EP2126341B1 - Optimised generation of a radio frequency ignition spark - Google Patents

Abstract

The method involves receiving measuring signals representing a function of a combustion engine, and receiving electric measuring signal representing a generated spark. A parameter is regulated based on the received signals in a real time to promoting the ramification of the generated spark, where the parameters are selected from the intermediate voltage level, order of frequency and duration of control pulse train. An independent claim is also included for a plasma generating device.

Description

The present invention relates to controlling the power supply of a plasma generation resonator, in particular in a plasma automotive ignition application by radio-frequency biasing of the resonator of a multi-spark plug.

In the field of modern automotive ignitions, the BME multi-spark plug has a significant innovation and a different geometry from conventional spark plugs. Such BME is described in detail in the following publications of patent applications in the name of the Applicant. FR 2,859,830 , FR 2,859,869 , FR 2,859,831 , FR 2,878,086 and FR 2 881 281 .

A BME includes a resonator whose resonant frequency F _c is located in the high frequencies, typically between 4 and 6 MHz, to supply the candle with a resonance amplified voltage. The application by the resonator to the electrodes of the candle of an AC voltage in the range of radio frequencies, allows to develop multi-filament discharges between the electrodes of the candle, over distances of the order of a centimeter, at high pressure and for peak voltages below 20 kV.

These are referred to as branched sparks, insofar as they involve the simultaneous generation of at least several lines or ionization paths in a given volume, their branches being moreover omnidirectional.

The control of the power supply of such a BME requires the use of a high voltage generator whose operating frequency is very close to the resonance frequency of the radio frequency resonator. The greater the difference between the resonance frequency of the resonator and the operating frequency of the generator, the higher the resonator overvoltage coefficient (ratio between the amplitude of its output voltage and its input voltage) is high.

Such a voltage generator, detailed in the patent application FR 03-10767 , consists mainly in using a resonator control frequency as close as possible to the resonance resonance frequency, in order to benefit from the highest possible overvoltage coefficient.

However, it is found that if the total amplitude of voltage applied at the output of the resonator to the electrodes of the candle is too high, there is a risk of seeing the spark concentrate in a single filament. This phenomenon, which we will describe under the term "bridging" in the following description, locates the energy in a small filamentous zone, thus making the discharge much less effective to initiate the ignition of the air-fuel mixture between the electrodes. , compared to a branched spark.

The present invention aims to overcome this disadvantage, by making it possible to maximize in real time the volume of the spark generated while reducing the occurrence of bridging, that is to say the appearance of filament discharges.

• un circuit d'alimentation, présentant un interrupteur commandé par un signal de commande sous la forme d'au moins un train d'impulsions de commande, appliquant une tension intermédiaire sur une sortie du circuit d'alimentation à la fréquence définie par le signal de commande,
• un résonateur, connecté à la sortie du circuit d'alimentation et apte à générer une étincelle entre deux électrodes lorsqu'un niveau haute tension est appliqué sur la sortie du circuit d'alimentation, ledit procédé étant caractérisé en ce qu'il comprend :
• la réception de premiers signaux de mesure représentatifs du fonctionnement d'un moteur à combustion,
• la réception de seconds signaux de mesure électrique représentatifs du type d'étincelle générée, et
• la régulation en temps réel, en fonction des premier et second signaux de mesure reçus, d'au moins un paramètre pris parmi au moins le niveau de la tension intermédiaire, la fréquence de commande, la durée du train d'impulsions de commande, de sorte à favoriser une ramification de l'étincelle générée, et
• la régulation conjointe du niveau de la tension intermédiaire et de la durée du train d'impulsions de commande.

With this object in view, the subject of the invention is a method for controlling a radiofrequency plasma generator, comprising:

• a supply circuit, having a switch controlled by a control signal in the form of at least one control pulse train, applying an intermediate voltage to an output of the supply circuit at the frequency defined by the control signal; ordered,
• a resonator, connected to the output of the supply circuit and able to generate a spark between two electrodes when a high voltage level is applied to the output of the supply circuit, said method being characterized in that it comprises:
• receiving first measurement signals representative of the operation of a combustion engine,
• receiving second electrical measurement signals representative of the type of spark generated, and
• the real-time regulation, as a function of the first and second measurement signals received, of at least one parameter taken from at least the intermediate voltage level, the control frequency, the duration of the control pulse train, to promote branching of the generated spark, and
• the joint regulation of the intermediate voltage level and the duration of the control pulse train.

Advantageously, the control signal being generated in the form of a plurality of pulse trains of control, the regulation concerns the number of said trains and the inter-train time.

Advantageously, the method comprises the memorization of relations between measurement signals and the value of parameters to be regulated, the regulation consisting of determining and applying the value of at least the parameter to be regulated according to the measurement signals received and the memorized relationships. .

Preferably, the first measurement signals are selected from the group consisting of engine oil temperature, engine coolant temperature, engine torque, engine speed, ignition angle, air temperature. intake pressure, manifold pressure, atmospheric pressure, combustion chamber pressure or maximum pressure angle.

Preferably, the second measurement signals comprise at least one measurement of the voltage at the terminals of a storage capacitor supplying the intermediate voltage at the input of the resonator and / or at least one measurement of the current in the resonator.

According to one embodiment, a first measurement of the voltage at the terminals of the storage capacitor before or at the beginning of the control pulse train is carried out and a second measurement of the said voltage after or at the end of the pulse train of ordered.

According to one variant, a plurality of measurements are carried out during the duration of the control pulse train.

Preferably, the method comprises regulating the control frequency to a set point substantially equal to the resonance frequency of the resonator.

• un circuit d'alimentation présentant un interrupteur commandé par un signal de commande sous la forme d'au moins un train d'impulsions de commande, l'interrupteur appliquant une tension intermédiaire sur une sortie du circuit d'alimentation à la fréquence définie par le signal de commande,
• un résonateur, connecté à la sortie du circuit d'alimentation et apte à générer une étincelle entre deux électrodes lorsqu'un niveau haute tension est appliqué sur la sortie du circuit d'alimentation,

ledit dispositif étant caractérisé en ce qu'il comprend un module de contrôle adapté à mettre en oeuvre le procédé selon l'une quelconque des revendications précédentes.The invention also relates to a radiofrequency plasma generation device comprising:

• a supply circuit having a switch controlled by a control signal in the form of at least one control pulse train, the switch applying an intermediate voltage to an output of the supply circuit at the frequency defined by the control signal,
• a resonator, connected to the output of the supply circuit and able to generate a spark between two electrodes when a high voltage level is applied to the output of the supply circuit,

said device being characterized in that it comprises a control module adapted to implement the method according to any one of the preceding claims.

• la figure 1 illustre un mode de réalisation d'un dispositif de génération de plasma ;
• la figure 2 illustre un modèle électrique utilisé pour le résonateur ;
• la figure 3 illustre un schéma de principe de l'allumage radiofréquence ;
• la figure 4 illustre un dispositif de génération de la tension intermédiaire intervenant dans l'allumage radiofréquence intégrant un module de contrôle selon l'invention.

Other characteristics and advantages of the present invention will emerge more clearly on reading the following description given by way of illustrative and nonlimiting example and with reference to the appended figures in which:

• the figure 1 illustrates an embodiment of a plasma generating device;
• the figure 2 illustrates an electric model used for the resonator;
• the figure 3 illustrates a schematic diagram of radio frequency ignition;
• the figure 4 illustrates a device for generating the intermediate voltage involved in the ignition radio frequency integrating a control module according to the invention.

• une alimentation 2, prévue pour faire résonner une structure L-C à une fréquence supérieure à 1MHz avec une tension aux bornes du condensateur supérieure à 5kV, de préférence supérieure à 6kV ;
• un résonateur 6, connecté en sortie du circuit d'alimentation, présentant un facteur de surtension supérieur à 40 et une fréquence de résonance supérieure à 1 MHz ;
• une tête de bougie 110, comprenant deux électrodes 103 et 106 séparées par un isolant 100, permettant de générer un plasma ramifié lors de l'application de l'excitation radiofréquence aux bornes de ses électrodes.

With reference to the figure 1 , a plasma generating device mainly comprises three functional subassemblies:

• a power supply 2, designed to resonate an LC structure at a frequency greater than 1 MHz with a voltage across the capacitor greater than 5 kV, preferably greater than 6 kV;
• a resonator 6, connected at the output of the supply circuit, having an overvoltage factor greater than 40 and a resonance frequency greater than 1 MHz;
• a candle head 110, comprising two electrodes 103 and 106 separated by an insulator 100, for generating a branched plasma when radiofrequency excitation is applied across its electrodes.

• une alimentation basse tension 3 (générant une tension continue inférieure à 1000 V);
• un amplificateur radiofréquence 5, amplifiant la tension continue et générant une tension alternative à la fréquence commandée par la commande de commutation 4.

The supply circuit 2 advantageously comprises:

• a low voltage supply 3 (generating a DC voltage of less than 1000 V);
• a radio frequency amplifier 5, amplifying the DC voltage and generating an AC voltage at the frequency controlled by the switching control 4.

The AC voltage generated by the amplifier 5 is applied to the LC resonator 6. The LC resonator 6 applies the AC voltage between the electrodes 103 and 106 of the candle head.

The voltage supplied by the power supply 3 is less than 1000V and the power supply preferably has a limited power. We can thus foresee that the energy applied between the electrodes is limited to 300mJ by ignition, for safety reasons. This also clamps the intensity in the voltage generator 2 and its power consumption. To generate DC voltages greater than 12 V in an automotive application, the power supply 3 may include a 12-volt converter to Y Volt, where Y is the voltage supplied by the power supply to the amplifier. It is thus possible to generate the desired DC voltage level from a battery voltage. The stability of the DC voltage generated is not a priori a decisive criterion, it can be expected to use a switching power supply to power the amplifier, for its qualities of robustness and simplicity.

The supply circuit 2 makes it possible to concentrate the highest voltages on the resonator 6. The amplifier 5 thus deals with much lower voltages than the voltages applied between the electrodes of the candle.

The amplifier 5 accumulates energy in the resonator 6 at each alternation of its voltage. An amplifier 5 is preferably used in class E, as detailed in the patent U.S. 5,187,580 . Such an amplifier makes it possible to maximize the overvoltage factor. Those skilled in the art will of course associate a switching device adapted to the chosen amplifier, to support the requirements of voltage increases and to have an adequate switching speed.

The figure 2 illustrates an electrical model of the resonator 6. Thus, the inductance series 65 has in series an inductance Ls and a resistor Rs taking into account the skin effect in the radiofrequency domain. The capacitor 119 has in parallel capacitance Cs and resistor Rp. Ignition electrodes 106 and 103 are connected across capacitor Cs.

l'amplitude aux bornes de la capacité Cs est amplifiée du coefficient de surtension Q défini par la formule suivante: $$Q=\frac{1}{\frac{\sqrt{\frac{\mathit{Ls}}{\mathit{Cs}}}}{\mathit{Rp}}+\frac{\mathit{Rs}}{\sqrt{\frac{\mathit{Ls}}{\mathit{Cs}}}}}\mathrm{.}$$

The resistance Rp is added to model the discharge and corresponds where appropriate to the dissipation in the ceramic candle. When the resonator is powered by a voltage at its resonance frequency f ₀ $(1/\left(2\mathrm{\pi }\sqrt{\mathrm{The}*\mathrm{VS}}\right),$

the amplitude across the capacitance Cs is amplified by the overvoltage coefficient Q defined by the following formula: $$Q=\frac{1}{\frac{\sqrt{\frac{\mathit{ls}}{\mathit{cs}}}}{\mathit{rp}}+\frac{\mathit{Rs}}{\sqrt{\frac{\mathit{ls}}{\mathit{cs}}}}}\mathrm{.}$$

The plasma generating device which has been described may comprise a plasma generation resonator adapted to achieve a combustion engine controlled ignition, an ignition in a particle filter, or a decontamination ignition in an air conditioning system.

The figure 3 illustrates a block diagram of the radio frequency ignition according to an embodiment of an amplifier 5, having a power MOSFET transistor as a switch controlling the commutations across the resonator 6.

Thus, a control signal generator 8 applies a control signal V1 to a control frequency on the gate of a power MOSFET 9, via an amplification device 10 shown schematically. In order to control the production of sparks between the electrodes of the candle when its resonator is excited via the control signal V1, the latter is not permanent but is present in the form of control pulse trains at the control frequency.

As described in the patent application EP-A-1,515,594 a parallel resonant circuit 62 is connected between an intermediate voltage source Vinter and the drain of the transistor 9. This circuit 62 comprises an inductance Lp in parallel with a capacitance Cp.

The parallel resonator transforms the intermediate voltage Vinter into an amplified voltage Va, which is supplied on the drain of the transistor 9 connected to the input of the resonator 6.

The transistor 9 therefore acts as a switch and transmits (respectively blocks) the voltage Va at the input of the resonator 6 when the control signal V1 is at the logic high (respectively low).

The intermediate voltage Vinter, supplied at the input of the parallel resonant circuit 62, is typically generated by means of a voltage booster, shown schematically in FIG. figure 4 .

The voltage booster circuit is for example supplied from a battery voltage Vbat and is composed of a Lboost inductor, a MOSFET K, which serves as a switch controlled by a control module 20, a diode Dboost, and a Cboost capacitor. The control module delivers a control signal V2 in the form of high frequency pulse train, so that switch K is periodically made conductive. When K is closed, the Lboost inductor loads with the voltage Vbat at its terminals. When K is open, the Dboost diode drives and the energy stored in the inductor causes a current to flow to the output and the capacitor Cboost to charge it.

The Cboost storage capacity is loaded in this way until the desired value of Vinter is reached. A regulation loop, not shown, measures the value of the voltage across the capacitor Cboost at any time and controls the control module to stop the output voltage rise when the desired value is reached.

The voltage rise process is inhibited in all cases at the beginning and during the ignition control train.

To generate the discharge of the candle, a certain amount of energy is taken from the Cboost capacity to be supplied, after amplification by the resonant circuit 62, at the input of the resonator 6, so as to allow the application of a high level voltage between the terminals of the electrodes at a frequency defined by the control signal applied to the switch 9. Upon ignition, the voltage Vinter across the capacitor Cboost drops. It is therefore necessary to recharge it for the next discharge. Thus, between two discharges, the voltage rise process as explained above is repeated.

The invention provides for acting on a certain number of operating parameters of the system, or on at least one of them, in order to limit as much as possible the bridging phenomenon during the discharge of the spark plug, in particular: the supply voltage of the resonator provided for applying the high voltage across the electrodes, the excitation frequency of the resonator, the duration of the control train, the possibility of achieving several trains and their number, as well as the time between the trains. These parameters can be advantageously adjustable during the operating time of the system and their adjustment in real time, as will be explained in more detail later, must make it possible to obtain an optimal branching of the discharge by limiting the occurrence of the bypasses.

Since the level of voltage applied between the terminals of the electrodes intervenes first of all in the development of the discharge (and therefore in the event of the appearance of the bridging), it is possible at first to envisage limiting during the discharge to avoid the bridging phenomenon.

To do this, it is possible to envisage using an intermediate voltage level at the terminals of the Cboost capacitance before the reduced ignition, with respect to the Vinter voltage level used during the bridged plasma generation, by defining a voltage setpoint to be achieved. at the terminals of the Cboost storage capacity adjustable in real time. In real time is meant the updating of this instruction between one ignition and the next on the same cylinder. Indeed the voltage across Cboost before ignition finally determines the amplitude of the voltage across the electrodes of the resonator during discharge.

The applied voltage setpoint must be such that it allows the system to be placed under optimal conditions from the point of view of combustion, namely a branching of the maximum volume spark for a voltage amplitude applied across the electrodes just below the high voltage limit from which bridging occurs.

The real-time regulation of the intermediate voltage value to be carried out at the terminals of Cboost takes into account measurement signals of operating parameters of the combustion engine.

Advantageously, the real-time regulation of the optimum intermediate voltage value to be achieved at the terminals of the Cboost capacitor can be refined by also taking into account electrical measurement signals of the resonator 6 power supply, representative of the type of spark. realized.

Indeed, the analysis of certain signals makes it possible to know more or less accurately the type of spark produced and the type of combustion that resulted. The processing of these signals then makes it possible to control the value of the voltage to be produced at the terminals of the Cboost capacitor before ignition, so as to optimize the type of spark developed in the combustion chamber, in particular their volume.

The regulation process then determines the value of the setpoint of the voltage to be achieved before lighting at the terminals of Cboost, as a function of the relationships stored between these measurement signals and the voltage value to be applied across Cboost.

By thus adapting in real time the value of the voltage to be applied across the capacitor Cboost before ignition, according to engine operating parameters, on the one hand and electrical measurements of the resonator power representative of the type of spark generated, on the other hand, it will be possible to maintain this voltage very precisely at a value both sufficient to generate a spark between the electrodes and thus initiate ignition, when it is applied via the resonator across the electrodes, while being below the limit high voltage from which bridging occurs.

Such a real-time control of the intermediate voltage across Cboost before ignition is achieved via the control module 20.

The latter thus comprises an interface 21 for receiving signals for measuring operating parameters of the combustion engine. Engine operating parameters measured include engine oil temperature, engine coolant temperature, engine torque, engine speed, ignition angle, intake air temperature. pressure at the manifold, atmospheric pressure, pressure in the combustion chamber, maximum pressure angle or any characteristic quantity of engine operation. These types of measurement can be carried out in a manner known per se by those skilled in the art.

Advantageously, the control module 20 also comprises an interface 22 for receiving electrical measurement signals, representative of the type of spark generated.

The control module 20 comprises a memory module 26 in which are stored the relationships between the measurement signals and the voltage value to be achieved across the Cboost capacity before ignition. These relationships can be established based on tests prerequisites. The memory module 26 can memorize the relations in the form of a function associating predetermined measurement signals with a single voltage setpoint to be achieved. For example, a linear function or a polynomial function can be extrapolated according to the results of prior tests on a resonator by varying the different parameters taken into account. The memory module can also store the relationships as a multidimensional array having as input measurement signals.

The control module 20 comprises a module 25 determining the voltage setpoint to be made as a function of the measurement signals received and the relationships stored in the memory 26. The setpoint is supplied by the module 25 to a module 27, applying a control signal V2 on an output interface 24 adapted to control the process of voltage rise as explained above until the voltage value across the capacitance Cboost reaches the setpoint. The module 27 is for example a clock generator suitably chosen by those skilled in the art.

A programming interface 23 can be provided for receiving and executing commands for modifying the relationships or parameters stored in the memory module 26. The programming interface 23 can in particular be a wireless communication interface. Thus, one can consider updating the relationships stored in the module 26 to optimize the operation of the ignition system after delivery.

The reception interface 22 preferably receives one or more measurements of the value of the intermediate voltage across the storage capacitor Cboost and / or one or more measurements of the current entering the resonator 6 and this, for the duration of (or) the train (s) of control pulses V1 controlling the generation of 'spark.

Indeed, as will be seen more precisely later, the measurement of the evolution of the voltage across Cboost during an ignition control carries a lot of information about the branching of the spark.

As for the current entering the resonator, it is an image of the high voltage across the electrodes of the resonator. This modulated signal at the resonant frequency (typically 5MHz) has a characteristic envelope of the branched discharge and bridging phenomena. The analysis of the envelope of the current signal during the duration of an ignition control, requires the use of a device of the type of peak detector, known per se, which only outputs the peak values of the modulated sinusoid of the current signal.

The study of these measurement signals makes it possible to diagnose the type of discharge or spark produced and to modify accordingly, according to predetermined laws stored in the control module, the parameter or parameters chosen, in this case the value of the intermediate voltage to be made at the terminals of Cboost before ignition, according to the embodiment example above.

The realization of the regulation based on the electrical measurements described above can be implemented in several ways.

According to a first mode, it is possible to consider the taking into account of a single measurement characteristic of the type generated spark, performed at the most representative instant of the development of the spark, either after or at the end of the spark generation control train.

• si la mesure réalisée à la fin du train de commande est inférieure à cette valeur seuil, on en déduit qu'il s'est produit un pontage ;
• si la mesure réalisée est supérieure à cette valeur seuil, on en déduit qu'il ne s'est pas produit de pontage.

If the measurement chosen is the measurement of the current in the resonator, we can then determine a threshold value M1, such that:

• if the measurement made at the end of the control train is below this threshold value, it is deduced that a bypass has occurred;
• if the measurement made is greater than this threshold value, it can be deduced that no bridging has occurred.

In the case where the measurement of the voltage at the terminals of the Cboost storage capacity is used, it is then necessary to consider the difference between the voltage at the terminals of this capacitor before (or at the beginning) and after (or at the end) of the spark generation control train. Indeed, the observation in particular of the voltage at the terminals of the Cboost storage capacity before ignition (it is then the regulated voltage setpoint at the terminals of this capacitor) and after ignition (measurement performed at the end of the train. command), allows to deduce the energy consumed by the resonator during the ignition. We can thus deduce the type of discharge performed, between no spark at all, branching and bridging, depending on the amount of energy that has been consumed by the resonator during the discharge.

• si la mesure réalisée à la fin du train de commande implique une énergie consommée inférieure à cette valeur seuil, on en déduit qu'il s'est produit un pontage (lequel diminue en effet la valeur d'énergie transmise au résonareur) ;
• si la mesure réalisée implique une énergie consommée supérieure à cette valeur seuil, on en déduit qu'il ne s'est pas produit de pontage.

Indeed, it can be shown that when bridging has occurred, the amount of energy absorbed is minimized. We can then determine in the same way as above, a threshold value M2 for which:

• if the measurement carried out at the end of the control train implies a consumed energy lower than this threshold value, it is deduced that a bridging has occurred (which in fact decreases the value of energy transmitted to the resonator);
• if the measurement carried out implies a consumed energy higher than this threshold value, it is deduced that no bridging has occurred.

However, it can be seen that a regulation based, as has just been explained, on a single measurement (of the current in the resonator or of the voltage on the storage capacity) per control train, preferably carried out at the end of the control train, is not robust enough. In fact, the measurement made is not only representative of the type of spark produced, but also of the frequency agreement between the supply circuit and the resonator, the fouling of the spark plug and other phenomena independent of the spark development.

Also, according to another mode, to achieve robust control, it is preferably carried out multiple electrical measurements during and / or before and / or after the control train. The analysis of the evolution of these multiple measurements makes it possible to extract more easily relevant parameters for the qualification of the development of the spark and thus to realize a regulation, in particular of the value of the intermediate voltage to be realized at the terminals of Cboost before ignition, more efficient.

In particular, the measurement of the evolution of the voltage at the terminals of Cboost during and / or before and / or after the duration of the control train is a carrier of numerous information about the branching of the spark. During the development of the discharge, the energy consumption of the resonator results in a voltage drop across the Cboost capacity, which can be followed. It is noted that an optimal branching of the generated spark is very energy consuming while the bridging phase greatly limits the consumption. The analysis of the voltage drop slopes at the terminals of Cboost thus makes it possible to detect the bridging and its instant of appearance.

It has also been seen that the analysis of the occurrence of the bridging may be based on the analysis of the input current envelope of the resonator. By performing multiple electrical measurements during and / or before and / or after the duration of the control train, we can then follow the evolution of this current envelope. Bridging systematically results in a sudden drop on the current envelope, while in the case of a branched discharge, the current envelope shows a slight decrease or a change in the envelope slower. It is thus possible to detect bridging phenomena by using "derivative" type mathematical tools applied to the multiple input current measurements of the resonator during and / or before and / or after the duration of the control train.

The regulation evoked so far to promote an optimal branching of the spark while avoiding the bridging phenomenon as much as possible acts preferably on the value of the intermediate voltage to be produced at the terminals of the Cboost storage capacitor for each ignition. The regulation process thus makes it possible to define a voltage setpoint to be reached at the beginning of each ignition, depending on the one hand, measuring signals representative of the operation of the engine and, on the other hand, electrical measurement signals representative of the type of spark generated.

However, other control parameters of the system can also be taken into account in the real-time control process and thus be adjusted during the operating time of the system, in the same manner as explained above with reference to the control of the system. value of the intermediate voltage across Cboost for each ignition.

The other operating parameters of the system involved in the development of the spark and likely to be modified during operation to adjust the system in real time are the resonator control frequency, the duration of the control pulse train. spark generation, or alternatively consisting of making multi-ignitions, the number of such control trains and the spacing between each train.

According to a preferred embodiment, the regulation according to the invention relates jointly to the value of the intermediate voltage across Cboost for each ignition and the duration of the control pulse train V1, controlling the generation of the spark.

To do this, the control module 20, or a similar module, is also used to generate the ignition control pulse train V1, the duration of which is then adjusted according to the measurement signals received and the memorized relationships. .

Indeed, the bridging phenomenon occurring during the train command and, generally, starting occur at the end of the control train, it can be avoided by shortening the duration of the control pulse train so as to stop it just before the bypass (or just after the desired effect on the control train). combustion).

However, this requires that the bridging does not occur at the very beginning of the control train and, moreover, it is necessary to know how to predict the time of appearance of the bridging so as to adjust the optimal duration of the control train accordingly. .

For these reasons, this technique of limiting the bridging probabilities by reducing the duration of the ignition control train can be considered in conjunction with the technique of regulating the supply voltage of the resonator. Indeed, regulating the supply voltage of the resonator, consisting in defining a reduced level of intermediate voltage across the Cboost capacitor before ignition, advantageously makes it possible to push the bridging phenomenon as far as possible from the start of the control train. .

According to one variant, it is proposed to control the resonator during ignition by means of a control signal in the form of a plurality of control pulse trains, each train having a very short duration, for example of order of 5 to 10 μs, so that no bridging has time to occur. In this variant of making multi-ignitions, it is necessary to reproduce the control trains a number of times, of the order of 2 to 50 times, for example, to ensure sufficient energy transfer to the mixture of which one seeks to initiate combustion. In addition, to allow good dissociation between the trains and thus avoid bridging, the spacing between the different pulse trains of the control signal can be regulated in the direction of an increase. The ignition time is however increased, which may be unfavorable to the conditions of initiation of the mixture.

Also, during ignition, the frequency of the resonator control signal is preferably chosen from the order of magnitude of the resonance frequency of the resonator 6. Indeed, the match between the resonance frequency of the resonator and the resonator frequency at which this is controlled (ie the frequency of the control signal), determines the ratio between the voltage amplitude at the input and the output of the resonator. Thus, by preferably using a control frequency substantially equal to the resonance frequency of the resonator, the resonator efficiency is favored, insofar as its overvoltage coefficient Q is then the highest possible.

However, in order to limit the voltage applied between the electrodes of the resonator and thus to limit the probabilities of appearance of the bridging phenomena, it is possible to consider degrading the overvoltage coefficient by shifting, for this purpose, the control frequency around the resonance frequency of the resonator. Thus, the value of the control frequency can also be subject to the anti-bridging regulation as explained above, by determining an optimum value of control frequency shifted with respect to the resonant frequency, as a function of the received measurements. (motor and electric operation). This parameter can be regulated alone, or together with the value of the intermediate voltage, the duration of the control train, or even together with the latter two parameters.

Claims (9)

1. Method of controlling a radiofrequency plasma generator, comprising:

   - a supply circuit (2) with a switch (9) controlled by a control signal (V1) in the form of at least one control pulse train, applying an intermediate voltage (Vinter) to an output of the supply circuit at the frequency defined by the control signal,

   - a resonator (6), connected to the output of the supply circuit and able to generate a spark between two electrodes (103, 106) when a high voltage level is applied to the output of the supply circuit, said method being characterized in that it comprises:

   - the reception of first measurement signals representative of the operation of a combustion engine,

   - the reception of second electrical measurement signals representative of the type of spark generated, and

   - the combined and real time regulation, according to the first and second measurement signals received, of the level of the intermediate voltage and of the duration of the control pulse train.
2. Method according to Claim 1, characterized in that, the control signal being generated in the form of a plurality of control pulse trains, the regulation relates to the number of said trains and the inter-train time.
3. Method according to Claim 1 or 2, characterized in that it comprises the storage of relationships between measurement signals and the value of the parameters to be regulated, the regulation consisting in determining and applying the value of the parameters to be regulated according to the measurement signals received and the stored relationships.
4. Method according to any one of the preceding claims, characterized in that the first measurement signals are chosen from the group comprising the engine oil temperature, the engine coolant temperature, the engine torque, the engine speed, the ignition angle, the intake air temperature, the manifold pressure, atmospheric pressure, pressure in the combustion chamber or the maximum pressure angle.
5. Method according to any one of the preceding claims, characterized in that the second measurement signals comprise at least one measurement of the voltage at the terminals of a storage capacitor (Cboost) supplying the intermediate voltage at the input of the resonator and/or at least one measurement of the current in the resonator (6).
6. Method according to Claim 5, characterized in that a first measurement of the voltage at the terminals of the storage capacitor (Cboost) is made before, or at the start of, the control pulse train, and a second measurement of said voltage is made after, or at the end of, the control pulse train.
7. Method according to Claim 5 or 6, characterized in that a plurality of measurements are performed during the control pulse train.
8. Method according to any one of the preceding claims, characterized in that it comprises the regulation of the control frequency to a setpoint value that is roughly equal to the resonance frequency of the resonator.
9. Device for generating radiofrequency plasma comprising:

   - a supply circuit (2) with a switch (9) controlled by a control signal (V1) in the form of at least one control pulse train, the switch applying an intermediate voltage (Vinter) to an output of the supply circuit at the frequency defined by the control signal,

   - a resonator (6), connected to the output of the supply circuit and able to generate a spark between two electrodes (103, 106) when a high voltage level is applied to the output of the supply circuit,

   said device being characterized in that it comprises a control module (20) suitable for implementing the method according to any one of the preceding claims.

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