Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
  • F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
  • F02D41/1476—Biasing of the sensor
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/02—Circuit arrangements for generating control signals
  • F02D41/14—Introducing closed-loop corrections
  • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
  • F02D41/1493—Details
  • F02D41/1495—Detection of abnormalities in the air/fuel ratio feedback system

Definitions

• the present invention relates to a method of electrical diagnosis of an oxygen sensor of the lambda type mounted on the exhaust line of an internal combustion engine.
• the present invention relates more particularly to the diagnosis of a lambda probe equipping the exhaust line of an internal combustion engine supplied with carbide mixtures of suitable richnesses and in particular with lean mixtures.
• Internal combustion engines are conventionally equipped with an electronic control system which adjusts, from preprogrammed strategies and according to the operating conditions of the engine, the quantity of fuel injected and the ignition time for spark-ignition engines .
• Some engines are powered today with a fuel mixture whose richness is adapted to the conditions. engine operation and which are notably supplied with lean burn during the partial load operation phases.
• the oxygen sensor or sensors placed on the engine exhaust line have function of informing the electronic control system of the actual oxygen concentration in the exhaust gases.
• diagnostic means to cause, when there is a failure of an element acting on the level of pollution of the engine, either the activation of degraded operating modes and / or the lighting of a warning light on the switchboard. on board warning the driver (light regulations), either implementing corrective measures, or even stopping the vehicle (strict regulations).
• Equipment manufacturers and car manufacturers have therefore developed a certain number of technical devices making it possible to diagnose malfunctions of the sensors fitted to the engines in general and oxygen sensors in particular.
• This process is however not of general application because it does not make it possible to diagnose the electrical connection of an oxygen probe of the lambda type, which indicates only one rich or poor state compared to the stoichiometry (or richness 1), when such a probe is positioned downstream of a treatment catalytic converter accelerating in particular the oxidation reactions of the exhaust gases.
• Such downstream positioning of an oxygen sensor is used to allow the operation of the catalytic converter to be controlled or to operate a so-called "double loop" regulation when the engine operating conditions require operating with a mixture stoichiometric, such as in slow motion, etc.
• oxidation catalytic converter intended to accelerate oxidation reactions
• oxidation catalytic converter it being understood that such a pot n is not limited only to the acceleration of oxidation reactions and that it can also accelerate reduction reactions as in the case of three-way pots (called selective or trifunctional) with one or more beds
• oxidation catalytic converter it being understood that such a pot n is not limited only to the acceleration of oxidation reactions and that it can also accelerate reduction reactions as in the case of three-way pots (called selective or trifunctional) with one or more beds
• the signal of a lambda oxygen sensor placed downstream of this pot only switches between the extreme values of tension corresponding to the "rich” or “poor” states only over relatively periods Long, the simple observation of the non-tilting of the probe on either side of the bias voltage therefore does not allow to diagnose the state of the electrical connection.
• the object of the invention is therefore to remedy the drawbacks of the prior art by proposing a method of electrical diagnosis of a lambda oxygen sensor disposed downstream of an oxidation catalytic converter.
• This diagnostic method which is more particularly adapted to an engine supplied with lean mixture under predetermined operating conditions, does not require any specific measurement means and is therefore simple to implement.
• the electrical diagnostic method relates to an oxygen sensor of an internal combustion engine operating according to several richness values and in particular in lean mixture, this oxygen sensor of the lambda type being disposed on the exhaust line downstream of a catalytic converter for treatment by oxidation of polluting gases and emitting an electrical signal, the voltage level of which is representative of the difference in richness with the stoichiometric ratio, intended for the electronic engine control system by means of an electrical connection in response to a suitable bias current.
• the method for diagnosing an oxygen sensor comprises the following steps: monitoring the operation of the engine; when predetermined operating conditions are observed where the richness of the fuel mixture remains different from the stoichiometry for a sufficient period, such as the lean mixture operating phases, measure the voltage level of the signal emitted by the oxygen sensor; compare this voltage value to the bias voltage; deduce therefrom if the voltage value is substantially equal to the bias voltage the existence of a fault on the electrical connection of the probe, and otherwise the absence of a fault on the electrical connection of the probe.
• these predetermined operating conditions during which the voltage level of the signal emitted by the oxygen sensor is measured include the operating phases of the engine in lean mixture.
• these operating conditions during which the voltage level of the signal emitted by the oxygen probe is measured include the operating phases of the engine in admixture rich.
• these predetermined operating conditions during which the voltage level of the signal emitted by the oxygen probe is measured include the operating phases of the engine in rich mixture used for the treatment of nitrogen oxides generated during the lean mixture operating phases and which are stored in a suitable catalytic converter.
• the measurement of the voltage level of the signal emitted by the oxygen sensor under the predetermined engine operating conditions is observed only after a suitable delay period.
• FIG. 1 is a schematic view of an internal combustion engine equipped with an electronic control device for implementing the method according to the invention
• FIG. 2 is a detailed view of the electrical circuit connecting a measurement sensor, such as the downstream oxygen sensor, to the electronic control device presented in FIG. 1.
• a measurement sensor such as the downstream oxygen sensor
• an internal combustion engine more particularly intended to equip a motor vehicle.
• This engine is a four-stroke multi-cylinder engine, of the direct injection and controlled ignition type operating according to several richness values and in particular in lean mixture.
• the present invention is not limited to a direct injection engine and can also be applied to an indirect injection engine provided that the latter operates according to several richness values and in particular in lean mixture.
• the illustrated motor conventionally comprises an air intake circuit 3 provided with a butterfly type flap 4 making it possible to adjust the quantity of air admitted and an idle bypass circuit cooperating with a regulating valve 5.
• the fuel is injected directly into each combustion chamber 12 thanks to an electro-injector 2 housed in the cylinder head of the engine and opening into the roof of the chamber 12.
• a spark plug ignition system 6 initiates combustion fuel mixture previously compressed in the engine cylinders.
• the burnt gases are discharged into the atmosphere through an exhaust line 10 equipped with a catalytic converter 13 intended in particular to treat by oxidation the polluting gases and more particularly the unburnt hydrocarbons HC and carbon monoxide CO and, a catalytic converter 19 for treating polluting gases and more particularly nitrogen oxides NOx by reduction.
• a catalytic converter 13 intended in particular to treat by oxidation the polluting gases and more particularly the unburnt hydrocarbons HC and carbon monoxide CO and, a catalytic converter 19 for treating polluting gases and more particularly nitrogen oxides NOx by reduction.
• the catalytic converter 19 also called NOx trap more particularly has the function of storing the nitrogen oxides produced in particular during the lean mixture operating phases and of regularly operating their catalytic conversion in the presence of hydrocarbon during the mixed operating phases. rich.
• each electro-injector 2 as well as the advance of the ignition of the spark plugs 6 or the opening of the regulation valve idle 5 are directly controlled by an electronic control system or injection computer 7.
• the formulas and the fundamental parameters for the optimal adjustment of the engine are stored, these parameters being obtained beforehand at the engine test bench. These are in particular the parameters relating to the time of start of injection or fuel injection phase, the duration of opening of the injectors 2 which corresponds to an amount of fuel injected and therefore to a richness of the fuel mixture filling the combustion 12, or else the spark plug ignition phase 6, etc.
• the injection computer 7 essentially consists of a microprocessor or central processing unit CPU, random access memories RAM, read-only memories ROM, analog-digital converters A / D, and various interfaces of inputs and outputs.
• the microprocessor of the injection computer 7 includes electronic circuits and appropriate software to process the signals from different suitable sensors, to deduce the states of the engine and to implement predefined operations in order to generate the appropriate control signals at destination. including injectors and ignition coils.
• the input signals of the injection computer 7 are: the "load” information given by a throttle position sensor, the "manifold pressure” information given by a pressure sensor 9 disposed in the circuit d admission 3 downstream of the throttle body 4, the "speed” information given by an angular position sensor 8 cooperating with a toothed target carried by the crankshaft and the "richness” information given by the output signals of two sensors or oxygen probes 14 and 15 arranged on the exhaust line 10 of the engine on either side of the catalytic converter 13.
• the opening time Ti of the injectors determining the dosage of the quantity of fuel injected and the richness of the fuel mixture filling each combustion chamber 12 is adapted according to the operating conditions of the engine, for example from predetermined values stored in the form of pressure / speed maps in the memories of the electronic engine control device 7.
• the theoretical values of the duration of the injections read are then modulated by correcting parameters depending in particular on the air temperature, the water temperature, the voltage battery, accelerations, rattling, etc., as well as by the output signal from oxygen sensors 14 and 15.
• the oxygen probes 14 and 15 are connected via a connecting wire to a specific input / output stage of the injection computer 7.
• the signal supplied by the probe 14 arranged at the outlet of the exhaust manifold upstream of the catalytic converter 13, a probe which is preferably of the proportional or UEGO type, serves to correct the quantity of fuel which is injected upstream of the engine cylinders by means of a suitable feedback loop, so as to adjust the richness value of the fuel mixture to the value chosen taking into account the operating conditions of the engine.
• the second probe 15 disposed downstream of the catalytic converter 13 is a non-linear or lambda type probe, adjusted to the richness 1 corresponding to the stoichiometric ratio.
• the probe 15 is shown in Figure 1 also downstream of the pot 19 but this is not limiting of the invention and it is perfectly possible to have the probe 15 upstream of the pot 19, this position upstream of the pot 19 being preferable in particular to operate a rapid diagnosis in the rich operating phase, in particular to purge the pot 19.
• Such a lambda probe 15 has several uses, it is used to measure the performance of the catalytic converter 13 as well as to adapt the air / fuel ratio supplied by the first loop during the richness operating phases 1, by changing for example its point of operation or the transfer function used to alleviate in particular the aging of the upstream probe 14 or else to operate the real-time regulation of the fuel / air ratio.
• a probe 15 is conventionally formed by a ceramic body (such as zirconium dioxide) of which one part is in the flow of the exhaust gases and the other is connected to atmospheric air, the two sides of the body. being coated by gas permeable platinum electrodes.
• the electrodes of the lambda probe 15 supplied by a suitable electric current called polarization, in return supply a voltage characteristic of the richness of the fuel mixture.
• the voltage between the terminals of the electrodes is found to be significantly modified on either side of the bias voltage corresponding to richness 1, by the differences in oxygen concentration between the two sides of the probe, due particular properties of the materials used. Monitoring this voltage therefore makes it possible to determine the evolution of the richness of the gases relative to the stoichiometry.
• This stage 17 intended to supply a suitable bias current comprises an electronic circuit comprising two resistors in series RI and R2 at the terminals of which a substantially constant voltage Va is applied.
• the lambda probe 15 is connected to this circuit via its connecting wire 16 in parallel with the resistance RI.
• the voltage Vs which is read across the resistor RI by a resistive circuit R3 and capacitive Cl which is connected to an analog / digital converter (not shown), is the output voltage Vs of the lambda probe 15.
• the choice of the various components of the electronic circuit of the interface 17 and in particular of the resistors RI and R2 are adapted, so that the output voltage fluctuates for example between "low” states of around 100 mV and "high” of about. 700 mV, for respectively “lean” or “rich” wealth of the fuel mixture, that is to say when the content of the exhaust gases is respectively below or above the set value of the wealth, the bias voltage substantially corresponding to the output voltage when the richness of the fuel mixture is at the set value being approximately 400 mV.
• the sensitivity of the sensor 15 is adapted so that any variation in the richness around the set value causes the output voltage to switch to its high or low limit values.
• the method for diagnosing the connecting wire 16 between the injection computer and the downstream lambda probe 15 using the injection computer 7 is then as follows.
• a short circuit of the wire 16 to ground is identified by a probe output voltage Vs below a suitable threshold value Vccm such as for example 50 V.
• Vccm a suitable threshold value
• the comparison between Vs and Vccm is therefore carried out at regular intervals during the engine operation and condition link 16 is considered satisfactory if the output voltage Vs is greater than Vccm, on the other hand if Vs becomes less than Vccm then the probe 15 is declared to short-circuit to ground and suitable strategies such as operation in degraded mode or again the emission of an alert signal intended to warn the driver by means notably of an indicator light or also the storage of a corresponding diagnostic code in order to orient the repairman on the defective element, are triggered by the injection computer 7.
• a short circuit of the connecting wire 16 at the battery voltage is identified by a probe output voltage Vs greater than a second suitable threshold value Vccb such as for example 1.5 V.
• Vccb a second suitable threshold value
• the comparison between Vs and Vccb is therefore made at regular intervals during engine operation and the state of the link 16 is deemed satisfactory if the output voltage Vs is lower Vccb, on the other hand if Vs becomes higher than Vccb then the probe 15 is declared as battery short-circuit and strategies adapted to the aforementioned type are then triggered by the injection computer 7.
• the strategy implemented consists in waiting for the occurrence of predetermined operating conditions of the motor 1 which involves the switching of the output voltage Vs the lambda 15 probe to a low value (or high) and to observe if indeed we have such a value.
• the first step of the process therefore consists in monitoring the operating conditions of the engine and in identifying the occurrence of a predetermined operating phase of the engine 1 during which the richness of the fuel mixture remains different from the stoichiometry for a sufficient duration such that the phases operating under partial load during which the engine is supplied with lean mixture (richness 0.7).
• Partial loads during which the fuel injection is depleted are characterized by maintaining the accelerator pedal in an intermediate position between the raised foot and full foot position (information provided by a position sensor linked to the pedal accelerator or throttle valve) and on the other hand, by an engine rotation speed between predetermined threshold values.
• the diagnostic strategy then consists in comparing to each operating phase in lean mixture (or according to any other periodicity, for example the first operating phase in lean mixture of each operating cycle of the engine) the output voltage.
• Vs of probe 15 (which must then be at its low level of 100 mV characteristic of a lean fuel mixture) at a third threshold value Vco such as for example 200 mV.
• the oxidation catalytic converters generally used have the primary function of completing the combustion of the fuel mixture which is only incomplete inside the engine. It is then a question of grouping on catalytic sites oxidizing molecules and reducing molecules present in the exhaust gases so that they combine in order to produce water and carbon dioxide. These sites are formed on a monolith which is a porous structure having a large contact area with the exhaust gases passing through the pot, and which is coated with various chemical substances having catalytic properties.
• This function makes it possible to compensate for the incomplete combustion inside the cylinders of the engine but does not make it possible to eliminate the polluting substances only when the initial fuel mixture is a stoichiometric mixture.
• the catalytic converters also have the ability to "store" oxygen atoms by oxidation of chemicals present in the catalyst, such as cerium.
• the exhaust gases which enter the catalytic converter come from the combustion of a lean mixture, they contain excess oxygen atoms and these are stored in the catalytic converter.
• the exhaust gases which arrive in the pot contain reducing molecules but these can combine with the oxygen atoms, previously stored in the catalytic converter during a phase operating with a lean mixture to produce water and carbon dioxide.
• the catalytic converter therefore has the function not only of promoting chemical reactions between substances contained in the exhaust gases, but it also has the function of being a buffer stock of oxygen molecules which makes it possible to regulate the composition of gas emitted into the atmosphere at the outlet of the pot.
• the adapted delay period T is therefore determined according to the engine operating conditions and in particular the evolution of the operating regime, the engine displacement and the oxygen adsorption capacity of the catalytic converter used, so that the mass of air discharged to the exhaust after this period exceeds the oxygen adsorption capacity of the catalytic converter and therefore that the gases leaving the catalytic converter 13 are poor.
• the lean mixture operating phase continues after period T, we then, and only then, compares Vs and Vco and if Vs remains greater than Vco then the probe 15 is declared in open circuit and corresponding strategies are triggered by the injection computer. If the lean mixture operating phase is interrupted before the end of the period T, the diagnostic strategy is then stopped and it is restarted during the next lean mixture operating phase.
• the conditions for implementing the diagnostic process of the open circuit are therefore twofold, namely the operation of the engine 1 in lean mixture and the maintenance of such operation beyond a given duration necessary for the air saturation of the catalytic converter 13.
• the injection computer 7 compares the output voltage Vs of the probe 15 with the threshold value Vco.
• This effective control of the link state 16 is operated as far as possible at least once during each engine operation.
• the diagnostic method according to the invention can also be implemented during the phases of operation in a rich mixture (richness between 1.1 and 1.7) necessary for the catalytic treatment of nitrogen oxides NOx.
• the pot 19 only stores nitrogen oxides during the lean mixture operating phases.
• the catalytic conversion of nitrogen oxides requires a reducing medium, which is the case for hydrocarbons. It is therefore necessary to operate regularly, before the storage sites are saturated, destocking phases with a fuel mixture of suitable richness.
• the transient phases of purging the stock of nitrogen oxides in a rich mixture therefore constitute engine operating phases during which the richness of the fuel mixture remains clearly distinct from the richness 1 corresponding to the stoichiometry and therefore during which it is possible to d '' observe or not the tilting of the output voltage of the probe 15.
• the procedure for the diagnostic process is substantially identical to that described for the lean mixture operating phases, except that it is necessary to provide a suitable period T ′ and to reverse the comparison since the probe 15 must, if everything works well, switch to its high threshold and not to its low threshold.
• This time delay period T 'required to operate the diagnosis is determined so as to guarantee that the catalytic converter 13 has, by this deadline, completely emptied its buffer stock of oxygen molecules and that consequently the exhaust gases at the outlet of pot are very rich in hydrocarbons and normally imply, if everything works correctly, the switching of the output voltage of the probe to its rich level.
• the engine may not be equipped with the catalytic converter 19 intended for the treatment of nitrogen oxides.
• the electronic control system can control the quantity of petrol injected independently of the signal from the upstream oxygen sensor 14, using other regulation criteria than the richness of the fuel mixture such as for example the stability of the combustions.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
• Exhaust Gas After Treatment (AREA)
• Combined Controls Of Internal Combustion Engines (AREA)

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• 1996
  • 1996-12-20 FR FR9615724A patent/FR2757634B1/fr not_active Expired - Lifetime
• 1997
  • 1997-12-12 ES ES97951321T patent/ES2213842T3/es not_active Expired - Lifetime
  • 1997-12-12 WO PCT/FR1997/002284 patent/WO1998028615A1/fr active IP Right Grant
  • 1997-12-12 EP EP97951321A patent/EP0946868B1/de not_active Expired - Lifetime
  • 1997-12-12 DE DE69727588T patent/DE69727588T2/de not_active Expired - Lifetime
  • 1997-12-12 AU AU54891/98A patent/AU5489198A/en not_active Abandoned

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