EP1777397B1 - Method and system for estimating pressure in the intake manifold of an internal combustion engine - Google Patents

Abstract

The method involves taking a value of pressure in a combustion chamber (3) of a cylinder (1) of an engine, based on an angular position of a crankshaft (5), at an instant of an engine cycle close to an instant of closing of an inlet valve (6a) of the cylinder. A ratio between a value (p col) of a pressure to be obtained and the value (p cyl rfa) of the taken pressure is modeled. The pressure in an intake manifold (6) is calculated for each taken value. The value of the pressure to be obtained and taken pressure value are related by an equation P col=Axp cyl rfa +>B, where A, B are constants. An independent claim is also included for a device for estimating pressure in an intake manifold.

Description

The present invention relates to the estimation of the pressure prevailing in the intake manifold of an internal combustion engine.

One of the important parameters for operating the anti-pollution devices of such engines in motor vehicles is the intake pressure, because it allows to determine the mass of air sucked by the engine. This setting is also important for engine performance policies. It can still be used for the diagnosis of a good operation of a turbo-compressor, if the internal combustion engine is equipped with it.

The intake pressure can of course be measured by a pressure sensor installed in the engine intake manifold. It is an expensive solution.

So we already thought to get the parameter in another way. For example, it is known by FR 2,885,216 or EP 1 162 357 to estimate the intake pressure from the gas flow rate in the engine from which the mass of gas in the intake circuit is calculated, and then to calculate the pressure in the intake manifold using as additional parameter the temperature of the gases flowing in this manifold.

However, although this method of determining the inlet pressure gives good results, it turns out to be relatively complicated especially with regard to the establishment of the value of the gas flow in the engine. It also involves fairly important calculation means.

The invention thus aims to provide a method and a device for estimating the intake pressure of an internal combustion engine involving only a minimum of equipment and requiring a very simple calculation of the desired value.

• à relever périodiquement la valeur de la pression dans la chambre de combustion d'au moins un cylindre dudit moteur à un instant du cycle moteur proche de l'instant de fermeture de la soupape d'admission dudit cylindre,
• à modéliser par l'expérimentation le rapport entre la valeur de pression à obtenir et les valeurs de pression relevées, et
• à calculer la pression régnant dans ledit collecteur en fonction du modèle ainsi obtenu pour chaque valeur de pression relevée dans ladite chambre de combustion.

The invention therefore mainly relates to a method for determining the pressure in the intake manifold of a remarkable internal combustion engine in that it consists of:

• periodically reading the value of the pressure in the combustion chamber of at least one cylinder of said engine at a time of the engine cycle close to the closing time of the intake valve of said cylinder,
• to model by experimentation the ratio between the pressure value to be obtained and the pressure values recorded, and
• calculating the pressure prevailing in said manifold according to the model thus obtained for each pressure value recorded in said combustion chamber.

Thanks to these characteristics, it becomes possible to estimate with a very good approximation the pressure in the intake manifold of the engine without the need to provide an expensive sensor in this manifold. Indeed, to thus determine the pressure in the manifold, one can use other sensors already usually provided for the management of the engine, while the necessary calculation means are very simple.

• l'opération de modélisation est réalisée sur la base d'une équation de la forme $$p_{\mathit{col}}=A\cdot {\mathit{p}}_{{\mathit{cyl}}_{\mathit{rfa}}}+B$$
  

dans laquelle:

p_col =

pression à obtenir

p_cylrfa =

pression relevée dans la chambre de combustion

A et B =

constantes déterminées expérimentalement

• l'instant auquel est relevée ladite pression dans la chambre de combustion au cours du cycle de combustion dudit moteur, correspond de préférence à la position angulaire de 15° du vilebrequin après le point mort bas en fin d'admission.

According to other advantageous features of this process:

• the modeling operation is performed on the basis of an equation of the form $$p_{\mathit{collar}}=\mathrm{AT}\cdot {\mathit{p}}_{{\mathit{cyl}}_{\mathit{rfa}}}+B$$
  

in which:

p _col =

pressure to get

p _{cyl rfa} =

pressure in the combustion chamber

A and B =

Experimentally determined constants

• the moment at which said pressure is noted in the combustion chamber during the combustion cycle of said engine, preferably corresponds to the angular position of 15 ° of the crankshaft after the bottom dead center at the end of admission.

• des moyens pour relever la pression dans la chambre de combustion d'au moins un cylindre dudit moteur à un instant du cycle moteur proche de l'instant de fermeture de la soupape d'admission dudit cylindre, et
• des moyens de calcul qui, d'après un modèle déterminé expérimentalement établissent un rapport entre la pression ainsi relevée et la pression à obtenir, calculent celle-ci en fonction de chaque valeur de la pression relevée dans la chambre de combustion.

The invention also relates to a device for estimating the pressure prevailing in the intake manifold of an internal combustion engine, remarkable in that it comprises:

• means for measuring the pressure in the combustion chamber of at least one cylinder of said engine at a time of the engine cycle close to the closing time of the intake valve of said cylinder, and
• calculation means which, according to an experimentally determined model, establish a ratio between the pressure thus measured and the pressure to be obtained, calculate this pressure as a function of each value of the pressure recorded in the combustion chamber.

• le modèle mis en oeuvre dans lesdits moyens de calcul est basé sur une équation de la forme: $$p_{\mathit{col}}=A\cdot {\mathit{p}}_{{\mathit{cyl}}_{\mathit{rfa}}}+B$$
  

dans laquelle:

p_col =

pression à obtenir

p_cylrfa =

pression relevée dans la chambre de combustion

A et B =

constantes déterminées expérimentalement

• lesdits moyens de mesure sont agencés pour relever ladite pression à un instant au cours du cycle de combustion dudit moteur, qui correspond de préférence à la position angulaire de 15° du vilebrequin après le point mort bas en fin d'admission.

According to other advantageous features of this device:

• the model implemented in said calculation means is based on an equation of the form: $$p_{\mathit{collar}}=\mathrm{AT}\cdot {\mathit{p}}_{{\mathit{cyl}}_{\mathit{rfa}}}+B$$
  

in which:

p _col =

pressure to get

p _{cyl rfa} =

pressure in the combustion chamber

A and B =

Experimentally determined constants

• said measuring means are arranged to raise said pressure at a time during the combustion cycle of said engine, which preferably corresponds to the angular position of 15 ° of the crankshaft after the bottom dead center at the end of admission.

• la figure 1 est une illustration symbolique de la mise en oeuvre du procédé et du dispositif selon l'invention.
• la figure 2 est un relevé de points donnant les angles vilebrequin pour lesquels la valeur absolue de la différence entre la pression dans le cylindre et la pression dans le collecteur d'admission est inférieure à une seuil prédéterminé.
• la figure 3 est un relevé de points donnant la pression dans le collecteur d'admission, déterminée grâce au procédé selon l'invention en fonction de la pression dans le cylindre.
• la figure 4 est un relevé de points donnant pour chaque point l'erreur relative entre une pression collecteur mesurée par un capteur de pression et une pression estimée par le procédé selon l'invention.

Other features and advantages of the invention will become apparent from the following description, given solely by way of example and with reference to the appended drawing in which:

• the figure 1 is a symbolic illustration of the implementation of the method and the device according to the invention.
• the figure 2 is a survey of points giving the crank angles for which the absolute value of the difference between the pressure in the cylinder and the pressure in the intake manifold is below a predetermined threshold.
• the figure 3 is a record of points giving the pressure in the intake manifold determined by the method according to the invention as a function of the pressure in the cylinder.
• the figure 4 is a record of points giving for each point the relative error between a manifold pressure measured by a pressure sensor and a pressure estimated by the method according to the invention.

Referring to the figure 1 it is possible to recognize the diagram of a cylinder 1 of an internal combustion engine, which may be of the gasoline or diesel type and comprise one or more cylinders.

Also shown are a piston 2 delimiting the combustion chamber 3, a connecting rod 4, a crankshaft 5, a gas intake manifold 6 and a device 7 for exhausting gases.

According to the exemplary embodiment shown, at least one of the cylinders of the engine is also equipped with a sensor 8 continuously measuring the angular position of the crankshaft 5 and a sensor 9 making it possible to measure the In the place of these sensors, it is also possible to provide equivalent means capable of respectively supplying the one and the other parameters.

The value θ recorded by the sensor 8 represents the instantaneous angle of the crankshaft 5 and that p _θ measured by the sensor 9, the instantaneous pressure in the combustion chamber 3. They are applied to a computing device 10 which can be set up. for example, in the program of the on-board computer of the motor vehicle or in the form of an autonomous computing device.

The computing device 10 comprises a functional block 11 which detects a predefined value θ _rfa of the angular position of the crankshaft. The instant corresponding to this angular position is chosen close to the closing time rfa of the intake valve (referenced 6a in the figure) during each cycle of the engine. By way of example, it is possible to choose the angular position of 15 ° of the crankshaft after the bottom dead center at the end of admission.

We refer to the figure 2 in order to understand the choice of the θ _rfa value In order to determine the best moment for raising the cylinder pressure in order to estimate the pressure in the intake manifold, the test bench has been fitted with 2500 points (20) for which the pressure difference between the cylinder pressure and the pressure in the intake manifold is less than two percent. Indeed, the estimation of the pressure in the intake manifold from the pressure in the cylinder is more accurate than the difference between the two pressures is low. The results of these surveys are presented to the figure 2 . On the abscissa we have the number of the point and on the ordinate the crank angle to which it has been measured. It is found that the crankshaft angle which is most frequently located in the middle of the point cloud has a value of 195 degrees crankshaft (21) after the top dead center of the cylinder considered (ie 15 ° crankshaft after the bottom dead center as specified upper). It is therefore possible to choose this crank angle value for measuring the pressure in the cylinder in the context of the process according to the invention.

The successive predefined values θ _rfa determined in the functional block 11 are correlated with the pressure values p _θ recorded at the corresponding instants by the sensor 9, which operation is performed by the functional block 12. The pressure value called p _{cyl rfa} is very close to that of the pressure prevailing in the intake manifold 6.

To calculate the value of the desired pressure, a model of the ratio between the pressure p _{cyl rfa} and the pressure value Desired _collar p prevailing in the intake manifold 6. This modeling can be performed on each engine individually or optionally on an engine type taken from a series of the same model of motor to be valid for all motors of this series.

The figure 3 is a reading of points giving the value of the collector pressure p _col as a function of the value of the pressure in the cylinder P _{cyl eng} for a crankshaft angle of 195 ° after the top dead center of the cylinder considered. It is observed that the relation between the pressure in the cylinder P _{cyl eng} and the collector pressure p _col is almost linear.

dans laquelle A et B sont des constantes déterminées à calibrer expérimentalement lors de la modélisation et la courbe de cette équation est la droite 23 de la figure 3. Dans un exemple concret de moteur type on a relevé pour ces constantes les valeurs suivantes:
A=0,98 et
B=2526The modeling is therefore preferably done on the basis of an equation of the form: $$p_{\mathit{collar}}=\mathrm{AT}\cdot {\mathit{p}}_{{\mathit{cyl}}_{\mathit{rfa}}}+B$$

in which A and B are determined constants to be calibrated experimentally during the modeling and the curve of this equation is the line 23 of the figure 3 . In a concrete example of a typical engine, the following values were found for these constants:
A = 0.98 and
B = 2526

The method according to the invention finally consists, during the operation of each engine concerned in operating the calculation of the pressure in the intake manifold 6, during each combustion cycle, as a function of the pressure value recorded in the combustion chamber. 3. This calculation operation is illustrated in the figure by the function block 13.

The method according to the invention thus makes it possible to estimate the value p _col of the pressure in the intake manifold 6 of an internal combustion engine by using only very few calculation means and by means of sensors which Anyway are usually provided to manage the operation of the engine. It turned out that the thus estimated _neck pressure p approaches very close to the values that would be measured in situ in the intake manifold with the aid of a sensor which would be placed specially for this purpose.

Indeed, the figure 4 is a record of 2500 points 24 representing the relative error between the collector pressure p _col estimated by the method according to the invention and a collector pressure measured P _mes using a pressure sensor. The relative error is given by the formula: $$\epsilon =\frac{\left|P_{\mathit{my}}-p_{\mathit{collar}}\right|}{P_{\mathit{my}}}$$

The term "relative error" here refers to the absolute value of the difference between a measured collector pressure P _mes by a pressure sensor and the estimated collector pressure p _col from the cylinder pressure by means of the process of the invention, all divided by the measured collector pressure value P _mes . The figure 4 shows that with the method according to the invention the error made with respect to a collector pressure measured with a pressure sensor is very small.

In addition, thanks to the invention, it can save a pressure sensor.

Claims (5)

1. Method for estimating the pressure prevailing in the intake manifold (6) of an internal combustion engine, which involves:

   - periodically recording the value of the pressure in the combustion chamber (3) of at least one cylinder (1) of the said engine as a function of the angular position of its crankshaft,

   - modelling by experimentation the ratio between the pressure value to be obtained (p_col) and the recorded pressure values (p_cylrfa ), and

   - calculating the pressure (p_col) prevailing in the said manifold (6) as a function of the model thus obtained for each pressure value (p_cylrfa ) recorded in the said combustion chamber (3),

   characterized in that:

   - the value of the pressure (p_cylrfa ) in the said combustion chamber is recorded at an instant of the engine cycle close to the instant of closure of the intake valve (6a) of the said cylinder (1), and

   - in that the modelling operation is carried out on the basis of an equation of the form: $${\mathrm{p}}_{\mathrm{col}}\mathrm{=}\mathrm{A}\mathrm{\cdot }{\mathrm{p}}_{{\mathrm{cyl}}_{\mathrm{rfa}}}\mathrm{+}\mathrm{B}$$

   

   in which:

   p_col = pressure to be obtained,

   p_cylrfa = pressure recorded in the combustion chamber, and

   A and B = experimentally determined constants.
2. Method according to Claim 1, characterized in that the instant at which the said pressure in the combustion chamber is recorded corresponds, during the combustion cycle of the said engine, to the angular position (θ) of 15° of the crankshaft (5) after bottom dead centre at the end of intake.
3. Device for estimating the pressure prevailing in the intake manifold (6) of an internal combustion engine, comprising:

   measuring means (8, 9, 11, 12) for periodically recording the pressure (p_cylrfa ) in the combustion chamber (3) of at least one cylinder (1) of the said engine as a function of the angular position of its crankshaft, and

   calculating means (13) which, using an experimentally determined model, establish a ratio between the pressure thus recorded (p_cylrfa ) and the pressure to be

   obtained (p_col) and calculate the latter pressure as a function of each value of the pressure recorded in the combustion chamber (3),

   characterized in that the said measuring means (8, 9, 10, 11) are designed to record the said pressure (p_cylrfa ) at an instant of the engine cycle close to the instant of closure of the intake valve (6a) of the said cylinder, and in that the model employed in the said calculating means (13) is based on an equation of the form: $${\mathrm{p}}_{\mathrm{col}}\mathrm{=}\mathrm{A}\mathrm{\cdot }{\mathrm{p}}_{{\mathrm{cyl}}_{\mathrm{rfa}}}\mathrm{+}\mathrm{B}$$

   

   
   in which:

   p_col = pressure to be obtained,

   p_cylrfa = pressure recorded in the combustion chamber, and

   A and B = experimentally determined constants.
4. Device according to Claim 3, characterized in that the said measuring means (8, 9, 11, 12) are designed to record the said pressure at an instant which corresponds, during the combustion cycle of the said engine, to the angular position of 15° of the crankshaft (5) after bottom dead centre at the end of intake.
5. Internal combustion engine equipped with a device according to either one of Claims 3 and 4.

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