FR3160433A1 - Method for adjusting the richness of a spark-ignition internal combustion engine equipped with a three-way catalyst - Google Patents

Abstract

This method for adjusting the richness of a spark-ignition internal combustion engine (1) equipped with a three-way catalyst (5) configured to treat pollutant emissions from the engine (1), comprises the steps of: modulating the richness at a first predetermined frequency and with a predetermined richness amplitude centered around a constant average richness; monitoring the voltage across a binary richness probe (7b) arranged downstream of the catalyst (5) and identifying voltage peaks representative of a leak; calculating a second frequency representative of a frequency of occurrence of the identified voltage peaks; comparing the second frequency with the first frequency; and reducing the richness amplitude when the absolute value of the difference between the second and first frequencies is less than or equal to a predetermined threshold value. Figure for abstract: Figure 1

Description

Method for adjusting the richness of a spark-ignition internal combustion engine equipped with a three-way catalyst

The technical field of the invention is the depollution of exhaust gases from a spark-ignition internal combustion engine equipped with a three-way catalyst.

Previous techniques

In spark-ignition internal combustion engines, particularly those used in motor vehicles and running on petrol, it is known to carry out the depollution of the engine's combustion gases using a three-way catalyst mounted on the engine exhaust.

Such pollutant emission treatment devices make it possible to reduce nitrogen oxide (NOx) molecules and oxidize unburned hydrocarbon (HC) and carbon monoxide (CO) molecules emitted by the engine during operation.

Conventionally, two lambda probes quantify the oxygen concentration respectively upstream and downstream of the catalyst while the richness varies between rich and lean compositions at a given frequency and amplitude, in order to stimulate the conversion of pollutants within the catalyst and to have optimal efficiency in the treatment of pollutant emissions.

This richness modulation strategy works correctly as long as the catalyst has sufficient oxygen storage capacity (OSC), defined by a lower limit called OS_min and an upper limit called OS_max. When the oxygen stored in the catalyst (OS for Oxygen Storage) is between these two limits, the catalyst is able to correctly treat polluting emissions.

If the OS is lower than the lower bound OS_min, there is no longer enough oxygen in the catalyst to process the rich species, in particular CO emissions.

If the OS is greater than the upper bound OS_max, there is too much oxygen in the catalyst to treat lean species, especially NOx emissions.

However, the OSC value of a catalyst decreases with age.

Therefore, we understand that it is not possible to adopt the same richness modulation amplitude for a new catalyst and an aged catalyst.

In current systems, the richness modulation amplitude is generally chosen to optimize the treatment of pollutant emissions when the catalysts are aged. Pollution control is therefore not optimal over the entire life of the catalysts and in particular when the catalysts are new.

In view of the above, the invention aims to provide a method for adjusting the richness of a spark-ignition type internal combustion engine equipped with a three-way catalyst which optimizes the treatment of polluting emissions over the entire life of the catalyst.

• modulation de la richesse à une première fréquence prédéterminée et avec une amplitude de richesse prédéterminée centrée autour d’une richesse moyenne constante, de manière à réaliser une alternance de phases de fonctionnement du moteur en régime riche et en régime pauvre ;
• suivi de la tension aux bornes d’une sonde de richesse binaire disposée à l’aval du catalyseur et identification de pics de tension représentatifs d’une fuite lorsque la tension aux bornes de la sonde dépasse de manière répétée une tension de seuil prédéterminée supérieure à une tension nominale prédéterminée de la sonde;
• calcul d’une deuxième fréquence représentative d’une fréquence d’apparition des pics de tension identifiés;
• comparaison entre la deuxième fréquence et la première fréquence; et
• réduction de l’amplitude de richesse lorsque la valeur absolue de l’écart entre les deuxième et première fréquences est inférieure ou égale à une valeur de seuil prédéterminée, de manière à faire disparaître les pics de tension.

The subject of the invention is a method for adjusting the richness of a spark-ignition internal combustion engine equipped with a three-way catalyst configured to treat polluting emissions from the engine. The method comprises steps of:

• modulation of the richness at a first predetermined frequency and with a predetermined richness amplitude centered around a constant average richness, so as to achieve an alternation of engine operating phases in rich and lean regimes;
• monitoring the voltage across a binary richness probe arranged downstream of the catalyst and identifying voltage peaks representative of a leak when the voltage across the probe repeatedly exceeds a predetermined threshold voltage greater than a predetermined nominal voltage of the probe;
• calculation of a second frequency representative of a frequency of appearance of the identified voltage peaks;
• comparison between the second frequency and the first frequency; and
• reduction of the richness amplitude when the absolute value of the difference between the second and first frequencies is less than or equal to a predetermined threshold value, so as to eliminate the voltage peaks.

Such a process makes it possible to optimize the treatment of polluting emissions over the entire life of the catalyst.

According to one characteristic, the average richness has a value between 1.001 and 1.002, and preferably is equal to 1.0015. Such an average richness value constitutes a very good compromise for the treatment of NOx and CO.

Advantageously, voltage monitoring is carried out over stabilized phases of motor operation.

According to another feature, the operation in rich and lean regime of the engine is carried out respectively at a first constant richness and at a second constant richness, the second richness being lower than the first richness, the difference between the first richness and the second richness corresponding to the richness amplitude. Such operation allows a linear variation of the OS of the catalyst.

Preferably, the richness amplitude is adjusted according to the engine speed and load. Such a richness adjustment allows optimal treatment of pollutant emissions.

For example, the calculation of the second frequency is carried out from a frequency analysis of the voltage signal at the terminals of the probe.

According to another aspect, the invention relates to an internal combustion engine equipped with a three-way catalyst configured to treat polluting emissions from the engine, said engine further comprising an electronic control unit configured to implement a method as defined above.

According to another aspect, the invention relates to a motor vehicle equipped with an engine as defined above.

Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

FIG. 1 is a schematic view of an engine according to an exemplary embodiment of the invention;

FIG. 2 illustrates the richness/voltage characteristic of a binary richness sensor of the engine of the FIG. 1 ;

FIG. 3 is a flowchart illustrating the different stages of a process for adjusting the richness of the engine of the FIG. 1 according to an exemplary embodiment of the invention; and

FIG. 4 has FIG. 6 illustrate an example of implementation of the process of the FIG. 3 .

Detailed description of at least one embodiment

In the example illustrated on the FIG. 1 , the internal combustion engine 1 is of the atmospheric spark ignition type. In an embodiment not shown, the engine 1 may be supercharged, for example by a turbocharger or by a volumetric compressor.

The engine 1 draws in air in the direction of arrow E via an intake pipe 2, and discharges its exhaust gases via an exhaust pipe 3 in order to direct them to a pollution control device 4.

The pollution control device 4 comprises a three-way catalyst 5 and preferably a particle filter 6. In the example illustrated in the FIG. 1 , the particulate filter 6 is housed in the same post-treatment volume as the three-way catalyst 5 to promote its temperature rise. Alternatively, it is possible for the particulate filter 6 not to be housed in the same post-treatment volume as the catalyst 5.

The exhaust pipe 3 is equipped upstream of the pollution control device 4 with a proportional richness sensor 7a allowing the richness of the air-fuel mixture of the engine 1 to be regulated.

The exhaust pipe 3 is provided downstream of the pollution control device 4 with a binary richness probe 7b which returns in a manner known per se a voltage value as a function of the richness level ( FIG. 2 ). For example, the 7b richness sensor can be set to return a nominal voltage of 700 mV equivalent to a richness of 1.0015 which optimizes the treatment of NOx and CO emissions.

The fuel, for example gasoline, a mixture of gasoline and ethanol, or even pure ethanol, is supplied to the engine 1 by means of an injection system (not shown), for example a direct injection system which comprises a fuel rail common to the cylinders 8 and at least one fuel injector per cylinder capable of injecting the fuel directly into each of the cylinders 8. In the example illustrated in FIG. FIG. 1 , the engine is provided with three cylinders arranged in line. For example, the engine 1 may comprise a different number of cylinders. Other cylinder configurations may be envisaged, without departing from the scope of the invention.

At the outlet of exhaust circuit 3, the exhaust gases are discharged into the outside atmosphere in the direction of arrow S.

In the air intake duct 2, in a non-limiting manner, there may be found an air filter 9 which makes it possible to eliminate the dust contained in the air and an intake flap 10, or throttle body 10 which makes it possible to regulate the flow admitted into the engine 1 by more or less obstructing the intake duct 2. The air is distributed to the cylinders 8 through an intake manifold 11 arranged downstream of the throttle body 10.

In the example illustrated on the FIG. 1 , an exhaust manifold 12 is directly integrated into a cylinder head 13 of the engine 1 in order to minimize the distance between the exhaust valves of the cylinders 8 and the catalyst 5. The catalyst 5 is thus positioned in the vicinity of an exhaust outlet 3a of the cylinder head 13. This configuration allows a rapid rise in temperature of the catalyst by maximizing the number of calories available for heating the catalyst 5. Alternatively, it remains possible to place the exhaust manifold 12 outside the cylinder head 13.

The engine 1 further comprises an electronic control unit 14 configured to control the various elements of the engine 1 from data collected by sensors at different locations of the engine.

The electronic control unit 14 comprises a calculation module 15, a measurement module 16 and a control module 17.

The measurement module 16 is for example capable of receiving measurements from the richness probes 7a and 7b.

The control module 17 is for example capable of controlling the fuel injection system and the opening and closing of the throttle body 10 in order to adjust the value of the richness of the air-fuel mixture of the engine 1 to a set value.

There FIG. 3 illustrates the different steps of a method for adjusting the richness of the engine 1 according to an exemplary embodiment of the invention.

The method is implemented in particular by means of an electronic control unit 14 of the engine 1.

The method begins with a step 20 of modulating the richness at a first predetermined frequency F1 and with a predetermined richness amplitude A centered around a constant average richness Rmoy, so as to achieve an alternation of engine operating phases in rich and lean regimes. As indicated previously, such an alternation of engine operating phases in rich and lean regimes makes it possible to stimulate the conversion of pollutants within the catalyst 5 and thus to increase the efficiency of treatment of pollutant emissions.

For example, the average wealth value Rmoy has a value between 1.001 and 1.002, and preferably is equal to 1.0015. According to an example illustrated in Figures 4 to 6, the average wealth value Rmoy is equal to 1.

Advantageously, the value of the richness amplitude A is adjusted according to the rotation speed and the load of the engine 1.

According to an exemplary embodiment, the operation in rich and lean mode of the engine is carried out respectively at a first constant richness R1 and at a second constant richness R2 lower than the first richness R1 ( FIG. 4 ). The difference between the first wealth R1 and the second wealth R2 corresponds to the wealth amplitude A.

The method continues with a step 21 of monitoring the voltage across the binary richness probe 7b arranged downstream of the catalyst 5, and of identifying voltage peaks representative of a leak when the voltage across the probe 7b repeatedly reaches a predetermined threshold voltage higher than the predetermined nominal voltage of the probe 7b. For example, the predetermined nominal voltage may have a value of approximately 700 mV and the predetermined threshold voltage may have a value of approximately 850 mV. Preferably, the monitoring of the voltage across the probe 7b is carried out over stabilized phases of operation of the engine 1.

After step 21 of identifying voltage peaks, the electronic control unit 14 calculates a second frequency F2 representative of a frequency of appearance of the identified voltage peaks (step 22). For example, the calculation of the second frequency F2 is carried out from a frequency analysis of the voltage signal at the terminals of the probe 7b.

In the next comparison step 23, the second frequency F2 and the first frequency F1 are compared.

If the absolute value of the difference between the second and first frequencies F2, F1 is less than or equal to a predetermined threshold value ε, the richness amplitude A is reduced, so as to eliminate the voltage peaks (step 24).

If the absolute value of the difference between the second and first frequencies F2, F1 is greater than the predetermined threshold value ε, the method resumes at step 21 of voltage monitoring of the probe 7b.

Figures 4 to 6 illustrate an example of implementation of the method of the FIG. 3 . It should be noted that identical or similar elements bear the same references from one figure to another.

There FIG. 4 is an example of the richness modulation of engine 1 associated with a new catalyst 5. Curve 30 illustrates the voltage across the binary richness sensor 7b. Curve 31 represents the variation over time of the quantity of stored oxygen OS of catalyst 5. Curve 32 illustrates the variation over time of the richness upstream of catalyst 5 as measured by the proportional richness sensor 7a.

The richness upstream of the catalyst 5 is controlled by the electronic control unit 14 to achieve an alternation of engine operating phases in rich and lean mode.

The alternation of the engine operating phases in rich and lean mode is carried out at a period dt equivalent to a frequency F1 equal to 1/dt.

Here, richness slots of an amplitude A equal to 0.1 are carried out, centered around an average richness Rmoy unit. This value of the amplitude A makes it possible to keep the OS level of the new catalyst outside the lean 33 and rich 34 leakage zones. It should be noted that the value of the amplitude A can be adjusted according to the rotation speed and the load of the engine 1 in order to optimize the treatment of polluting emissions.

There FIG. 5 highlights the effect of catalyst 5 aging on the OS value in the catalyst. As shown in the FIG. 5 , in the case of an aged catalyst the OSC is more reduced and the leakage zones 33 and 34 are closer to each other. By keeping the same modulation of frequency F1 and amplitude A as in the new state of the catalyst, it is observed that the OS periodically enters the leakage zone 34 and the appearance of voltage peaks 35 is observed at the terminals of the probe 7b. The analysis of the voltage signal at the terminals of the probe 7b shows that the frequency of appearance F2 of the voltage peaks 35 corresponds to the frequency F1 of the richness modulation. Indeed, the same period dt is observed for both the richness modulation and for the appearance of the voltage peaks 35.

There FIG. 6 shows the effect of a reduction in the richness amplitude A on the OS value in the aged catalyst 5. According to the method, the richness amplitude A is reduced so as to make the voltage peaks 35 disappear. Here, it can be seen that a reduction in the amplitude A of 0.06 makes it possible to make the voltage peaks 35 disappear and to put the OS value of the catalyst 5 outside the leakage zone 34.

Claims (8)

Method for adjusting the richness of a spark-ignition internal combustion engine (1) equipped with a three-way catalyst (5) configured to treat polluting emissions from the engine (1), characterized in that the method comprises steps of:

• modulation of the richness at a first predetermined frequency (F1) and with a predetermined richness amplitude (A) centered around a constant average richness (Rmoy), so as to achieve an alternation of engine operating phases in rich and lean regimes;
• monitoring the voltage across a binary richness probe (7b) arranged downstream of the catalyst (5) and identification of voltage peaks (35) representative of a leak when the voltage across the probe (7b) repeatedly exceeds a predetermined threshold voltage greater than a predetermined nominal voltage of the probe (7b);
• calculating a second frequency (F2) representative of a frequency of appearance of the identified voltage peaks (35);
• comparison between the second frequency (F2) and the first frequency (F1); and
• reduction of the richness amplitude (A) when the absolute value of the difference between the second and first frequencies (F2, F1) is less than or equal to a predetermined threshold value (ε), so as to eliminate the voltage peaks (35).

Method according to claim 1, in which the average richness (Rmoy) has a value between 1.001 and 1.002, and preferably is equal to 1.0015. Method according to claim 1 or 2, in which the voltage monitoring is carried out over stabilized phases of operation of the motor (1). Method according to any one of claims 1 to 3, in which the operation in rich and lean mode of the engine is carried out respectively at a constant first richness (R1) and at a constant second richness (R2), the second richness (R2) being lower than the first richness (R1), the difference between the first richness and the second richness corresponding to the richness amplitude (A). Method according to any one of claims 1 to 4, in which the richness amplitude (A) is adjusted as a function of the rotation speed and the load of the engine (1). Method according to any one of claims 1 to 5, in which the calculation of the second frequency (F2) is carried out from a frequency analysis of the voltage signal at the terminals of the probe (7b). Internal combustion engine (1) provided with a three-way catalyst (5) configured to treat polluting emissions from the engine (1), said engine (1) further comprising an electronic control unit (14) configured to implement a method according to any one of claims 1 to 6. Motor vehicle equipped with an engine (1) according to claim 7.