METHOD AND INSTALLATION FOR MONITORING THE OPERATION OF A CATALYTIC CONVERTER IN THE EXHAUST GASES OF AN INTERNAL COMBUSTION ENGINE

Abstract

The invention relates in particular to a method for diagnosing the operation of a catalytic converter (6) in the exhaust gases of an internal combustion engine (1), the engine having at least two cylinders (2, 3, 4), each comprising a gas discharge duct (20, 30, 40) which opens into a common discharge duct (50). The catalytic converter is positioned at the end of the common discharge duct (50), the method taking into account a signal (S1) emitted by a first sensor (71) placed downstream of the catalytic converter (6). A stable state of engine operation is monitored and, if the stable state is satisfactory, fuel is supplied to said at least two cylinders according to a predetermined supply cycle, an oscillating output signal (S2, S3) is generated for each of said at least two cylinders, and the oscillating output signals are compared with said signal (S1) to establish the diagnosis. Figure for the abbreviation: Figure 1.

Description

Title of the invention: METHOD AND INSTALLATION TO CHECK THE OPERATION OF A CATALYTIC CONVERTER IN THE EXHAUST GASES OF AN INTERNAL COMBUSTION ENGINE technical field

[0001] The invention relates to a method and an installation for controlling the operation of a catalytic converter in the exhaust gases of an internal combustion engine, for example in vehicles, particularly automobiles, and for controlling the operation of cylinders of the internal combustion engine to allow said control of the operation of the catalytic converter. State of the art

[0002] We know of processes and installations which make it possible to control and observe the aging of a catalytic converter in the exhaust gases of combustion engines of vehicles, including (but not exclusively) automobiles.

[0003] It is known, for example, to detect a catalytic converter that is functioning correctly by detecting the presence of polluting compounds at the inlet of the catalytic converter and by detecting the absence of these same polluting compounds at the outlet of the catalytic converter. Such an embodiment is described, for example, in patent application EP 1 201 900.

[0004] Furthermore, document DE 38 41 685 describes a method which is based on the signals from two exhaust gas measurement probes:

[0005] The result of the phase shift measurement of the signals is used as an additional input parameter for conventional control of the combustion engine and thus allows control interventions based on execution time.

[0006] However, these methods are not necessarily reliable: indeed, the catalytic converter may receive a "scrambled" gas mixture and the signal perceived by the probe, located downstream of the catalytic converter, is then not representative of good catalysis (or bad catalysis) carried out by the catalytic converter.

[0007] To ensure that the catalytic converter is tested under optimal conditions, it is necessary that the signal representing the exhaust gases at the inlet of the catalytic converter include clear variations in the presence of more or less significant polluting compounds as a function of time, these variations illustrating a variation of rich or lean supply in the engine cylinders. Description of the invention

[0008] To this end, the invention relates to a diagnostic method for checking the operation of a catalytic converter in the exhaust gases of an internal combustion engine, the engine comprising at least two moving cylinders in a cylinder chamber in response to fuel combustion, each cylinder comprising a gas discharge duct which opens into a common discharge duct, said catalytic converter being positioned at the end of said common discharge duct, said method ensuring the diagnosis of the operation of said catalytic converter by taking into consideration a signal emitted by a first probe placed downstream of the catalytic converter, said first probe detecting the presence of a first quantity of polluting compounds at the outlet of the catalytic converter.

[0009] According to the invention, the process comprises the following steps:

[0010] - monitoring the stability of engine operation by analyzing data relating to a predetermined engine load range and, if the stability state is satisfactory: - control of the fuel supply to said at least two cylinders according to a predetermined fuel supply cycle comprising alternating over-injection and under-injection of fuel during predetermined time intervals, - detection of the presence of polluting compounds at the direct outlet of at least one of said at least two cylinders, by at least one second probe, among second probes placed downstream of each of the cylinders and upstream of said common evacuation duct, so as to generate, for each of said at least two cylinders, an oscillating cylinder outlet signal representative of the quantity of polluting compounds at the outlet of each of said at least two cylinders, - comparison of the oscillating signals from the cylinder output with said signal from said first probe by a diagnostic module, and - diagnosis made by said diagnostic module.

[0011] Thanks to this method as defined, the signal upstream of the catalyst which is analyzed cannot be scrambled - thus, the comparison of the signals upstream of the catalyst and downstream is based on reliable data, which makes it possible to determine whether the catalyst is working correctly or not.

[0012] According to a first embodiment, the step of controlling the fuel supply to said at least two cylinders, according to said fuel supply cycle, is carried out simultaneously for said at least two cylinders of said combustion engine.

[0013] According to an alternative implementation, the step of controlling the fuel supply to said at least two cylinders is carried out independently for each of said at least two cylinders, in the following manner: - among the aforementioned at least two cylinders, determination of one master cylinder, and at least one slave cylinder, - command of said predetermined power cycle for said master cylinder, - command of a power cycle similar to said predetermined power cycle for said at least one slave cylinder, and - monitoring of oscillating output signals from master and slave cylinder(s).

[0014] In this embodiment, during the monitoring step of the oscillating output signals of the master and slave cylinder(s), if an absence of oscillation is observed in the signal of said at least one slave cylinder, then the fuel supply is stopped according to said predetermined cycle of said at least one slave cylinder and the fuel supply is resumed in said at least one slave cylinder independently of the other cylinders until oscillations of the signal of said at least one slave cylinder are read again and, if the stability state is correct, the fuel supply is resumed according to said predetermined cycle of said at least one slave cylinder.

[0015] The invention also relates to an installation for implementing the process as defined above, the installation comprising an internal combustion engine having at least two cylinders supplied independently with fuel, each cylinder having a gas exhaust duct which opens into a common exhaust duct, a catalytic converter being placed at the end of the common exhaust duct and a first probe being placed downstream of the catalytic converter, said first probe detecting the presence of a first quantity of polluting compounds at the outlet of the catalytic converter. The installation according to the invention is remarkable in that it comprises:

[0016] - at least a second probe and a third probe, each of the probes being positioned in an exhaust duct of a cylinder of the internal combustion engine upstream of said common exhaust duct,

[0017] - a module for monitoring the stability of engine operation by analysis data relating to a predetermined engine load interval,

[0018] - a fuel supply control module of said at least two cylinders of said internal combustion engine following a predetermined cycle of over-injection or under-injection of fuel, at predetermined intervals,

[0019] - a diagnostic module, capable of analyzing: said at least two oscillating cylinder output signals representative of the quantity of polluting compounds at the outlet of each of said at least two cylinders, and said a signal emitted by said first probe placed downstream of the catalytic converter,

[0020] and capable of establishing a diagnostic of the operation of said catalytic converter. Brief description of the figures

[0021] The invention will be better understood upon reading 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 representation of a device according to the invention, implementing the process according to the invention, and

[0023] [Fig.2] is a functional block diagram of a process according to the invention.

[0024] It is understood that the embodiments which will be described below will not These provisions are by no means limiting. In particular, variants of the invention may be conceived comprising only a selection of features described hereafter, isolated from the other described features, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0025] In particular, all the variants and all the embodiments described are combinable with each other if nothing prevents this combination from a technical point of view.

[0026] In the figures and in the rest of the description, elements common to several figures retain the same reference. Detailed description

[0027] Fig. 1 represents schematically the elements comprising an installation according to the invention and the exchanges between the different elements.

[0028] In the context of the example described, the installation is implemented in a vehicle, in particular a motor vehicle, but not exclusively: such an installation could be implemented in a truck or on a two- or three-wheeled vehicle.

[0029] The installation includes an internal combustion engine 1 which, in the illustrated example, comprises at least two cylinders 2 and 3 supplied independently with fuel.

[0030] A cylinder 4 is illustrated in dotted lines to make the reader understand that the combustion engine could include three cylinders, four cylinders etc., without going out of the scope of the invention.

[0031] According to the invention, each cylinder 2, 3 (or 4) respectively comprises a gas evacuation conduit 20, 30 (or 40), which opens into a common evacuation conduit 50.

[0032] A catalytic pot 6 is positioned at the end of the common exhaust duct 50.

[0033] A final conduit 60 is located downstream of the catalytic pot 6 and ensures the evacuation of the gases treated by the catalytic pot 6.

[0034] A first probe 71 is placed downstream of the catalytic pot 6: it ensures the detection of the presence of a first quantity of polluting compounds at the outlet of the catalytic pot 6 and this quantity of polluting compounds is characterized by a signal SI which is transmitted to a diagnostic module 8 which includes the installation according to the invention.

[0035] According to the invention, the installation also includes a second probe 72, a third probe 73 (and possibly a fourth probe 74), each of the probes 72, 73 (and possibly 74) being positioned in the exhaust ducts of the cylinders 2, 3 (and possibly 4) of the internal combustion engine 1, upstream of the common exhaust duct 50.

[0036] Like probe 71, probes 72, 73 (and possibly 74) detect the presence of polluting compounds at the outlet of each of cylinders 2, 3 (and possibly 4) and this quantity of polluting compounds is characterized by, respectively, signals S2, S3 (and possibly S4) which are also transmitted to the diagnostic module 8.

[0037] More specifically, the SI signal is transmitted to a sub-module 81 which analyzes it and which communicates with a control module 9 which comprises the diagnostic module 8.

[0038] The S2 and S3 signals are transmitted to a sub-module 82 which analyzes them independently and which also communicates with the control module 9.

[0039] The installation further includes a module 83 for monitoring the stability of the operation of motor 1. Figure 2 illustrates such a module, which analyzes the data it receives from a predetermined motor load interval. In Figure 1, the motor stability conditions transmitted to the diagnostic and control module are schematically represented by the letter C.

[0040] The control module 9, meanwhile, controls the fuel supply to cylinders 2 and 3 (and 4, if the engine has more than two cylinders) of the internal combustion engine 1.

[0041] The control of the supply of cylinders 2 and 3 is carried out according to a predetermined cycle of over-injection or under-injection of fuel, according to predetermined intervals.

[0042] The diagnostic module 8 ensures the analysis of the signals SI, S2 and S3 (and possibly S4, and following) which represent the quantity of polluting compounds at the outlet of each of the cylinders 2 and 3, and The system downstream of the catalytic converter is used to diagnose its operation. If signal S2, or S3, or both, indicate the presence of pollutants, and signal S1 indicates a lower, or ideally almost zero, presence, then the catalytic converter is considered to be functioning correctly. Conversely, if signals S2 (or S3, or both) are close to signal S1, then the catalytic converter is considered faulty, and the system emits a warning signal A to the vehicle driver, alerting them that it is time to replace the catalytic converter.

[0043] The signals SI (if the pot is faulty), S2, S3 are oscillating signals, which represent the presence of pollutants emitted following a command of an alternation of over-injection and under-injection of fuels in cylinders 2 and 3, the rising oscillations being representative of episodes of over-injection of fuel (commands 01 of the control module) and the falling oscillations being representative of episodes of under-injection (commands 02 of the control module).

[0044] Reference will now be made to [Fig.2] to describe in more detail a method according to the invention.

[0045] As indicated above, the first step of the method according to the invention is to monitor the stability state of the motor's operation by analyzing data relating to a predetermined motor load range.

[0046] The engine operation stability monitoring module 83 performs this step continuously, so as to determine the times when the diagnosis of the operation of the catalytic converter can be carried out, during the operation of the vehicle.

[0047] In other words, the process is implemented in the vehicle when the vehicle is in use, when it is moving.

[0048] If the stability state conforms to the instructions C, i.e., if stable operating data Dm are recorded (for example, detection of an engine temperature within a predetermined temperature range, stable engine idle within a predetermined revolutions per minute range, etc.), then the following steps are implemented:

[0049] Among the two cylinders 2 and 3 (or even 4), we will determine a master cylinder 2 and a slave cylinder 3. In other words, we will choose one cylinder from among the engine cylinders, which will be the reference cylinder for the operation of the other cylinders.

[0050] We will then command, for said master cylinder 2, a predetermined fuel supply cycle: for example, we will alternate an over-injection of fuel into cylinder 2 followed by an under-injection, during predetermined time intervals and several times in succession (this is only an example, any other cycle could be accepted provided that there is an alternation of over-injection and under-injection stages).

[0051] The slave cylinder 3 (and / or 4) will be controlled in the same way: in other words, the control module 9 will control the same supply cycle as that applied to the master cylinder 2.

[0052] Then, following a further step, the oscillations of the signals transmitted by the probes 20 and 30 at the output of the master cylinder 2 and slave cylinder(s) 3 (and / or 4) will be monitored. This step is carried out by the sub-module 82 on the [Fig.2].

[0053] If an absence of oscillation is observed in the signal of said at least one slave cylinder, then the fuel supply is stopped according to said predetermined cycle of said at least one slave cylinder 3 (step “stop” on the [Fig.2]) until oscillations of the signal of said at least one slave cylinder 3 are read again and, if the state of stability is compliant, the fuel supply is resumed according to said predetermined cycle of the slave cylinder 3.

[0054] In other words: During master / slave control mode, when oscillations of the slave cylinder signal are no longer observed, this means that its combustion mixture has shifted towards a richer or leaner mixture, and it no longer switches from one side to the other. In this situation, according to the invention, the slave cylinder 3 is no longer controlled with the same command as the master cylinder 2; however, it is reactivated with its dedicated command, adapted solely to this slave cylinder 3, through an alternating over / under injection specific to it.

[0055] When the signal from the probe 73 of the slave cylinder 3 starts to oscillate again, then the piloting of the slave cylinder 3 is again commanded according to the predetermined cycle based on the cycle of the master cylinder 2. If, on the other hand, the signal emitted by the probe 73 of the slave cylinder 3 is considered coherent, then the signal SI at the output of the catalytic converter 6 is compared to the signal S2 of the master cylinder and the diagnostic module 8 makes the diagnosis on the operating state of the catalytic converter 6.

[0056] In the event of failure of said catalytic pot 6 (observation of an oscillating signal by the probe 71 which corresponds to the signal S2) then an alert signal A can be transmitted to the driver via the dashboard of the vehicle.

[0057] Preferably, several diagnostic loops may be carried out before transmitting the warning signal, in order to ensure the result of the faulty catalysis diagnosis made by the diagnostic module 8. The number of loops that must lead to the same conclusion of "failure", before alerting the driver of the vehicle, can be calibrated by the manufacturer.

[0058] If the diagnostic module determines that the catalytic converter is in good working order (arrow "yes" at the output of the diagnostic module 8 - [Fig.2]), then the diagnostic loop is repeated to re-establish the operating diagnosis. of the catalytic converter at the next time when engine operating conditions are stable.

[0059] The method of implementing the process according to the invention, which has just been described, relates to an engine operating mode where the cylinders are controlled independently.

[0060] The method according to the invention can also make it possible to diagnose the proper functioning of the catalytic converter in the case where the fuel supply to cylinders 2, 3 (and 4 possibly), according to said supply cycle, is carried out simultaneously for said cylinders of said combustion engine.

[0061] The fuel supply control of the cylinders is also carried out according to a predetermined supply cycle which includes an alternation of fuel over-injection and fuel under-injection during predetermined time intervals.

[0062] As for the process described above, the presence of polluting compounds is detected at the direct outlet of at least one of the cylinders 2 and 3, by at least one of the probes 72 or 73, upstream of said common evacuation conduit 50, so as to generate an oscillating output signal from cylinders S2 or S3, which is representative of the quantity of polluting compounds evacuated by the cylinder concerned.

[0063] Then, this oscillating signal S2 or S3 is compared with the signal SI of said probe 71 by the diagnostic module 8.

[0064] If the SI signal reveals no or few oscillations, then the catalytic converter 6 is working perfectly.

[0065] If, on the other hand, the signal SI includes oscillations which correspond substantially to those of the signal S2 or S3, depending on the intensity of the oscillating signal, the wear of the catalytic converter is determined and whether or not it should be diagnosed as being faulty.

[0066] It is understood from the preceding description how the invention makes it possible to achieve its objective of determining the state of operation of a catalytic converter, by allowing a comparison of signals upstream and downstream of the converter which leaves no doubt about the presence of pollutants, upstream of the converter, thanks to the positioning of the probes at the direct outlet of cylinders 2 and 3 of the engine, upstream of the common exhaust duct.

[0067] It is also understood how the steps of the process, aimed at producing a controlled upstream signal S2 and / or S3, to compare it to the downstream signal of the catalytic pot SI, make it possible to ensure the relevance of the diagnosis obtained.

[0068] It should be understood, however, that the invention is not limited to the examples described and illustrated and that it extends to the implementation of any equivalent means.

Claims

1. Demands Diagnostic method for checking the operation of a catalytic converter (6) in the exhaust gases of an internal combustion engine (1), the engine having at least two cylinders (2, 3, 4) supplied independently with fuel, each cylinder (2, 3, 4) comprising a gas discharge duct (20, 30, 40) which opens into a common discharge duct (50), said catalytic converter (6) being positioned at the end of said common discharge duct (50), said method ensuring the diagnosis of the operation of said catalytic converter (6) by taking into consideration a signal (SI) emitted by a first probe (71) placed downstream of the catalytic converter (6), said first probe (71) detecting the presence of a first quantity of polluting compounds at the outlet of the catalytic converter (6), said method comprising the following steps: - monitoring of a stable state of engine operation by analysis of data (Dm) relating to a predetermined engine load interval (1) and, if the stable state is compliant: - control of a fuel supply to said at least two cylinders (2, 3, 4) according to a predetermined supply cycle comprising an alternation of fuel over-injection and fuel under-injection during predetermined time intervals, - detection, at the direct outlet of at least one of said at least two cylinders (2, 3, 4), by at least one second probe (72, 73, 74) among second probes placed downstream of each of the cylinders (2, 3, 4) upstream of said common evacuation conduit (50), of the presence of polluting compounds so as to generate, for each of said at least two cylinders (2, 3, 4), an oscillating output signal (S2, S3) of cylinders (2, 3, 4) representative of the quantity of polluting compounds at the outlet of each of said at least two cylinders (2, 3, 4), - comparison of the oscillating output signals (S2, S3) of cylinders with said signal (SI) of said first probe (71) by a diagnostic module (8), - diagnosis made by said diagnostic module (8).

2. Diagnostic method according to claim 1, characterized in that the step of controlling the fuel supply to said at least two cylinders (2, 3, 4), according to said supply cycle, is carried out simultaneously for said at least two cylinders (2, 3, 4) of said combustion engine.

3. Diagnostic method according to claim 1, characterized in that the step of controlling the fuel supply of said at least two cylinders (2, 3, 4) is carried out independently for each of said at least two cylinders (2, 3, 4), in the following manner: - among said at least two cylinders (2, 3, 4), determination of a master cylinder (2), and of at least one slave cylinder (3, 4), - control of said predetermined supply cycle for said master cylinder (2), - control of a supply cycle similar to said predetermined supply cycle for said at least one slave cylinder (3, 4), and - monitoring of the oscillating output signals (S2, S3) of the master and slave cylinder(s).

4. A method according to claim 3, characterized in that, during the step of monitoring the oscillating output signals (S2, S3) of the master (2) and slave(s) cylinders (3, 4), an absence of oscillation of the signal (S3) of said at least one slave cylinder (3, 4) is observed, then the fuel supply is stopped according to said predetermined cycle of said at least one slave cylinder (3, 4) and the fuel supply is resumed to said at least one slave cylinder (3, 4) independently of the other cylinders until oscillations of the signal of said at least one slave cylinder (3, 4) are read again and, if the stability state (Dm) is compliant, the fuel supply is resumed according to said predetermined cycle of said at least one slave cylinder (3, 4).

5. An installation for carrying out the method according to any one of the preceding claims, the installation comprising an internal combustion engine (1) having at least two cylinders (2, 3, 4) supplied independently with fuel, each cylinder (2, 3, 4) having a gas exhaust duct (20, 30, 40) which opens into a common exhaust duct (50), a catalytic converter (6) being placed at the end of the common exhaust duct (50) and a first probe (71) being placed downstream of the catalytic converter (6), said first probe (71) detecting the presence of a first quantity of polluting compounds at the outlet of the catalytic converter (6), said installation being characterized in that it comprises: - at least one second and one third probes (72, 73, 74), each of the probes being positioned in an exhaust duct (20, 30, 40) of a cylinder (2, 3, 4) of the internal combustion engine (1) upstream of said common exhaust duct (50), - a monitoring module (C) for the stability of engine operation by analyzing data (Dm) relating to a predetermined engine load range, - a control module (9) for supplying fuel to said at least two cylinders (2, 3, 4) of said internal combustion engine (1) according to a predetermined cycle of fuel injection or non-injection, at predetermined intervals, - a diagnostic module (8), capable of analyzing: said at least two oscillating signals (S2, S3) from cylinder output (2, 3, 4) representative of the quantity of polluting compounds at the output of each of said at least two cylinders (2, 3, 4), and said a signal (SI) emitted by said first probe (71) placed downstream of the catalytic converter (6), and capable of establishing a diagnostic of the operation of said catalytic converter (6).