EP1377734A1

EP1377734A1 - Method for calculating the mass of air admitted into the cylinder of an internal combustion engine in a motor vehicle and injection calculator carrying out said method

Info

Publication number: EP1377734A1
Application number: EP02708417A
Authority: EP
Inventors: Christophe Cazali; Edouard Valanciennes
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2001-02-28
Filing date: 2002-02-26
Publication date: 2004-01-07
Anticipated expiration: 2022-02-26
Also published as: EP1377734B1; ES2243696T3; JP2004528504A; FR2821388B1; WO2002068806A1; DE60205732T2; DE60205732D1; FR2821388A1

Abstract

The invention relates to a method for calculating the mass of air admitted into the cylinder of an internal combustion chamber in a motor vehicle and an injection calculator carrying out said method. According to the invention, a value for predicting the pressure at the collector is predicted for each cylinder of the internal combustion engine for the time of closure (t3) of the inlet valve(s) on the basis of the measurement of the parameters describing the operation of the engine. The prediction value (Pres pred) is derived from the execution of a collector solved by an original method which is the object of the invention.

Description

"Method for calculating the mass of air admitted into the cylinder of an internal combustion engine fitted to a motor vehicle and injection computer implementing the method" The present invention relates to a method for calculating the mass of air admitted into the cylinder of an internal combustion engine fitted to a motor vehicle and an injection computer implementing the method.

In the state of the art, such a calculation method has already been described which applies mainly to an injection computer for a thermal engine intended to drive a motor vehicle. In particular, reference will be made to patent FR-A-2,709,151 filed in the name of the same applicant.

In this state of the art, it has been indicated how to predict the mass of air necessary for the best combustion in a cylinder. To this end, it has been defined that the intake air mass should be predicted from the measurement of the pressure at the manifold P _co ι at date t, for a prediction duration of Δt, according to the relationship :

In the process defined in patent FR-A-2,709,151, dP is used to calculate - - at step i the modeled value of P _co ι in the previous calculation step dt (i-1).

It follows that, if at high load (P _{co /} is close to the value of the pressure upstream), the pressure at the manifold modeled at the calculation step i-1 is different from that which the model will calculate, for step i, then the model will oscillate or even diverge.

In other words, the process defined in patent FR-A-2,709.1 51 is correct when the heat engine is operating at low load, and that it requires measures of increasingly difficult real-time correction when the heat engine is operating near full load.

It is to remedy this drawback of the state of the art that the present invention relates to a method of calculating the mass of air admitted into an internal combustion engine cylinder in order to determine the quantity of fuel to be injected. in said cylinder, said engine being of the type comprising an injection computer controlling the operation of the fuel injectors from the values supplied by a pressure sensor disposed in the intake manifold supplying air to the various cylinders, the mass of admitted air being calculated from the pressure at the measured manifold Pcoll, characterized in that it consists in each iteration: to measure or estimate parameters (alpha_pap, N, Tcoll, Pamont, PresMes) describing the actual operation of the engine at the time of calculation, certain parameters integrating a measurement delay with respect to the quantity measured); then in calculating a behavior model of the manifold so that the air flow rate at the intake throttle and the air flow rate at the intake of the engine are found, at the time of the calculation considered; then to deduce therefrom a prediction of the pressure at the manifold for the instant of closure of the intake valve, so that it is possible the predictive calculation of the mass of air entered into the cylinder at the instant of closure of the intake valve associated with the cylinder.

According to another aspect, the method of the invention consists in carrying out, during cycle i, the prediction of values of air flow rates at the engine and at the butterfly on the basis of a state variable, representative of the ratio of the pressure at the manifold relative to the pressure upstream of the manifold deduced from an operating model of the manifold in the form: ix, ^≈ x, -x + - K _l xf _tw (X _l ) - X_ + - 0 /

1 + r, E „. in which: τ, is a function of the engine speed N, of the geometry of the manifold and of the cylinders, of the volumetric efficiency of the engine size and of the recurrence of the injection calculation;

Ki is a function of the engine speed N, the volumetric efficiency remp and the geometry of the engine r, the temperature of the manifold and the butterfly section, and f _bsv is a function predefined by a function generator to define the coefficient throttle flow.

According to another aspect, the method of the invention consists in using the function f _bsv to define the flow coefficient at the butterfly, represented graphically as a function of the state variable Xi: by a first horizontal section for the low values of Xi , by a third substantially vertical section at the highest values of Xi, and by a second decreasing monotonic section at the intermediate values of Xi.

According to another aspect, the method of the invention consists in using the value of the state variable determined in the previous cycle to generate a rectified function f _rβd defining the flow coefficient at the butterfly in an approximate manner, by determining the slope (slope ) and the ordinate at the origin (Y0) of a line segment approaching the curve representative of the real function f _bsv so that the value of a state variable Xi can be determined using the relationship :

1

X, = τ, x X ^• ι, -, l + K, x Y, + -

1 + r, - K, x slope P ...

According to another aspect, the method of the invention consists in finding, for the real function f _bsv the true value r of the state variable (Xi true) which corresponds to the value Xi calculated by the rectified function f _red according to the relation connecting the point (,. / "/ (,)) with the point (*, _TO , /,„ (,. „,)).

According to another aspect, by the method of the invention, the collector is modeled by the parameters describing the operation of the engine, respectively:

- the opening angle of the alpha_pap intake throttle measured by means of a throttle angle sensor;

- the engine speed N, or engine speed, measured by a speed or engine speed sensor; - the air temperature at the Tcoll collector, measured by means of a temperature sensor placed on the air collector;

- the air pressure upstream of the Pamont butterfly, measured by a pressure sensor, or estimated;

- the pressure measured at the collector (Near Mes) by a pressure sensor.

According to another aspect, the method of the invention also includes a step of predicting the mass of air deduced from the prediction of the pressure at the manifold.

The invention also relates to an injection computer, characterized in that it implements the method according to the invention. According to another aspect, the injection computer of the invention comprises: a module implementing a collector model producing a state variable (Xi) representative of the ratio of the pressure at the collector modeled at the upstream pressure measured at the time of the calculation , a module for correcting said state variable (Xi), correction deduced from a relationship between the rectified function (f _red ) and the real function (f _bsv ) of the flow coefficient at the intake throttle _valve ; a module for calculating the air flow rates at the intake (Dpap) and at the engine (Dmot); a module for predicting the value (Near pred) of the pressure at the manifold when the inlet valve of the cylinder in question is closed.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which:

- Figure 1 is a graph explaining the principle on which the invention is based; - Figure 2 is a block diagram of a device implementing the method of the invention;

- Figure 3 is a graph explaining one. improvement provided by the method of the invention.

In Figure 1, there is shown a graph explaining the principle on which the invention is based. Reference is made to the description of patent FR 2,709.1 51 issued in the name of the same applicant for any further explanation of this state of the art.

In the fuel injection technique used to control internal combustion engines, the operation of a cylinder and its valves is considered. The estimation of the air pressure at the time of closing of the cylinder intake valve (s) under control makes it possible to know the value of the mass of air supplied to the cylinder and to deduce therefrom the amount of gasoline to inject for optimized combustion. However, in indirect injection, because of the physics of vaporization, this quantity of gasoline must be introduced before the opening of the intake valve, and in any type of injection, the last measurement is not known. pressure at the collector only with a long delay which makes it impossible to be satisfied with the measurement.

At the Figu re 1, there is shown the evolution between two dates t1 and t3 of the pressure P r collecteu _co ιι • the time t1, was performed, using a suitable means such as a sensor pressure arranged on the intake manifold, measuring the pressure at the manifold P _{co //} (t1).

On the date t2, which is the date of calculation of the injection, an estimate is made of the instantaneous variation of the pressure at the manifold thanks to a physical model of neck reader which makes it possible to predict at the date t3 of closing of the intake manifold pressure with a time difference Δt = t3 - t1 by the relation: dP E _{) /} (tl + Δt) = R _c „ _/ (tl) + Δt x ^

Pcollpred = Pcol (t3) = P _col (tl) + ΔPcoll which corresponds to a prediction of P _co ιι from a prior measurement of P _co u •

Referring to the graph in FIG. 1, it can be seen that the pressure Pcoll pred which corresponds to the sum of the value measured at the date t1 P _co u of the pressure at the manifold with an increment or a decrement AP _{co /} ι may not not correspond with a point on the actual curve of the instantaneous change in pressure at the manifold.

In Figure 2, there is shown a block diagram representing the various components of an injection computer implementing the method of the invention. In the process of the invention, the prediction of the value of the pressure at the manifold Near pred on the date of closure of the intake valve is carried out to prepare the next injection from the measured data available at the time calcu l. These parameters (alpha_pap, N, Tcoll, Pamont, PresMes) are descriptive of the actual operation of the engine at the time of the calculation and they are:

- The opening angle of the alpha pap intake throttle measured by means of a throttle angle sensor 1;

- the engine speed N, or engine rpm, measured by a speed or engine speed sensor; the air temperature at the collector Tcoll, measured by means of a temperature sensor 3 disposed on the air collector; the air pressure upstream of the Pamont butterfly valve, measured by a pressure sensor, or estimated on the basis of another model of the air pressure upstream; the pressure measured at the manifold, noted here Pres es, by a pressure sensor 6. This measurement having a non-negligible acquisition time constant is representative of engine operation, a certain time before.

The first four data are supplied to a module 7 which is constituted by a computer in which the physical collector model defined according to the present invention is programmed and which is adapted to the controlled motor. The collector model used in the invention is based on the principle of a representative volume of the collector which is filled by an air flow entering from upstream with a butterfly flow Dpap and which is emptied by a flow d air coming downstream with a flow to the cylinders Dmot.

In one embodiment, the module 7 includes a means for generating a function representative of the air flow to the butterfly valve Dpap defined by:

pap ô (2) function depending essentially on the considered model of P _co ιι and in which g is a function representing the aeraulic behavior of the butterfly and f _bsv is a function defined in mod ule 7 by a function generator which is defined according to the curve shown in the Figure 3 which will be described later. The function g depends on the parameters S _pap . which indicates the cross-section of the butterfly, Pamont and T _upstream respectively represent the pressure and the temperature upstream of the butterfly. These data are respectively recorded in module 7 or received from one of the modules for detecting input parameters 1 to 5. In general, as seen in Figure 3, the function f _bsv to define the flow coefficient of the intake throttle depends on the state variable X, representative of the Pcol / Pamont pressure ratio to the collector related to the upstream pressure. The graphical representation of the rectification function f _bsv comprises a first horizontal section for the low values of X ,, a third substantially vertical section at the highest values of X ,, and a second decreasing monotonic section at the intermediate values of X ,.

In one embodiment, the module 7 comprises means for generating a function representative of the air flow to the cylinder of the engine Dmot defined by:

D _nml = h (N, T _coll , remp) χ {P _col - P) (3) function depending essentially, for the model considered, on Pcoii and in which h is a function representing the aeraulic behavior of the cylinder in admission which is produced by a function generator h (not shown) and which receives the parameters N, T _∞ ιι from the input parameter input modules 2 and 3 and where PO is the minimum pressure at the manifold which ensures a flow of air to the considered cylinder of the engine. The h function also depends on the ramp coefficient characteristic of the volumetric efficiency of the thermal engine on which the injection computer works.

The collector model is implemented in the mod ule 7 by a differential equation drawn from the model and from the functions f, g and h above and which is defined for the cylinder re considered, during the cycle number i being predicted, by ^•

1

X. = X ι.-, l + K, χ f _hsv {X,) - X ^ ₊ (4)

1 + r relation in which: Xi is the ratio of the pressure to the collector modeled, in cycle number i, to the upstream pressure measured or estimated; τ, is a function of the engine speed N, of the geometry of the manifold and of the cylinders, of the permeability remp of the engine and of the recurrence of the calculation of the injection;

Ki is a function of engine speed N, ramp permeability and engine geometry, manifold temperature and throttle section.

Because of the particular form of the function f _bsv , this relation does not allow to draw Xi as a function of Xi-1 analytically in real time, because we do not know how to reverse this function.

To solve this problem, according to the method of the invention, the function f _bsv is replaced by a function f _red approaching the function f _bsv by a succession of predefined line segments. In this step of the method, we therefore perform a piecewise linearization of the function f _bsv Each segment of the function f _rβd represented in FIG. 3, has the equation: f _re ΛX,) = slope χ X, + Y ₀ (5 ) in which “slope” is the slope of the segment of _red identified by the abscissa point (Xi-1) acquired during the previous prediction and Y0 is the ordinate at the origin of the line carrying this segment. These values can be tabulated in a generating means (not shown) of the _redesigned function f _re . It is then possible to solve the model in Xi in the form:

X. = (6) in which slope and Y0 are the characteristics of the rectified function f _rβ which replaces, in the approximation of the invention, the function f _bsv .

Therefore, in one embodiment, the collector modeling module 7 produces a state variable Xi during the prediction instant t2 in FIG. 1 which is transmitted to the module 8 of the means for calculating the pressure predicted at the manifold at the date t3.

The module 8 includes a correction means which makes it possible to correct the state variable Xi when the abscissa point X, is very close to the maximum value of X = 1.0. (See FIG. 3). Indeed, the rectified function f _red deviates not appreciably from the real function f _bsv near the theoretical maximum abscissa (X = 1) so as to avoid looping the model on one or more almost vertical segments. The last segment of f _red therefore has a non-infinite slope. The looping of the model on this last segment therefore leads to inaccurate values of Xi and /> _ed (Xi) which must be corrected.

In the method of the invention, during step (E1), the segment concerned of the rectified function f _red is chosen (and therefore the values “slope” and Y0 of the rectified function f _rθd ) from the value of the variable XM.

Then, during a step (E2), the module 7 executing the collector model described above produces a value X, from the value X, -. Ι acquired previously and which corresponds to the point Mj on the d representative right _red of the redesigned function. Then, outside the loop of the collector model (module 7), we obtain the corresponding point Mi 'on the representative curve f _bsv of the real function approached by the preceding line. For this, the correction module 8 (FIG. 2) makes it possible to produce, during a step (E3) (FIG. 3), the true values of the state variable Xj and of the value of the function f _sv {X _t ) real by using a tabulated function connecting the point [X ,, / y _e d (Xι)] on the curve with the corresponding point [ _{Xj ιVr} ai _> fûsv (i. raι)] on the real cou rbe f _bsv . These values Xj, _vra true and f i _bS v (Xi, vrat) true are then transmitted to a module 9 for calculating the air flow at the engine dword and butterfly DPAP having respectively a générateu r dword function and a generator of Dpap function performing the pre-registered functions g and h described above. The two generators receive as input the calculated values Xi true and / ùsv (Xi, true) true as well as the Pamont value of the pressure upstream of the butterfly valve, measured by the sensor 5 or estimated, this value being that which is available at the time t2 of the manifold pressure prediction.

The prediction values Dmot and Dpap of air flow to the engine and air flow to the throttle produced by the calculation module 9 are then transmitted to the input of a last calculation module 10 of the predicted value of the pressure at collector that will execute a GP function (Dmot, Dpap, PresMes) by a function generator. The PresMes value corresponds to the last available measured value of the pressure at the manifold, measurement made at time t2 of the graph in FIG. 1 and corresponding to a value at time t1.

In one embodiment, the function GP is written in the form GP = PresMes + gp (Dmot, Dpap), where the function gp () is a predetermined function of the prediction values Dmot and Dpap of air flow at motor and butterfly air flow produced by the calculation module 9. In one embodiment, the function gp () is expressed by:

gp = At x mol, I) in which r is a multiplier coefficient T _CO ι and V _C0 | are the conditions of temperature and volume at the collector and Δt is the integration or modeling time.

The output value of the calculation module 10 represents the prediction of the value of the pressure at the manifold at the date t3 (FIG. 1), so that this value, transmitted to the rest (not shown) of the injection computer, allows the improved calculation of the injection air mass for each engine cylinder.

The invention makes it possible to ensure better dynamics on the models of the prior art, in particular because there is no compromise to be made with the stability of the model which is acquired by the linear nature of the rectified function f _re d-

The invention makes it possible to develop an injection computer facilitated by the stability of the model whatever the load (pressure at the manifold).

The invention makes it possible to reduce, on the solutions of the prior art, the phase shift of the collector model to the measured physical reality which ensures a better relevance of the prediction of the pressure at the collector at the date t3. Finally, the accuracy of the prediction of pressure and therefore of the injection is improved at high loads. The invention allows the use of adjustment parameters corresponding to physical drivers of the heat engine which are measurable or calculable and common with other calculations carried out by the injection computer while in the injection computers of the engine. he state of the art of the specific and not physical parameters resulting from an optimization tool took into account the constraints of stability of the old solutions.

Claims

1. Method for calculating the mass of air admitted into a cylinder of an internal combustion engine in order to determine the quantity of fuel to be injected into said cylinder, said engine being of the type comprising an injection computer controlling the operation of the fuel injectors from the values supplied by a pressure sensor placed in the intake manifold bringing the air to the different cylinders, the admitted air mass being calculated from the pressure at the manifold Pcoll, characterized in that it consists of each iteration: to measure or estimate parameters (alpha pap, N, Tcoll, Pamont, PresMes) describing the actual operation of the engine at the time of calculation; then - calculating a behavior model of the manifold so that the air flow rate at the intake throttle valve (Dpap) and the air flow rate at the engine intake (Dmot) are found at the time of calculation; then to deduce a prediction (Near Pred) of the pressure at the manifold, for the moment of closing of the intake valve, so that is possible the predictive calculation of the mass of air entered into the cylinder at the closing time (t3) of the intake valve associated with the cylinder.

2. Method according to claim 1, characterized in that it consists in carrying out, during cycle i, the prediction of values of air flow rates to the engine (Dmot) and to the butterfly valve (Dpap) on the basis of a variable state (X,), representative of the ratio of the pressure to the collector (Pcoll) compared to the pressure upstream of the collector (Pamont) deduced from an operating model of the collector of the form:

in which: xi is a function of the engine speed N, of the geometry of the manifold and of the cylinders, of the volumetric efficiency remp of the engine and of the recurrence of the calculation of the injection; Ki is a function of the engine speed N, the volumetric efficiency remp and the geometry of the engine, the temperature of the manifold and the throttle section, and f _bsv is a function predefined by a function generator to define the coefficient of butterfly flow.

3. Method according to claim 2, characterized in that it consists in using the function f _bsv to define the flow coefficient at the butterfly represented g raphically as a function of the state variable Xj: by a first horizontal section for the weak values of Xj, by a third substantially vertical section at the highest values of X and by a second decreasing monotonic section at the intermediate values of X ,.

4. Method according to claim 3, characterized in that it consists in using the value of the state variable (X, .ι) determined in the previous cycle to generate a redesigned function f _red defining the flow coefficient at the butterfly of intake in an approximate way, by determining the slope (slope) and the ordinate at the origin (Y0) of a line segment approaching the curve representative of the real function f _bsv so that we can be able to determine the value of the state variable (Xi) using the relation:

5. Method according to claim 4, characterized in that it consists in searching for the real function f _bsv the true value of the state variable (X, _ιV raι) which corresponds to the value r Xi calculated by the function red _ressée f _rβd , according to the relation connecting the point

( ^χ „f ^χ ,)) ^{with the p} ° ^int (^, _™ , .. ,,) -

6. Method according to claim 5, characterized in that the collector model is loaded by the descriptive parameters of the operation of the engine, respectively:

- the opening angle of the alpha_pap intake throttle measured by means of a throttle angle sensor (1);

- the engine speed N, or engine speed, measured by a speed or engine speed sensor (2);

- the air temperature at the Tcoll collector, measured by means of a temperature sensor (3) arranged on the air collector; - the air pressure upstream of the Pamont butterfly, measured by a pressure sensor (5) or estimated;

- the pressure measured at the collector (Near Mes) by a pressure sensor (6).

7. Method according to one of the preceding claims, characterized in that it also comprises a step of predicting the mass of air deduced from the prediction of the pressure at the manifold.

8. injection computer, implementing the method according to one of claims 1 to 7 for controlling the operation of an internal combustion engine comprising at least one cylinder re and a fuel injector, characterized in that it includes: a module (7) implementing a cylinder collector model considered producing a state variable (Xi) representative of the ratio of the collector pressure r Pcol modeled to the upstream pressure at the time of calculation, a module (8) correction of the said state variable (Xi), correction deduced from a relationship between the rectified function (f _re d) and the real function (f _bsv ) of the flow coefficient at the mission throttle _valve ; a mod ule (9) for calculating the air flow rates at the intake (Dpap) and at the manifold (Dmot) for the cylinder considered; a module (10) for predicting the value (Near pred) of the pressure at the manifold when the inlet valve of the cylinder in question is closed.