Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
  • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
  • F01N3/0842—Nitrogen oxides
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
  • F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • 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
  • 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
  • F01N2250/00—Combinations of different methods of purification
  • F01N2250/12—Combinations of different methods of purification absorption or adsorption, and catalytic conversion
• • 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
  • F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
  • F01N2550/03—Monitoring or diagnosing the deterioration of exhaust systems of sorbing activity of adsorbents or absorbents
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D2200/00—Input parameters for engine control
  • F02D2200/02—Input parameters for engine control the parameters being related to the engine
  • F02D2200/08—Exhaust gas treatment apparatus parameters
  • F02D2200/0806—NOx storage amount, i.e. amount of NOx stored on NOx trap
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D2200/00—Input parameters for engine control
  • F02D2200/02—Input parameters for engine control the parameters being related to the engine
  • F02D2200/08—Exhaust gas treatment apparatus parameters
  • F02D2200/0811—NOx storage efficiency

Definitions

• the present invention relates to a method for controlling the purging of a catalytic converter for treating the exhaust gases of an internal combustion engine comprising means for adsorption of nitrogen oxides contained in these gases, type according to which such a purge is triggered by an increase in the richness of the air / fuel mixture supplying the engine, from a richness corresponding to a lean or stoichiometric mixture.
• the exhaust lines of these gases are commonly fitted with a catalytic converter having the function transform the harmful chemical species contained in these gases into less harmful, even harmless, chemical species.
• the aforementioned European patent proposes to control the richness of the air / fuel mixture supplying the engine so as to periodically switch the richness of this mixture from a value corresponding to a lean mixture to a value corresponding to a stoichiometric or superstoichiometric mixture, this switching causing the desorption of the NOx adsorbed in the pot then their reduction by HC and carbon monoxide CO then in the pot due to the increase in the richness of the mixture, these last two chemical species must themselves be oxidized into less polluting species, in accordance with two of the three functions classics of the catalytic converter.
• the decision to purge the pot is made when the NOx pot filling rate is exceeded.
• the NOx adsorption capacity of the pot is a function of the temperature of the pot, not taken into account in this strategy.
• the duration of a purge depends only on the temperature of the pot. It therefore does not take into account another essential variable, namely the flow rate of the engine in reducing materials (HC, CO).
• Also known from European patent application No. 733 786 is a device comprising, downstream of the pot, an oxygen sensor.
• an oxygen sensor During a purge, when this probe indicates that the richness of the air / fuel mixture supplying the engine, evaluated from the composition of the exhaust gases, is greater than 1, the purge of the pot is considered to be complete and is arrested.
• the purge time is then a function of the quantity of NOx destocked, which is a function of the engine speed, the opening time of fuel injectors in the engine, the richness of the air / fuel mixture and a function parameter. the deterioration of the pot, taken into account by the signal delivered by the oxygen sensor.
• This device has the drawback of requiring the presence of an oxygen sensor downstream of the catalytic converter.
• the object of the present invention is to provide a method for controlling the purging of a catalytic converter for treating the exhaust gases of an internal combustion engine comprising means for adsorption of nitrogen oxides contained in these gases. , a process which does not have the drawbacks mentioned above of the processes for purging catalytic converters of this type known in the prior art, and which in particular makes it possible to further reduce the overconsumption due to the purging of the NOx pot by closer monitoring storage and destocking of NOx in the catalytic converter and by a more precise measurement of the purge times of the pot.
• the present invention also aims to provide such a process which does not require the presence of an oxygen sensor at the outlet of the catalytic converter.
• a method of controlling the purging of a catalytic converter for treating the exhaust gases of an engine with internal combustion said pot comprising means for adsorption of nitrogen oxides contained in these gases, according to which such a purge is triggered by an increase in the richness of an air / fuel mixture supplying the engine, starting of a richness corresponding to a lean or stoichiometric mixture, this process being remarkable in that a) one evaluates, using a table depending on the temperature of the pot and its filling rate with nitrogen oxides, the pot's efficiency in terms of adsorption and reduction of nitrogen oxides, and b) a purge of the pot is triggered when said efficiency falls below a predetermined value, depending on the temperature of the pot.
• said rate of filling of the pot with nitrogen oxides is evaluated on the basis of an evaluation of the current quantity of oxides stored during an operating phase of the engine in lean mixture, said rate is taken from this evaluation and a table giving the maximum quantity of nitrogen oxides adsorbable by the pot, according to the temperature of the pot and the current concentration of nitrogen oxides in the engine exhaust gases.
• EFFDENOX For the evaluation of the current quantity of nitrogen oxides stored, the EFFDENOX ratio between the flow of nitrogen oxides treated by the jar and the flow of nitrogen oxides leaving the engine is taken into account. report EFFDENOX being taken from a table depending on the temperature of the pot.
• the quantities of nitrogen oxides destocked successively by the pot are continuously evaluated by the quantities of fuel successively injected into the engine and the purging is stopped when the efficiency of the pot rises above said value of predetermined threshold due to said successive destocking.
• the overall instantaneous efficiency of the pot is measured by the EFFNOX ratio of the flow of nitrogen oxides at the outlet of an engine exhaust line, to the flow of said oxides at the outlet of the engine.
• said efficiency is the instantaneous EFFSTOCK storage efficiency such that:
• FIG. 1 is a diagram of an internal combustion engine equipped with means allowing executing the purge control method according to the invention
• FIG. 2 is a graph of the overall instantaneous efficiency EFFNOX as a function of the filling rate and the temperature of the pot
• FIG. 3 is a graph of the maximum storage capacity NSC of the pot
• - Figure 4 is a graph of EFFDENOX efficiency as a function of the temperature of the pot
• - Figure 5 is a graph of the dNS / dM ratio of the amount dNS of NOx destocked by an amount dM of reducing materials present in the pot , depending on the filling rate of the pot, at a pot temperature of 350 ° C.
• - Figure 6 is the flow diagram of an expert system implementing the control method according to the present invention
• Figures 7 to 12 are groups of timing diagrams illustrating various phases of the control method according to the present invention.
• FIG. 1 of the accompanying drawing an internal combustion engine 1 controlled by a digital electronic computer 2.
• the computer 2 receives and processes signals from various sensors, in particular from a sensor 3 of the pressure P (or flow) of the air admitted into the engine 1, to control in particular the opening time ti of fuel injectors 7 in the engine 1.
• the engine exhaust gases pass through an exhaust line 4 ⁇ , 4 2 , 4 3 which successively passes through, and in this order, a catalytic pot of possible priming 5 and trifunctional catalytic pot 6 of the type of those mentioned in the aforementioned patents, namely a pot comprising means for adsorption of nitrogen oxides NOx when the engine operates in a lean mixture, these oxides being desorbed, or "destocked", when the engine is supplied with an air / fuel mixture of richness greater than or equal to 1 suitable for leaving in the engine exhaust gas reducing chemical species (HC, CO) capable of reducing the desorbed NOx, unburnt hydrocarbons HC and CO being themselves then oxidized into less polluting or non-polluting chemical species (C0 2 , H 2 0, etc ).
• a temperature sensor 8 supplies the temperature T cat of the pot 6 to the computer 2.
• This digital computer 2 is duly programmed to execute, in addition to the tasks which are conventionally entrusted to it, the method according to the invention for controlling the purging of the catalytic converter 6, and for treating NOx desorbed during the purges, which will be described below.
• This process makes use of models for the evaluation of the quantities of nitrogen oxides which are successively stored by the pot, destocked and reduced by this pot.
• NOx storage operation in storage of nitrogen oxides
• destocking of NOx which is observed when the engine is supplied with a rich mixture
• destocked NOx being then reduced thanks to the excess of hydrocarbons (HC) and monoxide carbon (CO) that is found in the engine exhaust due to the incomplete combustion of the air / fuel mixture
• the pot 6 then adsorbs part of the NOx formed in the engine, reduces another part of it thanks to any unburnt hydrocarbons and carbon monoxide and releases into the exhaust line 4 a third part of these NOx, corresponding to oxides of which are neither stored nor reduced.
• the overall instantaneous efficiency EFFNOX, the instantaneous treatment efficiency EFFDENOX and the instantaneous storage efficiency EFFSTOCK of the pot are defined as follows: NOx flow rate at the outlet of the exhaust line
• EFFNOX is a function of the temperature of the pot 6, the filling rate NS / NSC as well as, to a lesser extent, the flow rate of the engine in NOx.
• the graphs in Figure 2 show variations in EFFNOX depending on the temperature and the filling rate.
• FIG. 3 shows the shape of the variations in NSC as a function of the temperature of the pot, for two concentration values [NOxJi and [NOx]; . nitrogen oxides in the gases leaving the exhaust line.
• FIG. 4 shows the variations of EFFDENOX as a function of the temperature of the pot.
• NS__ is the quantity of nitrogen oxide adsorbed at the instant of sampling î (corresponding for example, as is conventional, to the change to top dead center TDC 3.
• NSj . NS ⁇ - 1 + DNSSTOCK (1)
• DNSSTOCK being the quantity of NOx stored between the TDCs of order (1 - 1) and 1.
• DNSSTOCK is evaluated by:
• DNSSTOCK [NOx]. (1 - EFFDENOx).
• [NOx] is the NOx concentration, ie the ratio of the mass of NOx produced by the engine to the mass of air admitted to each combustion of this engine.
• [NOx] is the NOx concentration, ie the ratio of the mass of NOx produced by the engine to the mass of air admitted to each combustion of this engine.
• [NOx] is the NOx concentration, ie the ratio of the mass of NOx produced by the engine to the mass of air admitted to each combustion of this engine.
• [NOx] is the NOx concentration, ie the ratio of the mass of NOx produced by the engine to the mass of air admitted to each combustion of this engine.
• [NOx] is the NOx concentration, ie the ratio of the mass of NOx produced by the engine to the mass of air admitted to each combustion of this engine.
• [NOx] is the NOx concentration, ie the
• this destocking and this reduction occur when the richness of the air / fuel mixture supplying the engine is greater than or equal to 1.
• Measurements on the bench made it possible to establish the graph of FIG. 5, which represents the variations in the dNS / dM ratio of the quantity of NOx destocked by a mass dM of reducing agents (H 2 , CO, unburnt hydrocarbons) as a function of the filling rate NS / NSC of pot 6, for a temperature of this pot equal to 350 ° C.
• the graph in FIG. 5, and other similar ones corresponding to other values of the temperature are stored in the computer 2 in the form of a map, like the graphs in FIGS. 2 to 4.
• the destocking occurs when the richness of the air / fuel mixture exceeds a RICPURGE threshold value, the quantity NSi of NOx remaining stored in the pot at TDC of order i being decremented by a quantity DNSPURGE corresponding to the quantity of NOx destocked between the TDCs (i - 1) and i, that is:
• NSi ⁇ NSi-i - DNSPURGE, with: DNSPURGE + QNOXTRAPi.
• dNS / dM where: dNS / dM is known by the cartography corresponding to the graphs of FIG. 5, and QNOXTRAPi is the mass of reducers received between two TDCs of order (i - 1) and i by the pot 6.
• the exhaust line comprises, as shown in FIG. 1, a priming catalytic converter 5 in front of the pot 6, the reducers which leave the engine 1 are subjected to oxidation in the pot 5 by the oxygen stored therein. It is only the excess quantity, not oxidized by this oxygen stored in the pot, which can be used in pot 6 to destock or reduce the stored NOx.
• QNOXTRAP is therefore equal to the mass of QESSi reducers delivered to the engine exhaust between two TDCs of order (i-1) and i when the combustion of the air / fuel mixture is incomplete and that the priming catalytic converter 5 is oxygen vacuum, either:
• - DINJV opening time of a fuel injector 6 in the engine 1
• - C flow rate scaling coefficient.
• ME ⁇ SLO being a threshold value of the quantity of reducing agents necessary to purge the priming catalyst 5 from the oxygen stored in this catalyst.
• the taking of a destocking decision involves either the overall instantaneous efficiency EFFNOX, or the instantaneous storage efficiency EFFSTOCK.
• Each of these two quantities can be taken into account either by its instantaneous value or by its current average value since the last purge.
• FIG. 6 presents the flow diagram of this expert system.
• -protlean 1 indicates that the purge has been triggered since a lean mixture operation and that a return to lean mixture operation of the engine is authorized, as soon as the conditions for such a return are met.
• - mony_nox 1 indicates an authorization to switch to "purge" mode.
• ox_state 0 indicates a purge stop authorization.
• the flow diagram of FIG. 6 illustrates the conditions which govern the changes in the richness setpoint of the air / fuel mixture supplying the engine, as a function of the conditions which determine a switching of the operating mode of the engine between three modes: the mode "purge”, the "stoichiometric mixture” mode and the “lean mixture” mode. It is the switches between any of these modes and any of the other two that are managed by the expert system. This is how it manages the triggering and stopping of the catalytic converter purge phases.
• the purge operations of the catalytic converter 6 can be triggered while the engine is operating either in lean mixture or in stoichiometric mixture, it being understood that when the engine operates at a richness greater than 1, this operation is naturally accompanied by a purge of the pot.
• the richness of the mixture is then fixed at a RICPURGE value taken from a "carlean” map depending on the pressure P at the manifold. engine intake and N speed of this engine.
• the models described above allow permanent monitoring of the evolution of the pot's efficiency, for example the instantaneous EFFNOX efficiency. When this falls below a predetermined threshold Eff_min_lean depending on the temperature of the pot, the system commands a purge of the pot (the nox state bit goes to 1).
• the present invention there is then an obligatory transition from the richness of the air / fuel mixture to a richness greater than or equal to 1 suitable for satisfying the torque demand, in order to purge the pot, which reduces the overconsumption of fuel due to bleeding.
• Purge since the engine is running in stoichiometric mixture The engine then operates at a RICSTOC richness drawn from a "carstoc" map whose inputs are the pressure at the intake manifold and the engine speed.
• the computer 2 When a purge is requested, the computer 2 reads a wealth of destocking or RICPURGE purge in a "cardenox" table, the inputs of which are the pressure P at the engine manifold and the speed N of the latter.
• the computer then changes the richness setpoint of the air / fuel mixture, either from the RICSTOC value taken from the carstoc map if the engine was previously operating in stoichiometry mode, or from the RICLEAN value if the engine previously operated in lean mode, to a RICPURGE purge richness instruction taken from the "cardenox" table.
• this compensation is carried out either a) by an action on the angle of advance at ignition of the air / fuel mixture when the vehicle does not include means making it possible to automatically control the flow of incoming air in the mixture either b) by an action on such means, a "motorized" throttle controlling this air flow, for example.
• pot 6 then rises gradually. As soon as this (at time t 2 ) exceeds a threshold value Eff_max, depending on the temperature of the pot, the purge is stopped (nox_state is set to 0). The richness R returns to the RICLEAN set value stored in the carlean table, the protlean bit is reset to 0 and the lowering of the torque following the lowering of the richness is compensated by a cancellation of the advance withdrawal ordered at the start purge.
• FIG. 11 illustrates the development of such a purge, triggered by the transition from efficiency to a low threshold Eff_min at time tg.
• the richness then gradually rises to the RICPURGE value while the advance Av is maintained at the previous value suitable for operation at stoichiometry.
• the purging stops at the instant tio when the efficiency has returned to a high threshold Eff_max. Wealth is gradually brought back to RICSTOC.
• the advance is then gradually increased to a value suitable for the combustion of a lean mixture.
• the invention makes it possible to achieve the set goals, namely to provide a process for controlling the NOx purge of a catalytic converter comprising means for adsorption / desorption of such oxides contained in the exhaust from an internal combustion engine, capable of organizing this purge so as to minimize the overconsumption of fuel that it implies.
• the savings thus obtained by implementing this process are further increased by the fact that this process does not require the presence of an oxygen sensor at the outlet of the catalytic converter.
• the method according to the invention compensates for the variations in the engine torque that could otherwise be observed during the purging of the pot, for the benefit of the comfort of driving the vehicle and, more generally, of the comfort of the passengers of the vehicle.
• the invention is not limited to the embodiment described and shown which has been given only by way of example. This is how compensation for the variations in torque mentioned above could be obtained other than by acting on the ignition advance.
• the engine management computer such as a so-called "motorized" butterfly
• compensation for excess torque due to the enrichment of the air / fuel mixture during purges, compared to the setpoint set by the driver, can be obtained by a reduction concomitant with the amount of air entering the engine.
• the general strategy for initiating and stopping the purges described above in conjunction with the timing diagrams of FIGS. 7 to 12 remains substantially the same.
• the present invention obviously extends to a control method in which the variations in torque mentioned above are compensated by a combined action on the ignition advance and on the quantity of air entering the engine, when this last is possible.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Exhaust Gas After Treatment (AREA)
• Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=9514535

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• 1997
  • 1997-12-12 FR FR9715775A patent/FR2772428B1/fr not_active Expired - Fee Related
• 1998
  • 1998-12-11 WO PCT/FR1998/002696 patent/WO1999031368A1/fr active IP Right Grant
  • 1998-12-11 ES ES98959959T patent/ES2190123T3/es not_active Expired - Lifetime
  • 1998-12-11 DE DE69811863T patent/DE69811863T2/de not_active Expired - Lifetime
  • 1998-12-11 EP EP98959959A patent/EP0961875B1/de not_active Expired - Lifetime

Non-Patent Citations (1)

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