EP0522908A1 - Method and system to calculate the mass of air intake in a cylinder of an internal combustion engine - Google Patents

Abstract

The invention relates to internal combustion engines and, more particularly, to a method and a system for calculating the mass of fresh air maf present in the cylinder before combustion. For this purpose, each cylinder (C1 to C4) comprises a pressure sensor (CP1 to CP4) which provides a voltage U proportional to the pressure of the mixture contained in the cylinder. The relative pressure in each cylinder is measured at two different angular positions theta 1 and theta 2 which precede combustion after closure of the exhaust valve and these measurements make it possible to calculate the absolute pressure of the cylinder, which absolute pressure then makes it possible to calculate the mass of fresh air with the aid of a computer 27. The invention applies to motor vehicles. <IMAGE>

Description

The invention relates to internal combustion engines and, more particularly in such engines, a method and a system for calculating the mass of fresh air contained in a cylinder.

Numerous parameters are used to control an internal combustion engine, for example the instants of ignition of the spark plugs (petrol engine), the rate of recirculation of the exhaust gases and the quantity of fuel injected.

With regard to the air / fuel ratio, it is essential to know precisely the two elements of the ratio. The volume or the weight of the fuel can be known, with relative precision, by the duration of injection of the latter in the case of an injection engine. For the air mass, several methods are used such as the measurement of the air flow in the intake manifold to the different cylinders, the measurement of the pressure in the intake manifold combined with the measurement of the engine speed. , the measurement of the opening angle of the intake throttle valve combined with the measurement of the engine speed.

These methods do not lead to a precise value of the mass of air admitted into each cylinder being obtained since the measurements are carried out in the intake manifold common to all the cylinders and not inside each cylinder.

An object of the invention is therefore to implement a method for calculating the mass of fresh air contained in each cylinder of an internal combustion engine from pressure measurements inside each cylinder.

Another object of the invention is a system for calculating the mass of fresh air contained in each cylinder of an internal combustion engine.

• mesure de la tension de sortie de chaque capteur de pression pour au moins deux valeurs Θ₁ et Θ₂ de la position angulaire de l'arbre moteur après la fermeture de la soupape d'admission et avant la combustion de manière à obtenir au moins deux valeurs U_Θ₁ et U_Θ₂ de ladite tension,
• détermination de la masse de carburant m_c injecté dans le cylindre concerné et de la masse de gaz brûlés résiduels m_gbr selon un des procédés connus, et
• calcul de la masse d'air frais m_af à partir notamment, d'au moins les deux valeurs U_Θ₁ et U_Θ₂, de la masse de carburant m_c injectée et de la masse des gaz brûlés m_gbr.

The invention relates to a method for calculating the mass of fresh air contained in each cylinder of an internal combustion engine, each cylinder of which comprises an injector, a spark plug, a pressure sensor and at least one intake valve. minus an exhaust valve, the injectors and the spark plugs being controlled by the signals supplied by a computer, said computer receiving angular position information Θ from the engine shaft and the signals supplied by the pressure sensors, said calculation method the mass of fresh air m _af in each cylinder being characterized in that it comprises the following operations:

• measurement of the output voltage of each pressure sensor for at least two values Θ₁ and Θ₂ of the angular position of the drive shaft after closing the intake valve and before combustion so as to obtain at least two U values _Θ ₁ and U _Θ ₂ of said voltage,
• determination of the mass of fuel m _c injected into the cylinder concerned and of the mass of residual burnt gas m _gbr according to one of the known methods, and
• calculation of the mass of fresh air m _af from, in particular, at least the two values U _Θ ₁ and U _Θ ₂, the mass of fuel m _c injected and the mass of burnt gases m _gbr .

avec $$\text{a′ =}\frac{{\text{V}}_{\text{Θ1}}}{{\text{RT}}_{\text{Θ1}}}\text{x}\frac{{\text{kV}}_{\text{Θ2}}^{\text{x}}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}{\text{et b = m}}_{\text{c}}{\text{+ m}}_{\text{gbr}}$$

relations dans lesquelles :

V_Θ₁

est le volume du cylindre concerné pour la position Θ₁,

V_Θ₂

est le volume du cylindre concerné pour la position Θ₂,

T_Θ₁

la température absolue du mélange contenu dans le cylindre concerné pour la position Θ₁,

R

la constante des gaz parfaits,

k

la constante de proportionnalité du capteur de pression concerné,

x

un exposant qui est défini par la formule des gaz parfaits en compression polytropique tel que :

$${\text{P}}_{\text{Θ1}}{\text{x V}}_{\text{Θ1}}^{\text{x}}{\text{= P}}_{\text{Θ2}}{\text{x V}}_{\text{Θ2}}^{\text{x}}$$

According to the invention, the calculation of the mass of fresh air m _af is calculated by applying the following relationships: $${\text{m}}_{\text{af}}{\text{= a ′ (U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{) - b}$$

with $$\text{a ′ =}\frac{{\text{V}}_{\text{Θ1}}}{{\text{RT}}_{\text{Θ1}}}\text{x}\frac{{\text{kV}}_{\text{Θ2}}^{\text{x}}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}{\text{and b = m}}_{\text{vs}}{\text{+ m}}_{\text{gbr}}$$

relationships in which:

V _Θ ₁

is the volume of the cylinder concerned for position Θ₁,

V _Θ ₂

is the volume of the cylinder concerned for position Θ₂,

T _Θ ₁

the absolute temperature of the mixture contained in the cylinder concerned for position Θ₁,

R

the constant of ideal gases,

k

the proportionality constant of the pressure sensor concerned,

x

an exponent which is defined by the formula of ideal gases in polytropic compression such as:

$${\text{P}}_{\text{Θ1}}{\text{x V}}_{\text{Θ1}}^{\text{x}}{\text{= P}}_{\text{Θ2}}{\text{x V}}_{\text{Θ2}}^{\text{x}}$$

• la figure 1 montre des diagrammes qui permettent de valider le procédé selon l'invention, et
• la figure 2 est un schéma simplifié d'un moteur à combustion interne et de son système de mise en oeuvre du procédé selon l'invention.

The mass m _af of fresh air which is calculated per cylinder for each engine cycle is conventionally used to calculate: the mass of fuel to be injected into this cylinder during the next cycle, the ignition angle and more generally all the variables set by the filling of the cylinders. Other objects, characteristics and advantages of the present invention will appear on reading the following description of a particular embodiment, said description being made in relation to the accompanying drawings in which:

• FIG. 1 shows diagrams which make it possible to validate the method according to the invention, and
• FIG. 2 is a simplified diagram of an internal combustion engine and of its system for implementing the method according to the invention.

dans laquelle :

• P est la pression dans le cylindre,
• V le volume du mélange air/carburant dans le cylindre,
• m la masse du mélange air/carburant,
• R la constante des gaz parfaits,
• T la température absolue.

Comme P et V dépendent de la position du piston dans le cylindre, c'est-à-dire de l'angle Θ de rotation de l'arbre moteur, on peut écrire que la formule (1) est vraie pour chaque valeur de Θ, soit : $${\text{P}}_{\text{Θ}}{\text{V}}_{\text{Θ}}{\text{= mRT}}_{\text{Θ}}$$

avec m = m_af + m_c + M_gbr

• m_af étant la masse d'air frais,
• m_c étant la masse de carburant,
• m_gbr étant la masse des gaz brûlés résiduels,

   On peut alors déterminer m_af par la formule : $${\text{m}}_{\text{af}}\text{=}\frac{{\text{P}}_{\text{Θ}}{\text{V}}_{\text{Θ}}}{{\text{RT}}_{\text{Θ}}}{\text{- m}}_{\text{gbr}}{\text{- m}}_{\text{c}}{\text{= a P}}_{\text{Θ}}\text{- b}$$

avec : $$\text{a =}\frac{{\text{V}}_{\text{Θ}}}{{\text{RT}}_{\text{Θ}}}{\text{et b = m}}_{\text{gbr}}{\text{+ m}}_{\text{c}}\text{, coefficients}$$

dans lesquels :
V_Θ est déterminé par la position de l'arbre moteur, T_Θ est mesurée, m_c est la quantité connue de carburant injecté et m_gbr est connue par le taux des gaz brûlés qui restent dans le cylindre après échappement, masse qui peut être mesurée ou calculée pour un moteur donné. Par contre, P_Θ n'est pas connue et l'invention prévoit sa mesure dans chaque cylindre à l'aide d'un capteur de pression. Or, le capteur de pression ne donne qu'une valeur relative et il faut donc faire deux mesures successives pour deux positions Θ1 et Θ2 de l'arbre moteur.The method for calculating the mass of air in an internal combustion engine cylinder according to the invention is based on the application of the ideal gas law to the cylinder, valve closed, ie: $$\text{PV = mRT}$$

in which :

• P is the pressure in the cylinder,
• V the volume of the air / fuel mixture in the cylinder,
• m the mass of the air / fuel mixture,
• R the constant of ideal gases,
• T the absolute temperature.

As P and V depend on the position of the piston in the cylinder, i.e. on the angle Θ of rotation of the motor shaft, we can write that the formula (1) is true for each value of valeur , is : $${\text{P}}_{\text{Θ}}{\text{V}}_{\text{Θ}}{\text{= mRT}}_{\text{Θ}}$$

with m = m _af + m _c + M _gbr

• m _af being the mass of fresh air,
• m _c being the mass of fuel,
• m _gbr being the mass of the residual burnt gases,

We can then determine m _af by the formula: $${\text{m}}_{\text{af}}\text{=}\frac{{\text{P}}_{\text{Θ}}{\text{V}}_{\text{Θ}}}{{\text{RT}}_{\text{Θ}}}{\text{- m}}_{\text{gbr}}{\text{- m}}_{\text{vs}}{\text{= a P}}_{\text{Θ}}\text{- b}$$

with: $$\text{a =}\frac{{\text{V}}_{\text{Θ}}}{{\text{RT}}_{\text{Θ}}}{\text{and b = m}}_{\text{gbr}}{\text{+ m}}_{\text{vs}}\text{, coefficients}$$

wherein :
V _Θ is determined by the position of the motor shaft, T _Θ is measured, m _c is the known quantity of fuel injected and m _gbr is known by the rate of burnt gases which remain in the cylinder after exhaust, mass which can be measured or calculated for a given engine. On the other hand, P _Θ is not known and the invention provides for its measurement in each cylinder using a pressure sensor. However, the pressure sensor gives only a relative value and it is therefore necessary to make two successive measurements for two positions Θ1 and Θ2 of the motor shaft.

que l'on peut écrire sous la forme : $${\text{(kU}}_{\text{Θ1}}{\text{+ d) V}}_{\text{Θ1}}^{\text{x}}{\text{= (kU}}_{\text{Θ2}}{\text{+ d) V}}_{\text{Θ2}}^{\text{x}}$$

si U_Θ₁ et U_Θ₂ sont les tensions délivrées par le capteur de pression pour les angles Θ₁ et Θ₂ respectivement : On obtient alors : $$\text{d =}\frac{{\text{k (V}}_{\text{Θ2}}{\text{V}}_{\text{Θ2}}^{\text{x}}{\text{- U}}_{\text{Θ1}}{\text{V}}_{\text{Θ1}}^{\text{x}}\text{)}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}$$

et la pression absolue P_Θ1 par exemple est déterminée par : $${\text{P}}_{\text{Θ1}}{\text{= k U}}_{\text{Θ1}}{\text{+ d = k U}}_{\text{Θ1}}\text{+}\frac{{\text{k(U}}_{\text{Θ2}}{\text{V}}_{\text{Θ2}}^{\text{x}}{\text{- U}}_{\text{Θ1}}{\text{V}}_{\text{Θ1}}^{\text{x}}\text{)}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}$$

soit : $${\text{P}}_{\text{Θ1}}\text{=}\frac{{\text{k V}}_{\text{Θ2}}^{\text{x}}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}{\text{(U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}{\text{= K (U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{)}$$

La formule (3) peut alors s'écrire : $${\text{m}}_{\text{af}}{\text{= aK (U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{) - b, soit}$$

$${\text{m}}_{\text{af}}{\text{= a′ (U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{) - b}$$

avec $$\text{a′=}\frac{{\text{V}}_{\text{Θ1}}}{{\text{RT}}_{\text{Θ1}}}\text{x}\frac{{\text{k V}}_{\text{Θ2}}^{\text{x}}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}$$

Indeed, if we assume that the compression is polytropic before the start of combustion, we can write: $${\text{P}}_{\text{Θ1}}{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{= P}}_{\text{Θ2}}{\text{V}}_{\text{Θ2}}^{\text{x}}\text{= constant}$$

which can be written in the form: $${\text{(kU}}_{\text{Θ1}}{\text{+ d) V}}_{\text{Θ1}}^{\text{x}}{\text{= (kU}}_{\text{Θ2}}{\text{+ d) V}}_{\text{Θ2}}^{\text{x}}$$

if U _Θ ₁ and U _Θ ₂ are the voltages delivered by the pressure sensor for the angles Θ₁ and Θ₂ respectively: We then obtain: $$\text{d =}\frac{{\text{k (V}}_{\text{Θ2}}{\text{V}}_{\text{Θ2}}^{\text{x}}{\text{- U}}_{\text{Θ1}}{\text{V}}_{\text{Θ1}}^{\text{x}}\text{)}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}$$

and the absolute pressure P _Θ1 for example is determined by: $${\text{P}}_{\text{Θ1}}{\text{= k U}}_{\text{Θ1}}{\text{+ d = k U}}_{\text{Θ1}}\text{+}\frac{{\text{k (U}}_{\text{Θ2}}{\text{V}}_{\text{Θ2}}^{\text{x}}{\text{- U}}_{\text{Θ1}}{\text{V}}_{\text{Θ1}}^{\text{x}}\text{)}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}$$

is : $${\text{P}}_{\text{Θ1}}\text{=}\frac{{\text{k V}}_{\text{Θ2}}^{\text{x}}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}{\text{(U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}{\text{= K (U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{)}$$

Formula (3) can then be written: $${\text{m}}_{\text{af}}{\text{= aK (U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{) - b, that is}$$

$${\text{m}}_{\text{af}}{\text{= a ′ (U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{) - b}$$

with $$\text{a ′ =}\frac{{\text{V}}_{\text{Θ1}}}{{\text{RT}}_{\text{Θ1}}}\text{x}\frac{{\text{k V}}_{\text{Θ2}}^{\text{x}}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}$$

To validate the calculation process, the applicant carried out direct measurements on the engine test bench. For this purpose, measurements of the sensor voltage in polytropic phase were carried out, for example at Θ₁ = 40 ° and Θ₂ = 90 °, as well as measurements of m _af , m _c and m _gbr .

avec A = 1/a′ et B = b/a′
c'est-à-dire une droite de pente A et d'ordonnée B à l'origine.According to relation (5), we must have: $${\text{U}}_{\text{Θ2}}{\text{- U}}_{\text{Θ1}}\text{=}\frac{{\text{m}}_{\text{af}}\text{+ b}}{\text{at'}}{\text{= Am}}_{\text{af}}\text{+ B}$$

with A = 1 / a ′ and B = b / a ′
that is to say a straight line with slope A and ordinate B at the origin.

Direct measurements on the engine test bench consist of running the engine at a constant speed and measuring (U _{90 °} -U _{40 °} ) for different measured values of the mass of fresh air injected.

• (a) N = 1200 tours/minute
  
  soit une droite définie par l'équation : $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90°}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40°}}{\text{= 110 m}}_{\text{af}}\text{+ 8,41}$$
  
  avec un coefficient de corrélation de 0,9997.
• (b) N = 2.300 tours/minute
  
  soit une droite définie par l'équation : $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90°}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40°}}{\text{= 114 m}}_{\text{af}}\text{+ 5,96}$$
  
  avec un coefficient de corrélation de 0,9987.
• (c) N = 3.600 tours/minute
  
  soit une droite définie par l'équation : $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90°}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40°}}{\text{= 118 m}}_{\text{af}}\text{+ 6,97}$$
  
  avec un coefficient de corrélation de 0,9998.
• (d) N = 4.400 tours/minute
  
  soit une droite définie par l'équation : $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90°}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40°}}{\text{= 133 m}}_{\text{ag}}\text{+ 2,87}$$
  
  avec un coefficient de corrélation de 0,9995.

The following values were noted:

• (a) N = 1200 revolutions / minute
  
  either a line defined by the equation: $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90 °}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40 °}}{\text{= 110 m}}_{\text{af}}\text{+ 8.41}$$
  
  with a correlation coefficient of 0.9997.
• (b) N = 2,300 rpm
  
  either a line defined by the equation: $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90 °}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40 °}}{\text{= 114 m}}_{\text{af}}\text{+ 5.96}$$
  
  with a correlation coefficient of 0.9987.
• (c) N = 3,600 rpm
  
  either a line defined by the equation: $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90 °}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40 °}}{\text{= 118 m}}_{\text{af}}\text{+ 6.97}$$
  
  with a correlation coefficient of 0.9998.
• (d) N = 4,400 rpm
  
  either a line defined by the equation: $${\text{<figure-callout id="90" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{90 °}}{\text{-<figure-callout id="40" label="U" filenames="imgf0001.png" state="{{state}}">U</figure-callout>}}_{\text{40 °}}{\text{= 133 m}}_{\text{ag}}\text{+ 2.87}$$
  
  with a correlation coefficient of 0.9995.

These measurements and these lines have been plotted on FIG. 1, the abscissas having been graduated in values of m _af and the ordinates in values of (U _{90 °} -U _{40 °} ). Lines 10, 11, 12 and 13 correspond respectively to the motor speeds of 1,200 rpm, 2,300 rpm, 3,400 rpm and 4,400 rpm.

• mesure de la tension de sortie d'un capteur de pression associé à chaque cylindre pour deux valeurs Θ₁ et Θ₂ de l'arbre moteur après la fermeture de la soupape d'admission et avant la combustion du mélange de manière à obtenir deux valeurs U_Θ₁ et U_Θ₂ de ladite tension;
• détermination de la masse de carburant injecté m_c de l'injection correspondant au cycle en cours et de la masse m_gbr des gaz brûlés selon les procédés habituels;
• calcul de la masse d'air frais m_af par la relation (5) avec le coefficient a′ calculé par la formule (6) et b = m_gbr + m_c.

The method according to the invention therefore comprises the following operations:

• measurement of the output voltage of a pressure sensor associated with each cylinder for two values Θ₁ and Θ₂ of the motor shaft after closing the intake valve and before the combustion of the mixture so as to obtain two values U _Θ ₁ and U _Θ ₂ of said voltage;
• determination of the mass of fuel injected m _c of the injection corresponding to the cycle in progress and of the mass m _gbr of the burnt gases according to the usual methods;
• calculation of the mass of fresh air m _af by the relation (5) with the coefficient a ′ calculated by formula (6) and b = m _gbr + m _c .

This mass of fresh air m _af , resulting from the calculation corresponds to the current cycle, is used for the calculation of the injection time of the following cycle and this for each cylinder, the ignition angle and more generally of all the variables set by the filling of the cylinders.

The system which makes it possible to implement the method according to the invention will be described (FIG. 2) in its application to a four-cylinder engine C₁, C₂, C₃, and C₄ which are supplied with air by an intake manifold 20 common to four cylinders. The inlet of this intake manifold is controlled by a butterfly valve 21 linked to the accelerator. At the level of each cylinder, this conduit 20 is subdivided into four intake pipes T₁, T₂, T₃ and T₄ each leading to an intake valve SA₁, SA₂, SA₃ and SA₄. Each manifold is associated with a fuel injector I₁, I₂, I₃, and I₄.

Each cylinder has a spark plug B₁, B₂, B₃, or B₄ for igniting the detonating mixture and a pressure sensor CP₁, CP₂, CP₃, and CP₄.

After explosion of the detonating mixture, the burnt gases are evacuated to an exhaust pipe TE₁, TE₂, TE₃, and TE₄ by an exhaust valve SE₁, SE₂, SE₃ and SE₄, the four pipes joining to form a conduit for exhaust 22.

The angular position of the motor shaft is identified using a toothed wheel 25 secured to the motor shaft and associated with a detector 26, the output terminal of which is connected to an input of a computer 27.

The computer conventionally supplies the control signals of the injectors I₁ to I₄ and of the spark plugs B₁ to B₄ as a function of various parameters such as the engine speed, the position of the accelerator, that of the throttle valve 21.

According to the invention, the signals supplied by the pressure sensors CP₁ to CP₄ are applied to the computer 27 which performs, for each cylinder, the calculations defined by the method described above. Of course, from one cylinder to another, the values of Θ₁ and Θ₂ are different and the signals from the pressure sensors are only taken into account for the values Θ₁ and Θ₂ by appropriate sampling.

The fuel mass m _c of each cylinder for a given cycle is determined by the computer 27 from the value of m _af calculated for the previous cycle, this is what fixes the opening time of the injectors I₁ to I₄.

The description which has just been made of the method and system according to the invention allows a calculation of the mass of fresh air in each cylinder at each cycle and therefore to then calculate the mass of fuel to be injected into the corresponding cylinder during the following cycle, as well as the ignition angle and, more generally, all the variables set by the filling of the cylinders.

The pressure sensors CP₁ to CP₄ replace the pressure sensor of the intake manifold or the flowmeter, the information of which is usually used to control the engine via the computer 27.

Claims (3)

Method for calculating the mass of fresh air contained in each cylinder of an internal combustion engine each cylinder (C₁ to C₄) comprises an injector (I₁ to I₄), a spark plug (B₁ to B₄), a pressure sensor (CP₁ to CP₄) and at least one intake valve (SA₁ to SA₄) and at least one exhaust valve (SE₁ to SE₄), the injectors (I₁ to I₄) and the spark plugs (B₁ to B₄) being controlled by the signals supplied by a computer (27), said computer (27) receiving angular position information Θ from the motor shaft and the signals, supplied by the pressure sensors (CP₁ to CP₄), said method of calculating the mass of fresh air m _af in each cylinder being characterized in that it comprises the following operations: - measurement of the output voltage U of each pressure sensor for at least two values Θ₁ and Θ₂ of the angular position of the motor shaft before combustion so as to obtain at least two values U _Θ ₁ and U _Θ ₂ of said voltage , determination of the mass of fuel m _c injected into the cylinder concerned and of the mass of burnt gases m _gbr according to one of the known methods, and - calculation of the mass of fresh air m _af from in particular at least the two values U _Θ ₁ and U _Θ ₂, of the mass of fuel m _c injected and of the mass of burnt gases m _gbr . Method according to claim 1, characterized in that the calculation of the mass of fresh air m _af is obtained by applying the following relationships: $${\text{m}}_{\text{af}}{\text{= a ′ (U}}_{\text{Θ}}{\text{₂ - U}}_{\text{Θ}}\text{₁) - b}$$

with $$\text{a ′ =}\frac{{\text{V}}_{\text{Θ1}}}{{\text{RT}}_{\text{Θ1}}}\text{x}\frac{{\text{KV}}_{\text{Θ2}}^{\text{x}}}{{\text{V}}_{\text{Θ1}}^{\text{x}}{\text{- V}}_{\text{Θ2}}^{\text{x}}}{\text{and b = m}}_{\text{vs}}{\text{+ m}}_{\text{gbr}}$$

relationships in which: V _Θ ₁ is the volume of the cylinder concerned for position Θ₁, V _Θ ₂ is the volume of the cylinder concerned for position Θ₂, T _Θ ₁ is the absolute temperature of the mixture contained in the cylinder concerned for position Θ₁, R is the constant of ideal gases, k is the proportionality constant of the pressure sensor concerned, x is an exponent which is defined by the formula of ideal gases in polytropic compression such that: $${\text{P}}_{\text{Θ1}}{\text{x V}}_{\text{Θ1}}^{\text{x}}{\text{= P}}_{\text{Θ2}}{\text{x V}}_{\text{Θ2}}^{\text{x}}$$

System for calculating the mass of fresh air m _af contained in each cylinder of a combustion engine according to the method of claim 1 or 2, characterized in that it comprises: - a pressure sensor (CP₁ to CP₄) per cylinder which supplies an electrical signal representative of the pressure inside the cylinder with which it is associated, - means for measuring the electrical signal (U _Θ ₁, U _Θ ₂) supplied by each pressure sensor (CP₁ to CP₄) at two determined times Θ₁ and Θ₂ of each engine cycle, - a computer (27) for calculating, from the electrical signals (U _Θ ₁, U _Θ2 ) supplied by each sensor, the mass of fresh air m _af according to the relationship defined in claim 2.

Images