EP4166776A1 - Method for diagnosing the plausibility of an air flow sensor in an internal combustion engine - Google Patents

Abstract

This method for diagnosing the plausibility of drift of an air flowmeter sensor adapted for the direct measurement of the flow of fresh air entering a heat engine associated with an air intake circuit and an exhaust circuit burnt gases having exhaust gas recirculation to the intake controlled by a flow control valve or a throttle valve, the method comprising no step of shutting off the exhaust gas recirculation valve, and comprising a step for calculating the median of the first, second, third and fourth fresh air flow values by different methods, and a step for comparing the value returned by the air flow meter with the previously calculated median.

Description

Technical area

The present invention relates to methods for diagnosing a thermal engine flow meter making it possible to determine whether it is defective or whether it drifts, in particular in the event of an intake air leak.

The present invention aims to constitute a diagnostic method which makes it possible to diagnose practically continuously the drift of the air flowmeter or to diagnose an intake leak, without necessarily cutting off the recirculation of the exhaust gases.

Prior techniques

On petrol or diesel engines equipped with a flow meter, the standard requires on-board diagnostics of a drift of this sensor to check the absence of air leaks at the intake.

Current diagnostics compare an engine fill pattern, which uses pressure and temperature sensors, with the air flow meter.

This requires cutting off the exhaust gas recirculation for five to ten seconds, which has an impact on the efficiency of pollution control and increases consumption, since recirculation makes it possible, when it is not cut off, to reduce nitrogen oxide emissions from a diesel engine and fuel consumption and carbon dioxide emissions from a gasoline engine.

It is therefore necessary to be able to limit these cuts as much as possible without restricting the on-board diagnostic capabilities.

The patent application FR2010965 discloses a method for diagnosing an air flow meter in a supercharged internal combustion engine, comprising at least one circuit for partial recirculation at low pressure of the exhaust gases at the intake of the engine, and which may further comprise a circuit for high pressure partial recirculation of the exhaust gases at the intake of the engine, said method comprising at least one step of cutting off the recycling of the exhaust gas then a main diagnostic step in which: a first value of the air flow admitted into the engine by the flow meter is measured; a second value of the air flow is calculated thanks to a filling model of the cylinders of the engine; and, it is concluded that the flowmeter is in good condition or faulty respectively when the absolute value of the difference between said first and said second value is lower or higher than a threshold.

This process aims to solve the problem of a recirculation circuit cutoff, but lacks precision because the pre-diagnosis does not always make it possible to conclude.

On the contrary, the invention makes it possible to obtain a diagnosis which minimizes the uncertainty on the diagnosis and which does not require the systematic cutting off of the recirculation circuit.

The patent application US2008/0270011 uses a model comparison with the airflow meter, with many variations of combustion mode and temperature settings, and does not provide an accurate fresh airflow model.

The patent application JP2006329138 describes an estimate of the compressor flow rate based on the rotational speed of the turbocharger and the compression ratio to then compare it to the air flow meter. The problem is getting the turbocharger speed which either comes from a turbocharger rpm sensor which is not available on all engines or from an unreliable turbine model for turbochargers.

Patent applications DE102014105838 And FR3053117 describe the use of a pressure sensor in the cylinders, which is not present on all thermal vehicles, to determine the mass of air enclosed in the cylinder, which is not functional in practice.

Disclosure of Invention

The object of the invention is to overcome at least some of the aforementioned drawbacks and to propose a diagnostic method capable of combining the advantages of precision, stability and reliability for its implementation.

• une étape de mesure d'une première valeur de débit d'air frais dans la ligne d'admission par ledit débitmètre,
• une étape d'estimation d'une deuxième valeur de débit d'air frais dans la ligne d'admission à partir d'un modèle de remplissage appliqué au débit d'air gazeux total entrant dans le moteur et d'un premier ensemble de débits d'airs annexes à la ligne d'admission,
• une étape de calcul d'une troisième valeur de débit d'air frais dans la ligne d'admission à partir d'une équation d'hydrodynamique de Barré de Saint-Venant aux bornes du volet d'admission et d'un deuxième ensemble de débits gazeux annexes à la ligne d'admission,
• une étape de calcul d'une quatrième valeur de débit d'air frais dans la ligne d'admission donné par un débit de carburant et un signal d'une sonde de richesse montée dans le circuit d'échappement du moteur.

In view of the foregoing, the subject of the invention is a method for diagnosing the plausibility of drift of an air flow meter sensor suitable for the direct measurement of the flow of fresh air entering a heat engine associated with a air intake circuit and a burnt gas exhaust circuit having recirculation of the exhaust gases towards the intake, the intake being controlled by an intake flap and the recirculation of the exhaust gases by a recirculation valve, the method comprising the following steps:

• a step of measuring a first fresh air flow value in the intake line by said flow meter,
• a step of estimating a second fresh air flow rate value in the intake line from a filling model applied to the total gaseous air flow rate entering the engine and from a first set of flow rates additional air to the intake line,
• a step of calculating a third fresh air flow rate value in the intake line from a Barré de Saint-Venant hydrodynamic equation at the terminals of the intake flap and from a second set of gas flows annexed to the admission line,
• a step of calculating a fourth fresh air flow value in the intake line given by a fuel flow and a signal from a richness sensor mounted in the exhaust circuit of the engine.

The method therefore does not require the exhaust gas recirculation valve to be cut off, but further comprises a step of calculating the median of the first, second, third and fourth fresh air flow rate values, and a step comparing the value returned by the air flow meter with the previously calculated median.

Preferably, the first set of gas flow rates annexed to the intake line comprises a flow rate of exhaust gas recycled to the engine intake. It may be for example a flow of recycled exhaust gas at high pressure, or a flow of recycled exhaust gas at low pressure, or both in combination.

Furthermore, the first set of gaseous flow rates annexed to the intake line can comprise a gaseous flow originating from the venting of a tank of fuel vapors.

Advantageously, the fuel vapor tank is part of a purge circuit having a first outlet point just after the flowmeter and a second outlet point after the intake flap. Alternatively, only one outlet point of the two may be present.

, est donnée par le calcul correspondant à l'équation 1 suivante : $$\begin{array}{l}{\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{mdl}}_{\mathrm{remplissage}}}}\\ ={\mathrm{Q}}_{{\mathrm{tot}}_{{\mathrm{mdl}}_{\mathrm{remplissage}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}\\ -{\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{amont}}_{\mathrm{compresseur}}}}-{\mathrm{Q}}_{{\mathrm{canister}}_{\mathrm{collecteur}}}\end{array}$$

The second airflow value, denoted ${\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}$

, is given by the calculation corresponding to the following equation 1: $$\begin{array}{l}{\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}\\ ={\mathrm{Q}}_{{\mathrm{early}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}\\ -{\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}-{\mathrm{Q}}_{{\mathrm{canister}}_{\mathrm{manifold}}}\end{array}$$

• o ${\mathrm{Q}}_{{\mathrm{tot}}_{{\mathrm{mdl}}_{\mathrm{remplissage}}}}$
  
  est le débit total donné par le modèle de remplissage en fonction au moins de la pression et de la température dans le collecteur d'admission du moteur et du régime moteur,
• o ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}$
  
  est un débit de gaz d'échappement recyclés à haute pression, calculé en utilisant la relation de Barré de Saint-Venant aux bornes du circuit de recirculation des gaz d'échappement à haute pression : $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{hp}}}\cdot {\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}{{\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}}$$
  
  où :
  • ▪ Se_egrhp est la section aéraulique de la vanne de recirculation à haute pression, calibrée en fonction de la recopie de position angulaire de ladite vanne,
  • ▪r est la constante massique des gaz parfaits pour l'air,
  • ▪ ${\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    est la pression en amont de la vanne de recirculation des gaz d'échappement à haute pression, issue d'un capteur ou d'un modèle,
  • ▪ ${\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    est la pression en aval de la vanne de recirculation des gaz d'échappement à haute pression, issue d'un capteur ou d'un modèle,
  • ▪ ${\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    est la température en amont de la vanne de recirculation des gaz d'échappement à haute pression, issue d'un capteur ou d'un modèle
  • ▪ $\mathrm{bsv}\left(\frac{{\mathrm{P}}_{\mathrm{amont}}}{{\mathrm{P}}_{\mathrm{aval}}}\right)$
    
    est la fonction de Barré de Saint-Venant,
  • ▪ ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}$
    
    est le débit des gaz d'échappement recyclés à basse pression calculé en utilisant la relation de Barré de Saint-Venant aux bornes du circuit de recirculation des gaz d'échappement à basse pression : $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{bp}}}\cdot {\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}{{\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}}$$
    

With :

• oh ${\mathrm{Q}}_{{\mathrm{early}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}$
  
  is the total flow given by the filling model as a function of at least the pressure and temperature in the engine intake manifold and the engine speed,
• oh ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}$
  
  is a high-pressure recirculated exhaust gas flow rate, calculated using the Barré de Saint-Venant relationship at the terminals of the high-pressure exhaust gas recirculation circuit: $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{hp}}}\cdot {\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}}$$
  
  Or :
  • ▪ Se _{egr hp} is the aeraulic section of the high pressure recirculation valve, calibrated according to the copy of the angular position of said valve,
  • ▪r is the ideal gas constant for air,
  • ▪ ${\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    is the pressure upstream of the high pressure exhaust gas recirculation valve, taken from a sensor or model,
  • ▪ ${\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    is the pressure downstream of the high pressure exhaust gas recirculation valve, taken from a sensor or model,
  • ▪ ${\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    is the temperature upstream of the high pressure exhaust gas recirculation valve, taken from a sensor or model
  • ▪ $\mathrm{bsv}\left(\frac{{\mathrm{P}}_{\mathrm{upstream}}}{{\mathrm{P}}_{\mathrm{downstream}}}\right)$
    
    is the Barré de Saint-Venant function,
  • ▪ ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}$
    
    is the low pressure recirculated exhaust gas flow rate calculated using the Barré de Saint-Venant relationship at the terminals of the low pressure exhaust gas recirculation circuit: $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{bp}}}\cdot {\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}}$$
    

• ▪ Se_egrbp est la section aéraulique de la vanne de recirculation à basse pression calibrée en fonction de la recopie de position angulaire de ladite vanne,
• ▪ ${\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
  
  est la pression en amont de la vanne de recirculation des gaz d'échappement à basse pression, issue d'un capteur ou d'un modèle,
• ▪ ${\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
  
  est la pression en aval de la vanne de recirculation des gaz d'échappement à basse pression, issue d'un capteur de pression ou d'un modèle,
• ▪ ${\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
  
  est la température en amont de la vanne de recirculation des gaz d'échappement à basse pression, issue d'un capteur ou d'un modèle,
• ▪ ${\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{amont}}_{\mathrm{compresseur}}}}$
  
  et Q_{canistercollecteur} sont les débits estimés de vapeurs de carburant réintroduits à l'admission du moteur respectivement en aval du débitmètre et en aval du volet d'admission, l'estimation étant réalisée par exemple en utilisant également le principe de Barré de Saint-Venant sur des vannes de commande des circuits de purge reliant le réservoir de vapeurs de carburant à l'admission du moteur.

With :

• ▪ Se _{egr bp} is the air section of the low-pressure recirculation valve calibrated according to the copy of the angular position of said valve,
• ▪ ${\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
  
  is the pressure upstream of the low pressure exhaust gas recirculation valve, taken from a sensor or model,
• ▪ ${\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
  
  is the pressure downstream of the low pressure exhaust gas recirculation valve, taken from a pressure sensor or model,
• ▪ ${\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
  
  is the temperature upstream of the low pressure exhaust gas recirculation valve, taken from a sensor or model,
• ▪ ${\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}$
  
  and Q _{canister manifold} are the estimated flow rates of fuel vapors reintroduced to the intake of the engine respectively downstream of the flow meter and downstream of the intake flap, the estimation being carried out for example by also using the principle of Barré de Saint-Venant on valves for controlling the purge circuits connecting the fuel vapor tank to engine intake.

• en calculant un ratio de diagnostic donné par le quotient de ladite première valeur sur la médiane, auquel quotient est soustrait un, puis
• en calculant l'erreur de diagnostic donnée par la différence entre ledit ratio de diagnostic et zéro, puis
• en intégrant dans le temps ladite erreur de diagnostic, puis
• en comparant l'intégrale de diagnostic obtenue à une première valeur seuil prédéfinie permettant le diagnostic de dérive du débitmètre d'air.

According to one embodiment, the calculated median is compared to the first fresh air flow rate value:

• by calculating a diagnostic ratio given by the quotient of said first value on the median, from which quotient is subtracted one, then
• by calculating the diagnostic error given by the difference between said diagnostic ratio and zero, then
• by integrating said diagnostic error over time, then
• by comparing the diagnostic integral obtained with a first predefined threshold value allowing the diagnosis of drift of the air flow meter.

• si le ratio de diagnostic est inférieur à la deuxième valeur seuil, l'intégrale de diagnostic est diminuée de ladite deuxième valeur seuil moins la valeur absolue du ratio, avant sa comparaison à la première valeur seuil,
• si le ratio de diagnostic est dans l'intervalle de non-diagnostic, l'intégrale de diagnostic est maintenue égale à elle-même pour sa comparaison à la première valeur seuil,
• si le ratio de diagnostic est supérieur à la troisième valeur seuil, l'intégrale de diagnostic est diminuée de ladite troisième valeur seuil moins la valeur absolue du ratio, avant sa comparaison à la première valeur seuil.

In one embodiment, a non-diagnosis interval defined by a second threshold value and a third threshold value less than said second threshold value is defined, and

• if the diagnostic ratio is lower than the second threshold value, the diagnostic integral is reduced by said second threshold value minus the absolute value of the ratio, before its comparison with the first threshold value,
• if the diagnostic ratio is in the non-diagnostic interval, the diagnostic integral is kept equal to itself for its comparison with the first threshold value,
• if the diagnostic ratio is greater than the third threshold value, the diagnostic integral is reduced by said third threshold value minus the absolute value of the ratio, before its comparison with the first threshold value.

For example, without limitation, the first threshold value is between fifteen and twenty-five hundredths.

où : $${\mathrm{Q}}_{{\mathrm{tot}}_{\mathrm{thr}}}=\frac{{\mathrm{Se}}_{\mathrm{thr}}\cdot {\mathrm{P}}_{{\mathrm{amont}}_{\mathrm{thr}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{amont}}_{\mathrm{thr}}}}{{\mathrm{P}}_{{\mathrm{aval}}_{\mathrm{thr}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{amont}}_{\mathrm{thr}}}}}$$

désigne le débit gazeux traversant le volet d'admission

• ▪ Se_thr est la section aéraulique calibrée en fonction de la recopie de position angulaire du volet d'admission,
• ▪ P_amontthr est la pression en amont du volet d'admission donnée par un capteur de pression,
• ▪ P_avalthr : Pression en aval du volet d'admission (capteur de pression collecteur ou modèle de pression aval volet d'admission),
• ▪ T_amontthr : température en amont du volet d'admission (issue d'un capteur ou d'un modèle),
  r est la constante massique des gaz parfaits pour l'air.

For example, the method can provide that the third air flow rate value, denoted Q _{air thr} , or given by the calculation corresponding to the following equation 2: $${\mathrm{Q}}_{{\mathrm{air}}_{\mathrm{thr}}}={\mathrm{Q}}_{{\mathrm{early}}_{\mathrm{thr}}}-{\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}$$

Or : $${\mathrm{Q}}_{{\mathrm{early}}_{\mathrm{thr}}}=\frac{{\mathrm{Se}}_{\mathrm{thr}}\cdot {\mathrm{P}}_{{\mathrm{upstream}}_{\mathrm{thr}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{\mathrm{thr}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{\mathrm{thr}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{\mathrm{thr}}}}}$$

designates the gas flow passing through the inlet flap

• ▪ Se _thr is the airflow section calibrated according to the copy of the angular position of the intake flap,
• ▪ P _{upstream thr} is the pressure upstream of the intake flap given by a pressure sensor,
• ▪ P _{downstream thr} : Pressure downstream of the inlet flap (manifold pressure sensor or model of pressure downstream of the inlet flap),
• ▪ T _{upstream thr} : temperature upstream of the inlet flap (from a sensor or a model),
  r is the ideal gas constant for air.

It should be noted that in this equation 2, contrary to the total gas flow estimated using the filling model, the gas flow passing through the intake flap does not include either the flow of exhaust gas recycled at high pressure, nor the flow of vapors of fuel introduced at the inlet of the intake manifold, these two flows being introduced downstream of said flap.

Preferably, whether or not each of the first, second, third and fourth flow rate values is taken into account is conditioned to calculate the median at a stability of said flow rate values, so as to take into account that the flow rates are not temporally synchronized and to rule out transient effects on the flow rates likely to move them away from their stable operating points.

• pour chaque équation d'hydrodynamique de Barré de Saint-Venant, exiger que le rapport entre la pression amont et la pression aval dépasse une quatrième valeur seuil,
• pour le calcul de la quatrième valeur de débit, exiger que le débit carburant ne passe sous une cinquième valeur seuil au-dessous de laquelle la dispersion de réalisation de la quantité injectée réelle de carburant par rapport à sa consigne est trop élevée,
• pour le calcul de la quatrième valeur de débit, exiger que la richesse ne passe sous une sixième valeur seuil au-dessous de laquelle l'imprécision de mesure de la sonde de richesse est grande, notamment supérieure à un pourcent.

The invention also relates to a method in which at least one of the following precision conditions is added which makes it possible to take into account or not the first, second, third and fourth flow rate values to calculate the median:

• for each Barré de Saint-Venant hydrodynamic equation, require that the ratio between the upstream pressure and the downstream pressure exceed a fourth threshold value,
• for the calculation of the fourth flow rate value, requiring that the fuel flow rate does not fall below a fifth threshold value below which the dispersion of realization of the actual injected quantity of fuel with respect to its setpoint is too high,
• for the calculation of the fourth flow rate value, requiring that the richness does not fall below a sixth threshold value below which the measurement inaccuracy of the richness probe is high, in particular greater than one percent.

detailed description

The method is aimed at diagnosing the plausibility of drift of a fresh air flowmeter sensor of a vehicle combustion engine, that is to say the flow of air taken from outside the vehicle.

• un filtre à air,
• un débitmètre adapté pour la mesure directe du débit d'air entrant dans le moteur,
• un compresseur de turbocompresseur adapté pour comprimer l'air combiné le cas échéant à des gaz d'échappement recyclés à basse pression à l'admission du moteur,
• un échangeur thermique adapté pour refroidir les gaz d'admission après leur compression dans le compresseur,
• un volet d'admission, dit aussi « boîtier papillon » dans le cas d'un moteur à essence, pour le réglage du débit d'air et de gaz d'échappement recyclés à basse pression entrant dans le moteur,
• un répartiteur ou collecteur d'admission du moteur,
  le circuit d'échappement comprenant, d'amont en aval dans le sens de circulation des gaz brûlés :
  • un collecteur d'échappement,
  • une turbine du turbocompresseur, montée sur un arbre commun avec le compresseur, qui sert à prélever de l'énergie sur les gaz d'échappement qui la traversent, cette énergie de détente étant transmise au compresseur, via l'arbre commun, pour la compression des gaz d'admission,
  • une pluralité de dispositifs de dépollution des gaz de combustion du moteur,
  • un ou deux circuits de recirculation partielle des gaz d'échappement à l'admission, dont par exemple un premier circuit de recirculation à haute pression prenant naissance en un point du circuit d'échappement situé en amont de la turbine et renvoyant les gaz en un point du circuit d'admission situé en aval du compresseur, et plus précisément en aval du volet d'admission, et par exemple un deuxième circuit de recirculation à basse pression adapté pour prélever des gaz d'échappement situés en aval de la turbine, généralement en aval d'au moins un des dispositifs de dépollution, et pour les renvoyer en un point du circuit d'admission situé en amont du compresseur, mais en tout cas en aval du débitmètre qui ne mesure donc qu'un débit d'air seul,
  • un filtre dans le circuit de recirculation des gaz d'échappement basse pression, ayant un refroidisseur et une vanne, dite vanne de recirculation à basse pression, qui permet d'obtenir un débit plus ou moins important de gaz recyclés à basse pression,
  • une vanne, dite vanne de recirculation à haute pression, qui permet d'obtenir un débit plus ou moins important de gaz recyclés à haute pression.

The method applies to a vehicle intake circuit which may include, for example, from upstream to downstream in the direction of air circulation:

• an air filter,
• a flow meter adapted for the direct measurement of the air flow entering the engine,
• a turbocharger compressor suitable for compressing the air combined, where appropriate, with low-pressure recycled exhaust gases at the engine intake,
• a heat exchanger adapted to cool the intake gases after their compression in the compressor,
• an intake flap, also called "throttle body" in the case of a gasoline engine, for adjusting the flow of air and low-pressure recycled exhaust gas entering the engine,
• an engine intake distributor or manifold,
  the exhaust circuit comprising, from upstream to downstream in the direction of circulation of the burnt gases:
  • an exhaust manifold,
  • a turbine of the turbocharger, mounted on a common shaft with the compressor, which is used to take energy from the exhaust gases which pass through it, this expansion energy being transmitted to the compressor, via the common shaft, for compression of the intake gases,
  • a plurality of engine combustion gas pollution control devices,
  • one or two partial exhaust gas recirculation circuits at the intake, including for example a first high pressure recirculation circuit originating at a point of the exhaust circuit located upstream of the turbine and returning the gases to a point of the intake circuit located downstream of the compressor, and more precisely downstream of the intake flap, and for example a second low-pressure recirculation circuit adapted to take exhaust gases located downstream of the turbine, generally downstream of at least one of the pollution control devices, and to return them to a point of the intake circuit located upstream of the compressor, but in any case downstream of the flow meter which therefore only measures an air flow alone ,
  • a filter in the low pressure exhaust gas recirculation circuit, having a cooler and a valve, called the low pressure recirculation valve, which makes it possible to obtain a greater or lesser flow rate of recycled gas at low pressure,
  • a valve, called a high pressure recirculation valve, which makes it possible to obtain a greater or lesser flow rate of recycled gas at high pressure.

In addition, the engine may include a fuel vapor purge circuit, having a first outlet point after the flowmeter and a second outlet point after the intake flap. Alternatively, only one outlet point of the two may be present.

The method allows in particular the diagnosis of the plausibility of drift of the air flowmeter sensor adapted for the direct measurement of the flow of fresh air entering the heat engine associated with the air intake circuit and the exhaust circuit of the burnt gases having a partial exhaust gas recirculation circuit at the intake, the intake being controlled by an intake flap and the recirculation of the exhaust gases by a recirculation valve.

• une étape de mesure d'une première valeur de débit d'air frais dans la ligne d'admission par ledit débitmètre,
• une étape d'estimation d'une deuxième valeur de débit d'air frais dans la ligne d'admission à partir d'un modèle de remplissage appliqué au débit gazeux total entrant dans le moteur et d'un premier ensemble de débits gazeux annexes à la ligne d'admission,
• une étape de calcul d'une troisième valeur de débit d'air frais dans la ligne d'admission par l'application d'une équation d'hydrodynamique de Barré de Saint-Venant aux bornes du volet d'admission et d'un deuxième ensemble de débits gazeux annexes à la ligne d'admission,
• une étape de calcul d'une quatrième valeur de débit d'air frais dans la ligne d'admission donné par un débit de carburant et un signal d'une sonde de richesse montée dans le circuit d'échappement du moteur.

The process includes the following steps:

• a step of measuring a first fresh air flow value in the intake line by said flow meter,
• a step of estimating a second fresh air flow rate value in the intake line from a filling model applied to the total gas flow rate entering the engine and from a first set of gas flow rates annexed to admission line,
• a step of calculating a third fresh air flow rate value in the intake line by applying a Barré de Saint-Venant hydrodynamic equation to the terminals of the intake flap and a second set of gas flows annexed to the admission line,
• a step of calculating a fourth fresh air flow value in the intake line given by a fuel flow and a signal from a richness sensor mounted in the exhaust circuit of the engine.

The step of estimating the second air flow value is carried out using equation 1 mentioned above and recalled below, in which the total gas flow is obtained from a filling model and the or the additional gas flow rates of the first set by Barré de Saint Venant equations (also mentioned above).

In general, the first set is made up of all of the gas flows, with the exception of the air flow, which enter the cylinders of the engine. In the example of Equation 1, these are the low and high pressure recirculated exhaust gas flows and the fuel vapor purge flows returned downstream of the flow meter and downstream of the intake flap . However, the list is not exhaustive.

formule dans laquelle :

• η_rdvl désigne le rendement volumétrique
• Qmot désigne le débit total entrant réellement, en kilogrammes par seconde
• Cylindrée désigne la cylindrée du moteur, en mètres cubes,
• Pcoll désigne la pression dans le collecteur d'admission, en Pascals
• Tcoll désigne la température dans le collecteur d'admission, en Kelvins
• r désigne la constante massique des gaz parfaits pour l'air
• N désigne le régime, en tours par minute

La valeur du rendement volumétrique dépend au moins du régime et de la pression dans le collecteur.The correspondence between the pressure in said manifold and the total gas flow in the engine Qmot is ensured by the following equation corresponding to the so-called engine filling model, the filling being the mass of air actually sucked in compared to the mass of air that could have entered considering the total volume of the cylinders: $${\mathrm{\eta }}_{\mathrm{appointment}}=\frac{{\mathrm{Q}}_{\mathrm{word}}.120}{\mathrm{NOT}.\mathrm{Displacement}.\frac{{\mathrm{P}}_{\mathrm{coll}}}{{\mathrm{T}}_{\mathrm{coll}}.\mathrm{r}}}$$

formula in which:

• η _rdvl is the volumetric efficiency
• Qmot is the actual total incoming flow, in kilograms per second
• Displacement means the displacement of the engine, in cubic meters,
• Pcoll is the pressure in the intake manifold, in Pascals
• Tcoll is the temperature in the intake manifold, in Kelvins
• r denotes the mass constant of ideal gases for air
• N is the speed, in revolutions per minute

The value of the volumetric efficiency depends at least on the speed and the pressure in the manifold.

If the engine is fitted with camshaft shifters allowing variable valve timing, and/or a variable valve lift system, the efficiency depends on their position since the valve opening law and the phasing in the combustion cycle affect the permeability of the combustion chambers.

The step of estimating the third air flow value is carried out using equation 2 mentioned above and recalled below, in which the gas flow passing through the intake flap is estimated by applying an equation of Barré de Saint Venant, and the additional gas flows of the second set as well.

In general, the second set consists of all the gas flows, with the exception of the air flow, which pass through the inlet flap. In the example of Equation 2, these are the low pressure recirculated exhaust gas flow (but not the high pressure recirculated gas flow) and the fuel vapor purge flow returned downstream of the flow meter (but not flow returned downstream of the intake flap). However, other types of gas flows are possible depending on the configuration of the engine. On the other hand, it is possible for the second set to be identical to the first set (for example: case of an engine having only a low-pressure exhaust gas recirculation circuit and no fuel vapor purge circuit).

est faite par le calcul suivant à partir du débit de carburant et du signal d'une sonde de richesse montée dans le circuit d'échappement du moteur, par exemple en amont du premier dispositif de dépollution du moteur, tel qu'un catalyseur trois voies pour le moteur essence par exemple : $${\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{inj}}_{\mathrm{rich}}}}={\mathrm{Q}}_{\mathrm{inj}}.\frac{\mathrm{PCO}}{{\mathrm{\varphi }}_{\mathrm{sonde}}}$$

• o Q_inj désigne le débit carburant basé sur un modèle prenant en compte la pression, le temps d'injection, la pression dans le collecteur, le régime moteur...
• o ϕ_sonde désigne la richesse échappement basée sur un capteur tel qu'une sonde à oxygène proportionnelle
• o PCO désigne le rapport stœchiométrique de remplissage.

The step of estimating the fourth fresh air flow rate value ${\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{inj}}_{\mathrm{rich}}}}$

is made by the following calculation from the fuel flow and the signal from a richness sensor mounted in the exhaust circuit of the engine, for example upstream of the first engine pollution control device, such as a three-way catalyst for the gasoline engine for example: $${\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{inj}}_{\mathrm{rich}}}}={\mathrm{Q}}_{\mathrm{inj}}.\frac{\mathrm{PCO}}{{\mathrm{\varphi }}_{\mathrm{probe}}}$$

• o Q _inj designates the fuel flow based on a model taking into account the pressure, the injection time, the pressure in the manifold, the engine speed...
• o ϕ _sensor designates the richness exhaust based on a sensor such as a proportional oxygen sensor
• o PCO designates the stoichiometric filling ratio.

Thus, the method does not include a step of prolonged shut-off of the exhaust gas recirculation valve.

It further comprises a step for calculating the median of the first, second, third and fourth fresh air flow rate values, and a step for comparing the value returned by the air flow meter with the previously calculated median.

, est donnée par le calcul selon l'équation 1 suivante : $$\begin{array}{l}{\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{mdl}}_{\mathrm{remplissage}}}}\\ ={\mathrm{Q}}_{{\mathrm{tot}}_{{\mathrm{mdl}}_{\mathrm{remplissage}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}\\ -{\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{amont}}_{\mathrm{compresseur}}}}-{\mathrm{Q}}_{{\mathrm{canister}}_{\mathrm{collecteur}}}\end{array}$$

avec :

• o ${\mathrm{Q}}_{{\mathrm{tot}}_{{\mathrm{mdl}}_{\mathrm{remplissage}}}}$
  
  est le débit total donné par le modèle de remplissage en fonction de la pression et de la température dans le collecteur, et du régime moteur en tours par minute,,
• o ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}$
  
  est le débit des gaz d'échappement recyclés à haute pression calculé en utilisant la relation de Barré de Saint-Venant aux bornes du circuit de recirculation des gaz d'échappement à haute pression : $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{hp}}}\cdot {\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}{{\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}}$$
  
  où :
  • ▪ Se_egrhp est la section aéraulique de la vanne de recirculation à haute pression, calibrée en fonction de la recopie de position angulaire de ladite vanne,
  • ▪ r est la constante massique des gaz parfaits pour l'air,
  • ▪ ${\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    est la pression en amont de ladite vanne,
  • ▪ ${\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    est la pression en aval de ladite vanne,
  • ▪ ${\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    est la température en amont de ladite vanne
  • ▪ $\mathrm{bsv}\left(\frac{{\mathrm{P}}_{\mathrm{amont}}}{{\mathrm{P}}_{\mathrm{aval}}}\right)$
    
    est la fonction de Barré de Saint-Venant,
• o ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}$
  
  est le débit des gaz d'échappement recyclés à basse pression, calculé en utilisant la relation de Barré de Saint-Venant aux bornes du circuit de recirculation des gaz d'échappement à basse pression : $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{bp}}}\cdot {\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}{{\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}}$$
  
  avec :
  • ▪ Se_egrbp est la section aéraulique de la vanne de recirculation à basse pression, calibrée en fonction de la recopie de position angulaire de ladite vanne,
  • ▪ ${\mathrm{P}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
    
    est la pression en amont de ladite vanne,
  • ▪ ${\mathrm{P}}_{{\mathrm{aval}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
    
    est la pression en aval de ladite vanne,
  • ▪ ${\mathrm{T}}_{{\mathrm{amont}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
    
    est la température en amont de ladite vanne,

${\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{amont}}_{\mathrm{compresseur}}}}$

et Q_{canistercollecteur} sont les débits estimés, en utilisant également le principe du Barré Saint-Venant, des gaz chargés de vapeurs de carburant provenant du circuit de purge et renvoyés respectivement en aval du débitmètre et en aval du volet d'admission..The fuel vapor tank is for example part of a purge circuit having two outlet points, one after the flow meter and the other after the intake flap, and the second flow rate value, denoted ${\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}$

, is given by the calculation according to the following equation 1: $$\begin{array}{l}{\mathrm{Q}}_{{\mathrm{air}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}\\ ={\mathrm{Q}}_{{\mathrm{early}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}\\ -{\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}-{\mathrm{Q}}_{{\mathrm{canister}}_{\mathrm{manifold}}}\end{array}$$

with :

• oh ${\mathrm{Q}}_{{\mathrm{early}}_{{\mathrm{mdl}}_{\mathrm{filling}}}}$
  
  is the total flow given by the filling model as a function of the pressure and the temperature in the manifold, and of the engine speed in revolutions per minute,,
• oh ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}$
  
  is the high pressure recirculated exhaust gas flow rate calculated using the Barré de Saint-Venant relationship at the terminals of the high pressure exhaust gas recirculation circuit: $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{hp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{hp}}}\cdot {\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}}}$$
  
  Or :
  • ▪ Se _{egr hp} is the aeraulic section of the high pressure recirculation valve, calibrated according to the copy of the angular position of said valve,
  • ▪ r is the ideal gas constant for air,
  • ▪ ${\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    is the pressure upstream of said valve,
  • ▪ ${\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    is the pressure downstream of said valve,
  • ▪ ${\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{hp}}}}$
    
    is the temperature upstream of said valve
  • ▪ $\mathrm{bsv}\left(\frac{{\mathrm{P}}_{\mathrm{upstream}}}{{\mathrm{P}}_{\mathrm{downstream}}}\right)$
    
    is the Barré de Saint-Venant function,
• oh ${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}$
  
  is the low-pressure recirculated exhaust gas flow rate, calculated using the Barré de Saint-Venant relationship at the terminals of the low-pressure exhaust gas recirculation circuit: $${\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}=\frac{{\mathrm{Se}}_{{\mathrm{egr}}_{\mathrm{bp}}}\cdot {\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}}$$
  
  with :
  • ▪ Se _{egr bp} is the air section of the low-pressure recirculation valve, calibrated according to the copy of the angular position of said valve,
  • ▪ ${\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
    
    is the pressure upstream of said valve,
  • ▪ ${\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
    
    is the pressure downstream of said valve,
  • ▪ ${\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$
    
    is the temperature upstream of said valve,

${\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}$

and Q _{canister manifold} are the estimated flow rates, also using the Barré Saint-Venant principle, of the gases laden with fuel vapors coming from the purge circuit and returned respectively downstream of the flowmeter and downstream of the inlet flap.

To diagnose a drift of the air flow meter, or the intake leak, you can compare the value returned by the air flow meter with the previously calculated median.

Indeed, once at least three flow rates present stable conditions, and that they are in their stability and validity interval, the use of the calculation of the median on the selected flow rates has the advantage, rather than an average, not to be influenced by the faulty flow, since in a case without fault, the median and the mean are practically superimposed, whereas in the case where one of the flow rates is out of step, for example because of of a drift, the median will remain centered while the average will be impacted by this difference in flow.

• en calculant un ratio de diagnostic donné par le quotient de ladite première valeur sur la médiane, auquel quotient est soustrait un, puis
• en calculant l'erreur de diagnostic donnée par la différence entre ledit ratio de diagnostic et zéro, puis
• en intégrant dans le temps ladite erreur de diagnostic, puis
• en comparant l'intégrale de diagnostic obtenue à une première valeur seuil prédéfinie permettant le diagnostic de dérive du débitmètre d'air.

Optionally, the calculated median is therefore compared to the first fresh air flow value:

• by calculating a diagnostic ratio given by the quotient of said first value on the median, from which quotient is subtracted one, then
• by calculating the diagnostic error given by the difference between said diagnostic ratio and zero, then
• by integrating said diagnostic error over time, then
• by comparing the diagnostic integral obtained with a first predefined threshold value allowing the diagnosis of drift of the air flowmeter.

• si le ratio de diagnostic est inférieur à la deuxième valeur seuil, l'intégrale de diagnostic est diminuée de ladite deuxième valeur seuil moins la valeur absolue du ratio, avant sa comparaison à la première valeur seuil,
• si le ratio de diagnostic est dans l'intervalle de non-diagnostic, l'intégrale de diagnostic est maintenue égale à elle-même pour sa comparaison à la première valeur seuil,
  si le ratio de diagnostic est supérieur à la troisième valeur seuil, l'intégrale de diagnostic est diminuée de ladite troisième valeur seuil moins la valeur absolue du ratio, avant sa comparaison à la première valeur seuil.

Furthermore, a non-diagnosis interval defined by a second threshold value and a third threshold value less than said second threshold value can be defined, and

• if the diagnostic ratio is less than the second threshold value, the diagnostic integral is decreased by said second threshold value minus the absolute value of the ratio, before its comparison with the first threshold value,
• if the diagnostic ratio is in the non-diagnostic interval, the diagnostic integral is kept equal to itself for its comparison with the first threshold value,
  if the diagnostic ratio is greater than the third threshold value, the diagnostic integral is reduced by said third threshold value minus the absolute value of the ratio, before its comparison with the first threshold value.

When there is no fault, this ratio is close to zero, conversely when there is a drift of the flowmeter leading to an overestimation of twenty percent, it will give substantially two tenths.

Ratio compensation makes it possible to take into account that the flow models are not perfect and can provide wide dispersions of values.

The standard requires the diagnosis of a deviation of approximately twenty percent of the air flow meter for safety and regulatory reasons of drifts in polluting emissions beyond the authorized thresholds, this compensated ratio reinforces the consideration of the dispersion of the various sensors used. .

A non-diagnostic interval is thus produced between the second and third threshold values, thanks to which the diagnostic values which are not reliable enough are not retained because they could correspond to failure states as well as singular operating states. or outliers corresponding only to anecdotal deviations of flow values from their usual trends.

The process thus reports fewer faults that may correspond to false positives, which makes the flowmeter drift diagnosis more reliable.

The first threshold value is for example between fifteen and twenty-five hundredths.

• ▪ Se_thr est la section aéraulique du volet d'admission calibrée en fonction de la recopie de position angulaire dudit volet d'admission,
• ▪ P_amontthr est la pression en amont dudit volet,
• ▪ P_avalthr : est la pression en aval dudit volet,
• ▪ T_amontthr : est la température en amont dudit volet,
  r est la constante massique des gaz parfaits pour l'air.

The method can further provide that the third flow rate value, denoted Q _{air thr} , or given by the calculation corresponding to the following equation 2:
Or : $$\begin{array}{l}{\mathrm{Q}}_{{\mathrm{air}}_{\mathrm{thr}}}={\mathrm{Q}}_{{\mathrm{early}}_{\mathrm{thr}}}-{\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}\\ {\mathrm{Q}}_{{\mathrm{early}}_{\mathrm{thr}}}=\frac{{\mathrm{Se}}_{\mathrm{thr}}\cdot {\mathrm{P}}_{{\mathrm{upstream}}_{\mathrm{thr}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{\mathrm{thr}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{\mathrm{thr}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{\mathrm{thr}}}}}\end{array}$$

• ▪ Se _thr is the airflow section of the intake flap calibrated according to the copy of the angular position of said intake flap,
• ▪ P _{upstream thr} is the pressure upstream of said flap,
• ▪ P _{downstream thr} : is the pressure downstream of said flap,
• ▪ T _{upstream thr} : is the temperature upstream of said shutter,
  r is the ideal gas constant for air.

Preferably, whether or not each of the first, second, third and fourth flow rate values is taken into account is conditioned to calculate the median at a stability of said flow rate values, so as to take into account that the flow rates are not temporally synchronized and to rule out transient effects on the flow rates likely to move them away from their stable operating points.

• pour chaque équation d'hydrodynamique de Barré de Saint-Venant, exiger que le rapport entre la pression amont et la pression aval dépasse une quatrième valeur seuil,
• pour le calcul de la quatrième valeur de débit, exiger que le débit carburant ne passe sous une cinquième valeur seuil au-dessous de laquelle la dispersion de réalisation de la quantité injectée réelle de carburant par rapport à sa consigne est trop élevée,
• pour le calcul de la quatrième valeur de débit, exiger que la richesse ne passe sous une sixième valeur seuil au-dessous de laquelle l'imprécision de mesure de la sonde de richesse est grande, notamment supérieure à un pour cent.

The invention also relates to a method in which at least one of the following precision conditions is added which makes it possible to take into account or not the first, second, third and fourth flow rate values to calculate the median:

• for each Barré de Saint-Venant hydrodynamic equation, require that the ratio between the upstream pressure and the downstream pressure exceed a fourth threshold value,
• for the calculation of the fourth flow rate value, requiring that the fuel flow rate does not fall below a fifth threshold value below which the dispersion of realization of the actual injected quantity of fuel with respect to its setpoint is too high,
• for the calculation of the fourth debit value, requiring that the wealth does not fall below a sixth threshold value below which the richness sensor measurement inaccuracy is high, in particular greater than one percent.

Thanks to the invented method, a diagnosis is thus carried out which makes it possible to calculate the flow of fresh air and to identify the drift of its sensor; in several different ways particularly reliable, when the particular conditions of stability and precision are respected on at least three flow rate values, thanks to the calculation of the median of these flow rates compared to the measurement of the air flow meter via a ratio making it possible to integrating the error, with a non-diagnostic deadband, to then compare this integral with a fault threshold.

The advantages are to be able to diagnose the air flow meter in its drift or an intake leak, with little or no intrusion on the recirculation circuit, very reliably, and using information already present elsewhere since it is already necessary for the regulation of recirculation, the management of the purge of a fuel vapor tank and the management of air flow rates, which makes it possible and facilitates the integration of the process on very diverse engine variants.

Claims (11)

Method for diagnosing the plausibility of drift of an air flowmeter sensor adapted for the direct measurement of the flow of fresh air entering a heat engine associated with an air intake circuit and an exhaust circuit of burnt gases having a partial exhaust gas recirculation circuit at the intake, the intake being controlled by an intake flap and the recirculation of the exhaust gases by a recirculation valve, the method comprising the following steps: - a step of measuring a first fresh air flow value in the intake line by said flow meter, - a step of estimating a second fresh air flow rate value in the intake line from a filling model applied to the total gas flow rate entering the engine and from a first set of additional gas flow rates at the admission line, - a step of calculating a third fresh air flow rate value in the intake line from a Barré de Saint-Venant hydrodynamic equation at the terminals of the intake flap and a second set gas flow rates ancillary to the inlet line, - a step of calculating a fourth value of fresh air flow in the intake line given by a fuel flow and a signal from a richness sensor mounted in the exhaust circuit of the engine,
the method being characterized in that it does not require the exhaust gas recirculation valve to be shut off, and in that it further comprises a step of calculating the median of the first, second, third and fourth fresh air flow values, and a step of comparing the value returned by the air flow meter with the previously calculated median. A method according to claim 1, wherein the first set of gaseous flows incidental to the intake line comprises a flow of exhaust gases recirculated to the intake of the engine. A method according to any preceding claim, wherein the first set of gas flows incidental to the intake line comprises a gas flow from the venting of a fuel vapor tank. A method according to claim 3, wherein the fuel vapor tank forms part of a purge circuit having at least a first outlet point after the flow meter or at least a second outlet point after the intake flap, and in which the second flow rate value, denoted $Q_{{\mathit{early}}_{{\mathit{mdl}}_{\mathit{filling}}}}$

, is given by the following calculation: $$\begin{array}{l}{Q}_{{\mathit{air}}_{{\mathit{mdl}}_{\mathit{filling}}}}\\ =Q_{{\mathit{early}}_{{\mathit{mdl}}_{\mathit{filling}}}}-Q_{{\mathit{egr}}_{{\mathit{hp}}_{\mathit{bsv}}}}-Q_{{\mathit{egr}}_{{\mathit{bp}}_{\mathit{bsv}}}}\\ -Q_{{\mathit{canister}}_{{\mathit{upstream}}_{\mathit{compressor}}}}-Q_{{\mathit{canister}}_{\mathit{manifold}}}\end{array}$$

With : oh $Q_{{\mathit{early}}_{{\mathit{mdl}}_{\mathit{filling}}}}$

is the total gas flow in the engine given by the filling model as a function of at least the pressure and the temperature in the engine intake manifold, and the engine speed, oh $Q_{{\mathit{egr}}_{{\mathit{hp}}_{\mathit{bsv}}}}$

is a high-pressure recirculated exhaust gas flow rate, calculated using the Barré de Saint-Venant relationship at the terminals of the high-pressure exhaust gas recirculation circuit: $$Q_{{\mathit{egr}}_{{\mathit{hp}}_{\mathit{bsv}}}}=\frac{{\mathit{Se}}_{{\mathit{egr}}_{\mathit{hp}}}\cdot P_{{\mathit{upstream}}_{{\mathit{egr}}_{\mathit{hp}}}}\cdot \mathit{bsv}\left(\frac{P_{{\mathit{upstream}}_{{\mathit{egr}}_{\mathit{hp}}}}}{P_{{\mathit{downstream}}_{{\mathit{egr}}_{\mathit{hp}}}}}\right)}{\sqrt{r\cdot T_{{\mathit{upstream}}_{{\mathit{egr}}_{\mathit{hp}}}}}}$$

Or : ▪ Se _{egr hp} is the aeraulic section of the recirculation valve of the high pressure recirculation circuit, calibrated according to the copy of the angular position of said high pressure exhaust valve, ▪ r is the ideal gas constant for air, ▪ $P_{{\mathit{upstream}}_{{\mathit{egr}}_{\mathit{hp}}}}$

is the pressure upstream of said valve, taken from a sensor or a model, ▪ $P_{{\mathit{downstream}}_{{\mathit{egr}}_{\mathit{hp}}}}$

is the pressure downstream of said valve, taken from a sensor or a model, ▪ $T_{{\mathit{upstream}}_{{\mathit{egr}}_{\mathit{hp}}}}$

is the temperature upstream of said valve, taken from a sensor or a model ▪ $\mathit{bsv}\left(\frac{P_{\mathit{upstream}}}{P_{\mathit{downstream}}}\right)$

is the Barré de Saint-Venant function, oh $Q_{{\mathit{egr}}_{{\mathit{bp}}_{\mathit{bsv}}}}$

is a low-pressure recirculated exhaust gas flow rate, calculated using the Barré de Saint-Venant relationship at the terminals of the low-pressure exhaust gas recirculation circuit: $$Q_{{\mathit{egr}}_{{\mathit{bp}}_{\mathit{bsv}}}}=\frac{{\mathit{Se}}_{{\mathit{egr}}_{\mathit{bp}}}\cdot P_{{\mathit{upstream}}_{{\mathit{egr}}_{\mathit{bp}}}}\cdot b\mathrm{please}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}}}$$

With : ▪ Se _{egr bp} is the aeraulic section of the recirculation valve of the low-pressure recirculation circuit, calibrated according to the copy of the angular position of said valve, ▪ ${\mathrm{P}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$

is the pressure upstream of said valve, taken from a sensor or a model, ▪ ${\mathrm{P}}_{{\mathrm{downstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$

is the pressure downstream of said valve, taken from a pressure sensor or a model, ▪ ${\mathrm{T}}_{{\mathrm{upstream}}_{{\mathrm{egr}}_{\mathrm{bp}}}}$

is the temperature upstream of said valve, taken from a sensor or a model, oh ${\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}$

and Q _{canister manifold} are the estimated flow rates, also using the Barré de Saint-Venant relationship, of gas coming from the purge of the fuel vapor tank returned respectively downstream of the flow meter and downstream of the inlet flap. Method according to one of Claims 3 and 4, in which the calculated median is compared with the first value of fresh air flow - by calculating a diagnostic ratio given by the quotient of said first value on the median, from which quotient is subtracted one, then - by calculating the diagnostic error given by the difference between said diagnostic ratio and zero, then - by integrating said diagnostic error over time, then - by comparing the diagnostic integral obtained with a first predefined threshold value allowing the diagnosis of drift of the air flow meter. Method according to any one of the preceding claims, in which a non-diagnosis interval defined by a second threshold value and a third threshold value less than said second threshold value is defined, and - if the diagnostic ratio is lower than the second threshold value, the diagnostic integral is reduced by said second threshold value minus the absolute value of the ratio, before its comparison with the first threshold value, - if the diagnosis ratio is in the non-diagnosis interval, the diagnosis integral is kept equal to itself for its comparison with the first threshold value, - if the diagnostic ratio is greater than the third threshold value, the diagnostic integral is reduced by said third threshold value minus the absolute value of the ratio, before its comparison with the first threshold value. A method according to any preceding claim, wherein the second set of auxiliary gas streams comprises at least one low pressure recirculated exhaust gas stream. A method according to any preceding claim, wherein the second set of ancillary gas flows comprises at least one gas flow from the purge of the fuel vapor tank returned downstream of the flowmeter. Method according to any one of Claims 3 to 8, in which the third flow rate value, denoted Q _airthr , is given by the following calculation: $${\mathrm{Q}}_{{\mathrm{air}}_{\mathrm{thr}}}={\mathrm{Q}}_{{\mathrm{early}}_{\mathrm{thr}}}-{\mathrm{Q}}_{{\mathrm{canister}}_{{\mathrm{upstream}}_{\mathrm{compressor}}}}-{\mathrm{Q}}_{{\mathrm{egr}}_{{\mathrm{bp}}_{\mathrm{bsv}}}}$$

Or : $${\mathrm{Q}}_{{\mathrm{early}}_{\mathrm{thr}}}=\frac{{\mathrm{Se}}_{\mathrm{thr}}\cdot {\mathrm{P}}_{{\mathrm{upstream}}_{\mathrm{thr}}}\cdot \mathrm{bsv}\left(\frac{{\mathrm{P}}_{{\mathrm{upstream}}_{\mathrm{thr}}}}{{\mathrm{P}}_{{\mathrm{downstream}}_{\mathrm{thr}}}}\right)}{\sqrt{\mathrm{r}\cdot {\mathrm{T}}_{{\mathrm{upstream}}_{\mathrm{thr}}}}}$$

designates the gas flow passing through the inlet flap, ▪ Se _thr is the airflow section of the intake flap calibrated according to the copy of the angular position of said flap ▪ P _{upstream thr} is the pressure upstream of the intake flap given by a pressure sensor on the engine, ▪ P _{downstream thr} : is the pressure downstream of the intake flap ▪ T _{upstream thr} : is the temperature upstream of the intake flap ▪ r is the ideal gas constant for air. Method according to any one of the preceding claims, in which the taking into account or not of each of the first, second, third and fourth flowrate values is conditional on calculating the median at a stability of the said flowrate values, so as to take into account account that the flow rates are not temporally synchronized and to rule out transient effects on the flow rates likely to move them away from their stabilized operating points. Method according to any one of the preceding claims, in which at least one of the following precision conditions is added which makes it possible to take into account or not the first, second, third and fourth flow rate values to calculate the median: - for each Barré de Saint-Venant hydrodynamic equation, require that the ratio between the upstream pressure and the downstream pressure exceed a fourth threshold value, - for the calculation of the fourth flow rate value, requiring that the fuel flow rate does not fall below a fifth threshold value below which the dispersion of realization of the actual injected quantity of fuel compared to its setpoint is too high, - for the calculation of the fourth flow rate value, requiring that the richness does not fall below a sixth threshold value below which the measurement inaccuracy of the richness probe is great, in particular greater than one percent.