EP0146426A1 - Method of controlling a lambda probe regulated fuel injection and controlled ignition engine - Google Patents

Abstract

1. A process for controlling a fuel injection engine fitted with an electronic injection and ignition computer coupled to a probe for detecting the oxygen content of the exhaust gases, comprising the following steps : a) determining at least the operating speed and the load of the engine as engine operating parameters, b) determining in dependence on said parameters a nominal injection time Tin corresponding to lean fuel metering of the fuel mixture, c) periodically causing temporary enrichment of said mixture by a predetermined increase in the nominal injection time Tin , said increase being equal to Tin . x in which x is a coefficient of less than 1, which predetermined enrichment is to restore the lean fuel mixture to a stoichiometric mixture, d) determining if the signal supplied by the probe for detecting the oxygen content of the exhaust gases and corresponding to the enriched mixture indicates a stoichiometric mixture or a richer mixture than stoichiometric or a leaner mixture than stoichiometric, e) in dependence on said determining step modifying the nominal injection time Tin so as to bring the enriched mixture closer to a stoichiometric mixture, and f) continuing the control mode corresponding to a lean fuel metering in the fuel mixture on the basis of the modified nominal injection time Tin , characterised by the following steps : g) determining in dependence on the engine operating parameters a nominal ignition advance angle AVn corresponding to the nominal injection time Tin , and h) causing, with a predetermined delay with respect to the beginning of periodic enrichment of step c) above, a temporary reduction in the nominal ignition advance angle AVn equal to k . x . AVn in which x is the coefficient of less than 1 used for computing the enrichment Tin . x and k is a constant of predetermined value.

Description

The present invention relates to a method for controlling a fuel injection and spark-ignition engine by means of an electronic computer coupled to a probe for detecting the oxygen content of the exhaust gases, hereinafter called probe _/ \.

The probe A is an all-or-nothing sensor whose output voltage is either higher or lower than a certain threshold depending on whether the oxygen content of the exhaust gases is lower or higher than a predetermined value. This oxygen content of the exhaust gases is itself an image of the mixture of air and fuel admitted into the engine: a lean mixture generates an excess of oxygen in the exhaust gases and a rich mixture a deficit of oxygen, the threshold of the probe A corresponding to the stoichiometric ratio.

Such a probe A can thus be used in combination with an injection computer to measure the air / fuel mixture admitted into the engine as a function of the oxygen content of the exhaust gases. This regulation makes it possible in particular to reduce the emissions of toxic components from spark-ignition engines as required by national regulations in a certain number of countries.

Another advantage of such regulation by probe lies in the possibility of operating the engine in a lean mixture, at least in certain areas of its operating range, in order to minimize fuel consumption and reduce carbon monoxide and unburnt hydrocarbon emissions.

It is therefore desirable to run an engine with a lean mixture and to check during operation the changes in richness due to a drift in the initial characteristics of the engine.

To this end, it is already known, in particular by patent FR-A 2,035,177, to supply an engine with a lean mixture and to cause an enrichment having known characteristics, while checking during this process the state of the probe. .

However, such a method has the effect of generating during the enrichment phases an excess of engine torque which is felt by the driver of the vehicle. It is also known, in particular from patent application EP-A-0007 998, to avoid an excessively sudden increase in the torque of an engine during the refueling thereof following the interruption of this supply. , temporarily reducing the ignition advance angle. However, this strategy of reducing the ignition advance angle described in patent application EP-A-0007 998 cannot be directly transposed to solve the problem posed by the supply of an engine with a mixture. poor using a regulation by λ probe, especially for reasons related to driving comfort which requires the most regular possible operation of the engine that would not allow this simple transposition.

The invention aims to solve this problem and, for this purpose, it relates to a method for controlling a fuel injection engine and controlled ignition equipped with an electronic injection and ignition computer coupled to a detection probe. the oxygen content of the exhaust gases, according to which a nominal advance advance angle is developed as a function of the engine operating parameters which is temporarily reduced in certain operating conditions of the engine and a nominal injection time corresponding to a low-fuel dosage of the fuel mixture and a temporary enrichment of said mixture is periodically caused by an increase in injection time, characterized in that, in response to said temporary enrichment , said temporary reduction in the angle of advance at nominal ignition is caused and in that the amplitude of the reduction in the angle of advance at ignition is proportional to said nominal angle of advance and depends on the value of the temporary increase in injection time.

According to a characteristic of the invention, the temporary advance reduction is generated a predetermined number of engine revolutions after the start of the temporary enrichment.

• - la figure 1 est une vue schématique d'un système électronique d'injection de carburant pour la mise en oeuvre du procédé suivant l'invention ;
• - la figure 2 est un chronogramme illustrant l'évolution du temps d'injection Ti et de l'angle d'avance à l'allumage Av en fonction du nombre de tours moteurs t conformément à l'invention ;
• - la figure 3 est un organigramme de fonctionnement d'un calculateur numérique d'injection et d'allumage assurant une régulation conforme au procédé de l'invention.

Other characteristics and advantages of the invention will emerge from the description which follows of an embodiment given only by way of example and illustrated by the appended drawings in which:

• - Figure 1 is a schematic view of an electronic fuel injection system for implementing the method according to the invention;
• - Figure 2 is a timing diagram illustrating the evolution of the injection time Ti and the ignition advance angle Av as a function of the number of engine revolutions t according to the invention;
• - Figure 3 is a flowchart of operation of a digital injection and ignition computer providing regulation according to the method of the invention.

Referring to FIG. 1, a positive-ignition engine 1 comprises an intake pipe 2, in which an injector 3 is arranged downstream of a throttle valve 4, and an exhaust pipe 5, The time

opening of the injector 3, which determines the dosage of the air / fuel mixture, is controlled by a digital computer 6 which receives from a pressure sensor 7 information relating to the air pressure in the supply line intake 2 and a speed sensor 8 information relating to the speed of rotation of the engine 1. The sensor 8 is associated with a toothed target 9 integral in rotation with the crankshaft (not shown) of the engine 1 and some of whose teeth have been suppressed the output signal from the sensor 8 is thus used by the computer 6 to determine both the speed and the angular position of the crankshaft as described in patent FR-A- 79.00 386. Finally, the computer 6 also receives the signals from output of a probe A 10 arranged in the exhaust pipe 5 and of a temperature sensor 11 disposed in the cooling water circuit 12 of the engine 1.

The computer 6 also develops the ignition advance angle as a function of the engine speed and load parameters and controls the instant of ignition of the mixture in a cylinder 13 of the engine by a spark plug 14.

The system described so far is only a particular example of a device for implementing the method according to the invention and it should be understood that any other type of injection and ignition system with digital or analog computer regulating the injection time and the ignition advance as a function of the engine speed and load, and possibly other parameters such as the temperature of air, water, oil, etc., may also be suitable. It should also be noted that the the process which will be described below is applicable both to a single-point injection system (a single injector for all the cylinders) and to a multi-point system (one injector per cylinder).

The process according to the invention will now be described briefly with reference also to FIG. 2. The computer 6 has in memory a map making it possible to calculate the injection time as a function of the speed and of the engine load. This mapping corresponds to a basic injection time TIo determining an operation of the engine in lean mixture. In the example in FIG. 2, the speed and the load of the engine, and therefore the basic injection time TIo, are assumed to be constant.

Periodically, the computer 6 causes an additional enrichment of the mixture by increasing the injection time by a value b during a number of engine revolutions a. The quantities a and b are calculated so that, at the operating point considered, the probe A is at the limit of tilting. After a number of engine revolutions c, it is examined whether the probe has switched from one state to another during this period c: if so, the basic injection time is reduced by a small amount and, if not, it is increased by an equally small amount, which leads to a nominal injection time TIn different from the basic time TIo. These modifications of the basic injection time have not been shown in FIG. 2 for the purpose of simplification, but this regulation process making it possible to operate in lean mixture will clearly result from the description of the flow diagram of FIG. 3. After a number of engine revolutions d, the computer 6 generates a new wealth pulse and the whole process described above takes place again.

As indicated previously, this temporary enrichment (a, b) tends to generate an increase in torque which, in accordance with the invention, is compensated by an equally temporary reduction in the angle of advance on ignition. In the case of a digital computer as described in FIG. 1, this comprises in memory an addressable advance map as a function of the pressure and the engine speed and generates a basic advance angle Avo. In response to an enrichment pulse (a, b), the advance angle Avo is reduced by an amount e during a number of revolutions f. Preferably, this niche of dimming or reduction of advance is out of phase lagged by a number of revolutions g relative to the enrichment pulse and is maintained for a number of engine revolutions identical to that of the temporary enrichment , i.e. a = f.

Of course, the values of a, b, c, d, e, f and g depend on the type of injection system and on the characteristics of the engine considered. Thus, for example, in the case of a multi-point injection system, the duration of the advance enrichment and blurring slots (a, f) can be fixed because the injectors deliver the fuel directly on the intake valves. On the other hand, the fuel transfer times between the injector and the intake valves being much longer in a single-point injection system, the duration of the slots enrichment and advance blurring should then preferably depend on the engine operating point, which can be achieved by memorization, of a specific mapping in the digital advance and injection computer 6.

The amplitude b of the enrichment slot is preferably inversely proportional to the nominal richness, that is to say to the nominal injection time, for the considered operating point of the engine, while the value e of the Advance shading is preferably proportional to the amplitude b of the enrichment window.

The phase shift g between the enrichment slot and the advance dimming slot can be either fixed, or a function of the engine load and speed. The same goes for the repetition period d of the temporary enrichment process and for the number of revolutions c at the end of which the condition of the probe is examined. If a is fixed, it is preferably also, but if a depends on the load and the engine speed, c can either depend on the same parameters, or be a predetermined number of turns counted from the end of the slot. enrichment.

Furthermore, the regulation by temporary enrichment and blurring described above may only be carried out in certain engine operating zones. This type of regulation will preferably be avoided in the field of high loads (rich mixture), low loads (deceleration zones) and low speeds (stability problems). This regulation should preferably also be prohibited during transient or cold operations because of deceleration cuts and acceleration and cold enrichments that can be expected and that the regulation described would disturb.

The flow diagram of FIG. 3 precisely illustrates an embodiment of the invention which eliminates regulation by temporary enrichment and blurring in advance in the above-mentioned operating zones. In this example applicable to a multi-point injection system, the values of a, c, d, f and g will be assumed to be fixed.

• - le premier test 21 a pour objet de déterminer si le régime du moteur est stationnaire ou non ; dans l'affirmative on passe au test 22 et dans la négative à un test 25 ;
• - le test 22 porte sur la valeur de la pression à l'admission du moteur ; si la pression est inférieure à une valeur Pmin (faibles charges) ou supérieure à une pression Pmax (fortes charges), on passe au test 25 ; dans le cas contraire on passe au test 23 ;
• - test 23 : on compare le régime à une valeur de seuil "Régime min" ; si le régime est inférieur à ce seuil (faibles régimes), on passe au test 25 et dans le cas contraire au test 24 ;
• - test 24 : il consiste à comparer la température d'eau de refroidissement du moteur fournie par le capteur 11 à un seuil T min ; si la température d'eau est inférieure à T min (fonctionnement à froid) on passe au test 25, et si elle est supérieure à Tmin on passe à l'étape 26 ;
• - étape 26 : on incrémente un compteur de tours moteur d'une unité, compteur dont le contenu CPT est supposé avoir été initialisé à zéro à l'étape 20 lors de la première passe du programme ;
• - l'étape suivante 27 est un test sur le contenu CPT du compteur de tours moteur ; si CPT est supérieur ou égal à N1 et inférieur à N1 + a, on passe à l'étape 28 qui assure un enrichissement temporaire. Autrement dit, on effectue un enrichissement pendant a tours moteur consécutifs décomptés Nl tours après la remise à zéro du compteur de tours CPT.
• - Etape 28 : l'enrichissement effectué à chacun de ces a tours est de la forme :
  TI = TIn + b = TIn (1 + x), où :
  • ^* TI est le temps d'injection engendré ;
  • ^* TIn est le temps d'injection nominal calculé en fonction des paramètres de fonctionnement du moteur (au minimum pression et régime) et qui serait normalement engendré en l'absence d'enrichissement temporaire ;
  • ^* x est un coefficient exprimé en % et qui peut être soit fixe, soit fonction du point de fonctionnement du moteur (charge, régime).
• - Après l'étape 28 ou en cas de réponse négative au test 27 on passe au test 29 qui concerne également le contenu CPT du compteur de tours ; si CPT est supérieur ou égal à N1 + get inférieur à N1 + g + f , on effectue à l'étape 30 un estompage ou réduction d'avance ; dans le cas contraire, on passe à un test 31.
• - Etape 30 : l'estompage ou réduction d'avance est de la forme :
  AV = AVn - e = AVn (1 - kx), où :
  • ^* AV : est l'angle d'avance à l'allumage engendré;
  • ^* AVn : est l'angle d'avance à l'allumage nominal calculé en fonction des paramètres de fonctionnement du moteur (au minimum pression et vitesse) et qui serait normalement engendré en l'absence d'enrichissement temporaire ;
  • ^* x est le coefficient (%) servant au calcul-de l'enrichissement à l'étape 28 ;
  • ^* k est une constante de valeur prédéterminée.
• - Après l'étape 30, on passe au test 31 qui porte toujours sur le contenu CPT du compteur de tours :
  • ^* si CPT = N1 + c , on passe à un test 32 pour déterminer si la sonde a changé d'état entre les tours moteur Nl et Nl + c ;
  • * si CPT ≠ N1 + c , on passe à un test 33.
• - Test 32 :
  • ^* si la réponse à ce test est négative, c'est que le moteur fonctionne toujours en mélange pauvre malgré l'enrichissement temporaire pratiqué aux tours N1 à N1 +a ; on commande alors un faible enrichissement par augmentation du temps d'injection nominal. A cet effet, on incrémente à l'étape 34 d'une unité le contenue d'un compteur (α étant initialisé à zéro lors de la première passe du programme) et on calcule à l'étape 35 le temps d'injection :
    
    où
  • . TIn est le temps d'injection nominal engendré ;
  • . TIo est le temps d'injection de base déterminé par le calculateur à partir de sa cartographie adressable en fonction de la pression et du régime.
• ^* Si la réponse au test 32 est positive, c'est au contraire que l'on est passé en mélange riche et l'on suscite un faible appauvrissement du dosage nominal en décrémentant α d'une unité à l'étape 36 et en calculant ensuite à l'étape 35 un nouveau temps d'injection nominal fonction de la nouvelle valeur de α.

After an initial phase 20 which marks the start of the program, four tests 21, 22, 23 and 24 are carried out successively to determine the operating conditions of the engine:

• - The purpose of the first test 21 is to determine whether the engine speed is stationary or not; in the affirmative we go to test 22 and in the negative to test 25;
• - test 22 relates to the value of the pressure at the intake of the engine; if the pressure is less than a Pmin value (low loads) or greater than a Pmax pressure (heavy loads), we go to test 25; otherwise we go to test 23;
• - test 23: the speed is compared to a threshold value "Minimum speed"; if the speed is below this threshold (low speeds), we go to test 25 and otherwise test 24;
• - test 24: it consists in comparing the engine cooling water temperature supplied by the sensor 11 to a threshold T min; if the water temperature is less than T min (cold operation) we go to test 25, and if it is greater than Tmin we go to step 26;
• step 26: an engine revolution counter is incremented by a unit, a counter whose CPT content is assumed to have been initialized to zero in step 20 during the first pass of the program;
• - The next step 27 is a test on the CPT content of the engine revolution counter; if CPT is greater than or equal to N1 and less than N1 + a, we go to step 28 which ensures temporary enrichment. In other words, an enrichment is carried out during a counted consecutive engine revolutions Nl revolutions after the reset of the rev counter CPT.
• - Step 28: the enrichment carried out at each of these turns is of the form:
  TI = TIn + b = TIn (1 + x), where:
  • ^* TI is the injection time generated;
  • ^* TIn is the nominal injection time calculated as a function of the engine operating parameters (at minimum pressure and speed) and which would normally be generated in the absence of temporary enrichment;
  • ^* x is a coefficient expressed in% and which can be either fixed or depending on the engine operating point (load, speed).
• - After step 28 or in the event of a negative response to test 27, we pass to test 29 which also relates to the CPT content of the revolution counter; if CPT is greater than or equal to N1 + get less than N1 + g + f, step fading or reduction is carried out in step 30; otherwise, we pass to a test 31.
• - Step 30: dimming or reduction in advance is of the form:
  AV = AVn - e = AVn (1 - kx), where:
  • ^* AV: is the ignition advance angle generated;
  • ^* AVn: is the nominal ignition advance angle calculated according to the engine operating parameters (at minimum pressure and speed) and which would normally be generated in the absence of temporary enrichment;
  • ^* x is the coefficient (%) used for the calculation of the enrichment in step 28;
  • ^* k is a constant of predetermined value.
• - After step 30, we pass to test 31 which always relates to the CPT content of the revolution counter:
  • ^* if CPT = N1 + c, we pass to a test 32 to determine if the probe has changed state between the engine revolutions Nl and Nl + c;
  • * if CPT ≠ N1 + c, we pass to a test 33.
• - Test 32:
  • ^* if the answer to this test is negative, it means that the engine is still operating in a lean mixture despite the temporary enrichment carried out on turns N1 to N1 + a; a small enrichment is then controlled by increasing the nominal injection time. To this end, the content of a counter is incremented in step 34 by a unit (α being initialized to zero during the first pass of the program) and the injection time is calculated in step 35:
    
    or
  • . TIn is the nominal injection time generated;
  • . TIo is the basic injection time determined by the computer from its addressable mapping as a function of pressure and speed.
• ^* If the response to test 32 is positive, it is on the contrary that we have switched to a rich mixture and we cause a slight depletion of the nominal dosage by decreasing α by one unit in step 36 and calculating then in step 35 a new nominal injection time depending on the new value of α.

• - dans la négative, on passe à la fin 37 du programme dans l'attente d'un nouveau déroulement de celui-ci au cycle moteur suivant ;
• - dans l'affirmative, on réinitialise le contenu CPT du compteur de tours moteur à zéro à l'étape 38, puis on passe également à la fin 37 du programme.

In step 33, it is examined whether the content CPT of the engine revolution counter is equal to a predetermined value d, which represents the period of repetition of the temporary advance enrichment and blurring process:

• - if not, we go to the end of the program 37 while waiting for a new course of it in the next engine cycle;
• - in the affirmative, the content CPT of the engine revolution counter is reset to zero in step 38, then we also go to the end 37 of the program.

In the event that the engine operating conditions do not allow the temporary advance enrichment and blurring process, the response to at least one of tests 21 to 24 is negative and we pass to test 25.

• - dans la négative, on passe directement à la fin- 37 du programme ;
• - dans l'affirmative, on réinitialise CPT à zéro à l'étape 39 puis on passe à la fin 37 du programme.

This test consists in determining if the CPT content of the engine rev counter is between N1 and N1 + c:

• - if not, we go directly to the end of the program;
• - in the affirmative, CPT is reset to zero in step 39 and then we go to the end 37 of the program.

It can be seen that with the method according to the invention, the state of the probe λ, used as a looping criterion for an injection system programmed to operate in lean mixture, is used so as to periodically make the mixture generated tend to the stoichiometric report. This results in changes to the programmed base injection time which provide self-adaptive control of the nominal wealth for each engine operating point programmed in the computer mapping, which overcomes variations in characteristics due to engine aging.

This regulation is made acceptable in its application on a motor vehicle by the fact that the excess torque normally generated by the periodic enrichment is considerably attenuated by the periodic blurring in advance carried out.

Claims (13)

l _o Method for controlling a fuel injection and spark ignition engine equipped with an electronic injection and ignition computer coupled to a sensor for detecting the oxygen content of the exhaust gases, according to which one develops , depending on the engine operating parameters, a nominal ignition advance angle that is temporarily reduced in certain engine operating conditions and a nominal injection time (TIn) corresponding to a low fuel dosage of the fuel mixture and a temporary enrichment of said mixture is periodically caused by increasing the injection time, characterized in that, in response to said temporary enrichment, said temporary reduction in the advance angle at nominal ignition and in that the amplitude of the decrease in the ignition advance angle (e = kxAVn) is proportional to said nominal advance angle (AVn) and depends on the value of the temporary increase in time d 'injection. Method according to claim 1, characterized in that the reduction in temporary advance is generated a predetermined number (g) of engine revolutions after the start (N1) of temporary enrichment. 3. Method according to any one of claims 1 and 2, characterized in that one causes the enrichment and the temporary advance decrease during a number of revolutions (a, f) of the engine depending on its load and its regimeo 4. Method according to any one of claims 1 and 2, characterized in that one causes the enrichment and the temporary advance decrease during a predetermined fixed number of revolutions (a, f) of the engine. 5. Method according to any one of claims 3 and 4, charac terrified in that one provokes the temporary enrichment and reduction of advance during an identical number (a = f) of engine revolutions. 6. Method according to any one of claims 1 to 5, characterized in that one generates the temporary enrichment and reduction of advance with a periodicity equal to a predetermined fixed number (d) of engine revolutions. 7. Method according to any one of claims 1 to 6, characterized in that, following a temporary enrichment phase, an increase in the nominal injection time (TIn) is caused if the probe (10) has not not changed state and a decrease in nominal injection time (TIn) if the probe has changed state 8. Method according to claim 7, characterized in that the said increase or the said reduction in the nominal injection time (TIn) is caused according to whether the probe has not or has changed state after a period of time equal to a predetermined number (c) of engine revolutions and beginning with the temporary enrichment phase. 9. Method according to claim 8, characterized in that said nominal injection time (Tln) is equal to the sum of a basic injection time (TIo) determined as a function of the load and of the engine speed and d '' a fraction (TIo. α) of said basic injection time as a function of a coefficient (α) which is incremented in the absence of a change in state of the probe at the end of each period ( ^c ) consecutive to a temporary enrichment and which is decremented otherwise. 10. Method according to any one of claims 7 to 9, characterized in that the value of the temporary increase (b = TIn.x) of the injection time (TI) is proportional to the nominal injection time (TIn ). 11. Method according to claim 10, characterized in that the value of the temporary increase (b = TInox) of the injection time (TI) is a function of the load and the engine speed. 12. Method according to any one of claims 1 to 11, characterized in that the enrichment and the temporary advance reduction in some at least of several predetermined engine operating zones are prohibited. 13. The method of claim 12, characterized in that said predetermined engine operating zones include transient deceleration and acceleration regimes, loads below a first predetermined threshold (P min), loads above a second threshold predetermined (P max), engine speeds below a third predetermined threshold (engine speed min) and operation at an engine coolant temperature below a fourth predetermined threshold (T engine) o

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