EP0654604B1 - Coil ignition method and device with additional discharges for diagnostics - Google Patents

Description

The subject of the invention is a method and a device electronic ignition, for internal combustion engine controlled ignition, in each engine cylinder, by at minus one spark plug in series with a secondary coil ignition, the primary of which is supplied with current electrical from an electrical source, such as the battery of a vehicle equipped with the engine, by a switch placed in a primary charging circuit, and itself controlled by a calculation and control unit, comprising advantageously a microcontroller.

The invention more specifically relates to a method and a device of the type mentioned above, allowing perform a diagnosis of the engine ignition, thanks to the calculation and control unit, or calculator, which manages the ignition function as well as possibly the function injection, when the engine is fitted with an installation fuel injection system, the calculation and command then being a calculator called "of engine control ".

The method and the device according to the invention are intended to be used not only on board vehicles, but also on recording equipment and service station.

The ignition diagnosis consists in giving information qualitative information relating to the sparks produced by the spark plugs in the combustion chambers of the engine. This information should make it possible to determine whether there is absence or presence of a spark, and, in the latter case, if the spark is correct.

Many methods and devices have already been proposed to provide such a diagnosis, which is obtained either by measuring the current passing through the spark plug, using a shunt, either by performing a voltage analysis at ignition coil primary terminals, during spark real or presumed.

An ignition device, with ignition diagnosis of the second type mentioned above, was proposed by the Applicant in European patent application EP 559 540: on the one hand, it includes means for measuring the current of load, intended to provide, on an output, a signal in response to exceedances of a specified, lower value at the current needed to create the ignition voltage at secondary of the coil by breaking the primary current, and, on the other hand, means of transposing the tension primary, to form the image of the secondary voltage and provide, on said output, a signal when the voltage secondary becomes below a specified threshold indicating the end of the spark at the candle. These means of transposition include, in series between the terminal of the primary not connected to the source and the ground, the emitter-collector junction a transistor and collector resistors and transmitter, so that the voltage across one of resistances be representative of the difference between the voltage across the primary and source voltage.

A first drawback of such a device is that it does not allow, in a simple way, to discriminate sparks from different cylinders, at high revs, due of a superposition between the transpositions of tensions secondary and primary charges. For example, in a inline four-cylinder four-stroke engine, load of cylinder # 3 coil primary can start while the spark at the spark plug of cylinder n ° 1 is not finished.

To remedy this drawback, it is necessary duplicate certain components of the circuit, and / or provide a diode between the primary of each coil and means of transposition which may be common to two cylinders, if not all cylinders.

Another disadvantage is that such a device is expensive to carry out, because the resistors and diodes which it features are high voltage components, and occupy a relatively large area on circuits prints used.

The object of the invention is to remedy the drawbacks of the aforementioned device known from EP 0 559 540, and propose a method and a device allowing a control the quality of the ignition by detecting whether the spark is neither too short nor too long, and if the spark is of sufficient quality for a sufficient period of time.

Another object of the invention is to propose a method and device for further monitoring wear of the spark plug, or more generally degradation of the secondary circuit which comprises it in series with the secondary of the coil and a resistive interference suppression wire, for example integrated into the candle.

Yet another object of the invention is to propose a method allowing an implementation by a device many components of which may be common to all engine cylinders, and therefore in a single copy in a more economical and less bulky production device.

Another aim, finally, is to propose a method of ignition diagnosis also compatible with calculation and the primary charge time control, in the way already known, in particular from the aforementioned document EP 559 540, the method according to the invention being able to be implemented by a device which is structurally only slightly different known devices to perform this calculation and this primary charge time control.

The idea behind the invention is that an image of the quality of the spark to the candle is given by the dynamic impedance of this candle during the spark, and that the observation of the intensity of a current that we circulates in the coil primary, for spark allows analysis of the rate of increase for at least one diagnostic period, this speed increasing the intensity of the dependent primary current especially the dynamic impedance of the candle during the spark.

In summary, according to the invention, the quality of the spark is determined from the speed measurement increasing the intensity of the current flowing in the coil primary for at least one diagnostic time determined for the duration of the assumed spark.

• entre deux durées de charge successives, et pendant la durée de l'étincelle présumée à la suite de la première desdites deux durées de charge successies, à commander le passage d'un courant de mesure dans le primaire pendant au moins une durée de diagnostic et à un instant définis par l'unité de calcul et de commande,
• à déterminer une vitesse d'accroissement de l'intensité du courant dans le primaire pendant au moins une durée de diagnostic,
• à discriminer une vitesse d'accroissement élevée d'une vitesse d'accroissement faible, et
• à en déduire une information sur la présence et/ou la qualité d'une étincelle à la bougie, après la fin de la durée de charge antérieure.

To this end, the invention provides an electronic ignition method of the type presented above and comprising the step of cyclically controlling the charge of the primary during defined charge times and at times defined by the calculation unit. and control, so that the cut-off of the charge, at the end of each charging period, is intended to cause a spark to the spark plug, and is characterized in that it further comprises the steps consisting:

• between two successive charging durations, and during the duration of the presumed spark following the first of said two successive charging durations, to control the passage of a measurement current in the primary for at least one diagnostic duration and at a time defined by the calculation and control unit,
• determining a rate of increase in the intensity of the current in the primary for at least one diagnostic period,
• to discriminate between a high rate of increase and a low rate of increase, and
• to deduce therefrom information on the presence and / or the quality of a spark plug, after the end of the previous charge period.

Discrimination in the rate of increase of the intensity of the current in the primary during each duration can be ensured by comparison with minus a corresponding threshold, to deliver a signal presence of spark if this threshold is exceeded corresponding. But, in a variant of implementation particularly simple, we measure the intensity of the current in primary for at least each diagnostic period, and we discriminate the rate of increase by comparing the maximum intensity measured during the duration of diagnosis corresponding to a corresponding intensity threshold, to issue a spark presence signal if the maximum intensity measured is greater than the intensity threshold.

It has certainly already been proposed by US-A-5,174,267 from control the flow of a measurement current in the primary an ignition circuit of the type presented above, between two successive charging times, from an instant defined by the calculation and control unit, and to be determined a rate of increase of the intensity of the current in primary by taking into account an intensity threshold corresponding.

But the subject of US-A-5,174,267 is very different from that of the present application, since this document describes a method of identifying the cylinder in the compression phase and the cylinder in exhaust phase, in a pair of cylinders for which the ignition control is simultaneous, at least at the start of engine operation comprising an even number of cylinders, and the installation of which ignition system has one coil per cylinder, while the present application relates to a method and a device of ignition control with ignition diagnosis relating to less on the presence of sparks, not identification compression cylinders and cylinders in exhaust.

In US-A-5,174,267, this identification is ensured by monitoring signals caused by spark plugs on coil primaries ignition, in an ignition circuit which, by necessity structural, includes the well known basic components the ignition circuit to which the process and the operative part of this application.

The variant of the cylinder identification process described in US-A-5,174,267 with reference to Figure 3 implements certain means in common with the process of the present application, but for industrial application final which is different, as mentioned above.

In particular, between two successive charging times on the primary, the switch opening is fine ordered one or more times, at least once defined by the calculation and control unit.

But this or these switch openings is or are ordered only after a maximum duration presumed spark, unlike the process of the request in which at least one additional opening of the switch is controlled for the presumed duration of the spark. In addition, in US-A-5,174,267, the passage of the primary current is stopped as soon as it reaches a threshold intensity, whereas on the contrary, in the process of request, this or these additional passages of the current primary is or are ordered for at least a period of determined diagnosis, since in the request process it is detected whether, at the end of each predetermined duration, the primary intensity measured is higher or lower than the threshold, whereas on the contrary, in US-A-5,174,267, the passage of primary current is extended until a threshold of current is reached, and, this is the duration of passage of the primary current until reaching the threshold which is measured, and which is then compared to the corresponding duration for a second cylinder, to determine that the time measured longer is that obtained in the cylinder in phase of compression.

The process described in US-A-5,174,267 does not allow to provide information on the presence and / or quality from a spark to the candle, depending on whether the primary current maximum measured or not exceeds the threshold fixed at the end of a diagnostic duration imposed, because, precisely, in this document, we wait as long as it takes for the primary current threshold is reached, and the time for this result to be achieved.

Consequently, even if the process of the present request and US-A-5,174,267 make use of means these common means are not implemented from the same way, and the industrial results resulting from these different implementations are also very different.

Advantageously, the method of the invention consists to order at least two successive diagnostic durations between two successive charge durations, and to deduce therefrom, on the one hand, the presence of a spark if at least one presence signal is delivered in a first interval of predetermined time, following the end of the charging time earlier, and ending at the same time as the first diagnostic duration, and secondly, a duration minimum of a spark of sufficient quality in function the number of presence signals issued.

In addition, the method may further include deduce that the spark is too short if a second signal attendance is not issued in a second interval of predetermined time, greater than the first interval of time, also following the end of the charging time earlier, and ending at the same time as the second duration of the diagnosis.

In a preferred embodiment, the method of the invention is to also order a third diagnostic time between two successive charging times, and deduce that the spark plug is short-circuited if a third presence signal is issued before the end of a third predetermined time interval, also following the end of the previous charge duration, greater than first and, if applicable, the second time interval predetermined, and ending at the earliest at the same time as the third diagnostic duration.

In order to monitor the wear of the spark plug and the secondary circuit which comprises it in series with the secondary, the process can also consist of measuring the intensity maximum current in the primary for at least a diagnostic duration of the same rank after durations of successive loads, compare the measurements with each other and / or at least a maximum intensity threshold, and to deduce therefrom minus a signal testifying to the deterioration of the circuit secondary.

• l'unité de calcul et de commande comprend des moyens générateurs d'un signal de commande du commutateur pour le passage du courant dans le primaire pendant au moins une durée de diagnostic et à au moins un instant définis par ladite unité, entre deux durées de charge successives du primaire, et pendant la durée de l'étincelle présumée à la suite de la première desdites deux durées de charge successives, et
• les moyens de détection comprennent des moyens discriminant la vitesse d'accroissement de l'intensité du courant dans le primaire et délivrant un signal à ladite unité de calcul et de commande lorsque l'intensité mesurée du courant dans le primaire est supérieure à un seuil, au moins pendant chaque durée de diagnostic.

The invention also relates to an electronic ignition device, of the aforementioned type, further comprising means for measuring the current in the primary, mounted in series in the charging circuit between the switch and the ground, and connected to detection means, themselves connected to the calculation and control unit, as known from EP 559 540, and which is characterized in that:

• the calculation and control unit comprises means generating a switch control signal for the passage of current through the primary for at least one diagnostic duration and at at least one instant defined by said unit, between two durations of successive charge of the primary, and for the duration of the presumed spark following the first of said two successive charge durations, and
• the detection means comprise means discriminating the speed of increase of the intensity of the current in the primary and delivering a signal to said calculation and control unit when the measured intensity of the current in the primary is greater than a threshold, at least during each diagnostic period.

According to a simple and economical embodiment, the switch is controlled, from a command output of the calculation and control unit, via an interface amplifier, the means for measuring the current in the primary include a shunt in series with the switch, between the latter and ground, and the means detection systems include at least a first and a second comparator, each receiving the shunt signal on a input and comparing it to a prime and a respectively second intensity threshold, received on another input of the corresponding comparator, the output of each comparator being connected to a diagnostic input of the computing unit and control, the second intensity threshold being higher to the first, but less than the current required to create an ignition voltage by cutting the primary, for the calculation by said unit of primary charge times.

Advantageously, to allow monitoring of the secondary circuit, the calculation and control unit includes a second diagnostic input, connected to the shunt, and transmitting the current intensity measurement to a analog / digital converter, itself connected to means for storing and comparing a maximum value intensity, measured during a diagnostic period corresponding to a maximum intensity threshold and / or comparison of several values maximum intensity measured over several diagnostic durations, and means delivering a circuit degradation signal secondary.

According to an economical embodiment, the device ignition includes means for measuring the current in the primary, detection means, a calculation and control, and possibly an interface amplifier, which are common to all engine cylinders.

• la figure 1 est un schéma fonctionnel de principe d'un dispositif selon un mode particulier de réalisation de l'invention ;
• la figure 2 montre les courbes représentatives de la variation, en fonction du temps t, du signal de commande délivré au commutateur, du courant Ip dans le primaire de la bobine, du courant Is dans le secondaire de la bobine, et du signal de diagnostic transmis à l'unité de calcul et de commande ;
• la figure 3 montre une constitution possible du dispositif de la figure 1 ;
• les figures 4 et 5 montrent les variations en fonction du temps des courants Ip et Is selon des courbes plus représentatives et à plus grande échelle que celles de la figure 2 ;
• la figure 6 représente, à plus grande échelle, quatre courbes représentatives du courant de mesure pendant une durée de diagnostic pour quatre valeurs différentes de la résistance du circuit secondaire, et
• la figure 7 représente les quatre courbes correspondantes d'évolution du courant Is.

Other characteristics and advantages of the invention will emerge from the description given below, without implied limitation, of an exemplary embodiment described with reference to the appended drawings in which:

• Figure 1 is a block diagram of a device according to a particular embodiment of the invention;
• FIG. 2 shows the curves representative of the variation, as a function of time t, of the control signal delivered to the switch, of the current Ip in the primary of the coil, of the current Is in the secondary of the coil, and of the diagnostic signal transmitted to the calculation and control unit;
• Figure 3 shows a possible constitution of the device of Figure 1;
• FIGS. 4 and 5 show the variations as a function of time of the currents Ip and Is according to more representative curves and on a larger scale than those of FIG. 2;
• FIG. 6 represents, on a larger scale, four curves representative of the measurement current during a diagnostic period for four different values of the resistance of the secondary circuit, and
• FIG. 7 represents the four corresponding curves of evolution of the current Is.

The system, the basic principle of which is shown in Figure 1, is intended for the ignition of a internal combustion engine combustion chamber, fitted with at least one spark plug 10, placed in series with the secondary 12 of an ignition coil 11. Primary 13 of coil 11 is connected to a power source (battery of the vehicle in general), of voltage Vbat. On the opposite side respectively at source Vbat and at candle 10, the primary 13 and secondary 12 have a common terminal connected to the collector of a bipolar transistor 14 of NPN type, of which the transmitter is connected to ground via a shunt resistor 15. Shunt 15 is thus in series in the primary 13 charging circuit from the source Vbat, between the ground and the ignition transistor 14, serving switch or cut-off switch, capable of switch from the blocked state to the saturated state and vice versa, to control the primary current Ip, which flows through the primary 13 when transistor 14 is conductive in the state saturated.

This switch 14 is controlled at closing and at opening from a calculation and control unit 16, via an amplifier 17 serving interface between the base of transistor 14 and unit 16, which is an engine control computer, of the microcontroller type, comprising at least one microprocessor, and having at minus an output S giving control information to amplifier 17.

The shunt 15 is used to measure the primary current Ip, and supplies across its terminals a voltage representative of this current. This information from shunt 15, and relating to the intensity of the primary current Ip, is treated, in the form analog or in logical or digital form, by a threshold detector 18 connected to at least one input E of the computer 16, allowing to receive information from diagnosis on the presence and quality of a spark produced between the two spark plug electrodes 10 and generated by the secondary 12 of the ignition coil 11 by switching off the primary charge 13.

Figure 1 shows the device for a single spark plug 10 in a single cylinder, so as not to overload the figure but the means of measuring the primary current consisting of shunt 15, the calculation and control unit 16, the interface amplifier 17 and the detection means consisting of the threshold detector 18 are common to all candles 10 of all cylinders, to which they are connected by selection diodes (not shown) so known, and are therefore each provided in single copy in the circuit.

The operation of the device according to the method of the invention is described below with reference to the four curves (a) to (d) of FIG. 2 for a single candle 10. Curve (a) represents a timing diagram of the signal control of switch 14 applied to output S of the unit 16. Curves (b) and (c) represent respectively the intensity of the primary current Ip and the secondary current Is as a function of time, and curve (d) represents the signal applied by detector 18 to input E of unit 16. On its output S, unit 16 applies cyclically an output signal from time t0 of closing the switch 14 until the instant t1 of cut-off. During the charge time of the primary 13, between these instants t0 and t1, the primary current Ip gradually increases as shown on curve (b). In about 1 µs after the time of cutoff t1, Ip is canceled from its maximum value of the order of 6 A, sufficient for its cut to give the ignition voltage required across spark plug 10, and the secondary current Is very quickly takes its value maximum of the order of 60 mA, as shown on curve (c). From this maximum value, Is gradually decreases, while Ip is zero.

Between t1 and the start of the charging time (t1-t0) next, unit 16 applies a command to its output S of closing switch 14 for three durations of successive diagnoses, preferably of the same value, and spaced in time, t3-t2, t5-t4 and t7-t6. The stream primary Ip gradually increases from the start t2, t4 or t6 of each diagnostic time to cancel quickly at the break in t3, t5 or t7 at the end of each duration diagnostic, as shown on curve (b). During the spark, during which the secondary current Is gradually decreases as shown on curve (c), until canceling out in t8, so that the duration of the spark T = t8-t1 is of the order of 1.5 ms, under conditions normal ignition, it corresponds to each pulse of a chosen positive sign of primary current Ip a impulse of a negative secondary current chosen sign Is, which is practically no longer sensitive outside the spark time T. During this spark time T, at during which the spark is normally present, after time t1 (at the end of the charging time t1-t0, about 3 ms, during which the charging current circulates in the primary 13), the impedance Z of the plug 10 is low (around 20 to 100 kΩ). After the spark (after t8), the impedance Z is high (greater than 1 MΩ).

où, Imax est le courant maximum de saturation du primaire 13 (de l'ordre de 24 A, pour une tension usuelle de batterie de 13 V),

Z est l'impédance de la bougie 10 (de l'ordre de 20 kΩ),

η est le rapport de transformation entre le secondaire 12 et le primaire 13 (de l'ordre de 100),

L_F est la self de fuite de l'ensemble primaire 13 et secondaire 12 (de l'ordre de 1 mH).

In theory, and during a normal spark, the speed τ of increase of the primary current Ip, is expressed by the following formula (1): (1) τ = Imax x Z η 2 x L F

where, Imax is the maximum saturation current of the primary 13 (of the order of 24 A, for a usual battery voltage of 13 V),

Z is the impedance of the plug 10 (of the order of 20 kΩ),

η is the transformation ratio between secondary 12 and primary 13 (of the order of 100),

L _F is the leakage choke of the primary 13 and secondary 12 assembly (of the order of 1 mH).

On the other hand, in the absence of a spark, this speed of increase of the primary current Ip, which corresponds to the slope of the curve of Ip as a function of time t, is given by the formula (2): (2) τ '= Vbat Lp where, Vbat is the battery voltage (around 13 V), and Lp is the self inductance (around 6 mH).

During the diagnostic times t3-t2, t5-t4 and t7-t6, and during a normal spark, the rate of increase of Ip is around 50 A / ms, while in the absence of spark, this rate of increase τ 'is of the order of 2 A / ms.

This rate of increase of Ip corresponds to velocity gradients during diagnostic times, which are calibrated to a constant value of the order of 20 µs for example. This rate of increase of Ip can therefore be expressed as the ratio of the maximum intensity of this current at the end of t3, t5 or t7 of each diagnostic time on said diagnostic duration, or more simply still, by the values of maximum intensity.

Strong gradients (50 A / ms) are discriminated from weak gradients (2 A / ms) by detector 18, comprising for example a threshold comparator. The Io threshold can be calibrated to a constant and unique value for all diagnostic times, and be set for example at 1 A. Each times and as long as Ip is greater than Io, the detector 18 applies a signal to input E of unit 16 not zero, as shown in (d) in Figure 2. The signal transmitted during t1-t'0 corresponds to a current primary Ip> Io = 1 A, during the charging time (t1-t0).

The signals transmitted during t3-t'2 and t5-t'4 correspond to a primary current Ip> Io, during diagnostic times t3-t2 and t5-t4, which took place before the end of the spark in t8. However, no signal is not given on input E during the diagnostic time t7-t6 after t8, because Ip remained below the threshold Io of 1 A during this time.

The signals received by input E of unit 16 at during diagnostic times such as t3-t2 and t5-t4 are therefore spark presence signals.

The specific diagnostic program implemented by the microprocessor of unit 16 allows, from spark presence signals from the detector 18, to determine that the spark was of sufficient quality during a time interval at least equal to t5-t1, in this example, therefore T ≥ t5-t1, and the spark has most likely extinguished before t7, therefore T <t7-t1.

In general, if during an interval of predetermined time T1, beginning in tl and ending at earlier in t3, but not after t4, unit 16 does not receive of the detector spark signal signal 18, it delivers a spark fault diagnosis, meaning that the spark plug circuit 10 is probably open.

If unit 16 receives a first presence signal during T1 (for example t3-t'2), but no second signal presence during a predetermined time interval T2, also starting in t1 and ending at the earliest in t5 (but not after t6), unit 16 considers that there has been a spark, but that it was not of a quality suitable for a sufficient time. Unit 16 delivers then a diagnosis of spark too short.

If the unit 16 receives two successive signals presence of spark during T2, including the first during T1, but no third presence signal for a third predetermined time interval T3, starting at t1 and ending at the earliest in t7, but not before the start (t0) of the next charging time, the unit 16 delivers a proper quality spark diagnosis during a sufficient time.

Finally, if the unit 16 successively receives three spark presence signals during T3, it delivers a too long spark diagnosis, signifying that the spark plug 10 is probably short-circuited.

For more detailed detection of a possible short circuit, the detector 18 can, during the third duration of diagnosis t7-t6, compare the measured current Ip to a threshold a particular short circuit, for example less than 1 A.

Generally, the detector 18 can compare the intensity of the current measured, during each duration of diagnosis, at a threshold specific to each of the diagnostic durations, especially if these are not the same value.

The unit 16 can thus diagnose the presence or the absence of a suitable quality spark, and the duration of such a spark comprised, for example, between 0.4 ms and 2 ms.

The measurement of the spark time can be taken count by unit 16 to adjust the I2 value of the current primary Ip for which the cut is performed, in order to guarantee for example a sufficient spark duration for avoid unburned, such a duration for less than 0.4 ms indicating a high probability of open circuit, while that a spark duration greater than 2 ms indicating a high probability of short circuit, these two values defining a range of spark times that experience revealed as normal.

In FIG. 3, the elements of the similar device to those of figure 1 have been indicated by the same references. Amplifier 17 includes two transistors bipolar, including a 19 NPN type connected by its base to the output S of unit 16 via a resistor 21, while its transmitter is grounded and its collector connected by a resistor 22 to the base of the other transistor 20, of PNP type, the transmitter of which is put on the voltage of the source Vbat, and the collector connected by a resistor 23 to the base of the ignition transistor 14, which comprises, on its collector connected to primary 13, an integrated Zener diode (and not shown) in a known manner.

The detector 18 comprises an input RC filter 24-25, filtering primary current measurements across the shunt 15, and passing them to a negative input of a first threshold comparator 26, receiving on an input positive a voltage threshold corresponding to the intensity threshold Spark detection Io, and defined, from a logic voltage source Vcc (of + 5 V for example) by through a resistance bridge 27, 28 and 29.

The output of comparator 26 is connected in parallel at the voltage source + Vcc through the resistor 30 and at the input of an inverter 31. The output of the RC filter 24-25 is also connected in parallel to the positive input a second threshold comparator 32 receiving at its input negative another voltage threshold defined by the bridge resistors 27, 28 and 29 from the voltage source + Vcc. As for comparator 26, the comparator output 32 is connected in parallel to the source + Vcc through of the resistor 30 and at the input of the inverter 31, in being isolated from the mass by the capacity 33. All of the two comparators 26 and 32 constitute an OR circuit, which attacks the diagnostic input E of unit 16 via of the inverter 40.

Comparator 26 compares current measurements with Io threshold, of 1 A for example, for the delivery of signals presence of spark as described above. The comparator 32 compare the measurements of the intensity of the primary current Ip at a second intensity threshold I1, higher than that Io of comparator 26, for example equal to 4.5 A, to provide a signal when the charge current Ip in the primary 13 exceeds this second threshold I1, when the current Ip to be cut to obtain a spark of satisfactory quality is I2, for example 6 A, as shown on curve (b) of the figure 2. From the duration (t'1-t0) between the start t0 of the charge of the primary 13, fixed by the unit 16, and the instant t'1 if I1 is exceeded, unit 16 can determine the time t1-t'1 necessary to arrive at current I2 and, for the next ignition, determine t0 appropriately. The time of the start of the charge can thus be adjusted by optimally by unit 16 without additional output from the detector 18 to control unit 16.

In the device of Figure 3, as in that of figure 1, it is very important to note that the shunt 15, the calculation and control unit 16 and the detector thresholds 18 are common to all cylinders and to all candles, and are therefore each mounted in a single copy in the circuit, thus more compact and economical.

For a candle, the curves of the currents Ip and Is measured on such a device are shown respectively in Figures 4 and 5, with an offset of the origin times for Is with respect to Ip. After a period of primary charge of around 3 ms, for which Ip increases by 0 to almost 6 V, there are two sign points selected positive primary current Ip measured during first two diagnostic durations of 20 µs starting respectively at around 3.2 ms and 4 ms. At these peaks of current Ip, correspond to points of chosen sign negative of the secondary current Is, which vanishes around 5 ms, indicating a spark duration slightly less than 2 ms.

The primary current measurement signals Ip aux shunt terminals 15 are also transmitted from the output of the RC 24-25 filter in parallel directly over one second input E 'of the computer 16 and applied to a converter analog / digital 34, itself connected to means of digital counting, memories, registers and comparators 35 of the computer 16. The primary current Ip, measured for diagnostic times, is used as analog signal diagnostic transmitted to the analog input E 'of the microprocessor of the computer 16. Thanks to the converter 34 and to digital memories and comparators 35, the comparison of the maximum intensities of the primary current Ipmax, as measured during diagnostic times, of the same rank (for example always during the first duration diagnostic) between successive charging times, and these Ipmax values are compared to each other as well as a maximum current intensity threshold Imax primary, adapted according to the order of the duration of diagnosis considered in the following of these durations of diagnosis between two consecutive charging times, in order to detect the decrease in Ipmax values, depending on the operating time of the installation, which translates wear of the spark plug 10 and, more generally, degradation of the secondary circuit, comprising this spark plug 10, the secondary 12 as well as a suppression interference, in series with the candle 10 and / or integrated therein. Indeed, the degradation of this secondary circuit is reflected by a gradual increase in equivalent resistance of this circuit, hence a correlative decrease in maximum intensity signals Ipmax, as shown in figure 6.

This figure 6 represents four curves of Ip measured during the first diagnostic period t3-t2, curve 36 corresponding to a spark plug 10 in new condition, while curves 37, 38 and 39 correspond to the use of the same candle 10 after periods of use gradually increasing. We see that the intensity maximum primary current Ipmax gradually decreases when the duration of use of the candle 10 increases, by curve 36 to curve 39. Monitoring of Ipmax gives therefore an image of the degradation of the secondary circuit, and by comparison with a maximum intensity threshold Imax, by example of 1 A, we can consider that curves 36 and 37 match a candle 10 in an acceptable state because Ipmax is greater than the Imax threshold, while the curves 38 and 39 correspond to a candle 10, or, more generally, to an overly degraded secondary circuit, requiring by example the change of the candle.

In Figure 7, the four curves are shown secondary current Is 40, 41, 42 and 43, obtained during sparks during which we have respectively measured, during the first diagnostic period, the curves 36 to 39 of Ip which correspond to the points of negative sign of current Is visible and superimposed for the four curves 40 to 43 of FIG. 7. It can be seen that the curves 42 and 43, corresponding to sparks obtained with a candle 10 in a degraded state, reflected by the curves 38 and 39 in FIG. 6 correspond to excess sparks short duration, while the duration of the sparks of the curves 40 and 41, obtained with a candle 10 in good condition, such as reflected by curves 36 and 37 in Figure 6, is sufficient to obtain a suitable quality spark for a sufficient time.

It should be noted that the diagnostic method described above can be implemented by a device (see Figures 1 and 3), which is both structurally sparse modified compared to that described in EP 0 559 540, and much more economical than the latter, since does not require high voltage components.

Claims (12)

1. Electronic ignition process for an internal combustion engine with controlled ignition, in each engine cylinder, by means of at least one spark plug (10) in series with a secondary winding (12) of an ignition coil (11) whose primary winding (13) is fed with electric current from a source (Vbat) through a commutator (14) mounted in a charging circuit of the primary (13), and itself controlled by a calculator control unit (16), comprising the stage of controlling cyclically the charging of the primary (13) during defined charging periods (t1-t0) and at moments (t0) defined by the calculator control unit (16) so that the cutting of the charge at the end (t1) of each charging period (t1-t0) is intended to cause a spark at the spark plug (10), characterised in that it also comprises the following stages:

   between two successive charging periods (t1-t0) and during the period of the spark presumed to follow the first of the said two successive charging periods, measuring the passage of a measuring current in the primary (13) during at least one diagnosis period (t3-t2) and at at least one moment (t2) defined by the calculator control unit (16);

   determining a rate of increase of the intensity (Ip) of the current in the primary (13) during at least one diagnosis period;

   distinguishing a high rate of increase from a weak rate of increase; and

   from this deducing information on the presence and/or quality of a spark at the spark plug (10) at the end of the previous charging period (t1-t0).
2. Process according to claim 1 characterised in that it consists in distinguishing the rate of increase of the intensity (Ip) of the current in the primary (13) during each diagnosis period (t3-t2) through comparison with at least one corresponding threshold, and sending a signal showing the presence of a spark in the event of exceeding the corresponding threshold.
3. Process according to claim 2 characterised in that it comprises furthermore the stage of measuring the intensity (Ip) of the current in the primary (13) during at least each diagnosis period (t3-t2) and of distinguishing the rate of increase by comparing the maximum intensity measured during the corresponding diagnosis period with a corresponding threshold of intensity (Io) in order to issue a signal showing the presence of a spark if the maximum intensity measured is higher than the intensity threshold (Io).
4. Process according to one of claims 2 and 3 characterised in that it consists furthermore in controlling at least two successive diagnosis periods (t3-t2, t5-t4) between two successive charging periods (t1-t0) and in deducing from here on the one hand the presence of a spark if at least one signal of presence (t3-t'2) is issued in a first predetermined time interval (T1), following the end (t1) of the previous charging period, and ending at the earliest at the same time (t3) as the first diagnosis period (t3-t2), and on the other hand, a minimum period of a spark of sufficient quality according to the number of presence signals issued.
5. Process according to claim 4 characterised in that it consists furthermore in deducing that the spark is too short if a second presence signal (t5-t'4) is not issued in a second predetermined time interval (T2), greater than the first time interval (T1), equally following the end (t1) of the previous charging period, and ending at the earliest at the same time (t5) as the second diagnosis period (t5-t4).
6. Process according to one of claims 4 and 5 characterised in that it consists in controlling likewise a third diagnosis period (t7-t6) between two successive charging periods (t1-t0), and in deducing from here that the spark plug (10) is short-circuited if a third presence signal is issued before the end of a third predetermined time interval (T3), likewise following the end (t1) of the previous charging period, greater than the first (T1) and, where applicable, the second predetermined time interval (T2), and ending at the earliest at the same time (t7) as the third diagnosis period (t7-t6).
7. Process according to any of claims 1 to 6 characterised in that it consists furthermore in measuring the maximum intensity of the current (Ip) in the primary (13) during at least one diagnosis period (t3-t2) of the same order after successive charging periods (t1-t0), in comparing the measurements among them and/or at at least one maximum threshold of intensity (Imax), and in deducing therefrom at least one signal showing the deterioration of the secondary circuit comprising the spark plug (10) and secondary winding (12) of the coil (11).
8. Process according to any of claims 1 to 7 characterised in that it consists in calibrating each diagnosis period (t3-t2, t5-t4, t7-t6) on a constant value and each corresponding threshold (Io) of intensity of current (Ip) on a value which is likewise constant.
9. Electronic ignition device, for internal combustion engines with controlled ignition, in each engine cylinder, by means of one spark plug (10) in series with a secondary winding (12) of an ignition coil (11) whose primary winding (13) is fed with electric current from a source (Vbat) through a commutator (14) mounted in a charging circuit of the primary (13), and itself controlled by a calculator control unit (16), means (15) for measuring the current (Ip) in the primary (13) being mounted in series in the charging circuit between the commutator (14) and the mass, and connected to detection means (18), connected in turn to the calculator control unit (16), characterised in that

   the calculator control unit (16) comprises means for generating a control signal of the commutator (14) for passing the current (Ip) in the primary (13) during at least one diagnosis period (t3-t2) and at at least one moment (t2), defined by the said unit (16), between two successive charging periods (t1-t0) of the primary (13), and during the period of the spark presumed to follow the first of the said two successive charging periods, and

   the detection means (18) comprise means (26) distinguishing the rate of increase of the intensity of the current (Ip) in the primary (13) and sending a signal to the said calculator control unit (16) when the measured intensity of the current (Ip) in the primary (13) is greater than a threshold (Io), at least during each diagnosis period.
10. Device according to claim 9 characterised in that the commutator (14) is controlled, from a control output (S) of the calculator control unit (16), by means of an interface amplifier (17), the means for measuring the current (Ip) in the primary (13) comprise a shunt (15) in series with the commutator (14), between the latter and the mass, and the means of detection (18) comprise at least a first (26) and a second (32) comparator, each receiving the signal of the shunt (15) on an input and comparing them respectively with a first (Io) and a second (I1) threshold of intensity, received on another input of the corresponding comparator (26,32), the output of each comparator being connected to a diagnosis input (E) of the calculator control unit (16), the second threshold of intensity (I1) being greater than the first (Io), but lower than the current (I2) necessary for creating an ignition voltage by cutting the primary (13), for the calculation by the said unit (16) of the charging periods (t1-t0) of the primary (13).
11. Device according to claim 10 characterised in that the calculator control unit (16) comprises a second diagnosis input (t1), connected to the shunt (15), and transmitting the measurement of the intensity of the current (Ip) to an analogue/digital converter (34), which is connected in turn to the memory and comparison means (35) for a maximum value of intensity (Ip), measured during a corresponding diagnosis period (t3-t2, t5-t4, t7-t6), at a maximum intensity threshold (Imax) and/or comparison between them of several maximum intensity values (Ip) measured during several diagnosis periods, and means issuing a signal of deterioration of the secondary circuit comprising the spark plug (10) and secondary (12) in the event of a maximum measured intensity (Ip) which is less than the said threshold (Imax).
12. Device according to any of claims 9 to 11 characterised in that the said means (15) for measuring the current (Ip) in the primary (13), the said calculator control unit (16), the said detection means (18) and, where applicable, the said interface amplifier (17) are common to all the spark plugs (10) of all the cylinders.

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