EP2221465A1 - Method to inject fuel in an internal combustion engine taking into account the time monitoring of the injectors variation - Google Patents

Abstract

- Method for injecting a mass m of fuel via an injector of a common rail equipping an internal combustion engine. - We define a physical model f, providing an estimate of a mass of fuel injected as a function of an injection time and a pressure in the common rail. Then, after measuring the pressure in the common rail, this model is used to calculate the fuel injection time t needed to inject the fuel mass m. Finally, fuel is injected via the injector during the time t. Then, when the aging of the motor is such that the difference between the desired injected mass and the mass actually injected is important, the physical model is recalibrated. - Application to the motor control.

Description

The present invention relates to the field of control of an internal combustion engine. More particularly, the invention relates to a method for improving the process of multiple injections of internal combustion engines.

High pressure direct injection, via a common rail , has the advantage of greatly reducing the pollution rate of diesel engines. From the tank, the system is conventionally composed of a fuel heater, a filter, a feed pump, a shut-off valve, the high-pressure pump, the common boom comprising a sensor and a pressure regulating valve, lines to the injectors, electromagnetic injectors and a fuel cooler back to the tank.

The nozzle common to the injectors consists of a thick tube that can withstand very high pressures, carrying at its ends a pressure sensor and a pressure regulator. The latter receives and stores the high-pressure fuel from the pump, it continuously supplies the injectors still under pressure. This pressure is regulated by the regulator which is controlled by the electronic unit according to a map in memory. A map is a set of data stored in the calculator. A map serves as a reference for the computer to optimally control its software called controller.

The use of a common ramp makes it possible to control the injection time. The computer, according to the multiple information sent by the different sensors, receives input signals and manages outputs according to engine operating criteria. To adapt the amount of fuel, the computer acts either on the fuel pressure in the ramp (valve of the pressure regulator and flow delivered by the pump), or on the duration of activation of the solenoid valves of the injectors, synchronizing well on these actions. The quantity injected depends on the control of the solenoid valves, the speed of opening and closing of the injector needle, the fuel pressure in the rail, the quantity passed through the injector and the lifting of the needle.

The technical and commercial success of fuel injection systems with a common rail is one of the most important reasons for the growth of diesel engines in the automotive market. The main factor in this success is the flexibility that this common rail system provides in terms of injection parameters such as injection time and fuel pressure.

Modern common-rail injection systems allow combustion with multiple injections. Pilot injections are useful for reducing combustion noise, especially during cold operation, and polluting emissions, particularly those of NOx and particulates. At medium load, the best compromise is expected with a separate main injection in two different injections.

On the other hand, late injections can reduce NOx emissions and promote the regeneration of particulate filters.

To optimize the fuel injection, a controller, that is to say a computer software, receives information on the operation of the engine and the expected performance, and deduces the mass of fuel to be injected, so as to optimize the operation of the engine.

State of the art

To do this, it is known to use engine maps on which the controller is based to perform the control. Mapping is a set of discrete values established before engine operation. We know, for example the documents EP 1 344 923 , US 5,609,140 and US 7,000,600 , which describes a device for controlling fuel injection for an internal combustion engine. These devices implement a method in which maps are used to determine the injection time required to inject a given mass of fuel.

However, these maps correspond to static operating points. Therefore, in operation, the setting values contained in the injection maps may be obsolete. In other words, while it is desired to inject a mass M of fuel via an injector, a mass. M ', different from M, will actually be injected. Now the mass M is determined by a controller, computer software, so as to optimize the operation of the engine. In addition, the number of data needed to map maps, even two-dimensional, is very important.

An alternative approach involves the use of a pressure sensor in each injection tube. As a result, the correction of the masses to be injected is possible with great precision. However, this solution for multicylinder engines requires the use of several sensors, for example magneto-elastic effect. Currently these sensors are not used in engines and therefore, even if their cost is down, their introduction increases the complexity of the system. In addition, a controller based on these measurements must necessarily be high frequency, which is not always compatible with the power of the control units embedded in the computer.

Thus, the object of the invention is an alternative method for improving the injection process of internal combustion engines, to overcome the use of engine mapping.

The invention is based on a continuous physical model describing the injection process, in which an explicit dependence between the injection times and the injected mass is defined, as well as on a calibration technique taking into account the drift of the physical characteristics. injectors over time.

The method according to the invention

• a.-on définit un modèle physique continu f, décrivant le procédé d'injection en terme de débit de masse à travers l'injecteur, dans lequel on définit une dépendance entre temps d'injection et masse injectée, en prenant en compte la pression dans ladite rampe commune ;
• b.-on mesure une pression p_r dans ladite rampe commune ;
• c.-on détermine un temps t d'injection de carburant nécessaire pour injecter la masse m de carburant, à l'aide dudit modèle physique et de ladite pression p_r ;
• d.-on injecte du carburant via l'injecteur pendant le temps t ; et
• e.- on prend en compte une évolution des injecteurs au cours du temps :
  • en déterminant une masse m ^* de carburant réellement injectée suite à l'étape d ; et
  • si la masse de carburant réellement injectée est sensiblement différente de la masse m, on effectue une calibration dudit modèle physique continu f, de façon à ce que le temps t d'injection de carburant, déterminé par le modèle ainsi calibré, permette d'injecter réellement la masse m pendant le temps t.

The invention relates to a method for injecting a mass m of fuel via at least one injector of a common rail having a plurality of injectors and equipping an internal combustion engine. The method has the following steps:

• a.-we define a continuous physical model f , describing the injection process in terms of mass flow through the injector, in which we define a dependence between injection time and mass injected, taking into account the pressure in said common rail;
• b. a pressure p _r is measured in said common ramp;
• a fuel injection time t necessary for injecting the mass m of fuel is determined using said physical model and said pressure p _r ;
• fuel is injected via the injector during the time t ; and
• e.- we take into account an evolution of injectors over time:
  • determining a mass m ^* of fuel actually injected following step d; and
  • if the mass of fuel actually injected is substantially different from the mass m , a calibration of said continuous physical model f is carried out, so that the fuel injection time t , determined by the model thus calibrated, makes it possible to inject actually the mass m during the time t .

• on écrit pour n paliers de stabilisation de la charge du moteur, une équation traduisant l'égalité de la masse de carburant telle que définie par le modèle et la masse de carburant réelle m ^* ;
• on résout ce système de n équations à n inconnues pour détermines les n paramètres du modèle.

According to one embodiment, it is possible to calibrate the model for all the injectors of the ramp at the same time, by applying the following steps to determine a number n of model parameters:

• n is written for n engine load stabilization stages, an equation representing the equality of the fuel mass as defined by the model and the actual fuel mass m ^* ;
• this system of n equations with n unknowns is solved to determine the n parameters of the model.

• on contrôle un calculateur du moteur de façon à ce qu'une différence de charge demandée par un conducteur soit assurée par modification d'une quantité injectée uniquement sur l'injecteur i ;
• on détermine une différence de masse réelle δQ _{inj_réelle,i} injectée par l'injecteur i et une différence de temps δt_i d'injection de l'injecteur i, pour répondre à la demande du conducteur ;
• on écrit pour n paliers de stabilisation de la charge du moteur, une équation traduisant l'égalité de la masse de carburant injectée par l'injecteur i pendant le temps δt_i telle que définie par le modèle, et la différence de masse réelle δQ _{inj_réelle,i} injectée par l'injecteur i ;
• on résout ce système de n équations à n inconnues pour détermines les n paramètres du modèle.

According to another embodiment, it is possible to calibrate the model for each injector of the ramp independently, by determining a number n of parameters of the model by applying the following steps for each injector i :

• an engine computer is controlled so that a load difference requested by a driver is ensured by modifying a quantity injected solely on the injector i ;
• determining a real mass difference δ Q _{inj_eal , i} injected by the injector i and a time difference δ t _i injection of the injector i , to meet the demand of the driver;
• n is written for n stabilization stages of the engine load, an equation reflecting the equality of the fuel mass injected by the injector i during the time δ t _i as defined by the model, and the difference in actual mass δ Q _{inj_real , i} injected by the injector i ;
• this system of n equations with n unknowns is solved to determine the n parameters of the model.

It is possible to determine the mass of fuel actually injected m ^* , at an operating point of the engine where there is no recirculation of exhaust gas, and by means of a wealth sensor positioned on an exhaust line. said engine.

Finally, according to the invention, the model f can be defined by applying the principle of conservation of the mass and the Bernoulli theorem. It may initially calibrate the physical model f from fuel consumption measurements from engine test bench with simple injections.

Other characteristics and advantages of the method according to the invention will appear on reading the following description of nonlimiting examples of embodiments, with reference to the appended figures and described below.

Brief presentation of the figures

• The figure 1 illustrates the steps of the method according to the invention to take into account the evolution of the injectors over time.
• The figure 2 shows the evolution of an injected mass M ₁ (mg) as a function of the injection duration t ₁ (μs) for six pressure levels of the ramp p _{r (1)} to p _{r (6)} .

Detailed description of the method

According to the invention, the engine computer of a controller is equipped with at least one compensator. This compensator makes it possible to determine the injection times necessary to obtain the desired fuel masses.

1. 1. détermination de la masse de carburant à injecter M _i par l'injecteur i ;
2. 2. détermination du temps t_i d'injection du carburant par l'injecteur i, pour injecter effectivement la masse M _i , au moyen d'un modèle physique ;
3. 3. injection du carburant par l'injecteur pendant le temps t_i ;
4. 4. recalibration du modèle physique continu

The method according to the invention, for injecting fuel via at least one injector, comprises the following steps for a given injector:

1. 1. determination of the mass of fuel to be injected M _i by the injector i ;
2. 2. determination of the time t _i of fuel injection by the injector i , to effectively inject the mass M _i , using a physical model;
3. 3. fuel injection by the injector during the time t _i ;
4. 4. recalibration of the continuous physical model

1. Determination of the mass of fuel to be injected

A mass of fuel to inject M _i is determined by a controller so as to optimize the operation of the motor. This mass of fuel M _i is determined according to engine operating conditions and expected performance.

2. Determination of the injection time t _i to obtain the desired fuel mass

The sought value t _i is the injection duration such that the physical system realizes the mass required M _i . To do this, instead of using static mapping, we build a physical model describing the injection process by connecting the injection time and the injected mass.

• on définit un modèle physique décrivant le procédé d'injection et fournissant une relation (fonctionnelle) explicite entre la masse injectée et le temps d'injection ;
• on calibre le modèle ;
• on applique le modèle.

We proceed as follows:

• defining a physical model describing the injection process and providing an explicit (functional) relationship between the injected mass and the injection time;
• we calibrate the model;
• we apply the model.

Definition of a continuous physical model

A continuous model differs from a cartography in that it allows to provide desired parameter values continuously, at each moment, during the operation of the engine, and regardless of the input values. This model can therefore be applied during the actual operation of the engine. On the contrary, a map constitutes a set of discrete values established before the operation of the engine, and for a limited number of input values.

A physical model is a model that is based on a description of physical phenomena to model a particular phenomenon.

La fonction continue f (le modèle) doit être calibrée. De façon explicite, le modèle est construit de façon à décrire le procédé d'injection en terme de débit de masse à travers l'injecteur. Pour ce faire, on écrit que la masse injectée correspond à l'intégrale du débit de masse à travers l'injecteur, puis on applique le principe de conservation de la masse et le théorème de Bernoulli. Le théorème de Bernoulli exprime le bilan hydraulique simplifié d'un fluide dans une conduite. Ce théorème pose les bases de l'hydrodynamique et, d'une façon plus générale, de la mécanique des fluides.According to the invention, the model describing the injection method in an injector i is defined so as to estimate an injected mass M _i as a function of an injection time D _{inj, j} and the pressure in the ramp pr : $$M_i=f\left(p_r{D}_{\mathit{inj},i}\right)$$

The function continues f (the model) must be calibrated. Explicitly, the model is constructed to describe the injection process in terms of mass flow through the injector. To do this, we write that the injected mass corresponds to the integral of the mass flow through the injector, then we apply the principle of conservation of the mass and Bernoulli's theorem. Bernoulli's theorem expresses the simplified hydraulic balance of a fluid in a pipe. This theorem lays the foundations for hydrodynamics and, more generally, for fluid mechanics.

1. (i) on considère la pression d'injection constante pendant la durée d'injection et égale à la pression dans le rail,
2. (ii) on représente la dynamique de l'aiguille avec une loi dynamique du premier ordre, et
3. (iii) on linéarise l'influence de la pression sur le coefficient de décharge et sur la vitesse d'injection du carburant par rapport à la racine carré de la pression elle-même.

The more precise a model is, the more complex it is. A model that is too complex would not be usable in a vehicle. Simplifying assumptions are therefore necessary. We can admit the following hypotheses:

1. (i) the injection pressure is considered constant during the injection period and equal to the pressure in the rail,
2. (ii) the dynamics of the needle are represented with a dynamic law of the first order, and
3. (iii) the influence of the pressure on the discharge coefficient and on the injection speed of the fuel with respect to the square root of the pressure itself is linearized.

Avec :

• p_r : pression dans la rampe
• $k_i\left(x\right)\approx {\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="imgf0002.png"\; state="\{\{state\}\}">c</figure-callout>}}_{1,i}\sqrt{x}+c_{2,i},$
  
  avec c_{1, i} et c_{2, i} des paramètres additionnels du modèle
• t _{0, i} : : instant au dessous duquel il n'y a pas de masse de carburant injectée
• D_i : un paramètre additionnel à calibrer

Les paramètres du modèle à calibrer sont donc c_{1, i}, c₂, _i, t_{0, i}, et D_i.The following model is then obtained to describe the injection process: $$M_i\approx k_i\left(p_r\right)\left\{\left(t_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)+\frac{1}{D_i}\left[e^{-D_i\left(t_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)-1}\right]\right\}$$

With:

• p _r : pressure in the ramp
• $k_i\left(x\right)\approx {\mathrm{<figure-callout\; id="1"\; label="vs"\; filenames="imgf0002.png"\; state="\{\{state\}\}">vs</figure-callout>}}_{1,i}\sqrt{x}+{\mathrm{vs}}_{2,i},$
  
  with c _{1, i} and c _{2, i} additional parameters of the model
• t _{0, i} :: instant below which there is no fuel mass injected
• D _i : an additional parameter to calibrate

The parameters of the model to be calibrated are therefore c _{1, i} , c ₂ , _i , t _{0, i} , and D _i .

Calibration of parameters

The model parameters used in the compensator are calibrated from the fuel consumption measurements during engine tests with simple injections. These tests can be performed on a conventional engine test bench by modifying the parameters of a motor mounted on a test bench. Preferably, a bench dedicated to the injection system is used. In this configuration, the system is isolated from the rest of the engine and then mounted on a bench. This configuration has the advantage of being able to vary a larger number of parameters of the injection system, and in ranges that would not necessarily be acceptable on an engine. Several tests are thus carried out at different pressures of the ramp, pr. An example of such a calibration is shown on the figure 2 . This figure shows an injected mass M _i (mg) as a function of the injection duration t _i (μs) for six pressure levels of the ramp pr ₍₁₎ to pr ₍₆₎ . The solid lines represent experimental data, while the dots represent outputs of the model describing the injection process. The average error is below 5%. The calibrated model parameters are: $${\mathrm{vs}}_{\mathrm{1}\mathrm{,}\mathrm{i}}\mathrm{=}\mathrm{0010}\mathrm{,}{\mathrm{vs}}_{\mathrm{2}\mathrm{,}\mathrm{i}}\mathrm{=}\mathrm{-}\mathrm{0183}\mathrm{,}{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{\mathrm{0}\mathrm{,}\mathrm{i}}\mathrm{=}\mathrm{108}\mathrm{microseconds}\mathrm{,}{\mathrm{and\; D}}_{\mathrm{i}}\mathrm{=}\mathrm{0.0015.}$$

Application of parameterized models

The physical model, describing the injection method and thus parameterized, allows the compensator to determine the injection time t _i necessary to obtain the mass. M _i of fuel. $${\tilde{M}}_i=f\left(p_{r,i}{D}_{\mathit{inj},i}\right)$$

3. Injection of the fuel via the injector during the time t _i

Fuel is injected for a time t _i via the injector i, so as to inject the desired fuel mass.

4. Recalibration of the continuous physical model

The physical characteristics of the diesel injectors are derived during the life of the engine. Thus, for the same injected quantity requested, the injected quantity produced will be different for a new engine or for a motor having 1000 hours of operation. This phenomenon is particularly sensitive for small amounts injected (pilot injection type).

Thus, the initial quality of the engine depollution evolves during the life of the vehicle. To overcome such a problem, we can impose levels of pollution more severe than the standard to ensure that the engine meets the standard after 80 000 km for example.

According to the invention, to overcome this problem, the evolution of the injectors over time is taken into account by determining a mass m * of fuel actually injected, and if this mass is substantially different from the mass m that is desired injected, the continuous physical model f is recalibrated, so that the fuel injection time t , determined by the model thus calibrated, makes it possible to actually inject the mass m during the time t .

The figure 1 illustrates the steps of the method according to the invention to take into account the evolution of the injectors during the life of the engine: the mass m of fuel to be injected is determined. By means of the continuous physical model f , defined inter alia by the parameters c ₁ , t ₀ and D, the fuel injection time t is determined for actually inject the mass m . The mass m ^* of fuel actually injected during the time t is also measured. If the equality m ≈ m ^* is verified, the control of the injection is continued using the same parameter values to define the model f . On the other hand, if m ≠ m ^* , then the parameters (Δc ₁ , Δt ₀ and ΔD) of the model are recalibrated to obtain a better estimate of the time t , necessary for the injection of the mass m .

According to a first embodiment, the continuous physical model is recalibrated on all the injectors at the same time. It is considered that the same model applies to all injectors. Thus, the indices i are deleted.

Determination of the fuel mass actually injected by the injectors

• la masse d'air Q_air passant par le moteur par cycle moteur : elle ne dépend que de la perméabilité du moteur et du régime moteur ;
• la richesse réelle des gaz à l'échappement Φ_réelle : elle est mesurée par la sonde de richesse ;
• la masse de carburant théoriquement injectée par tous les injecteurs $\bar{M}={\displaystyle \sum _i}\overline{M_i}\mathrm{.}$
  
  Elle est connue par le calculateur du moteur.

To determine the fuel mass actually injected by the injectors following step 3, it is possible to use a wealth sensor placed on the exhaust line. This wealth probe makes it possible to determine the composition of the exhaust gases. It is then placed on an operating point of the engine where there is no exhaust gas recirculation (EGR for "Exhaust gas recirculation"). For example, a motor operating point corresponding to a high speed on the highway can be set. We then know:

• the mass of air Q _air passing through the engine per engine cycle: it depends only on the permeability of the engine and the engine speed;
• the real wealth of exhaust gases Φ _real : it is measured by the wealth probe;
• the fuel mass theoretically injected by all injectors $\tilde{M}={\displaystyle \underset{i}{\Sigma }}\widetilde{M_i}\mathrm{.}$
  
  It is known by the engine calculator.

où ψ_s est le pouvoir comburivore du carburant.The theoretical richness of the exhaust gases is then determined: ${\mathrm{\Phi }}_{\mathit{th}}\mathit{=}{\mathit{\psi }}_{\mathit{s}}\mathrm{.}\frac{\stackrel{\mathit{~}}{\mathit{M}}}{{\mathit{Q}}_{\mathit{air}}}\mathit{,}$

where ψ _s is the comburivorous power of the fuel.

Finally, we deduce the fuel mass actually injected by the injectors: $${\mathit{Q}}_{\mathit{inj\_reelle}}\mathit{=}{\mathit{Q}}_{\mathit{air}}\mathrm{.}\frac{Q_{\mathit{real}}}{{\psi }_s}$$

Fuel mass injected is the mass of fuel injected per engine cycle.

Physical model correction

From the quantity of fuel injected, determined by the model, and the actual quantity of injected fuel (determined by the richness probe), the parameters of the physical model are calibrated so that the quantity of fuel injected determined by the model is substantially equal to the actual quantity: Q _{inj_reele} ≈ M .

• on écrit pour n paliers de stabilisation de la charge du moteur, une équation traduisant l'égalité de la masse de carburant telle que définie par le modèle, et la masse de carburant réelle m ^* ;
• on résout ce système de n équations à n inconnues pour déterminer les n paramètres du modèle.

This model calibration is performed for all the injectors of the ramp at the same time, by applying the following steps to determine a number n of the parameters of the model:

• n is written for n engine load stabilization stages, an equation representing the equality of the fuel mass as defined by the model, and the actual fuel mass m ^* ;
• we solve this system of n equations with n unknowns to determine the n parameters of the model.

It is assumed that all model parameters are known when the engine is in new condition. The parameters we are trying to readjust are c ₁ , t ₀ and D. It is assumed that c ₂ does not evolve over time. The pr and t parameters are known by the calculator.

We define a system of three equations with three unknowns, to determine the three unknowns c ₁ , t ₀ and D so that: Q _{inj_reelle} = M .

To do this, one can use three stabilized load stages of the engine, which leads to the following system of equations: $$\{\begin{array}{c}{\left({\mathit{Q}}_{\mathit{inj\_réelle}}\right)}_1=({\displaystyle \underset{i}{\Sigma }}k\left(p_r\right)\left\{\left(t-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_0\right)+\frac{1}{D}\left[e^{-D\left(t-t_0\right)-1}\right]\right\}{)}_1\\ {\left({\mathit{Q}}_{\mathit{inj\_réelle}}\right)}_2=({\displaystyle \underset{i}{\Sigma }}k\left(p_r\right)\left\{\left(t-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_0\right)+\frac{1}{D}\left[e^{-D\left(t-t_0\right)-1}\right]\right\}{)}_2\\ {\left({\mathit{<figure-callout\; id="3"\; label="Q\; inj\_réelle"\; filenames="imgf0001.png"\; state="\{\{state\}\}">Q\; </figure-callout>}}_{\mathit{inj\_réelle}}\right)}_3=({\displaystyle \underset{i}{\Sigma }}k\left(p_r\right)\left\{\left(t-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_0\right)+\frac{1}{D}\left[e^{-D\left(t-t_0\right)-1}\right]\right\}{)}_3\end{array}$$

The indices 1, 2 and 3 indicate the values obtained for the three levels.

The inversion of this system allows the calculation of the parameters c ₁ , t ₀ and D.

The use of these parameters adjusted, therefore allows to adjust the activation time of the injectors to the evolution of the injectors over time so that the amount of fuel injected corresponds to the requested amount.

According to a second embodiment, the continuous physical model is recalibrated on each injector independently. Indeed, the injectors do not necessarily all derive in the same way, and it may be wise to want to reset the injector laws (continuous physical model), injector injector.

The method for recalibrating the law of the injector of the cylinder i , to be reproduced subsequently to reset all the other cylinders, is described below.

Determination of the fuel mass actually injected by the injectors

• la masse d'air Q_air passant par le moteur sur un cycle moteur : elle ne dépend que de la perméabilité du moteur et du régime moteur ;
• la richesse réelle des gaz à l'échappement Φ_réelle : elle est mesurée par la sonde de richesse ;
• la masse de carburant théoriquement injectée par chacun des injecteurs : M _i . Elle est connue par le calculateur du moteur.

As for the case of the registration of all the injectors at the same time (first embodiment), the mass of fuel effectively injected is determined by means of a wealth sensor placed on the exhaust line. We then know:

• the mass of air Q _air passing through the engine on an engine cycle: it depends only on the permeability of the engine and the engine speed;
• the real wealth of exhaust gases Φ _real : it is measured by the wealth probe;
• the mass of fuel theoretically injected by each of the injectors: M _i . It is known by the engine calculator.

où ψ_s est le pouvoir comburivore du carburant. Enfin, on en déduit la quantité de carburant réellement injectée par les injecteurs : $${\mathit{Q}}_{\mathit{inj\_reelle}}\mathit{=}{\mathit{Q}}_{\mathit{air}}\mathrm{.}\frac{Q_{\mathit{reelle}}}{{\psi }_s}$$

The theoretical richness of the exhaust gases is then determined: ${\mathrm{\Phi }}_{\mathit{th}}\mathit{=}{\mathit{\psi }}_{\mathit{s}}\mathrm{.}\frac{\underset{i}{\Sigma }{\tilde{M}}_i}{{\mathit{Q}}_{\mathit{air}}}\mathit{,}$

where ψ _s is the comburivorous power of the fuel. Finally, we deduce the amount of fuel actually injected by the injectors: $${\mathit{Q}}_{\mathit{inj\_reelle}}\mathit{=}{\mathit{Q}}_{\mathit{air}}\mathrm{.}\frac{Q_{\mathit{real}}}{{\psi }_s}$$

Physical model correction

From the quantity of fuel injected, determined by the model, and from the actual quantity of fuel injected (determined by the richness probe), the parameters of the physical model are recalibrated so that, for each injector i , the quantity of fuel injected determined by the model is equal to the actual quantity: Q _{injective , i} = M _i .

It is assumed that all model parameters are known when the engine is in new condition. The parameters that one seeks to recalibrate are c _{1, i} , t _{0, i} and D _i . It is assumed that c _{2, i} does not change during the life of the engine. The parameters pr and t _i are known by the computer.

We define a system of three equations with three unknowns, to determine the three unknowns c _{1, i} , t _{0, i} and D _i so that: Q _{inj_reel , i} = M _i.

However, the value of Q _{inj_réelle, i} is unknown: this value is not necessarily equal to Q _{inj_réelle} divided by the number of injectors, since the injectors could evolve differently from each other.

To overcome this problem, it ensures, at least once, the load differences requested by the driver by changing the amount injected only on the injector No. i . Thanks to the richness probe, the difference in quantity injected by the injector No. i is determined , which is noted δQ _{injelect, i} . This difference in quantity is achieved by a difference in activation time of the injector No. i noted: δt _i .

Les indices 1, 2 et 3 indiquent les valeurs obtenues pour les trois paliers.
L'inversion de ce système permet le calcul des paramètres c_1,i, t_0,i et D_i pour l'injecteur i.Then, using again three stabilized stages of load of the motor, one can write the following system of equations: $$\{\begin{array}{c}{\left({\mathit{\delta Q}}_{\mathit{inj\_réelle}\mathit{,}\mathit{i}}\right)}_1=(k_i\left(p_r\right)\left\{{\mathit{.delta.t}}_i+\frac{1}{D_i}\left[e^{-D_i\left(t_i+{\mathit{.delta.t}}_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)}-e^{-D_i\left(t_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)}\right]\right\}{)}_1\\ {\left({\mathit{\delta Q}}_{\mathit{inj\_réelle}\mathit{,}\mathit{i}}\right)}_2=(k_i\left(p_r\right)\left\{{\mathit{.delta.t}}_i+\frac{1}{D_i}\left[e^{-D_i\left(t_i+{\mathit{.delta.t}}_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)}-e^{-D_i\left(t_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)}\right]\right\}{)}_2\\ {\left({\mathit{\delta Q}}_{\mathit{inj\_réelle}\mathit{,}\mathit{i}}\right)}_3=(k_i\left(p_r\right)\left\{{\mathit{.delta.t}}_i+\frac{1}{D_i}\left[e^{-D_i\left(t_i+{\mathit{.delta.t}}_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)}-e^{-D_i\left(t_i-{\mathrm{<figure-callout\; id="0"\; label="t"\; filenames="imgf0002.png"\; state="\{\{state\}\}">t</figure-callout>}}_{0,i}\right)}\right]\right\}{)}_3\end{array}$$

The indices 1, 2 and 3 indicate the values obtained for the three levels.
The inversion of this system allows the calculation of the parameters c _{1, i} , t _{0, i} and D _i for the injector i .

• on contrôle le calculateur de façon à ce qu'une différence de charge demandée par le conducteur soit assurée par modification de la quantité injectée uniquement sur l'injecteur i ;
• on détermine la différence de masse réelle δQ _{inj_réelle,i} injectée par l'injecteur i et la différence de temps δt_i d'injection de l'injecteur i, pour répondre à la demande du conducteur ;
• on écrit pour n paliers de stabilisation de la charge du moteur, l'équation traduisant l'égalité de la masse de carburant injectée par l'injecteur i pendant le temps δt_i telle que définie par le modèle, et la différence de masse réelle δQ _{inj_réelle,i} injectée par l'injecteur i ;
• on résout ce système de n équations à n inconnues pour détermines les n paramètres du modèle.

Thus, according to this embodiment, the calibration of the model is carried out for each injector of the ramp independently, by applying the following steps to determine a number n of parameters of the model:

• the computer is controlled so that a load difference requested by the driver is ensured by changing the quantity injected only on the injector i ;
• determining the actual mass difference δ Q _{inj_real , i} injected by the injector i and the time difference δ t _i injection of the injector i , to meet the driver's demand;
• it is written for n levels of stabilization of the engine load, the equation reflecting the equality of the fuel mass injected by the injector i during the time δ t _i as defined by the model, and the actual mass difference δ Q _{inj_réelle , i} injected by the injector i ;
• this system of n equations with n unknowns is solved to determine the n parameters of the model.

The use of these parameters adjusted, therefore allows to adapt the activation time of the injector i to the evolution of this injector over time so that the amount of fuel injected corresponds to the requested amount. Simply repeat the operation independently for each injector of the engine to proceed with the registration of all the injectors.

According to another embodiment, the registration of the continuous physical model is implemented only if the difference is too large between Φ _real and Φ _th .

Advantages

The use of a physical model makes it possible to extrapolate in operating areas where an experimental characterization of the offline system is not possible, or is not practical to obtain. The characterization times are reduced with a parametric model.

The parametric nature of the model isolates the effects of the main phenomena and their influence on the overall process. While the influence variables are explicitly taken into account in the model, the permanent effects of the geometry, manufacturing, etc., of the system are reduced in some parameters to be calibrated. The number of these parameters is much smaller than the number of data needed to fill two-dimensional maps.

The distinction between the various injectors of the multicylinder engines is naturally achieved by differentiating the parameters of each model for each injector.

Finally, the use of special sensors is not necessary.

Claims (6)

Method for injecting a mass m of fuel via at least one injector of a common rail comprising a plurality of injectors and equipping an internal combustion engine, in which the following steps are carried out: a.- we define a continuous physical model f , describing the injection process in terms of mass flow through the injector, in which we define a dependence between injection time and mass injected, taking into account the pressure in said common rail; b. a pressure p _r is measured in said common ramp; a fuel injection time t necessary to inject the mass m of fuel is determined using said physical model and said pressure p _r ; d.- fuel is injected via the injector during the time t ; and characterized in that an evolution of the injectors is taken into account over time: by determining a mass m ^* of fuel actually injected following step d; and if the mass of fuel actually injected is substantially different from the mass m , a calibration of said continuous physical model f is carried out , so that the fuel injection time, determined by the model thus calibrated, makes it possible to actually inject the mass m during the time t . The method of claim 1, wherein the model calibration is performed for all injectors of the ramp at the same time, by applying the following steps to determine a number n of model parameters: - n is written for n stabilization stages of the engine load, an equation reflecting the equality of the mass of fuel as defined by the model and the actual fuel mass m ^* ; this system of n equations with n unknowns is solved to determine the n parameters of the model. The method of claim 1, wherein the model calibration is performed for each injector of the ramp independently, by determining a number n of model parameters by applying the following steps for each injector i : a motor calculator is controlled so that a load difference requested by a driver is ensured by modifying an injected quantity only on the injector i ; a real mass difference δ Q _{inj eal , i} injected by the injector i and a time difference δ t _i of injection of the injector i , to determine the demand of the driver; it is written for n levels of stabilization of the engine load, an equation representing the equality of the fuel mass injected by the injector i during the time δ t _i as defined by the model, and the difference in actual mass δ Q _{inj_réelle, i} injected by the injector i ; this system of n equations with n unknowns is solved to determine the n parameters of the model. Method according to one of the preceding claims, in which the mass of fuel actually injected m ^{* is determined} at an operating point of the engine where there is no exhaust gas recirculation, and by means of a wealth sensor positioned on an exhaust line of said engine. Method according to one of the preceding claims, wherein said model f is defined by applying the principle of conservation of the mass and the Bernoulli theorem. Method according to one of the preceding claims, wherein initially calibrating said physical model f from fuel consumption measurements from engine test bench with single injections.

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