FR2862085A1 - Method of controlling the state of clogging of a catalytic converter for a vehicle by measuring the richness of exhaust gases upstream of the converter for a known richness from the engine - Google Patents

Abstract

The richness of the exhaust gases from an engine is modified so it is in a range of predetermined values and during at least one predetermined period an electrical voltage leaving a probe (8) measuring the richness of the exhaust gases upstream of the converter (6) is analyzed. Comparison with preset threshold voltage values allows the amount of clogging to be determined : The modification stage is controlled following reception of data about the state of the vehicle, or independently of the state of the vehicle. The range is for a ratio of theoretical air mass supplied to the engine during a predetermined period in stoichiometric quantity for combustion of a fuel and a mass of air supplied to the engine over the same time, and is between 0.8 and 1.1. The analysis is carried out over two predetermined periods. One period starts when a measure of the richness is for the first time in the preset range after modification, or after this moment. If the probe is a Lambda probe, the method involves determining if, between preset instants Tx and T1, the voltage is at least once below a preset threshold U1 and if, between preset instants T0 and T2, the tension becomes less than a preset threshold U2. Alternatively, the method involves determining if, between preset instants T0 and T1 the voltage becomes greater than a preset threshold U1 and if between preset instants T0 and T2 the voltage becomes less than a preset threshold U2. If the probe is a proportional probe, the method involves determining if, between preset instants T0 and T3 the voltage becomes greater than a preset threshold U3 and if between preset instants Ty and T4 the voltage becomes greater than a preset threshold U4. The driver of the vehicle is informed of the state of the converter. The converter is a first converter and the vehicle has a second catalytic converter upstream of the probe. The engine is a compression ignition engine. An independent claim is made for a control system to carry out the above process, with means of modifying the richness of the exhaust gases so they are in a predetermined range of values and means of analyzing an electrical voltage over a predetermined period to measure the richness of the exhaust gases upstream of the converter.

Description

The invention relates to controlling the clogging state of a converter

  catalytic converter implanted in the exhaust line of a motor vehicle engine.

  The invention is part of the innovations that currently lead to the development of exhaust aftertreatment systems, particularly for engines operating in lean mixture, and associated onboard diagnostics.

  It concerns both diesel engines and gasoline engines.

  Internal combustion engines are known to produce exhaust gases which contain polluting substances, such as nitrogen oxides or NOx, unburned hydrocarbons or HC, and carbon monoxide or CO and solid particles, which it is necessary to treat.

  The thresholds allowed for the emission of gaseous pollutants from motor vehicles are regularly revised downward as part of the evolution of the regulations on the depollution. In addition, in order to meet the European E-OBD pollution regulations, an on-board diagnostic system, integrated with engine management, is set up on vehicles.

  This monitoring system has two functions: it must detect failures of the components of the pollution control equipment used on the vehicle, and it must report to the driver any failure leading to exceeding the emission thresholds allowed for repair. fast. This monitoring system can indeed activate the ignition of an indicator on the dashboard to warn the driver and store a specific error code on the computer memory, in order to make repair easier.

  Known devices for reducing pollutant emissions include catalytic converters arranged in the exhaust line of the engine that can oxidize the reducing molecules that are carbon monoxide CO and HC unburned hydrocarbons. The catalytic converter is one of the components of the aftertreatment of the exhaust gases that must be monitored by the on-board diagnostic system.

  Such a converter is obtained by impregnating a catalytic phase in the channels of a monolith which is a porous structure having a large area of contact with the exhaust gas.

  This monolith can also be a particulate filter or NOx traps, also called NOx trap, in order to couple the oxidation post-treatment of CO and HC to post-treatment of particles and NOx.

  The catalytic phase consists of various chemical substances (precious metals: platinum, rhodium palladium) having catalytic properties. The purpose of these substances is to accelerate the oxidation kinetics of HC unburned hydrocarbons and CO carbon monoxide present in the exhaust gases, H2O water vapor and CO2 carbon dioxide.

  If the catalytic converter filters the carbonaceous particles, the catalytic phase accelerates when it kinetics oxidation of soot stored carbon dioxide CO, itself immediately oxidized to carbon dioxide 002.

  The precious metal catalytic phase can be coupled with zeolites to trap HC cold when the initiation temperatures of the oxidation reactions are not yet reached. HCs condense in the trap before being oxidized when the oxidation reactions begin. The catalytic phase also makes it possible to oxidize the hydrocarbons usually called SOF (soluble or soluble fractions or fractions of gasoline) which are bonded to the carbon core of the soot, which has the effect of reducing the size of the particles. In a certain defined temperature range, the nitrogen oxides are also converted.

  Thus, to meet the lower thresholds for emissions of gaseous pollutants from vehicles, one or more catalytic converters are arranged in the exhaust line of diesel engines for: oxidation of carbon monoxide CO and HC unburned hydrocarbons; filtering the particles and storing them in order to oxidize them during regeneration; and - store the NOx in order to reduce them during a purge.

  The catalytic converters used for this purpose may consist of an oxidation catalyst, a catalyzed particulate filter or a NOx trap, which may be combined in a single line (4-cylinder engine) or in several exhaust lines (V6 engine) of an internal combustion engine.

  But it appears that the operation of a converter can be damaged by progressive clogging with soot or any other substance such as residues from the fuel and the lubricant.

  Therefore, the diagnostic system must monitor, so that the vehicle is repaired, the good efficiency of the treatment of the contents of the catalytic converters and detect a malfunction that would increase the emissions of gaseous pollutants to the threshold that would simply decrease the efficiency of the system, which would also result in an increase in the exhaust back pressure (EPC) and which would be detrimental to the heat resistance of the turbo compressor.

  In order not to inconvenience the driver, it is important that the diagnostic strategy of the catalytic converter is robust and reliable so as to warn it only if there is certainty of a persistent malfunction of the post-processing system.

  In this context, the clogging of a component related to post-processing is a dysfunction that must be known to diagnose, the effect felt by the driver may be a lack of performance, or worse a breakage of the turbo compressor.

  An object of the invention is therefore to improve the monitoring of clogging of a catalytic converter which may be a simple oxidation catalyst such as a catalyzed particle filter or a NOx trap.

  For this purpose, the invention provides a method for monitoring the state of a catalytic converter of a vehicle, comprising the steps of: modifying the richness of the exhaust gases of an engine so that the richness is within a predetermined range of values; and then analyzing, for at least a predetermined period, an electrical voltage at the output of a probe for measuring the richness of the exhaust gases, arranged upstream of the converter.

  Thus the invention proposes to monitor the clogging of a catalytic converter using a wealth probe disposed upstream of the latter. This type of probe is already used in spark-ignition engines for the rich loopback necessary for the optimal operation of the three-way catalysis. The principle of use is the monitoring of the signal of the probe during an increase of the richness in order to detect a possible clogging of the latter by soot or any other substance (such as residues coming from the fuel and the lubricant ).

  Indeed, the coupling of the information processing from a wealth probe disposed upstream of the converter with an increase in the richness (operation a little less poor or transition to wealth close to 1) makes it possible to monitor the clogging of the component concerned. As will be discussed below, the diagnostic principle discussed herein is based on comparing the probe voltage with at least one threshold when the richness is within a certain range where the richness probes are particularly accurate. The increase in richness implemented in the context of the invention, whether normal or induced (purge NOx trap or regeneration FAP) can detect that the converter is clogged. It is then necessary to memorize a fault in the memory of the computer associated with the engine. The jump of wealth can be directly triggered by the diagnostic sequence.

  In case of noticeable effect on the driver of the vehicle such as for example a lack of performance of the vehicle, or in case of risk of breakage of the turbo compressor, a warning light can be activated or any similar system. It is also possible to trigger a degraded operating mode of the engine. Finally, it will be possible to limit the speed and / or the torque of the engine.

  The method according to the invention may furthermore exhibit at least any of the following characteristics: the modification step is controlled because of the reception of information concerning the state of the vehicle; the modification step is controlled independently of the state. of the vehicle; the range is the range [0.8-1.1], the richness being the ratio between: a theoretical air mass to be supplied to the engine for a predetermined duration in stoichiometric quantity for the combustion of a fuel; and a theoretical air mass actually supplied to the engine for the same duration; the analysis is carried out for two predetermined periods; the or at least one of the periods begins when a measure of the richness is for the first time in the predetermined range after the modification; the or at least one of the periods begins after the moment when a measure of the richness is located for the first time in the predetermined range after the modification; the probe is of LAMBDA type; - it is determined whether, between predetermined times Tx and Ti, the voltage is at least once less than a predetermined threshold U1, and if, between predetermined times TO and T2, the voltage remains below a predetermined threshold U2; - it is determined whether, between predetermined times TO and T1, the voltage remains greater than a predetermined threshold U1, and if, between predetermined times TO and T2, the voltage remains below a predetermined threshold U2; the probe is a proportional probe; it is determined whether, between predetermined times T0 and T3, the voltage remains greater than a predetermined threshold U3; it is furthermore determined whether, between predetermined times T 1 and T 4, the voltage remains greater than a predetermined threshold U 4; it comprises the step of notifying a driver of the vehicle of the state of the converter; - The converter being a first converter, the vehicle comprises a second catalytic converter disposed upstream of the probe; and the engine is a compression ignition engine.

  According to the invention there is also provided a system for monitoring the state of a catalytic converter of a vehicle, comprising: means for modifying the richness of the exhaust gases of an engine so that the wealth is in a predetermined range of values; and means for analyzing, for at least a predetermined period, an electrical voltage at the output of a probe for measuring the richness of the exhaust gases, arranged upstream of the converter.

  Other features and advantages of the invention will become apparent in the following description of a preferred embodiment and an alternative given by way of nonlimiting example with reference to the accompanying drawings, in which: FIG. schematic view of an engine for carrying out the method of the invention; - Figures 2 and 3 show each in two cases the evolution of the voltage of the probe in the context of this implementation; FIG. 4 illustrates a variant of the constitution of the motor of FIG. 1.

  FIG. 1 illustrates a motor 2 with its environment enabling the method according to the invention to be implemented. The engine is controlled by a control computer 4. It comprises in its exhaust line a post-processing component 6 in the form of a catalytic converter. It comprises in this same line a richness probe 8 arranged with reference to the flow of exhaust gases upstream of the component 6 to be diagnosed and making it possible to measure the air richness in the exhaust gases of the engine 2. The engine comprises a motor speed sensor 10, a pressure sensor 12 in the engine air intake circuit, a flow meter and a temperature sensor 14 disposed in the engine air intake circuit, and a circuit 16 recirculation of cooled exhaust gas.

  In the case in point, this engine is arranged to allow the realization of several injections (at least three) in the same cylinder 20 and during the same cycle, the engine comprising 4 cylinders 20 in the present example.

  The engine comprises a supercharger 22 and an inlet flap 24 both arranged in the intake circuit upstream of the pressure and intake temperature sensor 12. The exhaust gas recirculation circuit is associated with a heat exchanger 26. The engine comprises a turbo compressor 28 at the junction between the intake and exhaust circuits.

  The electronic computer 4 is associated in a manner known per se to maps and strategies adapted for the control of the engine and in particular for adjusting the air richness of the fuel air mixture. This adjustment is carried out in particular by means of the richness probe 8.

  The clogging of a converter such as the converter 6 is reflected in practice by a modification of the pressure levels in the exhaust line 30. Such a modification will influence the signal of the probe 8 disposed upstream of the converter when an increase of wealth is ordered. This increase in richness may, for example, be a richness pass 1 for purging a NOx trap type converter.

  In the present example, the richness probe 8 is of the voltage jump type or LAMBDA probe or alternatively of the proportional type (UEGO probe).

  The diagnosis of the state of the converter 6 takes place during the running of the vehicle. For this purpose, the computer 4 constantly receives voltage information from the probe.

  The implementation of the method will first be presented by means of a LAMBDA probe.

  It is assumed that the computer controls the modification of the air richness of the exhaust gases so that this richness is within a predetermined value range. The richness is defined here as the ratio between: a theoretical air mass to be supplied to the engine for a predetermined duration in stoichiometric quantity for the combustion of a fuel, and a mass of air actually supplied to the engine for the same duration.

  This will be for example the range between 0.8 and 1, 1.

  This modification step can be controlled due to the receipt by the computer of information concerning the state of the vehicle. This will for example the crossing of a threshold value by an operating parameter of the engine or more generally of the vehicle. Alternatively, it is conceivable that this modification step is controlled by the computer independently of the state of the vehicle, that is to say it is caused.

  The computer then monitors when the voltage across the probe 8 will be located for the first time in the aforementioned predetermined range.

  The calculator then determines whether, between instants Tx and Ti predetermined, the voltage U across the probe is at least once less than a predetermined threshold U1. The instant Tx corresponds in this case to a time being several seconds after the moment in which the wealth was located for the first time in the predetermined range. This instant has been indicated as TO + X in FIG. 2. The number of seconds separating these two instants can be parameterized.

  The computer also monitors whether, between the instant TO and a predetermined time T2, the voltage remains below a predetermined threshold U2. The instant T2 is later than the instant T1. The threshold U2 is greater than the threshold U1. If both of the above conditions are fulfilled, then it can be deduced that the converter 6 is clogged.

  Similarly, the computer 4 determines whether between the times TO and T1, the voltage remains greater than the threshold U1 and if between the times TO and T2, the voltage remains below the threshold U2. If this is the case, it is deduced that the converter 6 is being clogged.

  These different values have been illustrated in FIG. 2 which shows the evolution over time of the voltage U at the terminals of the probe 8 and illustrates these different periods and these different windows. One of these curves illustrates the behavior of the voltage U for a non-clogged converter while the other curve illustrates its behavior for a clogged converter. It is also possible to choose the value TO as a function of a voltage threshold UO specific to the probe and resulting from a prior calibration.

  If the computer determines that the converter is clogged, we can provide a driver information step, for example by means of a light. It will also provide the recording of the malfunction in the computer memory.

  If the probe 8 is a proportional probe, the operation is as follows.

  The computer determines whether, between predetermined times TO and T3, the probe remains greater than a predetermined voltage threshold U3. The time TO is that during which for the first time the measured wealth by the probe is in the predetermined range. If the above condition is fulfilled, then the computer determines that the converter downstream of the probe is being clogged.

  The computer further determines whether, between predetermined times Ty and T4, the voltage remains greater than a predetermined threshold U4. The threshold U4 is greater than the threshold U3. The instant T4 is later than the instant T3. The instant Ty is posterior of one or more seconds at the instant TO and has been represented by TO + YS in FIG. 3. The latter illustrates the behavior of the voltage as a function of time respectively in the case of a converter little charged and a clogged converter. If the two aforementioned conditions are met, then the computer 4 determines that the converter downstream of the probe is clogged. And again, the number of seconds between the TO and Ty instants can be chosen by the designer.

  An alternative embodiment of the invention has been illustrated in FIG. 4. On this, the motor is in all respects similar to that of FIG. 1 except that it comprises a second catalytic converter 40 located upstream of the probe 8 in the exhaust line 30. Therefore, the probe 8 is interposed in the exhaust gas circuit between the converter 40 and the converter 6 which remains the one to be diagnosed.

  The aforementioned thresholds and predetermined instants may be chosen experimentally without difficulty by those skilled in the art.

  The engine just described is a compression ignition engine. It can be a diesel engine or a gasoline engine.

  Of course, many modifications can be made to the invention without departing from the scope thereof.

Claims (17)

  1. A method of controlling the clogging condition of a catalytic converter (6) of a vehicle, characterized in that it comprises the steps of: modifying the richness of the exhaust gases of an engine for that the wealth is in a predetermined range of values; and then analyzing for at least a predetermined period an electrical voltage output of a probe (8) for measuring the richness of the exhaust gas disposed upstream of the converter.   2. Method according to claim 1 characterized in that the modification step is controlled due to the receipt of information on the state of the vehicle.   3. Method according to claim 1 characterized in that the modification step is controlled independently of the state of the vehicle.   4. Method according to any one of claims 1 to 25 3 characterized in that the range is the range [0.8-1.1], the richness is the ratio between: a theoretical air mass to provide the engine for a predetermined period of time in stoichiometric quantity for the combustion of a fuel; and a mass of air actually supplied to the engine for the same duration.   5. Method according to any one of the preceding claims, characterized in that the analysis is carried out for two predetermined periods.   6. Method according to any one of the preceding claims, characterized in that the or at least one of the periods starts when a measure of the richness is located for the first time in the predetermined range after the modification.   7. Method according to any one of the preceding claims, characterized in that the or at least one of the periods begins after the moment when a measure of the richness is located for the first time in the predetermined range after the modification.   8. Method according to any one of the preceding claims, characterized in that the probe (6) is of LAMBDA type.   9. Method according to any one of the preceding claims, characterized in that it is determined whether, between predetermined times Tx and Tl, the voltage is at least once less than a predetermined threshold U1, and if, between times TO and T2 predetermined, the voltage remains below a predetermined threshold U2.   10. Method according to any one of the preceding claims, characterized in that it is determined whether, between predetermined times TO and Tl, the voltage remains greater than a predetermined threshold U1, and if, between predetermined times TO and T2, the voltage remains below a predetermined threshold U2.   11. Method according to any one of claims 1 to 7 characterized in that the probe is a proportional probe.   12. Method according to any one of claims 1 to 7 or 11 characterized in that it is determined whether, between predetermined times TO and T3, the voltage remains greater than a predetermined threshold U3.   13. Method according to any one of claims 1 to 7 or 11 or 12 characterized in that it is further determined whether between predetermined times Ty and T4, the voltage remains greater than a predetermined threshold U4.   14. Method according to any one of the preceding claims, characterized in that it comprises the step of notifying a driver of the vehicle of the state of the converter.   15. Method according to any one of the preceding claims characterized in that, the converter (6) being a first converter, the vehicle comprises a second catalytic converter (40) disposed upstream of the probe (8).   16. Method according to any one of the preceding claims, characterized in that the engine is a compression ignition engine.   17. A system for monitoring the state of a catalytic converter (6) of a vehicle, characterized in that it comprises: means for modifying the richness of the exhaust gases of an engine (2) for the richness 10 is within a predetermined range of values; and O - means for analyzing, for at least a predetermined period, an electrical voltage at the output of a probe (8) for measuring the richness of the exhaust gases, arranged upstream of the converter.