WO2008113946A1

WO2008113946A1 - Method for draining a nitrogen oxide trap by reformat injection and related method

Info

Publication number: WO2008113946A1
Application number: PCT/FR2008/050300
Authority: WO
Inventors: François Fresnet; Pierre Darcy; Stéphane Eymerie
Original assignee: Renault S.A.S
Priority date: 2007-02-23
Filing date: 2008-02-22
Publication date: 2008-09-25
Also published as: FR2913056A1

Abstract

The invention relates to a method for draining a processing module (1) for exhaust gases including a nitrogen oxide (NOχ) trap (2), and a reformer device (8) capable of providing a hydrogen- and/or carbon monoxide-rich gas, that comprises: evaluating the loading state of the NOχ trap (2); comparing said evaluated loading state with a stored or predetermined loading state; determining values of operational parameters; comparing said values of operational parameters with stored or predetermined value ranges; and controlling the reformer (8) and/or an engine (16) and/or a bypass valve (6) in order to drain the NOχ trap (2) or in order to modify said operational parameter values closer to the stored or predetermined value ranges.

Description

Process for purging a nitrogen oxide trap by reformate injection and associated device

The present invention relates to a method of purging a nitrogen oxide trap disposed in the exhaust line of an internal combustion engine. In particular, the invention relates to the purge of nitrogen oxides and sulfur oxides stored in the nitrogen oxide trap.

The treatment of nitrogen oxides (NOx), especially NO or NO2, in the exhaust gases of an engine, for example diesel, is important to meet anti-pollution standards. A possible solution to the treatment of N0χ in an oxidizing medium is the use of nitrogen oxide traps (N0χ trap). In the presence of an excess of oxygen (poor conditions, that is to say less than 1 richness), this type of system traps N0χ in the form of nitrites or nitrates on chemical storage elements, most often oxides of barium. The reduction in the number of available storage sites inherent in this loading phase leads to a decrease in the trapping efficiency of NOx. In order to maintain high storage efficiencies, it is therefore necessary to periodically purge the N0χ trap.

This purging is carried out under rich conditions (ie, richness greater than 1), that is, in the presence of an excess of reducing agents. During this purge, the nitrated species adsorbed on the N0χ trap desorb and then are reduced to nitrogen by the excess of reducing agents.

Conventionally, the passage in rich conditions in the exhaust is operated via the use of the engine control, injecting into the cylinders air and fuel at a richness of between 1, 01 and 1, 05. However, the operation of the engine with a value greater than 1 has possible repercussions on the driving pleasure and the engine performance. In addition, this type of operation can lead to lubricant dilution problems. in the cylinders, which can: decrease the durability of the engine, reduce the emptying intervals and lead to a clear overconsumption of fuel.

The NOχ trap is also continuously poisoned by sulfur in the fuel and lubricant. The various sulfur oxides (SOχ), in particular SO2 or SO3, are oxidized in the form of sulphates in the NOχ trap, and are trapped on the sites initially intended for the storage of N0χs. This poisoning reduces the trapping capacity of the NOχ trap. To ensure a conversion efficiency of NOχ compatible with future standards, desulphating is therefore periodically necessary.

This desulfation occurs under rich conditions, that is, when the gas richness at the NOχ trap is greater than 1, and at high temperatures. It typically requires engine control intervention, which makes these desulfation steps expensive in terms of dilution and overconsumption.

An alternative solution to the only motor control consists of injecting reformate into the exhaust line, upstream of the NOχ trap, to bring the excess of reducing agents and / or the temperature necessary for the N0 pur purges and the desulfation (or SO pur purge) ). This reformate, produced from fuel and air, contains reducing agents (hydrogen H ₂ and carbon monoxide CO), as well as the chemical species (H ₂ O, CO ₂ ...) necessary for the accomplishment of the reduction of N0χ and sulphates.

In order to limit the need for reducers necessary for the passage of richness 1 in the N0χ trap, it is possible to carry out N0χ and / or SOχ purge steps by partially or completely bypassing the exhaust gases of the N0χ trap. The oxygen - rich exhaust gases are then diverted from the N0χ trap and can either be directed to a second N0χ trap or sent directly to the exhaust. Such systems or methods are described, for example, in US Pat. No. 6,843,054, or in US Patent Applications 2005/0000210, US 2005/0103001 and WO 2004/075646.

The aim of the invention is to improve the N0χ and / or SOχ purges, in particular in terms of speed, efficiency, and flexibility with respect to the engine and / or with respect to the various devices used. to perform the purge.

According to the invention, the method is suitable for purging a module for treating the exhaust gases produced by an internal combustion engine of a motor vehicle. The exhaust treatment module includes:

- an exhaust gas routing circuit, a nitrogen oxide trap (N0χ) mounted in the conveying circuit and traversed by a gaseous mixture; the N0χ trap being capable of trapping oxides of nitrogen and / or oxides of sulfur present in the gaseous mixture when the richness of the gaseous mixture is less than 1,

- a bypass line mounted in the routing circuit, in parallel with the N0χ trap, and - a reformer device capable of providing a gas rich in hydrogen and / or carbon monoxide. According to the method: the loading state of the N0χ trap is evaluated, said evaluated loading state is compared to a stored or determined threshold, operating parameters of the routing circuit and / or the motor are determined. comparing said operating parameter values to stored or determined ranges of values, the reformer and / or the motor and / or a bypass valve are controlled to purge the trap at N0χ, or to modify said operating parameter values to the ranges of stored or determined values. The operating parameter (s) of the routing circuit and the motor are chosen from: the internal temperature or the exit temperature of the N0χ trap, the operating point of the motor (for example the speed or the load), the instantaneous position of the accelerator pedal or its time derivative and the temperature of a particulate filter or an oxidation catalyst mounted downstream of the N0χ trap CAT.INIST logo CNRS logo INIST Accueil / Home Imprimer / Print Contact / Contact PARTAGER / SHARE EXPORT Bookmark and Share Mendeley.

The values of the operating parameters are changed to ranges of values which correspond to a favorable operation for purging. Thus, when the determined values of the operating parameters are already in the determined range of values, the operating parameters are favorable for purging the trap N0χ and it is not necessary to change the value of these parameters. On the other hand, when the determined values of the parameters are not included in the value ranges, the reformer and / or the motor are controlled so as to change the values of the parameters towards the ranges of values.

Thus, taking into account the operating parameters and, possibly, by modifying these parameters in the desired direction, it is possible to choose the purging procedure most suited to the operating conditions of the motor and the processing module. This results in a purge faster, more efficient and above all more flexible vis-à-vis the operating conditions of the routing circuit and / or the engine.

The operating parameter values can be changed by adding gas rich in hydrogen and / or carbon monoxide to the gas mixture.

The values of the operating parameters can also be modified by modifying the operation and / or the supply of the engine so that the exhaust gas included in the gas mixture has a higher richness and / or a higher temperature. The values of the operating parameters can also be modified by modifying the operation and / or the power supply of the engine so as to reduce the quantities of hydrocarbons, carbon monoxide (CO) or NOx in the engine exhaust gases. .

According to one embodiment, the N0χ trap is purged by adding gas rich in hydrogen and / or carbon monoxide, and decreasing the proportion of the exhaust gases in the gaseous mixture passing through said N0χ trap. According to the same mode of implementation, the trap is purged

N0χ by varying: the richness of the gas rich in hydrogen and / or carbon monoxide, and / or the relative proportion of gas rich in hydrogen and / or carbon monoxide, and exhaust gas in the gas mixture, so as to successively obtain a reducing gas mixture, an oxidizing gas mixture and a reducing gas mixture.

According to another embodiment, the N0χ trap is purged by modifying the composition of the fuel-air mixture supplied to the engine so as to increase the richness of the exhaust gas included in the gas mixture.

The exhaust gases, in particular of a diesel engine, have a richness lower than 1, that is to say that they contain oxidizing species in excess relative to the reducing species.

In this embodiment, the engine is supplied with a modified fuel-air mixture so as to increase the richness of the exhaust gas, that is to say so as to reduce the oxidizing species contained in the exhaust gases. 'exhaust. According to the same embodiment, the NO.sub.O trap can be purged by varying the richness of the exhaust gases in the gas mixture, so as to successively obtain a reducing gas mixture, an oxidizing gas mixture and a reducing gas mixture. . According to another embodiment, the bypass pipe comprises an N0χ trap and each NO piè trap is purged alternately or simultaneously.

The invention also relates to a module for the treatment of exhaust gases produced by an internal combustion engine of a motor vehicle comprising: an exhaust gas exhaust system,

- a NOχ trap mounted in the routing circuit and capable of being traversed by a gaseous mixture; the NO piè trap being capable of trapping nitrogen oxides and / or sulfur oxides present in the gas mixture when the richness of the gaseous mixture is less than 1, a bypass pipe mounted in the conveying circuit, in parallel with the N0χ trap, and - a reformer device capable of providing a gas rich in hydrogen and / or carbon monoxide.

The module also includes an electronic control unit comprising:

a first means capable of evaluating the state of loading of the N0χ trap, a second means capable of comparing the state of loading evaluated by the first means with a threshold stored in or determined by the second means, a third means capable of determining values of operating parameters of the routing circuit and / or the motor, a fourth means capable of comparing said values of operating parameters with ranges of values stored or determined by the fourth means, - a fifth means capable of controlling the reformer and / or the motor and / or a bypass valve so as to purge the NO piè trap or modify said operating parameter values to the ranges of values stored or determined by the fourth means. Preferably, the bypass pipe also comprises an NO _x trap.

The invention also relates to a propulsion system of a motor vehicle. The propulsion system comprises an internal combustion engine and an exhaust gas treatment module according to the present invention.

Other advantages and characteristics will become apparent upon examination of the detailed description of embodiments and embodiments that are in no way limiting, and the accompanying drawings, in which: FIGS. 1 and 2 show schematically two embodiments of a module; Figure 3 shows the flowchart of a process for determining a purge strategy or a purge promotion strategy, and Figures 4 to 8 show flowcharts of various methods for purging. purge according to the invention. FIG. 1 represents a first embodiment of a treatment module 1 for exhaust gas. The processing module 1 comprises an exhaust gas routing circuit. The routing circuit comprises an N0 2 trap mounted upstream of a catalyzed particle filter system 3, itself mounted upstream of an oxidation catalyst 4.

The NOχ 2 trap is used to process NOχ by alternative phases of storage and reduction of stored N0χ. The trap to

N0χ 2 can consist of any material commonly used for this application (cordierite, mullite, metal, ...) and can be impregnated with any conventional catalytic material commonly used for this application (Ba, Ce, Cs, Zr, K, Al , Pt, Rh, Pd, ...). In addition, the NO 2 trap may also be impregnated with a composition promoting the oxidation of carbon monoxide CO at low temperature and the oxidation of CH ₄ methane.

The particulate filter 3 may be of silicon carbide (SiC), cordierite, mullite or of any other material to be used for the realization of a filtering system. It can also be impregnated with a coating promoting the combustion of soot or the oxidation of hydrocarbons, carbon monoxide CO, hydrogen H ₂ and any other undesired species such as H ₂ S, NH ₃ , NCO be produced during a purge N0χ or SOχ of the trap

N0χ 2. In particular, the particulate filter 3 may be impregnated with a copper-based coating promoting the oxidation of H ₂ S.

The oxidation catalyst 4 may consist of any material conventionally used for this application (cordierite, mullite, metal, etc.) and may be impregnated with any conventional catalytic material commonly used for this application (Ce, Zr, Al, Pt , Rh, Pd, ...). It can be impregnated with a coating promoting the low temperature oxidation of carbon monoxide CO emitted by the engine or produced by the regeneration of the particulate filter 3. This impregnation can also promote the oxidation of hydrocarbons, hydrogen H ₂ and any other undesired species such as H ₂ S, NH ₃ , NCO that can be produced during a N0χ or SOχ purge of the N0χ trap 2. In particular, the particulate filter 3 may be impregnated with a coating based on of copper or any other material for oxidizing H ₂ S.

A bypass line 5 is connected to the routing circuit on the one hand by a bypass valve 6 mounted upstream of the N0 2 trap, and on the other hand by a branch located downstream of the N0 2 trap. and upstream of the particulate filter 3. The control valve 6 allows the exhaust gases to be directed either entirely to the NO 2 trap, or entirely to the bypass line 5, or simultaneously to the NO 2 trap and to the bypass line 5.

The treatment module 1 also comprises a reformer 8 which makes it possible to produce a gas rich in hydrogen and / or carbon monoxide, called reformate, which can be introduced into the conveying circuit by an injection system 7 mounted upstream of the trap N0χ 2 and downstream of the bypass valve 6. The reformate is produced during an operation of transformation of an air-hydrocarbon mixture in a gaseous mixture, rich in hydrogen and carbon monoxide. The major constituents of reformate are nitrogen, hydrogen and carbon monoxide, and their relative proportion depends on the reforming technology used. Among the most common technologies are the partial oxidation of the hydrocarbon by oxygen O2 ("Partial OXidation" or POX), the endothermic reforming by steam (in English: "Steam Reforming"). ) or the exothermic reformation by carbon dioxide CO2 (in English: "Dry Reforming"). A suitable combination of Steam Reforming and Partial Oxidation technologies can allow autothermal reforming (in English: "Auto Thermal Reforming" or ATR). A reformat gas phase ignition system 9 is placed upstream of the NO 2 trap and downstream of the reformate injection system 7, in order to possibly initiate an oxidation reaction of the reformate before the reformate falls into the trap of

NO _x 2.

The processing module 1 comprises an electronic control unit (ECU) 10 capable of controlling and managing the various favoring strategies or the different strategies for purging the N0 2 trap. The ECU 10 comprises a first means 1 1, a second means 12, a third means 13, a fourth means 14 and a fifth means 15.

The first means 11 is a means for evaluating the state of loading of the NO 2 trap. The first means 1 1 evaluates the state of loading from measured or calculated quantities which can be: the cumulative efficiency on the storage of NOχ, the amount of NOχ stored in the NOχ 2 trap, the amount of SOχ stored in the N0χ 2 trap, the time elapsed since the last N0χ purge or the last SO pur purge, or the distances traveled since the last purge N0χ or the last purge SOχ.

For example, the cumulative storage efficiency of the N0χ 2 trap can be: measured using an N0χ probe placed in position P 1 (located upstream of the bypass valve 6) or P2 (located between the bypass valve 6 and the reformate injection system 7) and an NO _x probe placed in position P3 (located between the trap N0 2 and the branch of the branch pipe 5) or P 4 (located between the connection of the bypass line 5 and the particulate filter 3) or

P5 (located between the particle filter 3 and the oxidation catalyst 4) or P6 (located downstream of the oxidation catalyst 4), or calculated by a stored model or a stored map depending on other parameters of the module for processing 1, for example an onboard model using, as input data, rolling conditions encountered since the last purge N0χ by integrating the duration since the last SOχ purge and simulating from these the engine N0χ emissions and the This type of model can also simulate the N0 pur purge and / or SOχ purge phases of the N0χ 2 trap and predict the efficiency of the last purge. The second means 12 is a means for comparing the state of loading evaluated by the first means 1 1, with respect to a threshold stored or determined by the second means 12. According to the different quantities determined by the first means 1 1 to evaluate the loading state of the N0 2 trap, the associated thresholds can be:

a minimum value of the cumulative storage efficiency of the N0 2 trap since the last N0χ purge or over a shorter period of time,

a maximum quantity of N0χ stored in the trap N0χ 2 since the last purge N0χ, a maximum quantity of SOχ stored in the trap N0χ

2, minimum and maximum durations between two N0χ purges and two SO _x purges, minimum and maximum milestones between two NO _x purges or two SO pur purges.

The threshold or thresholds are determined by the second means 12 from stored values, a stored model or a stored map. Thus, the value of the threshold may for example be: fixed, a function of the mileage of the vehicle, the aging of the reformer 8 or the aging of the trap at N0χ 2, or - auto-adaptive: the second means 1 1 for example identifies profiles of rolling types of the user and changes, depending on the type of driving observed from N purges, the threshold.

The second means 12 thus makes it possible to evaluate the importance of performing a purge more or less short term. In addition, the second means 12 can also associate different quantities measured and / or calculated, and their corresponding thresholds, in order to best estimate the importance of purging. For example, we can associate the cumulative efficiency on the storage of N0χ with the duration since the last purge.

The third means 13 is a means for determining the operating parameter values of the routing circuit and / or of an internal combustion engine 16. The parameters are for example the operating point of the motor 16, the pedal information, the temperature at the outlet of the NO 2 trap, or else the temperature upstream and downstream of the particulate filter 3 and / or the oxidation catalyst 4. The third means 13 determines the values:

by simulation, from a stored model or a stored map depending on other parameters of the processing module 1, or from measured quantities, for example: o by three temperature sensors, the first sensor positioned at P1 or P2, the second at P3 or P4, and the third at P5 or P6, o by two richness probes, the first positioned in position P1 or P2, the second in P3 or P4 or P5 or P6.

The third means 13 thus makes it possible to evaluate the operating state of the routing circuit and / or the motor 16, and in particular the parameters that can influence the efficiency of a purge. The fourth means 14 is a means for comparing the parameter values determined by the third means 13, with respect to ranges of values stored or determined by the fourth means 14. The fourth means 14 determines the ranges of values from stored values , a stored model, or even from a stored map and having different inputs corresponding to other parameters of the processing module 1. These ranges of values can be determined in particular with respect to constraints imposed during the procedures purge. These constraints can thus be: - maximum permissible overconsumption during purge, maximum methane emissions, maximum hydrocarbon, carbon monoxide or NOχ emissions, - maximum dilution costs, or even performance declines. or maximum driving pleasure.

The various parameters measured by the third means 13 are, for example, and non-exhaustively, associated by the fourth means 14 with a multi-input mapping taking into account the preceding constraints and making it possible to identify areas favorable to purge strategies or to purge promotion strategies. For example, a situation in which the emissions of the engine 16 to hydrocarbons or carbon monoxide are within the corresponding range of values determined by the fourth means 14, and wherein the outlet temperature of the NO 2 trap is also included in the corresponding range of values, can be identified by the fourth means 14 as a situation favorable to a reformer purge strategy 8 alone. Likewise, a trap exit temperature at N0χ 2 within the corresponding range of values, together with an estimated dilution within the corresponding range of values for engine control purge, can be identified as a favorable situation for a fueling strategy. purge by motor control assisted by the reformer 8, or a bleed strategy by motor control alone.

The fourth means 14 is thus intended to determine whether conditions favorable to a particular purge strategy are met or not. In other words, the fourth means 14 determines whether the operating conditions of the processing module 1 can improve the efficiency of a particular purge strategy or, on the contrary, reduce the efficiency thereof. The fifth means 15 is a control means for the reformer 8 and / or the motor 16 and / or the bypass valve 6. The fifth means 15 allows either to purge the trap NOχ 2 or to modify one or a plurality of operating parameter values among those determined by the third means 13. The fifth means 15 thus receives data from the second and fourth means 12, 14 and determines, from these data, the purge strategy adapted to implement, or the purge promotion strategy adapted to implement. The term "purge favoring strategy" is understood here to mean a method making it possible to modify the operating conditions of the treatment module 1 so that these conditions become favorable to a purge strategy performed later.

Thus, when the fourth means 14 indicates that certain values of operating parameters are outside ranges corresponding values and that the second means 12 indicates that the loading state of the trap N0χ 2 is greater than a certain threshold, the fifth means 15 can then control the reformer 8 and / or the motor 16 and / or the valve of derivation 6 to perform an adequate purge promotion strategy. The purge promotion strategy is chosen by the fifth means 15 for example so as to cause a variation of said values to the desired ranges of values so that the operating conditions of the processing module 1 can become favorable to a purge strategy. The fifth means 15 can therefore change parameter values that are not favorable to the purge strategy.

When, on the contrary, the fourth means 14 determined that the values of the operating parameters were located in certain ranges of corresponding values adapted to a particular purge procedure, and that the second means 12 indicates that the loading state of the trap is N0χ 2 is above a certain threshold, the fifth means 15 can then control the reformer 8 and / or the motor 16 and / or the bypass valve 6 so as to implement the appropriate purge strategy (by reformer 8 alone, by motor control alone, or by reformer 8 and motor control). The purge strategy can thus for example be chosen according to the indications given by the fourth means 14 and / or according to the purging favoring strategy used previously.

An exemplary flowchart implemented by the fifth means 15 for determining purge purging or purging strategies is shown in FIG.

According to other variants of the first embodiment shown in FIG. 1, instead of using a catalyzed particle filter 3 followed by an oxidation catalyst 4, it will be possible to use only a catalyzed particulate filter or not, or well an oxidation catalyst followed by a particle filter catalyzed or not.

FIG. 2 shows a second embodiment in which the elements common to the first embodiment bear the same references. The second embodiment relates to a processing module 17 in which the bypass line 5 comprises an NO _x trap 18. In this embodiment, the bypass valve 6 thus allows the exhaust gases to be directed either towards the NO 2 trap or to trap N0χ 18, either simultaneously to the two traps N0χ 2, 18. Just like trap N0χ 2, trap N0χ 18 also includes, downstream of the bypass valve 6 and upstream of the trap N0χ 18, a reformate injection system 19 produced by the reformer 8. A reformat gas phase ignition system 20 is placed downstream of the reformate injection system 19 and upstream of the N0χ trap. reformate introduced into the gas routing circuit is determined by a reformate valve 21 which makes it possible to determine the amount of reformate introduced by the injection system 7 and by the injection system 19. The treatment module 17 comprises also a unit of Electronic control (ECU) 22. The ECU 22 comprises a first means 23, a second means 24, a third means 25, a fourth means 26 and a fifth means 27.

The first means 23 is a means for evaluating the loading states of traps N0χ 2, 18. The first means 23 has the same purpose as the first means 1 1 (shown in Figure 1), but adapted to the second mode of production. The first means 23 evaluates the states of loading from measured or calculated quantities which are those used by the first means 1 1 (represented in FIG. 1) but applied to the N0 2 trap and the NO 8 trap. For example, the cumulative storage efficiency can be determined, for the trap of N0χ 2, identically to the first embodiment. On the other hand, for the N0χ 18 trap, the determination of the cumulative storage efficiency will be done by a method adapted to the N0χ 18 trap; for example, the measurement of the cumulative storage efficiency of the N0χ trap will be by N0χ probes placed in the P1 or P20 position.

(located between the bypass valve 6 and the reformat injection system 19) and in position P30 (located between the N0χ trap and the branch of the branch pipe 5) or P4 or P5 or P6. The second means 24 is a means for comparing the loading states evaluated by the first means 23, with respect to thresholds stored or determined by the second means 24. The second means 24 has the same purpose as the second means 12 (shown in FIG. Figure 1), but adapted to the second embodiment. Thus, the thresholds and their values may be those used by the second means 12 (shown in FIG. 1) but applied to the NOχ 2 trap and the NOχ trap 18.

The third means 25 is a means for determining the operating parameter values of the routing circuit and / or an internal combustion engine 16. The third means 25 has the same purpose as the third means 13 (shown in FIG. 1), but adapted to the second embodiment. Thus, the parameters determined can be those used by the third means 13 (shown in FIG. 1) but applied to the NO 2 trap and to the NO x trap 18. For example, the temperature sensors or the wealth probes capable of to be placed in position P2 and P3 for the NOχ 2 trap, will be placed respectively in position P20 and P30 for the NOχ trap 18. The fourth means 26 is a means for comparing the parameter values determined by the third means 25, by relative to ranges of values stored or determined by the fourth means 26. The fourth means 26 has the same purpose as the fourth means 14 (shown in Figure 1), but adapted to the second embodiment. Thus, the ranges of values may be those used by the fourth means 14 (shown in FIG. 1) but applied to the NOχ 2 trap and the NOχ trap 18.

The fifth means 27 is a control means for the motor 16 and / or the bypass valve 6 and / or the reformer 8 and reformate valve 21. The fifth means 27 has the same purpose as the fifth means 15 (shown in FIG. Figure 1), but adapted to the second embodiment. Thus, the fifth means 27 can also control the reformate valve 21 to direct the reformate to the NOχ trap 2 and / or the NOχ trap 18. In addition, the fifth means 27 allows either to modify one or more values of operating parameters among those determined by the third means 25, or to purge one of the two traps N0χ 2, 18 or both simultaneously. In the rest of the description, the various methods described

(Purge promotion strategies or purge strategies) will apply to the two embodiments described above and illustrated in Figures 1 and 2.

FIG. 3 represents a flowchart of a method for determining a purge strategy or a purge promotion strategy. The method is implemented in particular by the fifth means (15, 27). The method may be the same or different for the two embodiments illustrated in FIGS. 1 and 2, including the implementation of the purge strategies or the purge promotion strategies determined by the flowchart of FIG. 3.

In the example described, the method follows the evolution of the quantity of N0χ stored in an N0χ trap and, depending on the quantity of N0χ stored and the operating conditions of the treatment module, performs a suitable purge strategy or a strategy favored purge.

Thus, in a step 28, for example, it is determined whether the quantity of N0χ stored in the N0χ trap is greater than or less than a first threshold. This step is performed by the first means (1 1, 23) and the second means (12, 24). When the quantity of

N0χ stored is less than the first threshold, the process starts again at step 28.

On the other hand, when the quantity of N0χ stored is greater than the first threshold, it is determined, in a step 29, whether the conditions are favorable to a strategy of purging the N0χ trap by motor control alone. Step 29 is implemented in particular by the third means (13, 25) and the fourth means (14, 26). When the operating conditions are favorable to an engine control bleed strategy, the fifth means (15, 27) then controls the processing module so as to perform an engine control purge strategy in a step 30, and the process starts again in step 28.

When, on the other hand, the operating conditions are not favorable to an engine control bleed strategy, the operating state of the reformer is determined. Thus, in a step 31, it is determined whether the reformer is on and, if necessary, the reformer is turned on during a step 32 and then the process starts again in step 28. When the reformer is turned on, it is determined, when of a step 33, if it is initiated and, if necessary, the reformer is initiated during a step 34 and then the process starts again at step 28.

When the reformer is on and primed, it is determined in a step 35 whether the conditions are favorable for a reformer purge strategy. Step 35 is implemented in particular by the third means (13, 25) and the fourth means (14, 26). When the operating conditions are favorable for a reformer purge strategy, the fifth means (15, 27) then controls the processing module so as to perform a reformer purge strategy in a step 36, and the process starts again in step 28. When the operating conditions are not favorable to a reformer purge strategy, it is determined, in a step 37, whether the conditions are favorable for a reformer purge and engine control strategy. Step 37 is implemented in particular by the third means (13, 25) and the fourth means (14, 26). When the operating conditions are favorable for a reformer purge and engine control strategy, the fifth means (15, 27) then controls the processing module so as to perform a reformer purge and engine control strategy during a step 38, and the process starts again in step 28. When the operating conditions are not favorable to a strategy of purge by reformer and motor control, it is determined in a step 39, whether the conditions are favorable to a strategy. bleed by motor control alone. Step 39 is implemented in particular by the third means (13, 25) and the fourth medium (14, 26). When the operating conditions are favorable to an engine control purge strategy alone, the fifth means (15, 27) then controls the processing module so as to perform an engine control purge strategy alone during a step 30, and the process starts again at step 28.

When the operating conditions are not favorable either to an engine control purge strategy alone, it is determined in a step 40 whether the amount of NOχ stored in the NOχ trap is greater than a second threshold or not. . If the amount of NOχ stored is less than the second threshold, then the process starts again at step 28.

The comparison of the quantity of N0χ stored at the second threshold makes it possible to estimate the time available before having to purge the N0χ trap. Thus, if the operating conditions of the processing module are not favorable to any purge strategy envisaged, and if the quantity of N0χ remains below the second threshold, then the fifth means (15, 27) does not trigger any strategy until Whether the operating conditions change so as to be favorable to one of the purge strategies, the amount of N0χ becomes greater than the second threshold. If the operating conditions become favorable to a purge procedure, then it will be controlled during steps 29, 35, 37 or 39. If the quantity of NOχ becomes greater than the second threshold and the operating conditions are not favorable. in one of the purge strategies, then the fifth means (15, 27) will have to perform a purge promotion strategy in order to cause the operating conditions to become favorable to a purge strategy.

Thus, in a step 41, it is determined whether the quantity of N0χ stored in the N0χ trap is greater than a third threshold or not. If the quantity of N0χ stored in the N0χ trap is less than the third threshold, then a first or a third purge promotion strategy is commanded during a step 42, and the process resumes at step 28. On the other hand, if the quantity of N0χ stored in the N0χ trap is greater than the third threshold, then first controlling a second purge promotion strategy in a step 43, then a reformer purging alone in a step 36, and the process is repeated in step 28.

The various purging favoring strategies implemented during the process described in FIG. 3 are described below.

The first purge promotion strategy is to increase the trap temperature to N0χ. The temperature increase of the N0χ trap can be carried out using the reformer and / or by motor control. We can thus distinguish three different variants to implement the first promotion strategy.

According to a first variant of the first favoring strategy, reformate is injected upstream of the NO.sub.O trap and causes the temperature of said trap to be increased by oxidation in said trap or by gas-phase ignition of the reformate. The bypass valve is preferably controlled to completely direct the exhaust gas to the N0χ trap and the reformer is controlled to inject reformate upstream of the N0χ trap at a rate Qreformati determined by equation (1). ) below :

Q Uech - ^ P ech - ^y l target ^~ * ech) / γ \ φ ^rmaΛ % H ₂ .AH ₁ +% C0ΛH ₂ - Cp _ref M _ref . (T _M - T _ref )

in which: Qech represents the flow rate of the exhaust gases upstream of the bypass valve, Q _ec h being estimated for example from the flow rates of air and fuel injected into the engine,

Cpech represents the heat capacity of the exhaust gases as a function of temperature, T _cl bie represents the temperature at which it is desired to bring the trap to NO _x ,

Tech represents the temperature of the exhaust gases upstream of the bypass valve, % H ₂ and% CO represent the composition of the reformate, in percentage, hydrogen H ₂ and carbon monoxide CO, Cpref represents the heat capacity of the reformate, M _re f represents the molar mass of the reformate, T _re f represents the temperature reformat, and

ΔHi and ΔH ₂ respectively represent the oxidation enthalpies of hydrogen H ₂ and CO carbon monoxide.

The characteristics of the reformate (T _ref, Pc _ref,% _H2,% C0, M _ref) can be determined for example from the rich reformate and the air flow supplied to the reformer, or alternatively from maps.

For the first variant of the first purge promotion strategy, a temperature T _C ibie will be chosen, allowing the triggering of a N0χ and / or SOχ purge. When, for example, the temperature downstream of the N0χ trap has reached the temperature T _C ibie, the favoring strategy can be stopped.

In the case of the second embodiment (FIG. T), it is possible to simultaneously increase the temperature of the two traps at NO 2, 18 by controlling the reformer 8 and the reformate valve 21 so as to inject, upstream of each trap, at NO. 2, 18, reformat at a rate

Qreformati determined by equation (1).

Equation (1) can also be corrected according to several factors. Thus, equation (1) can be corrected with: a correction on the aging of the N0χ trap, which takes into account the reduction of the oxidation efficiency of the reducers, a self - adaptive correction of the reformate flow, which takes the difference between the controlled flow rate and the injected flow rate is accounted for, in particular due to the aging of the reformer, a correction on the heat losses in the treatment module, especially from the temperature T _{aV a} downstream of the N0χ trap; the corrected injected reformate flow Qref cor i can then be calculated by equation (2) below: Q ech ^• ^ P ech - K * - target * ech) T ¹ target - T ¹ ech

Q _n ? F horn 1 (2)

"/ 0H ₂ -AH ₁ +% COΛH ₂ - Cp _ref M _ref . (T _able - T _ref ) IT _downstream - T _ech

- a correction on the thermal losses due to the speed of the vehicle V _ve h; the rate of reformate inj ected corrected Q _re f cor 2 can then be calculated by equation (3) below:

Q Qech - CPech - ( ^T cable ^{~ T} ech) + ^H W veh) - ( ^T ext ^{~ T} ech) ^ Λ

^ ^{Ref COR2%} H ₂ +% CO.AH .AH ₁ ₂ - c _Pref M _{re {(τ} _CME - τ _ref).

in which T _ex t represents the outside temperature of the vehicle, and Η (V _ve h) is a function dependent on the speed V _ve h.

According to a second variant of the first favoring strategy, the temperature of the exhaust gas is increased by engine control in order to increase the temperature of the trap to N0χ. In this case, the fifth means (15, 27) controls firstly the bypass valve so as to, preferably, completely direct the exhaust gas to the trap N0χ, and secondly the engine so as to increase the temperature of the exhaust gases by engine control. When the temperature T _{aV a} downstream of the N0χ trap has reached the purge temperature N0χ and / or SOχ, the favoring strategy can be stopped.

In the case of the second embodiment (FIG. T), it is possible to simultaneously increase the temperature of the two traps at NO 2, 18 by controlling firstly the bypass valve 6 so as to orient, equally or otherwise, the exhaust gas to the two traps N0χ 2, 18, and on the other hand the engine 16 so as to increase the temperature of the exhaust gas by engine control.

According to a third variant of the first favoring strategy, the fifth means (15, 27) can increase the temperature of the NOχ trap by a strategy of motor control and reformate injection. In this case, the fifth means controls: the bypass valve to preferably direct the exhaust gas to the NO _x trap, the engine to increase the engine control exhaust gas temperature and the reformer to inject reformate into the engine. upstream of the N0χ trap at a rate Qreformati determined by the equation

(1).

For the third variant of the first purge promotion strategy, a temperature T _C ibie will be chosen, allowing the triggering of a NOx and / or SOχ purge. When the temperature T _ava i downstream of the N0χ trap has reached the temperature T _C ibie, the favoring strategy can be stopped.

In the case of the second embodiment (FIG. 2), it is possible to simultaneously increase the temperature of the two traps N0χ 2, 18 by controlling: the bypass valve 6 so as to orient, evenly or otherwise, the gases of escape to the two traps to

N0χ 2, 18, the engine 16 so as to increase the temperature of the exhaust gas by engine control, the reformer 8 and the reformate valve 21 so as to inject, upstream of each trap N0χ 2, 18, the reformate at a Qreformati rate determined by equation (1). The second purge favoring strategy consists in increasing the temperature of the particulate filter and / or the oxidation catalyst placed downstream of the N0χ trap. The temperature increase is carried out by increasing, by use of the reformer and / or by motor control, the temperature of the gases passing through the particulate filter and / or the oxidation catalyst. The increase of the temperature of the particulate filter and / or of the oxidation catalyst makes it possible to initiate their oxidation function and thus to limit the emissions of pollutants to the exhaust. We can again distinguish three different variants to implement the second promotion strategy: reformer, engine control, reformer and engine control.

The three variants can be implemented identically to the three variants of the first favoring strategy, with the exception of the value of the target temperature T _C i _b i _e - Indeed, For the second purge promotion strategy, the temperature T _C ibie will be chosen, for example, at the starting temperature of the particulate filter and / or the oxidation catalyst.

The third purge promotion strategy is to reduce pollutant emissions by the engine. The reduction of pollutant emissions by the engine, in particular hydrocarbons or carbon monoxide CO or nitrogen oxides N0χ, is achieved by any appropriate engine control strategy. The third purge favoring strategy can in particular be implemented during a strategy of purging the N0χ trap completely or partially bypassed (that is to say that the exhaust gases do not pass through or only partially trap at N0χ).

Slightly before or simultaneously at the beginning of the N0χ trap purging strategy, the fifth means (15, 27) controls the bypass valve on the one hand so as not to direct or direct only a portion of the exhaust gases. exhaust to the trap N0χ, and secondly the engine so as to limit emissions of carbon monoxide CO, hydrocarbons and nitrogen oxides N0χ. The engine control may for example consist of: - the increase of the injection advance, the increase of the air supercharging pressure, or even the shutdown of the exhaust gas recirculation system (in English " exhaust gas recirculation (better known under the name EGR).

However, depending on the case, the fifth means (15, 27) can control the engine so as to reduce the emissions of N0χ by the engine. In this case, the motor control can for example consist of: - the increase of the injection delay, the decrease of the air supercharging pressure, or even the opening of the exhaust gas recirculation system. The third purge promotion strategy can also be used to promote each of the purge strategies.

The different purge strategies implemented during the process described in FIG. 3 are described below. Figure 4 shows the flowchart of a first reformer purge strategy. In a step 44, the fifth means (15, 27) controls the bypass valve so as to completely or partially divert the exhaust from the N0χ trap to be purged and, in a step 45, the fifth means (15, 27 ) controls the injection, upstream of the NOχ trap to be purged, of reformate at a flow rate

Qreformat2. The reformate injection is triggered simultaneously or in slight time offset with the control of the bypass valve. An end of purge criterion is evaluated, in a step 46, to determine when the reformate injection step 45 can be stopped. When the end of purge criterion is reached, the reformate injection is stopped during a step 47, and the bypass valve is controlled, during a step 48, so as to redirect the exhaust gases towards the trap to N0χ.

In the case of the second embodiment (FIG. 2), the bypass valve 6 will be controlled, during step 48, so as to direct the exhaust gases towards the trap at NO 2, or at the trap at NO 18, or to the two traps at N0χ 2, 18 simultaneously.

In the remainder of the description, the term "partial or total opening of the bypass valve", the orientation of a portion or all of the exhaust gas to the NO trap to be purged, and "closure partial or total of the bypass valve »the bypass of the N0χ trap to be purged by some or all of the exhaust gas. In particular, the percentage of opening and closing of the bypass valve will correspond respectively to the proportion of gas directed towards the N0χ trap with respect to the total amount of gas arriving upstream of the bypass valve, and the proportion of gases diverted from the N0χ trap relative to the total amount of gas arriving upstream of the bypass valve. In step 45, the reformate is injected upstream of the NO.sub. Trap to be purged in order to ensure a richness greater than 1 in the trap. Thus, when the bypass valve is completely closed, the reformate can be injected, upstream of the N0χ trap, with a nominal richness or a degraded richness greater than 1. However, if the bypass valve is only partially closed , the injected reformate flow rate will be adjusted so as to obtain a richness greater than 1 within the N0 piè trap to be purged.

The determination of the rate of reformate to be injected during step 45 can be done according to two variants.

According to a first variant, the injected reformate flow rate is set at a predefined value making it possible to obtain a richness greater than 1 in the N0 piè trap to be purged. The duration of the purge is not fixed, and the purge end criterion, in step 46, may be for example the exceeding of a threshold by a quantity measured by a probe placed downstream of the trap to N0χ.

According to a second variant, the reformate flow rate and the duration of the reformate injection in the N0χ trap can be calculated from models or maps implanted in the fifth means (15, 27). Such a model or cartography can for example give the quantity of moles of reductants necessary for the purge of the NOχ trap, from values which can be: the quantity of NOχ and / or SOχ stored in the N0χ trap before the start purging strategy, - the internal temperature or output of the trap N0χ measured or calculated in simulation, the state of aging of the trap N0χ and the reformer, or vehicle mileage, rich reformate R _ref, R _re f can be fixed or variable during the purge, the opening% 0% of the bypass valve to NOO trap to be purged, or the richness of exhaust R _ec h, Rech is either estimated to from injected air and fuel flows in the motor is measured using a wealth of probe placed upstream or downstream of the NO _x trap to purge.

For example, a map may indicate a quantity of reducing gear necessary per mole of N0χ stored as a function of the internal temperature or output of the N0χ trap to be purged.

The fifth means (15, 27) can then deduce the reformate flow rate and / or the duration of the purge.

For example, when the bypass valve is fully closed, the fifth means (15,27) can: set the duration of the purge tp _Urge and deduce therefrom the reformate flow Q _r eformat2 to be injected from the equation ( 4):

I C r \ _ N reducer (Λ \

^{Qrφrmat2 ~} % H _2. % CO. t _purge ⁽⁴⁾

set the reformate flow Q _r eformat2 to inject and deduce the purge duration tp _Urge from equation (5): 0 ¹ reducer

(5)

% H _2. % CO. Q _n φrmatl

choose a pair of values tp _Urge -Qreformat2 optimal determined according to several sizes that can be for example overconsumption, emissions of methane 5 CH ₄ , hydrocarbons, carbon monoxide CO or

N0χ during the purge, or the power available on the alternator to supply the reformer with air. The end of purge criterion used in step 46 can then be the exceeding of the purge time tp _Urge determined previously.

When the bypass valve is partially closed, the fifth means can for example determine the reformate flow rate Q _r e _f o _{rm a} ₂ to inject instantaneously during purge, from equation (6):

o Qrφnna.2 - ^~ v '^" Vo ^• Qoech ^• ( ^P _p ^C _rn

^ PLU ⁰⁺ + ^R _R K _e - Λ _c 'J h fe ^ _[^ K _ref * t -zf C Rθ _cιbk J _⁽⁶ _₆₎₎

in which :

Rcibie represents the target richness at which it is desired to bring the gaseous mixture circulating in the N0 piè trap to be purged, and PCO represents the fuel comburivore power, that is to say the mass / fuel ratio in stoichiometric mixture.

In this case, the end of purge criterion used in step 46 may be, for example, the exceeding of the purge time determined by the fifth means (15, 27), the exceeding of a threshold by a magnitude. measured by a probe placed downstream of the N0χ trap, or the exceeding of a threshold by a variable determined by a model.

Figure 5 shows the flowchart of a second reformer purge strategy. The second reformer purge strategy implements one or more wealth cycles controlled by the bypass valve and the reformate injection. In particular, the bypass valve is periodically controlled during the N0χ and / or SOχ purge, in order to periodically direct the exhaust gases to the N0 piè trap to be purged. This increases the purge efficiency and accelerates the arrival of gases on the probe placed possibly downstream of the N0χ trap.

In a step 50, the fifth means (15, 27) partially or completely closes the bypass valve and, in a step 5 1, the fifth means (15, 27) controls the injection, upstream of the NOχ trap to be purged. , reformat. The reformate injection is triggered simultaneously or in slight time offset with the control of the bypass valve.

In order to carry out richness cycles, the second reformer purge strategy comprises a step 52 during which it is determined, in real time, whether the purge is carried out in a poor cycle or in a rich cycle.

When the purge is carried out in a rich cycle, which is the case for example after the steps 50 and 51, it is ordered, in a step 53, the partial or total opening of the bypass valve, and it stops totally or partially, during a step 54, the reformate injection upstream of the NOχ trap. The purge is then performed in a poor cycle.

When, on the other hand, the purge is carried out in a lean cycle, which is the case for example after the steps 53 and 54, during a step 55, the partial or total closure of the bypass valve is controlled, and injects, during a step 56, the reformate upstream of the NOχ trap. The purge is then performed in a rich cycle.

An end of purge criterion is evaluated, during a step 57, in order to determine when the richness cycles can be stopped. The end of purge criterion used in step 57 can be, for example, the exceeding of the purge time determined by the fifth means, the exceeding of a threshold by a quantity measured by a probe placed downstream of the trap. to NOχ, or the exceeding of a threshold by a variable determined by a model. When the end of purge criterion is not reached, the method returns to step 52 in order to implement an additional richness cycle. When the end of purge criterion is reached, the reformate injection is stopped during a step 58, and the bypass valve is controlled, during a step 59, so as to redirect the exhaust gases towards the NO piè trap.

In the case of the second embodiment (Figure T), the bypass valve 6 will be controlled, in step 59, so directing the exhaust gases to the trap at NO2, or to the trap at NOχ18, or at the two traps at NOχ2, 18 simultaneously.

Thus, the second reformer purge strategy can implement, every x seconds (x being between 0 and 10 for a purge NOχ, and between 0 and 180 for a purge SOχ) and for y seconds (y being between 0 and 10 for a NOχ purge, and between 0 and 180 for a SOχ purge), the opening of the bypass valve and the decrease or stop of the reformate injection upstream of the NOχ trap. After y seconds, the bypass valve can then be partially or completely closed, and the reformate can be injected again upstream of the NOχ trap.

In particular, the percentage of opening of the bypass valve and the rate of reformate injected upstream of the NOχ trap can vary continuously or abruptly during the course of the various richness cycles. Thus, according to a first variant, the percentage of opening of the bypass valve and the rate of injected reformate can each take a predefined value during the rich cycle and another predefined value during the lean cycle, with a rapid variation of a value to each other at each cycle change. In contrast, according to a second variant, the percentage of opening of the bypass valve and the rate of injected reformate can each take a sinusoidally evolving value in time between a maximum value corresponding to a cycle and a minimum value corresponding to the other cycle. However, continuous or sudden variations in the percentage of opening of the bypass valve and the rate of reformate injected can also be independent. For example, the reformate injection may vary according to a pattern stored in the fifth means (15, 27), while the opening percentage of the bypass valve may vary sinusoidally in time.

The reformate flow rate, the total purge time and the control law of the bypass valve can be determined from analogously from the same input quantities as in the first reformer purge strategy described in Figure 4.

In the case of the second embodiment (Figure T), the fifth means 27 can also take advantage of the second reformer purge strategy described above, to purge the two traps N0χ 2, 18 simultaneously. In this case, the purge steps for each N0χ trap are identical to the steps shown in FIG. 5, except for the reformate injection stop step 54 and the reformate injection step 56 which will respectively correspond to each other. to a partial or total closure and a partial or total opening of the reformate valve 21. Thus, by controlling the bypass valve 6 and the reformate valve 21, it is possible to simultaneously place a trap N0χ in a rich cycle and the other traps N0χ in a poor cycle. Since the second reformer purge strategy comprises richness cycles, it is then possible, by periodically controlling the bypass valve 6 and the reformate valve 21, to perform richness cycles for each NO _x 2 trap, 18. The time lag between a rich cycle in a N0χ trap, for example the N0χ 2 trap, and a rich cycle in the other N0χ trap, for example the N0χ trap, is then equal to the N0χ trap. 'a cycle. Finally, the bypass valve 6 and the reformate valve 21 may also vary abruptly or continuously in time.

Figure 6 shows the flowchart of a third reformer purge strategy. The third reformer purge strategy implements one or more wealth cycles controlled by the richness of the air-fuel mixture feeding the reformer. In particular, the reformer is periodically controlled during the N0χ and / or SOχ purge, in order to modify the richness of the reformate produced and injected upstream of the N0χ trap. This increases the efficiency of the purge.

In a step 60, the fifth means (15, 27) partially or completely closes the bypass valve and, in a step 61, the fifth means (15, 27) controls the injection, upstream of the NOχ trap to purge, reformate to a richness R _ref nominal greater than 1. The injection of reformate is triggered simultaneously or in slight time difference with the control of the bypass valve. In order to carry out richness cycles, the third reformer purge strategy comprises a step 62 during which it is determined, in real time, whether the purge is carried out in a poor cycle or in a rich cycle.

When the purge is carried out in a rich cycle, which is the case for example after steps 60 and 61, the partial or total opening of the bypass valve is controlled during a step 63, and during a step 64, the richness R _ref of the reformate injected upstream of the trap NOχ so that it is between 0 and 1. purging is then carried out in a poor cycle. When, on the other hand, the purge is carried out in a lean cycle, which is the case for example after the steps 63 and 64, the partial or total closure of the bypass valve is commanded during a step 65, and inj ect, in a step 66, the reformate to a richness R _ref nominal greater than 1. purging is then carried out in a rich cycle.

An end of purge criterion is evaluated, in a step 67, to determine when the richness cycles can be stopped. The end of purge criterion used in step 67 may be, for example, the exceeding of the purge time determined by the fifth means, the exceeding of a threshold by a quantity measured by a probe placed downstream of the trap. to NOχ, or the exceeding of a threshold by a variable determined by a model. When the end of purge criterion is not reached, the method returns to step 62 in order to implement an additional richness cycle. When the end of purge criterion is reached, the reformate injection is stopped during a step 68, and the bypass valve is controlled, during a step 69, so as to redirect the exhaust gases towards the NO piè trap. In the case of the second embodiment (FIG. 2), the bypass valve 6 will be controlled, during the step 69, so as to direct the exhaust gases towards the NO 2 trap or the NO 5 trap. 18, or to the two traps at N0χ 2, 18 simultaneously. Thus, the third reformer purge strategy can implement, every x seconds (x being between 0 and 10 for a purge N0χ, and between 0 and 180 for a purge SOχ) and for y seconds (y being between O and 10 for a purge N0χ, and between 0 and 180 for a purge SOχ), the opening of the bypass valve and the reduction of the richness R _re f of the reformate injected upstream of the trap.

NOχ. After y seconds, the bypass valve may then be partially or totally closed, and the reformate can be injected again upstream of the trap NOχ, with a richness R _re higher nominal f 1 in favor purge NOχ and / or SOχ. In particular, the percentage of opening of the bypass valve and the richness R _re f of the reformate injected upstream of the NOχ trap can vary continuously or abruptly during the course of the various richness cycles. Thus, according to a first variant, the percentage of opening of the bypass valve and the richness R _ref of the injected reformate can each take a predefined value during the rich cycle and another predefined value during the poor cycle, with rapid variation. from one value to another at each cycle change. On the contrary, in a second variant, the percentage of opening of the bypass valve and the richness R _ref of the reformate injected may each take a value evolving sinusoidally with time between a maximum value corresponding to a cycle and a value minimum corresponding to the other cycle. However, the variations, continuous or sudden, of the opening percentage of the bypass valve and the richness R _re f of the injected reformate can also be independent. For example, the richness R _ref of the injected reformate may vary according to a pattern stored in the fifth means (15, 27), while the opening percentage of the bypass valve may vary sinusoidally in time. According to another variant, the bypass valve can be controlled by the fifth means (15, 27) so as to be partially or completely closed at the beginning of the third reformer purge strategy, and open only at the end of the third strategy. purge. In this case, steps 63 and 65 of the flowchart shown in Figure 6 are deleted.

The reformate flow rate, the total purge time and the control law of the bypass valve can be determined analogously from the same input quantities as the first reformer purge strategy described in figure 4.

Figure 7 shows the flowchart of a first reformer purge and engine control strategy. At the initiation of the purge, during a step 70, the richness R _ec h of the exhaust gases from the engine is increased to a value between 0.9 and 1.0 by a suitable engine control strategy. This enrichment is carried out for example by an enrichment of the air-fuel mixture feeding the engine. The bypass valve is then preferably controlled so as to direct all of the exhaust gas to the NOχ trap to be purged. However, it is also possible to control the bypass valve so as to orient a portion of the exhaust gases to the NOχ trap.

Simultaneously or in slight time difference with step 70, the inj ection of a reformate flow rate Q _r eformat3 upstream of NOχ trap is triggered, during a step 71, so as to obtain a target richness R _C ibie greater than 1 in the NOχ trap.

The percentage of opening of the bypass valve and the target richness R _C ibie will be determined by the fifth means (15, 27), from a map or an implanted model. The model or mapping inputs may be: the temperature of the NOχ trap to be purged, the temperature of the particulate filter and / or the oxidation catalyst, the amount of NOχ and / or SOχ to be purged before and during the purge , the flow rate Q _ec h and the richness R _ech of the exhaust gas, or even the point of operation of the engine before and during the purge. These quantities can be measured or well calculated. Finally, the richness R _C ibie and the opening percentage of the bypass valve can be chosen so as to best meet the constraints taken into account by the fourth means.

The injected reformate flow Q _r eformat3 can be determined instantaneously during the purge, from equation (7):

An end of purge criterion is evaluated, in a step 72, to determine when the steps 70 and 71 can be stopped. The end of purge criterion used in step 72 may be, for example, the exceeding of the purge time determined by the fifth means (15, 27), the exceeding of a threshold by a quantity measured by a probe. placed downstream of the NO _x trap, or the exceeding of a threshold by a variable determined by a model.

When the end of purge criterion is not reached, the process returns to step 70 to continue the purge. When the end of purge criterion is reached, the reformate injection is stopped during a step 73 and, simultaneously or shortly thereafter, the engine control is stopped during a step 74, that is to say say that the motor is controlled so that it returns to nominal operation.

In the case of the second embodiment (FIG. 2), the fifth means 27 can also take advantage of the first reformer purge and motor control strategy described above, to purge the two NO à 2 traps 18 simultaneously. In this case, the different steps of the flowchart shown in FIG. 7 are applied to each trap at NOχ 2, 18.

More particularly, the bypass valve 6 is preferably controlled so as to direct the exhaust gases to the two NO piè traps. % O2, the percentage of opening of bypass valve 6 to NO le 2 trap, and% Ois, the percentage of opening of bypass valve 6 to the trap at NOχ 18, with:% Oi ₈ +% O2 = 1. In addition, the reformate is injected upstream of the trap N0χ 2 with a flow Q _r eformat4 so as to ensure a target richness R _C ibie2 greater than 1 in the trap at N0χ 2, and upstream of the NOχ 18 trap with a Qreformats rate so as to ensure a target richness R _C ibiei8 greater than 1 in the N0χ trap 18.

The percentage of opening of the bypass valve and the target richness R _C ibie2, Rcibieis in the traps at NO 2, 18 will be determined by the fifth means, from a mapping or an implanted model. The inputs of the model or the mapping may be: the temperature of the traps at NO 2, 18, the temperature of the particulate filter and / or the oxidation catalyst, the quantity of N0χ and / or SOχ to be purged before and during the purge, the flow rate Q _ec h and the richness R _ech of the exhaust gas, or even the point of operation of the engine before and during the purge. These quantities may be measured or calculated. Finally, the wealth R _C ibie2,

Rcibieis and the percentage of opening of the bypass valve may be chosen so as to best satisfy the constraints taken into account by the fourth means.

The injected reformate flows Q _r eformat4, Qreformats can be determined instantaneously during the purge, from equations (8) and (9): n, -OΛ

Qrφnna.Λ = o ^/ _/ ^θ n ^O 2 ^• n Qech ^• (»)

O _«" - -% Zo0O ₁₈ • OQ _{ech (} ( ₉ 9 ₎ )

The reformate valve 21 and the reformer 8 can then be controlled to obtain the desired reformate flow rates upstream of the NO _x 2, 18 traps.

Figure 8 shows the flowchart of a second reformer purge and engine control strategy during which the value of the target richness R _C ibie varies during the purge procedure. The second reformer purge and engine control strategy implements one or more wealth cycles. The richness is controlled for example by the rate of injected reformate, and / or by the richness of the reformate, and / or by the engine control command; in the example shown in Figure 8, the wealth will be controlled by the engine control command and by the injection or not of reformate. Thus, the reformer and the motor will be periodically controlled during the purge N0χ and / or SOχ, in order to modify the richness of the reformate and the exhaust gases. This increases the efficiency of the purge. In a step 80, the richness R _ec h of the exhaust gases from the engine is increased to a value between 0.9 and 1.0 by a suitable engine control strategy. This enrichment is carried out for example by an enrichment of the air-fuel mixture feeding the engine. The bypass valve is then preferably controlled so as to direct all of the exhaust gas to the NOx trap to be purged. However, it is also possible to control the bypass valve so as to direct only a portion of the exhaust gas to the NO _x trap.

Simultaneously or in slight time offset with step 80, the reformate injection upstream of the NOχ trap is triggered, during a step 81, so as to ensure a target richness R _C ibie greater than 1 in the trap. NOχ.

In order to carry out richness cycles, the second reformer purge and motor control strategy comprises a step 82 during which it is determined, in real time, whether the purging is carried out in a lean cycle or in a rich cycle.

When the purge is carried out in a rich cycle, which is the case for example after steps 80 and 81, it controls, in a step 83, the engine so that the exhaust gas regains a lower to 1 (nominal operation of the engine), and one stops, during a step 84, the injection of reformate upstream of the NOχ trap. The richness of the gaseous mixture passing through the NO piè trap to be purged is then less than 1: the purge is carried out in a poor cycle. When, on the other hand, the purge is carried out in a lean cycle, which is the case for example after steps 83 and 84, the engine is controlled, in a step 85, so that the exhaust gases present a richness close to 1, and is injected, in a step 86, the reformate upstream of the N0χ trap. The richness of the gaseous mixture passing through the NO.sub. Trap to be purged is then greater than 1: the purge is carried out in a rich cycle.

An end of purge criterion is evaluated, during a step 87, to determine when the richness cycles can be stopped. The end of purge criterion used in step 87 may be, for example, the exceeding of the purge time determined by the fifth means (15, 27), the exceeding of a threshold by a quantity measured by a probe. placed downstream of the N0χ trap, or the exceeding of a threshold by a variable determined by a model. When the end of purge criterion is not reached, the method returns to step 82 in order to implement an additional richness cycle. When the criterion of end of purge is reached, one stops, during a step 88, the injection of reformate upstream of the trap with N0χ and, simultaneously or shortly after, one controls, during a step 89, the engine so that the exhaust gas regains a richness of less than 1 (nominal engine operation).

Thus, the second strategy of purge by reformer and motor control can implement, every x seconds (x being between 0 and 10 for a purge NOχ, and between 0 and 180 for a purge

SOχ) and for y seconds (ranging between 0 and 10 for NO _x purge, and between 0 and 180 for SOχ purge), stopping engine control and stopping the reformate injected upstream of the N0χ trap. . After y seconds, the engine control can be used again to increase the richness of the exhaust gases, and the reformate can be injected again upstream of the NOχ trap.

In particular, the engine control and the reformate flow injected upstream of the NOχ trap can vary continuously or abruptly during the course of the various richness cycles. Thus, the motor control and the reformate flow injected upstream of the N0χ trap can each take a predefined value during the rich cycle and another predefined value during the lean cycle, with a rapid variation from one value to another at each cycle change. In contrast, according to a second variant, the motor control and the reformate flow injected upstream of the N0χ trap can each take a sinusoidal value in time between a maximum value corresponding to a cycle and a minimum value corresponding to 1 another cycle. However, the continuous or sudden variations of the motor control and the injected reformate flow can also be independent.

In the case of the second embodiment (FIG. 2), the fifth means 27 can also take advantage of the second reformer purge and engine control strategy described above, in order to purge the two traps at NO 2, 18 simultaneously. In this case, the different steps of the flow chart shown in FIG. 8 are applied to the two NO à 2, 18 traps. More particularly, the bypass valve 6 is preferably controlled so as to direct the exhaust gases towards both of them. traps NOχ 2, 18, and steps 80 to 89 are applied simultaneously to the two traps NOχ 2, 18. However, in the second embodiment, it is also possible to control the richness of the gases passing through traps NOχ 2 , 18, by controlling the opening percentage of the by - pass valve 6 and the reformate valve 21.

The fifth means (15, 27) can finally implement a bleed strategy by engine control alone. At the initiation of the purge, the richness R _ec h of the exhaust gases from the engine is increased to a value between 1.01 and 1.5 by a suitable engine control strategy. This enrichment is carried out for example by an enrichment of the air-fuel mixture feeding the engine. The bypass valve is then preferably controlled so as to direct all of the exhaust gas to the NOχ trap to be purged. However, it is also possible to order the bypass valve so as to orient a portion of the exhaust gases to the NO _x trap.

The percentage of opening of the bypass valve will be determined by the fifth means (15, 27) from a mapping or implanted model. Model or mapping inputs may be: N0χ trap temperature to be purged, particulate filter and / or oxidation catalyst temperature, N0χ and / or SOχ quantity to purge before and during purge the speed and extensive R _ec h of exhaust gas, or else the point of engine operation before and during purging. These quantities may be measured or calculated.

An end of purge criterion is evaluated to determine when the purge can be stopped. The end of purge criterion used can be, for example, the exceeding of the purge time determined by the fifth means (15, 27), the exceeding of a threshold by a quantity measured by a probe placed downstream of the trap. N0χ, or the exceeding of a threshold by a variable determined by a model. When the end of purge criterion is not reached, the purge continues. When the purge end criterion is reached, the motor control is stopped, that is, the motor is controlled so that it returns to a nominal operation.

In the case of the second embodiment (FIG. 2), the fifth means 27 can also take advantage of the strategy of purging by motor control alone described above, to purge the two traps N0χ 2, 18 simultaneously. In this case, the bypass valve 6 will be controlled so as to direct the exhaust gases towards the two NO _x traps.

The only engine control purge policy can also implement wealth of cycles during which the value of wealth R _ec h of exhaust gases varies during the purging procedure. Wealth is controlled by the engine control command. Thus, for example, the flow diagram of FIG. 8 can be resumed, with the exception of steps 81, 84, 86 and 89 of injection and reformate injection stoppage in the gas routing circuit, so that to implement the strategy of purging by engine control alone with cycles of wealth.

It should be noted that, depending on the evolution of the operating parameters of the routing circuit and / or the engine, a purge strategy may be interrupted in favor of another strategy for which the operating parameters have become favorable. For example, a purge by engine control and reformer can be transformed into purge by reformer alone if the operating conditions of the engine become unfavorable to the use of engine control. Similarly, a purge by engine control and reformer can be converted to purge by engine control only if the operating conditions of the engine become favorable to the use of engine control alone.

It should also be noted that, in the foregoing detailed description, the purge strategies can also be applied to a particulate filter impregnated with a catalyst for the adsorption and desorption of NO.sub.O and / or SO.sub.O in a manner analogous to a NO _x trap and can therefore be considered a N0χ trap.

Claims

A method of purging a NOx trap (2, 18) from a process module (1, 17) of exhaust gases produced by an internal combustion engine (16) of a motor vehicle, comprising:

- an exhaust gas routing circuit,

- a NO _x trap (2, 18) mounted in the conveying circuit and traversed by a gaseous mixture; the N0χ trap (2, 18) being capable of trapping oxides of nitrogen and / or oxides of sulfur present in the gaseous mixture when the richness of the gaseous mixture is less than 1,

- a bypass line (5) mounted in the routing circuit, in parallel with the N0χ trap (2, 18),

a reformer device (8) capable of supplying a gas rich in hydrogen and / or carbon monoxide, in which:

the state of loading of the N0χ trap (2, 18) is evaluated,

the evaluated loading state is compared with a stored or determined threshold, the values of the operating parameters of the routing circuit and / or the motor (16) are determined,

comparing said operating parameter values with stored or determined ranges of values,

the reformer (8) and / or the motor (16) are controlled so as to modify said values of operating parameters towards the stored or determined ranges of values when said values of operating parameters of the routing circuit and / or the motor (16) are not in said stored or determined range of values, and so as to purge the NOx trap (2, 18) when said values of operating parameters of the routing circuit and / or the motor (16) are in said ranges of stored or determined values.

2. Method according to claim 1, wherein the operating parameter or parameters of the routing circuit and the motor (16) are chosen from: the internal temperature or output of the N0χ trap (2, 18), the operating point; of the engine (16), the instantaneous position of the accelerator pedal or its time derivative, and the temperature of a particulate filter (3) or an oxidation catalyst (4) mounted downstream of the NO.sub.O trap. (2, 18).

3. Method according to claim 1 or 2 wherein the values of the operating parameters are modified by adding gas rich in hydrogen and / or carbon monoxide in the gaseous mixture.

4. Method according to one of claims 1 to 3 wherein the values of the operating parameters are modified by modifying the operation and / or the supply of the engine (16) so that the exhaust gases included in the gaseous mixture have a higher richness and / or a higher temperature.

5. Method according to one of claims 1 to 4 wherein the values of the operating parameters are modified by modifying the operation and / or the power supply of the engine (16) so as to reduce the quantities of hydrocarbons, carbon monoxide CO or N0χ carbon in the engine exhaust.

6. Method according to one of claims 1 to 5 wherein purge NO0 trap (2, 18) by adding gas rich in hydrogen and / or carbon monoxide, and decreasing or canceling the proportion of gases. exhaust in the gaseous mixture passing through said NO _x trap (2, 18).

7. Process according to claim 6, in which the NO 2 trap (2, 18) is purged by varying:

- the richness (R _ref) of the hydrogen rich gas and / or carbon monoxide, - and / or the relative proportion of hydrogen-rich gas and / or carbon monoxide, and exhaust gas in the mixture gaseous so as to successively obtain a reducing gas mixture, an oxidizing gas mixture and a reducing gas mixture.

8. Method according to one of claims 1 to 7 wherein the bypass line (5) comprises an N0χ trap (18), and wherein is purged each N0χ trap (2, 18) alternately or simultaneously.

9. Module for treating (1, 17) exhaust gases produced by an internal combustion engine (16) of a motor vehicle, comprising:

- an exhaust gas routing circuit,

- N0χ trap (2, 18) mounted in the routing circuit and capable of being traversed by a gaseous mixture; the NO à trap (2,

18) being capable of trapping oxides of nitrogen and / or oxides of sulfur present in the gas mixture when the richness of the gaseous mixture is less than 1,

a reformer device (8) capable of supplying a gas rich in hydrogen and / or carbon monoxide, characterized in that the module (1, 17) also comprises an electronic control unit (10, 22) comprising: first means (1 1, 23) capable of evaluating the state of loading of the NOχ trap (2, 18),

a second means (12, 24) capable of comparing the loading state evaluated by the first means (1 1, 23) with a threshold stored in or determined by the second means (12, 24), - a third means ( 13, 25) capable of determining values of operating parameters of the routing circuit and / or the motor (16),

fourth means (14, 26) capable of comparing said values of operating parameters with ranges of values stored or determined by the fourth means (14, 26),

a fifth means (15, 27) capable of controlling the reformer (8) and / or the motor (16) so as to modify said values of operating parameters towards the ranges of values stored or determined by the fourth means (14, 26) when said operating parameter values of the routing circuit and / or the motor (16) are not in said stored or determined range of values, and so as to purge the NOx trap (2, 18) when said parameter values operating mode of the routing circuit and / or the motor (16) are in said range of values stored or determined by the fourth means (14, 26).

The treatment module (1, 17) of claim 9 wherein the bypass line (5) comprises a NO x trap (18).

A propulsion system of a motor vehicle comprising an internal combustion engine and an exhaust gas treatment module (1, 17) according to claim 9 or 10.