|
(11) | EP 0 352 705 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
|
|
| (54) |
Process for regulating the fuel to air ratio of an air/fuel mixture feeding an internal-combustion engine, of the closed-loop type and without the working of a physical fuel to air ratio measurement Verfahren zum Regeln des Kraftstoff/Luft-Verhältnisses eines einem Verbrennungsmotor zugeführten Gemisches ohne physikalische Messung des Kraftstoff/Luft-Verhältnisses Procédé de régulation de la richesse d'un mélange air-carburant d'alimentation d'un moteur à combustion interne, du type boucle fermée, sans exploitation de mesure physique de richesse |
|
|
|||||||||||||||||||||||||||
| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to a process for regulating the fuel to air ratio of an air/fuel mixture feeding an internal-combustion engine and, more particularly, to such a process of the "closed-loop" type, without the working of any physical fuel to air ratio measurement, designed to replace a process for the closed-loop regulation of such an engine from the signal supplied by an oxygen sensor placed in the exhaust gases of this engine, as a result of a temporary or permanent failure of this sensor (compare with EP-A- 115 868).
[0002] There are known processes for regulating the fuel to air ratio of an air/fuel mixture by modulating an opening time (or duration) of a fuel injector by means of a multiplicative term, this regulation being adjusted so as to obtain a uniform and continuous oscillation of the air/fuel ratio about a nominal value. Whether the exhaust gases of the engine pass or do not pass through a catalytic converter limiting the pollution of the environment by these exhaust gases, the modulation of the air/fuel ratio is made the best possible, if appropriate in relation to the characteristics of this converter, by means of two types of correction, proportional and integral, introduced into the calculation of the opening time of the injectors equipping the engine to be regulated.
[0003] These corrections are usually calculated at the top dead centre of the engine cylinder in question. As a result of this, the frequency of the oscillations of the air/fuel ratio is not controlled correctly since this depends on the speed of the engine. Likewise, the amplitude of these oscillations cannot be controlled correctly because it depends on the amplitude of the corrections calculated and applied, and owing to the fact that the corrections are calculated systematically at the top dead centre it is not possible to take the dynamics of the system into account, thus causing a loss in the information to be processed and therefore less accuracy in the calculations used for controlling the amplitude of the oscillations of the mixture fuel to air ratio.
[0004] EP-A-352 704, entitled "Process and device for regulating the fuel to air ratio of an air/fuel mixture feeding an internal-combustion engine" describes a process for the closed-loop regulation of fuel to air ratio which works a signal supplied by an oxygen sensor placed in the exhaust gases of the engine and which makes it possible to control the frequency and amplitude of the oscillations of the fuel to air ratio completely by making these independent of the speed of the engine. The process employs a law of regulation of fuel to air ratio having a recurrent nature, that is to say depending on the prior states of the fuel to air ratio measurements and the values of the preceding corrections of the opening time of the injectors.
[0005] Whether a regulating process with proportional and integral correction or with a recurrent law of regulation is used, a failure of the device for carrying out the process is always to be feared. The failure is very often caused by a breakdown of the oxygen sensor used, because this detector is placed in an especially aggressive environment formed by the exhaust gases of the engine.
[0006] It is therefore expedient to provide means making it possible to ensure a suitable control of the fuel to air ratio of the air/fuel mixture in the event of a failure of the fuel to air ratio regulation normally used for this purpose and, more particularly, in the event of a failure of the oxygen sensor used for this regulation.
[0007] An object of the present invention is, therefore, to provide a process for regulating the fuel to air ratio of an air/fuel mixture feeding an internal-combustion engine, designed to function in the absence of fuel to air ratio information supplied by an oxygen sensor placed in the exhaust gases of the engine. This process will then be able to function independently or replace a fuel to air ratio-regulating process utilizing this fuel to air ratio information, in the event of a temporary or permanent failure of this oxygen sensor.
[0008] Another object of the present invention is to provide such a precess capable of ensuring a continuous control of the fuel to air ratio of the mixture from a nominal fuel to air ratio value which can be different from that corresponding to the stoichiometry, under some driving conditions.
[0009] Yet another object of the present invention is to provide such a process which is effectively protected from disturbances and which allows the use of corrections distributed according to the type of corrections, so as to reduce the calculation time for these corrections.
[0010] These objects of the invention are achieved by means of a process for regulating the fuel to air ratio of an air/fuel mixture feeding an internal-combustion engine according to claim 1.
[0011] The farthest moment of sampling (n-k) taken into account in this linear function defines the order of the control thus obtained.
[0012] According to a first implementation of the process according to the invention, said to be of the first order, the value
of the sampled signal representing the dynamic correction of the injection time is of the form:
where y and η are constants adjusted as a function of the dynamics desired for the regulation, On and ên-1 are the values of the estimated fuel to air ratio differences at the moments of sampling n and n-1.
[0013] According to a second implementation of the process according to the invention, said to be of the second order, the measurement
of the sampled signal representing the dynamic correction of the injection time is of the form:
where a, β, go, g1' g2 are constants adjusted as a function of the dynamics desired for the regulation, ên, ên-1, On-2 are values of the estimated fuel to air ratio differences of the moments of sampling n, n-1 and n-2.
[0014] The static injection time
to which the dynamic correction
is added, itself introduces an estimated value of the steady-state injection control with corrections attributable to certain operating conditions of the engine: correction of idling, of the recoupling of an air compressor or other auxiliary appliance, of altitude, etc.
[0015] Other corrections are applied to the nominal value of the fuel to air ratio of the mixture, to take into account other operating conditions of the engine: operation under full load, cold, during acceleration or deceleration, etc.
[0016] Corrections can also be applied to the static gain of the model of the response of the engine, to take into account some operating parameters of the engine, namely speed, intake pressure, temperature of the air, of the coolant, etc.
[0017] Other characterietics will emerge from a reading of the following description and from an examination of the single Figure which illustrates a functional diagram of the regulating process according to the invention.
[0018] By assumption, the process according to the invention cannot utilize a signal representing the actual fuel to air ratio of the air/fuel mixture, such as that supplied by an oxygen sensor, currently called a "lambda sensor", placed in the exhaust gases of the engine.
[0019] According to the present invention, the fuel to air ratio measurement, which can be obtained from the signal supplied by an oxygen sensor, is replaced by an estimation of this fuel to air ratio and this estimation substitutes the fuel to air ratio measurement normally supplied by the sensor in a regulating process operating by closed loop, so as to preserve the advantages afforded by such functioning in terms of stability and dynamics. It is, in fact, a "pseudo-regulation' by closed loop, since the fuel to air ratio measurement used is not a physical measurement, but merely an estimation calculated from a modelling of the process, as will be described in more detail later.
[0020] Thus, with reference to the single Figure of the accompanying drawing, the present invention makes use of a reference model
M representing the dynamic relation between the fuel to air ratio of the mixture and an opening time (or duration) of a fuel injector used to compose the air/fuel mixture burnt in an internal-combustion engine M, the fuel to air ratio of this mixture being regulated by means of the process according to the invention.
[0021] If:
Rc denotes a nominal fuel to air ratio set for the air/fuel mixture and A
R denotes the instantaneous fuel to air ratio of the mixture, estimated by means of the model, it appears from the functional diagram of the Figure that the A estimated A fuel to air ratio difference:
e = Rc - R
is sampled at E1 with a constant sampling period Te and is processed in a corrector C which supplies a signal representing the dynamic correction of the injection time
, itself added to an estimated "static" injection time
, the sum ti being sampled at E2 in synchronism with the sampling E1. The signal ti represents an effective resulting injection time used with the model n for establishing the estimated fuel to air ratio R.
[0022] According to a preferred embodiment of the present invention, the corrector C used is a digital corrector.
[0023] The modelling of the engine makes it necessary to determine a dynamic model M (p), such that:
where Gs is the static gain of the model in the stabilized state, Md(p) characterizes the dynamics of the response of the fuel to air ratio R as a function of the control signal ti, and p is the Laplace operator (sometimes referred to as s in English speaking countries.
[0024] In the steady state there is:
with:
where K is a coefficient characteristic of the engine and of the operating conditions,
R is the desired fuel to air ratio of the mixture set at R = 1 and
RA is the volumetric efficiency.
[0025] It is shown that:
where N is the speed of the engine, or engine rating, Pr is the pressure at the intake manifold of the engine,
go = ao [Pr + po],
ao and Po are constants.
[0026] Bench measurements made on the engine make it possible to prepare a mapping of the values of the coefficient R in the pressure Pr/speed N system.
[0027] The sampling of the above expression (1) of the dynamic model gives:
where Md(Z) is the Z-transform of the dynamic model (with Z-1 = discrete delay), Bo is the "zero-order hold" function introduced by sampling.
[0028] The model Md(Z) is thus a recurrent model which makes it possible to estimate the instantaneous fuel to air ratio at the moment of sampling n as a function of the effective injection time tin:
thus giving the sampled fuel to air ratio difference:
[0029] By means of the process according to the invention, it is possible to give the nominal fuel to air ratio any chosen value. It is possible, for example, to set:
Rc = 1 for pollution control functioning,
Rc > 1 in an acceleration period,
Rc < 1 for functioning with a "lean" mixture, likewise for pollution control purposes.
[0030] If a catalytic converter is associated with the engine in order to treat the exhaust gases, it is known that a proper functioning of this catalytic converter requires an oscillation of the fuel to air ratio of the mixture. For this purpose, according to the invention, a periodic variation as a function of the time of the nominal fuel to air ratio Rc is programmed in the form of a square-wave signal, for example alternating on either side of the desired mean value.
[0031] If C(Z) denotes the Z-transform of the transfer function of the corrector C used in the present invention, there is:
and the sampled effective injection time is given by:
where
is the estimated static injection time which introduces possible corrections, such as:
- an "idle speed" correction,
- a correction for the coupling to the engine of an air compressor forming part of an air-conditioning device supplied with mechanical energy by the engine,
- a correction of altitude.
[0032] Of course, the closed-loop dynamics will be characterized by the characteristic equation of the system:
[0033] Bench measurements of the fuel to air ratio of the mixture as a function of the injection time make it possible to identify the dynamic behaviour of the engine.
[0034] If these measurements reveal a dynamic relation of the first order in the fuel to air ratio and the mixture, transfer functions of the first order are chosen for the corrector C and the model
.
[0036] It is demonstrated that such a choice provides the following laws of recurrence:
where y, η are functions of a, of Gs and of the dynamics desired for the regulation.
[0037] If the bench measurements reveal a dynamic behaviour of the second order, transfer functions of the second order are chosen for the corrector C and the model, that is to say, for Md(Z):
thus giving the following recurrent relations for the estimated fuel to air ratio and the dynamic injection time:
with:
where a, β, go, g1' g2 are functions of a', β', y', 8' and of Gs(N,Pr) and of the desired closed-loop dynamics.
[0038] In order to integrate the physical disturbances acting on the actual engine system and affecting the static and dynamic behaviour of the latter, and to ensure a zero static error in the steady state, an integral 1/(Z-1) must be preserved in the writing of C(Z), thus implying:
[0039] The signals
and
obtained in this way and forming essential components of the total opening control time Ti of the injector must be combined with various corrections aimed at taking into account special operating conditions of the engine or even the ageing of the latter.
[0040] In particular, the static gain Gs = 1/K.go is subject to a mapped correction of the factor K as a function of N and of Pr, as seen above. This correction is of the "fast" type, that is to say it is capable of changing at each calculation cycle or at each moment of sampling.
[0041] A correction of the injector ageing can also be introduced by adding a term 8K to the factor K, the estimated value of which then becomes:
[0043] Likewise, the term go = ao (Pr + po) of Gs can experience a "slow" altimetric correction δPalt and a "slow" self-adaptive correction on estimated values ao and p of ao and of po. The corrected value:
is then used.
[0044] Finally, corrections of air temperature Cair and of coolant temperature Cwater can be applied to the static gain, the estimated and corrected value of which then becomes:
[0045] Furthermore, various corrections can be introduced by action on the nominal fuel to air ratio value Rc, particularly:
a "full load" correction,
a correction of fuel to air ratio during cold starting,
a correction of "transient phase" (acceleration/deceleration).
[0046] A correction, for example in the event of the coupling of an air compressor to the engine, can also be introduced by acting on the fuel to air ratio, in addition to that mentioned above, introduced by acting on the opening duration of the injector.
[0048] The total opening time of the injector can also include a term to, an "offset" correction representing a dead time in the injector control and a term 8tbt representing a variation in the electrical supply voltage of the injector, this voltage being supplied by the battery of the vehicle.
[0049] Thus, with the process according to the invention which provides a regulation of the closed-loop type without using a fuel to air ratio signal supplied by an oxygen sensor, the total duration Ti of the opening control signal of the injector is expressed by the relation:
with:
and:
[0050] This process, which is carried out by means of a law of recurrent control, is intended more particularly for replacing the regulating process described in the abovementioned patent application in the event of a failure in the oxygen sensor used, the latter process itself likewise being carried out by means of a law of recurrent control governing a sampled additive dynamic correction
which is added to an estimated static injection time in order to establish an effective resulting injection time ti.
[0051] If the failure is temporary, the regulation by means of the process according to the present invention is abandoned as soon as the sensor returns to its normal operation, and the regulating process of the abovementioned patent application resumes the control of the fuel to air ratio regulation of the air/fuel mixture.
[0052] Of course, the regulating process according to the invention could be used independently or, in the event of a failure of an oxygen sensor, be associated with a regulating process other than that described in the abovementioned patent application. However, the process according to the invention is closely complementary to the latter process in that they both employ recurrent laws of control which can be put into effect by calculation means of the same type.
[0053] Thus, by means of the regulating process according to the invention, a complete failure of the fuel to air ratio regulation of the mixture of an internal-combustion engine in the event of a breakdown of an oxygen sensor can be avoided by simulating the presence of this sensor.
[0054] The process according to the invention also has the advantage of allowing a continuous control of the fuel to air ratio from values below that corresponding to the stoichiometry up to values higher than this. The recurrent law of control used is designed to preserve the dynamics and stability of the regulation, despite the presence of disturbances. The corrections applied can be distributed according to the particular type (slow, fast, constant) and therefore made only at the appropriate time, thus achieving a saving of the calculation time for these corrections.
[0055] It will also be seen that the constant-interval sampling of period Te chosen in the process according to the invention, allows the law of control to be made insensitive to the variations in the engine speed, this not occurring when there is the conventional choice of a sampling at the moment of passage of a piston of the engine through the top dead centre.
A 1. Process for closed-loop control of the fuel to air ratio (R) of an air/fuel mixture
feeding an internal-combustion engine by controlling the opening time (tin) of a fuel
injector, this opening time consisting of the sum of at least a static injection time
(
) and a dynamic correction time (Δtid), the said process being characterized in that,
) and a dynamic correction time (Δtid), the said process being characterized in that,
- in absence of fuel to air ratio information of an oxygen sensor, the instantaneous fuel to air ratio of the mixture (R) is estimated by means of such a model of the response of the engine to a signal representing the opening time (tin-1), that the actual value (n) of such ratio is given by the sum of linear items comprising a least the preceding ratio (Rn-1) and the product of the preceding opening time (tin-i) and of the static gain (GS) of the model,
- a difference ratio (e) between the actual fuel to air ratio (R) and a nominal fuel to air ratio (Rc) is sampled and the sampled difference ratio processed in a corrector (C) producing an output sampled in synchronism with the sampling of the difference ratio (e) to form the dynamic correction time (At i d ) in the form of a linear combination of
-- the last k values preceding the actual sampling (n), with k being at least 1, of
the dynamic correction time
-- the last k values of difference ratio (ên-k) and
-- the actual difference ratio (ên) estimated at the actual sampling moment (n).
2. Process according to Claim 1, characterized in that the dynamic correction time
is of the form:
where y and η are constants adjusted as a function of the dynamics desired for the regulation, and ên and ên-1 are the values of the estimated fuel to air differences at the moments of sampling n and n-1.
is of the form:
where y and η are constants adjusted as a function of the dynamics desired for the regulation, and ên and ên-1 are the values of the estimated fuel to air differences at the moments of sampling n and n-1.
3. Process according to Claim 1, characterized in that the dynamic correction time
is of the form:
where a , β, go, g1' g2 are constants adjusted as a function of the dynamics desired for the regulation, and ên, ên-1 and ên-2 are the values of the estimated fuel to air ratio differences at the moments of sampling n, n-1 and n-2.
where a , β, go, g1' g2 are constants adjusted as a function of the dynamics desired for the regulation, and ên, ên-1 and ên-2 are the values of the estimated fuel to air ratio differences at the moments of sampling n, n-1 and n-2.
4. Process according to Claim 3, characterized in that the coefficients a and β satisfy
the relation:
5. Process according to any one of Claims 1 to 4, characterized in that the model
of the response of the engine to opening time of the injector comprises a component
consisting of a static gain of the form Gs = 1/K.go, the factor K being corrected depending on the intake pressure and engine speed,
and go = ao (Pr + po) where ao and po are constants with Pr representing the intake pressure.
6. Process according to Claim 5, characterized in that the factor K is corrected by
an additive corrections 8K, taking into account the ageing of the injectors.
7. Process according to Claim 5, characterized in that an additive altimetric correction
Pall is applied to the term (pr + po) of go.
8. Process according to Claim 7, characterized in that a self-adaptive correction
is applied to the coefficients ao and po of go.
9. Process according to any one of Claims 5 to 8, characterized in that a correction
of air temperature and a correction of water temperature are applied to the static
gain Gs.
10. Process according to any one of the preceding claims, characterized in that the
fuel to air difference ratio and the output signal from the corrector are sampled
at a constant interval (Te) independent of the rotational speed of the engine.
11. Process according to any one of the preceding claims, used on an engine associated
with a catalytic convereter , characterized in that the value of the nominal fuel
to air ratio (Rc) is controlled according to a periodic law as a function of time,
alternating on either side of the mean nominal value.
A 1. verfahren zum Regeln des Brennstoff-/Luftverhältnisses (R) eines Brennstoff-/Luftgemisches
für eine Brennkraftmaschine durch Regeln der Öffnungszeit (tin) einer Brennstoffeinspritzdüse, wobei die Öffnungszeit gleich der Summe mindestens
einer statische Einspritzzeit (
) und einer dynamischen Korrekturzeit (Atid ) ist, dadurch gekennzeichnet, daß
) und einer dynamischen Korrekturzeit (Atid ) ist, dadurch gekennzeichnet, daß
- in Abwesenheit einer Information eines Sauerstoffsensors über das Verhältnis von Brennstoff zu Luft das momentane Brennstoff-/Luftverhältnis des Gemisches (R) mittels eines Modells des Ansprechverhaltens des Motors auf ein Signal geschätzt wird, das die Öffnungszeit (tin-i) repräsentiert derart, daß der Ist-Wert (n) des Verhältnisses durch die Summe linearer Werte gegeben ist, die mindestens das vorhergehende Verhältnis (Rn-i) und das Produkt der vorhergehenden Öffnungszeit (tin-1) und der statischen Verstärkung (GS) des Modells umfassen,
- ein Differenzverhältnis (e) zwischen dem Ist-Wert des Brennstoff-/Luftverhältnis
(R) und einem Nennwert des Brennstoff-/Luftverhältnisses (Re) wird abgetastet und das getastete Differenzverhältnis in einer Korrektureinrichtung
(C) verarbeitet, die einen synchron mit dem Abtasten des Differenzverhältnis (e) getasteten
Ausgang erzeugt, um die dynamische Korrekturzeit (
) in Form einer linearen Kombination mit folgenden Werten zu bilden
-- den letzten, dem tatsächlichen Abtasten (n) vorangehenden k-Werten der dynamischen
Korrekturzeit
wobei k mindestens 1 ist,
-- den letzten k-Werten des Differenzverhältnisses (ên-k) und
-- dem tatsächlichen differenzverhältnis (ên), das zum tatsächlichen Abtast -Zeitpunkt (n) geschätzt wird.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die dynamische Korrekturzeit
folgender Form gehorcht:
wobei y und η Konstanten sind, die als Funktion des für die Regelung gewünschten dynamischen Haltens eingestellt sind und In und ên-1 Werte der geschätzten Brennstoff-/ Luftdifferenzen in den Abtastzeitpunkten n und n-1 sind.
folgender Form gehorcht:
wobei y und η Konstanten sind, die als Funktion des für die Regelung gewünschten dynamischen Haltens eingestellt sind und In und ên-1 Werte der geschätzten Brennstoff-/ Luftdifferenzen in den Abtastzeitpunkten n und n-1 sind.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die dynamische Korrekturzeit
der Form gehorcht:
wobei a, β, go, g1, g2 Konstanten sind, die als Funktion des für die Regelung gewünschten dynamischen Verhaltens eingestellt sind und ên, ên-1 und en-2 Werte der geschätzten Brennstoff-/Luftverhältnisdifferenzen in den Abtastzeitpunkten n, n-1 und n-2 sind.
wobei a, β, go, g1, g2 Konstanten sind, die als Funktion des für die Regelung gewünschten dynamischen Verhaltens eingestellt sind und ên, ên-1 und en-2 Werte der geschätzten Brennstoff-/Luftverhältnisdifferenzen in den Abtastzeitpunkten n, n-1 und n-2 sind.
4. verfahren nach Anspruch 3, dadurch gekennzeichnet, daß die Koeffizienten a und
β folgender Gleichung gehorchen:
a + β = 1.
5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß das Modell
für das Ansprechen des Motors auf die Öffnungszeit der Einspritzdüse eine Komponente
aufweist, die aus einer statischen Verstärkung Gs = 1/K.go besteht, wobei der Faktor K abhängig vom Einlaßdruck und der Motordrehzahl korrigiert
wird und go = ao(Pr + po), wobei ao und po Konstanten sind und Pr dem Einlaßdruck entspricht.
6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der Faktor K mit additiven
Korrekturwerten 8K korrigiert wird, indem die Alterung der Einspritzdüsen berücksichtigt
wird.
7. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der Ausdruck (pr + po) in go eine additive altimetrische Korrektur palt erfährt.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß die Koeffizienten ao und po in go eine selbstadaptive Korrektur erfahren.
9. Verfahren nach einem der Ansprüche 5 bis 8, dadurch gekennzeichnet, daß die statische
Verstärkung Gs eine Korrektur der Lufttemperatur und der Wassertemperatur erfährt.
10. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß
das Brennstoff- /Luftdifferenzverhältnis und das Ausgangssignal der Korrektureinrichtung
in einem konstanten Zeitintervall (Te) unabhängig von der Motordrehzahl getastet werden.
11. verfahren nach einem der vorhergehenden Ansprüche für eine mit einem Katalysator
versehenen Brennkraftmaschine, dadurch gekennzeichnet, daß der Wert des nominellen
Brennstoff-/Luftverhältnisses (Re) entsprechend einem periodischen Gesetz zeitabhängig geregelt wird und zu beiden
Seiten des mittleren Nennwertes alterniert.
A
1. Procédé de régulation en boucle fermée de la richesse (R) d'un mélange air-carburant
d'alimentation d'un moteur à combustion interne, par commande du temps d'ouverture
(tin) d'un injecteur de carburant, ce temps d'ouverture étant constitué par au moins
la somme d'un temps d'injection (
) et d'une correction dynamique (Δ tid) du temps d'injection, procédé caractérisé en ce que:
) et d'une correction dynamique (Δ tid) du temps d'injection, procédé caractérisé en ce que:
- en l'absence d'information de richesse délivrée par une sonde à oxygène, on réalise une estimation de la richesse instantanée (R) du mélange à l'aide d'un modèle de la réponse du moteur à un signal représentatif du temps d'ouverture (tin-i), tel que la valeur réelle à l'instant présent d'échantillonnage (n) de cette richesse soit donnée par la somme de terme linéaire comprenant au moins la richesse précédente (Rn-1) et le produit du temps d'ouverture précédent (tin-i) par le gain statique (Gs) du modèle,
- on échantillonne un écart de richesse (e) entre la richesse réelle (R) et une richesse
nominale (Rc) et l'écart échantillonné est traité dans un correcteur (C) à sortie
échantillonnée en synchronisme avec l'échantillonnage de l'écart (e) de richesse pour
former la correction dynamique (
) sous la forme d'une combinaison linéaire :
-- dans les dernières valeurs de ka correction
précédent l'instant présent (n) d'échantillonnage,
-- dans les dernières valeurs de l'écart (ên-k) et
-- de l'écart (ên) estimé à l'instant présent (n) d'échantillonnage.
2. Procédé conforme à la revendication 1, caractérisé en ce que la correction dynamique
du temps d'injection est de la forme :
ou y et η sont des constantes ajustées en fonction de la dynamique souhaitée pour la régulation, en et ên-1, les mesures des écarts de richesse estimés aux instants d'échantillonnage n et n-1.
du temps d'injection est de la forme :
ou y et η sont des constantes ajustées en fonction de la dynamique souhaitée pour la régulation, en et ên-1, les mesures des écarts de richesse estimés aux instants d'échantillonnage n et n-1.
3. Procédé conforme à la revendication 1, caractérisé en ce que la correction dynamique
du temps d'injection est de la forme :
où a, β, go, g1' g2 sont des constantes ajustées en fonction de la dynamique souhaitée pour la régulation, ên, ên-1, ên-2 sont les mesures des écarts de richesse estimés aux instants d'échantillonnage n, n-1, et n-2.
où a, β, go, g1' g2 sont des constantes ajustées en fonction de la dynamique souhaitée pour la régulation, ên, ên-1, ên-2 sont les mesures des écarts de richesse estimés aux instants d'échantillonnage n, n-1, et n-2.
4. Procédé conforme à la revendication 3, caractérisé en ce que les coefficients a
et β satisfont à la relation :
5. Procédé conforme à l'une quelconque des revendications 1 à 4, caractérisé en ce
que le modèle de la réponse du moteur à un temps d'ouverture de l'injecteur comprend
une composante constituée par un gain statique de la forme Gs = 1 K.go, K étant un facteur qui subit une correction cartographique en fonction de la pression
d'admission et de la vitesse du moteur, avec go = ao (Pr + po) où ao et po sont constantes et Pr représente la pression d'admission.
6. Procédé conforme à la revendication 5, caractérisé en ce qu'on corrige le facteur
K par une correction additive 5K tenant compte du vieillissement des injecteurs.
7. Procédé conforme à la revendication 5, caractérisé en ce qu'on applique une correction
altimétrique additive δpalt au terme (pr + po) de go.
8. Procédé conforme à la revendication 7, caractérisé en ce qu'on applique une correction
auto-adaptative aux coefficients ao et po de go.
9. Procédé conforme à l'une quelconque des revendications 5 à 8, caractérisé en ce
qu'on applique une correction de température d'air et une correction de température
d'eau au gain statique Gs.
10. Procédé conforme à l'une quelconque des revendications précédentes, caractérisé
en ce qu'on échantillonne l'écart de richesse et le signal de sortie du correcteur
avec un intervalle constant Te indépendant de la vitesse de rotation du moteur.
11. Procédé conforme à l'une quelconque des revendications précédentes, appliqué à
un moteur associé à un pot catalytique, caractérisé en ce qu'on commande la valeur
de la richesse de consigne (Rc) suivant une loi périodique en fonction du temps, alternative
de part et d'autre de la valeur moyenne de consigne.