EP0618360B1 - Device for detection of a function failure in an electronic ignition system of an engine, especially for motor vehicles - Google Patents

Description

The present invention relates to a device for detecting a malfunction of an electronic ignition system of an engine, in particular of a motor vehicle.

More particularly, the detection device according to the invention applies to an ignition system of a spark ignition engine of the type comprising a computer for controlling the supply of primary circuits of ignition coils including circuits secondary are connected to spark plugs associated with engine cylinders.

In such an ignition system, a spark plug is associated with each cylinder, an ignition coil is associated with one or two spark plugs, the ignition coils have a primary circuit and a secondary circuit and are used to accumulate and transfer the electrical energy in the direction of the spark plugs and the primary circuits of these coils are supplied under the control of the computer which manages the ignition instant and the distribution to the engine cylinders.

It has already been proposed in the prior art to monitor the operation of these ignition systems by controlling the amplitude and the duration of the voltage pulses present in the primary circuits of the coils and by comparing these parameters with calibrated thresholds for determine malfunctions.

Reference may for example be made to documents US-A-4,291,383 and DE-A-2,759,155, the first of which describes a device in accordance with the preamble of claim 1 and the second of which describes the use of the primary voltage of the coils for the acquisition of spark times.

However, these devices have a certain number of drawbacks in terms of the discrimination of operating faults.

The object of the invention is therefore to solve these problems.

To this end, the subject of the invention is a device for detecting a malfunction of an electronic ignition system of an engine, in particular of a motor vehicle, of the type comprising a computer for controlling the supply of primary circuits of ignition coils of which secondary circuits are connected to spark plugs associated with engine cylinders, the device comprising means for statistical analysis of the spark times between the spark plug electrodes to determine a malfunction, characterized in that these means of statistical analysis comprise means of acquiring the spark times from the voltages in the primary circuits of the coils, in that the means of statistical analysis further comprise means of calculation, for each cylinder, statistical indicators of mean value, instantaneous quadratic deviation and mean quadratic deviation, on N values of durations and means of ana lysis of these indicators to determine a fault, in that the indicator analysis means are suitable for comparing the statistical indicators relating to the different cylinders of the engine with each other and / or to calibrated thresholds depending on the operating conditions of the engine, for recognize a malfunction, in that the analysis means are adapted to compare the instantaneous quadratic deviation associated with a cylinder with a calibrated threshold to increment or decrement a counter whose value is compared with a filtering value to indicate a serious malfunction of the ignition system, in the event of an overshoot and in that the analysis means are suitable for comparing the mean square deviation and the mean value with calibrated thresholds to determine a fault critical operation of the ignition system, if exceeded.

• la Figure 1 représente un schéma synoptique illustrant la structure d'un dispositif de détection selon l'invention ;
• la Figure 2 représente un schéma électrique détaillé illustrant la partie d'acquisition de données d'un dispositif de détection selon l'invention ;
• la Figure 3 illustre les formes des signaux présents à différents points du circuit représenté sur la figure 2 ;
• la Figure 4 illustre le fonctionnement de moyens de calcul d'indicateurs statistiques entrant dans la constitution d'un dispositif de détection selon l'invention, et
• la Figure 5 illustre le fonctionnement de moyens d'analyse des indicateurs statistiques entrant dans la constitution d'un dispositif de détection selon l'invention.

The invention will be better understood with the aid of the description which follows, given solely by way of example and made with reference to the appended drawings in which:

• Figure 1 shows a block diagram illustrating the structure of a detection device according to the invention;
• FIG. 2 represents a detailed electrical diagram illustrating the data acquisition part of a detection device according to the invention;
• Figure 3 illustrates the shapes of the signals present at different points on the circuit shown in Figure 2;
• FIG. 4 illustrates the operation of means for calculating statistical indicators forming part of a detection device according to the invention, and
• Figure 5 illustrates the functioning of means of analysis of the statistical indicators entering into the constitution of a detection device according to the invention.

The purpose of the detection device according to the invention is to detect and identify operating faults in the high voltage stages of the electronic ignition systems of motor vehicle engines and thus to diagnose a failure of a spark plug, of a ignition coil or the connection between this spark plug and this coil.

• les défauts graves, de nature à provoquer une absence totale d'étincelle entre les électrodes de la bougie, et
• les défauts critiques susceptibles de provoquer une mauvaise initialisation de la combustion.

The detected faults can then be classified into two categories, namely:

• serious faults, such as to cause a total absence of spark between the spark plug electrodes, and
• critical faults likely to cause improper initialization of combustion.

It is therefore understandable that the advantage of this device lies in particular in the fact that it allows a convenience store to quickly know the state of the ignition system of an engine without having to dismantle the various elements mentioned above, which is particularly interesting when the ignition coils are arranged above the spark plugs. Furthermore, the detection of the total absence of spark for a given cylinder makes it possible to act on the fuel injection in order to preserve in particular the means of catalytic purification of the exhaust gases integrated in the exhaust line of the vehicle. .

Finally, it is also desirable that such a device does not require any additional component at the level of the high-voltage stages, which generally presents difficulties of installation, electrical isolation and reliability.

The block diagram of such a fault detection device is given in FIG. 1.

In this figure, the conventional structure of an electronic ignition system of an engine, in particular of a motor vehicle, can be recognized.

This includes a control computer (not shown) for controlling the supply of primary circuits of ignition coils, three of which, designated by the references 1, 2 and 3, are shown in FIG. 1 and correspond for example to spark plug ignition coils of a six-cylinder engine.

The control of the supply of the primary circuits of these coils is done in a conventional manner, for example by means of transistors 4, 5 and 6 whose collectors are connected to the primary circuits of the coils and whose bases are connected to the computer.

The secondary circuits of these coils are connected to spark plugs associated with the corresponding cylinders of the engine and it is understood that the computer controls the chain supply of these spark plugs to obtain a chain ignition of the engine cylinders.

The detection device according to the invention comprises means for statistical analysis of the sparking times between the spark plug electrodes to determine a malfunction of the ignition system.

These means of statistical analysis include, as can be seen in this FIG. 1, means 7 for acquiring spark times from the voltages in the primary circuits of the coils, the output of which is connected to calculation means. and statistical processing 8 making it possible, as will be described in more detail below, to calculate, for each cylinder, statistical indicators on N values of duration of sparks. The output of these processing means is connected to analysis and discrimination means 9 making it possible to recognize, from these indicators, serious and critical operating faults which will also be described in more detail below.

Thus, the means of acquisition 7 of the spark durations ensure, from the voltages in the primary circuits of the ignition coils, the multiplexing of the overvoltages generated by the sparks and the filtering then the reshaping of this multiplexed signal so to provide the rest of the device with a single binary signal comprising slots whose duration is representative of the successive spark durations.

This data acquisition stage is characterized by the fact that its operation is not disturbed by the switching of the different coils and that consequently it allows overlapping between the commands of these coils, this case being able to be encountered at high speed of operation on engines with more than five cylinders.

Part 8 of statistical processing of these spark durations is provided by a programmed microcontroller which acquires the spark duration signal via a time measurement stage. The values of the spark times are demultiplexed per cylinder and stored in memory means, as will be described in more detail below.

• écart quadratique instantané,
• écart quadratique moyen (variance), et
• valeur moyenne.

The processing carried out on the content of these storage means makes it possible to provide, for each cylinder, the following statistical indicators:

• instantaneous quadratic deviation,
• mean square deviation (variance), and
• average value.

The discrimination part 9 can also be provided by the microcontroller to compare the statistical indicators with each other and / or with calibrated thresholds in order to extract the signaling of a serious fault or critical. These faults can be materialized by a code entered in the memory of the microcontroller and whose value provides information on the type of fault detected and on the cylinder concerned.

The memorization of a fault can be filtered, that is, it is only effective after a certain number of successive detections, this number can also be chosen.

The structure of this device and its operation are illustrated in more detail in FIGS. 2 and 3.

It can indeed be seen in these figures that the acquisition means 7 comprise means for multiplexing the overvoltages generated at the primaries of the coils by the sparks, these multiplexing means being designated by the reference 10 in FIG. 2.

The output of these multiplexing means is connected to filtering means 11 and to means 12 for reshaping the output signal of these multiplexing means to deliver the binary signal mentioned above. These filtering and fitness means have a conventional structure based on operational amplifiers.

In this FIG. 2, the acquisition means are adapted to acquire data in a jumostatic ignition system for a six-cylinder engine.

The multiplexing means comprise an operational amplifier 13 connected as an adder for summing the voltages in the primary circuits of the coils, designated by the references V ₁ , V ₂ and V ₃ and subtracting from them the supply voltage multiplied by the number of non-active C ₁ , C ₂ and C ₃ commands.

In fact, this operational amplifier 13 receives on an input, the control voltages of the primary circuits of the coils and on another input, the voltages actually present in these circuits. primary to draw the overvoltages generated by the sparks between the spark plug electrodes.

It can therefore be seen that the voltage designated by the reference V ₄ at the output of this adder can be written to a factor near as follows: $${\text{<figure-callout id="4" label="V" filenames="imgf0001.png,imgf0003.png" state="{{state}}">V</figure-callout>}}_{\text{4}}{\text{= <figure-callout id="1" label="V" filenames="imgf0001.png,imgf0002.png" state="{{state}}">V</figure-callout>}}_{\text{1}}{\text{+ <figure-callout id="2" label="V" filenames="imgf0001.png,imgf0003.png" state="{{state}}">V</figure-callout>}}_{\text{2}}{\text{+ V}}_{\text{3}}{\text{- V}}_{\text{BAT}}\text{((}{\overline{\text{VS}}}_{\text{1}}\text{+}{\overline{\text{VS}}}_{\text{2}}\text{+}{\overline{\text{VS}}}_{\text{3}}\text{).}$$

This voltage signal V ₄ therefore restores only the overvoltages present in the primary circuits of the coils, which are the image of the secondary voltages at the terminals of the spark plugs.

This voltage signal V ₄ is then filtered in order to reduce the amplitude of the oscillations mainly due to turbulence in the combustion chamber of each cylinder.

The output voltage V ₅ of these filtering means It is then reshaped by a comparator stage and the voltage signal V ₆ thereof is in the form of a binary signal whose width of the status slots logic 0 for example, is representative of the duration of the sparks.

This binary signal is then introduced into the microcontroller constituting the means 8 for calculating the statistical indicators and for analyzing 9 of these, this microcontroller being generally designated by the reference 14 in FIG. 2.

The operation of this microcontroller for the calculation of the statistical indicators is illustrated in FIG. 4.

It can be seen with reference to this figure that the successive values of the spark times are sorted by cylinder and stored in FIFO first-in-first-out batteries assigned to each cylinder.

In the case of engine operation control systems having no engine phase information, the successive values of the same pair of cylinders must be alternately stored in two separate batteries assigned indifferently to one or the other of the two cylinders.

• calcul de la moyenne :
  
• calcul de l'écart quadratique instantané : $${\text{<figure-callout id="2" label="Δ n" filenames="imgf0001.png,imgf0003.png" state="{{state}}">Δ</figure-callout>}}_{\text{n}}{}^{\text{2}}{\text{= (t}}_{\text{n}}\text{-}\overline{\text{t}}{\text{)}}^{\text{2}}$$
  
• calcul de l'écart quadratique moyen (variance):
  

Then, this microcontroller performs in real time the following different operations on the last N values of spark duration of the active cylinder:

• averaging:
  
• calculation of the instantaneous quadratic deviation: $${\text{Δ}}_{\text{not}}{}^{\text{2}}{\text{= (t}}_{\text{not}}\text{-}\overline{\text{t}}{\text{)}}^{\text{2}}$$
  
• calculation of the mean square deviation (variance):
  

calculée à bas régime et, dans ce cas, seuls les défauts graves de fonctionnement seront surveillés.It will be noted that for the high engine operating speeds it is possible to limit the processing to the calculation of Δ _n , using the average value $\overline{\text{t}}$

calculated at low speed and, in this case, only serious operating faults will be monitored.

précise à 10 % près dans le cas de durées d'étincelles très instables. P peut quant à lui être inférieur ou égal à N et les calculs effectués par le microcontrôleur sont allégés si l'on choisit pour P et N une puissance de 2.The values of N and P are determined experimentally and it has been established that the order of magnitude of N is less than 10 to obtain the mean value $\overline{\text{t}}$

accurate to within 10% for very unstable spark times. P can meanwhile be less than or equal to N and the calculations performed by the microcontroller are lightened if a power of 2 is chosen for P and N.

The fault discrimination part is based on a comparison of these different indicators with each other and / or on calibrated thresholds to determine serious faults or critical operating faults.

Serious operating faults are likely to cause an alarm which leads to inhibition injecting fuel into the cylinder or cylinders for which the ignition is faulty. To detect these faults, the statistical indicator of instantaneous quadratic deviation Δ _n ² is used which is information in real time and corresponds to the cylinder active at the same time.

This instantaneous quadratic deviation is compared with a calibrated threshold and if it is greater than this threshold, a fault counter assigned to the active cylinder is incremented.

Otherwise, the counter is decremented.

The starting value of this counter is fixed at zero.

An alarm is generated when the counter reaches a calibrated filtering value F. Thus, it is understood that it is necessary to detect F consecutive faults to trigger this alarm and the recording of the corresponding fault code.

Ignition faults liable to cause such a serious fault may for example be a short circuit in the secondary circuit of the ignition coil, a secondary circuit open without sparking, or a plug that is very dirty, drowned or beaded.

FIG. 5 illustrates this operation of the microcontroller for the detection of this fault.

In the event that an anomaly is detected from the statistical indicators without generating the alarm described above, the fault is classified as a critical fault. This situation corresponds to the various cases in which the ignition is present but of poor quality.

Thus, the early warning signals of ignition failures cause the recording of fault codes in order to guide the repairman.

et d'écart quadratique moyen (variance) σ² sont utilisés.For this discrimination, the indicators of average value $\overline{\text{t}}$

and mean square deviation (variance) σ ² are used.

Three comparisons are made.

First of all, the variance is compared to a calibrated threshold which depends on the operating mode of the engine, the dispersion of the sparking times depending on the latter. Indeed, the dispersion is strong under acceleration and under heavy load and it is more moderate at idle, hot engine, as well as at deceleration with cut of the injection.

If the variance is less than the threshold, a critical fault is recorded and corresponds to the case where all or part of the spark occurs outside the combustion chamber and therefore is not subject to disturbances from the explosion.

This occurs in the case of a bad snap-on of the spark plug cap causing an arc on the olive thereof, a bad insulation causing an arc between the supply beam and metallic ground and an insulation fault between circuits primary and secondary circuit of the ignition coil.

Severe faults also induce a variance fault which is too small but with a longer delay.

est également comparée à un seuil calibré. Cette comparaison n'est réalisée que dans les modes de fonctionnement dans lesquels l'étincelle est stable et peu dépendante de l'environnement, en décélération par exemple. Si cette valeur moyenne est inférieure au seuil, un défaut critique correspondant à une usure des électrodes de la bougie est enregistré. Cette détection intervient également en cas de circuit secondaire ouvert.The average value $\overline{\text{t}}$

is also compared to a calibrated threshold. This comparison is only carried out in the operating modes in which the spark is stable and not very dependent on the environment, in deceleration for example. If this average value is below the threshold, a critical fault corresponding to wear of the spark plug electrodes is recorded. This detection also occurs in the event of an open secondary circuit.

est également comparée à la valeur moyenne de durées d'étincelles du cylindre qui est en phase d'échappement, c'est-à-dire le cylindre jumeau, en phase mécaniquement.The average value $\overline{\text{t}}$

is also compared to the average value of spark times of the cylinder which is in the exhaust phase, that is to say the twin cylinder, in the mechanical phase.

This particularly interesting test in the case of twin ignitions, makes it possible to detect an excessive dissymmetry between the sparks supplied by the same coil.

If the deviation is greater than a calibrated threshold depending on the engine operating conditions, a critical fault is memorized and corresponds to significant wear of the spark plugs, to a plug that is too tight that would have been damaged during assembly or to a significant fouling of these candles.

Critical faults thus recorded accompanied by a reference to the corresponding cylinder or cylinders then allow the repairman to dismantle the ignition components in an appropriate manner and above all to avoid the tests which consist in opening the high-voltage circuit to verify the presence sparks, at the risk of destroying the catalytic purification devices integrated in the vehicle's exhaust line.

Claims (8)

1. Device for detecting a fault in the functioning of an electronic ignition system of an engine, especially of a motor vehicle, of the type including a computer controlling the supply to the primary circuits of ignition coils (1, 2, 3), secondary circuits of which coils are connected to spark plugs associated with cylinders of the engine, the device including means (7, 8, 9) for the statistical analysis of the spark durations between the electrodes of the spark plugs in order to determine a function fault, characterized in that the means for statistical analysis comprise means (7) for acquiring the spark durations from the voltages in the primary circuits of the coils (1, 2, 3), in that the statistical analysis means additionally comprise means (8) for calculating, for each cylinder, statistical indicators of mean value, of momentary square deviation and of mean square deviation, on N values of durations, and means (9) for analysing these indicators in order to determine a fault, in that the means (9) for analysing the indicators are arranged to compare the statistical indicators, relating to the different cylinders of the engine, with one another and/or with calibrated thresholds depending on the operating conditions of the engine, in order to detect a function fault, in that the analysing means (9) are arranged to compare the momentary square deviation, associated with a cylinder, with a calibrated threshold in order to increment or decrement a counter the value of which is compared to a filtering value (F) in order to indicate a serious function fault in the ignition system, in the event that it is exceeded, and in that the analysing means (9) are arranged to compare the mean square deviation and the mean value with calibrated thresholds in order to determine a critical function fault in the ignition system, in the event that they are exceeded.
2. Detection device according to Claim 1, characterized in that the acquisition means (7) comprise means (10, 13) for multiplexing the overvoltages produced in the primary circuits of the coils by the sparks, and means (11, 12) for filtering and re-forming the output signal of the multiplexing means, in order to deliver to the remainder of the device a binary signal having indentations the duration of which represents the durations of the sparks.
3. Detection device according to Claim 2, characterized in that the multiplexing means (10,13) comprise an operational amplifier (13) receiving at one input the operating voltages of the primary circuits of the coils (1, 2, 3) and at another input the voltages actually present in the primary circuits in order to determine the overvoltages produced by the sparks.
4. Detection device according to any one of the preceding claims, characterized in that the means (8, 9) for calculating and analysing the statistical indicators comprise storage means assigned to each cylinder of the engine and in which are stored the values of the corresponding spark durations, from which these indicators are calculated and analysed.
5. Device according to any one of the preceding claims, characterized in that a serious fault in the functioning of the ignition system corresponds to the absence of ignition.
6. Device according to any one of the preceding claims, characterized in that a critical fault in the functioning of the ignition system corresponds to poor quality ignition.
7. Device according to any one of the preceding claims, characterized in that the analysing means (9) are arranged to compare the mean value, associated with a cylinder, with the mean value associated with the twin cylinder in the exhaust phase in order to determine a deviation, the deviation being compared with a calibrated threshold in order to determine a critical fault in the functioning of the ignition system, in the event that it is exceeded.
8. Device according to any one of the preceding claims, characterized in that the calculating and analysing means comprise a microcontroller (14).

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