EP1006270A1 - Control method of the purging of nitrogen oxides in a catalytic converter for exhaust gases of an internal combustion engine - Google Patents

Control method of the purging of nitrogen oxides in a catalytic converter for exhaust gases of an internal combustion engine Download PDF

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Publication number
EP1006270A1
EP1006270A1 EP99402945A EP99402945A EP1006270A1 EP 1006270 A1 EP1006270 A1 EP 1006270A1 EP 99402945 A EP99402945 A EP 99402945A EP 99402945 A EP99402945 A EP 99402945A EP 1006270 A1 EP1006270 A1 EP 1006270A1
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EP
European Patent Office
Prior art keywords
purge
richness
air
fuel
engine
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Granted
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EP99402945A
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German (de)
French (fr)
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EP1006270B1 (en
Inventor
Stephan Beurthey
Jean-François Leroux
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Renault SAS
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Renault SAS
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D37/00—Non-electrical conjoint control of two or more functions of engines, not otherwise provided for
    • F02D37/02—Non-electrical conjoint control of two or more functions of engines, not otherwise provided for one of the functions being ignition
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2250/00—Engine control related to specific problems or objectives
    • F02D2250/18—Control of the engine output torque
    • F02D2250/21—Control of the engine output torque during a transition between engine operation modes or states

Definitions

  • the present invention relates to a method of ordering the nitrogen oxide purge from a jar exhaust gas treatment catalytic internal combustion engine, said pot absorbing such oxides during operation in air / fuel mixture poor of said engine. More particularly, the invention relates to such a process of the type according to which order a purge of the pot by a temporary increase fuel richness of the air / fuel mixture.
  • the aforementioned patent proposes to switch periodically the richness of the air / fuel mixture at a value corresponding to a stoichiometric mixture or rich. This switching causes desorption of the nitrogen oxides adsorbed in the pot then their reduction by unburnt hydrocarbons and carbon monoxide present in the pot due to the increase in richness of the mixture.
  • the duration of the switching needed to desorb and reduce nitrogen oxides stored in the catalytic converter is proportional to the mass of nitrogen oxides stored.
  • the object of the present invention is precisely to provide a method for controlling the oxide purge of nitrogen from a catalytic converter for gas treatment exhaust from an internal combustion engine, which allows to maintain, during and after a pot purge phase, previous engine torque, all reducing engine fuel consumption during this purge and the amount of chemical species pollutants contained in the combustion gases of the engine.
  • FIG. 1 of the accompanying drawing where we schematically represents one of the cylinders of an engine 1 internal combustion, conventionally fitted with a piston la, an inlet valve 1b and a valve exhaust lc.
  • the exhaust valve lc controls the passage of combustion gases leaving the engine, in a exhaust line 2 on which a pot is mounted trifunctional catalytic 3 of the type described in the preamble of this description.
  • Fuel is supplied to the cylinder using a fuel injector 4 opening into the cylinder, in the case of an "injection” engine direct “, or from an injector 5 conventionally spraying the inlet valve 1b, as shown in line interrupted in Figure 1.
  • the air flow entering the cylinder through this valve 1b is regulated by an air intake circuit comprising a "motorized" throttle valve 6 controlled by a digital computer 7, as it is now classic.
  • the computer controls, in addition to the butterfly 7 and the injector 4 or 5, a spark plug 8 so to adjust the angle of advance at ignition of the mixture air / fuel introduced into the cylinder.
  • FIG. 2 shows the development, respectively, of the richness R of the air / fuel mixture, of the air flow rate D entering the engine and of the angle of advance of ignition, from d an instant t 1 of triggering a purge, instant determined by said expert system for example, these changes being determined by the purge control method according to the invention, as described in detail below.
  • the computer controls a sudden increase in the quantity of gasoline injected into the engine and therefore in the richness of the air / fuel mixture, so that it is suitable for purging the pot of oxides of nitrogen, this richness then passing from the previous value R 0 corresponding to a lean mixture, to a value R 1 greater than that (R 2 ) corresponding to the stoichiometry.
  • the computer 7 controls a progressive reduction in the air flow entering the engine from the previous value D 0 , and an abrupt reduction in the ignition advance angle ⁇ , which then goes from the previous value ⁇ 0 to a value ⁇ 1 .
  • the sudden reduction in the angle of advance ⁇ to the value ⁇ 1 is calculated to compensate for the sudden increase in engine torque which would otherwise result from the sudden increase in the value of the richness of the air / fuel mixture up to the value R 1 .
  • the engine torque is thus stabilized at its value prior to the purge, for the benefit of passenger comfort.
  • these torque changes are eliminated by gradually increasing the angle ⁇ of ignition advance, from the value ⁇ 1 to a value ⁇ 2 corresponding to optimum operation of the engine at the air flow rate D 1 and at the setpoint richness R 1 during the purge, this progressive rise in the angle of ignition advance ⁇ being slaved to the reduction of the air flow so as to follow it over time.
  • the response time of the air intake circuit is thus fully taken into account by the method according to the invention, which makes it possible to limit the fuel consumption of the engine during the purge as well as the emissions of polluting species, without disturb the engine torque.
  • Controlling the angle ⁇ to the air flow can be obtained simply by suitable programming of the computer 7.
  • the expert system determines that the catalytic converter 3 has regained its efficiency, it commands, at time t 2 , the stopping of the purge, that is to say the restoration in the long term of the values R 0 , D 0 and ⁇ 0 of the richness, the air flow rate and the ignition advance angle respectively.
  • this difficulty is overcome by returning to the lean mixture by passing through a mixture of richness of value R 2 intermediate between R 1 and R 0 , the value R 2 corresponding to a stoichiometric mixture, for example, richness value for which the three-way catalyst treats polluting emissions.
  • the computer controls the throttle valve 6 so as to increase the air flow entering the engine until gradually returning to an air / fuel mixture of richness R 0 , therefore to a "lean" mixture.
  • the computer suddenly raises the ignition advance angle ⁇ to the value ⁇ 3 , so as to compensate for the sudden reduction in the wealth observed at this time, ⁇ 3 corresponding to the optimal advance value when the air / fuel mixture is of stoichiometric composition.
  • the advance is again controlled by the air flow until this returns to the value D 0 , at the instant t 3 .
  • the advance ⁇ and the richness R are reduced to the values ⁇ 0 and R 0 respectively, corresponding to the lean mixture.
  • the present invention achieves the goal, namely to ensure the purge of nitrogen oxides from a catalytic converter, without disturbance of the torque delivered by the engine and without overconsumption of fuel and pollution peaks transients in engine exhaust.

Abstract

While the purge is being stopped in a process to purge nitrogen oxides from an engine exhaust, the air/fuel richness ratio is brought to a level (R2) between initial value R0 and purge value R1 and the angle is changed to a third set value ( alpha 3) before being increased to a fourth value ( alpha 4) as the air flow increases. The three variables are returned to their initial values (R0, D0, alpha 0) In a process to purge nitrogen oxides (NOx) from an internal combustion engine exhaust, a catalytic pot adsorbs the nitrous oxides when the motor operates with a fuel/air mixture poor in fuel. The purge is controlled by the temporary increase in richness of the fuel/air mixture by progressively reducing the air flow (D) into the engine so as to optimize the fuel consumption at the set richness. The angle of spark ( alpha ) is abruptly reduced to a set value ( alpha 1) to maintain the torque generated by the engine. The angle is then increased to a second value ( alpha 2) optimizing the fuel consumption of the engine as a function of the richness (R1) and the air flow (D1) fixed during the purge. The purge is stopped by returning the values of the richness (R), the air flow and the angle to their initial values. The intermediate value R1 matches a stoichiometric air/fuel ratio. While the purge is being stopped, the air/fuel richness ratio is brought to a level (R2) between initial value R0 and purge value R1 and the angle is changed to a third set value ( alpha 3) before being increased to a fourth value ( alpha 4) as the air flow increases. The three variables are returned to their initial values (R0, D0, alpha 0). The purge is started and stopped under the control of a system which measures the NOx load in the catalytic pot.

Description

La présente invention est relative à un procédé de commande de la purge en oxydes d'azote d'un pot catalytique de traitement des gaz d'échappement d'un moteur à combustion interne, ledit pot absorbant de tels oxydes lors du fonctionnement en mélange air/carburant pauvre dudit moteur. Plus particulièrement, l'invention est relative à un tel procédé du type suivant lequel on commande une purge du pot par un accroissement temporaire de la richesse en carburant du mélange air/carburant.The present invention relates to a method of ordering the nitrogen oxide purge from a jar exhaust gas treatment catalytic internal combustion engine, said pot absorbing such oxides during operation in air / fuel mixture poor of said engine. More particularly, the invention relates to such a process of the type according to which order a purge of the pot by a temporary increase fuel richness of the air / fuel mixture.

Pour réduire la pollution de l'atmosphère par les gaz d'échappement des moteurs à combustion interne, en particulier ceux qui assurent la propulsion des véhicules automobiles, on équipe couramment les lignes d'échappement de ces gaz d'un pot catalytique ayant pour fonction de transformer les espèces chimiques nocives contenues dans ces gaz en espèces moins nocives, voire inoffensives.To reduce air pollution by exhaust gases from internal combustion engines, especially those who propel vehicles automobiles, we currently equip exhaust lines with these gases from a catalytic converter having the function of transform the harmful chemical species contained in these gases in less harmful, even harmless, species.

C'est ainsi que l'on connaít un pot catalytique dit "à trois voies" ou "trifonctionnel", du fait qu'il assure une triple fonction d'oxydation des hydrocarbures imbrûlés (HC), d'oxydation du monoxyde de carbone (CO) en CO2 et de réduction des oxydes d'azote (NOx) en azote gazeux.This is how we know a catalytic converter called "three-way" or "trifunctional", because it provides a triple function of oxidation of unburnt hydrocarbons (HC), oxidation of carbon monoxide ( CO) to CO 2 and reduction of nitrogen oxides (NOx) to nitrogen gas.

Le souci de réduire les émissions de gaz et l'effet de serre, en particulier les émissions de gaz carbonique CO2 a provoqué de l'intérêt pour un moteur à combustion interne capable de fonctionner avec un rapport air/carburant dit "pauvre", c'est-à-dire supérieur à celui d'un mélange stoechiométrique. Cependant, lorsqu'on utilise un pot catalytique trifonctionnel classique pour dépolluer les gaz d'échappement d'un tel moteur fonctionnant en mélange pauvre, on observe une très faible efficacité du pot dans la réduction des oxydes d'azote (NOx).The concern to reduce gas emissions and the greenhouse effect, in particular carbon dioxide CO 2 emissions, has provoked interest in an internal combustion engine capable of operating with an air / fuel ratio called "lean", that is to say greater than that of a stoichiometric mixture. However, when a conventional three-way catalytic converter is used to clean up the exhaust gases of such an engine operating in a lean mixture, we observe a very low efficiency of the pot in reducing nitrogen oxides (NOx).

Pour pallier cet inconvénient, on propose dans le brevet européen n° 560 991 d'utiliser un pot catalytique trifonctionnel comprenant en outre des moyens d'adsorption des oxydes d'azote présents dans les gaz d'échappement, lorsque le mélange air/carburant provenant du moteur est pauvre.To overcome this drawback, we propose in the European patent n ° 560 991 to use a catalytic converter trifunctional further comprising means adsorption of nitrogen oxides present in gases exhaust, when the air / fuel mixture from engine is poor.

Pour éviter que cette adsorption ne provoque à la longue la saturation de la capacité d'adsorption du pot catalytique, le brevet précité propose de commuter périodiquement la richesse du mélange air/carburant à une valeur correspondant à un mélange stoechiométrique ou riche. Cette commutation provoque la désorption des oxydes d'azote adsorbés dans le pot puis leur réduction par les hydrocarbures imbrûlés et le monoxyde de carbone présents dans le pot du fait de l'accroissement de la richesse du mélange. La durée de la commutation nécessaire pour désorber et réduire les oxydes d'azote stockés dans le pot catalytique est proportionnelle à la masse des oxydes d'azote stockés.To prevent this adsorption from causing long saturation of the adsorption capacity of the pot catalytic, the aforementioned patent proposes to switch periodically the richness of the air / fuel mixture at a value corresponding to a stoichiometric mixture or rich. This switching causes desorption of the nitrogen oxides adsorbed in the pot then their reduction by unburnt hydrocarbons and carbon monoxide present in the pot due to the increase in richness of the mixture. The duration of the switching needed to desorb and reduce nitrogen oxides stored in the catalytic converter is proportional to the mass of nitrogen oxides stored.

Il faut veiller à ce que les opérations de purge du pot ne perturbe pas sensiblement le couple délivré par le moteur, de manière à ménager le confort des passagers du véhicule. A cet égard, les diverses stratégies de commande décrites dans le brevet précité ne sont pas satisfaisantes car, combinées à une telle commande en couple, elles provoqueraient des pics d'émission d'espèces polluantes (monoxyde de carbone, hydrocarbures imbrûlés) pendant les phases transitoires, notamment lors du retour en mélange pauvre à la fin d'une purge, du fait du temps de réponse de certains actionneurs utilisés tels que, notamment, le papillon des gaz motorisé et commandé par un calculateur, qui sert à régler le débit d'air entrant dans le moteur.Care must be taken to ensure that pot does not significantly disturb the torque delivered by the engine, so as to provide comfort for passengers in the vehicle. In this regard, the various strategies for command described in the aforementioned patent are not satisfactory because, combined with such an order in couple, they would cause emission peaks polluting species (carbon monoxide, hydrocarbons unburned) during transient phases, especially during of the return in lean mixture at the end of a purge, because the response time of certain actuators used such as that, in particular, the motorized and controlled throttle valve by a computer, which is used to regulate the air flow entering the engine.

La présente invention a précisément pour but de fournir un procédé de commande de la purge en oxydes d'azote d'un pot catalytique de traitement des gaz d'échappement d'un moteur à combustion interne, qui permette d'assurer le maintien, pendant et après une phase de purge du pot, du couple moteur antérieur, tout en réduisant la consommation en carburant du moteur pendant cette purge et la quantité d'espèces chimiques polluantes contenues dans les gaz de combustion du moteur.The object of the present invention is precisely to provide a method for controlling the oxide purge of nitrogen from a catalytic converter for gas treatment exhaust from an internal combustion engine, which allows to maintain, during and after a pot purge phase, previous engine torque, all reducing engine fuel consumption during this purge and the amount of chemical species pollutants contained in the combustion gases of the engine.

On atteint ce but de l'invention, ainsi que d'autres qui apparaítront à la lecture de la description qui va suivre, avec un procédé de commande de la purge en oxydes d'azote d'un pot catalytique de traitement des gaz d'échappement d'un moteur à combustion interne, ledit pot absorbant lesdits oxydes d'azote quand ledit moteur fonctionne en mélange air/carburant pauvre en carburant, ledit procédé étant du type suivant lequel

  • a) on commande une purge par un accroissement temporaire de la richesse en carburant dudit mélange en réduisant progressivement le débit d'air entrant dans le moteur de manière à optimiser la consommation en carburant du moteur à la richesse fixée, en réduisant brusquement, à une valeur prédéterminée, l'angle d'avance à l'allumage du mélange air/carburant, pour maintenir la constance du couple délivré par le moteur, et en asservissant ensuite une remontée dudit angle d'avance à ladite réduction du débit d'air, jusqu'à une deuxième valeur prédéterminée optimisant la consommation en carburant du moteur en fonction de la richesse et du débit d'air fixé pendant la purge,
  • b) on arrête la purge en ramenant les valeurs de la richesse du mélange air/carburant, du débit d'air et de l'angle d'avance à l'allumage dudit mélange, aux valeurs respectives antérieures au déclenchement de la purge,
    •    ce procédé étant remarquable en ce que, à l'étape b), on abaisse d'abord la richesse du mélange air/carburant à une valeur intermédiaire entre les richesses de purge et de mélange pauvre, avec commande concomitante d'une remontée progressive du débit d'air et d'une remontée brusque de l'angle d'avance à l'allumage à une troisième valeur prédéterminée fonction de ladite richesse intermédiaire, on asservit ensuite une décroissance dudit angle jusqu'à une quatrième valeur prédéterminée pendant la remontée du débit d'air, et on rétablit enfin la richesse du mélange, le débit d'air et l'angle d'avance à l'allumage aux valeurs respectives antérieures à la purge.This object of the invention is achieved, as well as others which will appear on reading the description which follows, with a method for controlling the purging of nitrogen oxides from a catalytic converter for treating gaseous gases. exhaust of an internal combustion engine, said pot absorbing said nitrogen oxides when said engine operates in an air / fuel mixture lean in fuel, said method being of the type according to which
  • a) a purge is controlled by a temporary increase in the fuel richness of said mixture by gradually reducing the air flow entering the engine so as to optimize the fuel consumption of the engine to the fixed richness, by abruptly reducing to a predetermined value, the angle of advance at ignition of the air / fuel mixture, to maintain the constancy of the torque delivered by the engine, and then slaving a rise in said angle of advance to said reduction in air flow, up to a second predetermined value optimizing the fuel consumption of the engine as a function of the richness and of the air flow rate fixed during the purge,
  • b) the purge is stopped by reducing the values of the richness of the air / fuel mixture, of the air flow rate and of the angle of advance on ignition of said mixture, to the respective values prior to the initiation of the purge,
    • this process being remarkable in that, in step b), the richness of the air / fuel mixture is first lowered to an intermediate value between the purge and lean mixture richnesses, with the concomitant control of a progressive rise in the air flow and a sudden rise in the ignition advance angle to a third predetermined value depending on said intermediate richness, a decrease in said angle is then enslaved to a fourth predetermined value during the rise of the air flow, and finally restores the richness of the mixture, the air flow and the ignition advance angle to the respective values prior to the purge.

    Comme on le verra plus loin en détail, en commandant ainsi simultanément le débit d'air entrant dans le moteur et l'angle d'avance à l'allumage du mélange air/carburant d'alimentation de ce moteur, on assure la constance du couple délivré par le moteur sans provoquer les surconsommations et les pics de pollution évoqués en préambule de la présente description.As will be seen below in detail, by ordering thus simultaneously the air flow entering the engine and the angle of advance at ignition of the air / fuel mixture power supply to this motor, the consistency of the torque delivered by the engine without causing overconsumption and the pollution peaks mentioned in preamble to this description.

    D'autres caractéristiques et avantages de la présente invention apparaítront à la lecture de la description qui va suivre et à l'examen du dessin annexé dans lequel :

    • la figure 1 représente schématiquement un moteur à combustion interne équipé pour assurer la mise en oeuvre du procédé suivant l'invention, et
    • la figure 2 rassemble des graphes utiles à la description du procédé suivant l'invention.
    Other characteristics and advantages of the present invention will appear on reading the description which follows and on examining the appended drawing in which:
    • FIG. 1 schematically represents an internal combustion engine equipped to ensure the implementation of the method according to the invention, and
    • FIG. 2 brings together graphs useful for describing the process according to the invention.

    On se réfère à la figure 1 du dessin annexé où l'on a représenté schématiquement un des cylindres d'un moteur 1 à combustion interne, muni classiquement d'un piston la, d'une soupape d'admission 1b et d'une soupape d'échappement lc. La soupape d'échappement lc commande le passage des gaz de combustion sortant du moteur, dans une ligne d'échappement 2 sur laquelle est monté un pot catalytique trifonctionnel 3 du type décrit en préambule de la présente description.We refer to Figure 1 of the accompanying drawing where we schematically represents one of the cylinders of an engine 1 internal combustion, conventionally fitted with a piston la, an inlet valve 1b and a valve exhaust lc. The exhaust valve lc controls the passage of combustion gases leaving the engine, in a exhaust line 2 on which a pot is mounted trifunctional catalytic 3 of the type described in the preamble of this description.

    L'alimentation en carburant du cylindre est réalisée à l'aide d'un injecteur de carburant 4 débouchant dans le cylindre, dans le cas d'un moteur dit à "injection directe", ou d'un injecteur 5 arrosant classiquement la soupape d'admission 1b, comme représenté en trait interrompu à la figure 1.Fuel is supplied to the cylinder using a fuel injector 4 opening into the cylinder, in the case of an "injection" engine direct ", or from an injector 5 conventionally spraying the inlet valve 1b, as shown in line interrupted in Figure 1.

    Le débit d'air entrant dans le cylindre par cette soupape 1b est réglé par un circuit d'admission d'air comprenant un papillon des gaz "motorisé" 6 commandé par un calculateur numérique 7, comme cela est maintenant classique. Le calculateur commande, outre le papillon 7 et l'injecteur 4 ou 5, une bougie d'allumage 8 de manière à ajuster l'angle d'avance à l'allumage du mélange air/carburant introduit dans le cylindre.The air flow entering the cylinder through this valve 1b is regulated by an air intake circuit comprising a "motorized" throttle valve 6 controlled by a digital computer 7, as it is now classic. The computer controls, in addition to the butterfly 7 and the injector 4 or 5, a spark plug 8 so to adjust the angle of advance at ignition of the mixture air / fuel introduced into the cylinder.

    On se réfère maintenant à la figure 2 du dessin annexé pour décrire le procédé de purge suivant l'invention. Celui-ci est mis en oeuvre alors que le moteur est alimenté en mélange air/carburant pauvre. On sait qu'alors le pot catalytique 3 se charge en oxydes d'azote. On connaít, par exemple de la demande de brevet français n° 97 15775 déposée le 12 décembre 1997 par la demanderesse, un système expert conçu pour évaluer continuellement l'efficacité du pot en matière d'adsorption des oxydes d'azote et pour déclencher une purge du pot, quand cette efficacité devient insuffisante.We now refer to Figure 2 of the drawing attached to describe the following purge process the invention. This is implemented while the engine is supplied with lean air / fuel mixture. We knows that then the catalytic converter 3 is charged with oxides nitrogen. We know, for example from the patent application French n ° 97 15775 filed on December 12, 1997 by the Applicant, an expert system designed to assess the pot’s effectiveness adsorption of nitrogen oxides and to trigger a purge of the pot, when this efficiency becomes insufficient.

    On a représenté à la figure 2 l'évolution, respectivement, de la richesse R du mélange air/carburant, du débit d'air D entrant dans le moteur et de l'angle α d'avance à l'allumage, à partir d'un instant t1 de déclenchement d'une purge, instant déterminé par ledit système expert par exemple, ces évolutions étant déterminées par le procédé de commande de purge suivant l'invention, tel qu'il est décrit en détail dans la suite.FIG. 2 shows the development, respectively, of the richness R of the air / fuel mixture, of the air flow rate D entering the engine and of the angle of advance of ignition, from d an instant t 1 of triggering a purge, instant determined by said expert system for example, these changes being determined by the purge control method according to the invention, as described in detail below.

    A l'instant t1, le calculateur commande un accroissement brusque de la quantité d'essence injectée dans le moteur et donc de la richesse du mélange air/carburant, de manière que celui-ci convienne à la purge du pot en oxydes d'azote, cette richesse passant alors de la valeur antérieure R0 correspondant à un mélange pauvre, à une valeur R1 supérieure à celle (R2) correspondant à la stoechiométrie.At time t 1 , the computer controls a sudden increase in the quantity of gasoline injected into the engine and therefore in the richness of the air / fuel mixture, so that it is suitable for purging the pot of oxides of nitrogen, this richness then passing from the previous value R 0 corresponding to a lean mixture, to a value R 1 greater than that (R 2 ) corresponding to the stoichiometry.

    Simultanément, suivant l'invention, le calculateur 7 commande une réduction progressive du débit d'air entrant dans le moteur à partir de la valeur D0 antérieure, et une réduction brusque de l'angle d'avance à l'allumage α, qui passe alors de la valeur antérieure α0 à une valeur α1.Simultaneously, according to the invention, the computer 7 controls a progressive reduction in the air flow entering the engine from the previous value D 0 , and an abrupt reduction in the ignition advance angle α, which then goes from the previous value α 0 to a value α 1 .

    La réduction commandée du débit d'air, concomitante à l'accroissement de richesse, permet d'adapter ce débit à la richesse demandée, et donc d'assurer un fonctionnement optimal du moteur du point de vue de la consommation en carburant et donc aussi du point de vue de la limitation de la production d'espèces polluantes que provoque la combustion du mélange air/carburant.The controlled reduction in air flow, concomitant to the increase in wealth, makes it possible to adapt this flow to the required wealth, and therefore to ensure an operation optimal engine from the consumption point of view fuel and therefore also from the point of view of limitation of the production of polluting species caused by combustion of the air / fuel mixture.

    La brusque réduction de l'angle d'avance α à la valeur α1 est calculée pour compenser le brusque accroissement du couple moteur qui résulterait autrement de l'accroissement brusque de la valeur de la richesse du mélange air/carburant jusqu'à la valeur R1. On stabilise ainsi le couple moteur à sa valeur antérieure à la purge, au profit du confort des passagers.The sudden reduction in the angle of advance α to the value α 1 is calculated to compensate for the sudden increase in engine torque which would otherwise result from the sudden increase in the value of the richness of the air / fuel mixture up to the value R 1 . The engine torque is thus stabilized at its value prior to the purge, for the benefit of passenger comfort.

    On observe cependant que certains actionneurs du système de commande du moteur ont un temps de réponse qui ne peut être négligé. Il en est ainsi notamment du système mécanique que constitue le papillon motorisé 6, qui ne peut s'ouvrir ou se fermer instantanément. Le phénomène de "mouillage de paroi" par le carburant injecté n'est pas non plus immédiatement réversible. D'autres phénomènes physiquestels que le remplissage/vidage en air du moteur ont une constante de temps importante. Ces temps de réponse et retards provoquent, dans les phases transitoires de la purge, des évolutions du couple moteur qui peuvent engendrer des désagréments de conduite si l'avance à l'allumage n'est pas asservie au débit d'air.However, it is observed that certain actuators of the engine control system have a response time that does can be overlooked. This is particularly the case with the system mechanical that constitutes the motorized butterfly 6, which does not can open or close instantly. The phenomenon of "wall wetting" by the injected fuel is also not immediately reversible. Other phenomena such as filling / emptying the engine with air have a large time constant. These times of response and delays cause, in phases purge transients, changes in engine torque which can cause driving inconvenience if the ignition advance is not controlled by the air flow.

    Suivant l'invention, on supprime ces évolutions de couple en remontant progressivement l'angle α d'avance à l'allumage, de la valeur α1 à une valeur α2 correspondant à un fonctionnement optimum du moteur au débit d'air D1 et à la richesse R1 de consigne pendant la purge, cette remontée progressive de l'angle α d'avance à l'allumage étant asservie à la réduction du débit d'air de manière à suivre celle-ci dans le temps. Le temps de réponse du circuit d'admission d'air est ainsi totalement pris en compte par le procédé suivant l'invention, ce qui permet de limiter la consommation en carburant du moteur pendant la purge ainsi que les émissions d'espèces polluantes, sans perturber le couple moteur.According to the invention, these torque changes are eliminated by gradually increasing the angle α of ignition advance, from the value α 1 to a value α 2 corresponding to optimum operation of the engine at the air flow rate D 1 and at the setpoint richness R 1 during the purge, this progressive rise in the angle of ignition advance α being slaved to the reduction of the air flow so as to follow it over time. The response time of the air intake circuit is thus fully taken into account by the method according to the invention, which makes it possible to limit the fuel consumption of the engine during the purge as well as the emissions of polluting species, without disturb the engine torque.

    L'asservissement de l'angle α au débit d'air peut être obtenu simplement par une programmation convenable du calculateur 7.Controlling the angle α to the air flow can be obtained simply by suitable programming of the computer 7.

    Quand le système expert détermine que le pot catalytique 3 a retrouvé son efficacité, il commande, à l'instant t2, l'arrêt de la purge, c'est-à-dire le rétablissement à terme des valeurs R0, D0 et α0 de la richesse, du débit d'air et l'angle d'avance à l'allumage respectivement.When the expert system determines that the catalytic converter 3 has regained its efficiency, it commands, at time t 2 , the stopping of the purge, that is to say the restoration in the long term of the values R 0 , D 0 and α 0 of the richness, the air flow rate and the ignition advance angle respectively.

    On pourrait revenir à ces valeurs par une stratégie symétrique de celle appliquée au déclenchement de la purge. Il faudrait alors attendre, le débit d'air étant maítre, que celui-ci revienne à sa valeur initiale (D0) alors que l'avance α, asservie au débit d'air, assure la conservation du couple. Si le pot 3 est entièrement purgé à l'instant t2, on observerait des pics de pollution (par hydrocarbures imbrûlés et oxydes d'azote) après l'instant t2, jusqu'au rétablissement du débit D0 du fait du temps de réponse du circuit d'admission d'air.We could return to these values by a strategy symmetrical to that applied when triggering the purge. It would then be necessary to wait, the air flow being master, for it to return to its initial value (D 0 ) while the advance α, controlled by the air flow, ensures the conservation of the torque. If the pot 3 is completely purged at time t 2 , pollution peaks (by unburnt hydrocarbons and nitrogen oxides) would be observed after time t 2 , until the flow D 0 is restored due to the time of air intake system response.

    Suivant l'invention, on surmonte cette difficulté en revenant au mélange pauvre en passant par un mélange de richesse de valeur R2 intermédiaire entre R1 et R0, la valeur R2 correspondant à un mélange stoechiométrique, par exemple, valeur de richesse pour laquelle le catalyseur à trois voies traite les émissions polluantes.According to the invention, this difficulty is overcome by returning to the lean mixture by passing through a mixture of richness of value R 2 intermediate between R 1 and R 0 , the value R 2 corresponding to a stoichiometric mixture, for example, richness value for which the three-way catalyst treats polluting emissions.

    Simultanément, le calculateur commande le papillon 6 de manière à accroítre le débit d'air entrant dans le moteur jusqu'à revenir progressivement à un mélange air/carburant de richesse R0, donc à un mélange "pauvre".Simultaneously, the computer controls the throttle valve 6 so as to increase the air flow entering the engine until gradually returning to an air / fuel mixture of richness R 0 , therefore to a "lean" mixture.

    A l'instant t2, suivant l'invention, le calculateur relève brusquement l'angle d'avance à l'allumage α à la valeur α3, de manière à compenser la réduction brutale de la richesse observée à cet instant, α3 correspondant à la valeur optimale de l'avance quand le mélange air/carburant est de composition stoechiométrique. Après l'instant t2, l'avance est de nouveau asservie au débit d'air jusqu'à ce que celui-ci revienne à la valeur D0, à l'instant t3. A cet instant, on ramène l'avance α et la richesse R aux valeurs α0 et R0 respectivement, correspondant au mélange pauvre.At time t 2 , according to the invention, the computer suddenly raises the ignition advance angle α to the value α 3 , so as to compensate for the sudden reduction in the wealth observed at this time, α 3 corresponding to the optimal advance value when the air / fuel mixture is of stoichiometric composition. After the instant t 2 , the advance is again controlled by the air flow until this returns to the value D 0 , at the instant t 3 . At this instant, the advance α and the richness R are reduced to the values α 0 and R 0 respectively, corresponding to the lean mixture.

    Cette stratégie d'évolution de la richesse R et de l'angle α d'avance à l'allumage dans l'intervalle de temps [t2,t3] permet d'adapter plus étroitement, grâce à l'asservissement utilisé, ces grandeurs aux variations du débit d'air D pendant cet intervalle de temps, ce débit étant tributaire d'un temps de réponse d'origine mécanique qui n'affecte pas les évolutions des grandeurs R et α.This strategy of evolution of the richness R and of the angle α of ignition advance in the time interval [t 2 , t 3 ] makes it possible to adapt more closely, thanks to the servoing used, these quantities at variations in the air flow D during this time interval, this flow being dependent on a response time of mechanical origin which does not affect the changes in the quantities R and α.

    Il apparaít maintenant que la présente invention permet bien d'atteindre le but fixé, à savoir assurer la purge en oxydes d'azote d'un pot catalytique, sans perturbation du couple délivré par le moteur et sans surconsommation de carburant et pics de pollution transitoires dans les gaz d'échappement du moteur.It now appears that the present invention achieves the goal, namely to ensure the purge of nitrogen oxides from a catalytic converter, without disturbance of the torque delivered by the engine and without overconsumption of fuel and pollution peaks transients in engine exhaust.

    Claims (3)

    Procédé de commande de la purge en oxydes d'azote (Nox) d'un pot catalytique (3) de traitement des gaz d'échappement d'un moteur (1) à combustion interne, ledit pot (3) absorbant lesdits oxydes d'azote quand ledit moteur (1) fonctionne en mélange air/carburant pauvre en carburant, ledit procédé étant du type suivant lequel a) on commande une purge du pot (3) par un accroissement temporaire de la richesse (R) en carburant du mélange en réduisant progressivement le débit d'air (D) entrant dans le moteur de manière à optimiser la consommation en carburant du moteur à la richesse fixée, en réduisant brusquement l'angle (α) d'avance à l'allumage du mélange air/carburant à une valeur prédéterminée (α1) pour maintenir la constance du couple délivré par le moteur (1), et en asservissant ensuite une remontée dudit angle (α) d'avance à ladite réduction du débit d'air (D), jusqu'à une deuxième valeur prédéterminée (α2) optimisant la consommation en carburant du moteur (1) en fonction de la richesse (R1) et du débit d'air (D1) fixé pendant la purge, b) on arrête la purge en ramenant les valeurs de la richesse (R) du mélange air/carburant, du débit d'air (D) et de l'angle (α) d'avance à l'allumage dudit mélange, aux valeurs (R0,D0,α0) respectives antérieures au déclenchement de la purge,    ce procédé étant caractérisé en ce que, à l'étape b), on abaisse d'abord la richesse du mélange air/carburant à une valeur (R2) intermédiaire entre les richesses de purge (R1) et de mélange pauvre (R0), avec commande concomitante d'une remontée progressive du débit d'air (D) et d'une remontée brusque de l'angle (α) d'avance à l'allumage à une troisième valeur prédéterminée (α3) fonction de ladite richesse intermédiaire, on asservit ensuite une décroissance dudit angle (α) jusqu'à une quatrième valeur (α4) prédéterminée pendant la remontée du débit d'air, et on rétablit enfin la richesse du mélange, le débit d'air et l'angle d'avance à l'allumage aux valeurs respectives (R0, D0, α0) antérieures à la purge.Method for controlling the purging of nitrogen oxides (Nox) from a catalytic converter (3) for treating the exhaust gases of an internal combustion engine (1), said container (3) absorbing said oxides of nitrogen when said engine (1) operates in an air / fuel mixture lean in fuel, said method being of the type according to which a) a purge of the pot (3) is controlled by a temporary increase in the fuel richness (R) of the mixture by progressively reducing the air flow (D) entering the engine so as to optimize the fuel consumption of the engine to the fixed richness, by abruptly reducing the angle (α) of advance on ignition of the air / fuel mixture to a predetermined value (α 1 ) to maintain the constancy of the torque delivered by the engine (1), and then controlling a rise in said angle (α) of advance to said reduction in the air flow (D), up to a second predetermined value (α 2 ) optimizing the fuel consumption of the engine (1) as a function of the richness (R 1 ) and the air flow (D 1 ) fixed during the purge, b) the purge is stopped by reducing the values of the richness (R) of the air / fuel mixture, of the air flow (D) and of the angle (α) of advance when the said mixture is ignited, to the values (R 0 , D 0 , α 0 ) respective prior to the initiation of the purge, this process being characterized in that, in step b), the richness of the air / fuel mixture is first lowered to a value (R 2 ) intermediate between the purge (R 1 ) and lean mixture (R 0 ), with concomitant control of a gradual rise in the air flow (D) and a sudden rise in the angle (α) of ignition advance to a third predetermined value (α 3 ) function of said intermediate richness, a decrease in said angle (α) is then enslaved to a fourth predetermined value (α 4 ) during the rise in the air flow rate, and finally the richness of the mixture, the air flow rate and l 'ignition advance angle at the respective values (R 0 , D 0 , α 0 ) prior to the purge. Procédé conforme à la revendication 1, caractérisé en ce que ladite valeur (R1) intermédiaire de la richesse (R) correspond à un mélange air/carburant stoechiométrique.Method according to claim 1, characterized in that said intermediate value (R 1 ) of the richness (R) corresponds to an air / fuel mixture stoichiometric. Procédé conforme à l'une quelconque des revendications 1 et 2, caractérisé en ce qu'on déclenche et on arrête la purge sous la commande d'un système d'évaluation du taux de chargement du pot catalytique (3) en oxydes d'azote.Process according to any of claims 1 and 2, characterized in that one triggers and we stop the purge under the control of a system for evaluating the loading rate of the catalytic converter (3) into nitrogen oxides.
    EP19990402945 1998-12-02 1999-11-26 Control method of the purging of nitrogen oxides in a catalytic converter for exhaust gases of an internal combustion engine Expired - Lifetime EP1006270B1 (en)

    Applications Claiming Priority (2)

    Application Number Priority Date Filing Date Title
    FR9815226A FR2786814B1 (en) 1998-12-02 1998-12-02 METHOD FOR CONTROLLING THE PURGE OF NITROGEN OXIDES FROM A CATALYTIC EXHAUST TREATMENT POT OF AN INTERNAL COMBUSTION ENGINE
    FR9815226 1998-12-02

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    EP1006270A1 true EP1006270A1 (en) 2000-06-07
    EP1006270B1 EP1006270B1 (en) 2003-03-12

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    WO2006095114A1 (en) * 2005-03-11 2006-09-14 Peugeot Citroën Automobiles SA System for controlling switchover of a motor vehicle operating conditions between lean and rich modes
    WO2006095113A1 (en) * 2005-03-11 2006-09-14 Peugeot Citroen Automobiles System for controlling switchover of a motor vehicle operating conditions between lean and rich modes
    FR2948418A3 (en) * 2009-07-23 2011-01-28 Renault Sa Nitrogen oxide trap purging managing method for internal combustion diesel engine of motor vehicle, involves modifying engine richness according to function, where function is decreasing function between initial and final values of richness
    US8589054B2 (en) * 2008-04-04 2013-11-19 Renault S.A.S. System and method for controlling the fresh air and burnt gases introduced into an internal combustion engine during transitions between the purging of a nitrogen oxides trap and the regeneration of a particulate filter

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    EP1167711A3 (en) * 2000-06-26 2003-04-23 Toyota Jidosha Kabushiki Kaisha Emission control method and apparatus of an internal combustion engine
    WO2006095114A1 (en) * 2005-03-11 2006-09-14 Peugeot Citroën Automobiles SA System for controlling switchover of a motor vehicle operating conditions between lean and rich modes
    WO2006095113A1 (en) * 2005-03-11 2006-09-14 Peugeot Citroen Automobiles System for controlling switchover of a motor vehicle operating conditions between lean and rich modes
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    US8589054B2 (en) * 2008-04-04 2013-11-19 Renault S.A.S. System and method for controlling the fresh air and burnt gases introduced into an internal combustion engine during transitions between the purging of a nitrogen oxides trap and the regeneration of a particulate filter
    FR2948418A3 (en) * 2009-07-23 2011-01-28 Renault Sa Nitrogen oxide trap purging managing method for internal combustion diesel engine of motor vehicle, involves modifying engine richness according to function, where function is decreasing function between initial and final values of richness

    Also Published As

    Publication number Publication date
    DE69905841T2 (en) 2003-11-20
    EP1006270B1 (en) 2003-03-12
    FR2786814B1 (en) 2001-02-09
    FR2786814A1 (en) 2000-06-09
    DE69905841D1 (en) 2003-04-17

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