WO2017121934A1

WO2017121934A1 - Method for estimating a mass of fresh air drawn inside a combustion chamber of a variable valve lift internal combustion engine

Info

Publication number: WO2017121934A1
Application number: PCT/FR2016/053469
Authority: WO
Inventors: Frederic Trelle; Christophe PACILLY; Felix GALLIENNE
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2016-01-11
Filing date: 2016-12-15
Publication date: 2017-07-20
Also published as: FR3046630B1; FR3046630A1

Abstract

The invention primarily relates to a method for estimating the mass of fresh air drawn inside a combustion chamber (5) of a cylinder (2) of an internal combustion engine (1) having at least one variable-lift valve during an engine cycle. The method is characterized in that it comprises: - a step of estimating an intake pressure in an intake air distributor, - a step of estimating a filling gradient, - a step of estimating said mass of fresh air drawn inside said combustion chamber (5) on the basis of a product between said intake pressure and said filling gradient, said filling gradient being corrected by a weighting factor dependent on a valve lift amplitude, and - a step of controlling said internal combustion engine (1) on the basis of said previously determined mass of air.

Description

METHOD OF ESTIMATING A FRESH AIR MASS ADMITTED INSIDE A COMBUSTION CHAMBER OF AN INTERNAL COMBUSTION ENGINE WITH VARIABLE VALVE LIFTING

The present invention relates to a method for estimating a fresh air mass admitted inside a combustion chamber of internal combustion engine with variable valve lift. The invention finds a particularly advantageous, but not exclusive, application in the field of motor vehicles.

In known manner, the intake valves and the engine exhaust valves are displaced by camshafts. In certain engine configurations, the relative position of each camshaft relative to the crankshaft can be modified by means of hydraulically or electrically controlled phase shifters. These phase shifters allow, according to the operating conditions, to advance or delay the opening and / or closing of the intake and exhaust valves, that is to say to vary the phasing of the lifting laws. of these valves with respect to a reference mode of operation. These phase shifters are known by the acronym VVA (Variable Valve Actuation) or VVT (Variable Valve Timing).

In the case of so-called "conventional" engines or without variable valve lift, it is known to estimate the air filling from a pressure variation in the inlet manifold. However, the existing estimation methods are imprecise and have poor control of the air filling on variable valve lift motor, since the physical phenomena between a conventional lift, called high lift, and a valve lift specific, so-called low lift, are different. It is recalled here that the high lift corresponds to a valve fully open position, and the low lift corresponds to an intermediate valve position located between the extreme positions of opening and closing complete valve.

However, the estimate of the fresh air mass admitted into the combustion chamber is important to effectively control the internal combustion engine. Indeed, this estimate is particularly useful for determining the amount of fuel to be injected and / or to adjust the ignition advance to optimize combustion. The invention aims to remedy this drawback by proposing a method for estimating the fresh air mass admitted inside a combustion chamber of an internal combustion engine cylinder provided with less a variable lift valve during an engine cycle characterized in that it comprises:

a step of estimating an intake pressure in an air distributor on admission,

a step of estimating a filling slope,

a step of estimating the fresh air mass admitted inside the combustion chamber as a function of a product between the inlet pressure and the filling slope, the filling slope being corrected by the product a weighting factor depending on a valve lift amplitude, and

a step of controlling the internal combustion engine as a function of the air mass previously determined.

The invention thus makes it possible, thanks to a precise estimate of the air filling inside the combustion chamber, to inject an adequate quantity of gasoline into the cylinders for optimal combustion. The richness of the air / fuel mixture is thus controlled, which leads to a minimization of the polluting particles generated by the internal combustion engine.

According to one implementation, the step of estimating the filling slope comprises a step of calculating a ratio between:

a first product between a correction coefficient whose value is a function of an engine speed and an end-of-intake crank angle, and a geometric volume of the combustion chamber calculated at the end crankshaft angle; admission, and

a second product between a constant equal to a ratio following R / M where R is the universal constant of perfect gases and M is a molar mass in kg. mol ^"1 mixed gases, and a fresh air temperature

According to one embodiment, the weighting factor is equal to 1 when the valve is raised high, or different from 1 when the valve is in low lift.

According to one embodiment, a shift of the weighting factor value between the high lift and the low lift is performed using a barycentric coefficient defined as follows:

X = Z + kx (l - Z) with: - = 1 in high lift,

- Χ = Ζ ≠ λ in low lift.

According to one embodiment, the barycentric coefficient having a value varying between 0 and 1 is defined according to the following relation:

with:

L represents said valve lift,

f (N) represents a transition lift between X = Z and X = 1,

g (N) represents a lift difference allowing the transition between X = Z and X = 1.

According to one embodiment, the low lift weighting factor is determined using an artificial neural network.

According to one embodiment, the artificial neural network notably takes into account an engine speed, a valve lift, a position of an intake phase-shifter, and a position of an exhaust phase-shifter.

According to one embodiment, the weighting factor in low lift is determined by means of a two-dimensional map dependent on engine speed and a valve lift.

The invention also relates to a motor vehicle engine computer having a memory storing software instructions for implementing the method as previously defined. The invention will be better understood on reading the description which follows and the examination of the figures that accompany it. These figures are given for illustrative but not limiting of the invention.

FIG. 1 represents a partial schematic sectional view of an internal combustion engine capable of implementing the method for estimating a fresh air mass admitted inside a combustion chamber according to FIG. the present invention;

Figure 2 is a diagram illustrating the operation of the neural network according to the invention for determining the weighting factor. Figure 1 shows a partial schematic sectional view of a gasoline internal combustion engine 1 having a plurality of cylinders 2 for example three or four in number.

Each cylinder 2 comprises a piston 3, a combustion chamber 5, a fuel injector 6, a spark plug 8 associated with an ignition angle setting system 9, at least one intake valve 1 1, at least one exhaust valve 12. The combustion chamber 5 is thus defined in the cylinder 2 between the lower face of a cylinder head 13 and the upper face of the piston 3.

The spark plug 8 is connected to the yoke 13 and provided with electrodes which produce a spark in the combustion chamber 5 when the piston 3 is in the vicinity of its top dead center. The inlet valves 1 1 and exhaust 12 are movably mounted in the cylinder head 13 and are disposed on either side of a median axial plane P of the cylinder 2 so as to define an intake side and an exhaust side.

The intake valves 1 1 are displaced by a first camshaft 171 so as to put the combustion chamber 5, at a chosen instant prior to compression, in communication with an intake duct 18. A valve 20 , in the form of a butterfly, manages the flow of air introduced into the cylinder 2.

Similarly, the exhaust valves 12 are displaced by a second camshaft 172 so as to put the combustion chamber 5 at a selected instant after combustion, in communication with an exhaust duct 23.

The relative position of each camshaft 171, 172 relative to the crankshaft of the engine 1 (not shown) can be modified respectively by means of a first phase shifter 21 1 said intake and a second phase shifter 212 said exhaust. Each phase shifter 21 1, 212 may be controlled hydraulically or electrically. The phase shifters 21 1, 212 allow, according to the operating conditions, to advance or delay the opening and / or closing of the intake valves 1 1 and exhaust 12 with respect to a reference operating mode.

An engine computer 33 provides control of the various elements of the architecture of the engine 1 in particular according to data from different sensors (not shown) implanted in the system. This calculator 33 comprises at this effect a memory 331 storing software instructions for the implementation of the method of estimating the fresh air mass Ma admitted inside the combustion chamber 5 of a cylinder 2 of the engine 1 with valve lift L variable during a motor cycle. The method consists in determining an air filling of the internal combustion engine 1 in low lift. For this purpose, the computer 33 determines a high lift filling according to the following relation:

My Mbal

Replaced early = 1

with: ^{Mo Mo}

- fill tot is the air filling of the engine 1,

- Ma is the fresh air mass contained in the combustion chamber 5 at the end of the intake phase of the fresh air,

- Mbal is a mass of swept gas (air) between the intake and the exhaust during a crossover of valves,

Mo is an air reference mass under normal conditions of temperature and pressure.

The fresh air mass Ma is a solution of the following equation system:

Mtot - ^ ^{ADM x} ^ ^{ADM x} ^ ° y ^l FA

T ^ mixture

Ma = Mtot - Mb

My x cpa x Ta + Mb x cpb x Tb

Tmelange = a X cpa + Mb X cpb

with:

- Mtot is a total mass of gas contained in the combustion chamber 5 at the end of the intake of the fresh air defined above,

Mb is a mass of burnt gases contained in the combustion chamber at the end of the escape of the flue gases,

- ^A ADM is a correction coefficient whose value is a function of a motor speed 30 and an end angle of admission,

- _ADM P is a pressure of intake air in an air distributor

- ^v cyi FA is a geometric volume of the combustion chamber 5 calculated end acceptance angle, - T is a _mixture temperature of the fresh mixture of air and of burnt gases contained in the combustion chamber 5,

r is a constant equal to the following ratio R / M where R is the universal constant of perfect gases and M is a molar mass in kg mol -1 of the mixed gases,

cpa and cpb are constant-pressure mass heat capacities, respectively, of fresh air and flue gases, and

Ta and Tb are temperatures, respectively, of fresh air and flue gases.

By realizing the approximation cpa = cpb, the fresh air mass Ma can be written:

^ ADM ^ ^ cvl FA Tb

Ma = PA _To D _n _{MX MX} _{rx Ta} - Mb x- _Ta

The mass of fresh air Ma admitted inside the combustion chamber 5 in high lift is thus estimated as a function of the product between the inlet pressure P _ADM and a filling slope ("slope") determined by the engine computer 33, namely more precisely:

Ma = P _ADM x offset-slope

The invention consists in correcting the filling slope by multiplying it by a weighting factor X depending on a valve lift amplitude L. The filling equation then becomes:

Ma = P _ADM x slope X X-offset

In high lift, the weighting factor X is forced equal to 1 so as not to impact the accuracy of the estimation of the high lift filling. In low lift, the weighting factor X is equal to Z and is different from 1.

To switch between the value of X = 1 in high lift and the value X = Z in low lift, we use a barycentric coefficient k defined as follows:

X = Z + k x (l - Z)

with:

- Χ = λ in high lift,

- Χ = Ζ ≠ λ in low lift. The barycentric coefficient k is a coefficient whose value varies between 0 and 1 making it possible to transit between the value of X = Z in low lift and X = 1 in high lift according to the following equation:

- L representing the valve lift,

f (N) representing a transition lift between X = Z and X = 1,

- g (N) representing a lifting difference allowing the transition between X = Z and X = 1.

The implementation of the method for determining the weighting factor Z in low lift is performed by means of an artificial neural network 25.

As illustrated in FIG. 2, the artificial neural network 25 is able to determine the value of the weighting factor Z in low lift from the following input variables: the engine speed 30, the valve lift L, the position of the intake phase shifter 21 1 and the position of the exhaust phase shifter 212.

Alternatively, the determination of Z may be performed by means of two-dimensional mapping dependent on the engine speed 30 and the valve lift L. The internal combustion engine 1 is controlled according to the mass of the engine. Ma fresh air previously determined.

Claims

1. Method for estimating the mass (Ma) of fresh air admitted inside a combustion chamber (5) of a cylinder (2) of an internal combustion engine (1) provided with at least a variable lift valve during an engine cycle characterized in that it comprises:

a step of estimating an inlet pressure (P _ADM ) in an intake air distributor,

a step of estimating a filling slope,

a step of estimating said fresh air mass (Ma) admitted inside said combustion chamber (5) as a function of a product between said inlet pressure

(P _A DM) ^and said filling slope, said filling slope being corrected by the product of a weighting factor (X) depending on a valve lift amplitude (L), and

a step of controlling said internal combustion engine (1) as a function of said mass (Ma) of air previously determined.

2. Method according to claim 1, characterized in that the step of estimating the filling slope comprises a step of calculating a ratio between:

- a first product between a correction coefficient (A _ADM ) whose value is a function of a motor speed (30) and a crank angle of end of admission, and a geometric volume {V _{cyl FA} ) of said chamber of combustion (5) calculated at said end of intake crankshaft angle, and

a second product between a constant (r) equal to a ratio following R / M where R is the universal constant of perfect gases and M is a molar mass in kg. mol ^"1 of the mixed gases, and a temperature (Ta) of fresh air.

3. Method according to claim 1 or 2, characterized in that said weighting factor (X) is equal to 1 when said valve is raised high, or different from 1 when said valve is in low lift.

4. Method according to claim 3, characterized in that a tilting of the value of said weighting factor (X) between the high lift and low lift is achieved using a barycentric coefficient (k) defined in the manner next:

X = Z + k x (l - Z)

with

- Χ = λ in high lift,

- Χ = Ζ ≠ λ in low lift.

5. Method according to claim 4, characterized in that said barycentric coefficient (k) having a value ranging between 0 to 1 is defined according to the following relation:

with:

L represents said valve lift,

f (N) represents a transition lift between X = Z and X = 1,

6. Method according to any one of claims 1 to 5, characterized in that said weighting factor (Z) in low lift is determined using an artificial neural network (25).

7. Method according to claim 6, characterized in that said network of artificial neurons (25) notably takes into account an engine speed (30), a valve lift (L), a position of an intake phase-shifter (21). 1), and a position of an exhaust phase shifter (212).

8. Method according to any one of claims 1 to 5, characterized in that said weighting factor (Z) in low lift is determined by means of a two-dimensional map dependent on a motor speed (30) and a valve lift (L).

9. Motor vehicle engine calculator having a memory storing software instructions for the implementation of said method as defined in any one of the preceding claims.