WO1997022803A2

WO1997022803A2 - Internal combustion engine ignition system monitoring device

Info

Publication number: WO1997022803A2
Application number: PCT/FR1996/001998
Authority: WO
Inventors: André AGNERAY; Eric Morillon
Original assignee: Renault
Priority date: 1995-12-15
Filing date: 1996-12-13
Publication date: 1997-06-26
Also published as: EP0866917A2; FR2742486B1; WO1997022803A3; FR2742486A1

Abstract

An internal combustion engine ignition system monitoring device including a measuring circuit for measuring the gas ionisation current in the cylinders. The circuit is connected to the secondary winding (L2) of the coil in parallel with the spark plug (3), and consists of a capacitor (6) that is charged when the ignition intake arrives and discharged when the spark stops, by two series of diodes (D1, D2) arranged head-to-tail, a current-limiting resistor (R), isolating means (9) between the coil and the spark plug, and an electronic ionisation signal processing system for sensing ignition control, the continuity of the ignition system, the charge of the measuring circuit, combustion, the presence of controlled aerodynamics or breakage of a spark plug.

Description

DEVICE FOR MONITORING THE IGNITION SYSTEM OF AN INTERNAL COMBUSTION ENGINE

The invention relates to a device for monitoring an ignition system of an internal combustion engine, the ignition of which is electronically controlled. This device must detect combustion faults and their causes, in particular a faulty ignition.

Currently, to lower fuel consumption and to meet increasingly stringent anti-pollution standards, requiring, among other things, the use of a catalytic converter and the operation of the engine in a closed loop, it is important to know the quality of combustion. In addition, to meet the new diagnostic standard On Board Diagnostic II (0.BD II), it is essential to detect any absence of persistent combustion in order to inform the driver of the vehicle. In the case of detection of combustion anomalies, it is essential to know the type of existing fault, such as rattling, fouling of spark plugs, malfunction of the ignition coil, etc. a gasoline engine, with spark ignition, the latter is produced, for each cylinder, by an ignition source - generally a single spark plug - and the propagation of a deflagration. The ignition device brings energy to a very localized area of the cylinder filled with the air-petrol mixture, in order to trigger its combustion. It is an auto-ignition produced by a spark, the temperature of which is greater than 3000 ° C. and which bursts between the electrodes of the spark plug. For a good functioning of the engine, it is necessary to detect the "misfire", that is to say misfires of combustion corresponding to a total absence of combustion in the chamber, due to a misfire of ignition for example or corresponding poor combustion in one or more cylinders. This can be damaging for the catalytic converter into which unburnt fuel is sent, which causes oxidation on contact with the very hot medium, which can destroy the catalyst. Abnormal combustion can also cause a rattling noise damaging to the cylinder head gasket and pistons.

One of the causes of poor combustion is misfiring, due to candles clogged with carbon residues which prevent the spark, or drowned by an excessive supply of gasoline in a cold cylinder which disturbs the electric discharge, or still whose electrodes are too far apart to allow an electric arc. Currently, there is a SAAB Trionic system that uses the measurement of the degree of ionization of gases in the cylinders, using spark plugs that serve as probes to study what happens in the combustion chamber while the engine is running. It is a capacitive ignition system, the current in the primary winding charging at 400 volts a capacity which is suddenly discharged in the secondary winding of the ignition coil. During the combustion of the air-fuel mixture, the temperature increases, the gases ionize and it is interesting to measure the current between the electrodes. For this, the SAAB system measures the current at the low voltage terminal of the secondary winding of the coil. The main drawback is that this current is only partially representative of the ionization current because the high frequency part of the signal is absorbed. In addition, it is necessary to supply the capacity at medium voltage, which is not naturally found in a motor vehicle except by using DC-DC converters. The choice of a capacitive ignition does not ensure combustion for all air-fuel mixtures. The object of the invention is to detect misfires and to identify the cylinder or cylinders in which they occurred, regardless of the number of cylinders of the engine and in all of its operating conditions.

For this, the object of the invention is a device for monitoring the ignition system of an internal combustion engine comprising, per cylinder, at least one spark plug between the electrodes of which a spark is created, comprising at least one ignition coil, the primary winding of which is connected to an ignition control module and the secondary winding of which is connected to an electrode of at least one spark plug, the second electrode of which is connected to ground, characterized in that '' it includes a circuit for measuring the ionization current of the gases in the cylinders, connected to the secondary winding of the coil and placed in parallel with the spark plug, and consisting of:

- Means for supplying the measurement produced by a capacitor which charges when the ignition front arrives and discharges when the spark stops;

means for converting the ionization current from the spark plug into voltage, produced by two series of head-to-tail diodes at the outlet of which the measuring point is located; - means for limiting the current flowing through the conversion means, at the time of charging the capacity, constituted by a resistor;

- isolation means placed between the coil and the spark plug and intended to allow the high voltage signal delivered by the secondary winding to pass at the time of ignition, and to isolate the measurement circuit when the spark is stopped ; and an electronic system for processing the ionization signal measured at the output of the conversion means. Other characteristics and advantages of the invention will appear on reading the description which follows, illustrated by the various figures which are:

- Figures 1 and 3 are two examples of ignition, respectively distributed and semi-static, comprising the monitoring device according to the invention;

- Figures 2 _a to 2 ^ are representations of the voltage and current signals appearing in an ignition system; - Figure 4 shows the ignition system monitoring device according to the invention;

- Figure 5 is an electrical diagram of the measuring circuit of the monitoring device according to the invention; - Figures 6 to 10 are electrical diagrams of different embodiments of the measurement circuit according to the invention;

- Figure 11 is the temporal representation of the ionization current, measured by the monitoring device according to the invention;

- Figure 12 is the electronic diagram of the detection means of the ignition control of the monitoring device according to the invention; - Figure 13 is the electronic diagram of the means for detecting the continuity of the ignition circuit according to the invention;

- Figures 14 and 15 are the electronic diagrams of two embodiments of the load detection means of the measurement circuit according to the invention;

- Figure 16 is an electronic diagram of an embodiment of the combustion detection means in the cylinders, according to the invention; - Figure 17 is an electronic diagram of an embodiment of the means for detecting the presence of controlled aerodynamics according to the invention;

- Figure 18 is an electronic diagram of an embodiment of the means of detecting a spark plug break according to the invention.

The elements bearing the same references in the different figures fulfill the same functions for the same results. According to a first embodiment of a conventional distributed ignition, represented in FIG. 1, the ignition system which creates the spark at the terminals of the spark plug assigned to each cylinder and which is controlled by a computer. electronic ignition, includes an ignition coil 1 whose primary winding L-, is connected on the one hand to the positive voltage of the vehicle battery, equal to 12 volts, and on the other hand to a control module d ignition 100 by means of a transistor 2. The secondary winding L ₂ of the coil is connected on the one hand to the 12 volts of the battery and on the other hand to each of the spark plugs 3 of the engine, successively by l 'Intermediate of an electromechanical distributor 32. The operation of the ignition system is as follows, described in relation to Figures 2 to 2 _ή . The module ignition control 100 produces a rectangular control signal S _c (Figure 2 _a ) which switches the transistor from the off state to the saturated state, at time t- ₁ . The current I ₁ flowing in the primary winding L- ^ increases to a maximum value 1- ^ due to current regulation, reached at time t ₂ (Figure 2 ^) and the energy accumulates during that the voltage V ₂ at the terminals of the secondary winding goes from a value equal to the battery voltage (12 volts) to a higher value (1 kilovolt) until time t ₂ when it drops to 100 volts, because the variation of the flux is not zero and the energy stabilizes (Figure 2). Then, at time t- _j , the control signal S _c switches from its maximum value 1, equal to a few volts, to its minimum value 0, blocking the transistor 2. The sudden interruption of the current l _j in the winding primary causes a high overvoltage which is amplified by the transformer in the secondary winding whose voltage V ₂ at its terminals has a peak at time t ₃ (Figure 2), reflecting a sudden drop in its value of the order of 40 kilovolts, which causes a breakdown at the spark plug electrodes. At the instant t ₃ of the spark, a current I 'circulates in the secondary circuit due to the transfer of the energy accumulated in the primary winding during the charging phase (Figure 2 ^). Then the discharge of the coil being completed at time t., The voltage V ₂ is close to zero and the current I ′ and the voltage V at the terminals of the spark plug become zero until the next charge cycle.

In the case of a second embodiment of a semi-static ignition, the ignition system comprises two ignition control modules which supply each, as shown in Figure 3, two candles 3 and 3 'assigned to cylinders offset by 360 degrees crankshaft. These two spark plugs produce two almost simultaneous sparks, one for a cylinder in compression whose air-gasoline mixture is thus ignited, the other for a cylinder in exhaust. In the case of such a semi-static ignition or double output coil, a coil supplying two cylinders, the two spark plugs are of opposite polarities. The device 4 for monitoring the ignition system according to the invention is intended to measure and process the ionization current between the electrodes of each spark plug which, outside the breakdown periods, is used as a probe for measuring the current appearing between its terminals when a voltage of the order of 200 volts is applied between its two electrodes. This monitoring device is placed in parallel on one or one of the two spark plugs 3 and connected to one of the terminals 7 of the secondary winding L ₂ of the ignition coil 1 which sends it the high ignition voltage (FIGS. 1 and 3). It comprises, as shown in FIG. 4, first of all a circuit 5 for measuring the ionization current, to which is then associated a system 6 for processing this current, intended to detect in particular the ignition command (14 ), the continuity of the ignition circuit (18), the load of the measurement circuit (22), the presence of controlled aerodynamics (33), the combustion (29) and the polarization of the cylinder, or even the candle wear, as described below. This processing system can be supplemented by display and / or alarm means 8, or by means of taking into account the information thus detected by the electronic engine computer or computers, or by the catalytic converter in the aim of improving the functioning of the engine in the following engine cycles.

The measurement circuit 5, detailed in FIG. 5, of the ionization current associated with a cylinder, is placed in parallel on the spark plug 3 and connected to one of the terminals 7 of the secondary winding L ₂ of the ignition coil . It includes isolation means 9 placed on the high voltage cable 10 connecting the coil to the spark plug and intended to allow the high voltage signal to pass physically at the time of ignition and to isolate the measurement circuit when the '' spark so as not to interfere with the operation of the motor and to restore it after bursting, and to physically allow only the high voltage signal. These isolation means can be the distributor itself, or a primary spark gap - the second spark plug in the case of semi-static ignition -, or even a high voltage diode of 1 to 2 kilovolts. The measurement circuit then comprises means 11 for supplying the measurement, produced by a capacitor C which charges when the ignition front arrives and discharges when the spark stops. A Zener Z diode can be added in parallel, which regulates the amount of energy stored in the capacitor C, regardless of the maximum value of the ignition front. The Zener diode also serves to prevent charging of the capacitor C in the opposite direction, thus avoiding a change in sign of the measured ionization signal. This capacitance C will supply the spark plug with a DC voltage of between 50 and 200 volts at most, measuring the ionization of the gases between its electrodes. The measurement then consists of determining the current flowing in the spark plug, from which the ignition problems will be detected. The voltage of 200 volts is supplied by the discharge of capacity C which will have been charged before by the energy of the bursting of the spark and chosen to support high tensions. This capacity is of the order of 100 picofarads to 10 nanofarads and the Zener diode from 50 to 300 volts.

The ionization current from the spark plug is converted into voltage by conversion means 12, produced for example by two series of head-to-tail diodes O- ^ and D ₂ used as logarithmic current-voltage transformer due to the increase amplitude of the ionization signal with engine speed. The output point of the measurement circuit according to the invention, called measurement point P, is located at the output of these conversion means 12. These diodes can be placed asymmetrically, 2 or 5 in the direction of the measurement of the combustion, therefore of the discharge of the capacity C and 1 in the direction of its charge, as shown in Figure 6, which is a diagram electronics of an exemplary embodiment of the circuit according to the invention using a negative high voltage, in single spark ignition, whether or not distributed with a pencil coil, for example. Two pairs of diodes can also be used, as shown in FIG. 7, which is an electrical diagram of another embodiment of the circuit according to the invention using a high negative voltage. In addition, the presence of several diodes makes it possible to amplify the signal from the spark plug or serves to limit the input voltage of a current amplifier, linear or not, used for measuring the current. The circuit finally comprises means 13 for limiting on the one hand, the current which flows through the conversion means 12, at the time of charging the capacitor C and on the other hand, coupled to the Zener diode Z, the maximum current which cross the capacity during the measurement of the ionization current which takes place at the point P _m located between the means 13 of limitation and the means 12 of conversion. These limiting means, which also define the charging period of the capacity C, are constituted by a resistance R, of value such that the time constant which it produces with the capacity C, r = R * C, is equal to the duration of the spark, of the order of 2.5 ms. For this, this resistance R is between 0.2 and 100 mega-ohms. These three supply means 11, limitation 13 and conversion 12 connected in series are placed in parallel with the two electrodes of the spark plug 3. This spark plug is generally provided with a resistor R ′ in series intended to limit the parasites. In the case of a distributed ignition, a measuring circuit according to the invention is provided per cylinder, because the arc in the distributor stops before the combustion signal is finished. In the case of a semi-static ignition, for which the secondary winding of the coil is connected to each of its two terminals to a spark plug and filters the signal from the spark plug slightly, a single circuit can be provided for two cylinders, the insulation being provided by said spark plug. Figure 8 is an electrical diagram of a first embodiment of such a measurement circuit used in the case of a semi-static double spark ignition, its connection being made to the positive terminal of the coil. However, for better separation of the two spark plugs, a coil can be used, one terminal of which is connected to the high-voltage circuit via a high-voltage diode and a measurement circuit per cylinder, as shown in the electrical diagram of Figure 9, showing a second embodiment of a measuring circuit according to the invention for a semi-static double spark ignition. This assembly, comprising two measurement circuits, two high voltage cables and delivering two output signals, can be used to distinguish the cylinder in combustion and that in exhaust.

The respective positions of the supply means, that is to say the capacitance C in parallel with the Zener diode Z, and of the current limiting means, that is to say the resistance R, can permute with respect to the two series of diodes, as shown in the electrical diagram. in Figure 10.

This ionization current measurement circuit, according to the invention, delivers a signal S _m at the measurement point P _m whose temporal representation makes it possible to distinguish several phases. FIG. 11 represents the ionization signal S _m as a function of time, measured by a circuit supplied by a negative high voltage and in the form of a voltage which is a monotonic function of the ionization current in the spark plug, in the case of the amplifier. The signal is of reverse sign if the measurement is made for positive high voltage. The phase FI, comprised between the instants t- ^ and t ₃ , corresponds to the charge of the ignition coil, the phase F2, between the instants t ₃ and t ₄ , corresponds to the duration of the spark, and the phase F3, between instants t ₄ and t ^, corresponds to the presence or absence of combustion in the cylinder, or to combustion with controlled aerodynamics of the mixture. The processing of this signal will make it possible to detect the actual operation of the engine.

In what follows, we place ourselves in the case of the signal of FIG. 11, that is to say for a measurement on the wire. negative high voltage, to explain the treatment.

To carry out the processing of the signal S _m , the monitoring device according to the invention further comprises means 14 for detecting the ignition control shown in the electronic diagram of FIG. 12. The high voltage insulating diode D, because 'it is slightly capacitive, lets through part of the signal corresponding to the primary load, which generates about 1 kilovolt in secondary. This signal modifies the state of charge of the measurement capacitor C, passes through the Zener diode Z and is detected by the current measurement stage in the form of a voltage peak p ^. The detection of the presence of the ignition control signal emitted by the ignition control module 100, or the ignition-injection computer of the vehicle, amounts to detecting this voltage peak p ^ and the means of this detection are constituted by means of comparison 15 of the measured signal S _m with a voltage threshold determined by the isolation means as a function of the probable value of the voltage peak, delivering a binary signal S - ^ of value equal to 1 if S is greater than the threshold, and equal to 0 otherwise. To be sure of detecting the control signal, between the instants t- ^ and t ₃ corresponding to the charge of the ignition coil, and not during the combustion phase, the signal SI is then sent to one of the inputs an AND logic circuit 16, the other input of which receives the ignition control signal S delivered by the ignition module or the ignition-injection computer. This ignition control signal is in the form of a rectangular signal of suitable duration corresponding to the load of the coil. This AND circuit delivers a signal logic S ₂ of value 1 when ignition control is detected and of value 0 in the event of a problem. The signal S- can also be compared, temporally or angularly, to the position of the top dead center TDC of the cylinder in which the spark took place, in comparison means 17, in order to measure the degree of advance on ignition.

The monitoring device according to the invention also comprises means 18 for detecting the continuity of the ignition system, represented on the electronic diagram of FIG. 13. The ionization signal (FIG. 11) can have a voltage variation, with possible sign changes, in the case where the circuit is continuous up to the measurement circuit. On the other hand, in the case where the circuit is interrupted just before the spark plug, the spark signal will be modified, and in the case where the break takes place before the measurement circuit, no signal is detected. The means for processing the measured signal S _m are intended to detect on the one hand the presence of the control signal S between the instants t- ^ and t ₃ ensuring the continuity of the measurement circuit, and on the other hand the presence of a negative high voltage representative of a spark in the spark plug ensuring continuity of the circuit to it. For this, they are constituted by means of comparison 19 of this measured signal with a positive threshold intended to signal the continuity of the measurement circuit by a logic signal S-, equal to 1 when the signal is greater than the threshold and, in the otherwise equal to 0, and by comparison means 20 with a negative threshold intended to signal the presence of a negative high output voltage by a binary signal S. equal to 1, but equal to 0 otherwise. By extending the release of the first means of comparison 19 for a few milliseconds, by a monostable circuit for example, the two output signals S ₃ and S ₄ are then combined in an AND logic circuit 21 which provides a global binary signal S ₅ of problem detection information or not.

The monitoring device according to the invention can also be provided with means 22 for detecting the load of the measurement circuit shown in the electronic diagram of FIG. 14. Indeed, at the instant of the spark, the signal of ionization presents a voltage plateau between instants t-, and t ₄ , if there is charge, with a possible brief reversal of the possible polarity at the end of the spark, represented by a second voltage peak p ₂ , in a semi-static ignition (figure 11). The detection means 22 comprise a circuit 23 generating a pulse S ₆ , created after a time delay of 0.5 to 1 ms triggered by the falling edge of the ignition control signal S coming from the ignition control module 100. Simultaneously, the signal of measured ionization S is compared to a fixed negative threshold in the case of a negative coil output polarity, in comparison means 20, identical to the means 20 described in FIG. 13, which deliver a binary signal S ₄ equal to 1 if the current is less than the threshold, otherwise equal to 0. The pulse S ₆ is sent to the "trigger" of an electronic flip-flop 25 of type D, in which enters the binary signal S ₄ , this flip-flop delivering a signal S _g of information on the existence of a normal charge or not at the time of the spark. Equivalently, the information S ₄ of the existence of a spark can then be integrated over a period which follows the command S _c as shown in FIG. 15, in an integrator 27 delivering a signal S ± _Q I then compared to a positive duration threshold in a comparator 28 to obtain information on the quality of the spark by measuring its duration, this latter information being in the form of a pulse S-, -, equal to 1 when the compared signal is greater than the duration threshold, knowing that the normal duration of a good quality spark is a few milliseconds. The monitoring device according to the invention also allows the detection of the combustion in the cylinder as well as the coding of the cylinder. Indeed, the ionization signal of FIG. 11 presents, after phase F ₂ corresponding to the spark, that is to say a rise C- ^ with a clear change of sign in the case of combustion carried out in the cylinder where s' the spark is produced, ie an ascent C ₂ simply towards the value zero in the case where no combustion has been started. In addition, in semi-static ignition, the comparison between the ionization signals coming from two cylinders in which a spark took place at the same time, makes it possible to easily distinguish the cylinder in combustion from that in exhaust, this information having to be taken into account on condition of comparing it to the injection control which can be cut in certain cases. The phase of the F ₃ ionization signal between the instants t ₄ and t ₅ corresponds to the combustion signal and, according to the invention, is processed to verify the current measured after the ignition command and after the spark signal of phase F ₂ . For this, the combustion detection means 29, represented in the electronic diagram of FIG. 16, are constituted by detection means 30 of the last phase of the ionization signal, receiving as input the signal S _c of controlling ignition and ionization signal S measured in order to extract the latter phase of the signal s p ^c which starts artir the first rising edge of Sm appearing after the falling edge of the control signal S _c - S ₁₂ signal thus obtained passes into integration means 31 over time, for 5 to 10 ms or 90 to 180 ° of crankshaft angle for example, which deliver a signal S ₁₃ which is then compared to a fixed voltage threshold in comparison means 32. The output signal Ξ-, ₄ of the latter gives information on combustion or non-combustion in the cylinder where the spark occurred. The monitoring device according to the invention also makes it possible to detect the presence of controlled aerodynamics. In fact, the ionization signal of FIG. 11 can have, during the combustion phase, successive maxima M ^, M ₂ , corresponding to the passages of alternately burnt and unburnt media. The variations on a very small scale correspond to the folding of the combustion front, the variations on a large scale correspond to the successive passages of the combustion core in front of the spark plug. This information can be used to verify the proper functioning of an aerodynamic component. The desired signal is obtained either by smoothing the signal on a large scale and by checking that there are maximums detected by bandpass filtering, or by using successive signals to remove part of the rapid variations due to the folding of the flame and by filtering. We can also reuse the combustion presence signal described above and pass it through a bandpass filter before comparing it to an amplitude or power threshold, as shown in Figure 17. This Figure 17 is the diagram electronics of an example of means 33 for detecting the presence of controlled aerodynamics, consisting firstly of trigger means 34 on the falling edge of the ignition control signal S _c creating a rectangular pulse S ₁₅ of 120 ° or 9 ms duration, and on the other hand by means of comparison 35 of the ionization signal measured S _m with a fixed positive threshold, delivering a pulse signal S ₁₆ each pulse of which is representative of a maximum of the signal of combustion, sent like the pulse S ₁₅ to an input of an AND logic gate 36, the binary output signal of which gives information on combustion or non-combustion. This signal S, ₇ passes through a bandpass filter 37, from which a threshold is exceeded either on the amplitude by comparison means 38 with a positive threshold delivering a signal having as many pulses as there are of maxima in the. ionization signal, ie on the power output of the filter by means 39.

The monitoring device according to the invention can also comprise means for detecting the fouling of the candles. A dirty candle is generally modeled as a resistance of a few mega-ohms in short circuit. If it does not prevent the breakdown of the spark, the latter will clean it up. On the other hand, if it prevents breakdown, there is a modification of the load signal of the measurement circuit of the monitoring device of the invention and an absence of combustion. As shown in Figure 11, the spark signal e-, is much shorter in the event of non-breakdown - less than 0.25 ms instead of a few milliseconds usually -. Reduced short circuit resistance this time again and weakens the negative maximum of the spark signal.

For this, the device includes the detection means shown in Figure 15 and already described, the duration threshold in this case being much lower.

It is also possible to detect a rupture of a spark plug in the vehicle. The insulator of the spark plug, as a result of a thermal shock or because of vibrations, can crack or break and the invention then makes it possible to detect the presence of a spark followed by the absence of combustion. For this, as shown in FIG. 18, it suffices to combine the means 29 for detecting a combustion (FIG. 16) and the means 22 for detecting a spark of good quality (FIG. 15), both operating at starting from the control signal S and the measured ionization signal S _m , and entering their respective output signals S ₁₄ and S ,, in a flip-flop 40 which delivers information on the normal operation or not of the spark plug.

It is also possible to detect the wear of the spark plugs revealed by the very long-term variations in the ionization signal. This wear information is obtained by averaging a point of the signal or a fixed part of it, but the times to be taken into account being very slow - on the scale of 10 to 100,000 km - it a memory must be added to the detection means. We can only do the averages over a hundred cycles when the engine is running at idle, in stable phase, following a cold start to maintain relatively constant measurement conditions. In certain cases of an ignition system, it can be envisaged to amplify the signal S _m representative of the ionization current by a monotonic function before carrying out the electrical treatment, without this modifying the preceding description.

The monitoring device according to the invention has the advantage of not making any modification to the semi-static ignition coil system, the device being interposed between the secondary of the ignition coil and the spark plug. It is also completely industrializable and compact, which is particularly appreciable for measurements under the hood. It also has excellent robustness and ease of use thanks to its easy connection. In addition, there is no need for an external power supply since it takes only a small part of the high voltage signal. In the case of ignition with a coil of the coil-pencil type, the device can be associated or integrated with this coil. It is the same for certain types of candle in the housing of which it is possible to integrate the device.

Claims

1. Device for monitoring the ignition system of an internal combustion engine comprising, per cylinder, at least one spark plug between the electrodes of which a spark is created, comprising an ignition coil whose primary winding is connected to an ignition power module, the secondary winding of which is connected to an electrode of at least one spark plug, the second electrode of which is connected to ground, between the electrodes from which sparks are created, characterized in that it comprises a circuit for measuring (5) the ionization current of the gases in the cylinders, connected to the secondary winding (L ₂ ) of the coil (1) and placed in parallel with the spark plug (3), and consisting of: - means for supplying (11) the measurement produced by a capacitor (C) which charges when the ignition front arrives, and discharges when the spark stops;

- means for converting (12) into voltage, the ionization current from the spark plug, produced by two series of head-to-tail diodes (D- ^ and D ₂ ), at the outlet of which is the measuring point (P );

- means (13) for limiting the current flowing through the conversion means (12), at the time of charging the capacitor (C), constituted by a resistor (R);

- means (9) of insulation placed between the coil (1) and the spark plug (3) and intended to let pass the high voltage signal delivered by the secondary winding at the instants of ignition, and to isolate the measurement circuit stopping the spark; and an electronic system for processing the ionization signal ( ^s _m ) measured at the output of the conversion means (12).

2. Monitoring device according to claim 1, characterized in that the means (11) for supplying the measuring circuit (5) also comprise a Zener diode (Z) in parallel on the capacitor (C), which regulates the quantity of energy stored in the capacity (C), whatever the maximum value of the ignition front and which, coupled to the means (13) for limiting the current, limits the maximum current which flows through the capacity during the measurement of the current ionization (S _m ).

3. Monitoring device according to claims 1 or 2, characterized in that the means (12) for converting the measurement circuit (5) consist of a first series of diodes passing in the direction of the combustion measurement in greater number the number of diodes of the second series passing in the direction of discharge.

4. Monitoring device according to claims 1 or 2, characterized in that the means (12) for converting the measurement circuit (5) consist of two pairs of head-to-tail diodes.

5. Monitoring device according to claims 1 or 2, characterized in that the means (9) for isolating the measurement circuit (5) are constituted by a primary spark gap or by a high voltage diode.

6. Device for monitoring a distributed type ignition system comprising an electromagnetic distributor (32) connecting the ignition coil (1) successively to each spark plug of the engine, characterized in that it comprises a measurement circuit ( 5) according to claims 1 to 5 per engine cylinder and in that the means (9) of insulation are constituted by the distributor (32) itself.

7. Device for monitoring a semi-static type ignition system in which each of the two terminals of the secondary winding (L ₂ ) of the ignition coil (1) is connected to a spark plug, characterized in that that it comprises a single measurement circuit provided for two cylinders, one of which operates in combustion while the other operates in exhaust, and in that the means (9) of insulation consist of the spark plug connected to the cylinder in exhaust.

8. Device for monitoring a semi-static type ignition system in which each of the two terminals of the secondary winding ( ^L 2 ^ of the ignition coil (1) is connected to a spark plug, characterized in that that it comprises a measuring circuit (5) per cylinder, each connected to a spark plug, and in that one of the terminals of the ignition coil is connected to the high voltage circuit by means of a high diode voltage (D).

9. Monitoring device according to claims 1 to 8, characterized in that the processing system (6) of the measured ionization signal is connected to display and or alarm means (8).

10. Monitoring device according to claims 1 to 8, characterized in that the processing system (6) of the measured ionization signal comprises detection means (14) of the ignition control constituted by:

- Means (15) for comparing the measured signal (S_) with a determined voltage threshold, delivering a binary signal (S- ^) of value equal to 1 if the measured signal (S) is greater than the threshold, and equal to 0 otherwise;

- an AND logic circuit (16) receiving as input said binary signal (SI) and the ignition control signal (S _c ), and delivering a logic signal (S ₂ ) of value equal to 1 when there is detection of ignition command and value equal to 0 in the event of a problem;

- Means (17) for temporal or angular comparison of the signal (SI) with the position of the top dead center of the cylinder in which the spark took place, delivering the degree of advance on ignition.

11. Monitoring device according to claims 1 to 8, characterized in that the processing system (6) of the measured ionization signal comprises means (18) for detecting the continuity of the ignition system, constituted by:

- comparison means (19) with a positive threshold intended to signal the continuity of the circuit up to the measurement point (P _m ) by a logic signal (S ₃ ) equal to 1 when the signal is greater than a threshold and, otherwise equal to 0;

- comparison means (20) with a negative threshold delivering a binary signal (S ₄ ) equal to 1 in the presence a negative high output voltage, otherwise equal to 0; a monostable circuit extending the output of the first comparison means (19) for a few milliseconds; an AND logic circuit (21) combining the two respective output signals (S ₃ ) and (S ₄ ) of the two comparison means (19) and (20) and delivering a binary problem detection signal (S ₅ ).

12. Monitoring device according to claims 1 to 8, characterized in that the processing system (6) of the measured ionization signal comprises means (22) for detecting the charge of the measurement circuit (5) constituted by:

- a circuit (23) generating a pulse (S ₆ ), created after a delay triggered on the falling edge of the ignition control signal (S _c );

- Means (20) for comparing the measured ionization signal (S _m ) with a fixed negative threshold, delivering a binary signal (S ₄ ) equal to 1 if the current is less than the threshold, otherwise equal to 0;

- an electronic flip-flop (25) receiving the binary signal (S ₄ ), and the impulse signal (S _& ) on its "trigger", and delivering a signal (S _g ) of information on the existence of a normal charge or not at the time of the spark.

13. Monitoring device according to claim 1, characterized in that the means (22) for detecting the load of the measurement circuit (5) further comprise:

- an integrator (27) receiving the binary signal (S ₄ ) and delivering a signal (S _1Q ); - Means (28) for comparing the signal (S ₁₀ ) with a positive duration threshold, delivering a binary signal (S -, -,) providing information on the quality of the spark produced by measuring its duration.

14. Monitoring device according to claim 1, characterized in that the processing system (6) of the measured ionization signal comprises means (29) for detecting combustion, constituted by: - detection means (30) the last phase of the ionisation signal, receiving in input the signal (s _c) for controlling ignition and ionisation signal _(m s) measured, and delivering a signal ^(s ^ i2 ^detection on the rising edge current, after triggering on the falling edge of the control signal;

- means (31) for integrating the detection signal (S ₁₂ ) over time, delivering a signal (S ₁₃ );

- Means (32) for comparing the signal (S ₁₃ ) with a fixed voltage threshold, delivering a signal ( ^s i4) of combustion or non-combustion information in the cylinder where the spark occurred.

15. Monitoring device according to claims 1 to 8, characterized in that the processing system

(6) of the measured ionization signal comprises means (33) for detecting the presence of controlled aerodynamics constituted by:

- means (34) for triggering on the falling edge of the ignition control signal (S _c ) creating a pulse signal (Ξ ₁₅ );

- Means (35) for comparing the measured ionization signal (S _m ) with a fixed positive threshold, delivering a pulse signal (S ₁₆ ) - an AND logic gate (36), receiving as input the two impulse signals ( ^s i ₅ / ^s _i6 ^ above and delivering an output binary signal (S ₁₇ ) giving information on combustion or non-combustion.

16. Monitoring device according to claims 1 to 8, characterized in that the detection of the rupture of a plug consisting of:

- The means (29) for detecting a combustion delivering a signal (S ₁₄ );

- The means (22) for detecting a spark delivering a signal (S _{1: L} );

- A flip-flop (40) receiving as input the signals (S _{1; L} and S- ^ ₄ ) above to deliver information on the function of a candle.

17. Monitoring device according to claims 1 to 16 characterized in that it is; associated or integrated .with the ignition coil in the case of a coil of the pencil-coil type and / or with the spark plug.

18. Monitoring device according to claims 1 to 17, characterized in that the measurement signal (S _m ) is amplified by a monotonic function before the electronic processing.