reduction rate and additional consumption could be achieved. In the following, a method for the regulation of an exhaust gas purification system will be explained, whereby the combination of NOx reduction rate and additional consumption could be optimized.

5 FIG. 11 is a flow chart showing the procedure for determining the operation mode of the engine. FIG. In doing so, the FI-ECU carries out repeated calculations at certain intervals. The engine operation is in 5 at the same time divided into the three types "poor" (see S9), "heated" (see S10), and "DeNOx" (see S11). By means of the procedure according to 5 Depending on the condition of the engine and the exhaust gas purification system, it is possible to determine the appropriate operating mode and thus to optimize both the exhaust gas purification balance and the total fuel consumption of the vehicle.

"Arm" means the mode under poor rather than stoichiometric air ratio. The "poor" mode of operation represents the most basic among the three modes.

"Heated" means the mode of operation whereby the temperatures of the exhaust gas in the LNT and SCR catalysts are increased above those in the "lean" mode to allow the temperatures of the LNT and SCR catalysts to increase in a very short time. The "heated" mode of operation is realized, for example, by delaying the times at which the "post", "after" and "main injection" are to be made with respect to the combustion parameters in the poor mode.

"DeNOx" means the mode in which accumulated NOx in the LNT catalyst is reduced by transferring the exhaust gas to a reducing atmosphere. DeNOx operation can be realized, for example, by narrowing the throttle and reducing the amount of air flowing in, increasing the amount of EGR, delaying the times at which the fuel injection is to take place, injecting more fuel or, in addition, burning the fuel. and post-injection is performed. Since the temperatures of the exhaust gas are higher in DeNOx operation than in poor operation, DeNOx operation also fulfills the function that is also fulfilled in the heated operating mode.

In S1, the FI-ECU determines if all nozzles (injectors, urea / water injectors) and sensors (air ratio sensor, upstream catalyst temperature sensor, downstream catalyst temperature sensor) are functioning.

In S2, the FI-ECU calculates the amount of NOx [mg] Eng_nox_hat (k) emitted by the engine. This is done by retrieving maps and tables using a variety of parameters as function arguments describing engine conditions such as engine load, number of revolutions, EGR rate, and times of fuel injection. Eng_nox_hat (k) can also be calculated by means of a neural network in which the aforementioned function arguments are entered. If an NOx sensor for determining the NOx concentration is arranged in the exhaust gas channel, Eng_nox_hat (k) can also be calculated therewith. Hereinafter, the current value calculated by the FI-ECU in a certain calculation cycle, with the reference character "k" in parentheses, and the value calculated n cycles before the current cycle are indicated by the reference symbol "k-n" in parentheses ,

In S3, the FI-ECU calculates the NOx amount [mg] St_nox_hat (k) accumulated in the LNT catalyst by known methods or by calculations based on the following formulas (1) to (4) in the order of their mention.

In formula (1), Rd_nox_hat (k) represents the amount of NOx [mg] reduced in DeNOx operation. In detail, this means the reduced amount of NOx in the LNT catalyst since the previous calculation process. If the LNT catalyst exposed to the exhaust gas in a reducing atmosphere, it comes, as already mentioned, to reduce the accumulated amount of NOx. In this case, the reduced amount of NOx is proportional to the amount of reducing agent supplied to the LNT catalyst. The reduced amount of NOx Rd_nox_hat (k) is thus calculated according to formula (1) by multiplying the amount of reducing agent [mg] supplied to the LNT catalyst by the positive coefficient K _red for converting the reducing agent amount into reduced amount. The reduced amount is obtained by multiplying the amount of exhaust gas [mg / sec] Gex_hat (k) by the deviation of the determined air ratio Af_act (k) from the stoichiometric air ratio Af_st. For Gex_hat (k), the values calculated by the FI-ECU on the basis of the air flow sensor data are used. Similarly, for Af_act (k), the values calculated by the FI-ECU based on the data from the airflow sensor are used. [Formula 1]

In formula (2), St_nox_hat_tmp (k) stands for the provisionally calculated accumulated NOx amount in the LNT catalyst. Specifically, this means the accumulated NO x amount in the LNT catalyst calculated neglecting the maximum and the minimum. The provisionally calculated accumulated NO x amount St_nox_hat_tmp (k) is given, according to the right side of the formula (2), by adding the NO x amount [mg] newly accumulated since the previous computation to the accumulated NO x calculated in the previous computation Quantity St_nox_hat (k-1) (see right side, second paragraph), and subtracting the reduced amount of NOx Rd_nox_hat (k) calculated according to formula (1). The newly accumulated NOx quantity on the right side, second paragraph, is calculated by multiplying the value in S2 calculated NOx discharge amount Eng_nox_hat (k) with the NOx reduction degree [%] of the LNT catalyst η_nox_lnt (k) (NOx storage performance of the LNT catalyst in the poor operation). [Formula 2]

The NOx reduction degree η_nox_lnt (k) according to formula (2) is given by multiplying the base reduction degree η_nox_lnt_base (k) determined by the temperatures of the LNT catalyst by the compensation coefficient determined by the NOx amount accumulated in the LNT catalyst ηk_nox_lnt (k), where η_nox_lnt_base (k) is about retrieving the table according to 6 calculated and the temperature Lnt_tmp (k) of the LNT catalyst serves as a function argument. 6 shows the N-shaped curve of the NOx reduction rate of the LNT catalyst and its maximum, which is slightly below the maximum value of the NOx reduction degree of the SCR catalyst of 200 ° C. The compensation coefficient ηk_nox_lnt (k) is calculated by retrieving, for example, the table according to FIG 7 wherein the NOx accumulation rate Rt_st_nox_hat (k-1) of the LNT catalyst calculated in the previous calculation (see formula (5) given below) serves as a function argument. 7 shows how the newly accumulated amount of NOx in the LNT catalyst decreases as the amount of NOx currently accumulated increases.

[Formula 3]

• η_nox_lnt (k) = η_nox_lnt_base (k) · ηk_nox_lnt (k) (3)

The amount of NOx St_nox_hat (k) in the LNT catalyst is calculated according to formula (4) by means of limiting the calculated according to the aforementioned calculation provisional NOx amount St_nox_hat_tmp (k) in the LNT catalyst. According to the formula (4), the minimum trappable NOx amount [NOx minimum] is 0, and the maximum trappable NOx amount (St_nox_max (k)) [NOx maximum] at the maximum NOx amount [mg] in the LNT Catalyst, wherein the maximum by retrieving about the table according to 9 calculated as a function argument, the determined temperature Lnt_tmp (k) of the LNT catalyst is used. 8th shows how the maximum amount of NOx that can be accumulated in the LNT catalyst decreases as the temperature of the LNT catalyst increases. [Formula 4]

5 shows how in S4 by means of the FI-ECU, the NOx accumulation rate (ratio of maximum trappable in the LNT catalyst NOx to actually accumulated amount of NOx) [%] in the LNT catalyst Rt_st_nox_hat (k) calculated. In this case, the NOx accumulation rate Rt_st_nox_hat (k) is calculated according to the below-mentioned formula (5) by dividing the actually accumulated NOx amount (St_nox_hat (k)) by the NOx maximum (St_nox_max (k)).

[Formula 5]

• Rt_st_nox_hat (k) = St_nox_hat (k) / St_nox_max (k) (5)

In S5, the FI-ECU determines if the right time to heat the SCR catalyst has arrived. If yes, the heat control flag F_heat (k) gets the value 1, otherwise 0.

In S6, the FI-ECU determines whether the right time to reduce the LNT catalyst has come, i. H. whether, as already mentioned, the right time to initiate DeNOx operation has come to reducing the amount of NOx accumulated in the LNT catalyst. If yes, the reduction control flag F_denox_mode (k) is given the value 1, otherwise 0. In the following, the exact calculation procedures of the processes in S6 are explained.

The reduction control flag F_denox_mode (k) obtains the value 1 according to the below-mentioned formula (6) when all the F_denox_cond (k), F_denox_st (k), F_denox_etrq (k), and F_denox_tscr (k) have the value 1; Flag, the value 0. In other words, the DeNOx operation for NOx reduction in the LNT catalyst is initiated only if the aforementioned four requirements are met. In the following, these four requirements will be explained in more detail. [Formula 6]

F_denox_cond indicates whether the temperature of the LNT catalyst assumed for the reduction is given. If the temperature of the LNT catalyst is too low, NO x reduction will occur despite exposure of the LNT catalyst to the reducing atmosphere. The temperature Lnt_tmp (k) of the LNT catalyst is calculated by the FI-ECU according to the formula (7) given below. If the temperature reaches or exceeds the determined DeNOx start temperature LNT_TNP_ACT (eg 190 ° C.), F_denox_cond (k) is given the value 1, otherwise 0. [Formula 7]

F_denox_st indicates whether the presumed accumulated amount of NOx in the LNT catalyst is given. If NOx is only slightly present in the LNT catalyst and the NOx reduction rate is only slightly attenuated, there is no particular need for DeNOx operation. The FI-ECU determines according to formula (8) F_denox_st (k) by comparing the NOx accumulation rate of the LNT catalyst Rt_st_nox_hat (k) to the thresholds RT_REG_REQ and RT_REG_DON. RT_REG_REQ stands for the threshold value, eg 0.7, at which it is decided that the reduction process is to be carried out. Similarly, RT_REG_DON stands for the threshold, for example, 0.4, at which it is decided that the reduction process is to be ended. In this way, the reduction process is started as soon as the NOx accumulation rate of the LNT catalyst rises above RT_REG_REQ, and ends when subsequently the NOx accumulation rate of the LNT catalyst decreases below RT_REG_DON. [Formula 8]

F_denox_etrq indicates whether the presumed engine operation is given. For example, if the engine is in low-load operation (eg, at idle) and the amount of exhaust gas is extremely low, NOx can not be effectively reduced in DeNOx operation. When the engine is in low-load operation and the amount of NOx discharged is small, there is no particular need to actively carry out the reduction process of the LNT catalyst. According to formula (9), the FI-ECU detects the driver-requested torque Drv_eng_trq (k) based on the determinations of an unillustrated accelerometer sensor and determines F_denox_etrq (k) by comparing Drv_eng_trq (k) to a predetermined threshold ENG_TRQ_REGEN (e.g. 150 Nm). In the present case, the torque requested by the driver was used as the function argument to determine F_denox_etrq (k), but other function arguments are also possible. A corresponding function argument may be any parameter that is approximately proportional to the engine load, such as the actual engine load, fuel injection amount, intake and intake pressure. [Formula 9]

F_denox_tscr indicates whether the temperature of the SCR catalyst assumed for LNT reduction is given. Since F_denox_tscr does not depend on the temperature of the LTN catalyst but on the SCR temperature, F_denox_tscr is independent of the abovementioned F_denox_cond. Given the aforementioned three prerequisites of formulas (7) to (9), the amount of NOx accumulated in the LNT catalyst can be effectively reduced in DeNOx mode and the NOx removed from the exhaust gas by the LNT catalyst. However, if it is reduced by means of the LNT catalyst even if the exhaust gas is already purified by the SCR catalyst of NOx, there is an increase in consumption, which is only a small increase in the NOx reduction rate of the entire system and resources are wasted. To counteract this, the FI-ECU determines the temperature of the SCR catalyst Scr_tmp (k) according to formula (10), compares the determined temperature to the threshold value SCR_LNT_MODE_TMP and determines F_denox_tscr (k). Specifically, F_DeNOx_tscr (k) is determined to be 1 by the FI-ECU (ie, DeNOx operation permitted) if Scr_tmp (k) is at or below the threshold SCR_LNT_MODE_TMP determined within the temperature range where NOx in the exhaust gas is controlled by the SCR. Catalyst is reducible. Similarly, F_DeNOx_tscr (k) is determined by the FI-ECU to be 0 (ie, DeNOx prohibited) if Scr_tmp (k) is higher than the SCR_LNT_MODE_TMP threshold. [Formula 10]

The threshold value SCR_LNT_MODE_TMP of the SCR temperature according to formula (10) serves to determine whether the LNT catalyst is necessary for the reduction. Although NOx is reduced by both the LNT and SCR catalysts when the SCR temperature is below SCR_LNT_MODE_TMP, NOx is primarily reduced by the SCR instead of the LNT catalyst when the SCR temperature is at or above SCR_LNT_MODE_TMP. It can thus be seen that the threshold value SCR_LNT_MODE_TMP therefore fulfills the function between the method for exhaust gas purification, after which NOx is reduced by means of both the LNT and the SCR catalyst, and the method for exhaust gas purification, after which NOx is reduced predominantly by means of the SCR catalytic converter , switch. SCR_LNT_MODE_TMP thus describes the threshold value of the switching temperature.

The switching temperature is, as already mentioned, in the temperature range where NOx is reduced by means of the SCR catalyst. In the same temperature range, NOx is removed from the exhaust gas by means of the hitherto accumulated NH ₃ or of the newly formed by the hydrolysis of the urea / water mixture NH _3. However, for longer urban journeys under low engine load or longer excursions at speeds between 60 and 80 km / h, the temperature of the SCR catalyst drops to a level where deposits of the urea / water mixture can occur. Therefore, in the case by means of the DCU urea / water spray control, injection of the urea / water mixture is suppressed, thus preventing deposits of the urea / water mixture from forming. If the urea / water injection is suppressed, the NH ₃ accumulated until then is used as the reducing agent, so that in the long term NOx can not be reduced by means of the SCR catalyst (see, for example, US Pat 3 second paragraph from above). Thus, to prevent the LNT and SCR catalyst from losing NOx reduction rate, the switching temperature SCR_LNT_MODE_TMP will settle above the temperature allowing deposits of the urea / water mixture sprayed by the urea / water injectors to be formed. This can suppress urea / water injection and avoid sedimentation without compromising the NOx reduction rate of the entire system.

5 Fig. 14 shows how the operation mode of the FI-ECU is determined in consideration of the reduction control flag F_denox_mode (k) and the thermal control flag F_heat (k) obtained in accordance with the aforementioned steps (see S7 and S8). If both F_denox_mode (k) and F_heat (k) have the value 0, the poor mode is selected (see S9). If F_denox_mode (k) has the value 0 but F_heat (k) the value 1, the heated operation by means of which the NOx reduction rate of the SCR catalyst rapidly increases (see S10) is selected, while with F_denox_mode (k) the value is 1 the DeNOx operation by means of which the NOx reduction rate of the LNT catalyst rises rapidly (see S11) is selected. If F_denox_mode (k) therefore has the value 1, DeNOx operation is selected independently of F_heat (k) since, as already mentioned, the temperatures in the exhaust duct are higher in DeNOx operation than in operation under a poor air ratio and so on the function of the heated operation is taken over.

9 is a flow chart showing the procedure of the heater detection. As explained below, heating is determined according to 9 depending on the temperature of the SCR catalyst and the NOx accumulation rate of the LNT catalyst, whether the heated operation for heating the SCR catalyst is to be initiated.

In S21, the FI-ECU determines the temperature of the SCR catalyst Scr_tmp (k) and determines whether Scr_tmp (k) is equal to or less than the switching temperature SCR_LNT_MODE_TMP. In S22, the FI-ECU determines the NOx accumulation rate of the LNT catalyst Rt_st_nox_hat (k) and determines whether Rt_st_nox_hat (k) is equal to or less than the threshold value from which to heat RT_ST_NOX_HUP. This refers to the value (eg, 0.8) that is above the threshold from which RT_REG_REQ is to be reduced.

If the determination in S21 and S22 is "YES", or the temperature of the SCR catalyst is equal to or lower than the switching temperature, and the NOx accumulation rate of the LNT catalyst is equal to or above the threshold value from which to be heated, the FI determines ECU that the SCR catalyst is to be heated, and assigns the value 1 to the heat management flag F_heat (k) (see S23) so as to cause the heated operation (see S10 in FIG 5 ). Similarly, the determination in S21 or S22 is "NO", the FI-ECU determines that the SCR catalyst is not to be heated, and assigns the value 0 to F_heat (k) (see S24) so as to prohibit the heated operation ,

According to the above procedure for determining whether to heat, the heated operation is caused when the temperature of the SCR catalyst is below the switching temperature and the NOx accumulation rate of the LNT catalyst is above the threshold value from which it is heated. In this case, as already mentioned, the threshold value from which to heat is determined to be higher than the threshold value from which it is to be reduced. As a reduction of the LNT catalyst is allowed, if, as already with reference to 5 As explained, the temperature of the SCR catalyst is below the switching temperature, it can not happen that the NOx accumulation rate of the LNT catalyst exceeds the threshold value from which is heated. Suppose, according to 9 should the SCR catalyst be heated if the temperature of the SCR catalyst, for whatever reason, after the NOx accumulation rate of the LNT catalyst is prohibited, while reducing the LNT catalyst is prohibited, the threshold value from being heated, exceeds, falls below the switching temperature. In this case, the FI-ECU determines that it is better, instead of vigorously reducing the LNT catalyst and regenerating the NOx reduction rate of the LNT catalyst, increasing the temperature of the SCR catalyst, and the NOx reduction rate of the SCR Regenerate the catalyst, and thus assigns the value 1 to the heat control flag F_heat (k).

The following section deals with the results of the exhaust gas purification system according to the aforementioned embodiment of the present invention.

10 FIG. 10 is a view showing, with respect to the exhaust gas purification system according to the embodiment of the present invention, which has been mounted on a vehicle, the same driving pattern as that of FIG 3 - shows the changes in the temperature of the SCR catalyst, in the reduction control flag F_denox_mode, in the NOx reduction rate of the entire system, and in the running speed. In 10 the switching temperature SCR_LNT_MODE_TMP was set to 200 ° C, which is set on the one hand in the temperature range in which NOx is reducible by means of the SCR catalyst, on the other hand so high that there are no deposits of urea / water mixture. To a comparison with the conventional emission control system according to 3 and 4 To simplify, the heated operation was avoided even if the temperatures of the SCR catalyst dropped, so that the heat control flag F_heat (k) always had the value 0. 11 FIG. 12 is a view showing the ratio of excess consumption to total NOx discharge amount when driving according to the driving pattern. FIG 10 shows.

10 shows how during driving the temperatures of the SCR catalytic converter "snuggle up" and locally exceed the switching temperature SCR_LNT_MODE_TMP. If the latter happens, the reduction control flag F_denox_mode (k) gets the value 0 and the DeNOx operation is suppressed. Thus, the reduction control flag F_denox_mode (k), particularly in high load operation, has the dashed line in FIG 10 can be seen, over a long time the value 0. As a result, by Restrict of DeNOx operation according to the embodiment of the present invention achieves lower excess consumption in the exhaust gas purification system than in the third exhaust gas purification system.

Further, in the exhaust gas purification system according to the embodiment of the present invention, the switching temperature SCR_LNT_MODE_TMP was determined in the temperature range in which NOx is reducible by the SCR catalyst. In other words, NOx can be reduced by means of the SCR catalyst in the time in which the temperatures of the SCR catalyst exceed the switching temperature SCR_LNT_MODE and the DeNOx operation is prohibited. Thus, if the DeNOx operation is prohibited and the NOx reduction rate of the LNT catalyst decreases, this decrease is sufficiently compensated by the high NOx reduction rate of the SCR catalyst, and thus the NOx reduction rate in the high load operation differs according to 10 hardly from the third emission control system according to 3 , As a result, the exhaust gas purification system according to the embodiment of the present invention generated only a slightly larger total NOx discharge amount while throttling the excess consumption. The fact that the total NOx discharge amount was slightly higher than the third exhaust gas purification system is because the excessive NOx reduction rate in high-load operation decreases due to restricting the DeNOx operation to the NOx reduction rate of the system using only the SCR catalyst.

11 shows the indicated as a dash-dot line course of the ratio of the total NOx emission amount to the additional consumption (hereinafter "brand") with continuous change of the switching temperature SCR_LNT_MODE_TMP. If the switching temperature SCR_LNT_MODE_TMP is lowered, one notices how the frequency of DeNOx operation or the use of the LNT catalyst decreases, and the exhaust gas purification system approaches the second, only the SCR catalyst-based exhaust gas purification system. Now, in the exhaust gas purifying system according to the embodiment of the present invention, the switching temperature SCR_LNT_MODE_TMP is determined as the threshold value, and the use of the LNT catalyst is throttled in the high load operation suitable for NOx reduction by means of the SCR catalyst. If the temperature is then lowered, moves accordingly 11 the mark of the exhaust gas purification system according to the embodiment of the present invention from the brand of the third exhaust gas purification system to the brand of the second exhaust gas purification system without emitting a total of more NOx in total. In other words, it can not be said that the total amount of NOx emissions increased in the same proportion as the excess consumption on the other side decreased.

It will be explained in more detail why the total NOx emission amount can be limited to a minimum. As with reference to 1 already explained, the temperature profile of the SCR catalyst behaves safter than that of the LNT catalyst. Thus, even when the temperatures decrease, the course of the NOx reduction rate of the SCR catalyst behaves more gently than the course of the NOx reduction rate of the LNT catalyst. In addition, the SCR catalyst has the property of trapping NH ₃ , so that the NO x reduction rate of the SCR catalyst does not necessarily decrease just because urea / water injection fails due to the drop in the temperature of the SCR catalyst. At the same time, a sufficient NOx reduction rate can not be achieved by means of the LNT catalyst at a high NOx accumulation rate. Therefore, if the DeNOx operation is permitted as a result of the temperature of the SCR catalyst falling below the switching temperature, the LNT catalyst may simply fail to achieve the supposed NOx reduction rate. In particular, when the DeNOx operation fails for a long time and the amount of NOx accumulated in the LNT catalyst reaches its maximum, the NOx reduction rate often drops visibly. Until then, the accumulated NOx in the LNT catalyst has been sufficiently reduced, the LNT catalyst can not achieve a sufficient NOx reduction rate. In contrast, in the exhaust gas purifying system according to the embodiment of the present invention, it is possible to prevent a steep decrease in the total NOx reduction rate after switching to DeNOx operation until regeneration of the NOx reduction rate of the LNT catalyst by retarding the temperature change. In other words, by delaying the temperature drop of the SCR catalyst, it is possible to sustain DeNOx operation for the LNT catalyst long enough.

The following section deals with the exhaust gas purification system according to a second embodiment of the present invention. As for the procedure for determining the operation mode of the engine, the exhaust gas purification system according to the second embodiment differs from the aforementioned exhaust gas purification system according to the first embodiment of the present invention.

12 FIG. 10 is a flowchart showing the procedure for determining the operation mode in the exhaust gas purification system according to the second embodiment of the present invention. FIG. From all steps S31 to S42 of the process according to 12 S31 to S35 and S37 to S41 correspond to the steps S1 to S5 and S7 to S11 of the process according to, respectively 5 Therefore, apart from their explanation in the following becomes. In the following, the process in step S42 according to 12 who in 5 not yet existing, as well as S36, which was partially modified due to the addition of S42.

In S42, the FI-ECU calculates below, using the 13 and 14 explained approach the value of the driving type detection parameter Pre_delta_v (k). In S36, the FI-ECU tunes by means of Pre_delta_v (k) whether the time appropriate for the DeNOx operation has come, and if so, assigns the value 1 to the reduction control flag F_denox_mode (k), otherwise the value 0.

The procedure for calculating the driving type recognition parameter Pre_delta_v (k) should be determined using the 13 and 14 be explained.

13 FIG. 13 is a view showing the principle behind the travel type recognition parameter.

The driving type recognition parameter Pre_delta_v shows the future driving state of the vehicle. If it turns out that the future travel speed will be about the same as the current travel speed (steady state), Pre_delta_v will get the value 0, if the future travel speed will be higher than the current travel speed (acceleration), Pre_delta_v will get a positive value, and if If the future driving speed is lower than the current driving speed (speed reduction), Pre_delta_v will be given a negative value. Depending on the acceleration or the speed reduction, the temperature of the catalyst in the exhaust gas duct also increases or decreases, which is why the driving type detection parameter Pre_delta_v also serves to ascertain the temperature changes of the catalytic converter.

Pre_delta_v (k) is generated by the FI-ECU, as schematically the 13 is calculated based on the travel history of the vehicle calculated. Specifically, the section average cruising speed in a certain drive cycle (hereinafter "section average cruising speed Drv_ave") is stored in a ring buffer, and the travel type recognition parameter Pre_delta_v (k) is determined by the buffer value of the next n drive cycle (Drv_ave (0), Drv_ave (1), ... Drv_ave (n), where "n" is arbitrarily selectable and subsequently receives the value 5) according to the formula (11) given below. The drive cycle is the time from startup to standstill of the vehicle. It is also the travel time within the maximum calculation period TM_DRV_MAX. [Formula 11]

There is rarely a great change in the driving environment (normal road, highway, mountain route, inner-city road, traffic jam, etc.). It can therefore be said that the travel type recognition parameter Pre_delta_v, which is calculated according to the formula (11) based on the travel history of the vehicle, also serves as an indication of the future driving state.

14 Fig. 10 is a flowchart showing the detailed procedure for calculating the driving type recognition parameter.

In S51, the FI-ECU determines the travel time Tm_drv (k-1), and determines whether the maximum calculation period TM_DRV_MAX has elapsed (Tm_drv (k-1) ≤ TM_DRV_MAX). In this case, the travel time Tm_drv is reset to the value 0 each time the travel time is updated in step S53 explained below, and it has been determined in step S56 explained below that the drive cycle has started. In S52, based on the determinations of the unillustrated cruise sensor, the FI-ECU determines the current cruise speed Vp (k), compares it to the cruise threshold VP_MAX, and thus determines whether the vehicle is traveling (VP_MAX ≦ Vp (k)).

If the findings in S51 and S52 were "YES", the FI-ECU determines that the driving cycle has not yet been completed and refers to S53. In S53, the FI-ECU updates the travel time Tm_drv (k) (Tm_drv (k) = Tm_drv (k-1) + .DELTA.T, where .DELTA.T is the calculation cycle of the operation according to FIG 14 is) and in S54 the distance covered Sum_vp (k) (Sum_vp (k) = Sum_vp (k-1) + ΔT × Vp (k)).

If the determination in S51 or S52 was "NO", the FI-ECU determines that the driving cycle has been completed and refers to S55. In S55, the FI-ECU updates the ring buffer of the section average travel speed (Drv_ave (0), ... Drv_ave (5)). Specifically, the FI-ECU calculates, using the distance Sum_vp (k) and travel time Tm_drv (k) determined in S53 and S54, the average travel speed of the next drive cycle and stores it in the buffer with the youngest digit Drv_ave (0), while the subsequent buffers to be shifted by the value 1. In S56, the FI-ECU resets the travel time Tm_drv (k) to 0, while resetting the traveled distance Sum_vp (k) to 0 in S57.

In S58, the FI-ECU calculates the travel type recognition parameter Pre_delta_v (k) by the formula (11) and ends the process.

In 12 the FI-ECU determines the flags F_denox_tscr (k), F_denox_st (k) and F_denox_etrq (k) according to the formulas (7) to (9) and the LNT according to the formulas (12) to (14) explained below. Temperature flag F_denox_tscr (k), and then determines the reduction control flag F_denox_mode (k) by means of these four flags according to the formula (6). The following section deals with the procedure for determining the LNT temperature flag by means of the travel type recognition parameter.

First, according to the below formula (12), the FI-ECU calculates the correction amount Delta_slmode_tmp (k) by multiplying the travel-type detection parameter Pre_delta_v (k) calculated in S42 by a specific switching temperature gain Kv2tmp. The switching temperature gain Kv2tmp determines to what extent the driving type recognition parameter influences the correction switching temperature Scr_lnt_mode_tmp_mod (k) explained below. Switching temperature gain Kv2tmp is thereby set negative, and may be fixed or variable, depending on the negative value of the driving type detection parameter Pre_delta_v (k). In the following, the switching temperature gain Kv2tmp is fixed.

[Formula 12]

• Delta_slmode_tmp (k) = Kv2tmp · Pre_delta_v (k) (12)

Next, according to the below-mentioned formula (13), the FI-ECU calculates the correction switching temperature Scr_lnt_mode_tmp_mod (k) by adding the correction amount Delta_slmode_tmp (k) to the fixed switching temperature SCR_LNT_MODE_TMP. Here too switching temperature gain Kv2tmp is set negative. With the fixed switching temperature SCR_LNT_MODE_TMP as a guideline, the correction switching temperature Scr_lnt_mode_tmp_mod (k) is then corrected so that its value, when the prognosis parameter value becomes positive, is smaller than the guideline value and its value, if the prognosis parameter value becomes negative, is greater than the guideline value ,

[Formula 13]

• Scr_lnt_mode_tmp_mod (k) = SCR_LNT_MODE_TMP + delta_slmode_tmp (k) (13)

Next, according to the below-mentioned formula (14), the FI-ECU determines the temperature of the SCR catalyst Scr_tmp (k), compares it with the aforementioned correction switching temperature Scr_lnt_mode_tmp_mod (k), and thus determines the LNT temperature flag F_DeNOx_tscr (k). [Formula 14]

This section deals with the results obtained by the aforementioned exhaust gas purification system according to the embodiment of the present invention.

15 FIG. 10 is a view showing, with respect to the exhaust gas purification system according to the embodiment of the present invention, which has been mounted on a vehicle, the same driving pattern as that of FIG 3 - shows the changes in the vehicle type recognition parameter, in the temperature of the SCR catalyst, in the reduction control flag F_denox_mode, in the NOx reduction rate of the entire system, and in the vehicle speed. 15 shows how the correction switching temperature Scr_lnt_mode_tmp_mod regulates between a certain lower limit (in detail 180 ° C) and upper limit (in detail 250 ° C) has been. It was set according to the formula (13), the correction switching temperature to the value of the lower limit when the correction switching temperature fell below the lower limit, and set to the value of the upper limit when the correction switching temperature exceeded the upper limit. At the same time, the fixed switching temperature became SCR_LNT_MODE_TMP, similar to 10 , fixed at 200 ° C. In addition, as already under consideration of the 10 explained that the heated operation was avoided even when the temperatures of the SCR catalyst dropped. 16 FIG. 12 is a view showing the ratio of excess consumption to total NOx discharge amount when driving according to the driving pattern. FIG 15 shows.

15 shows how in the exhaust gas purification system according to the embodiment of the present invention, in the same manner as in the exhaust gas purification system according to a first embodiment, in the high load operation, on the one hand, the NOx reduction rate increased and the excess consumption could be reduced, and on the other hand in low load operation, a sufficient NOx reduction rate can be achieved could. In the exhaust gas purification system according to the embodiment of the present invention, based on the travel history of the vehicle, the successive cruise detection parameter is calculated, and by means of which the correction shift temperature is set. Depending on the driving condition of the vehicle, it is possible to determine more precisely the time when the DeNOx operation is to be prohibited or permitted. As a result, like the 16 1, the total NOx discharge amount in the exhaust gas purification system according to the embodiment of the present invention is slightly higher than in the exhaust gas purification system according to the first embodiment. However, in the exhaust gas purification system according to the embodiment of the present invention, the excess consumption could be further reduced than in the exhaust gas purification system according to the first embodiment.

In the following section, a more detailed comparison of the results of the exhaust gas purification system according to the first embodiment with those of the exhaust gas purification system according to the embodiment of the present invention will be made.

17 FIG. 14 shows the comparison of the results of the exhaust gas purification system according to the first embodiment with those of the exhaust gas purification system according to the embodiment of the present invention. In 17 For example, the results of the exhaust gas purification system according to the first embodiment are indicated by a thin line, while the results of the exhaust gas purification system according to the embodiment of the present invention are indicated by a thick line.

In the exhaust gas purification system according to the embodiment of the present invention, the correction switching temperature dropped in places below 200 ° C. Although this allowed the additional consumption to be throttled more, the DeNOx operation was often suppressed. Thus was how the 17 It can be seen, the NOx reduction rate in the first section during the high load operation lower than in the exhaust gas purification system according to the first embodiment, in which the switching temperature was fixed at 200 ° C. As a result, the total NOx discharge amount in the exhaust gas purification system according to the embodiment of the present invention was slightly higher than in the exhaust gas purification system according to the first embodiment. However, the DeNOx operation in the exhaust gas purifying system according to the embodiment of the present invention could be prohibited by calculating the driving type recognition parameter, ie, by predicting the changes of the temperature of the SCR catalyst and the change of the correction switching temperature earlier than in the exhaust gas purifying system according to the first embodiment Therefore, in the exhaust gas purification system according to the embodiment of the present invention, the fluctuation range of the NOx reduction rate was lower than in the exhaust gas purification system according to the first embodiment. As a result, the surplus consumption could be throttled more, while the NOx reduction rate could be kept stable throughout the whole cycle.

The aforementioned section dealt with the exhaust gas purification system according to the second embodiment of the present invention. As mentioned above, the type of travel detection parameter Pre_delta_v indicated both the future driving condition and the future change in the temperature of the catalyst. Consequently, as a result, it was indifferent whether the correction switching temperature was changed by means of the travel type recognition parameter Pre_delta_v or the temperature of the SCR catalyst was predicted by means of the travel type recognition parameter Pre_delta_v.

In this case, instead of formulas (13) and (14) above, the FI-ECU expects formulas (15) and (16) below. Specifically, the FI-ECU calculates the predictive value Pre_dcr_tmp (k) for the future temperature of the SCR catalyst by subtracting the correction amount Δs_mode_tmp (k) obtained from the current temperature according to the above-mentioned formula (12), according to the below formula (15) of the SCR catalyst Scr_tmp (k).

[Formula 15]

• Pre_scr_tmp (k) = Scr_tmp (k) - Delta_slmode_tmp (k) (15)

In addition, according to the below-mentioned formula (16), the FI-ECU compared the predicted value Pre_dcr_tmp (k) to the fixed switching temperature SCR_LNT_MODE_TMP, thus determining the LNT temperature flag F_denox_tscr (k). Thereby, the same results as in the exhaust gas purification system according to the second embodiment were obtained. [Formula 16]

The upper section dealt with the embodiment of the present invention, but the present invention is not limited thereto. For example, in the second embodiment, the LNT temperature flag F_denox_tscr (k) has been determined by the method of FIG 14 calculated travel type recognition parameter, but the present invention is not limited thereto. It would also have a different approach than that according to 14 may be used, as long as the driving type recognition parameter for determining the LNT temperature flag value would have been suitable to perform the aforementioned function (to change the value according to the increase or decrease of the future driving speed). For example, the travel type recognition parameter provided with this prediction function could have been calculated by means of a neural network. Incidentally, other methods would have been suitable.

Further, in the above embodiment of the present invention, the exhaust gas in the LNT catalyst was converted to the reducing atmosphere by changing the operation mode of the engine to the DeNOx operation, but the present invention is not limited thereto. Thus, for example, the exhaust gas in the LNT catalytic converter could also be transferred into the reducing atmosphere by injecting fuel from injection nozzles which are arranged on the exhaust gas duct.

In addition, in the above embodiment of the present invention, for NOx reduction, an NH ₃ -SCR catalyst having NH _{3 was used} as the reducing agent, but the present invention is not so reduced. It would have been possible to use for NOx reduction as well, for example, an HC-SCR catalyst in which the reducing agent is in the form of hydrocarbon contained in exhaust gas discharged from the engine or in the form of the aforesaid fuel injected from the injectors becomes.

LIST OF REFERENCE NUMBERS

1

Engine (internal combustion engine)

2

emission Control system

31

upstream catalyst converter (LNT catalyst)

33

downstream catalyst converter (SCR catalyst)

42

Urea / water injector

52

upstream catalyst temperature sensor (temperature sensing element)

53

downstream catalyst temperature sensor (temperature sensing element)

71

FI-ECU (LNT catalyst reduction device, temperature sensing element, switching temperature control unit, catalyst heating)

The present invention has for its object to provide an exhaust gas purification system for internal combustion engines, comprising at least two catalysts with the task to reduce NOx in the exhaust gas, wherein at the same time throttled the excess consumption, and the overall NOx reduction rate is increased.

Means for Solving the Problem: The present invention uses the means for solving the problem to arrange the following elements in the aforementioned exhaust gas purification system:
a catalyst which traps NOx in an oxidizing atmosphere and reduces it in a reducing atmosphere;
an SCR catalyst that allows NH ₃ to react with NOx to reduce NOx; and
an FI-ECU, which, when certain conditions are met, performs a DeNOx operation for the reduction of NOx accumulated in the LNT catalyst and converts the LNT catalyst into a reducing atmosphere.

If the temperature of the SCR catalyst Scr_tmp exceeds the switching temperature SCR_LNT_MODE_TMP, which is regulated in the temperature range in which NOx is reducible by means of the SCR catalyst, the FI-ECU prohibits the execution of the DeNOx operation (reduction of the LNT catalyst).

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2000-265828 [0006]
• JP 2010-116784 [0006]
• JP 2009-85178 [0006]

Claims (6)

An exhaust gas purification system for internal combustion engines, comprising: an LNT catalyst disposed in an exhaust passage of an internal combustion engine and trapping NOx in an oxidizing atmosphere and reducing it in a reducing atmosphere; an LNT-cat reduction apparatus which, when certain conditions are met, for the reduction of NOx accumulated in the LNT catalyst, performs additional fuel injection, and converts the LNT catalyst into reducing atmosphere; an arranged in the exhaust passage of the internal combustion engine SCR catalyst, which reacts a reducing agent with NOx and thus reduces NOx; a feeder which directs the reducing agent or a precursor of the reducing agent into the SCR catalyst; and temperature detecting elements detecting the temperature of the SCR catalyst, characterized in that the LNT-cat reduction device prohibits the additional fuel injection when the temperature detected by the temperature detecting elements is higher than a switching temperature, which in turn is in a temperature range in which NOx is reducible by means of the SCR catalyst. An exhaust purification system for an internal combustion engine according to claim 1, characterized in that the exhaust gas purification system additionally includes a switching temperature control unit that changes the switching temperature based on the driving history of the vehicle. An exhaust purification system for an internal combustion engine according to claim 1, characterized in that the temperature detection elements, based on the driving history of the vehicle, detect the future temperature of the SCR catalyst. An exhaust purification system for an internal combustion engine according to any one of claims 1 to 3, characterized in that the exhaust gas purification system additionally comprises a catalyst heater which raises the temperature of the SCR catalyst when the temperature detected by the temperature detection elements is at or below the switching temperature, and when the NOx Accumulation rate of the LNT catalyst is at or above a certain value. An exhaust purification system for an internal combustion engine according to any one of claims 1 to 4, characterized in that the LNT catalyst and the SCR catalyst are arranged in the exhaust passage such that the temperature of the SCR catalyst changes more slowly than the temperature of the LNT catalyst. An exhaust purification system for an internal combustion engine according to any one of claims 1 to 5, characterized in that: the SCR catalyst is an NH ₃ -SCR catalyst, wherein NH ₃ serves as a reducing agent; the reducing agent supply means comprises a urea / water injection nozzle which injects a urea / water mixture, which is a precursor of NH ₃ , into the upstream side of the NH ₃ -SCR catalyst along the exhaust passage; and the switching temperature above the temperature at which the urea / water mixture sprayed from the urea / water injector generates deposits in the exhaust gas is determined.

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