EP2115296B1 - Control of a plurality of plug coils via a single power stage - Google Patents

Description

The present invention relates generally to systems for generating plasma between two electrodes of a spark plug, used in particular for radiofrequency ignition control of a gaseous mixture in combustion chambers of an internal combustion engine.

For such an application to automotive ignition plasma generation, plasma generation circuits incorporating coils-candles are used to generate multi-filament discharges between their electrodes, to initiate the combustion of the mixture in the chambers of combustion of the engine. The multi-spark plug is described in detail in the following patent applications in the name of the Applicant FR 03-10766 , FR 03-10767 and FR 03-10768 . Another example of a known system is described in US Patent 5,655,201 . Such a coil-plug is conventionally modeled by a resonator 1, whose resonant frequency F _c is greater than 1 MHz, typically close to 5 MHz. The resonator comprises in series a resistor R, an inductance L and a capacitance C. Ignition electrodes 10 and 12 of the coil-plug are connected across the capacitor C.

l'amplitude aux bornes de la capacité C est amplifiée, permettant de développer des décharges multi-filamentaires entre les électrodes de la bougie, sur des distances de l'ordre du centimètre, à forte pression et pour des tensions de crête inférieures à 30 kV.When the resonator is powered by a high voltage at its resonant frequency ${\mathrm{f}}_{\mathrm{vs}}(1/\left(2\mathrm{\pi }\sqrt{\mathrm{The}*\mathrm{VS}}\right),$

the amplitude across the capacitor C is amplified, making it possible to develop multi-filament discharges between the electrodes of the candle, on distances of the order of one centimeter, at high pressure and for peak voltages below 30 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 supply of such a coil-plug requires the use of a power supply circuit, capable of generating voltage pulses, typically of rise time of 100 ns, and amplitude of the order of 1 kV, at a frequency intended to be very close to the resonant frequency of the radiofrequency resonator of the coil-candle. 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 feed circuit, detailed elsewhere in the application for FR 03-10767 , is schematically represented at figure 2 . It conventionally uses a so-called "Class E power amplifier" assembly. This type of DC / AC converter makes it possible to create the voltage pulses with the aforementioned characteristics.

According to the embodiment of the figure 2 , the amplifier 2 comprises switch M for controlling the switches across the resonator 1, made according to this example in the form of a power MOSFET transistor.

Thus, a control device 5 generates and applies a control signal V1 to a control frequency on the gate of the power MOSFET M, via a control stage 3 shown schematically. In order to control the production of sparks between the electrodes of the coil-plug connected at the output of the amplifier when its resonator 1 is excited via the control signal V1, the latter is activated by the different ignition commands and is in the form of control pulse trains at the control frequency.

As described in the application for EP-A-1,515,594 a parallel resonant circuit 4 is connected between an intermediate voltage source Vinter and the drain of the transistor M. This circuit 4 comprises an inductance Lp in parallel with a capacitance Cp.

Near its resonance frequency, the parallel resonator transforms the intermediate voltage Vinter into an amplified voltage Va (illustrated in FIG. figure 5 ), corresponding to the intermediate voltage multiplied by the overvoltage coefficient of the parallel resonator. This amplified voltage is supplied on the drain of the transistor M, which is also connected to the input of the resonator 1.

The transistor M therefore acts as a switch and applies (respectively blocks) the voltage Va to the input of the resonator 1 when the control signal V1 is at the logic high (respectively low). The transistor M thus imposes a switching frequency, determined by the control signal V1, which is sought to make as close as possible to the resonant frequency of the coil-plug connected at the output (typically 5 MHz), in order to maintain and maximize the energy transfer between the parallel resonator 4 and the series resonator 1 forming the coil-candle.

At the resonance frequency of the coil-plug, then found across the capacitor C of the series resonator 1, either across the electrodes of the spark plug, the output voltage Va previously mentioned, multiplied by the overvoltage coefficient of the resonator series 1.

This phase of energy transfer from the power stage formed by the amplifier to the resonator of the coil-plug must be performed at the resonance frequency of the resonator, to ensure a good performance. Indeed, if the transistor M imposes a different switching frequency of the resonant frequency of the coil-candle, the energy transfer is degraded, because of the narrow bandwidth of the series resonator used for the candle coil .

In an automotive ignition application plasma generation, each combustion chamber is equipped with a coil-candle as described above to initiate, on command, combustion.

Consequently, for 4-cylinder engines, for example, it is necessary to have four power supply circuits of the class E amplifier type, as described above with reference to FIG. figure 2 , to feed and control the four bobbins respectively.

Such a configuration thus relying on as many amplification channels as there are spark plugs to be controlled limits the development potential of this type of automotive ignition by plasma generation, on the one hand because of the clutter caused by this installation under the bonnet, but also because of the cost of installation, which may be unaffordable to consider installing this type of ignition on standard vehicles.

The present invention aims to overcome this disadvantage, by allowing to control a plurality of coils-candles through the same and single amplification channel.

• un circuit d'alimentation, comprenant un interrupteur commandé par un signal de commande pour appliquer une tension intermédiaire sur une sortie du circuit d'alimentation à une fréquence définie par le signal de commande,
• au moins deux circuits de génération de plasma connectés en parallèle sur la sortie du circuit d'alimentation, chaque circuit de génération de plasma présentant une fréquence de résonance qui lui est propre et étant apte à générer un plasma lorsqu'un niveau haute tension est appliqué sur la sortie du circuit d'alimentation à une fréquence sensiblement égale à la fréquence de résonance du circuit de génération de plasma,
• un dispositif de commande du circuit d'alimentation, déterminant la fréquence du signal de commande parmi l'une des fréquences de résonance des circuits de génération de plasma, de façon à commander sélectivement chaque circuit de génération de plasma selon la fréquence de commande utilisée.

With this objective in view, the subject of the invention is a radiofrequency plasma generating device, characterized in that it comprises:

• a supply circuit, comprising a switch controlled by a control signal for applying an intermediate voltage to an output of the supply circuit at a frequency defined by the control signal,
• at least two plasma generation circuits connected in parallel with the output of the supply circuit, each plasma generating circuit having a resonant frequency of its own and capable of generating a plasma when a high voltage level is applied at the output of the supply circuit at a frequency substantially equal to the resonance frequency of the plasma generation circuit,
• a control device of the supply circuit, determining the frequency of the control signal among one of the resonance frequencies of the plasma generating circuits, so as to selectively control each plasma generating circuit according to the control frequency used.

According to an unclaimed embodiment, each plasma generating circuit comprises a resonator and each resonator comprises a distinct resonance frequency.

According to the invention, each plasma generation circuit comprises a resonator, each resonator having an identical resonance frequency, and at least one of the plasma generation circuits further comprises means for shifting the resonance frequency of its resonator.

Advantageously, the frequency shift means comprise an impedance matching circuit arranged in series between the output of the supply circuit and the resonator.

Preferably, the impedance matching circuit comprises an inductance.

According to one variant, the impedance matching circuit is constituted by an impedant connecting cable ensuring the connection between the output of the supply circuit and each resonator, the length of the portion of cable between the resonators defining the frequency offset. between the resonators.

Advantageously, each plasma generation circuit is adapted to achieve ignition in one of the following implementations: controlled ignition in a combustion engine cylinder, ignition in a particle filter, ignition decontamination in an air conditioning system.

• réception d'une requête de détermination d'une fréquence de commande ;
• détermination du circuit de génération de plasma à commander ;
• détermination d'une fréquence de commande sensiblement égale à la fréquence de résonance du circuit de génération de plasma à commander ;
• génération du signal de commande à la fréquence de commande déterminée.

The invention also relates to a method for controlling the power supply of a plasma generating device comprising a power supply circuit having a switch controlled by a control signal for applying an intermediate voltage to a frequency defined by the control signal on an output of the supply circuit, to which at least two plasma generating circuits are connected in parallel, each plasma generating circuit being arranged to be selectively controlled at a resonant frequency which is clean,
said method comprising the steps of:

• receiving a request to determine a control frequency;
• determining the plasma generating circuit to be controlled;
• determining a control frequency substantially equal to the resonant frequency of the plasma generating circuit to be controlled;
• generating the control signal at the determined control frequency.

• la figure 1 est un schéma illustrant un modèle électrique utilisé pour le résonateur modélisant une bobine-bougie de génération de plasma;
• la figure 2 est un schéma illustrant un dispositif de génération d'une haute tension intégrant un amplificateur, utilisé pour l'alimentation et la commande d'une bobine bougie;
• la figure 3 illustre un premier mode de réalisation de répartition des fréquences de résonance des bobines-bougies selon l'invention,
• la figure 4 illustre un deuxième mode de réalisation de répartition des fréquences de résonance des bobines-bougies selon l'invention,
• la figure 5 illustre un schéma complet d'un allumage radiofréquence comprenant N bougies-bobines selon l'invention ;
• la figure 6 illustre un organigramme d'un exemple de mise en oeuvre de la commande de l'allumage 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 is a diagram illustrating an electric model used for the resonator modeling a plasma generation coil-candle;
• the figure 2 is a diagram illustrating a device for generating a high voltage integrating an amplifier, used for powering and controlling a spark plug coil;
• the figure 3 illustrates a first embodiment of distribution of the resonant frequencies of the spark plugs according to the invention,
• the figure 4 illustrates a second embodiment of distribution of the resonant frequencies of the bobbins according to the invention,
• the figure 5 illustrates a complete diagram of a radiofrequency ignition comprising N candles-coils according to the invention;
• the figure 6 illustrates a flowchart of an example of implementation of the control of the ignition according to the invention.

The present invention therefore aims at controlling a plurality of coil-type plasma generation circuits, using a single amplification channel, in other words by using a single power supply circuit of the class E power amplifier type as previously described. to the figure 2 , for selectively supplying the plurality of plasma generation circuits connected in parallel at the output of this single supply circuit.

The principle on which this particular assembly is based consists in exploiting, at the level of the high voltage and high frequency control generated by the supply circuit, the resonance frequency specific to each plasma generation circuit connected at the output of the supply circuit. .

Indeed, it appears that a judicious distribution of the resonant frequencies of the plasma generation circuits makes it possible naturally to determine the desired power transfer from the supply circuit to one or the other of the plasma generation circuits. Thus, the same high voltage, applied simultaneously at the output of the power supply circuit at the terminals of the plurality of plasma generation circuits connected to it, selectively controls one of these plasma generation circuits, depending on whether the control frequency used at the power supply circuit is modeled substantially on the resonance frequency specific thereto.

The condition for allowing independent control of the plurality of plasma generating circuits through a single power supply circuit is therefore that each of these plasma generating circuits has a resonant frequency well separated from the others. This is indeed to avoid overlapping resonance frequency resonator domains forming each plasma generation circuit and thus to overcome the problems of multiple simultaneous ignitions.

The resonant frequency difference between the plural plasma generation circuits connected in parallel at the output of the single supply circuit must preferably be at least equal to a multiple of the bandwidth of each resonator. For example, it may be possible to shift the resonance frequency of each plasma generating circuit relative to each other by a value equal to two or three times the bandwidth of each circuit.

Several embodiments are possible to achieve such a frequency shift between the resonant frequencies of each plasma generation circuit.

A first way to do this is to use for each plasma generation circuit a coil-candle, as modeled at the figure 1 , different by construction, so that the coils-candles used have sufficiently distinct resonant frequencies in accordance with the principles outlined above.

This embodiment where each plasma generation circuit consists of a resonator as shown in FIG. figure 1 and where each resonator has a distinct resonant frequency, however, is not optimal for integration into an industrial process.

Indeed, it requires the adaptation of the industrial process to the production of a plurality of different types of coils-candles and then requires as many references of coils-candles as there are channels to control.

Also, with reference to Figures 3 and 4 , a preferred embodiment for carrying out the resonance frequency shift between the plurality of plasma generation circuits to be controlled, consists in using identical coil-plugs, the resonators of which model them have identical resonance frequencies, and to associate each resonator means for shifting its resonance frequency.

As illustrated in figure 3 , the resonance frequency shifting means of a plasma generating circuit comprises an impedance matching circuit 14, arranged to be arranged in series between the output of the supply circuit 2 and the resonator 1. In this way, the impedance-resonator pair forming the plasma generation circuit has its resonant frequency shifted with respect to the resonance frequency of the resonator 1 of the insulated coil-candle.

As illustrated in figure 5 the insertion of such impedance circuits of different respective values, respectively Z1, Z2, Z3 and Z4, in series between the output of the single supply circuit and each coil-candle respectively BB1, BB2, BB3 and BB4. , then makes it possible to achieve the desired distribution of the resonance frequencies of the plasma generation circuits connected in parallel at the output of the single supply circuit, according to the principles explained above.

The impedance values of the circuits 14 are thus chosen so that the difference in resonance frequency between each plasma generation circuit, each constituted by an impedance-resonator torque, is equal to at least one multiple of the bandwidth of each resonator.

It will be possible, for example, to use, for the added impedance circuits, inductances such that the resonance frequency of each plasma generation circuit is shifted by the desired value.

In the optics of an optimal performance of the supply circuit as well as an optimal operation of the coils-candles, it will be possible to use identical coils-candles whose resonant frequency is higher than the resonance frequency at which one wish to order the coils-candles. In this case, if the impedance circuits added are inductances, the effect of this addition must correspond to lowering the value of the overall resonant frequency of each inductance / coil-candle pair.

In a variant, it will be possible to use, for one of the channels to be controlled, a simple connection without adding additional passive element, such as an inductor, in series with the coil-candle.

According to another embodiment illustrated in figure 4 , the resonance frequency shifting means of a plasma generating circuit relative to another, use the connecting cable providing the connection between the output of the supply circuit and each coil-candle as series impedance, the coils -bougies are also identical, namely that their resonator have an identical resonant frequency. In this case, it is the length of the cable portion, respectively L1, L2, L3, between the spark-coils, respectively between BB1 and BB2, between BB2 and BB3 and between BB3 and BB4, which acts as an impedance , in particular of inductance, and thus defines the resonator frequency offset between the resonators of the coils-candles.

The fact of using an impedant cable between the spark-coils advantageously makes it possible to dispense with the use of additional components for the shifting of the spool-candles in frequency, as required by the embodiment of the invention. figure 3 .

The resonance frequencies of the different channels being distributed independently according to the principles described above, the control method of the single power supply circuit must then take into account the frequency adapted to the channel to be controlled for each ignition.

To do this, according to one embodiment, the control device 5 of the power supply circuit can have a memory capable of preserving the order of frequency classification corresponding to each of the channels to be controlled.

So, according to the example of the figure 6 Referring to an automotive ignition application for a four-cylinder combustion engine, upon receipt of an ignition request, the control device is firstly able to determine the cylinder to be controlled, numbered for example from 1 to 4 in the order of disposition on the motor. Each cylinder number is therefore associated with the resonance frequency, F1, F2, F3 and F4 respectively, specific to the corresponding plasma generating circuit to be controlled.

The control device then comprises a module determining the frequency of the control signal to be generated, among these frequencies F1, F2, F3 and F4, as a function of the number of the cylinder to be switched on and the order of classification of the frequencies previously memorized.

Once the control frequency has been determined, the control device applies the control signal to said frequency on an output interface intended to control the switch M.

The selective power transfer to the plasma generating circuit to be controlled for ignition is then naturally managed by the control frequency used for this ignition.

According to a particular embodiment, the determination of the resonant frequencies to be obtained at the output of the single feed circuit can be controlled by tabulation or servo-control methods as described in the French patent applications filed in the name of the Applicant. FR 05-127669 and FR 05-12770 .

For example, the control device may be provided with an interface for receiving engine operating parameter measurement signals (engine oil temperature, engine torque, engine speed, ignition angle, air temperature). inlet, pressure in the combustion chamber, etc.) and / or power supply operating parameter measurement signals, as well as a particular memory module storing relationships between measurement signals and the frequency of a control signal to be generated. The controller then determines the frequency of a control signal to be generated based on measurement signals received on the receiving interface and relationships stored in the memory module.

Other applications than the achievement of a controlled ignition of combustion engine can be envisaged without departing from the scope of the present invention, such as the realization of ignition in a particle filter, or ignition of decontamination in an air conditioning system.

Claims (6)

1. Radio frequency plasma generating device, characterized in that it comprises:

   - a power supply circuit (2), comprising a switch (M) controlled by a control signal (V1) for applying an intermediate voltage (Vinter) to an output of the power supply circuit at a frequency defined by the control signal,

   - at least two plasma generation circuits (BB1, BB2, BB3, BB4) connected in parallel to the output of the power supply circuit, each plasma generation circuit having its own resonance frequency and being capable of generating a plasma when a high voltage level is applied to the output of the power supply circuit at a frequency roughly equal to the resonance frequency of the plasma generation circuit,

   - a device (5) for controlling the power supply circuit, determining the frequency of the control signal from one of the resonance frequencies (F1, F2, F3, F4) of the plasma generation circuits, so as to selectively control each plasma generation circuit according to the control frequency used, characterized in that each plasma generation circuit comprises a resonator (1), each resonator having an identical resonance frequency, and in that at least one of the plasma generation circuits also comprises means of shifting the resonance frequency of its resonator.
2. Device according to Claim 1, characterized in that the frequency-shifting means comprise an impedance matching circuit (14) positioned in series between the output of the power supply circuit and the resonator.
3. Device according to Claim 2, characterized in that the impedance matching circuit comprises an inductance.
4. Device according to Claim 3, characterized in that the impedance matching circuit comprises an impeding link cable providing the connection between the output of the power supply circuit and each resonator, the length (L1, L2, L3) of the portion of cable between the resonators defining the frequency shift between the resonators.
5. Device according to any one of the preceding claims, characterized in that each plasma generation circuit is designed to produce an ignition in one of the following implementations: controlled ignition in a combustion engine cylinder, ignition in a particle filter, decontamination ignition in an air conditioning system.
6. Method of controlling the power supply of a plasma generating device, comprising a power supply circuit (2) having a switch (M) controlled by a control signal (V1) for applying an intermediate voltage (Vinter) at a frequency defined by the control signal to an output of the power supply circuit, to which at least two plasma generation circuits are connected in parallel, each plasma generation circuit comprising a resonator (1), each resonator having an identical resonance frequency, at least one of the plasma generation circuits also comprising means of shifting the resonance frequency of its resonator, each plasma generation circuit being designed to be selectively controlled at its own resonance frequency,
   said method comprising the steps of:

   - reception of a request to determine a control frequency;

   - determination of the plasma generation circuit to be controlled;

   - determination of a control frequency that is roughly equal to the resonance frequency of the plasma generation circuit to be controlled;

   - generation of the control signal at the determined control frequency.

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