EP1597468B1 - Method for calculating fuel injector gain - Google Patents

Abstract

A method for real time determination of the gain of a fuel injector (2) of an engine (1), fed by a circuit having a fixed volume devoid of a permanent return upstream from a pump (8) connected to a common feed ramp (3) for the injectors (2) controlled like the pump (8) by at least one computer (5), wherein the local gain of at least one injector (2) is determined according to the variation of the mass of fuel injected into the engine (1) by the set of injectors (2) and resulting from the application on said injector (2) which is considered from a command for a duration of injection which is different from that applied on the injector or other injectors (2). The invention can be used to determine the flow characteristics of injectors of internal combustion engines.

Description

The invention relates to a method for real-time determination of the gain, or static flow, of at least one fuel injector, of the electrically controlled type, supplying an internal combustion engine, and mounted in a fuel supply circuit. of the engine, this circuit comprising at least one pump, fed from a fuel tank, and connected to a common fuel supply rail of each injector of the engine.

More specifically, each injector, the gain of which is to be determined by the method according to the invention, is mounted in a fixed-volume type supply circuit and without permanent return of fuel from the downstream upstream of said pump. which is controlled in flow, each injector and said pump being controlled by at least one computer, generally belonging to an electronic control unit and motor control, so that each cycle of the engine the pump delivers in the circuit a mass of fuel known from the computer, and that each injector delivers to said engine a fuel mass injected determined by an injector flow rate, expressing the injected mass according to an increasing function of the injection duration of said injector, controlled by said computer, and for which corresponds to each value of the injection duration, a local gain defined by a ratio of a variation of mass injected, consecutive there is a variation in injection duration, in said variation of injection duration (the local gain thus corresponding to the local slope at any point on the curve representing the flow characteristic of the injector).

Injectors of this type are generally qualified by their manufacturer by a theoretical injector flow rate characteristic, a substantially linear portion of which is determined by a theoretical injector gain as well as an offset at the theoretical origin, or theoretical offset, corresponding to a minimum order duration for a zero injected mass, obtained at the intersection of the extrapolation, to the origin of the durations of control, of the linear part of the characteristic with the abscissa axis, expressing the control times, on a plane diagram on which the injected masses are indicated along the y-axis, while a non-linear part of the characteristic , at the low values of the injection duration, can be stored in the computer in the form of mapping or theoretical table.

Electrically operated fuel injectors of this type can be fitted to diesel or spark ignition engines, and can be mounted in direct or indirect injection fuel systems.

It is known that the injectors used to perform the injection of a predetermined amount of fuel by an engine control computer have dispersions and evolutions in time of their characteristics, which has the consequence that the injection of a mass fuel data requires a different injection time control depending on the injector ordered and the age of the latter. In fact, the dispersions of the characteristics of the injectors result from the manufacturing tolerances of the physical components of the injectors, and therefore from their dimensional dispersions and physical characteristics, in particular the number and diameter (s) of the injection orifices of the injectors, their orientations, the elastic characteristic of their springs, etc ..., and the evolution over time of the flow characteristics of the injectors results in particular from the aging of the physical components of the injectors.

Moreover, the vast majority of direct and indirect injection control and control systems fitted to internal combustion engines of motor vehicles provide a closed loop, and continuously during the operation of the engine, control of the fuel. using a sensor detecting the oxygen content of the engine exhaust gas, and connected to the computer, so as to ensure the dosing of the air-fuel mixture with the high accuracy that is required for the use of trifunctional catalysts. This closed-loop richness control satisfactorily compensates for the dispersions of all the components involved in determining the air-fuel ratio, which would have an impact on the performance in terms of emission control in the engine exhaust if the above-mentioned dispersions were not compensated. The components involved are those that calculate the intake air flow to the engine and control the flow of fuel injected into the engine, so that these components include the injectors. But, unless specific strategies, closed loop wealth controls do not identify the characteristics of each of the components involved, either globally or individually. In other words, the metering of the air-fuel mixture consists in controlling a flow of intake air to the engine and a corresponding fuel flow, and the closed-loop richness checks make it possible to compensate for the ratio of the air flow rate to the flow rate. of fuel, without identifying the part of correction to be made to the air flow or the fuel flow, and, in addition, these richness checks do not allow to calculate an individualized correction for each cylinder, and therefore each injector.

The problem underlying the invention therefore consists, from the knowledge of a theoretical injector flow rate characteristic, of determining in real time the gain of at least one fuel injector of an engine, in order to learn the relationship between the mass of fuel injected and the control time of at least one injector considered, during learning phases that occur regularly, during operation of the engine, on points operating conditions that are not necessarily steady state, and during learning periods short enough that the driver of the vehicle does not feel any change in engine operation that would be due to these learning phases.

The object of the invention is therefore to allow a better knowledge of the flow characteristic of at least one injector of a running engine by a real-time determination of the gain of the injector in question, in order to have a follow-up. the evolution of the individual flow characteristic of each injector.

It is particularly interesting to learn the gain in real time for a better knowledge of the injector flow characteristic on engines equipped with direct injection systems operating in lean mixture, because, compared to injection systems indirectly, on the one hand the injectors can be solicited in areas with a short controlled injection time, where the flow law is highly dispersed (nonlinear zone of the injector flow characteristic), and on the other hand , the errors on the fuel mass injected are felt proportionally on the internal torque developed by the engine, which is a source of discomfort for the passengers of the vehicle.

Moreover, he is known by EP-0 488 362-A a method for determining a parameter (K _pni ) of at least one fuel injector mounted in a fuel supply circuit of an internal combustion engine of the type shown above, the method comprising at least one step of determining this parameter according to the variation (Q _di ) of the mass of fuel injected into the engine by the set of injectors resulting from the application on said at least one injector considered a duration command of injection different from that applied to the other injector or injectors.

This K _pni parameter does not represent the local gain, but is directly related to the inverse of the gain.

• au moins les étapes consistant, pendant le fonctionnement du moteur, à :
  1. a) identifier une condition de fonctionnement du moteur relativement stable, dans laquelle la durée d'injection moyenne appliquée (Tinj.moy) est égale à la valeur d'une durée d'injection (Tinj) pour laquelle on souhaite définir le gain local (G), et, tant que la condition de stabilité est observée,
  2. b) introduire, dans la commande de ladite pompe, une perturbation de nature à provoquer une chute de pression dans ladite rampe commune, et maintenir ladite perturbation pendant une première phase, à la fin de laquelle est obtenue une première variation de pression (DP1),
  3. c) déterminer une première masse de carburant (MI) injectée par l'ensemble des injecteurs du moteur et correspondant à ladite première variation de pression (DP1),
  4. d) calculer un gain local moyen (Gmoy) de l'ensemble des injecteurs comme étant égal au rapport de la première masse de carburant (M1) à la somme (ΣTinj)1 de toutes les durées d'injection (Tinj) appliquées à tous les injecteurs pendant ladite première phase,
  5. e) introduire dans la commande de ladite pompe la même perturbation et la maintenir pendant une deuxième phase, à la fin de laquelle est obtenue une seconde variation de pression (DP2) dans la rampe commune, en modifiant la commande de l'injecteur dont on veut déterminer le gain local d'une variation (δTinj) pour chacune des injections effectuées pendant ladite deuxième phase, et telle que la somme des variations de durée d'injection appliquées pendant la deuxième phase sur ledit injecteur est égale à ΣδTinj,
  6. f) déterminer une seconde masse de carburant (M2) injectée par l'ensemble des injecteurs du moteur et correspondant à ladite seconde variation de pression (DP2), et considérer que ladite seconde masse (M2) est égale à: $$\mathrm{M}\mathrm{2}\mathrm{=}\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}\mathrm{+}\left(\mathrm{\Sigma }\delta \mathrm{Tinj}\right)\mathrm{x\; G}$$
     
     
     où (ΣTinj)2 est la somme de toutes les durées d'injection (Tinj) appliquées pendant ladite deuxième phase, et G est le gain local dudit injecteur considéré, et
  7. g) calculer ledit gain local (G) dudit injecteur considéré par la formule: $$\mathrm{G}=\frac{\mathrm{M}\mathrm{2}-\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}}{\mathrm{\Sigma }\mathit{\delta }\mathrm{Tinj}}$$
     

In order to remedy the aforementioned drawbacks, the method according to the invention for determining in real time the gain of at least one electrically controlled fuel injector, supplying an internal combustion engine and mounted in a fuel supply circuit. fuel of the type presented above, is characterized in that it consists in determining the local gain of said at least one injector considered according to the variation of the mass of fuel injected into said engine by all the injectors resulting from the applying to said at least one injector considered an injection duration control different from that applied to the other injector or injectors, said method comprising:

• at least the steps of, during operation of the engine, at:
  1. a) identifying a relatively stable engine operating condition, in which the average injection time applied (Tinj.moy) is equal to the value of an injection duration (Tinj) for which it is desired define the local gain (G), and, as long as the stability condition is observed,
  2. b) introducing into the control of said pump, a disturbance likely to cause a pressure drop in said common rail, and maintain said disturbance during a first phase, at the end of which is obtained a first pressure variation (DP1) ,
  3. c) determining a first mass of fuel (MI) injected by all the injectors of the engine and corresponding to said first variation of pressure (DP1),
  4. d) calculating an average local gain (Gmoy) of the set of injectors as being equal to the ratio of the first mass of fuel (M1) to the sum (ΣTinj) 1 of all the injection durations (Tinj) applied to all the injectors during said first phase,
  5. e) introducing into the control of said pump the same disturbance and maintain it during a second phase, at the end of which is obtained a second variation of pressure (DP2) in the common rail, by changing the control of the injector which one wants to determine the local gain of a variation (δTinj) for each of the injections made during said second phase, and such that the sum of the injection time variations applied during the second phase on said injector is equal to ΣδTinj,
  6. f) determining a second mass of fuel (M2) injected by all the injectors of the engine and corresponding to said second variation of pressure (DP2), and considering that said second mass (M2) is equal to: $$\mathrm{M}\mathrm{2}\mathrm{=}\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}\mathrm{+}\left(\mathrm{\Sigma }\delta \mathrm{Tinj}\right)\mathrm{x\; G}$$
     
     
     where (ΣTinj) 2 is the sum of all injection times (Tinj) applied during said second phase, and G is the local gain of said injector considered, and
  7. g) calculating said local gain (G) of said injector considered by the formula: $$\mathrm{BOY\; WUT}=\frac{\mathrm{M}\mathrm{2}-\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}}{\mathrm{\Sigma }\mathit{\delta }\mathrm{Tinj}}$$
     

The implementation of this method provides the advantage of allowing, without having to make the injectors, and therefore their components, with very tight tolerances, and thus without increasing the cost of the injection system, to guarantee greater accuracy. of the mass of fuel injected into each cylinder of the engine, and, consequently, to ensure the accuracy of the air-fuel dosage and the torque developed by the engine. This results in a good control of emissions in the exhaust, and a better driving pleasure of the motor vehicle. It is thus possible to simply equip the engine with less efficient injectors, since the implementation of the method according to the invention makes it possible to compensate for the dispersions at the level of the physical components of the injectors.

In addition, this embodiment is preferred, as appropriate to the actual operating conditions of the engine, in which the fuel requirement of the engine is not strictly stable during substantially successive phases of operation of the engine.

Given that the gain of an injector flow rate depends, among other parameters, the air pressure in the intake manifold to the engine, which conditions the engine load, so the duration of applied injection (Tinj), and the fuel pressure can be variable, the method according to the invention is furthermore to repeat the steps a) to g) presented above for different points of operation of the engine and / or for a plurality of values different from the injection times corresponding to different parts of the injector flow characteristic, so as to determine the individual gain of said at least one injector considered.

The learning of the gain is thus achieved for different operating points of the engine.

When the method according to the invention is implemented on a fuel supply circuit of the engine which is a direct injection circuit, in which said common rail is fed by a high pressure pump, itself fed by a booster pump connected to said tank, it is advantageous that said disturbance in the control of the high pressure pump is to cause a stoppage of said high pressure pump. In this case, according to the teachings of the patent FR 2 803 875 of the Applicant, the determination of the said first and second masses of fuel injected by all the injectors of the engine in correspondence with said determination of said first and second pressure variations is advantageously provided by means of a model of behavior of the supply circuit. As proposed in the aforementioned French patent, the behavior model of the circuit may be a model that takes into account the flow rate or mass entering the common rail, imposed by the high pressure pump and determined by the calculator, the flow or mass leaving the common rail and injected into the engine, and also determined by the computer, as well as the rigidity of the circuit.

The method of the invention can thus consist in determining the individual gain of a single injector of the engine at a time, by applying to this single injector commands of injection times different from those applied to the other injectors of the engine, during said second phase of the process. In the latter case, it is advantageous that the method consists in determining, in succession, the individual gain of each of the injectors of the same engine in operation, in order to optimize the contribution of each injector to the supply of the corresponding cylinder of the engine.

• la figure 1 est un schéma d'un circuit d'alimentation en carburant d'un moteur à combustion interne de véhicule automobile par injection directe, pour la mise en oeuvre du procédé de l'invention,
• la figure 2 représente une caractéristique de débit d'un injecteur du circuit de la figure 1, et
• la figure 3 représente l'évolution de la pression dans la rampe commune du circuit de la figure 1, en fonction du temps, dans le cas de deux chutes de pression provoquées par l'arrêt de la pompe du circuit de la figure 1, et dont chacune est obtenue pour l'une respectivement de deux durées différentes d'injection, commandées pour un nombre d'injections, pouvant être le même ou différent, sur un même injecteur.

Other advantages and characteristics of the invention will emerge from the description given below, without limitation, of an exemplary embodiment described with reference to the accompanying drawings in which:

• the figure 1 is a diagram of a fuel supply circuit of an internal combustion engine of a motor vehicle by direct injection, for the implementation of the method of the invention,
• the figure 2 represents a flow characteristic of an injector of the circuit of the figure 1 , and
• the figure 3 represents the evolution of the pressure in the common rail of the circuit of the figure 1 , as a function of time, in the case of two pressure drops caused by the stopping of the circuit pump of the figure 1 , and each of which is obtained for one respectively of two different injection times, controlled for a number of injections, which may be the same or different, on the same injector.

On the figure 1 is schematically shown an internal combustion engine 1 for a motor vehicle. For example, the engine considered 1 is an in-line four-cylinder engine, four-stroke spark ignition and four-stroke engine fuel supplied by direct injection fuel, although the method of the invention is applicable to an injection engine indirect and / or diesel type.

Fuel injection is provided in each cylinder of the engine by one respectively of the four injectors 2.

These injectors 2 are supplied with fuel at high pressure by a common fuel rail 3, in which the fuel pressure is measured, at least at certain times of the engine cycle, by a pressure sensor 4 transmitting the pressure signal measured at a maximum speed. motor control unit 5.

The engine control unit 5 is an electronic unit controlling the injection of the fuel into the engine 1, by controlling the instants and injector injection timing times of the injectors 2 with the control electrical conductor beam 6, as well as the ignition in the cylinders of the engine 1, in the example of a spark ignition engine, and possibly other functions, such as the control of air intake to the engine, via a motorized throttle body, in particular according to the depressing of the accelerator pedal, and other safety functions, such as anti-slip, traction control and / or anti-lock braking of the vehicle wheels. This electronic unit 5 comprises, in a well known manner, at least one computer with calculation means, memory means and comparison means in particular, and in its injection control function, the control and control unit 5 the quantity of fuel injected by each of the injectors 2 into the corresponding cylinder of the engine 1, as a function of the engine times in each of the cylinders, of the parameters and operating conditions of the engine, in particular of its speed, its load or its temperature, and the fuel demand, depending in particular on the air intake flow rate in the engine 1 and the torque that the engine must develop, these parameters being entered at 7 in the engine control unit 5.

The common rail 3 is supplied with high pressure fuel by a high pressure pump 8, controlled in flow and connected to the ramp 3 by a pipe 9, in which the fuel flows in the direction of the arrow F1, and the the engine control unit 5 controls the high pressure pump 8 by the logic link 10 and thus determines the mass of fuel sent by the high pressure pump 8 in the ramp 3, at each cycle of the engine 1.

The high pressure pump 8 is rotated by the motor 1 via a mechanical connection schematized at 11, in a manner known per se. The high-pressure pump 8 is itself fed with fuel by a feeding circuit comprising, from upstream to downstream, a fuel tank 12, a booster pump or low-pressure pump 13, immersed in the tank 12 and fed through a filter (not shown), and a fuel pressure regulator 14, an output of which returns excess fuel in the tank 12, and another output is connected to the intake of the high pump pressure 8, at which is implanted a solenoid valve (not shown) controlled in all or nothing from the unit 5 by the logic link 10, so that the fuel flow of the high pressure pump 8 is known to the unit control 5, which can control the inlet solenoid valve so as to impose the high pressure pump 8 a zero flow.

The fuel supply circuit 1 of the engine by direct injection is thus a high pressure circuit, comprising the high pressure pump 8 and the downstream members thereof, namely the pipe 9 and the common rail 3, and this high circuit pressure, which is a fixed volume circuit and without permanent return of fuel or without fuel recirculation from the downstream to the upstream of the high pressure pump 8, is fed by a low pressure feeding circuit, upstream of the high pressure pump 8, and comprising the reservoir 12, the pump 13 and the regulator 14.

Thus, the mass of fuel present in the high-pressure circuit results only from filling actions by the high-pressure pump 8 and injection of fuel into the engine 1 by the injectors 2, these actions being controlled by the unit 5.

The flow characteristic of an injector 2, expressing the injected fuel mass M as a function of the injection control time Tinj, determined by the unit 5, corresponds to an increasing function whose curve, represented in FIG. figure 2 , has a slope equal to the local gain G of the injector, which is associated with any value of the injection duration and defined by the ratio between a mass variation injected following a small variation of injection duration , and this same variation in injection duration. This curve comprises a substantially linear part 15, in which the gain is constant, and a non-linear part 16 with small values of the injection duration (values less than the injection control duration corresponding to the lower limit of linearity TinfL ), and in which the local gain is rapidly variable.

The linear part 15 of the characteristic is determined not only by its slope or constant gain of the injector in this part, but also by an offset at the origin or offset Ot, at the intersection of the extrapolation or extension of the linear part 15 of the curve to the origin with the abscissa axis indicating the injection times Tinj.

It is known that the mass MinfL which is injected for an injection control duration equal to the lower limit TinfL of the linear part 15 is equal to the sum of the masses injected during the transitional phases corresponding to the phases of establishment and cutting respectively. instantaneous flow of an injector 2 caused respectively by the opening and closing of the injector resulting from displacements of a shutter respectively at the establishment and the breaking of an excitation current in a coil of the electromagnetically controlled injector, and respectively following the beginning and the end of a logical order of injection control developed in the unit 5 and transmitted by the latter to the injector 2 considered by the corresponding conductor of the beam 6.

In general, the injectors 2 of the same type are qualified by a theoretical injector flow rate characteristic determined, on the one hand, by a theoretical gain Gt and a theoretical offset Ot, to define the theoretical linear part 15 of the curve, and, on the other hand, by a theoretical nonlinear part 16, stored in the unit 5 in the form of tables or mappings indicating the injected mass M for an injection control duration Tinj between the lower linearity limit TinfL and the theoretical offset Ot and in the injection duration range corresponds to the nonlinear part 16.

Starting from this theoretical characteristic, the method of the invention aims to determine in real time (engine 1 in operation) the local gain G, as defined above, in order to have a better knowledge of the injected masses in function. controlled injection times, and taking into account the dispersions of characteristics from one injector to another, and / or variations in the characteristic of an injector as a function of time, particularly because of the aging of this injector. The method makes it possible to learn the individual characteristic of an injector 2 under consideration, then by changing the injector considered, to learn the individual characteristics of all injectors equipping the same engine.

To learn the local gain of an injector 2 considered individually, on an operating point of the engine 1, the method of the invention comprises two main phases. These phases lead to determining the variation ΔM of the mass M of fuel that is injected into the engine 1 by all the injectors 2, and which results from the application to the injector 2 whose gain G, an injection time control which is different from that applied to the other injectors 2 of the engine 1, with respect to the mass of fuel injected into the engine 1 by the set of injectors 2 on which the same control of injection duration, preferably a normal injection time, taking into account the operating point of the engine 1. This mass variation therefore corresponds to the contribution of the injector 2 whose injection control time has been modified relative to that of the other injectors 2. The variation ΔM of the mass of fuel injected is determined, according to the method of the invention, by taking into account a variation of a pressure drop in the supply circuit, in which the pressure drop results from a control of a disturbance of the operation of the pump 8, whereas the variation of the pressure drop results from the control of the different injection duration, applied on the injector 2, which we want to know the gain G, during the duration of the disturbance.

This disturbance of the operation of the pump 8 preferably consists of stopping the operation of this pump, whose flow is thus canceled, so that the pressure drop in the common rail 3 results from the continued application of commands of injection times to the injectors 2, the correspondence between the pressure drop in the ramp 3 and the mass of fuel injected into the engine 1 being ensured in the unit 5 by a module 18 of the behavior of the high pressure supply circuit , this module comprising a memory in which is stored, in the form of tables or maps, a law giving the variation of fuel mass in the high pressure circuit as a function of the pressure drop determined in this circuit during the stop of the pump 8, and can be constituted as described in the French patent FR 2 803 875 , which will be referred to for further details on this subject.

As a simplified example, to facilitate the understanding of the invention, in an ideal embodiment, assuming that the fuel requirement of the engine is stable during the learning phases, the method consists, from of a working point of the engine 1 in steady state and in a first learning phase, to command by the unit 5 the cancellation of the flow rate of the high pressure pump 8, and to maintain this command for a predetermined number of engine cycles, this number being sufficient to obtain a first pressure variation, determinable with sufficient accuracy, in the common rail 3, while a number N of injections is applied during this time to all the injectors 2 of the engine 1, with the same injection control time Tinj, for example normally established by the unit 5 according to the operating point of the engine 1.

On the figure 3 , which represents the evolution of the pressure P as a function of the time t in the common ramp 3, it can be seen that the pressure P drops from P0, from the stop time t0 of the pump 8, to P1 at the time t1 corresponding to the end of the flow blocking period of the pump 8, and therefore after the predetermined number of motor cycles corresponding to the number N of injections on all the injectors 2; the pressure P has therefore fallen by a value DP1 with respect to the initial pressure P0 in the ramp 3. This pressure variation DP1 = P1-P0 is measured by the sensor 4.

Thanks to the behavior model of the circuit, stored in the module 18 of the unit 5 and based for example on the mass entering the ramp 3 and imposed by the high pressure pump 8 being determined by the computer 17, and on the mass leaving the ramp 3 being injected into the engine 1, and also determined by the unit 5, as well as the rigidity of the high pressure circuit, it corresponds to the pressure difference DP1 thus determined, a first mass M1 of fuel injected into engine 1 by all injectors 2.

After removal of the disturbance of the operation of the high-pressure pump 8, and resumption of normal operation of the engine 1 on the stabilized operating point in question, a second phase of the process for learning the real gain of the injector 2 under consideration is initiated, and consists in reintroducing the same perturbation as above on the operation of the high pressure pump 8, namely to cut its flow rate during a time interval corresponding to the same predetermined number of motor cycles as in the previous phase, and by controlling the application of the same number N of injections on all the injectors 2 as during the previous phase, but with a modification of a known value of the injection times applied to the particular injector 2, which is to be determined the gain G, while we continue to apply to the other injectors 2 of the engine the same injection times that during the previous phase, it is that is to say for the same number N of injections occurring during the same predetermined number of motor cycles, the latter number and the known value of the modification of the injection times being chosen to be equally sufficient to obtain a second pressure variation, determinable with sufficient accuracy, in the common rail 3.

On the figure 3 this second learning phase corresponds, after stopping the pump 8 at the instant t0, and up to the instant t1 posterior, to the pressure variation DP2 = P0-P2, where P0 is the initial pressure in the ramp 3 and P2 the pressure in this same ramp 3 at time t1, in the case of a modified value of the injection times applied to the injector 2 in question, which is greater (for example by 10%) the value of the injection time applied to the other injectors 2. It follows that DP2 is greater than DP1, and that the module 18 of the unit 5, in which is recorded and stored the behavior model of the circuit of high pressure supply, corresponds to the pressure drop DP2 a second M2 mass fuel left this high pressure circuit, and therefore having been injected by the injectors 2 in the engine 1.

dans laquelle :

• G est le gain local de l'injecteur 2 auquel il a été appliqué la commande spécifique ou différente de durée d'injection,
• ΔM et ΔTinj sont les variations respectivement des masses injectées et des durées d'injection entre les deux phases,
• M1 et M2 sont les masses de carburant injectées, déterminées d'après le modèle de comportement du circuit haute pression respectivement lors de la première et de la deuxième des deux phases d'apprentissage décrites ci-dessus,
• N est le nombre d'injections appliquées à l'injecteur 2 considéré pendant chacune de ces deux phases d'apprentissage, et
• δTinj est la variation de la durée d'injection appliquée à l'injecteur 2 considéré, c'est-à-dire la différence T'inj - Tinj, où Tinj est la durée d'injection, de préférence normale, commandée pendant la première phase, et T'inj est la durée d'injection spécifique, supérieure dans cet exemple, commandée sur le seul injecteur 2 considéré pendant la deuxième phase précitée.

The substantially instantaneous gain G of the injector 2 considered is then given, in the simplified hypothetical case specified above, by the following formula: $$\mathrm{BOY\; WUT}\mathrm{=}\frac{\mathrm{.DELTA.M}}{\mathrm{\Delta Tinj}}\mathrm{=}\frac{\mathrm{M}\mathrm{2}\mathrm{-}\mathrm{M}\mathrm{1}}{\mathrm{N\delta Tinj}}$$

in which :

• G is the local gain of the injector 2 to which the specific or different control of injection duration has been applied,
• ΔM and ΔTinj are the variations of the injected masses and the injection times respectively between the two phases,
• M1 and M2 are the fuel masses injected, determined according to the model of behavior of the high pressure circuit respectively during the first and second of the two learning phases described above,
• N is the number of injections applied to the injector 2 considered during each of these two learning phases, and
• δTinj is the variation of the injection duration applied to the injector 2 considered, that is to say the difference T'inj-Tinj, where Tinj is the duration of injection, of normal preference, controlled during the first phase, and T'inj is the specific injection time, higher in this example, controlled on the single injector 2 considered during the second phase mentioned above.

It should be noted that the two phases can be reversed, the injected mass M2 with specific injection duration being determined before the mass M1 with normal or reference injection duration, or the non-adjacent succession of the two phases can be repeated. a certain number of times by alternating the order of the phases, but in order to obtain a good learning of the individual gain G of the injector 2 under consideration, this learning procedure must be renewed for a sufficient number of values of the duration of the control, and for different stabilized operating points of the engine.

Now considering the more real case, in which the fuel requirement of the engine is not rigorously stable during the two successive phases of learning, or, more precisely, in which the integrals of the engine fuel requirement profile. during the duration of the two phases, are not identical, it is understood that the difference M2-M1 of the numerator of the formula given above is due not only to the application of the command of a specific injection duration on the injector 2 whose gain is to be determined, but also to the fact that the engine 1 has not presented the same demand for fuel during the two phases.

The method according to the invention remains substantially as described above, except that the number of injections N applied during the first and second phases is not necessarily identical, each phase being interrupted when the corresponding pressure drop has reaches a value sufficient to be measurable with a sufficient degree of accuracy. The processing of the measurements consists in finding out by calculation what the mass M1 would have been if, during the first phase, the integral of the fuel requirement of the engine had been the same one as during the second phase of learning.

In this case, we first identify an operating condition of the motor 1 which is relatively stable, i.e., for example, a time interval during which the difference between the values maximum and minimum of the injection duration (Tinj.max - Tinj.min) remains below a threshold, and the average injection time Tinj.moy applied in this condition is equal to the value of the injection duration Tinj for which the local gain G of the injector 2 considered must be defined. Then, as long as this stability condition is observed, the procedure is as follows: the first phase is carried out as in the ideal example described above, namely that a pump 8 is introduced into the pump. disturbance, namely the shutdown of the pump 8, which causes a pressure drop in the common rail 3, and this disturbance is maintained during this first phase, at the end of which a first change in pressure DP1 is obtained in the ramp 3 (thus controlling the same injection time Tinj, not necessarily constant, applied to all the injectors 2 for all injections made during this first phase). Then, the first mass of fuel M1 injected by all the injectors 2 of the engine 1, and corresponding to the first pressure variation DP1, is determined by applying the behavior model of the circuit. If (ΣTinj) 1 represents the sum of all the injection durations applied to all the injectors 2 during the first phase, an average local gain Gmoy is calculated, such that $$\mathrm{Gmoy}\mathrm{=}\frac{\mathrm{M}\mathrm{1}}{\left(\mathrm{\Sigma Tinj}\right)\mathrm{1}}$$

Then, during the second phase, is introduced again into the control of the pump 8 the same disturbance, namely the cutting of its flow, and this disturbance is maintained during this second phase, which is not necessarily of the same duration that the first, and at the end of which one obtains the second pressure variation DP2 in the common ramp 3, by modifying the control of the only injector 2 whose local gain is to be determined by an injection duration variation δTinj, for each of the injections made during this second learning phase.

It should be noted that the variation of injection duration δTinj is not necessarily constant. In general, δTinj is not constant, since, typically, this variation can be relative, and fixed at some percents, for example 10%, of the injection time Tinj, which is precisely strictly constant during the second learning phase.

The second phase takes place by applying injection times whose sum is equal to (ΣTinj) 2 increased da ΣδTinj, where δTinj is the sum of all the injection duration variations applied to the injector 2 considered during the injection. second phase, and (ΣTinj) 2 is the sum of all injection times Tinj applied to all injectors 2 during this same second phase.

Using the circuit behavior model, the second mass of fuel M2 injected by all the injectors 2 of the engine 1, during the second phase, which corresponds to the second pressure variation DP2, is determined.

The sum (ΣTinj) 2 has a value close to the sum (ΣTinj) 1, but differs from it, however, since the operating conditions of the motor have probably changed during the course of the two phases and between them.

de sorte que le gain G de l'injecteur considéré, sur lequel a été appliquée la variation de durée d'injection (par exemple l'augmentation) δTinj, se calcule par la formule : $$\mathrm{G}=\frac{\mathrm{M}\mathrm{2}-\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}}{\mathrm{\Sigma }\mathrm{\delta Tinj}}$$

The second injected mass M2, determined as explained above, from the behavior model of the circuit and the second pressure drop DP2, can also be considered as equal to: $$\mathrm{M}\mathrm{2}\mathrm{=}\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}\mathrm{+}\left(\mathrm{\Sigma }\mathrm{\delta }\mathrm{Tinj}\right)\mathrm{x\; G}$$

so that the gain G of the considered injector, on which the injection duration variation (for example the increase) δTinj has been applied, is calculated by the formula: $$\mathrm{BOY\; WUT}=\frac{\mathrm{M}\mathrm{2}-\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}}{\mathrm{\Sigma }\mathrm{\delta Tinj}}$$

It can be seen that, compared to the formula given for the simplified hypothetical case described above, the first injected mass M1 has been replaced by Gmoy x (ΣTinj) 2, which represents what would have been the first injected mass M1, if the full engine fuel requirement profile during the first training phase was identical to the full engine fuel requirement profile during the second learning phase.

The different values of M determined and δTinj, ΣδTinj, (ΣTinj) 1, (ΣTinj) 2 and Gmoy, commanded or calculated are stored and updated cyclically to follow in real time the G gain variations.

This learning method is in fact applicable on any point of the injector flow characteristic, ie not only on any point of its linear part 15 (see figure 2 ) but also at any point of its non-linear part 16, for small values of the injection control time, when the engine 1 is operating at idle or in areas of low load operation.

After determining the individual gain of a given injector 2 of the engine 1, by applying to this single injector 2, as described above, orders of injection times T'inj different from those Tinj applied to the other injectors of the engine, during one of the two phases during which the flow rate of the high pressure pump 8 is kept zero to cause pressure drops in the ramp 3, the individual gain of each of the other injectors 2 of the same motor 1 can be successively determined 1 .

It is thus possible to control the injection taking into account an individual gain specific to each of the injectors 2.

Since the parameters determining the characteristic depend on the pressure, in particular the fuel pressure, the repetition of the learning process for different operating points makes it possible to ensure a pressure sweep, for a better determination of the local individual gain of its injectors. 2, and a better knowledge of the individual flow characteristics of the injectors 2 is thus obtained, by adopting the gain determined in real time and keeping the theoretical offset ΔT, which can also advantageously be replaced by a real offset, of which learning is achieved by an appropriate strategy.

Claims (7)

1. Method for determining in real time the gain of at least one electrically controlled fuel injector (2) supplying an internal combustion engine (1) and mounted in a fuel supply circuit of the said engine (1), the said circuit comprising at least one pump (8) supplied from a fuel reservoir (12) and connected to a common rail (3) for supplying each injector (2) of the engine (1) with fuel, the said circuit being of the type having a fixed volume and without permanent return of fuel from the downstream side to the upstream side of the said pump (8), which is output-piloted, each injector (2) and the said pump (8) being controlled by at least one computer (5) so that with each cycle of the engine the said pump (8) delivers into the said circuit a mass of fuel known by the computer (5), and that each injector (2) delivers to the said engine (1) a mass of injected fuel (M) determined by an injector output characteristic expressing the injected mass (M) according to an increasing function of the duration of injection (Tinj) of the said injector (2), which duration is controlled by the said computer (5) and for which a local gain (G) corresponds to each value of the duration of injection (Tinj), this local gain being defined by a ratio of an injected mass variation, consecutive to an injection duration variation, to the said injection duration variation, characterised in that it consists of determining the local gain (G) of the said at least one injector (2) concerned according to the variation (ΔM) of the mass of fuel (M) injected into the said engine (1) by the group of injectors (2) resulting from the application to the said at least one injector (2) concerned of an injection duration command (T'inj) which is different from that (Tinj) applied to the other injector or injectors (2), the said method comprising:

   at least the steps consisting, during operation of the engine (1), of:

   a) identifying a relatively stable operational condition of the engine (1) in which the average injection duration applied (Tinj.moy) is equal to the value of an injection duration (Tinj) for which it is desired to define the local gain (G), and, while the stability condition is observed,

   b) introducing, into the control of the said pump (8), a disturbance such as to cause a drop in pressure in the said common rail (3), and maintaining the said disturbance during a first phase, at the end of which a first pressure variation (DP1) is obtained,

   c) determining a first mass of fuel (MI) injected by the group of injectors (2) of the engine (1) and corresponding to the said first pressure variation (DP1),

   d) calculating an average local gain (Gmoy) of the group of injectors (2) as being equal to the ratio of the first fuel mass (M1) to the sum (ΣTinj)1 of all the injection durations (Tinj) applied to all the injectors (2) during the said first phase,

   e) introducing the same disturbance into the control of the said pump (8) and maintaining it during a second phase, at the end of which a second pressure variation (DP2) in the common rail (3) is obtained, modifying the control of the injector (2) of which it is desired to determine the local gain of a variation (δTinj) for each of the injections effected during the said second phase, and such that the sum of the injection duration variations applied during the second phase on the said injector (2) is equal to ΣδTinj,

   f) determining a second fuel mass (M2) injected by the group of injectors (2) of the engine (1) and corresponding to the said second pressure variation (DP2), and considering that the said second mass (M2) is equal to: $$\mathrm{M}\mathrm{2}\mathrm{=}\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}\mathrm{+}\left(\mathrm{\Sigma }\mathrm{\delta }\mathrm{Tinj}\right)\mathrm{x\; G}$$

   

   
   where (ΣTinj)2 is the sum of all the injection durations (Tinj) applied during the said second phase, and G is the local gain of the said injector (2) concerned, and

   g) calculating the said local gain (G) of the said injector (2) concerned by means of the formula: $$\mathrm{G}=\frac{\mathrm{M}\mathrm{2}-\mathrm{Gmoy\; x}\left(\mathrm{\Sigma Tinj}\right)\mathrm{2}}{\mathrm{\Sigma }\mathrm{\delta Tinj}}$$

   
2. Method as claimed in claim 1, characterised in that it also consists of repeating steps a) to g) for different points of operation of the engine (1) and/or for a plurality of different values of the injection durations (Tinj) corresponding to different parts (15, 16) of the injector output characteristic so as to determine the individual gain of the said at least one injector (2).
3. Method as claimed in any one of claims 1 and 2, implemented on a fuel supply circuit of the engine (1) which is a direct injection circuit in which the said common rail (3) is supplied by a high-pressure pump (8) which is itself supplied by a booster pump (13) connected to the said reservoir (12), characterised in that the said disturbance in the control of the high pressure pump (8) consists of causing a stoppage of the said high pressure pump (8).
4. Method as claimed in claim 3, characterised in that the determination of the said first (M1) and second (M2) masses of fuel injected by the group of injectors (2) of the engine (1) in correspondence with the said determination of the said first (DP1) and second (DP2) pressure variations is ensured by means of a behaviour model (18) of the supply circuit.
5. Method as claimed in claim 4, characterised in that the said behaviour model of the circuit is a model (18) which takes into account the output entering into the common rail (3) imposed by the high pressure pump (8) and determined by the computer (5), the output leaving the common rail (3) and injected into the engine (1), and also determined by the computer (5), as well as the rigidity of the circuit.
6. Method as claimed in any one of claims 1 to 5, characterised in that it consists of determining the individual gain (G) of a single injector (2) of the engine (1) at the same time, by applying to this single injector (2) injection duration commands which are different from those (TinJ) applied to the other injectors (2) of the engine (1) during the said second phase.
7. Method as claimed in claim 6, characterised in that it consists of determining in succession the individual gain (G) of each of the injectors (2) of a single engine (1) in operation.

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