EP0175596A1 - Adaptive method for regulating the injection in an injection motor - Google Patents

Abstract

Adaptive method of regulating the injection of an injection engine, according to which the injection time is permanently determined by conventional regulation as a function of the intake pressure (P) or of the air flow at the admission from a regulation line defined by its slope and its ordinate at the origin, and the values of the slope (f) and of the ordinate at l are periodically readjusted, by successive adaptation cycles 'origin (b) of the regulation line as a function of any wealth differences observed by an exhaust gas analysis probe using the flowchart shown.

Description

The invention relates to the precise regulation of the injection of fuel into an internal combustion engine by analysis of the exhaust gases.

It is known to permanently determine the injection time by conventional regulation as a function of the pressure in the intake manifold, or also of the air flow at the intake, from a regulation line defined by its slope and its ordinate at the origin in the diagram of the injection times as a function of the pressures. These values are calculated as accurately as possible during the engine development period; but it is known that they vary randomly over time as a function of various parameters, for example the clogging of the air filter which reduces the air flow for the same pressure. It is therefore necessary for precise regulation to periodically readjust the parameters of this regulation line.

For this, there is a process, called "American process", described in particular in the article "A Closed-Loop A / F Control Model for Internal Combustion Engines" by Douglas R.HAMBOURG and Michael Λ.SH0L MΛN, published in 1980 by the "Society of Automotive Engineers, Inc." This process consists in using a so-called "Lambda probe" for analyzing exhaust gases which gives a signal which varies when there is a lack of oxygen in the exhaust gases, which testifies to a richness. crossing the value 1 corresponding to the stoichiometric mixture. When this occurs, the parameters on the control line are corrected as follows: if the inlet pressure P is less than a determined threshold, a correction is applied only to the ordinate at the origin of the line , while if the pressure value is greater than this threshold, a correction is applied only to the slope of the line. This process is therefore approximate. Indeed, if the current conditions are maintained, the recalculated line always ends up passing through the current operating point, but a local anomaly can distort the calculation of all the other points. In addition, this process only works with unit richness, while the problems of energy saving and pollution lead more and more to use wealth less than unity.

We also know the process called "overinjection", described in French patent application 83 17 538 in the name of the applicant, and which consists, when the injection is regulated at a richness less than unity, to be carried out periodically. a gradual increase in richness until the gas analysis probe is triggered, then return to the initial richness while retaining the value of the relative increase in injection time which has been thus necessary, which, compared to the theoretical increase resulting from the desired wealth, gives the necessary correction. The aforementioned patent application indicates how the jolts resulting from this momentary foray into wealth can be avoided by action on the ignition advance. However, these over-injections must be sufficiently spaced in time, with a period for example of 10 minutes.

Naturally, depending on this state of the art, consider using the American method, even with a richness less than 1, by combining it with the over-injection method. However, in this case, the lack of precision of this American process would be further increased by the significant increase in the readjustment period due to the over-injection process.

The object of the invention is to eliminate the above drawbacks by carrying out an adaptive method of regulating injection, the adaptation of which is more precise in all its points and less sensitive to local anomalies, while accommodating n ' no matter what periodicity.

• On mesure la pression d'admission P et l'on calcule le numéro j de zone dans laquelle elle se trouve par division entière ou arrondi;
• A partir des indications d'une sonde d'analyse des gaz d'échappement et de la richesse voulue, on détermine le facteur de correction
• α par rapport à la droite actuelle tel que le point de fonctionnement correct à l'abscisse considérée soit dans le rapport (1 + α ) avec le point correspondant de la droite actuelle;

The invention essentially consists in dividing the space of the usable pressures into a certain number of zones, and in assigning to each zone j the central pressure P _i of the zone, the n values P being stored in ROM, then periodically, with any periodicity determined in advance, to carry out the following operating cycle:

• The intake pressure P is measured and the number j of the zone in which it is located is calculated by whole or rounded division;
• From the indications of an exhaust gas and desired wealth analysis probe, the correction factor is determined
• α with respect to the current line such that the correct operating point at the abscissa considered is in the ratio (1 + α) with the corresponding point of the current line;

We then calculate, for the index j considered, the value of the corrective factor p with respect to the initial line, the parameters of which are in read-only memory, using a simple linear formula as a function of coefficients in read-only memory and parameters in RAM, and the new calculated value is assigned to the variable β _j in RAM;

Finally, as a function of the various values of t> found in memory, the new values of the slope and of the gold given at the origin of the control line are calculated using linear formulas involving only weighting constants in read only memory.

Other features of the invention will appear in the following description of an embodiment taken as an example and shown in the attached drawing, in which:

FIG. 1 is a diagram of the control lines in the pressure / time space, and

FIG. 2 represents the flow diagram of the process.

As long as the engine is running, and at a speed higher than that of the idle, the injection time T is permanently determined by conventional regulation as a function of the intake pressure P, or in certain cases, of the flow rate. intake air measured by a flow meter, and from a control line that can be expressed by the equation:
^T _i = aP + b
where a = (1 + c / 256) (1 + c '/ 256) (...) (1 + f / 256)
c, c '... being corrections according to measured parameters, such as water temperature, air temperature, etc. and f being the scale coefficient. The denominators 256 are arbitrary values preferably corresponding to the storage capacity of a byte so that the low correction values are reduced to integer values. The values f and b can be considered as representing respectively the slope and the ordinate at the origin of the control line, without taking into account the other corrections.

In addition, and this is why the regulation process is adaptive, the values of f and b are readjusted periodically as a function of the differences in richness observed by an exhaust gas analysis probe. It can be a Lambda zirconium oxide probe sensitive to an excess of oxygen, or any other probe or analysis method.

If the engine operates with a unit richness, that is to say in stoichiometric mixture, according to the most frequent standards in use in the United States, the signal from the probe immediately indicates whether the richness should be increased or reduced , i.e. the injection time.

If on the contrary, the engine operates with a constant or variable richness depending on the circumstances but less than unity, for example 0.8, as is more and more frequently the use according to European standards in order to reduce consumption and pollution, the value of the correction is a little more complex to establish. We can in particular use the so-called overinjection process, described in the aforementioned French patent, which consists, with each adaptation cycle, of gradually increasing the injection time until the analysis probe switches, then to quickly return to the previous wealth. If for example the richness is fixed at 0.8, it suffices, from the current injection time, to increase it by 25% to theoretically obtain this changeover. If this changeover takes place sooner or later, a simple rule of three gives the value of the correction to be made.

On the diagram of FIG. 1, the theoretical operating point M is thus determined from point A with the same abscissa on the current operating line D by a corrective term ₀ (such that the ordinate of N is equal to the ordinate of A multiplied by (1 + α). The known method of over-injection also includes measures to prevent the incursion into higher riches, although brief, from introducing a sudden in the operation of the vehicle, and this by temporarily altering the ignition advance proportionately.

Each adaptation cycle therefore determines a theoretical operating point M at the abscissa P corresponding to the current inlet pressure. If this point M is on the regulation line D, of course there is no correction to be made. If, on the contrary, the point is outside the line, it may be necessary to correct it.

For this, according to the state of the art, and in particular according to the American method indicated above, a medium pressure threshold is determined, and if the current pressure P is less than this threshold, only the ordinate is corrected at l origin b of line D without modifying the slope f of this line so that it progressively passes through the point theoretical M, whereas on the contrary, if this pressure is greater than the threshold, only the slope f is corrected without modifying the ordinate at the origin b so that this straight line progressively passes through the new point M. This process is therefore simple but not very precise and is very sensitive to possible local anomalies.

On the contrary, according to the invention, the space of pressures P is divided into a certain number n of zones, for example four in the example of FIG. 1, and for each zone of rank j the average pressure P _j is defined corresponding to the abscissa of the center of the zone.

During the development of the engine, the ideal initial regulation line D is determined, the parameters f and b of which are loaded into read-only memories. On the contrary, the parameters f and b of the current regulation line D are loaded into random access memories and contain the values resulting from the previous use. Failing this, that is to say in the event of erasing the RAMs, these are loaded with the values f and b.

o

The adaptation cycles follow one another, which can be relatively short (a fraction of a second) if unit richness is used, and which have an interest in being more spaced apart, for example 10 minutes, if one uses a richness lower than the unit and the method of overinjection for the reason indicated above.

At each new adaptation cycle, illustrated by the flow diagram of FIG. 2, the current intake pressure P is measured and the number j of the zone in which this pressure P is found is determined. For this, we usually operates digitally and just perform a full division or rounding.

Having determined j, we proceed to analyze the signal from the probe and calculate the corrective term 1 + 0 (compared to the current regulation line D. This implies in particular, in the case of using a richness less than unity, the application of the over-injection process as a whole. It is indeed from point A that the incursion in wealth is carried out up to point M and return to point A, the ratio ordinates of M and A, compared to the fixed richness, making it possible to directly determine 1 + α. These calculations are carried out by confusing the value P of the pressure with the closest value, for example P2 in the example of the figure 1 if j = 2.

There are also n random access memories containing various values of β _j , varying from 1 to n, the coefficients β being defined as the coefficients α but from the initial regulation line D. In other words, we pass from point B on this straight line to point M by multiplying the ordinates by the factor 1 + β.

For the value of j calculated at the start of the cycle, the value indicated in FIG. 2 is calculated and assigned to the memory β _j , a value which results from a purely linear expression as a function of α, since 1 / f _o and 1 / f _o P _j are constants, as well as b _o , while f and b are the current values in random access memories of the parameters of the regulation line D. This purely linear computation is thus easy and fast. Of course, it only affects the β _j , while the other β _i , for i different from j remain at their old value.

Continuing the adaptation cycle, we then calculate and assign to the memories f and b also purely linear values expressing themselves as a function of the βi, for all the values of i from 1 to n, with weighting coefficients k _i and k " _i .

These 2n constants k _i and k ' _i are naturally contained in read-only memories and are determined, experimentally or by calculation, in such a way that the new line D thus determined passes as close as possible to all the points such as M previously calculated.

The regulation of the injection time continues with the new values of the parameters f and b of the regulation line, while independently the adaptation cycle continues with a waiting loop for the fixed period before starting again at the beginning of the cycle.

During the operation of the engine, the intake pressure P naturally varies and passes more or less frequently through all the values of the space provided, which makes it possible to update successively and periodically the various points corresponding to the various zones. But it is clear that each adaptation cycle takes into account not only the operating point M of the zone j considered, but also all of the other points calculated previously, that is to say the history which precedes. In particular, each new straight line D does not generally pass through all the points but consequently attenuates the influence of any local anomalies.

The calculator uses only a few variables: P, j, α, f, b, β ₁ (n values) and few constants: 1 / f _o , 1 / f P, b _o , k (n values), k ' _i (n values), richness, periodicity. In addition, the calculations are extremely simple, since they are all linear and with a small number of terms, and nevertheless precise enough to ensure rapid convergence possibly accommodating a high cycle period.

Naturally, the process applies equally to the stoichiometric mixture or to the different riches of the unit, even variables as we have seen, and it is always possible to add an additional weighting by performing only a fraction each time calculated corrections, or by increasing the coefficients only by one unit at a time in the calculated direction, and this in a known manner.

Claims (5)

1. Adaptive method of regulating the injection of an injection engine, according to which the injection time (Ti) is permanently determined by conventional regulation as a function of the intake pressure (P) or of the flow rate d air at intake from a control line (D) defined by its slope (f) and its ordinate at origin (b), apart from other possible corrections (c, c '... ), and the values of the slope (f) and the ordinate at origin (b) of the control line are adjusted periodically, by successive adaptation cycles according to a determined period. any wealth found by an exhaust gas analysis probe, the pressure space being divided into a certain number (n) of zones to each of which corresponds a central value (P _j ) of the pressure,
process characterized in that after each adjustment cycle of a fixed period, after having measured the current inlet pressure (P) and determining the corresponding zone number (j), the following operations are carried out successively: - according to the indications of the probe and the desired richness, the corrective factor (1 + α) is determined relative to the current regulation line (D); - a corrective factor (β _j ), relative to an initial straight line (D _o , f _o , b) defined in read-only memory, is calculated and individually assigned for each zone, by a purely linear calculation as a function of the corrective factor (1 + α) defined previously, and as a function of the parameters (f, b) of the current line, as well as of constants; - as a function of the various values (β _i ) in random access memory of this last corrective parameter, new values of the parameters (f, b) of the control line (D) are calculated and assigned by purely linear formulas and by application constants (k _i , k ' ₁ , b) in read-only memory; - the coefficients of poderation (k., k '.), used for the calculation of the parameters (f, b) of the regulation line during each adaptation cycle, being determined so that this line passes closest possible from the various points (M) corresponding to the various zones. 2. Method according to claim 1, characterized in that one uses a unit richness (stoichiometric mixture), and a short period for the adaptation cycle. 3. Method according to claim 1, characterized in that one uses a richness less than unity, constant or variable, and a relatively high period, compatible with the use of the known method of over-injection for evaluation of the corrective term (1 + α) compared to the current line. 4. Method according to one of the preceding claims, characterized in that an additional weight is added thereto by applying to each adaptation cycle only part of the correction. 5. Device for regulating the injection of an injection engine, characterized by the implementation of the method according to one of the preceding claims.

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