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

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 polluting emissions from the engine (1), comprises 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 at the terminals of 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 appearance 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 the abstract: Figure 1

Description

Title of the invention: Method for adjusting the richness of a spark-ignition internal combustion engine equipped with a three-way catalyst Technical field

[0001] 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

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

[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 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.

[0005] This richness modulation strategy works correctly to the extent that the catalyst has sufficient oxygen storage capacity (OSC for “Oxygen Storage Capacity”), defined by a lower limit called 0S_min and by 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 ensure the treatment of polluting emissions.

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

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

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

[0010] In current systems, the richness modulation amplitude is generally chosen to optimize the treatment of polluting 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. Statement of the invention

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

[0012] 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 identification of 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 wealth amplitude when the absolute value of the gap between the second and first frequencies are less than or equal to a predetermined threshold value, so as to eliminate the voltage peaks.

[0013] Such a process makes it possible to optimize the treatment of polluting emissions over the entire lifetime 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, the voltage monitoring is carried out over stabilized phases of operation of the motor.

[0016] According to another characteristic, the operation in rich mode and in lean mode of the engine is carried out respectively at a first constant richness and at a constant second 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.

[0017] Preferably, the richness amplitude is adjusted according to the rotation speed and the load of the engine. Such a richness adjustment allows optimal treatment of polluting 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 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.

[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 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:

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

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

[0024] [Fig.3] is a flowchart illustrating the different steps of a method for adjusting the richness of the engine of [Fig.l] according to an exemplary embodiment of the invention; and

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

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

[0027] 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 towards a pollution control device 4.

[0028] The pollution control device 4 comprises a three-way catalyst 5 and preferably a particulate filter 6. In the example illustrated in [Fig.l], 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 that the particulate filter 6 is not housed in the same post-treatment volume as the catalyst 5.

[0029] The exhaust pipe 3 is provided upstream of the pollution control device 4 with a proportional richness sensor 7a making it possible to regulate the richness of the air-fuel mixture of the engine 1.

[0030] 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 richness probe 7b can be adjusted so as to return a nominal voltage of 700 mV equivalent to a richness 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 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.l], 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.

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

[0033] 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 butterfly valve 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 butterfly valve 10.

[0034] In the example illustrated in [Fig.l], 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.

[0035] 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.

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

[0037] The measurement module 16 is for example capable of receiving the 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 richness of the air-fuel mixture of the engine 1 to a set value.

[0039] [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.

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

[0041] The method begins with a step 20 of modulating the richness at a first predetermined frequency Fl 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.

[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 as a function of the rotation speed and the load of the engine 1.

[0044] According to an exemplary embodiment, the operation in rich and lean regime of the engine is carried out respectively at a constant first richness RI and at a constant second richness R2 lower than the first richness RI ([Fig.4]). The difference between the first richness RI and the second richness R2 corresponds to the richness amplitude A.

[0045] 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.

[0046] After step 21 of identifying voltage peaks, the electronic unit of command 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.

[0047] In the following 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 method resumes at step 21 of voltage monitoring of the probe 7b.

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

[0051] [Fig.4] is an example of the richness modulation of the engine 1 associated with a new catalyst 5. Curve 30 illustrates the voltage across the binary richness probe 7b. Curve 31 represents the variation over time of the quantity of stored oxygen OS of the catalyst 5. Curve 32 illustrates the variation over time of the richness upstream of the catalyst 5 as measured by the proportional richness probe 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 mode.

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

[0054] Here, richness slots of an amplitude A equal to 0.1 are made, centered around a unitary average richness Rmoy. 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.

[0055] [Fig. 5] highlights the effect of aging of the catalyst 5 on the OS value in the catalyst. As illustrated in [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 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 the appearance of voltage peaks 35 at the terminals of the probe 7b is observed. The analysis of the voltage signal at the terminals of probe 7b shows that the frequency of appearance F2 of the voltage peaks 35 corresponds to the frequency Fl of the richness modulation. In fact, the same period dt is observed for both the richness modulation and the appearance of the voltage peaks 35.

[0056] [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

Claims

1. Method for adjusting the richness of a spark-ignition internal combustion engine (1) provided with a three-way catalyst (5) configured to treat polluting emissions from the engine (1), characterized in that the method comprises steps of: - modulating the richness at a first predetermined frequency (Fl) 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 mode and in lean mode; - monitoring the voltage across a binary richness probe (7b) arranged downstream of the catalyst (5) and identifying 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);- calculation of 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 (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. 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.

3. Method according to claim 1 or 2, in which the voltage monitoring is carried out on stabilized phases of operation of the motor (1).

4. Method according to any one of claims 1 to 3, in which the operation in rich regime and in lean regime of the engine is carried out respectively at a first constant richness (RI) and at a second constant richness (R2), the second richness (R2) being more lower than the first wealth (RI), the gap between the first wealth and the second wealth corresponding to the wealth amplitude (A).

5. 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).

6. 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).

7. 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.

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

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