WO2004079176A1

WO2004079176A1 - Method for calculating fuel injector gain

Info

Publication number: WO2004079176A1
Application number: PCT/FR2004/000349
Authority: WO
Inventors: Henri Mazet
Original assignee: Magneti Marelli Motopropulsion France Sas
Priority date: 2003-02-28
Filing date: 2004-02-16
Publication date: 2004-09-16
Also published as: FR2851788B1; DE602004029865D1; FR2851788A1; EP1597468B1; EP1597468A1

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

"METHOD FOR DETERMINING THE GAIN OF A FUEL INJECTOR"

The invention relates to a method for determining in real time the gain, or static flow rate, 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, supplied from a fuel tank, and connected to a common fuel supply rail of each injector of the engine.

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

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

Electrically controlled fuel injectors of this type can be fitted to diesel or spark-ignition engines, and be fitted in direct or indirect injection fuel circuits. We know that the injectors used to inject a predetermined amount of fuel by an engine control computer exhibit dispersions and changes over time in their characteristics, which means that the injection of a mass fuel data requires a different injection time command 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 of 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 development over time of the flow characteristics of the injectors results in particular from the aging of the physical components of the injectors.

In addition, the vast majority of command and control systems for injection, direct or indirect, fitted to internal combustion engines of motor vehicles ensures richness control in closed loop, and continuously during engine operation, at using a probe detecting the oxygen content of the engine exhaust gases, and connected to the computer, so as to guarantee the metering of the air-fuel mixture with the high precision which is required for the use of trifunctional catalysts. This closed-loop richness control makes it possible to compensate satisfactorily for the dispersions of all the components which are involved in determining the air-fuel dosage, and which would have an impact on the performance in terms of controlling exhaust emissions from the engine, if the aforementioned dispersions were not compensated. The components concerned are those which make it possible to calculate the flow rate of intake air to the engine and to control the flow rate of fuel injected into the engine, so that these components include the injectors. However, unless there are specific strategies, the closed-loop richness controls do not allow the characteristics of each of the components concerned to be identified, whether globally or individually. In other words, the metering of the air-fuel mixture consists in controlling a flow rate of intake air to the engine and a corresponding fuel flow rate, and the richness controls in closed loop make it possible to compensate for the ratio of air flow rate to flow rate. of fuel, without identifying the part of correction to be made to the air flow or to the fuel flow, and, in addition, these richness checks do not make it possible to calculate an individual correction for each cylinder, and therefore each injector.

The problem underlying the invention therefore consists, from the knowledge of a theoretical injector flow 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 duration of control of at least one considered injector, during learning phases that take place regularly, during engine operation, on points of operation which are not necessarily in steady state, and for sufficiently short learning periods so that the driver of the vehicle does not feel any modification of the operation of the engine which 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 an engine in operation by a determination in real time of the gain of the injector considered, 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 understanding of the injector flow characteristic on engines equipped with direct injection systems operating in lean mixture, because, compared to injection systems indirect, on the one hand the injectors can be used in areas with a short duration of controlled injection, where the flow law is highly dispersed (non-linear area of the injector flow characteristic), and, on the other hand , errors on the mass of fuel injected are felt proportionally on the internal torque developed by the engine, which is a source of discomfort for the passengers of the vehicle.

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 supply circuit in fuel of the type presented above, is characterized in that it comprises at least one step consisting in determining the local gain of said at least one injector considered from the variation in the mass of fuel injected into said engine by the assembly injectors resulting from the application to said at least one considered injector of an injection duration control different from that applied to the other injector (s).

Advantageously also, this method comprises at least one step consisting in determining said variation in the mass of fuel injected into said engine by taking into account a variation in a pressure drop in said supply circuit, which pressure drop results from a command for a disturbance in the operation of said pump, said variation in the pressure drop resulting from said control of a different injection duration during said disturbance.

The implementation of this method provides the advantage of allowing, without having to produce the injectors, and therefore their components, with very tight tolerances, and thus without increasing the cost of the injection system, to guarantee greater accuracy. the mass of fuel injected into each cylinder of the engine, and, consequently, to guarantee the accuracy of the air-fuel dosage and the torque developed by the engine. This results in good control of emissions in the exhaust gases, and better driving pleasure of the motor vehicle. It is thus possible to be satisfied with equipping 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 a preferred embodiment, since it is suitable for real engine operating conditions, in which the engine's fuel requirement is not strictly stable during substantially successive engine operating phases, the method of the invention comprises at minus the steps consisting, during engine operation, in: a) identifying a relatively stable engine operating condition, in which the average applied injection time Tinj.moy is equal to the value of an injection duration Tinj for which it is desired to define the local gain G, and, as long as the condition of stability is observed, b) introduce, in the control of said pump, a disturbance such as to cause a drop in pressure in said common rail, and maintain 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 M1 injected by all of the engine injectors and corresponding to said first pressure variation DP1, d) calculating an average local gain Gmoy of all the injectors as being equal to the ratio of the first mass of fuel 1 to the sum ( ∑Tinjl) of all the injection times Tinj applied to all the injectors during said first phase, e) introduce the same disturbance into the control of said pump and maintain it during a second phase, at the end of which a second is obtained pressure variation DP2 in the common rail, by modifying the control of the injector whose local gain is to be determined by a variation δTinj for each of the injections carried out during said second phase, and such that the sum of the variations in injection duration applied during the second phase on said injector is equal to ∑δTinj, f) determining a second mass of fuel M2 injected by all of the injectors of the engine and corresponding to said second pressure variation DP2, and consider that said second mass M2 is equal to:

M2 = Gmoy x (∑Tinj) 2 + (∑δTinj) x G where (∑Tinj) 2 is the sum of all the injection times Tinj applied during said second phase, and G is the local gain of said injector considered, and g) calculate said local gain G of said injector considered by the formula:

G = M2 - Gmov x (7Tini) 2. ΣδTinj

Taking into account that the gain of an injector flow characteristic depends, among other parameters, on the air pressure in the engine intake manifold, which conditions the engine load, therefore the duration of applied injection (Tinj), and the fuel pressure which can be variable, the method according to the invention also consists in repeating steps a) to g) presented above for different engine operating points and / or for a plurality of different values of the injection durations corresponding to different parts of the injector flow characteristic, so as to determine the individual gain of said at least one injector considered. Learning the gain is thus carried out for different engine operating points.

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 supplied by a high pressure pump, itself supplied by a booster pump connected to said tank, it is advantageous that said disturbance in the control of the high pressure pump consists in causing a shutdown of said high pressure pump. In this case, in accordance with the teachings of patent FR 2 803 875 of the Applicant, the determination of said first and second mass of fuel injected by all of the engine injectors in correspondence with said determination of said first and second pressure variations is advantageously ensured by means of a behavior model of the supply circuit. As proposed in the aforementioned French patent, the behavior model of the circuit can be a model which takes into account the flow or mass entering the common rail, imposed by the high pressure pump and determined by the computer, 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 engine injector at a time, by applying to this single injector commands of injection durations different from those applied to the other engine injectors, 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.

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

- 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, - Figure 2 shows a characteristic of flow rate of an injector of the circuit of FIG. 1, and

FIG. 3 represents the evolution of the pressure in the common rail of the circuit of FIG. 1, as a function of time, in the case of two pressure drops caused by the stopping of the pump of the circuit of FIG. 1, and each of which is obtained for one of two different injection durations respectively, controlled for a number of injections, which may be the same or different, on the same injector. In Figure 1 is shown schematically an internal combustion engine 1 for a motor vehicle. For example, the engine considered 1 is an in-line four-cylinder engine, with spark ignition and with a four-stroke engine cycle, supplied with fuel by so-called direct injection, although the method of the invention is applicable to an injection engine. indirect and / or diesel type.

Fuel is injected into each cylinder of the engine 1 by one of the four injectors 2 respectively.

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 to a engine control unit 5.

The engine control unit 5 is an electronic unit controlling the injection of fuel into the engine 1, by controlling by the bundle of electrical control conductors 6 the instants and durations of injection control injectors 2, as well as the ignition in the cylinders of engine 1, in the example considered of a spark ignition engine, and possibly other functions, such as the control of air intake to the engine, by means of a motorized throttle body, depending in particular on the depressing of the accelerator pedal, and other safety functions, such as anti-skid, traction control and / or anti-lock 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 command 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 its speed, its load or its temperature, and fuel demand, depending in particular on the air intake flow rate in engine 1 and the torque to be developed by the engine, 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 rail 3 by a line 9, in which the fuel flows in the direction of the arrow F1, and l the engine control unit 5 controls the high pressure pump 8 via the logic link 10 and thus determines the mass of fuel sent by the high pressure pump 8 into the rail 3, at each cycle of the engine 1.

The high pressure pump 8 is rotated by the motor 1 via a mechanical connection shown diagrammatically at 11, in a manner known per se. The high pressure pump 8 is itself supplied with fuel by a booster circuit comprising, from upstream to downstream, a fuel tank 12, a booster pump or low pressure pump 13, immersed in the tank 12 and supplied through a filter (not shown), and a fuel pressure regulator 14, one outlet of which allows excess fuel to be returned to the tank 12, and another outlet of which is connected to the inlet of the high pump pressure 8, at the level of which is installed a solenoid valve (not shown) controlled in all or nothing from the unit 5 by the logic link 10, so that the fuel flow rate of the high pressure pump 8 is known to the unit 5 control, which can control this input solenoid valve so as to impose on the high pressure pump 8 a zero flow.

The fuel supply circuit for the engine 1 by direct injection is thus a high pressure circuit, comprising the high pressure pump 8 and the members downstream of the latter, namely the line 9 and the common rail 3, and this high circuit pressure, which is a fixed volume circuit and without permanent fuel return or without fuel recirculation from downstream to upstream of the high pressure pump 8, is supplied by a low pressure booster 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 fuel injection 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 mass of fuel injected ivl as a function of the injection control time Tinj, determined by unit 5, corresponds to an increasing function whose curve, represented in FIG. 2 , has a slope equal to the local gain G of the injector, which is associated with any value of the duration of injection and defined by the ratio between a variation of mass injected following a small variation of duration of injection , 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 at low 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 constant slope or 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 towards the origin with the abscissa axis indicating the injection times Tinj. We know 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 transient phases corresponding to the establishment and cut-off phases respectively. of the instantaneous flow of an injector 2 caused respectively by the opening and the closing of the injector resulting from the displacements of a shutter respectively to the establishment and the cut of an excitation current in a coil of the injector with electromagnetic control, and respectively following the start and the end of a logic order of injection control developed in unit 5 and transmitted by the latter to injector 2 considered by the corresponding conductor of bundle 6.

In general, the injectors 2 of the same type are qualified by a theoretical characteristic of injector flow, 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 non-linear part 16, stored in unit 5 in the form of tables or maps indicating the injected mass M for an injection control duration Tinj comprised between the lower limit of linearity TinfL and the theoretical offset Of and in the injection duration range corresponds to the non-linear part 16.

Based on 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 masses injected as a function controlled injection durations, 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, in particular due to the aging of this injector. The method makes it possible to learn the individual characteristic of an injector 2 considered, then by changing the injector considered, to learn the individual characteristics of all the 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 which is injected into the engine 1 by all of the injectors 2, and which results from the application to the injector 2 for which the gain G, d is to be known. an injection duration 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 all of the injectors 2 on which the same control is applied injection duration, preferably a normal injection duration, taking into account the operating point considered of the engine 1. This variation in mass therefore corresponds to the contribution of the injector 2, the injection control duration of which 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, 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 in the operation of the pump 8, while the variation of the pressure drop results from the control of the different injection duration, applied on injector 2, whose gain G is to be known, for the duration of the disturbance.

This disturbance in the operation of the pump 8 preferably consists in stopping the operation of this pump, the flow of which is thus canceled, so that the pressure drop in the common rail 3 results from the continued application of commands injection injection times 2, the correspondence between the pressure drop in the rail 3 and the mass of fuel injected into the engine 1 being ensured in the unit 5 by a module 18 of 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 in fuel mass in the high pressure circuit as a function of the pressure drop determined in this circuit during the stopping of the pump 8, and which can be constituted as described in French patent FR 2 803 875, to which reference will be made for further details on this subject.

By way of a simplified example, in order to facilitate understanding of the invention, in an ideal implementation mode, assuming that the fuel requirement of the engine is stable during the learning phases, the method consists in starting from of an operating point of the engine 1 in steady state and in a first learning phase, to be controlled by the unit 5 to cancel the flow 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 precision, 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 duration Tinj, for example normally established by the unit 5 as a function of the operating point of the engine 1. In FIG. 3, which represents the evolution of the pressure P as a function of time t in the common rail 3, it can be seen that the pressure P drops from PO, from the instant tO when the pump 8 stops, up to P1 at time t1 corresponding to the end of the blocking period of the flow rate of the pump 8, and therefore after the predetermined number of engine cycles corresponding to the number N of injections on all the injectors 2; the pressure P has therefore dropped by a value DP1 relative to the initial pressure PO in the ramp 3. This pressure variation DP1 = P1-P0 is measured by the sensor 4.

Thanks to the circuit behavior model, stored in module 18 of unit 5 and based for example on the mass entering ramp 3 and imposed by high pressure pump 8 being determined by computer 17, and on the mass leaving the ramp 3 being injected into the motor 1, and also determined by the unit 5, as well as on 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 in the operation of the high pressure pump 8, and resumption of normal operation of the engine 1 at the stabilized operating point considered, a second phase of the process for learning the real gain of the injector 2 considered is initiated, and consists in reintroducing the same disturbance as previously on the operation of the high pressure pump 8, namely to cut its flow during a time interval corresponding to the same predetermined number of engine cycles as in the previous phase, and by controlling l 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 durations applied to the particular injector 2, which one seeks to determine the gain G, while we continue to apply to the other injectors 2 of the engine the same injection durations as during the previous phase, this is i.e. for the same number N of injections occurring during the same predetermined number of engine cycles, this latter number as well as the known value of the modification of the injection times being chosen to be also sufficient to obtain a second pressure variation, determinable with sufficient precision, in the common rail 3.

In FIG. 3, this second learning phase corresponds, after the pump 8 has stopped at time t0, and until time t1 later, to the pressure variation DP2 = PO - P2, where PO is the initial pressure in ramp 3 and P2 the pressure in this same ramp 3 at time t1, in the case of a modified value of the injection durations applied to the injector 2 considered, which is greater (for example 10%) to the value of the injection duration applied to the other injectors 2. As a result, DP2 is greater than DP1, and that module 18 of unit 5, in which the behavior model is recorded and memorized of the high pressure supply circuit, corresponds to the pressure drop DP2 a second mass M2 of fuel having left this high pressure circuit, and therefore having been injected by the injectors 2 into the engine 1. The practically instantaneous gain G of l injector 2 considered is then given, in the case hy simplified prosthetics specified above, by the following formula:

ΔM M2 - M1

G = ΔTinj NδTinj in which:

G is the local gain of the injector 2 to which the specific or different injection duration control has been applied, ΔM and ΔTinj are the variations respectively of the masses injected and of the injection durations between the two phases,

M1 and M2 are the masses of fuel injected, determined according to the behavior model of the high pressure circuit respectively during the first and the 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 time applied to the injector 2 considered, that is to say the difference T'inj - Tinj, where Tinj is the injection time, from normal preference, ordered during the first phase, and T'inj is the specific injection duration, greater in this example, ordered on the only injector 2 considered during the aforementioned second phase.

It should be noted that the two phases can be reversed, the mass injected M2 with specific injection duration being determined before the mass 1V11 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 achieve good learning of the individual gain G of the injector 2 considered, this learning procedure must be repeated for a sufficient number of values of the control time, and for different stabilized engine operating points.

Now considering the more real case, in which the engine fuel requirement is not strictly stable during the two successive learning phases, 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 did not present the same fuel demand during the two phases.

The process 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 reached a sufficient value to be measurable with a sufficient degree of precision. The processing of the measurements consists in finding 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 as during the second learning phase. In this case, we start by identifying an operating condition of the motor 1 which is relatively stable, that is to say, 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 duration 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 condition of stability is observed, the procedure is as follows: the first phase takes place as in the ideal example described above, namely that one introduces, in the control of the pump 8, a disturbance, namely the cut off in the flow rate 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 pressure variation DP1 is obtained in the ramp 3 (therefore ordering the same injection duration Tinj, not necessarily constant, applied to all the injectors 2 for all the injections carried out during this first phase). Then, the first mass of fuel M1 injected by all of 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 (∑Tinj) 1 represents the sum of all the injection durations applied to all the injectors 2 during the first phase, we calculate an average local gain Gmoy, such that Gmoy = M1 (∑Tinj) 1

Then, during the second phase, the same disturbance, namely the cutoff of its flow rate, is again introduced into the control of the pump 8, and this disturbance is maintained during this second phase, which is not necessarily of the same duration as the first, and at the end of which the second pressure variation DP2 is obtained in the common rail 3, by modifying the control of the single injector 2 for which it is desired to determine the local gain of a variation in injection duration δTinj, for each of the injections carried out during this second learning phase. It should be noted that the variation in injection duration δTinj is not necessarily constant. In general, δTinj is not constant, because, typically, this variation can be relative, and fixed at a few percent, for example 10%, of the duration of injection Tinj, which is precisely not strictly constant during the second learning phase.

The second phase takes place by therefore applying injection durations the sum of which is equal to (∑Tinj) 2 increased by ∑δTinj, where δTinj is the sum of all the variations in injection duration applied to the injector 2 considered during the second phase, and (∑Tinj) 2 is the sum of all the injection times Tinj applied to all the injectors 2 during this same second phase. Using the circuit behavior model, the second mass of fuel M2 injected by all of the injectors 2 of the engine 1 is determined during the second phase, which corresponds to the second pressure variation DP2.

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

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 to be equal to:

M2 = Gmoy x (∑Tinj) 2 + (∑δTinj) x G so that the gain G of the injector considered, to which the variation in injection duration (for example the increase) appliquéeTinj has been applied, is calculate by the formula: G = M2 - Gmoy x (TTini) 2 ∑δTinj

We note that, compared to the formula given for the simplified hypothetical case described above, the first injected mass M1 has been replaced by Gmoy x (∑Tinj) 2, which represents what the first injected mass M1 would have been, if the integral of the engine fuel requirement profile during the first learning phase had been identical to the integral of the engine fuel requirement profile during the second learning phase. The different values of M determined and of δTinj, ∑δTinj, (∑Tinj) 1, (∑Tinj) 2 and Gmoy, controlled or calculated are memorized and cyclically updated to follow in real time the variations in the gain G. This method of learning is in fact applicable on any point of the injector flow characteristic, that is to say not only on any point of its linear part 15 (see FIG. 2) but also on n ' any point in its non-linear part 16, for low values of the injection control duration, when the engine 1 is operating at idle or in low load operating zones. After determining the individual gain of an injector considered 2 of the engine 1, by applying to this single injector 2, as described above, commands for injection durations 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 maintained zero to cause pressure drops in the manifold 3, one can successively determine the individual gain of each of the other injectors 2 of this same engine 1 .

It is thus possible to control the injection taking into account an individual gain, specific to each of the injectors 2. As the parameters determining the characteristic depend on the pressure, in particular on the fuel pressure, the repetition of the learning process for different operating points ensures a pressure sweep, for a better determination of the local individual gain of its injectors 2, and thus a better knowledge of the individual flow characteristic of the injectors 2 is obtained, by adopting the gain determined in real time and retaining the theoretical offset Ot, which can also be advantageously replaced by a real offset, the learning of which is obtained by an appropriate strategy.

Claims

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 said engine (1) , said circuit comprising at least one pump (8), supplied from a fuel tank (12), and connected to a common rail (3) for supplying fuel to each injector (2) of the engine (1), said circuit being of the type with fixed volume and without permanent return of fuel from downstream to upstream of said pump (8), controlled in flow rate, each injector (2) and said pump (8) being controlled by at least one computer ( 5), so that at each engine cycle said pump (8) delivers in said circuit a mass of fuel known to the computer (5), and each injector (2) delivers to said engine (1) a mass of injected fuel (M) determined by an injector flow characteristic expressing the injected mass e (M) according to an increasing function of the duration of injection (Tinj) of said injector, (2) controlled by said computer (5), and for which it corresponds, to each value of the duration of injection (Tinj), a local gain (G) defined by a ratio of a variation of injected mass, consecutive to a variation of injection duration, to said variation of injection duration, characterized in that it comprises at least one step consisting in determine the local gain (G) of said at least one injector (2) considered from the variation (ΔM) of the mass of fuel injected (M) into said engine (1) by all of the injectors (2) resulting from applying to said at least one injector (2) considered an injection duration control (T'inj) different from that (Tinj) applied to the other injector (s) (2).

2. Method according to claim 1, characterized in that it comprises at least one step consisting in determining said variation. (ΔM) of the mass of fuel injected into said engine (1) taking into account a variation of a fall pressure (DP1, DP2) in said circuit supply pressure, which pressure drop (DP1, DP2) results from a control of a disturbance in the operation of said pump (8), said variation in pressure drop resulting from said control of different injection duration (T 'inj) during said disruption.

3. Method according to claim 2, characterized in that it comprises at least the steps consisting, during the operation of the engine (1), in: a) identifying a relatively stable engine operating condition (1), in which the applied mean injection time (Tinj.moy) is equal to the value of an injection duration (Tinj) for which one wishes to define the local gain (G), and, as long as the condition of stability is observed, b ) introduce, in the control of said pump (8), a disturbance such as to cause a pressure drop in said common rail (3), and maintain said disturbance during a first phase, at the end of which a first variation is obtained pressure (DP1), c) determining a first mass of fuel (M1) injected by all of the injectors (2) of the engine (1) and corresponding to said first pressure variation (DP1), d) calculating a local gain mean (Gmoy) of all injectors (2) c as being equal to the ratio of the first fuel mass (M1) to the sum (∑Tinj) 1 of all the injection times (Tinj) applied to all the injectors (2) during said first phase, e) introduce into the control of said pump (8) the same disturbance and maintain it during a second phase, at the end of which a second pressure variation (DP2) is obtained in the common rail (3), by modifying the control of the injector ( 2) for which we want to determine the local gain of a variation (δTinj) for each of the injections performed during said second phase, and such that the sum of the variations in injection duration applied during the second phase to said injector (2) is equal to ∑δTinj, f) determine a second mass of fuel (M2) injected by all of the injectors (2) of the engine (1) and corresponding to said second pressure variation (DP2), and consider that said second mass (M2) is equal to:

M2 = Gmoy x (∑Tinj) 2 + (∑δTinj) x G where (∑Tinj) 2 is the sum of all the injection times (Tinj) applied during said second phase, and G is the local gain of said injector ( 2) considered, and g) calculate said local gain (G) of said injector (2) considered by the formula: G = M2 - Gmoy x (TTini) 2

ΣδTinj

4. Method according to claim 3, characterized in that it further consists in repeating steps a) to g) for different engine operating points (1) and / or for a plurality of different values of the injection times. (Tinj) corresponding to different parts (15, 16) of the injector flow characteristic, so as to determine the individual gain of said at least one injector (2).

5. Method according to any one of claims 3 and 4, implemented on a fuel supply circuit of the engine (1) which is a direct injection circuit, in which said common rail (3) is supplied by a high pressure pump (8), itself supplied by a booster pump (13) connected to said reservoir (12), characterized in that said disturbance in the control of the high pressure pump (8) consists in causing a stopping said high pressure pump (8).

6. Method according to claim 5, characterized in that the determination of said first (M1) and second (M2) masses of fuel injected by all of the injectors (2) of the engine (1) in correspondence with said determination of said first ( DP1) and second (DP2) pressure variations is ensured by means of a model (18) of behavior of the supply circuit.

7. Method according to claim 6, characterized in that said circuit behavior model is a model (18) which takes into account the flow entering the common rail (3), imposed by the high pressure pump (8) and determined by the computer (5), the flow 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.

8. Method according to any one of claims 3 to 7, characterized in that it consists in determining the individual gain (G) of a single injector (2) of the engine (1) at a time, by applying to this single injector (2) commands for injection durations different from those (Tinj) applied to the other injectors (2) of the engine (1), during said second phase.

9. Method according to claim 8, characterized in that it consists in determining, in succession, the individual gain (G) of each of the injectors (2) of the same engine (1) in operation.