EP0637685A1 - Process and apparatus for auto-adaptation of air/fuel ratio in an internal combustion engine with canister purge system - Google Patents

Abstract

According to the invention, in a fuel-injected engine for which the basic period of injection is defined as a function of a shift and of a gain of a straight line expressing this period as a function of the pressure in the pipe, for a given speed and load condition, auto-adaptation is prevented by modifying the gain or the shift simultaneously when the purge valve of the canister is delivering, and auto-adaptation is allowed respectively in shift or in gain during at most a maximum number of n1 or n2 cycles, in an operating range 1 at low pressure, or respectively 2 at high pressure, the purge valve is allowed to deliver only after the maximum number of n1 or respectively n2 cycles has been accomplished, and a further auto-adaptation in gain and likewise in shift is permitted only after all the permitted cycles in gain and in shift have been accomplished. Application to fuel-injected engines with a canister purge circuit and auto-adaptation of the mixture richness on the basis of a lambda probe in the exhaust gases. <IMAGE>

Description

The invention relates to a method of self-adaptation of the richness and authorization of the purge of a purge circuit comprising a canister, for an internal combustion engine, of the spark-ignition type, equipped with a supply installation. in injection fuel, and therefore referred to as an injection engine in the remainder of this description, and preferably, but not exclusively, with a four-stroke engine cycle.

It is known that the fuel supply installation of such an injection engine comprises an air intake manifold to the engine, on the upstream of which a shutter for controlling the air flow, most often in disc shape, called butterfly, is rotatably mounted in a body. The injection installation comprises at least one injector delivering fuel into the intake manifold. The injector or each injector is supplied with fuel at a pressure given by a regulator, which drifts towards the injector a part of the fuel which it receives from the tank by a pump, and which returns to the tank the quantity of excess fuel by relative to that injected, which is a function of the duration of opening of the injector, called injection duration, and determined by a computer connected to sensors for operating parameters of the engine. From these sensors, the computer generally receives signals representative of the engine water or coolant temperature, the air temperature in the intake manifold, the throttle opening angle, and above all it receives engine rotation signals, supplied for example by a sensor cooperating with a toothed wheel integral with the flywheel, and having a singularity, for example a missing tooth, for detecting dead center top (TDC) of a reference cylinder, allowing the computer to determine the injection phases or times in the different cylinders, the engine speed being calculated from the signal modulated by the movement of the teeth. The computer can also receive a pressure signal measured directly in the intake manifold, or can calculate this pressure signal from two measurements chosen from the group comprising the throttle opening angle, the air flow and engine speed.

This computer, which determines the instant and duration of injection of each injector, is generally simultaneously an engine control computer, fulfilling other command and control functions, and determining in particular the instants of ignition of the spark plugs of the engine cylinders.

In order to comply with anti-pollution standards and to obtain proper operation of the catalytic converter, in terms of emission of polluting gases, it is known to connect to the computer an oxygen probe, called a λ probe, placed in the engine exhaust gases and sensitive to the presence of oxygen in these exhaust gases. The richness signal provided by the λ probe is used to regulate the operation of the engine around a richness value equal to 1, corresponding to the stoichiometric mixture. From a basic injection duration, calculated essentially as a function of the engine speed and of the pressure in the manifold, it is known to provide regulation from the oxygen sensor by correcting this injection duration basic taking into account a richness coefficient KO2, determined, in particular by applying value transitions, as a function of the richness signal of the oxygen sensor in the engine operating zones in closed loop, and fixed equal to a nominal value in the case of open-loop motor operation, for example in low temperature operation (after starting the engine cold), or in deceleration, or at full load, and finally if the engine speed is above a given high threshold.

If the correction of the basic injection duration as a function of the richness coefficient KO2 is carried out by multiplication by this coefficient KO2, then the nominal value of the latter is equal to 1.

Taking into account the richness coefficient KO2 by the computer makes it possible to increase or reduce the basic injection time, to center the operation of the engine on a richness equal to 1. Furthermore, it is known to express, for a given engine speed, the basic injection duration as a substantially linear function increasing, in the useful operating range of the engine, of the absolute pressure in the intake manifold, representing the engine torque, i.e. the engine load, and neglecting correction coefficients from maps, for example as a function of engine speed, pressure in the manifold or the throttle opening angle, to reflect the inflection of the straight in an S curve, in areas of low and high pressure in the tubing.

This substantially linear increasing function is represented by a straight line having a pressure offset at the origin, called offset, and a gain (or slope of the straight line) which are each drawn from a map, depending at least on the engine speed.

It is also known to use the computer to correct in a second step, by a cyclic self-adaptation, the basic injection time taken from the line and corrected in a first step by multiplication with the richness coefficient KO2. The aim of this cyclic self-adaptation is to ensure that the richness coefficient KO2 remains close to 1, by correcting any drift of this richness coefficient KO2. To this end, it is known to perform a so-called "first order" self-adaptation, by modifying the adaptation terms that are the offset and the gain in first and second engine operating ranges, respectively at low and high pressure in the intake manifold, respectively.

To meet the anti-pollution standards relating to fuel vapor emissions, with the engine stopped or in operation, motor vehicles are equipped with a receptacle, called a canister, containing means for absorbing fuel vapors. This canister is connected to the tank by a recovery pipe, is provided with a vent putting the fuel tank in the open air and is connected to the intake circuit, preferably downstream of the butterfly valve, by a suction pipe. on which is mounted an electrically controlled canister purge valve, the flow of which is controlled by the computer. The purge circuit thus produced allows, when the valve is open, and due to the vacuum prevailing downstream of the butterfly in the pipe, to suck in ambient air through the vent, through the canister, and to purge thus the canister of the fuel that it contains by mixing it with this ambient air so that it is sucked with it in the intake circuit. The electrically operated purge valve is generally a solenoid valve controlled at constant frequency, and the control parameter of which is the opening duty cycle (RCO) which is variable, that is to say the opening time , for a constant period, corresponds to a variable fraction of this period, which corresponds to the length of the slot of the electric control current applied.

In order to purge the canister so as to simultaneously comply with the anti-pollution standards relating to emissions of hydrocarbon vapors, and obtain smooth operation of the engine to ensure the comfort of the occupants of the vehicle (driving quality ), while respecting the anti-pollution standards relating to unburnt emissions and preserving the proper functioning of the catalytic converter, the opening cyclic ratio is defined by a map based mainly on the pressure in the intake manifold and engine speed.

However, this mapping does not take into account the filling state of the canister, and is therefore deliberately limited to low flow rates to reduce the contribution of the canister.

In addition, the purging of the canister and the self-adaptation of the offset and gain terms occur simultaneously, at all speeds: we adopt, as the self-adaptation term, an idle offset when the engine is running at idle, and, without idling , an offset except idle at low pressures, where the influence of the offset is preponderant, and a gain at high pressure. In addition, the purge state is taken into account by the self-adaptation by calculating a purge offset, when the purge is authorized. Indeed, as the flow rate of the canister depends little on the pressure in a large operating range of the engine, the purging of the canister is felt as an offset and not as a gain.

Consequently, the self-adaptation does not ensure a continuous monitoring of the contribution of the canister, and, in the operating range at high pressure of tubing, it does not suitably modulate the gain.

The simultaneous purging and self-adaptation is particularly disadvantageous under certain engine operating conditions, at low loads, where the overabundant supply of fuel vapor from the canister vis-à-vis the engine requirement causes excessive drift. the richness coefficient KO2.

In these operating conditions, in fact, in an environment heated by the engine in operation, the return to the hot fuel tank coming from the injector supply pressure regulator and the resulting fuel mixing, as well as the operation of the pump, are the causes of an intense production of fuel vapors in the tank.

Consequently, the known embodiment presented above has the drawback that the absence of a difference between the gain under purge and the gain outside purge, and the course of the first order self-adaptation under purge lead to poor first order adaptation.

Poor monitoring of the evolution of the purge results from adaptation ranges under purge in limited engine operating zones, which are the adaptation range of the offset under purge and the gain adaptation range. In addition, the known method does not differentiate between the first order adaptation rates and the purge, while the first order drift and the evolution of the purge are two very different phenomena.

The known method of self-adaptation of richness and authorization of purging does not allow an obvious estimate of the injection time resulting from the application of the purge offset, since the injection time applied can be less than the time minimum below which the flow characteristic of an injector is no longer linear or reproducible. As the purge is felt as an offset, and not as a gain, the multiplicative enrichments apply to the purge offset, and the adaptation of the gain under purge is an aberration.

The problem underlying the invention is to remedy these drawbacks.

• à interdire l'autoadaptation simultanément au débit de la vanne de purge,
• à chaque entrée en phase d'autoadaptation, à autoriser celle-ci pendant au plus un nombre maximum de n1 cycles, dans la première plage de fonctionnement, et pendant au plus un nombre maximum de n2 cycles dans la seconde plage de fonctionnement,
• à n'autoriser le débit de la vanne de purge qu'après l'exécution dudit nombre maximum de respectivement n1 ou n2 cycles d'autoadaptation, et
• à ne permettre une nouvelle autoadaptation en décalage ou en gain qu'après exécution de tous les cycles d'autoadaptation permis en gain et en décalage.

To this end, the invention provides a method of self-adaptation of the richness and authorization to purge a purge circuit of an injection engine, of the known type for which the purge circuit comprises a canister collecting vapors. of fuel coming from a tank, and connected to an engine intake manifold fitted with a shutter or butterfly for controlling the air flow, by an electrically controlled canister purge valve, the flow of which is controlled by a computer connected to engine operating parameter sensors from which it receives at least engine rotation signals and signals allowing to know the pressure in the intake manifold, as well as to an oxygen sensor in the engine exhaust gases, said computer calculating an injection duration, transmitted to at least one injector, and obtained from of a base injection duration expressed, for a given engine speed, as a substantially linear increasing function of the pressure in the manifold, with an offset (offset) at the origin and a gain which are taken from maps as a function at least engine speed, and corrected by taking into account a richness coefficient (KO2) determined as a function of the richness signal of the oxygen sensor in the engine operating zones in closed loop and fixed equal to a nominal value in the motor operating zones in open loop, to ensure the centering of the motor operation on a richness equal to 1, the offset and the gain being the subject of a cyclic self-adaptation for assu rer that the richness coefficient (KO2) remains close to its nominal value, by correction of any drift of this richness coefficient (KO2), in at least a first operating range of the engine, at low manifold pressure, by modification of '' at least the offset, and in at least a second operating range of the engine, at high manifold pressure, by modification of at least the gain, and is characterized in that it consists:

• to prohibit self-adaptation simultaneously with the flow rate of the purge valve,
• at each entry into the self-adaptation phase, to authorize it for at most a maximum number of n1 cycles, in the first operating range, and for at most a maximum number of n2 cycles in the second operating range,
• to authorize the flow rate of the purge valve only after the execution of said maximum number of respectively n1 or n2 self-adaptation cycles, and
• not to allow a new self-adaptation in offset or gain only after execution of all the self-adaptation cycles allowed in gain and offset.

Preferably, only the offset or the gain is adapted respectively during self-adaptation cycles executed only in the first range or respectively the second operating range of the motor.

In addition, whatever the self-adaptation conditions, the flow rate of the purge valve is not prohibited in the operating range of the engine which extends between the first and second ranges.

Therefore, when the engine is running without idling, each time the adaptation conditions are entered, the purge is interrupted to allow the adjustment of the offset or gain, a certain number of times, and when this maximum possible number of cycles is carried out. , the purge is then re-authorized. To allow a new self-adaptation, it is necessary to have executed the maximum allowed number of self-adaptation of the other term (gain or offset).

At the entry of the engine into an idling operating range, the method consists in prohibiting the flow rate of the purge valve, in replacing the self-adaptation in offset with a cyclic self-adaptation in idle offset, which is interrupted as soon as the value the idle shift after a given cycle is sufficiently close to that obtained after the previous cycle, and then authorize the flow of the purge valve.

In addition, the idle offset self-adaptation can be repeated cyclically until a constant value of the idle offset is obtained.

The subject of the invention is also a device, intended for implementing the method specific to the invention, and as presented above, and which is characterized in that the computer comprises at least one programmed microprocessor and / or carried out so as to control the progress of this process.

• la figure 1 représente schématiquement un moteur à injection, avec un circuit de purge de canister, et un calculateur de commande,
• la figure 2 représente, pour un régime moteur donné, une courbe exprimant la durée d'injection en fonction de la pression absolue dans la tubulure d'admission, et
• la figure 3 est un graphique représentant, en fonction du régime moteur et de la pression dans la tubulure, différentes zones de fonctionnement du moteur, dont les zones d'adaptation en décalage et en gain, et de fonctionnement au ralenti.

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

• FIG. 1 schematically represents an injection engine, with a canister purge circuit, and a control computer,
• FIG. 2 represents, for a given engine speed, a curve expressing the duration of injection as a function of the absolute pressure in the intake manifold, and
• FIG. 3 is a graph representing, as a function of the engine speed and of the pressure in the manifold, different areas of engine operation, including the offset and gain adaptation areas, and of idle operation.

In Figure 1 is schematically shown in 1, an injection engine, four-cylinder four-stroke, and spark ignition, equipped with an indirect fuel injection system of the multipoint type. This installation comprises four injectors 2 each mounted in one respectively of the four branches 3 downstream of an intake manifold 4, and each opening into the cylinder head of the engine 1, at the level of the intake valve of a cylinder corresponding. A throttle valve 5 for controlling the intake air flow is rotatably mounted in a throttle body 6 in the upstream part of the pipe 4, the throttle body 6 having a bypass pipe 7 on the throttle valve 5, and the passage section is regulated by a valve shown diagrammatically at 8 and controlled by a stepping motor 9.

The injectors 2 are supplied with fuel under a pressure defined by the regulator 10, itself supplied from the tank 11, closed by a tight plug, by means of the pump 12 on the supply line 13 on which is also fitted the filter 14. The remainder of the quantity of fuel diverted by the regulator 10 to the injectors 2 is returned to the tank 11 by the return line 15.

The fuel vapors forming in the tank 11 are collected by a canister 16, containing an absorbent charge of these vapors, for example activated carbon, and connected to the tank by the recovery pipe 17. The canister 16 has a vent 18, by which it puts the reservoir 11 in the open air, and is connected to the intake manifold 4, downstream of the throttle valve 5 by a suction pipe 19 on which is mounted an electrically controlled valve 20, for purging the canister 16. This valve 20 is a solenoid valve normally closed at rest and with opening controlled by RCO variable.

The R.C.O. variable of this valve 20, therefore the purge flow of the canister 16 of the fuel vapors it contains, as well as the position of the electric stepper motor 9 are controlled by electrical commands which are transmitted to them from the computer 21 by the conductors 22 and 23. Likewise, the duration of opening or injection of the injectors 2, depending on the amount of fuel injected by each injector 2 into the corresponding cylinder, (since the pressure difference applied to the injectors 2 is constant and fixed by the regulator 10), is controlled by electrical commands applied by the computer 21 to the injectors 2 by the conductor 24.

These electrical orders (injection duration, variable RCO, stepping motor control) are produced by the computer 21 from signals received from various sensors of engine operating parameters, including an air temperature signal of intake 25, delivered by a temperature probe 26 placed in the air stream, an absolute pressure signal for tubing 27 delivered by a pressure probe 28 in tubing 4, a temperature signal 29 for engine cooling water 1, supplied by a sensor not shown, and a signal 30 of engine rotation, making it possible to determine the engine speed, as well as the passages at TDC in the various cylinders for determining the instants of injection. This signal 30 can be supplied by a sensor cooperating with a toothed wheel driven by the flywheel and having a singularity of detection of the transition to TDC of a reference cylinder. The computer 21 also receives a signal 31 of the butterfly opening angle 5 supplied by an appropriate sensor, such as a potentiometer for copying the angular position of the butterfly 5, and mounted on the axis of rotation of the latter, and delivers at 33 a fuel consumption signal. Finally, the computer 21 receives at 32 a richness signal R delivered, in the form of electrical voltage, by an oxygen probe called the λ probe, placed in the engine exhaust gases, of which it indicates the oxygen content. In operation of the engine in closed loop, the richness signal R is used by the computer 21 to center the operation of the engine on a richness equal to 1. For this, the computer 21 first calculates a basic injection duration , with reference to a network of curves stored in the computer 21 and such as that shown in FIG. 2, which gives, for a given constant engine speed, the basic injection time T inj B as a function of the absolute pressure P tub in the manifold 4, this curve being, over most of the useful operating range of the engine, comparable to an increasing linear function defined by a pressure offset at the origin D and by a gain G corresponding to the slope of the line representative of this function. D and G are each drawn from a map depending in particular on the engine speed N (functions f (N) and g (N)). In the high and low pressure zones, the curve has rounded parts in S obtained from the right after multiplicative correction by a cartographic coefficient K carto, function in particular of the engine speed N, and of the pressure P tub or of the butterfly opening angle 5 (function h (N, P)).

L'application de cette durée d'injection aux injecteurs conduit à un signal de richesse R de la sonde λ en général différent de 1. Le calculateur 21 augmente ou réduit alors la durée d'injection appliquée aux injecteurs 2 pour obtenir un signal de richesse R égal à 1. Pour cela, le calculateur 21 calcule un coefficient de richesse KO2 par lequel il multiplie la durée d'injection de base T inj B donnée par la formule (1).So, for a given speed N and a given intake pressure P tub, the basic injection duration is given by the formula (1): $$\text{(1) T inj B = (P tub - D) x G x K carto}$$

The application of this injection duration to the injectors leads to a richness signal R of the probe λ generally different from 1. The computer 21 then increases or reduces the injection duration applied to the injectors 2 to obtain a richness signal R equal to 1. For this, the computer 21 calculates a richness coefficient KO2 by which it multiplies the basic injection time T inj B given by the formula (1).

In the open-loop engine operating zones, the richness coefficient KO2 is chosen equal to 1. These zones correspond in particular to operation with a faulty λ probe, or with an air temperature below an input threshold in a closed loop, for example in the event of a cold start of the engine, or when the open loop is imposed by the speed or the opening angle of the throttle, for example in deceleration or at full load, or if the engine speed N is higher than a given high threshold, for example 4500 rpm, and, in general, each time the target wealth differs from 1.

After correction by multiplication by the richness coefficient KO2, the value of the offset D or of the gain G is modified by a cyclic self-adaptation, so as to correct all the drifts of this richness coefficient KO2 so that it remains close to 1. In this example, we consider that KO2 is a corrective multiplier coefficient of nominal value equal to 1.

This self-adaptation is ensured in the manner now described with the aid of FIG. 3.

This FIG. 3 represents three characteristic operating ranges of the engine 1, defined by the engine speed N on the ordinate and by the pressure in the pipe P tub on the abscissa, in which it is possible to carry out the cyclic self-adaptation calculations for an operation engine idle in ranges 1 and 2, and idling in range 3.

Tracks 1 and 2 are operating ranges respectively at low and high tubing pressure, each defined between a lower threshold and an upper threshold of P tub, respectively P1 and P2 or P3 and P4, such as P1 <P2 <P3 <P4 , so that tracks 1 and 2 are not adjacent. In addition, ranges 1 and 2 are defined between the same lower speed threshold N1, for example of 1200 rpm, and the same higher speed threshold N2, for example of 4000 rpm.

Range 1 is that in which the cyclic self-adaptation is only ensured on the offset D without idling, while in range 2, the self-adaptation is only ensured on the gain G.

When the engine operating point, defined by its speed N and its manifold pressure P tub, has entered range 1 or 2, as soon as the computer 21 detects, as a function of the richness signal R of the probe λ and the richness coefficient KO2, that a self-adaptation of the richness is necessary, it controls the purge valve 20 so as to prohibit its flow and begins the self-adaptation modifying the value of the offset D out of idle in range 1 or of the gain G in range 2. It therefore prohibits purging simultaneously with self-adaptation in ranges 1 and 2.

In range 1, it authorizes the self-adaptation of D out of idle for at most a maximum number of n1 cycles, for example equal to 2, thanks to a first counter which is initialized to this value when the computer is powered up and decremented by the value of one unit for each cycle performed. Similarly, in range 2, the computer 21 authorizes the self-adaptation of G for at most a maximum number of n2 cycles, for example equal to 1, thanks to a second counter which is also initialized at this value when the power is turned on. calculator, and decremented by one at each cycle.

In range 1, after n1 cycles of adaptation of the offset without idling D, if the second counter is not at zero, the computer 21 authorizes the purge, and it is no longer possible to adapt D. Similarly, in range 2, after n2 gain adjustment cycles G, if the first counter is not at zero, the computer authorizes the purge and prohibit further adjustment of gain G.

On the other hand, as soon as the two counters are at zero, the computer 21 resets the two counters respectively to n1 and n2, and again authorizes self-adaptation cycles, if necessary, then prohibiting the purging.

In summary, when the adaptation of a term D or G is authorized, the purging is prohibited by the computer 21. With each self-adaptation term D and G is associated a counter in the computer 21. Each counter is decremented by one unit after each self-adaptation cycle of its associated term. When a counter is zero, self-adaptation of its associated term is prohibited and purging is authorized. The offset D idle and gain G counters are initialized each time the power is turned on, then when the two counters are simultaneously zero.

Between ranges 1 and 2, purging is never prohibited by the computer 21, whatever the self-adaptation conditions chosen.

For this reason, between the speed thresholds N1 and N2, the purging of the canister 16 by the purge valve 20 is not prohibited by the computer 21 unless the engine operating point is in range 1, and the first counter is not zero, or the engine operating point is in range 2 and the second counter is not zero.

The idling range 3 is limited by an upper threshold of engine speed N which is lower or, at most, equal to the lower threshold N1 of ranges 1 and 2. On the other hand, under pressure, range 3 can extend on either side of the lower pressure threshold P1 of range 1, or always be less than P1. This idle range corresponds to a low speed and a throttle angle weak or zero. In this range 3, the self-adaptation is carried out by substituting for the term offset D without idling, an offset in idling DR. On entering range 3, the computer 21 prohibits the flow of the purge valve 20, and begins the cyclic self-adaptation of DR, chosen independent of the engine speed, and interrupts this adaptation as soon as the value of DR after a cycle given is equal to that obtained after the previous cycle. The computer 21 then authorizes the flow rate from the purge valve 20.

DR self-adaptation can be authorized for at most a maximum number of n3 cycles, using a third counter initialized at each power-up and then at each entry in idle mode (entry in range 3). However, preferably, the method consists in cyclically repeating the self-adaptation of DR until a constant value is obtained which is taken into account for the calculation of the injection duration. After execution of the n3 cycles in the first case, or obtaining a constant value of DR in the second case, the computer 21 again authorizes the purge.

The method of self-adaptation of the richness and authorization of the purging of the canister purge circuit described above thus ensures a dissociation between the self-adaptation and the purge, which overcomes the drawbacks of the methods of the prior art , and allows a good first order adaptation, and in particular a good modulation of the gain in range 2.

The implementation of this method is ensured by the device described above, in particular with reference to FIG. 1, in which the computer 21, which is in fact a central computing and control unit, with in particular the circuits of calculation, memories, counters, registers and other regulation and control circuits, necessary and of known structure, comprises at least one microprocessor or microcontroller programmed and / or produced so as to control the progress of this process.

Claims (9)

Method for self-adaptation of the richness and authorization of purging of a purge circuit of an injection engine (1), for which the purge circuit comprises a canister (16) collecting fuel vapors from a tank (11), and connected to an intake manifold (4) of the engine (1), provided with a shutter or butterfly valve (5) for controlling the air flow, by a valve (20) for purging the canister (16) electrically controlled, the flow rate of which is controlled by a computer (21) connected to sensors (26, 28) of engine operating parameters (1) from which it receives at least engine rotation signals (30) and signals (27, 30, 31) making it possible to know the pressure (P tub) in the intake manifold (4), as well as to an oxygen sensor in the engine exhaust gases, said computer ( 21) calculating an injection duration, transmitted to at least one injector (2), and obtained from a basic injection duration (T inj B) expressed, for a reg ime given motor (N), as a substantially linear increasing function of the pressure in the tubing (P tub), with an offset (D) at the origin and a gain (G) which are drawn from maps according to at least the engine speed (N), and corrected by taking into account a richness coefficient (KO2) determined as a function of the richness signal of the oxygen sensor (32) in the engine operating zones (1) in closed and fixed loop equal to a nominal value in the motor operating zones (1) in open loop, to ensure the centering of the motor operation on a richness equal to 1, the offset (D) and the gain (G) making moreover the subject to cyclic self-adaptation to ensure that the richness coefficient (KO2) remains close to its nominal value, by correction of any drift of this richness coefficient (KO2), in at least a first engine operating range, at low tubing pressure (P1, P2), by modification of at least the offset (D), and in at least a second range of operation of the engine, at high manifold pressure (P3, P4), by modifying at least the gain (G),
characterized in that it consists: - to prohibit self-adaptation simultaneously with the flow rate of the purge valve (20), - at each entry into the self-adaptation phase, to authorize it for at most a maximum number of n1 cycles, in the first operating range, and for at most a maximum number of n2 cycles in the second operating range, - to authorize the flow rate of the purge valve (20) only after the execution of said maximum number of respectively n1 or n2 self-adaptation cycles, and - to allow a new self-adaptation in offset (D) or gain (G) only after execution of all the self-adaptation cycles allowed in gain and offset. Method according to claim 1, characterized in that it consists in adapting only the offset (D) or respectively the gain (G) during self-adaptation cycles executed only in the first range or respectively the second operating range of the motor. Method according to any one of the preceding claims, characterized in that it consists in choosing maximum numbers of n1 and n2 self-adaptation cycles equal to 2 and 1 respectively. Method according to any one of the preceding claims, characterized in that it consists in not prohibiting the flow rate of the purge valve (20), whatever the self-adaptation conditions, in the range (P2-P3) of operation of the engine which extends between said first and second ranges. Method according to any one of the preceding claims, characterized in that it consists, at the entry of the engine into an idling operating range, to prohibit the flow of the purge valve (20), to replace the offset self-adaptation (D) self-adaptation cyclic idling offset (DR) which is interrupted as soon as the value of the idling offset (DR) after a given cycle is sufficiently close to that obtained after the previous cycle, and then to authorize the flow of the purge valve (20 ). Method according to claim 5, characterized in that it consists, on each entry into the idling shift (DR) self-adaptation phase, in authorizing the latter for at most a maximum number of n3 cycles. Method according to claim 5, characterized in that it consists in cyclically repeating the idling offset self-adaptation (DR) until a constant value of the idling offset is obtained. Method according to any one of Claims 5 to 7, characterized in that it consists in limiting the idle operating range to an upper engine speed threshold which is less than or equal to a lower engine speed threshold (N1) for the first and second operating ranges corresponding to the offset self-adaptation (D) and gain (G) respectively. Device for self-adaptation of the richness and authorization for purging of a purge circuit (16, 17, 19, 20) in a canister (16), for an injection engine (1), comprising a computer (21) connected to sensors (26, 28) of engine operating parameters (1) as well as an oxygen sensor in the engine exhaust gases (1), and controlling an electrically controlled valve (20) connecting the canister (16) to an intake manifold (4) provided with a shutter (5) for controlling the air flow, said computer (21) calculating an injection duration, applied to at least one injector (2) of the engine (1), and obtained from a basic injection duration (T inj B) expressed as a function of the pressure in the pipe (4) with an offset (D) at the origin and a gain ( G) taken from maps in memory in the computer (21), and corrected using a richness coefficient (KO2) determined by the computer (21) as a function of the richness signal (R) of the oxygen sensor in closed loop operation and equal to a nominal value in open loop operation, to ensure the centering of the operation of the engine (1) on a richness equal to 1, the computer (21) performing a cyclic self-adaptation of the offset (D) and of the gain (G) to ensure that KO2 remains close and its nominal value, by correction of any drift of KO2, characterized in that the computer ( 21) comprises at least one microprocessor programmed and / or produced so as to control the progress of the process according to any one of claims 1 to 8.

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