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
  • 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
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
  • F02D41/146—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration
  • F02D41/1461—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration of the exhaust gases emitted by the engine
  • F02D41/1462—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an NOx content or concentration of the exhaust gases emitted by the engine with determination means using an estimation
• • 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
  • F02D2200/0802—Temperature of the exhaust gas treatment apparatus
• • 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
  • F02D2200/0808—NOx storage capacity, i.e. maximum amount of NOx that can be 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 of controlling the purging of means for storing nitrogen oxides (NOx) associated with a catalytic converter for treating the exhaust gases of an internal combustion engine, an oxygen sensor being rise in the flow of gases leaving the pot and, more particularly, to such a method according to which, when the engine operates in an air / fuel mixture lean in fuel, it is followed, using a management model of said means of storage, the evolution of the storage efficiency of NOx in said storage means and, when said model indicates that said efficiency drops below a predetermined threshold, a purge of said storage means is ordered and said purge is stopped when said model indicates that the quantity of NOx remaining stored has fallen below another predetermined threshold.
• NOx nitrogen oxides
• the exhaust lines of these gases are commonly fitted with a catalytic converter having the function transform harmful chemical species into less harmful, even harmless species.
• the aforementioned patent proposes to control the richness of the air / fuel mixture of the engine so as to periodically switch the richness of this mixture to a value corresponding to a stoichiometric or rich mixture. This switching causes the desorption of the NOx to be adsorbed in the pot and then their reduction by the HC and CO present in the pot due to the increase in the richness of the mixture.
• the duration of the switching required to absorb and reduce the NOx stored in the catalytic converter is proportional to the mass of the NOx stored. When this period is too short, NOx remains stored in the catalytic converter and thus reduces its adsorption capacity. On the other hand, if it is too long, all of the stored NOx are destocked, but part of the unburnt HC and CO resulting from the increase in the richness of the mixture is released into the atmosphere, thereby causing an increase in discharges of chemical pollutants in the environment.
• the object of the present invention is precisely to provide a method for controlling the purging of NOx storage means associated with a catalytic converter, which makes it possible to minimize the discharges of polluting chemical species by refining, by appropriate corrections, several parameters of operation of the NOx storage means.
• said corrections are made by correcting a difference (D) between a value (NS-is-dp) of the NOx stock contained in the storage means, at the start (dp) of a purge, value estimated using the model, and a value
• NS-mes-dp ⁇ NS + NSres
• ⁇ NS is a measure of the mass of NOx which will be destocked during the purge
• NSres a measure of a residual stock of NOx remaining in the storage means at the end of a stopped purge under the control of the probe signal.
• ⁇ NS is measured during a double purge using transition delay measurements TIC1, TIC2 at the start of the purge, of the signal delivered by the probe, on the corresponding transition of the richness in reducers of the air / fuel mixture entering the catalytic converter, the storage means being empty and full, respectively. If a simple purge is used, ⁇ NS is measured using transition delay measurements TIC1 at the start of the purge and TIC3 at the end of the purge.
• FIG. 1 graphically illustrates a model for managing the NOx storage means, according to the control method according to the invention
• FIG. 2 is a flow diagram of a strategy for correcting the operating parameters of these storage means, used in the model of FIG. 1, and
• FIGS. 3 to 6 are graphs illustrating the successive stages of the flow diagram of FIG. 2.
• the purge control method according to the present invention which will now be described is advantageously executed by software means loaded in a computer for managing the operation of the engine.
• the method makes use of a model for managing the NOx storage means of a catalytic converter comprising such means and conventionally placed in the line for removing the exhaust gases from the engine in order to treat them, a probe with oxygen placed in this line immediately downstream of the pot delivering to the computer a signal representative of the richness in reducing chemical species of these exhaust gases, at the outlet of the pot.
• Figure 1 of the accompanying drawing which illustrates schematically the structure of the management model of the NOx storage means used in the present invention.
• the purge is triggered when the storage efficiency Effstoc of the Nox in the storage means falls below a predetermined threshold.
• Ef f stOC 1 - CNOx-in / CNOx-out
• C N ⁇ -i n and Cno x -out are respectively the NOx concentration of the exhaust gases entering and leaving the pot.
• This efficiency is maximum when the NOx storage means are empty, and minimum when they are full. It is therefore a decreasing function of the filling rate of these means, ie of the NS / NSC ratio of the quantity NS of NOx stored - to the maximum storage capacity NSC of these means. It is also an increasing function of the temperature T cat of the catalytic converter.
• a mapping 1 (see Figure 1) stored in the computer provides an estimated value Effstoc-is of this efficiency,.
• Kstoc.Qnox-is .Effstoc-is where Kstoc is a constant and Qnox-is an estimate of the amount of NOx emitted by the engine, this calculation being performed by blocks 3, 4 and 6 of the model in Figure 1.
• Blocks 5, 4 and 6 execute the various phases of this calculation of estimation of NS. According to a preferred embodiment of the invention, the choice is made to represent Effpurge, the average Effpurge-avg efficiency of the purge, to simplify the calculations. This average efficiency is mapped as a function of the pot temperature Tcat and the NS / NSC ratio as shown in block 2.
• Blocks 7 and 8 of JFig.l illustrate the conditions for stopping the storage phases (condition on Effstoc-est) and the purging phases (condition on NS- est) respectively, depending on the temperature Tcat of the catalytic converter .
• the management model Figure 1 if, during storage, the temperature of the pot is below a low threshold or higher than a high threshold, the Effstoc value at which storage is stopped is lowered (see block 7).
• the value of NS-is at which the purging is stopped is noted.
• Qnox is estimated using a map whose input variables characterize the operation of the engine, ie the richness of the air / fuel mixture, the speed temperature, engine temperature and angle of advance of ignition of the mixture.
• Effstoc is estimated by the cartography represented in block 1, which involves NS-est, this quantity being calculated as described above.
• NS-est is calculated by the model and Effstoc-est is a function of NS-est, NSC-est, T cat and Qnox-est.
• Qred-est and T cat are known to the computer with good precision, since it also manages the operation of the engine.
• Qnox-est, NSC-est and Effpurge-est are parameters that are not well known. The error made on these parameters is also likely to change over time, in particular due to the aging of the catalytic converter.
• the purpose of the present invention is precisely to correct all of these three parameters, so as to reduce this error by successive corrections thereof, according to the sequence illustrated by the flowchart in FIG. 2, these successive corrections avoiding interactions of the influences of these parameters on the estimation to be made of NS.
• This sequence essentially comprises four phases marked respectively 0, 1, 2 and 3, corresponding respectively to an initialization phase, a Qnox correction phase, a Effpurge correction phase and an NSC correction phase.
• the non-linear nature of the operation of the NOx storage means is exploited, both during a storage phase and during a purge phase.
• the following time intervals are then measured: - in the case of a double purge, the TIC1 interval, or transition delay, between the changeover from "poor” to "rich” of the richness of the exhaust gases at the inlet of the empty NOx pot, c that is to say during the second purge, and the detection of this tilting by the oxygen sensor placed at the outlet of the pot, in the case of a single or double purging, the interval TIC2 between the switching of " poor "to” rich “of this richness at the entry of the pot, full of NOx, and the detection of this tilting by the probe.
• the TIC3 interval, or transition delay, between the changeover from "rich” to “poor” of the richness of the exhaust gases at the inlet of the pot, that is ie at the end of the purge, and the detection of this tilting by the probe is a simple purge, the TIC3 interval, or transition delay, between the changeover from "rich” to "poor” of the richness of the exhaust gases at the inlet of the pot, that is ie at the end of the purge, and the detection of this tilting by the probe.
• ⁇ NS K [(ICT1-ICT.2) -Qgaz / (R eference -1)] where K is a constant, Qgas engine gas flow, R ⁇ _ r ⁇ che has richness of the air / fuel ratio during purging.
• the probe signal allows to calculate ⁇ NS.
• ⁇ NS J [TICI. Qgaz / (R iche -1) -TIC3. Qgaz / (R ⁇ " vrc - 1)] where J is a constant and ft p j_- has richness of the air / fuel mixture during the storage phase.
• the TICI ⁇ TIC2 test of the flowchart of figure 2 is then replaced by the ⁇ NS ⁇ 0 test.
• NSres is estimated by the procedure according to the invention, illustrated by the graph in FIG. 3. According to this procedure, a long purge (purge 1) is first carried out, extended beyond the tilting of the probe so as to empty completely the NOx stock in the pot.
• This long purge is followed by a storage phase of duration Tstoc.l during which the stock is charged with an amount of NOx equal to (NSres + ⁇ NS1) equal to that observed when the first purge is triggered (purge 1)
• the quantity NS of NOx stored is equal to ⁇ NS + NSres.
• the value Effpurge-is given by the model is initialized with the value estimated in phase 0 of initialization. As illustrated by the graph in FIG. 5, there is, during successive storage / purging cycles, the difference D at the start of purging between NS-is-dp and NS-mes-dp.
• the computer increments Effpurge-est until the difference D becomes greater than a predetermined threshold S 2 .
• NS-mes-dp is then passed over NS-est-dp. We cancel the last Effpurge correction to bring it closer to the actual value.
• this initial value is incremented during successive storage / purge cycles (see Figure 6) until the difference D is greater than a threshold predetermined S 3 > S 2 . As before, the last correction of NSC is then canceled.
• the invention makes it possible to achieve the announced aim, namely to reduce the discharge of polluting species into the atmosphere by more precise management of the purges of the NOx storage means of a catalytic converter for treating exhaust gas from an internal combustion engine designed to operate as a lean air / fuel mixture.
• This precise management is obtained thanks to a model and to corrections of essential parameters of this model, drawn from the observation of the tilting of the signal delivered by an oxygen sensor placed downstream of the pot, tilting observed while the storage means of NOx of the pot are placed in an operating mode such that only the parameter being corrected influences these switches.
• the invention uses in an original way the non-linearities that are observed in the operation of these storage means both in the storage phase and in the purge phase, and organizes successive and ordered corrections of the parameters in cause, capable of avoiding interactions between their influences during these corrections.

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

Applications Claiming Priority (3)

Publications (2)

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• 1999
  • 1999-09-13 FR FR9911426A patent/FR2798425B1/fr not_active Expired - Fee Related
• 2000
  • 2000-09-08 DE DE60024103T patent/DE60024103T2/de not_active Expired - Lifetime
  • 2000-09-08 EP EP00962586A patent/EP1212527B1/de not_active Expired - Lifetime
  • 2000-09-08 WO PCT/FR2000/002485 patent/WO2001020153A1/fr active IP Right Grant
  • 2000-09-08 ES ES00962586T patent/ES2248117T3/es not_active Expired - Lifetime

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