Method for adjusting the fuel mixture of a spark-ignition internal combustion engine equipped with a three-way catalytic converter

Abstract

This method for adjusting the fuel mixture of a spark-ignition internal combustion engine (1) equipped with a three-way catalytic converter (5) configured to treat pollutant emissions from the engine (1) comprises the steps of: modulating the fuel mixture at a first predetermined frequency and with a predetermined amplitude centered around a constant average mixture; monitoring the voltage across a binary mixture sensor (7b) located downstream of the catalytic converter (5) and identifying voltage peaks representative of a leak; calculating a second frequency representative of the frequency at which the identified voltage peaks occur; comparing the second frequency with the first frequency; and reducing the 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 1

Description

Title of the invention: Method for adjusting the fuel mixture of a spark-ignition internal combustion engine equipped with a three-way catalytic converter technical field

[0001] The invention has as its technical field the depollution of the exhaust gases of a spark-ignition internal combustion engine equipped with a three-way type catalyst. Previous techniques

[0002] In internal combustion engines of the spark-ignition type, particularly those used in motor vehicles and running on gasoline, it is known to achieve the depollution of the combustion gases of the engine by means of a three-way type catalyst mounted at the exhaust of the engine.

[0003] Such pollutant emission treatment devices make it possible to reduce nitrogen oxide (NOx) molecules, and to oxidize unburned hydrocarbon (HC) and carbon monoxide (CO) molecules emitted by the engine during its operation.

[0004] Conventionally, two lambda probes quantify the oxygen concentration upstream and downstream of the catalyst respectively 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 of the treatment of pollutant emissions.

[0005] This fuel-air mixture modulation strategy functions correctly provided that the catalyst has sufficient oxygen storage capacity (OSC), defined by a lower bound called 0S_min and an upper bound called OS_max. When the oxygen stored in the catalyst (OS) is between these two bounds, the catalyst is able to properly treat pollutant emissions.

[0006] If VOS is less than the lower bound 0S_min, there is no longer enough oxygen in the catalyst to treat rich species, in particular CO emissions.

[0007] If VOS is greater than the upper bound 0S_max, there is too much oxygen in the catalyst to treat the lean species, in particular NOx emissions.

[0008] However, the OSC value of a catalyst decreases with age.

[0009] Therefore, it is understood that it is not possible to adopt the same amplitude of richness modulation for a new catalyst and an aged catalyst.

[0010] In current systems, the fuel mixture modulation amplitude is generally chosen to optimize the treatment of pollutant emissions when the catalysts are aged. Therefore, pollution control is not optimal over the entire lifespan of the catalysts, and particularly when the catalysts are new. Description of the invention

[0011] In view of the foregoing, the invention aims to provide a method for adjusting the fuel mixture of a spark-ignition type internal combustion engine equipped with a three-way catalyst which optimizes the treatment of pollutant emissions over the entire life of the catalyst.

[0012] The invention relates to a method for adjusting the fuel mixture of a spark-ignition internal combustion engine equipped with a three-way catalytic converter configured to treat engine pollutant emissions. The method comprises the following steps: - 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 located downstream of the catalyst and identifying voltage peaks representative of a leak when the voltage across the probe repeatedly exceeds a predetermined threshold voltage higher than a predetermined nominal voltage of the probe; - calculation of a second frequency representative of the frequency of occurrence 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 gap between the second and first frequencies is less than or equal to a predetermined threshold value, so as to eliminate voltage spikes.

[0013] Such a process makes it possible to optimize the treatment of polluting emissions over the entire life of the catalyst.

[0014] 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.

[0015] Advantageously, voltage monitoring is carried out on stabilized phases of motor operation.

[0016] According to another feature, the rich and lean operating conditions of the engine are achieved respectively at a first constant richness and at a The second constant richness, being lower than the first richness, means that the difference between the first and second richnesses corresponds to the richness amplitude. This type of operation allows for a linear variation of the catalyst's operating viscosity (OS).

[0017] Preferably, the fuel mixture range is adjusted according to the engine speed and load. Such a fuel mixture adjustment allows for optimal treatment of pollutant emissions.

[0018] 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.

[0019] According to another aspect, the invention relates to an internal combustion engine equipped with a three-way type catalyst configured to treat polluting emissions from the engine, said engine further comprising an electronic control unit configured to implement a process as defined above.

[0020] According to another aspect, the invention relates to a motor vehicle equipped with an engine as defined above. Brief description of the drawings

[0021] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0022] [Fig.1] is a schematic view of an engine according to an example of an embodiment of the invention;

[0023] [Fig.2] illustrates the richness / voltage characteristic of a binary richness probe of the engine of [Fig.1];

[0024] [Fig.3] is a flowchart illustrating the different steps of a method for adjusting the fuel mixture of the engine of [Fig.1] according to an example of an embodiment of the invention; and

[0025] [Fig.4] to [Fig.6] illustrate an example of implementation of the process of [Fig.3]. Detailed description of at least one embodiment

[0026] In the example illustrated in [Fig. 1], the internal combustion engine 1 is of the naturally aspirated, spark-ignition type. In an embodiment not shown, the engine 1 may be supercharged, for example by a turbocharger or a supercharger.

[0027] The engine 1 draws in air in the direction of arrow E through an intake duct 2, and expels its exhaust gases through an exhaust duct 3 in order to direct them to a pollution control device 4.

[0028] The pollution control device 4 comprises a three-way catalyst 5 and preferably a particle filter 6. In the example illustrated in [Fig. 1], the particle filter 6 is housed in the same aftertreatment unit as the three-way catalyst 5 to facilitate its temperature rise. Alternatively, the particulate filter 6 may not be housed in the same aftertreatment unit as the catalyst 5.

[0029] 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.

[0030] The exhaust pipe 3 is equipped downstream of the pollution control device 4 with a binary mixture sensor 7b which returns a voltage value known per se as a function of the mixture level ([Fig. 2]). For example, the mixture sensor 7b can be adjusted to return a nominal voltage of 700 mV, corresponding to a mixture of 1.0015, which optimizes the treatment of NOx and CO emissions.

[0031] 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 comprising a common fuel rail for 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. 1], the engine has three cylinders arranged in line. For example, the engine 1 may have a different number of cylinders. Other cylinder configurations may be considered without departing from the scope of the invention.

[0032] At the outlet of the exhaust circuit 3, the exhaust gases are evacuated into the outside atmosphere in the direction of arrow S.

[0033] In the air intake duct 2, by way of non-limitation, there may be an air filter 9 which allows the removal of dust contained in the air and an intake flap 10, or throttle body 10 which allows the flow admitted into the engine 1 to be regulated 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.

[0034] In the example illustrated in [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 for a rapid temperature rise of the catalyst by maximizing the amount of heat available for heating the catalyst 5. Alternatively, it remains possible to place the exhaust manifold 12 outside the cylinder head 13.

[0035] The motor 1 further includes an electronic control unit 14 configured to control the various elements of the motor 1 from data collected by sensors at different locations in the motor.

[0036] The electronic control unit 14 comprises a calculation module 15, a measurement module 16 and a control module 17.

[0037] The measuring module 16 is for example suitable for receiving measurements from the richness probes 7a and 7b.

[0038] 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 air-fuel mixture of the engine 1 to a setpoint value.

[0039] Fig. 3 illustrates the different steps of a method for adjusting the fuel mixture of engine 1 according to an example of an embodiment of the invention.

[0040] The method is in particular implemented by means of an electronic control unit 14 of the motor 1.

[0041] The process begins with a step 20 of modulating the fuel mixture at a predetermined first frequency Fl and with a predetermined fuel mixture amplitude A centered around a constant average fuel mixture Rmoy, so as to achieve an alternation of rich and lean engine operating phases. As previously indicated, such an alternation of rich and lean engine operating phases stimulates the conversion of pollutants within the catalyst 5 and thus increases the efficiency of pollutant emission treatment.

[0042] 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.

[0043] Advantageously, the value of the richness amplitude A is adjusted according to the rotational speed and load of the engine 1.

[0044] According to one embodiment, the rich and lean operating conditions of the engine are achieved respectively at a first constant air-fuel ratio RI and at a second constant air-fuel ratio R2 that is lower than the first air-fuel ratio RI ([Fig.4]). The difference between the first air-fuel ratio RI and the second air-fuel ratio R2 corresponds to the air-fuel ratio amplitude A.

[0045] The method continues with a step 21 of monitoring the voltage across the binary mixture sensor 7b located downstream of the catalyst 5, and of identifying voltage spikes representative of a leak when the voltage across the sensor 7b repeatedly reaches a predetermined threshold voltage higher than the predetermined nominal voltage of the sensor 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 sensor 7b is carried out during stabilized phases of engine 1 operation.

[0046] After step 21 of voltage peak identification, the electronic unit of Command 14 calculates a second frequency F2 representative of the frequency of occurrence 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 across probe 7b.

[0047] In the next comparison step 23, the second frequency F2 and the first frequency Fl are compared.

[0048] If the absolute value of the difference between the second and first frequencies F2, Fl is less than or equal to a predetermined threshold value e, the richness amplitude A is reduced so as to make the voltage peaks disappear (step 24).

[0049] If the absolute value of the difference between the second and first frequencies F2, Fl is greater than the predetermined threshold value e, the process resumes at step 21 of voltage monitoring of probe 7b.

[0050] Figures 4 to 6 illustrate an example of implementation of the process in [Fig. 3]. It should be noted that identical or similar elements bear the same reference numerals from one figure to another.

[0051] Figure 4 is an example of the fuel mixture modulation of the engine 1 associated with a new catalyst 5. Curve 30 illustrates the voltage across the binary fuel mixture sensor 7b. Curve 31 represents the variation over time of the amount of oxygen stored OS in the catalyst 5. Curve 32 illustrates the variation over time of the fuel mixture upstream of the catalyst 5 as measured by the proportional fuel mixture sensor 7a.

[0052] 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 regimes.

[0053] The alternation of the engine operating phases in rich and lean regime is carried out at a period dt equivalent to a frequency Fl equal to 1 / dt.

[0054] Here, richness intervals of an amplitude A of 0.1 centered around a unit average richness Rmoy are performed. This value of amplitude A keeps the OS level of the new catalyst outside the lean 33 and rich 34 leak zones. It should be noted that the value of amplitude A can be adjusted according to the engine speed and load 1 in order to optimize the treatment of pollutant emissions.

[0055] Figure 5 highlights the effect of catalyst aging on the OS value in the catalyst. As illustrated in Figure 5, in the case of an aged catalyst, the OSC is lower and the leakage zones 33 and 34 are closer together. Maintaining the same frequency modulation Fl and amplitude A as in the new state of the catalyst, it is observed that the OS periodically enters the leakage zone 34 and that voltage peaks 35 appear across the probe 7b. The analysis The voltage signal across probe 7b shows that the frequency F2 of the voltage peaks 35 corresponds to the frequency Fl of the fuel mixture modulation. Indeed, the same period dt is observed for both the fuel mixture modulation and the occurrence of the voltage peaks 35.

[0056] Figure 6 shows the effect of reducing the richness amplitude A on the OS value in the aged catalyst 5. According to the process, the richness amplitude A is reduced so as to eliminate the voltage peaks 35. Here, it can be seen that a reduction in the amplitude A of 0.06 makes the voltage peaks 35 disappear and brings the OS value of the catalyst 5 back outside the leakage zone 34.

Claims

Demands

1. Method for adjusting the fuel mixture of a spark-ignition internal combustion engine (1) equipped with a three-way catalyst (5) configured to treat pollutant emissions from the engine (1), characterized in that the method comprises steps of: - modulating the fuel mixture at a predetermined first frequency (Fl) and with a predetermined fuel mixture amplitude (A) centered around a constant average fuel mixture (Rmoy), so as to achieve an alternation of engine operating phases in rich and lean conditions; - monitoring the voltage across a binary fuel mixture sensor (7b) disposed downstream of the catalyst (5) and identifying voltage peaks (35) representative of a leak when the voltage across the sensor (7b) repeatedly exceeds a predetermined threshold voltage greater than a predetermined nominal voltage of the sensor (7b);- calculation of a second frequency (F2) representative of a frequency of occurrence of the identified voltage peaks (35); - comparison between the second frequency (F2) and the first frequency (Fl); and - reduction of the richness amplitude (A) when the absolute value of the difference between the second and first frequencies (F2, Fl) is less than or equal to a predetermined threshold value (e), so as to make the voltage peaks (35) disappear.;

2. A method according to claim 1, wherein the average richness (Rmoy) has a value between 1.001 and 1.002, and preferably is equal to 1.0015.

3. Method according to claim 1 or 2, wherein voltage tracking is carried out on stabilized phases of motor operation (1).

4. A method according to any one of claims 1 to 3, wherein the rich and lean operating conditions of the engine are achieved respectively at a constant first air-fuel ratio (RI) and a constant second air-fuel ratio (R2), the second air-fuel ratio (R2) being more lower than the first wealth (RI), the gap between the first wealth and the second wealth corresponds to the wealth amplitude (A).

5. A method according to any one of claims 1 to 4, wherein the richness amplitude (A) is adjusted as a function of the engine speed and load (1).

6. A method according to any one of claims 1 to 5, wherein the calculation of the second frequency (F2) is carried out from a frequency analysis of the voltage signal across the terminals of the probe (7b).

7. Internal combustion engine (1) equipped with a three-way type 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.

8. Motor vehicle equipped with an engine (1) according to claim 7.

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