EP0736680A1 - Method of self-correction of physical parameters in a dynamic system such as an internal combustion engine - Google Patents

Abstract

The correction system provides automatic correction of at least one physical parameter during the operation of the i.c. engine, by simulating the parameter using a function in terms of the parameter gradient (X). The error between the simulated parameter value calculated using this function and the actual measured parameter value is determined at the same time as the calculation of the simulated parameter and used for correction of the parameter gradient, for improving the simulation accuracy for the next simulation calculation.

Description

The present invention relates to a method for self-correcting physical parameters of a dynamic system, such as an internal combustion engine.

To operate an internal combustion engine in an optimized manner, it is already known to place it under the control of an electronic control circuit. This electronic circuit manages all the parameters necessary for the proper functioning of the engine.

Unfortunately, not all of these parameters can be measured. Indeed to know certain parameters would require sensors placed in places very difficult to access, and for others the electronic control circuit needs to know at a given moment the value that will have a parameter in the future. In this case it is imperative to estimate or simulate the value of certain parameters instead of actually measuring them.

There are already many methods of simulating the future value of certain parameters, such as, for example, the intake pressure in the manifold, or the quantity of fuel to be injected.

The problem inherent in these methods of simulation or prediction is that it is imperative to ensure that they follow as closely as possible the real value of the parameter. To this end, conventionally, the simulated value of a parameter at a given instant is compared with the real value of this parameter at this same instant. A correction coefficient is deduced from this comparison which realigns the simulated parameter, on the measured parameter. However, we do not come to act directly on the calculation of the simulated parameter. We are satisfied with additive or subtractive corrections which in no way correct the relation allowing the simulated parameter to be obtained.

Such methods of resetting the simulated values to the real values are not satisfactory, because they do not make it possible to follow as closely as possible the variations of the real parameters, in particular during the transient regime phases. These transient regime phases appear at each regime change, in particular when decelerating or accelerating. During these transient regimes, the simulated parameters are always behind or ahead of the real parameters and the operation of the engine is not optimized.

For example, the inlet pressure simulation methods, known to date, consist in introducing additive or multiplicative corrections on the measurement of the pressure carried out before opening the inlet valves. These corrections are determined as a function of the engine operating point and / or as a function of variations in the throttle opening angle, in order to anticipate foreseeable variations in filling with real air.

These correction elements on the intake pressure do not, however, provide a real simulation of the future pressure, but only introduce equivalent corrective terms, with no real physical significance with the future evolution of the pressure. Therefore the methods known to date do not use physical models sufficiently representative of the future state of the intake system, which makes empirical, for example, the development of strategies for calculating the amount of fuel to be injected at each engine cycle.

The aim of the present invention is to create a method allowing an automatic correction of the divergences between the simulated parameters and the real parameters, acting directly on the relation allowing the calculation of the simulated parameters and taking into account the variations of the real parameters between each calculation step. .

• mesurer une erreur entre la valeur réelle mesurée du paramètre à un pas de calcul donné et la valeur simulée de ce paramètre à ce même pas de calcul,
• en déduire une correction à appliquer au calcul du gradient de ce paramètre, afin de modifier simultanément, pour le pas de calcul suivant, la fonction de simulation permettant d'obtenir la valeur simulée de ce paramètre et son gradient.

To this end, the present invention relates to a method of self-correction of at least one physical parameter of a dynamic system, such as an internal combustion engine, in which the evolution over time of said parameter is simulated by a function taking into account the gradient of this parameter, so that at each calculation step the simulation function calculates a simulated parameter, the said method according to the invention being characterized in that it consists in:

• measure an error between the actual measured value of the parameter at a given calculation step and the simulated value of this parameter at this same calculation step,
• deduce therefrom a correction to be applied to the calculation of the gradient of this parameter, in order to simultaneously modify, for the next calculation step, the simulation function making it possible to obtain the simulated value of this parameter and its gradient.

The method according to the invention thus makes it possible at each calculation step, in general at each top dead center (TDC), to compare a simulated parameter and a real parameter. From this comparison, a correction coefficient is removed, not from the simulated parameter, but from the instantaneous derivative (gradient) of this parameter.

This makes it possible to take account of the variations in the gradient between each calculation step and not to consider that this gradient is constant over the iteration horizon. Consequently, the transient variations during an engine cycle are closely monitored.

Advantageously, the present invention can be applied to all simulated parameters whose gradient is taken into account in the simulation function. This is the case, for example, with the intake pressure in the manifold, or with the engine speed. Thus the method according to the invention makes it possible to follow closely, even during a transient regime, the variations of these parameters.

Advantageously also, it will be noted that the correction coefficient determined by the method according to the invention applies both in static (that is to say if the speed is stabilized), as in dynamics (that is to say in the transient phases of engine operation). In fact, the determined correction coefficient corrects not only the agreement between simulated values and measured values, but also their derivatives (gradients or variations).

Intrinsically, the system gradient is therefore corrected, which accentuates the interest of this process, whatever the parameter concerned (pressure or speed ... etc.) and really acts on the simulation function and not only on the final result (ie the simulated parameter).

• la figure 1 est une vue schématique illustrant la mise en oeuvre du procédé selon l'invention, et
• la figure 2 est une vue schématique illustrant le fonctionnement d'un moteur classique à quatre temps, auquel le procédé selon l'invention est appliqué, à titre d'exemple.

Other objects, characteristics and advantages of the present invention will emerge from the following description, by way of non-limiting example, and with reference to the appended drawings in which:

• FIG. 1 is a schematic view illustrating the implementation of the method according to the invention, and
• Figure 2 is a schematic view illustrating the operation of a conventional four-stroke engine, to which the method according to the invention is applied, by way of example.

With reference to FIG. 1, the self-correction method according to the invention is first described in a general framework. In a second step, by way of example, we will apply it to the monitoring of two specific parameters such as the intake pressure in the manifold and the engine speed.

The self-correction method according to the invention makes it possible to follow as closely as possible the variations of a parameter X, of a dynamic system. In this case, this dynamic system is the internal combustion engine of a motor vehicle.

The evolution of this parameter X is simulated by a function taking into account the gradient Ẋ of this parameter. Let Xs be the value of the simulated parameter at time t. We have the following relation: $$\text{Xs = f (}\dot{\text{X}}\text{).}$$

It follows from this relation that the simulated value Xs of the parameter is a function of the derivative Ẋ of this parameter.

As shown in FIG. 1, regularly, for example at each top dead center (TDC), a comparison is made between the simulated parameter Xs and the actual measured value X of this parameter. We deduce an error called ε according to the following relation: $$\text{ε = X - Xs.}$$

From this error, a correction method ± δc is determined by a conventional method (for example by an analog or digital PID electronic circuit). This correction coefficient ± δc is applied not to the simulated value of the parameter but to the gradient Ẋ of this parameter.

In the particular cases of monitoring the intake pressure and the engine speed, the gradient Ẋ of the physical parameter is expressed more precisely as follows: $$\dot{\text{X}}\text{= k [a (X) -b (X)].}$$

The correction coefficient ± δc is then applied either to the first term a (X), or to the second term b (X) according to a confidence coefficient attached to each of these two terms. We have: $$\dot{\text{X}}\text{= k [a (X) -b (X) ± δc].}$$

When the gradient of the parameter has thus been corrected, the simulated parameter Xs for the next step is calculated using the corrected gradient. Consequently it is the simulation function f (Ẋ) which is thus modified to follow as closely as possible the variations of the real parameter.

It should be noted that the coefficient ± δc, can be interpreted as representing a variation of the first term a (X) or the second term b (X), or else apply to both terms in a balanced way (half on each term ) or unbalanced. Everything depends on the measurement and simulation conditions and is left to the discretion of the person skilled in the art. The important thing is that this correction coefficient is applied in its entirety to the calculation of the gradient of the parameter X.

This self-correction method according to the invention will be better understood with the aid of a first application example in which the parameter X is the manifold inlet pressure. To this end, to better place the invention in context, the operation of a four-stroke engine is briefly recalled.

We have chosen to illustrate in Figure 2 the application of the method according to the invention, to an internal combustion engine, four times. Of course, those skilled in the art can extrapolate this example to internal combustion engines having a cycle of any type (two or more times).

Such an engine 10 comprises four cylinders 11 (only one is shown in FIG. 2) which, during an engine cycle, fill with an air / fuel mixture. Each cylinder 11 is supplied with a mixture when an intake valve 12 formed in this cylinder opens. Upstream of this intake valve 12 there is a manifold 13, optionally provided with an air filter 14. The manifold 13 is provided with a throttle valve 15, whose role is to allow more or less to penetrate air inside the manifold. This throttle 15 is coupled to an accelerator pedal (not shown in Figure 2) operated by a driver.

By pressing more or less on his accelerator pedal, the driver varies the opening angle a of the butterfly which has the consequence of varying the amount of air admitted into the cylinder.

A fuel injector 16 sends a quantity of fuel predetermined by a computer 18 to the manifold.

When the intake valve 12 of the cylinder 11 opens, the air / fuel mixture accumulated in the manifold 13 enters the cylinder in question.

FIG. 2 also shows an idle regulation system r, an ignition device All of the compressed air / fuel mixture in the cylinder and a catalyst 17 recycling the exhaust gases discharged by the cylinder 11. These devices known types, are not detailed.

The electronic computer 18, associated with the engine 10 receives the value of the pressure P prevailing in the intake manifold 13. This pressure is measured by an appropriate sensor 19, known per se. The computer 18 is also kept informed by suitable sensors of the rotation speed of the engine N (engine speed), of the water temperature θ, etc.

One of the functions of the electronic calculator is to calculate the quantity of fuel to be injected into a cylinder, in order to produce an air / fuel mixture in determined proportions. For this purpose the computer needs to know the pressure prevailing in the intake manifold when the intake valve closes. It is indeed considered that the pressure prevailing in the intake manifold when a valve closes is equal to the pressure prevailing in the cylinder in question. Knowing the pressure prevailing in a cylinder, and knowing the volume of this cylinder and the temperature of the gases, we deduce the amount of air present inside the cylinder. The amount of gasoline that had to be injected to have an air / fuel mixture in given proportions is therefore easy to deduce. It is therefore important to be able to predict the pressure that will prevail in the manifold of a cylinder when the intake valve of this cylinder opens and closes.

The method according to the present invention makes it possible to automatically correct all the differences which may exist between the simulated or predicted inlet pressure and the actual inlet pressure as measured.

The simulated inlet pressure Ps is a function of the inlet pressure gradient as measured. So we have: $$\text{Ps = f (}\dot{\text{P}}\text{).}$$

The gradient Ṗ of the intake pressure is expressed as follows: $$\dot{\text{P}}\text{=}\frac{\text{1}}{\text{VS}}\text{× [Q (P, PA, α) -Q (P, N)].}$$

In this relationship the coefficient 1 / C is known, Pa is the atmospheric pressure, the first term Q (P, Pa, α) is representative of the air flow entering the intake manifold, and the second term Q (P , N) is representative of the filling of the cylinder.

The first and second terms of the pressure derivative are determined by mapping for each type of engine.

. on déduit de cette différence un coefficient de correction ±δc, que l'on aplique au calcul de la dérivée de la pression d'admission Ṗ.According to the invention, the difference is measured at a given instant. $\text{ε = P - Ps}$

. a correction coefficient ± δc is deduced from this difference, which is applied to the calculation of the derivative of the intake pressure Ṗ.

When the engine is running at medium or high loads the correction coefficient ± δc is applied to the first term Q (P, Pa, α), because it is this term which has the lowest confidence coefficient. Indeed, this term varies the most without any direct means of verifying the importance of these variations.

In the example given, the flow rate Q (P, Pa, α) indeed reflects the variations in the flow rate of the throttle valve, of the idle speed control valve and of the altimetric correction. However, all of these variables are difficult to measure, and highly unstable. The term Q (P, N) is better known and its variations are easier to determine.

In the case where the engine operates at low loads, ie at idle, contrary to the above, it is the term Q (P, N) which has the lowest confidence coefficient. Indeed the incoming air flow Q (P, Pa, α) is low and regulated since the engine idles, on the other hand due to the phenomena of suction of the engine (pulsations of the engine at low loads) it is the flow Q (P, N) which is difficult to control.

In this case the correction coefficient of ± δc applies to the second term of the relation allowing the computation of the derivative Ṗ.

Thus the comparison between the value of the pressure predicted at a calculation step and the real value of this pressure at this same step, is not directly used to readjust the predicted value to the measured value using an additive correction coefficient, but is used to redefine the relation allowing the calculation of the predicted pressure.

Similarly, the method according to the present invention can be applied to the self-correction of the engine speed N of rotation, with respect to the simulated value Ns of this engine speed.

The speed of an internal combustion engine can be simulated according to the following law: $$\text{Ns = g (}\dot{\text{NOT}}\text{).}$$

The gradient Ṅ of this regime is given by the following relation: $$\dot{\text{NOT}}{\text{= k [Γ}}_{\text{1}}{\text{(N) -Γ}}_{\text{2}}\text{(NOT)].}$$

, à un instant donné. De cette erreur on tire de manière classique un coefficient de correction ±δc que l'on applique au couple (moteur ou résistant) présentant le coefficient de confiance le plus faible. Dans le cas du suivi du régime de rotation du moteur, le couple dont les variations sont les plus difficiles à simuler est le couple résistant. Selon l'invention le coefficient de correction ±δc s'applique donc de la manière suivante: $$\dot{\text{N}}{\text{=k[Γ}}_{\text{1}}{\text{(N)-Γ}}_{\text{2}}\text{(N) ± δc].}$$

In this relation Γ ₁ is the driving torque and Γ ₂ is the resisting torque. In the same way as previously described we measure an error $\text{ε = N - Ns}$

, at a given time. From this error, a correction coefficient ± δc is conventionally drawn which is applied to the torque (motor or resistor) having the lowest confidence coefficient. In the case of monitoring the engine speed, the torque whose variations are the most difficult to simulate is the resisting torque. According to the invention, the correction coefficient ± δc therefore applies as follows: $$\dot{\text{NOT}}{\text{= k [Γ}}_{\text{1}}{\text{(N) -Γ}}_{\text{2}}\text{(N) ± δc].}$$

This corrected gradient makes it possible to recalculate a simulated rotation regime taking account of the variations of the gradient, and therefore as closely as possible the variations of the real parameter N. In addition the term [Γ ₂ (N) ± δc] is an image of the resistant couple, that it is difficult to apprehend by known measurement means.

Of course, the self-correction method according to the invention is not limited to the embodiments described above. Thus this self-correction method can be implemented to correct the discrepancies between a parameter simulated according to a certain model (for example a so-called recalibrated model) with this same parameter but simulated according to a second model (for example a model not recalibrated says "free").

Claims (8)

Method for self-correcting at least one physical parameter (X) of a dynamic system, such as an internal combustion engine, in which the evolution over time of said parameter is simulated by a function taking into account the gradient (Ẋ) of this parameter, so that at each calculation step the simulation function calculates a simulated parameter (Xs), the method according to the invention consisting in: - measure an error (ε) between the actual value (X) measured of the parameter at a given calculation step and the simulated value (Xs) of this parameter at this same calculation step, and being characterized in that it consists of: - deduce a correction (± δc) to apply to the calculation of the gradient (Ẋ) of this parameter, in order to simultaneously modify, for the next calculation step, the simulation function making it possible to obtain the simulated value (Xs) of this parameter and its gradient (Ẋ). Method according to claim 1, characterized in that, the gradient (Ẋ) of the parameter is expressed by the following relation:
$\dot{\text{X}}\text{= k [a (X) -b (X)]}$

, and in that the correction coefficient ± δc, applies to the first term a (X) or to the second term b (X) according to a confidence coefficient attached to each of these two terms. Method according to Claim 2, characterized in that the parameter followed is the intake pressure (P) of an internal combustion engine, and in that the gradient Ṗ of this pressure is given by the following relation: $$\dot{\text{P}}\text{=}\frac{\text{1}}{\text{VS}}\text{× [Q (P, Pa, α) -Q (P, N)],}$$

in which 1 / C is a known coefficient, the first term Q (P, Pa, α) is representative of an air flow entering the intake manifold, the second term Q (P, N) is representative of '' a quantity of mixture actually absorbed by a cylinder, (P) is the intake pressure, (Pa) is the atmospheric pressure, (α) is the opening angle of the intake butterfly, and (N) is engine rotation speed. Self-correction method according to claim 3, characterized in that, when the motor is at high or medium loads, the correction coefficient (± δc) is applied to the first term. Method according to claim 3, characterized in that when the engine is at low load the correction coefficient (± δc) is applied to the second term. Method according to claim 2, characterized in that the parameter followed, is the rotation speed (N) of an internal combustion engine, the gradient (Ṅ) of this parameter is expressed according to the following relation:
$\dot{\text{NOT}}{\text{= k (Γ}}_{\text{1}}{\text{(N) -Γ}}_{\text{2}}\text{(NOT))}$

, in which Γ1 is a driving torque and Γ2 is a resisting torque, the coefficient (± δc) being applied to the torque having the lowest confidence coefficient. Method according to claim 6, characterized in that the corrected gradient of the engine speed is expressed according to the following relation: $$\dot{\text{NOT}}{\text{= k (Γ}}_{\text{1}}{\text{(N) -Γ}}_{\text{2}}\text{(N) ± δc).}$$

Method according to one of the preceding claims, characterized in that the parameter evolving over time is itself a simulated parameter.

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