FR3072419A1 - METHOD FOR REPLACING A REDUCING AGENT INJECTION IN AN EXHAUST LINE OF A THERMAL ENGINE - Google Patents

Abstract

The invention relates mainly to a method for resetting a reducing agent injection in an exhaust line (1) of a heat engine (2), in particular a vehicle automobile, said exhaust line (1) comprising a system for exhaust gas pollution (3) comprising: - a system for reducing nitrogen oxides contained in the exhaust gases; Exhaust comprising a reducing agent injection system (5) and a catalyst (6), and - a combined probe (10) placed upstream of the catalyst (6) and downstream of the system injection device (5), characterized in that said method comprises: - a tipping step of information relating to a measurement of nitrogen oxides from the combined probe ( 10) to information relating to a measurement of ammonia from the combined probe (10), - a comparison step between a quantity of injected reducing agent and a quantity of agent Result © requested driver, and - a step of adjusting the reducing agent injection according to this comparison.

Description

The present invention relates to a method for adjusting the injection of a reducing agent into an exhaust line of the present invention. a heat engine.

In a manner known per se, the heat engines are cleaned using several functional pollution control elements. Thus, for a diesel type engine for example, it is possible to install on the exhaust line an oxidation catalyst (or DOC for Diesel Oxidation Catalyst in English) allowing the oxidation of hydrocarbons (HC) and carbon monoxide (CO) in carbon dioxide and in water, or a passive nitrogen oxide adsorber (or PNA for Passive NOx Adsorber) which allows to carry out the same reactions as an oxidation catalyst and has in addition, an ability to store nitrogen oxides at low temperature (when an SCR catalyst is not active) and to destock them at higher temperature (when the SCR catalyst is active).

The selective catalytic reduction system catalyst (or SCR for Selective Catalytic Reduction in English) makes it possible to store the ammonia resulting from an injection of reducing agent to reduce the nitrogen oxides (NOx) contained in the gases. exhaust. A particulate filter makes it possible to trap particles contained in the exhaust gases, in particular in the form of soot. It is also possible to use a reduction catalyst (or ASC for Ammonia Slip Catalyst in English) to remove the ammonia (NH ₃ ) in excess in the exhaust gases.

The operation of the SCR system is based on a chemical reaction between the nitrogen oxides and a reducing agent conventionally taking the form of ammonia. The injection of ammonia into the exhaust line is generally carried out via another chemical species, such as a urea-based reducing agent which decomposes into ammonia and carbon dioxide under the effect of heat.

A nitrogen oxide measurement probe, called a NOx probe, placed upstream of the SCR system makes it possible to calculate an amount of ammonia to be injected into the exhaust line to treat it. This NOx probe is replaced by a model of nitrogen oxide emissions at the engine outlet in certain life cases.

A second NOx probe placed downstream of the SCR catalyst makes it possible to regulate the depollution system and also to diagnose its operation. Thus, if the production of nitrogen oxides measured at the outlet of the SCR system is not at the required level, the engine ECU adjusts the amount of reducing agent injected.

However, each of these elements is dispersed, that is to say imprecise in relation to the expected behavior. These dispersions lead either to cases of excess emission of nitrogen oxides downstream of the SCR system due to insufficient injections, or to cases of excess emission of ammonia downstream of the SCR system due to excess injections .

There are strategies for correcting these dispersions based on the information from the two NOx probes. Indeed, these probes measure nitrogen oxides and ammonia but cannot distinguish them when these two chemical species are present simultaneously.

Known strategies correct the overall effect of dispersions taken individually or simultaneously. An injector which over-injects X% or a NOx probe upstream of the SCR system which tailor-made by X% will create the same phenomenon of excess ammonia release. These strategies can correct it but without differentiating the source of the dispersion. Similarly, an injector which over-injects X% and a NOx probe upstream of the SCR system which tailor-made by X% will create even more ammonia release in the exhaust. These strategies can correct it but without assigning a specific correction to each of the dispersions.

The invention aims to effectively remedy this drawback by proposing a method of registration of an injection of reducing agent in an exhaust line of a heat engine, in particular of a motor vehicle, said line of exhaust comprising an exhaust gas depollution system comprising:

a system for reducing nitrogen oxides contained in the exhaust gases comprising a system for injecting a reducing agent and a catalyst, and

- a combined probe placed upstream of the catalyst and downstream of the injection system, characterized in that said method comprises:

a step for switching information relating to a measurement of nitrogen oxides from the combined probe to information relating to a measurement of ammonia originating from the combined probe,

a step of comparison between a quantity of reducing agent injected and a quantity of reducing agent requested, and

a step of adjusting the injection of reducing agent as a function of this comparison.

The invention thus makes it possible to carry out a targeted correction of the dispersion of the injection system compared to the other sources of dispersion. In particular, this correction is carried out independently of the dispersion of the NOx probes. The invention also makes it possible to obtain a better compromise between the control of nitrogen oxides at the cannula to comply with regulatory requirements (WLTC approval for Worldwide harmonized Light vehicles Test Cycle in English and RDE criterion for Real Drive Emissions in English) and reducing the release of ammonia, which generates an unpleasant odor for pedestrians.

According to one implementation, the comparison step is implemented when a cumulative reducing agent injected exceeds a calibratable threshold. This makes it possible to limit calculation errors.

According to one implementation, the comparison step is performed by comparing a ratio between a cumulative injected reducing agent and a cumulative requested reducing agent with a calibratable threshold.

According to one implementation, the step of adjusting the injection of reducing agent is carried out by adapting a correction factor applied to the injections.

According to one implementation:

- in the case where the ratio is greater than the calibratable threshold, the correction factor is adjusted by removing a calibratable value, and

- in the case where the ratio is lower than the calibratable threshold, the correction factor is adjusted by adding a calibratable value.

According to one implementation, following the switching of the combined probe to information relating to an ammonia measurement, the method comprises a step of estimating nitrogen oxides using a model of estimation of nitrogen oxide emissions at the outlet of the heat engine.

According to one implementation, the method is implemented at the start of each run.

According to one implementation, the method is implemented at a calibrated kilometer frequency.

The invention also relates to an engine computer comprising a memory storing software instructions for the implementation of the method of registration of an injection of reducing agent in an exhaust line of a heat engine such as previously defined.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given only by way of illustration but in no way limit the invention.

Figure 1 is a schematic representation of an exhaust gas depollution system capable of implementing the method according to the invention of registration of an injection of reducing agent in an exhaust line;

Figure 2 is a schematic representation of the different functions implemented in the engine computer and implemented with the method according to the invention of registration of an injection of reducing agent in the exhaust line of a heat engine .

Figure 1 shows an exhaust line 1 of a heat engine 2, in particular of a motor vehicle, on which is mounted a pollution control system 3 of the exhaust gases.

This pollution control system 3 includes functional elements, such as a 4-oxidation catalyst Diesel (or DOC for Diesel Oxidation Catalyst) allowing the oxidation of hydrocarbons (HC) and carbon monoxide (CO) in carbon dioxide and water.

A selective catalytic reduction system (or SCR for Selective Catalytic Reduction in English) comprises an injection system 5 for injecting a reducing agent into the exhaust line 1, such as urea, which breaks down into ammonia and carbon dioxide under the effect of heat. One or more catalysts 6 make it possible to store the ammonia in order to transform the nitrogen oxides (NOx) contained in the exhaust gases into nitrogen and water. Advantageously, a mixing box 7 promotes the decomposition of the urea necessary for the reactions for treating nitrogen oxides.

A particle filter 8 allows to trap solid or liquid particles consisting essentially of carbon-based soot, and / or oil droplets. These particles typically have a size of between a few nanometers and a micrometer.

In addition, an ASC type reduction catalyst 9 (for Ammonia Slip Catalyst in English) is able to remove at least partially the ammonia particles contained in the exhaust gas.

A combined measurement probe 10, disposed upstream of the SCR catalyst 6 and downstream of the injection system 5, makes it possible to selectively supply INOx information relating to a measurement of nitrogen oxides or relative l_NH ₃ information to a measurement of ammonia. Preferably, the probe 10 is positioned downstream of the mixing box 7. Information provided by the probe 10 is for example a rate of these substances in the exhaust gases. This rate is for example expressed in ppm (Part Per Million) and could be transformed, if necessary, into a flow rate by the engine computer 12. This probe 10 is however not capable of supplying these two pieces of information I NOx, l_NH ₃ at the same time. This probe 10 is replaced by a model for estimating emissions of nitrogen oxides at the outlet of engine 2 in certain life cases, in particular when the information coming from probe 10 is unavailable, as is explained more in detail. details below.

A second probe 11 placed downstream of the SCR catalyst 6 makes it possible to regulate the depollution system 3 and to diagnose its operation. Thus, if the production of nitrogen oxides measured at the outlet of the SCR system is not at the required level, it is possible to adjust the quantity of reducing agent injected.

The engine computer 12 (or ECU for Engine Control Unit in English) in particular controls the heat engine 2, as well as management of the various functional elements 4, 5, 6, 8, 9, 10, 11.

Described below, with reference to FIG. 2, the method for managing the various functions implemented by the engine computer 12 as a function of the tilting of the combined probe 10 of a mode of measurement of oxides d 'nitrogen M_mes_NOx to an ammonia measurement mode M_mes_NH ₃ .

In the measurement mode of nitrogen oxides M_mes_NOx, the combined probe 10 provides the I NOx information relating to the measurement of nitrogen oxides Mes_NOx to allow the implementation of the oxides treatment function d 'nitrogen Trait_NOx. This Trait_NOx function calculates the quantity of ammonia to be injected as a function of the I NOx information relating to the measurement of nitrogen oxides Mes_NOx returned by the probe 10.

The estimation function of nitrogen oxides Est_NOx on the basis of a Mod_NOx model as well as the correction function Corrsysjnj of the dispersion of the injection system 5 are deactivated.

In the ammonia measurement mode M_mes_NH ₃ , the combined probe 10 provides information l_NH ₃ relating to the measurement of ammonia Mes_NH ₃ to allow the implementation of the correction function Corr sysjnj of the dispersion of the system 5. This Corr sysjnj function is used to measure the ammonia actually injected and to compare it with the ammonia required by the injection system 5. The dispersions of the injection system 5 are then corrected according to this comparison .

To this end, a correction factor K inj is provided, which is applied continuously to the injections and which is saved between each run in a memory of the engine control unit 12. This factor K inj is equal to 1 at the start of the vehicle's life .

More specifically, during the activation of the Corr sysjnj function, the amount of ammonia requested by the SCR system as well as the amount of ammonia actually injected by the SCR system are integrated as a function of time. If the cumulative ammonia to be injected exceeds a calibratable threshold S_NH ₃ , the computer 12 performs a fault detection calculation. The calibratable threshold S_NH ₃ is high enough to reduce the calculation errors. The threshold S_NH ₃ is for example between 100 mg and 1 g.

According to the fault detection calculation, the computer 12 determines the ratio R between the cumulative ammonia injected and the cumulative ammonia requested.

If this ratio R is greater than a calibratable threshold S_max, this means that the injection system 5 over-injects ammonia with respect to the quantity necessary for the treatment of nitrogen oxides. The correction factor K inj is then adjusted by subtracting from it a certain calibratable value. This calibratable value can for example have a working step of between 0.01 and 0.1. The smaller the working step, the more precise the adjustment.

If this ratio R is less than a calibratable threshold S_min, the injection system 5 sub-injects ammonia with respect to the quantity necessary for the treatment of nitrogen oxides. The correction factor K inj is then adjusted by adding a certain calibratable value to it. This calibratable value can for example have a working step of between 0.01 and 0.1. The smaller the working step, the more precise the adjustment.

In the case where the ratio R is between S_min and S_max, the correction factor K inj is unchanged. A dead band is thus defined to avoid inadvertent registration of the reducing agent injection system 5.

It should be noted that when the combined probe 10 measures the ammonia to allow the operation of the correction function Corrsysjnj of the dispersion of the injection system 5, the probe 10 can no longer measure the nitrogen oxides and therefore no longer provides the INOx information to the nitrogen oxides treatment function Trait_NOx.

However, it is essential to continue the ammonia injections to continue the treatment of nitrogen oxides. Consequently, in the ammonia measurement mode M_mes_NH ₃ , the computer 12 activates the function for estimating the emissions of nitrogen oxides Est_NOx at the output of the engine 2 to provide an estimate of the information I NOx to the nitrogen oxides treatment function Trait_NOx.

This Est_NOx estimate based on a Mod_NOx model implemented in the engine computer 12 is less precise than the Mes_NOx measurement carried out by the probe 10, but this does not pose any problem for the management of nitrogen oxides, insofar as its use is temporary and lasts only the time to correct the dispersion of the injection system 5.

The injection system 5 is dispersed from the factory because of manufacturing dispersions. This dispersion also changes over time. It is therefore useful to launch this dispersion correction strategy during the life of the vehicle. The correction function Corr sysjnj of the dispersion of the injection system 5 can thus be activated at the start of each taxiing and / or at a calibratable mileage frequency.

Claims (9)

1. Method for the registration of an injection of a reducing agent in an exhaust line (1) of a heat engine (2), in particular of a motor vehicle, said exhaust line (1) comprising a depollution of exhaust gases comprising: a system for reducing nitrogen oxides contained in the exhaust gases comprising an injection system (5) of reducing agent and a catalyst (6), and - a combined probe (10) placed upstream of the catalyst (6) and downstream of the injection system (5), characterized in that said method comprises: - a step for switching information (I NOx) relating to a nitrogen oxide measurement (Mes_NOx) from the combined probe (10) to information (l_NH ₃ ) relating to an ammonia measurement (Mes_NH ₃ ) from the combined probe (10), a step of comparison between a quantity of reducing agent injected and a quantity of reducing agent requested, and a step of adjusting the injection of reducing agent as a function of this comparison. 2. Method according to claim 1, characterized in that the comparison step is implemented when a cumulative reducing agent injected exceeds a calibratable threshold (S_NH ₃ ). 3. Method according to claim 1 or 2, characterized in that the comparison step is carried out by comparing a ratio (R) between a cumulative of reducing agent injected and a cumulative of reducing agent requested with a calibratable threshold (S_max , S_min). 4. Method according to any one of claims 1 to 3, characterized in that the step of adjusting the injection of reducing agent is carried out by adapting a correction factor (KJnj) applied to the injections. 5. Method according to claims 3 and 4, characterized in that: - in the case where the ratio (R) is greater than the calibratable threshold (S_max), the correction factor (KJnj) is adjusted by withdrawal of a calibratable value, and - in the case where the ratio (R) is lower than the calibratable threshold (S_min), the correction factor (KJnj) is adjusted by adding a calibratable value. 6. Method according to any one of claims 1 to 5, characterized in that following the switching of the combined probe (10) to information (l_NH ₃ ) relating to an ammonia measurement (Mes_NH ₃ ), the method comprises an estimation step (Est_NOx) of nitrogen oxides using a model (Mod_NOx) of estimation of oxide emissions 5 of nitrogen at the outlet of the heat engine (2). 7. Method according to any one of claims 1 to 6, characterized in that it is implemented at the start of each run. 8. Method according to any one of claims 1 to 7, characterized in that it is implemented at a calibratable kilometric frequency. 10 9. Engine computer (12) comprising a memory storing software instructions for implementing the method of resetting an injection of reducing agent in an exhaust line (1) of a heat engine (2) such as defined in any one of the preceding claims.