阅读说明：本技术 控制内燃机点火线圈的电子装置及其用于检测内燃机失火的电子点火系统 (Electronic device for controlling ignition coil of internal combustion engine and electronic ignition system for detecting fire of internal combustion engine ) 是由 欧金尼奥·卡鲁加蒂 斯特凡诺·席尔瓦 帕斯夸莱·福特 于 2020-02-19 设计创作，主要内容包括：公开了一种控制内燃机点火线圈的电子装置(1)。该装置包括高压开关(4)、驱动单元(5)、偏置电路(6)和积分电路(7)。高压开关与线圈的初级绕组串联连接,并且被配置为在闭合位置和打开位置之间切换。驱动单元被配置为在将能量充入初级绕组的阶段(T-chg)期间控制高压开关的闭合,其被配置为在从线圈的初级绕组到次级绕组的能量转移阶段(T-tr)期间以及在能量转移阶段之后的电离电流(I-ion)的测量阶段(T-ion)期间控制高压开关的打开,其中,所述电离电流借助于在能量转移阶段中由火花塞(3)生成的火花,由在发动机汽缸的燃烧室中的助燃可燃混合物的燃烧过程期间产生的离子生成。偏置电路被配置为在电离电流的测量阶段(T-ion)期间生成所述电离电流(I-ion),其中,所述偏置电路串联连接到次级绕组的第二端子。积分电路(7)置于偏置电路和参考电压(GND)之间。积分电路包括串联连接到偏置电路(6)并连接在偏置电路和参考电压之间的积分电容器(C4)。积分电容器被配置为在从初级绕组到次级绕组的能量转移阶段(T-tr)期间借助于流经次级绕组的电流完全放电,其被配置为在电离电流(I-ion)的测量阶段(T-ion)期间,充电(t5,t7)至不为零的值,以便在助燃可燃混合物的正确点火的情况下测量电离电流的积分值,并且其被配置为在电离电流(I-ion)的测量阶段(T-ion)期间保持基本为零的电荷(t25,t27),以便在助燃可燃混合物失火的情况下测量电离电流积分的基本为零的值。(An electronic device (1) for controlling an ignition coil of an internal combustion engine is disclosed. The device comprises a high-voltage switch (4), a driving unit (5), a biasing circuit (6) and an integrating circuit (7). A high voltage switch is connected in series with the primary winding of the coil and is configured to switch between a closed position and an open position. The drive unit is configured to control the closing of the high-voltage switch during a phase (T _ chg) of charging energy into the primary winding, it is configured to control the opening of the high-voltage switch during an energy transfer phase (T _ tr) from the primary winding to the secondary winding of the coil and during a measurement phase (T _ ion) of an ionization current (I _ ion) following the energy transfer phase, wherein the ionization current is generated by ions generated during a combustion process of a comburent combustible mixture in a combustion chamber of an engine cylinder by means of a spark generated by a spark plug (3) in the energy transfer phase. A bias circuit is configured to generate an ionization current (I _ ion) during a measurement phase (T _ ion) of the ionization current, wherein the bias circuit is connected in series to the second terminal of the secondary winding. An integration circuit (7) is interposed between the bias circuit and the reference voltage (GND). The integrating circuit includes an integrating capacitor (C4) connected in series to the bias circuit (6) and connected between the bias circuit and a reference voltage. The integrating capacitor is configured to be completely discharged by means of the current flowing through the secondary winding during an energy transfer phase (T _ tr) from the primary winding to the secondary winding, it is configured to be charged (T5, T7) to a value different from zero during a measurement phase (T _ ion) of the ionization current (I _ ion) in order to measure the integrated value of the ionization current in case of correct ignition of the comburent combustible mixture, and it is configured to maintain a substantially zero charge (T25, T27) during the measurement phase (T _ ion) of the ionization current (I _ ion) in order to measure a substantially zero value of the ionization current integration in case of misfire of the comburent combustible mixture.)

1. An electronic device (1) that controls an ignition coil of an internal combustion engine, the electronic control device comprising:

-a high voltage switch (4) connected in series to the primary winding of the coil and configured to switch between a closed position and an open position;

-a drive unit (5) configured to:

-controlling the closing of the high voltage switch during a phase (T chg) of charging energy into the primary winding;

-controlling the opening of the high-voltage switch during an energy transfer phase (T tr) from the primary winding to the secondary winding of the coil and during a measurement phase (T _ ion) of an ionization current (I _ ion) following the energy transfer phase, wherein the ionization current is generated by means of the spark generated by a spark plug (3) in the energy transfer phase, by ions produced during the combustion process of a comburent combustible mixture in the combustion chamber of the cylinder of the engine;

-a bias circuit (6) configured to generate the ionization current (I _ ion) during a measurement phase (T _ ion) of the ionization current, wherein the bias circuit is connected in series to the second terminal of the secondary winding;

-an integration circuit (7) interposed between the bias circuit and a reference voltage (GND); characterized in that the integrating circuit comprises an integrating capacitor (C4) connected in series to the biasing circuit (6) and connected between the biasing circuit and the reference voltage,

wherein the integration capacitor is configured to:

-fully discharging by means of a current flowing through the secondary winding during an energy transfer phase (T tr) from the primary winding to the secondary winding;

-charging (T5, T7) during a measurement phase (T _ ion) of the ionization current (I _ ion) to a value different from zero, in order to measure the integral value of the ionization current in the case of correct ignition of the comburent combustible mixture;

-maintaining a substantially zero charge (T25, T27) during a measurement phase (T _ ion) of the ionization current (I _ ion) in order to measure a substantially zero value of the integral of the ionization current in case of fire of the comburent combustible mixture.

2. The electronic control device according to claim 1, wherein the integrating circuit (7) comprises a parallel connection of the integrating capacitor (C4) and a zener diode (DZ11) having an anode terminal connected to the biasing circuit and having a cathode terminal connected towards the reference voltage,

wherein during the measurement phase of the ionization current the zener diode (DZ11) is reverse biased and it is configured to limit the voltage across the integration capacitor (C4) during the charging of the integration capacitor to be equal to a maximum defined value (Vint _ max) of the zener voltage of the zener diode (DZ11),

and wherein, during the energy transfer phase, the zener diode (DZ11) is forward biased and it is configured to bias the voltage across the integrating capacitor (C4) to a value of substantially zero.

3. The electronic control device of claim 1 or 2, wherein the biasing circuit comprises a parallel connection of a biasing capacitor (C6) and a further zener diode (DZ8) having an anode terminal connected to the integrating circuit and having a cathode terminal connected to the second terminal of the secondary winding,

wherein the biasing capacitor (C6) is configured to:

-charging (t2, t3) during the energy transfer phase by means of a current flowing through the secondary winding generated by a spark of the spark plug;

-discharging (t5) at least partly by means of the ionization current during a measurement phase of the ionization current;

wherein during the energy transfer phase the further zener diode (DZ8) is reverse biased and it is configured to limit the voltage across the biasing capacitor (C6) during charging of the biasing capacitor to be equal to a maximum defined value (V _ DZ8) of the zener voltage of the further zener diode (DZ 8).

4. The electronic device of any preceding claim, wherein the integrating capacitor (C4) is further configured to:

-in the case in which a pre-ignition of the comburent combustible mixture occurs in the combustion chamber during a charging phase (T10.2, T12), pre-charging during a phase of charging energy into the primary winding by means of an ionization current flowing through the secondary winding (2-2) during the charging phase (T chg), so as to measure an integral value of the ionization current flowing through the secondary winding during the charging phase due to the pre-ignition;

-maintaining the state of charge substantially constant during the energy charging phase in the case in which said comburent combustible mixture does not undergo pre-ignition.

5. An electronic ignition system (15) for detecting misfire in an internal combustion engine, the system comprising:

-a coil (2) having a primary winding (2-1) with a first terminal connected to the battery voltage, and having a secondary winding (2-2) with a first terminal connected to a spark plug (3);

-an electronic control device (1) according to any of the preceding claims, wherein the primary winding has a second terminal connected to the high voltage switch (4);

-an electronic control unit (20) connected to a drive unit (5) of the electronic control device (1) and comprising output terminals adapted to generate an ignition signal (Sac) having a first value indicative of the start of a charging phase of the primary winding and having a second value indicative of the start of an energy transfer phase from the primary winding to the secondary winding,

and wherein the drive unit (5) is further configured to receive the ignition signal and to generate a control signal (S _ ctrl) for opening and closing the high-voltage switch in dependence on the ignition signal.

6. Electronic ignition system (15) according to claim 5, the electronic device further comprising a local control unit (9) connected to the integration circuit (7) and to the electronic control unit (20),

wherein the local control unit (9) comprises:

-a first input terminal adapted to receive said ignition signal (Sac);

-a second input terminal adapted to receive an integrated voltage signal (V _ int _ I _ ion) representing the voltage across said integrating capacitor (C4);

-an output terminal adapted to generate a combustion monitoring signal (S _ ID) carrying, during a phase of charging energy, a voltage pulse (I2, I3, I4) having a length (Δ T2, Δ T3, Δ T4) that increases with an increase in the value of the integrated voltage signal (V _ int _ I _ ion) in a measurement phase of the ionization current of the previous cycle;

wherein the electronic control unit (20) further comprises an input terminal adapted to receive the combustion monitoring signal (S _ id),

and wherein the electronic control unit (20) is configured to detect the presence or absence of misfire according to a comparison between a length (Δ T2, Δ T3, Δ T4) of the voltage pulse (I2, I3, I4) and an ignition threshold.

7. The electronic ignition system (115) of claim 5, said electronic device further comprising:

a local control unit (109) connected to the integration circuit (7) and the electronic control unit (20),

-a current generator (11) adapted to generate a trigger current controlled by the local control unit (109);

wherein the local control unit (9) comprises:

-a first input terminal adapted to receive said ignition signal (Sac);

-a second input terminal adapted to receive an integrated voltage signal (V _ int _ I _ ion) representing the voltage across said integrating capacitor (C4);

-an output terminal adapted to generate a control signal (S _ ctrl _ i) of the current generator;

wherein the current generator is configured to generate a current pulse having two varying edges during a phase of charging energy, the two varying edges defining a distance that increases with an increase of a value of the integrated voltage signal (V _ int _ I _ ion) in a measurement phase of the ionization current of a previous cycle,

and wherein the electronic control unit (20) is configured to detect the presence or absence of misfire from a comparison between a distance (Δ T6, Δ T7, Δ T8) of the current pulses (I6, I7, I8) and an ignition threshold.

8. An electronic ignition system (15) according to claim 6 or 7, wherein the value of the ignition threshold is variable and depends at least on engine revolutions and engine load.

9. Electronic ignition system (15) according to any of claims 5 to 8, wherein the biasing circuit (6) and the integrating circuit (7) are enclosed in a single housing.

10. Electronic system according to claim 9, wherein the housing further comprises the high voltage switch (4) and the drive unit (5).

11. Electronic system according to claim 10, wherein the electronic control unit (20), the high voltage switch (4) and the drive unit (5) are enclosed in another housing.

Technical Field

The present invention relates generally to the field of electronic ignition of internal combustion engines, such as for example the engines of motor vehicles.

More particularly, the present invention relates to an electronic device for controlling an ignition coil of an internal combustion engine and an electronic ignition system thereof, which are capable of detecting a misfire (misfire) of a combustion-supporting combustible mixture (for example, oxygen in the air as a comburent and fuel as a combustible) in a cylinder of the engine by means of measuring an ionization current generated in the cylinder in question.

Prior Art

Modern internal combustion engines of motor vehicles are equipped with systems for monitoring the internal combustion process, with the aim of maximizing the efficiency and performance of the engine.

It is known to measure the ionization current in order to obtain data indicative of a parameter of the combustion process of the air-fuel mixture directly from the combustion chamber.

In particular, spark plugs are used as ions (usually CHO)⁺、H₃O⁺、C₃H₃ ⁺、NO₂ ⁺Type) that are generated in the combustion chamber after a spark between the electrodes of the spark plug has been generated and combustion of the air-fuel mixture has occurred.

Therefore, the ionization current is generated by applying a potential difference to the electrodes of the spark plug and by measuring the current generated by the ions generated in the combustion chamber.

By means of the measurement of the ionization current, it is possible to detect in real time the misfire of the air-fuel mixture (more generally, the mixture of comburent and combustible), and then to take measures in time to prevent the malfunction of the engine.

US 5534781 a1 discloses a system for detecting ionization current that uses (see fig. 1 and 2) an integrating circuit 45 to calculate a voltage proportional to the integral of the ionization current.

The integrator 45 is based on an operational amplifier 46 and it comprises two diodes 40, 42 connected in parallel in opposite directions and a series connection of a resistor 44 and a capacitor 48.

The signal generated at the output of the integrator 45 is read by an Electronic Control Unit (ECU) 10.

The applicant has observed that the integrating circuit 45 of US 5534781 a1 is overly complex in that it requires the use of an operational amplifier 46 and many other electronic components.

Furthermore, US 5534781 does not mention the way in which information about the detection of a misfire is sent from the coil 25 to the electronic control unit 10.

Summary of The Invention

The present invention relates to an electronic device for controlling an ignition coil of an internal combustion engine and an electronic ignition system thereof for detecting misfire in an internal combustion engine as defined in the appended claims 1 and 5 and their preferred embodiments disclosed in the dependent claims 2 to 4 and 6 to 11, respectively.

The applicant has perceived that the electronic control device and the electronic ignition system according to the present invention allow detecting the misfire of a combustible comburent mixture (for example, an air-fuel mixture) in the combustion chamber of a cylinder in an engine by measuring the integral value of the ionization current with an integrating circuit that is very easy to implement and sufficiently reliable and accurate for the application considered, while also significantly reducing the calculations required by an electronic control unit located outside the coil.

The integration circuit of the invention is reliable because it reduces the risk of detecting false misfire alarms or false combustion presence events because it provides the electronic control unit with an integrated value of the ionization current by means of which it is able to detect the presence or absence of a misfire.

According to a first aspect of the present invention, there is disclosed an electronic control device that controls an ignition coil of an internal combustion engine, the electronic control device including:

-a high voltage switch connected in series to the primary winding of the coil and configured to switch between a closed position and an open position;

-a drive unit configured to:

controlling the closing of the high-voltage switch during the phase of charging energy into the primary winding;

controlling the opening of the high-voltage switch during an energy transfer phase from the primary winding to the secondary winding of the coil and during a measurement phase of an ionization current following the energy transfer phase, wherein the ionization current is generated by means of a spark generated by a spark plug in the energy transfer phase, by ions produced during a combustion process of a comburent combustible mixture in a combustion chamber of an engine cylinder;

-a bias circuit configured to generate an ionization current during a measurement phase of the ionization current, wherein the bias circuit is connected in series to a second terminal of the secondary winding;

-an integrating circuit interposed between the biasing circuit and a reference voltage;

wherein the integration circuit includes an integration capacitor connected in series to the bias circuit and connected between the bias circuit and a reference voltage,

wherein the integration capacitor is configured to:

-fully discharging by means of the current flowing through the secondary winding during the energy transfer phase from the primary winding to the secondary winding;

-charging to a value different from zero during a measurement phase of the ionization current, in order to measure the integral value of the ionization current with correct ignition of the comburent combustible mixture;

-maintaining a substantially zero charge during the measurement phase of the ionization current, so as to measure a substantially zero value of the integral of the ionization current in the event of a misfire of the comburent combustible mixture.

Preferably, the integration circuit comprises a parallel connection of an integration capacitor and a Zener diode, the Zener diode having an anode terminal connected to the bias circuit and having a cathode terminal connected towards the reference voltage,

wherein the zener diode is reverse biased during a measurement phase of the ionization current and is configured to limit a voltage across the integration capacitor to be equal to a maximum defined value of a zener voltage of the zener diode during charging of the integration capacitor,

and wherein during the energy transfer phase the zener diode is forward biased and is configured to bias the voltage across the integration capacitor to a substantially zero value.

Preferably, the bias circuit comprises a parallel connection of the bias capacitor and a further zener diode, the further zener diode having an anode terminal connected to the integrating circuit and having a cathode terminal connected to the second terminal of the secondary winding,

wherein the bias capacitor is configured to:

-charging during the energy transfer phase by means of a current generated by a spark of a spark plug flowing through the secondary winding;

-discharging at least partly by means of the ionization current during a measurement phase of the ionization current;

wherein during the energy transfer phase the further zener diode is reverse biased and it is configured to limit the voltage across the bias capacitor during charging of the bias capacitor to be equal to a maximum defined value of the zener voltage of the further zener diode.

Preferably, the integration capacitor is further configured to:

-in the case in which a pre-ignition of the comburent combustible mixture occurs in the combustion chamber during the charging phase, pre-charging is carried out during the phase of charging energy into the primary winding by means of the ionization current flowing through the secondary winding during the charging phase, so as to measure the integral value of the ionization current flowing through the secondary winding during the charging phase due to said pre-ignition;

-maintaining the state of charge substantially constant during the energy charging phase, in the case in which the comburent combustible mixture does not undergo pre-ignition.

According to a second aspect of the present invention, there is disclosed an electronic ignition system for detecting misfire in an internal combustion engine, the system comprising:

-a coil having a primary winding with a first terminal connected to the battery voltage and having a secondary winding with a first terminal connected to the spark plug;

-an electronic control device according to the first aspect of the invention, wherein the primary winding has a second terminal connected to the high voltage switch;

an electronic control unit connected to the drive unit of the electronic control device and comprising output terminals adapted to generate an ignition signal having a first value indicative of the start of a charging phase of the primary winding and having a second value indicative of the start of an energy transfer phase from the primary winding to the secondary winding,

and wherein the drive unit is further configured to receive the ignition signal and to generate a control signal for opening and closing the high voltage switch in dependence on the ignition signal.

Preferably, the electronic device according to the second aspect of the invention further comprises a local control unit connected to the integration circuit and the electronic control unit,

wherein, local control unit includes:

a first input terminal adapted to receive an ignition signal;

a second input terminal adapted to receive an integrated voltage signal representative of the voltage across the integrating capacitor;

an output terminal adapted to generate a combustion monitoring signal carrying a voltage pulse during the phase of charging energy, the voltage pulse having a length that increases with an increase in the value of the integrated voltage signal in the measurement phase of the ionization current of the previous cycle;

wherein the electronic control unit further comprises an input terminal adapted to receive a combustion monitoring signal,

and wherein the electronic control unit is configured to detect the presence or absence of misfire from a comparison between the length of the voltage pulse and an ignition threshold value.

Preferably, the electronic device according to the second aspect of the present invention further comprises:

a local control unit connected to the integrating circuit and the electronic control unit,

-a current generator adapted to generate a trigger current controlled by a local control unit;

wherein, local control unit includes:

a first input terminal adapted to receive an ignition signal;

a second input terminal adapted to receive an integrated voltage signal representative of the voltage across the integrating capacitor;

an output terminal adapted to generate a control signal of the current generator;

wherein the current generator is configured to generate a current pulse during the phase of charging the energy with two varying edges defining a distance that increases with an increase in the value of the integrated voltage signal in the measurement phase of the ionization current of a previous cycle,

and wherein the electronic control unit is configured to detect the presence or absence of misfire from a comparison between a distance of the current pulses and an ignition threshold value.

Preferably, the value of the ignition threshold is variable and depends at least on the number of engine revolutions and the engine load.

Preferably, the bias circuit and the integrating circuit are enclosed in a single housing.

Preferably, the housing further comprises a high voltage switch and a drive unit.

Preferably, the electronic control unit, the high voltage switch and the drive unit are enclosed in a further housing.

The applicant has also realised that the integrating circuit of the invention also allows to detect in a simple and reliable manner the pre-ignition of the comburent combustible mixture (caused for example by the fouling of the spark plug itself) that occurs during the phase of charging energy into the primary winding.

Furthermore, the electronic control device and the electronic ignition system according to the present invention provide at least two possible particularly effective solutions for transmitting measurement information of the ionization current integral to an electronic control unit located outside the coil in order to detect the presence or absence of misfires of the comburent combustible mixture and/or the presence of pre-ignitions of the comburent combustible mixture during the phase of charging energy into the primary winding.

Brief description of the drawings

Additional features and advantages of the present invention will become more apparent from the following description of preferred embodiments and variations thereof, provided by way of example with reference to the accompanying drawings in which:

FIGS. 1A-1C show block diagrams of an electronic ignition system according to an embodiment of the invention;

figures 2A-2C schematically show possible trends of some signals generated in the electronic ignition system during three combustion cycles according to an embodiment of the invention, in the case where two correct ignitions of the combustion-supporting combustible mixture and one misfire of the combustion-supporting combustible mixture occur;

figure 3 shows a block diagram of an electronic ignition system according to a variant of the embodiment of the invention;

4A-4C schematically show possible trends of some signals generated in an electronic ignition system according to a variant of the embodiment of the invention;

fig. 5 schematically shows the possible trends of some of the signals generated in the electronic ignition system according to the invention in the case in which pre-ignition of the comburent combustible mixture occurs.

Detailed description of the invention

It should be observed that in the following description, identical or similar blocks, components or modules are denoted by the same reference numerals in the figures, even though they are shown in different embodiments of the present invention.

Referring to fig. 1A, 1B, 1C, an electronic ignition system 15 for an internal combustion engine according to an embodiment of the present invention is shown.

The electronic ignition system 15 may be mounted on any motorized vehicle, such as, for example, a motor vehicle, a motorcycle, or a truck.

The ignition system 15 includes:

-an ignition coil 2;

-a spark plug 3;

-an electronic control device 1;

-an electronic control unit 20 for controlling the operation of the electronic control unit,

the electronic control unit 20, generally indicated by ECU, is a processing unit (for example a microprocessor) located sufficiently far from the engine head to be protected from the high operating temperature of the ignition coil 2.

In contrast, the electronic control device 1 and the coil 2 are positioned near the engine head and are designed to withstand the high operating temperature of the engine head.

The spark plug 3 is connected to the secondary winding 2-2 of the ignition coil 2.

In particular, the spark plug 3 comprises a first electrode connected to the secondary winding 2-2 and comprises a second electrode connected to a ground reference voltage.

The spark plugs 3 have a function of generating sparks at both ends of their electrodes, and the sparks allow combustion of an air-fuel mixture included in the cylinders of the internal combustion engine.

It should be observed that for the purposes of explaining the invention, air-fuel mixtures are considered below, but more generally the invention applies to mixtures of comburent (also different from air) and combustible (also different from fuel).

The ignition coil 2 has a primary winding 2-1, a secondary winding 2-2 and a magnetic core 2-3 for inductively coupling the primary winding 2-1 with the secondary winding 2-2.

The ignition system 15 operates according to three operating phases:

a first charging phase, in which energy is charged into the primary winding 2-1 by means of a primary current I _ pr that flows with increasing trend through the primary winding 2-1;

a second energy transfer phase, in which energy is transferred from the primary winding 2-1 to the secondary winding 2-2, so as to generate a spark on the electrodes of the spark plug 3 and so as to burn the air/fuel mixture comprised in the cylinder of the internal combustion engine;

a third phase of ionization current measurement, in which a measurement of the ionization current I _ ion integration is performed, as will be explained in more detail below.

The third phase of the ionization current measurement also includes a chemical phase and a subsequent thermal phase.

The electronic control device 1 includes:

-a drive unit 5;

-a high voltage switch 4;

-a bias circuit 6;

-an integrating circuit 7;

a local control unit 9.

Preferably, the electronic control device 1 is a single component enclosed in a housing, i.e. the drive unit 5, the high voltage switch 4, the bias circuit 6 and the integrating circuit 7 are enclosed in a single housing; for example, the drive unit 5, the high voltage switch 4, the bias circuit 6 and the integration circuit 7 are mounted on the same printed circuit board.

Alternatively, the biasing circuit 6 and the integrating circuit 7 are enclosed in a single housing, while the drive unit 5 and the high-voltage switch 4 are outside said housing; for example, the drive unit 5 and/or the high voltage switch 4 are enclosed within the electronic control unit 20.

The primary winding 2-1 includes a first terminal adapted to receive the battery voltage V _ batt (e.g., equal to 12 volts) and also includes a second terminal connected to the high voltage switch 4 and adapted to generate a primary voltage V _ pr.

Further, hereinafter "voltage drop across the primary winding 2-1" will refer to the potential difference between the first and second terminals of the primary winding 2-1.

The secondary winding 2-2 is connected to a spark plug 3; in particular, secondary winding 2-2 includes a first terminal connected to a first electrode of spark plug 3 and adapted to generate a secondary voltage V _ sec, and includes a second terminal connected toward a ground reference voltage through a bias circuit 6 and an integration circuit 7, as shown in FIGS. 1A-1C.

Hereinafter, "primary current" I _ pr will be used to indicate the current flowing through the primary winding 2-1, and "secondary current" I _ sec will be used to indicate the current flowing through the secondary winding 2-2 during the second phase of energy transfer from the primary winding 2-1 to the secondary winding 2-2.

Preferably, a resistor is interposed between the spark plug 3 and the secondary winding 2-2, having a function of attenuating noise.

The high voltage switch 4 is connected in series to the primary winding 2.1.

The term "high voltage" means that the voltage at terminal I4I of switch 4 is greater than 200 volts.

In particular, the high voltage switch 4 comprises a first terminal I4I connected to the second terminal of the primary winding 2.1, comprises a second terminal I4o connected to a ground reference voltage, and comprises a control terminal I4c connected to the drive unit 5.

The high-voltage switch 4 can be switched between a closed position and an open position depending on the value of the control signal S _ ctrl received at the control terminal I4 c.

Preferably, the high-voltage switch 4 is realized by an IGBT-type transistor (insulated gate bipolar transistor) having a collector terminal (collector terminal) coinciding with the terminal I4I, having an emitter terminal coinciding with the terminal I4o, and having a gate terminal coinciding with the terminal I4 c; in this case, the primary voltage V _ pr is therefore equal to the voltage of the collector terminal of the IGBT transistor 4.

Specifically, the IGBT transistor 4 operates in the saturation region when it is closed, and operates in the cutoff region when it is opened.

The IGBT transistor 4 operates at a voltage value greater than 200 volts.

Alternatively, the high voltage switch 4 may be implemented with a field effect transistor (MOSFET, JFET) or with two Bipolar Junction Transistors (BJT), or it may be a solid state switch (relay).

The drive unit 5 is powered with a supply voltage VCC that is less than or equal to the battery voltage V _ batt.

For example, assuming that the battery voltage V _ batt has a value of 12V, the power supply voltage VCC may have a value of 8.2V, 5V, or 3.3V.

The biasing circuit 6 has the function of biasing the spark plug 3 in order to generate a flow of ionization current I _ ion during the third phase of ionization current measurement, which will be explained in more detail below.

A bias circuit 6 is disposed between the second terminal of the secondary winding 2-2 and the integrating circuit 7.

Preferably, the biasing circuit 6 comprises a parallel connection of a first capacitor C6 (hereinafter "biasing capacitor") and a first zener diode DZ8, which are electrically connected as shown in fig. 1A-1C.

The biasing capacitor C6 includes a first terminal connected to the cathode terminal of the first zener diode DZ8, the cathode terminal of the first zener diode DZ8 and the first terminal of the biasing capacitor C6 being connected to the second terminal of the secondary winding 2-2.

Bias capacitor C6 includes a second terminal connected to integrating circuit 7.

The bias capacitor C6 has a function of generating electric energy to force the ionization current I _ ion to flow after the end of the spark plug 3.

In fact, the biasing capacitor C6 is charged during the second phase of energy transfer from the primary winding to the secondary winding and is at least partially discharged by means of the ionization current I _ ion during the third phase of ionization current I _ ion measurement.

Hereinafter, V _ C6 will be used to indicate the voltage drop across the bias capacitor C6.

It should be noted that, as will be explained in more detail below, according to known solutions for measuring the ionization current, the capacitance value of the biasing capacitor C6 is much lower than the capacitance value of the capacitor used in the biasing circuit.

For example, the capacitance of the biasing capacitor C6 is comprised between 10 and 150 nanofarads.

In the third phase of the ionization current measurement, the bias capacitor C6 may be discharged (partially or fully) near the end of the ionization current (as shown in fig. 2A) or shortly after or before the end of the ionization current I _ ion.

The first zener diode DZ8 includes a cathode terminal connected to the second terminal of the secondary winding 2-2 and includes an anode terminal connected to the integrating circuit 7.

The first zener diode DZ8 has a first mode of operation in which the voltage drop across itself is equal to the zener voltage Vz (e.g., equal to 200 volts) when it is reverse biased (i.e., when the voltage at the anode terminal is less than the voltage at the cathode terminal), and a second mode of operation in which it operates as a normal diode when it is forward biased (i.e., when the voltage at the anode terminal exceeds the voltage at the cathode terminal, e.g., by about 0.7 volts).

During the second energy transfer phase, the first zener diode DZ8 is reverse biased and it has the function of limiting the value of the voltage across the biasing capacitor C6, which biasing capacitor C6 is charged up to a maximum value equal to the zener voltage of the first zener diode DZ8, hereinafter indicated with V _ DZ8 (for example, V _ DZ8 is equal to 200 volts) of the first zener diode DZ 8.

During the third phase of the ionization current measurement, the first zener diode DZ8 is forward biased; for example, the voltage across the first zener diode DZ8 is equal to about 0.7 volts.

The integration circuit 7 has the function of measuring the integrated value of the ionization current I _ ion, performing a current-voltage conversion, and generating an integrated voltage signal V _ int _ I _ ion representing the integrated value of the ionization current I _ ion measured during the third phase of the ignition cycle, as will be explained in more detail below.

The integrating circuit 7 is connected between the bias circuit 6 and a ground reference voltage.

During the second energy transfer phase, in which a spark occurs on the electrodes, a reset of the integrating circuit 7 is performed in order to allow a measurement of the integration of the ionization current I _ ion to be performed during the third phase, as will be explained in more detail below.

More particularly, the integration circuit 7 comprises a parallel connection of a second capacitor C4 (hereinafter indicated with "integration capacitor") and a second zener diode DZ11, as shown in fig. 1A-1C.

The integrating capacitor C4 includes a first terminal connected to the anode terminal of the second zener diode DZ11, the anode terminal of the second zener diode DZ11 and the first terminal of the integrating capacitor C4 are connected to the biasing circuit 6, in particular to the second terminal of the biasing capacitor C6 and the anode terminal of the first zener diode DZ 8.

The integration capacitor C4 also includes a second terminal connected to the cathode terminal of the second zener diode DZ11, the cathode terminal of the second zener diode DZ11, and the second terminal of the integration capacitor C4 being connected to the ground reference voltage.

The integrating capacitor C4 has the function of storing (during the third phase of the ionization current I _ ion measurement) the charge generated by the flow of the ionization current I _ ion, measuring the value as an integral function of the ionization current I _ ion; in particular, the value measured by means of the integrating capacitor C4 increases (for example, in direct proportion) with the increase of the integration value of the ionization current I _ ion.

Furthermore, the integrating capacitor C4 is automatically completely discharged (releases its possible residual charge) during the second energy transfer phase by means of a pulse of the secondary current I _ sec flowing through the secondary winding 2-2, i.e. when a spark occurs between the electrodes of the spark plug 3.

The integrated voltage signal V _ int _ I _ ion thus represents the voltage across the integrating capacitor C4, which is a function (e.g., proportional) of the integrated value of the ionization current I _ ion measured during the third phase of ionization current I _ ion measurement.

The second zener diode DZ11 comprises an anode terminal connected to the first terminal of the integration capacitor C4, the first terminal of the integration capacitor C4 and the anode terminal of the second zener diode DZ11 being connected to the biasing circuit 6, in particular to the second terminal of the biasing capacitor C6 and to the anode terminal of the first zener diode DZ 8.

The second zener diode DZ11 further includes a cathode terminal connected to the integration capacitor C4, the cathode terminals of the integration capacitor C4 and the second zener diode DZ11 being connected to a ground reference voltage.

The second zener diode DZ11 has a first mode of operation in which the voltage across itself is equal to the zener voltage Vz (e.g., equal to 15 volts) when it is reverse biased (i.e., when the voltage at the anode terminal is less than the voltage at the cathode terminal), and a second mode of operation in which it operates as a normal diode when it is forward biased (i.e., when the voltage at the anode terminal is greater than the voltage at the cathode terminal by about 0.7 volts).

During the third phase of the ionization current I _ ion measurement, the second zener diode DZ11 is reverse biased and it has the function of limiting the value of the integration voltage V _ int _ I _ ion across the integration capacitor C4 to be equal to the maximum value of the zener voltage V _ DZ11 of the second zener diode DZ11, in the case in which the value of the integration voltage V _ int _ I _ ion in the third phase reaches a high value: this allows to connect the first terminal of the integrating capacitor C4 (directly or indirectly) to the local control unit 9 (e.g. a small microprocessor) without damaging it.

For example, the zener voltage V _ DZ11 of the second zener diode DZ11 is equal to 15 volts, and therefore the value of the integration voltage V _ int _ I _ ion across the integration capacitor C4 is limited to a value Vint _ max-V _ DZ 11-15 volts, i.e. the voltage drop across the integration capacitor C4 (during the third phase of the ionization current measurement) is limited to a defined negative value equal to-15 volts.

During the second energy transfer phase, the second zener diode DZ11 is forward biased and has the function of keeping the voltage across the integrating capacitor C4 at a value substantially zero; for example, during the second energy transfer phase, the voltage across the integrating capacitor C4 is limited to a positive value equal to about 0.7 volts.

The electronic control unit 20 has a function of controlling the operation of the ignition coil 2 in order to generate a spark at the ignition plug 3 at the correct timing.

In particular, the electronic control unit 20 comprises output terminals adapted to generate an ignition signal S _ ac with a transition from a first value to a second value (for example, from a logic low value to a high value) in order to terminate a first phase of charging of the primary winding 2-1 and to activate a second phase of energy transfer from the primary winding 2-1 to the secondary winding 2-2, as will be explained in more detail below.

The driving unit 5 (e.g., a microcontroller) has a function of controlling the operation of the high-voltage switch.

The driving unit 5 comprises a first input terminal adapted to receive an ignition signal S _ ac having a transition from one value to another (for example, a transition from a logic high value to a low value, or vice versa) and comprises a first output terminal adapted to generate a control signal S _ ctrl for driving the opening or closing of the high-voltage switch 4 depending on the value of the ignition signal S _ ac.

In particular, the driving unit 5 is configured to receive the ignition signal S _ ac having a first value (for example a logic high value) and to generate the control signal S _ ctrl having a first value (for example a voltage value greater than zero) to drive the closure of the high-voltage switch 4.

Furthermore, the driving unit 5 is configured to receive the ignition signal S _ ac having a second value (for example a logic low value) and to generate the control signal S _ ctrl having a second value (for example a zero voltage value) to drive the opening of the high-voltage switch 4, so as to abruptly interrupt the primary current I _ pr flowing through the primary winding 2-1: this results in a voltage pulse of a short length, typically having a peak value of 200-450V and having a length of a few microseconds, on the second terminal of the primary winding 2-1.

Thus, the energy stored in the primary winding 2-1 is transferred to the secondary winding 2-2; in particular, a high value voltage pulse, typically 15-50kV, is generated at the first terminal of the secondary winding 2-2, which is sufficient to trigger a spark between the electrodes of the spark plug 3.

The local control unit 9 (for example, a microprocessor or microcontroller) has the function of collecting information of the integral value of the ionization current I _ ion and transferring it to the electronic control unit 20 for the purpose of detecting the presence or absence of misfiring of the air-fuel mixture in the combustion chamber of the cylinder in which the spark plug 3 is located, by means of using a separate communication channel.

Misfires may be caused by, for example, a faulty injector or a faulty spark plug 3 or other causes inside the combustion chamber.

The local control unit 9 is electrically connected to the integration circuit 7 and the electronic control unit 20.

In particular, the local control unit 9 comprises a first input terminal adapted to receive the ignition signal Sac, comprises a second input terminal adapted to receive an integrated voltage signal V _ int _ I _ ion representative of the voltage V _ C4 across the integrating capacitor C4 of the integrating circuit 7 (i.e. representative of the integration of the ionization current I _ ion), and comprises an output terminal adapted to generate a combustion monitoring voltage S _ id carrying voltage pulses of each cycle (see I1, I2, I3, I4 in fig. 2A-C) having a length Δ T (see Δ T1, Δ T2, Δ T3, Δ T4 in fig. 2A-2C) which depends on the measure of the integration of the ionization current I _ ion in the previous cycle, i.e. Δ T is a function of the value of the integrated voltage V _ int _ I _ ion detected in the previous cycle.

It should be observed that the value of the integrated voltage V _ int _ I _ ion generated during the third phase of the ionization current I _ ion measurement has a negative trend and therefore an inverter is used inside the control unit 9 in order to generate an integrated voltage with a positive trend.

The combustion monitoring voltage S _ id will be used by the electronic control unit 20 to detect the presence or absence of a misfire of the air-fuel mixture in the combustion chamber of the cylinder in which the ignition plug 3 is mounted in each combustion cycle, as will be explained in more detail below.

In particular, the length Δ T of the voltage pulse of the combustion monitoring voltage S _ id is a function (e.g. proportional) of the measured value of the integral of the ionization current I _ ion in the previous ignition cycle, i.e. it is a function (e.g. proportional) of the value of the integral voltage V _ int _ I _ ion detected across the integrating capacitor C4 in the previous ignition cycle.

Thus, in the previous cycle, the control unit 9 is configured to generate the combustion monitoring voltage S _ id from the ignition signal S _ ac and from the integrated voltage signal V _ int _ I _ ion carrying the measure of the integration of the ionization current I _ ion in the previous ignition cycle:

-generating a rising edge in the voltage pulse of the combustion monitoring voltage S _ id (see rising edges of voltage pulses I1, I2, I3, I4 in fig. 2A-C) when the ignition signal S _ ac has a rising edge (see times t1, t10, t20, t30 in fig. 2A-C):

the length Δ T of the voltage pulse of the combustion monitoring voltage S _ id is a function (for example, proportional) of the value of the integrated voltage V _ int _ I _ ion of the measurement phase of the ionization current I _ ion in the preceding ignition cycle (see the falling edges at the instants T1.1, T10.1, T20.1, T30.1 of the pulses I1, I2, I3, I4 with the respective lengths Δ T1, Δ T2, Δ T3, Δ T4 in fig. 2A-2C).

Therefore, the electronic control unit 20 has an additional function of detecting the presence or absence of misfire of the air-fuel mixture in the combustion chamber of the cylinder in which the ignition plug 3 is mounted.

In this case, the electronic control unit 20 comprises an input terminal adapted to receive a combustion monitoring voltage S _ id carrying, for each ignition cycle, a length Δ T having an integrated measurement value depending on the ionization current I _ ion.

The electronic control unit 20 is therefore configured to detect the presence or absence of misfiring of the air-fuel mixture in the combustion chamber of the cylinder in which the spark plug 3 is installed, from the integrated measurement value of the ionization current I _ ion.

More specifically, the electronic control unit 20 performs, for each ignition cycle, a comparison of the length Δ T of the voltage pulse (which depends on the integrated measurement of the ionization current I _ ion) with respect to the ignition threshold value, in order to detect the presence or absence of misfire in each ignition cycle.

Advantageously, the value of the ignition threshold is variable and depends on the operating conditions of the engine, such as, for example, the number of engine revolutions and the engine load.

The electronic control unit 20 also has the function of detecting the presence or absence of pre-ignition of the air-fuel mixture or of fouling of the spark plug 3, i.e. the presence of an undesired spark during the charging phase of the primary winding 2-1, from the integrated measurement of the ionization current I _ ion.

Fig. 1A shows the electronic ignition system 15 during a first phase of charging energy into the primary winding 2-1, wherein the high voltage switch 4 is closed: in this configuration, current I _ chg (see fig. 1A) flows from battery voltage V _ batt towards ground, through first primary winding 2-1 and high voltage switch 4; the value of the current I _ chg is therefore equal to the value of the primary current I _ pr flowing in the primary winding 2-1.

Fig. 1B shows the electronic ignition system 15 during a second phase of energy transfer from the primary winding 2-1 to the secondary winding 2-2, wherein the high voltage switch 10 is open: in this configuration, current I _ tr flows through (see FIG. 1B) spark plug 3, secondary winding 2-2, bias circuit 6, and integrating circuit 7.

Fig. 1C shows the electronic ignition system 15 during the third phase of the ionization current I _ ion measurement and shows the generation of an integrated voltage signal V _ int _ I _ ion representing the integrated measurement of the ionization current I _ ion.

It can be observed that the high voltage switch 4 is open and that the ionization current I _ ion flows through the integrating circuit 7, the biasing circuit 6, the secondary winding 2-2 and the spark plug 3 (see again fig. 1C and 2C).

Referring to fig. 2A-2C, there are shown possible trends for the ignition signal S _ ac, the control signal S _ ctrl, the primary current I _ pr, the secondary current I _ sec, the ionization current I _ ion, the integrated voltage V _ int _ I _ ion, and the combustion monitoring voltage S _ id, according to an embodiment of the present invention.

It should be noted that, for the purposes of explaining the invention, fig. 2A-2C show the signal of the secondary current I _ sec separately from the signal of the ionization current I _ ion, but in practice it is the current flowing through the secondary winding 2-2 in two different phases of operation of the electronic ignition system 15 (in the second energy transfer phase with length T _ tr and in the third phase of ionization current measurement with length T _ ion, respectively): this separation is also useful because the order of the currents is different, i.e. in the case of the secondary current I sec in the second energy transfer phase hundreds of mA [ milliamperes ], and in the case of the ionization current I ion hundreds of μ a [ microamperes ].

Note that the signals represented in fig. 2A-2C are not drawn to scale and are described in preference to values derived from the signals.

Fig. 2A shows a first ignition cycle comprised between t1 and t10, and fig. 2B shows a second ignition cycle comprised between times t10 and t 20: in both cycles, correct combustion of the air-fuel mixture occurs in the combustion chamber of the cylinder in the engine, i.e. correct spark occurs between the electrodes of the spark plug 3.

In contrast, fig. 2C shows a third ignition cycle included between times t10 and t20, in which a misfire of the air-fuel mixture occurs in the combustion chamber of a cylinder in the engine, i.e., no spark occurs between the electrodes of the spark plug 3 in the second energy transfer phase.

The trend of the signal continues in the ignition cycle after the third cycle, where only a portion of the fourth cycle after the third cycle is shown.

It can be observed that for the first ignition cycle and the second ignition cycle, there are three operating phases of the electronic ignition system 15:

the first phase of charging the primary winding 2-1 has a length T _ chg and it is comprised between the instants T1 and T2 of the first cycle and between the instants T10 and T12 of the second cycle: at these moments the integration circuit 7 starts to reset, in particular the integration capacitor C4 starts to discharge slowly, and it is partially discharged by the load seen from the terminal O4 of the integration capacitor C4;

the second phase of energy transfer from the primary winding 2-1 to the secondary winding 2-2 has a length T _ tr and it is comprised between the instants T2 and T5 of the first cycle, comprised between the instants T12 and T15 of the second cycle: at these moments, assuming that the spark is correctly generated across the electrodes of the spark plug 3, the integrating circuit 7 is reset (in particular the integrating capacitor C4 is rapidly discharged to a value substantially zero) and, moreover, the biasing capacitor C6 of the biasing circuit 6 is charged until it reaches the value of the zener voltage V _ DZ8 of the first zener diode DZ 8;

the third phase of measurement of the ionization current and generation of the integrated voltage V _ int _ I _ ion has a length T _ ion and it is comprised between the instants T5 and T10 of the first cycle, between the instants T15 and T20 of the second cycle: at these instants, the biasing capacitor C6 of the biasing circuit 6 operates as a power generator to force the ionization current I _ ion to flow and, consequently, the biasing capacitor C6 of the biasing circuit 6 is at least partially discharged by means of the flow of the ionization current I _ ion, and, in addition, the value as a function (for example, proportional) of the integration of the ionization current I _ ion is measured (by means of detecting the integrated voltage V _ int _ I _ ion across the integrating capacitor C4), by means of charging the integrating capacitor C4 until the integrated voltage V _ int _ I _ ion reaches a maximum value Vint _ max (in the case where the integrated value of the ionization current I _ ion is high, this maximum value is limited to the zener voltage V _ DZ11 of the zener diode DZ 11).

Furthermore, it can be observed that, for the third ignition cycle, there are also three operating phases of the electronic ignition system 15:

the first phase of charging the primary winding 2-1 has a length T _ chg and it is comprised between the times T20 and T22: at these times, charging of energy into the primary winding 2-1 is performed and the integrating capacitor C4 is partially and slowly discharged;

the second phase of energy transfer from the primary winding 2-1 to the secondary winding 2-2 has a length T _ tr and it is comprised between the instants T22 and T25: at these times, it is assumed that a misfire of the air-fuel mixture occurs in the combustion chamber in which the ignition plug 3 is installed;

the third phase of the measurement of the ionization current and of the generation of the integrated voltage V _ int _ I _ ion has a length T _ ion and it is comprised between the instants T25 and T30: in the third phase of the third cycle, unlike the third phases of the first and second cycles, the ionization current I _ ion is substantially zero due to the misfiring of the air-fuel mixture, and therefore the integrating capacitor C4 is not charged (i.e. it remains discharged at a substantially zero value (for example 0.7 volts)), so a substantially zero value (i.e. very small) of the integration of the ionization current I _ ion is measured (by means of the detection of the integration voltage V _ int _ I _ ion).

In more detail, in the first charging phase (including the instants between t1 and t2 of the first cycle, between t10 and t12 of the second cycle and between t20 and t22 of the third cycle), the high-voltage switch 4 is closed, the primary current I _ pr has an increasing trend from a zero value to a maximum value Ipr _ max, the value of the secondary current I _ sec is substantially zero, the ionization current I _ ion is zero, and the integrated voltage signal V _ int _ I _ ion is zero (first cycle) or increases slowly towards a value substantially zero (second cycle).

In the second energy transfer phase (including the time intervals between t2 and t5 of the first cycle, between t12 and t15 of the second cycle, and between t22 and t25 of the third cycle) the following occurs:

the high-voltage switch 4 is open, the primary current I _ pr is substantially zero, the secondary current I _ sec has a pulse with a maximum value Isec _ max at the times t2 (first cycle), t12 (second cycle) and t22 (third cycle), and then has a decreasing trend from the maximum value Isec _ max until reaching a substantially zero value at the times t4 (first cycle), t14 (second cycle) and t24 (third cycle), respectively;

capacitor C4 discharges rapidly, and therefore the integrated voltage signal V _ int _ I _ ion increases rapidly first towards zero at the beginning of the second cycle (i.e. between times t2 and t3 of the first cycle, between times t12 and t13 of the second cycle, between times t22 and t23 of the third cycle) until reaching a substantially zero value (e.g. about 0.7 volt, equal to the voltage across the forward biased zener diode DZ11), and then the integrated voltage signal V _ int _ I _ ion remains equal to a substantially zero value (e.g. about 0.7 volt) for the remaining time interval of the second cycle (i.e. between times t3 and t5 of the first cycle, between times t13 and t15 of the second cycle, between times t25 and t25 of the third cycle);

-the ionization current I _ ion is zero during the whole second phase of the first, second and third cycles.

In particular, the integration voltage V _ int _ I _ ion is the voltage drop V _ C4 across the integration capacitor C4, and thus during the second energy transfer phase of the second cycle, the integration capacitor C4 discharges until full discharge is reached at time t13 (not far from t12), at which time t13 the voltage drop across the integration capacitor C4 is substantially zero (e.g., 0.7 volts, equal to the voltage drop across the forward biased zener diode DZ 11).

In the third phase of the ionization current measurement (including the time intervals between t5 and t10 of the first cycle, between t15 and t20 of the second cycle, and between t25 and t30 of the third cycle), the high voltage switch 4 is opened.

The primary current I _ pr has a zero value after the time t2 of the first cycle, after the time t12 of the second cycle and after the time t22 of the third cycle.

The secondary current I _ sec is zero at the times comprised between t4 and t10 of the first cycle, between t14 and t20 of the second cycle and between t24 and t30 of the third cycle.

Further, the ionization current I _ ion flows through the secondary winding 2-2 at the times comprised between t5 and t7 of the first cycle and between t15 and t17 of the second cycle, since the correct combustion of the air-fuel mixture occurs in the first cycle and in the second cycle.

In particular, in the third phase of the ionization current measurement of the first and second cycles, the ionization current I _ ion has a first current peak P1 (chemical phase) at the times comprised between t5 and t6 of the first cycle and between t15 and t16 of the second cycle, then a second current peak P2 (thermal phase) between the times t6 and t7 of the first cycle and between t16 and t17 of the second cycle, then the ionization current I _ ion has a value substantially zero from the time t7 of the first cycle and the time t17 of the second cycle.

In contrast, in the third phase of the third cycle, the ionization current I _ ion is also substantially zero between times t25 and t27, since there is a misfire of the air-fuel mixture.

Furthermore, in the third phase of the ionization current measurement of the first and second cycles (including the instants between t5 and t10 of the first cycle and between t15 and t20 of the second cycle), the integrated voltage V _ int _ I _ ion instead has a monotonically decreasing trend starting from a value substantially zero at the instant t5 of the first cycle and at the instant t15 of the second cycle, until reaching a maximum negative value Vint _ max (for example equal to the zener voltage V _ DZ11 of the zener diode DZ 11): the detected value of the integrated voltage V _ int _ I _ ion at a given moment in the third phase of the ionization current measurement of the first and second cycles represents (without regard to the sign) the base area from the ionization current I _ ion to the moment under consideration, i.e. the integrated measured value of the ionization current I _ ion.

In particular, the integration voltage V _ int _ I _ ion is the voltage drop V _ C4 across the integration capacitor C4, and therefore during the third phase of the ionization current measurement of the first and second cycles, a charging of the integration capacitor C4 is performed, which is limited to negative values, so that the voltage across the integration capacitor C4 reaches a maximum negative value Vint _ max, which is equal to the zener voltage V _ DZ11 across the reverse biased zener diode DZ 11.

For example, the zener voltage V _ DZ11 of the second zener diode DZ11 is equal to 15 volts, so the value of the integration voltage V _ int _ I _ ion is limited to the value Vint _ max-V _ DZ 11-15 volts, i.e. the voltage across the integration capacitor C4 is limited to a defined negative value, for example equal to-15 volts, during the third phase of the ionization current measurement of the first and second cycles.

Otherwise, in the third phase of the ionization current measurement of the third cycle (including the time between t25 and t30), the integrated voltage V _ int _ I _ ion instead has a tendency to be substantially zero due to the misfire of the air-fuel mixture, and therefore the detected value of the integrated voltage V _ int _ I _ ion at a given time in the third phase of the ionization current measurement of the third cycle is a very small value (i.e., approximately zero), that is, the integrated measured value of the ionization current I _ ion is a very small value (i.e., approximately zero).

Referring also to fig. 1A-1C and 2A-2C, the operation of ignition system 15 according to an embodiment of the present invention in a portion including three ignition cycles between times t1 and t30 and a fourth ignition cycle after t30 will be described below.

For purposes of explaining the operation, the following assumptions are considered:

-the reference voltage V _ ref is equal to the ground reference voltage;

-battery voltage V _ batt ═ 12V;

-supply voltage VCC-5V;

the high-voltage switch 4 is realized with an IGBT transistor;

the biasing circuit 6 is implemented with a parallel connection of a biasing capacitor C6 and a zener diode DZ 8;

the integrating circuit 7 is realized with a parallel connection of an integrating capacitor C4 and a zener diode DZ 11;

assume that the integrating capacitor C4 is charged at an initial instant t1, in particular that the voltage across the integrating capacitor C4 is equal to the zener voltage V _ DZ11 of the zener diode DZ11 (e.g., -15 volts);

-the control signal S _ ctrl is a voltage signal;

the ignition signal S _ ac and the control signal S _ ctrl have logical values, where the logical low value is 0V and the logical high value is equal to the supply voltage VCC-5V.

The turns ratio of coil 2 is N;

in the case of correct combustion of the air-fuel mixture, the pulse length Δ T of the combustion monitoring voltage S _ id is proportional to the detected value of the integrated voltage V _ int _ I _ ion.

Assume that a condition is started in which proper ignition of the air-fuel mixture occurs in the ignition cycle before time t1.

At time t1, the first ignition cycle starts and the electronic control unit 20 generates an ignition signal S _ ac having a transition from a logic low value to a logic high value (equal to the supply voltage VCC), which indicates the start of the charging phase.

The drive unit 5 receives an ignition signal S _ ac equal to a logic high value and generates a control voltage signal S _ ctrl having a value equal to a logic high value on the control terminal of the IGBT transistor 4, which logic high value closes the IGBT transistor 4 (see the configuration of fig. 1A).

Further, at time t1, the local control unit 9 receives the detected value of the integrated voltage V _ int _ I _ ion and generates the combustion monitoring voltage S _ id having the voltage pulse I1 with a rising edge.

With IGBT transistor 4 closed, the first phase of charging energy begins in primary winding 2-1, where primary current I _ pr begins to flow from battery voltage V _ batt towards the ground reference voltage, through primary winding 2-1 and IGBT transistor 4.

Primary voltage V _ pr has a transition from a value V _ batt to a saturation voltage value Vds _ sat, the voltage of the first terminal of primary winding 2.1 remains equal to V _ batt, and therefore the voltage drop across primary winding 2-1 has a transition from a zero value to a value equal to V _ batt-Vds _ sat; furthermore, the secondary voltage V sec has a transition from a zero value to a value N (V batt-Vds sat).

the operation at the time included between t1 and t2 (excluding t2) is similar to the operation at the time of t1 described, with the following differences.

In particular:

the control voltage signal S _ ctrl maintains a value equal to the logic high value (equal to the supply voltage VCC), which keeps the IGBT transistor 4 closed;

the primary current I _ pr flowing through the primary winding 2-1 has an increasing trend which continues to charge the primary winding 2-1 with energy;

the voltage of the first terminal of the primary winding 2.1 remains equal to V _ batt;

as the primary current I _ pr increases, the primary voltage V _ pr has an increasing trend;

the voltage drop across the primary winding 2.1 has a decreasing tendency;

the secondary voltage V _ sec has a trend of decreasing from a value N × V _ batt to a value N (V _ batt-Vds _ sat), which follows the trend of the primary voltage V _ pr minus the value of the turns N ratio.

The integrating capacitor C4 remains charged at the zener voltage value of the zener diode DZ11 and therefore the integrating voltage V _ int _ I _ ion has a substantially constant trend equal to the zener voltage value of the zener diode DZ11 (for example, -15 volts).

Further, at the time included between t1 and t2, the ionization current I _ ion is zero, and the integration voltage V _ int _ I _ ion is also zero.

Finally, at the instants comprised between T1 and T2, the local control unit 9 receives the detected value of the integrated voltage V _ int _ I _ ion and generates from said detected value of the integrated voltage V _ int _ I _ ion a combustion monitoring voltage S _ id having the falling edge of the voltage pulse I1 at instant T1.1, generating a pulse I1 having a length Δ T1, which length Δ T1 is proportional to the detected value of the integrated voltage V _ int _ I _ ion in the ignition cycle (not shown in the figures) preceding the first cycle, assuming that a correct ignition of the air-fuel mixture has occurred in the ignition cycle preceding the first cycle: the electronic control unit 20 will use said length Δ T1 to detect the presence or absence of misfiring of the air-fuel mixture in the combustion chamber of the engine cylinder in which the spark plug 3 is installed.

At time t2, the electronic control unit 20 generates an ignition signal S _ ac with a transition from a logic high value (equal to the supply voltage VCC) to a logic low value, which indicates the end of the first phase of ignition and the start of the phase of energy transfer from the primary winding 2-1 to the secondary winding 2-2.

Drive unit 5 receives ignition signal S _ ac equal to a logic low value and generates a control voltage signal S _ ctrl having a logic low value on the control terminal of IGBT transistor 4, which turns on IGBT transistor 4 (see the configuration of fig. 1B).

With the IGBT transistor 4 turned on, the current I _ chg from the battery voltage V _ batt through the primary winding 2-1 towards ground is abruptly interrupted and thus energy (previously stored in the primary winding 2-1) begins to be transferred onto the secondary winding 2-2.

Thus, the primary voltage V _ pr has a high value (generally equal to 200-.

Furthermore, at time t2, the charging of the biasing capacitor C6 also starts by means of a pulse of the secondary current I _ sec, and the rapid and complete discharging of the integrating capacitor C4 starts: thus, in the second energy transfer phase, the voltage across the integrating capacitor C4 first has a rapid transition towards a substantially zero value and then remains equal to the substantially zero value (e.g., equal to a positive value of about 0.7 volts by means of the forward bias of the zener diode DZ 11).

Note that for the sake of simplicity it has been assumed that the primary current I _ pr has, at the instant t2, an instantaneous transition from the maximum value Ipr _ max to a zero value, but in practice said transition takes place in a time interval lasting, for example, between 2 and 15 microseconds: in this case, the absolute value of the secondary voltage V _ sec has an increasing trend with a high slope towards a maximum value, and the spark is emitted when the absolute value of the secondary voltage V _ sec has reached the maximum value (and therefore when the primary current I _ pr has reached the zero value).

At the time included between t2 and t5 (excluding t5), the spark between the electrodes of the spark plug 3 is maintained, and thus the combustion of the air-fuel mixture continues.

This operation is similar to the described operation at time t2, so the IGBT transistor 4 remains off.

Therefore, the value of the primary current I _ pr remains zero, while the secondary current I _ sec has a decreasing trend starting from the maximum value Isec _ max.

At a time comprised between t2 and t3, the secondary current I _ sec flows through the secondary winding 2-2 and then through the charged bias capacitor C6; at some point, the secondary current I _ sec (which flows through the secondary winding 2-2) begins to flow through the zener diode DZ8, which zener diode DZ8 is then reverse biased and limits the voltage V _ C6 across the bias capacitor C6 to be equal to the zener voltage V _ DZ8 of the first zener diode DZ8 (e.g., the zener voltage V _ DZ8 of the zener diode DZ8 is equal to 200V).

Further, at a time after t2, the secondary current I _ sec (which flows through the secondary winding 2-2 and then through the bias capacitor C6 or the zener diode DZ8, as explained above) flows through the fast discharging integration capacitor C4, and thus the voltage across the integration capacitor C4 has a fast transition from the maximum negative value Vint _ max towards a value substantially zero.

Therefore, when the bias capacitor C6 is charging (or when the bias capacitor C6 has been charged and is limited to the value of the zener voltage V _ DZ8 of the zener diode DZ8), the integrating capacitor C4 quickly discharges its previously stored residual charge in preparation for measuring the integrated value of the ionization current I _ ion in the third phase.

At some point after t2, the secondary current I _ sec (which flows through the secondary winding 2-2 and then through the bias capacitor C6 or zener diode DZ8, as explained above) begins to flow through the forward biased zener diode DZ11, and thus at time t3, the voltage V _ C4 across the integrating capacitor C4 (and thus the integrating voltage V _ int _ I _ ion) is a positive value equal to about 0.7 volts: because this value is very small relative to the value of the zener voltage V _ DZ11 of the zener diode DZ11, as indicated above (and also in fig. 2A), the integrating capacitor C4 in the second phase discharges to a value of "substantially zero" reaching the voltage V _ C4 across itself.

Further, at the time included between t2 and t5, the ionization current I _ ion is zero, and the integration voltage V _ int _ I _ ion is also zero.

At time t5, the measurement of the ionization current may be started because at the previous time t4 the value of the secondary current I _ sec has reached the zero value, and therefore only the contribution of the current generated at the electrodes of the spark plug 3 due to the ions generated during the combustion of the air-fuel mixture may be measured.

Thus, the third phase starts at time t 5: the bias circuit 6 starts generating a flow of the ionization current I _ ion flowing through the secondary winding 2-2, and thereby the integration circuit 7 starts measuring the integrated value of the intensity of the ionization current I _ ion.

In particular, at time t5, the biasing capacitor C6 operates as a generator of electrical energy (by means of the charge stored in the previous second phase) and starts the discharge of the biasing capacitor C6 by means of the ionization current I _ ion.

Further, at time t5, by storing the electric charges generated by the ions generated in the combustion chamber after the spark ends, the charging of the integrating capacitor C4 starts toward a negative value, and thus at time t5, the measurement of the integrated value of the ionization current I _ ion starts.

More particularly, at the instants comprised between t5 and t6, a first peak P1 of the ionization current I _ ion value is generated (by means of the biasing circuit 6), this first peak P1 representing the current generated by the ions generated during the chemical phase of the measurement phase of the ionization current, and moreover a value proportional to the integral of the intensity of the ionization current I _ ion is measured (by means of the integrating circuit 7, in particular by means of the integrating capacitor C4 being charged), generating an integrated voltage signal V _ int _ I _ ion.

Therefore, at the time comprised between t5 and t6, the charging of the integrating capacitor C4 continues, and the integrating voltage V _ int _ I _ ion has a decreasing trend from the zero value at the time t5 to the first negative value V1int (e.g., V1int — 2 volts) at the time t 6.

Similarly, at the instants comprised between t6 and t7, a second peak P2 of the ionization current I _ ion value is generated (by means of the bias circuit 6), this second peak P2 representing the current generated by the ions generated during the thermal phase of the third phase of the ionization current measurement, and the measurement of a value proportional to the integration of the ionization current intensity I _ ion is continued (by means of the integrating circuit 7, in particular by means of the integrating capacitor C4), generating an integrated voltage signal V _ int _ I _ ion; therefore, at the time included between t6 and t7, the integration capacitor C4 continues to charge, and the integration voltage V _ int _ I _ ion continues to have a decreasing trend from the first value V1int at the time t6 to the maximum negative value Vint _ max (absolute value greater than V1int) at the time t7 (e.g., Vint _ max ═ 15 volts).

At the instant comprised between t7 and t10, the ionization current I _ ion has a value substantially zero, the integrating capacitor C4 holds the charge and the integrating voltage V _ int _ I _ ion has a constant trend equal to the maximum negative value Vint _ max, since the activity on the electrodes of the spark plug 3 has ended.

In the assumption that the measurement value of the ionization current integration (at the time comprised between t6 and t7 of the third phase) reaches a high value, a reverse bias of zener diode DZ11 occurs and therefore a current flows through diode DZ11 from the ground reference terminal (while the current across the integrating capacitor C4 becomes zero), limiting the value of the voltage across the integrating capacitor C4 to a value equal to the zener voltage V _ DZ11 of zener diode DZ11 (for example equal to-15 volts); therefore, at a certain moment comprised between t6 and t7, the integrated voltage V _ int _ I _ ion reaches a value equal to the zener voltage V _ DZ11 (for example, -15 volts) of the zener diode DZ11, and at a subsequent moment, the integrated voltage V _ int _ I _ ion has a substantially constant trend equal to the zener voltage V _ DZ11 (for example, -15 volts) of the zener diode DZ 11.

It should be observed that in the known solutions for measuring the ionization current, the biasing capacitor C6 remains charged during the whole phase of the ionization current measurement (i.e. the voltage V _ C6 across the biasing capacitor C6 must be kept substantially constant at a value different from zero volts).

In contrast, according to the invention, it is sufficient to keep (during the third phase of the ionization current measurement) the biasing capacitor C6 charged within a time interval shorter than the length of the third phase of the ionization current measurement (by means of charging the integrating capacitor C4 and simultaneously discharging the biasing capacitor C6, and vice versa), thus allowing the use of a biasing capacitor C6 with a much lower capacitance value (and therefore a smaller size of the biasing capacitor C6); for example, fig. 2A shows that the voltage drop V _ C6 across the bias capacitor C6 reaches a very small value (at the zero limit) at about time t7 when the ionization current I _ ion reaches the zero value, but it is also possible that the voltage VC _6 reaches a very small value at a time before or after time t7, in which case the distance from time t7 is much less than the distance from time t10.

For example, the capacitance value of the biasing capacitor C6 has a value comprised between 50nF (nanofarad) and 150 nF.

At time t10, the first ignition cycle ends and the second ignition cycle begins, where it is assumed that correct combustion of the air-fuel mixture occurs again.

The operation between times t10 and t12 of the second ignition cycle (first phase of charging energy) is similar to the operation between times t1 and t2 of the first ignition cycle described above, except that the integrating capacitor C4 begins to discharge slowly and is partially discharged by the charge seen from terminal O4 of the integrating capacitor C4.

Furthermore, at the time t10, the control signal S _ ctrl has a rising edge, and the local control unit 9 generates a combustion monitoring voltage S _ id carrying a voltage pulse I2 with a rising edge, which voltage pulse I2 is to be used by the electronic control unit 20 in the first cycle to detect the presence of correct combustion of the air-fuel mixture in the combustion chamber of the engine cylinder in which the spark plug 3 is installed.

In particular, the local control unit 9 receives an integrated voltage V _ int _ I _ ion representing a value proportional to the integrated measurement value of the ionization current I _ ion in the first ignition cycle and generates a combustion monitoring voltage S _ id carrying a voltage pulse I2 having a length Δ T2, the length Δ T2 being proportional to the value of the integrated voltage V _ int _ I _ ion of the measurement phase of the ionization current I _ ion of the first ignition cycle.

Thus, at the instants comprised between T10 and T12, the local control unit 9 sends to the electronic control unit 20 a combustion monitoring voltage S _ id carrying a voltage pulse I2 having a length Δ T2; the electronic control unit 20 receives the combustion monitoring voltage S _ id, performs the comparison between the value of the time length Δ T2 and the value of the ignition threshold, detects that the value of the time length Δ T2 is greater than the value of the ignition threshold, and thus detects that no misfire of the air-fuel mixture occurs in the combustion chamber of the engine cylinder in which the ignition plug 3 is installed in the first ignition cycle (i.e., that a correct spark occurs between the electrodes of the ignition plug 3 in the first cycle, i.e., that a correct combustion of the air-fuel mixture occurs).

The operation between times t12 and t15 of the second ignition cycle (the second energy transfer phase in which the spark occurs) is the same as the previously described operation between times t2 and t5 of the first ignition cycle.

In particular, between times t12 and t13 of the second cycle (t13 is close to t12), a rapid discharge of the residual voltage across the integrating capacitor C4 occurs by means of the flow of the secondary current I _ sec (integrating capacitor C4 is charged in the previous ionization current measurement phase of the first cycle) until reaching a substantially zero value of the voltage across the integrating capacitor C4 (for example, about 0.7 volt) by means of the forward bias of the zener diode DZ11 at time t 13: the integrating capacitor C4, which is fully discharged, is thus ready for storing the charge generated during the measurement phase of the ionization current of the second cycle, and therefore the integrating circuit 7 is automatically reset, without intervention by the drive unit 5 or the electronic control unit 20.

It should be noted that during the first phase of the second cycle, the discharge of the residual voltage across the integrating capacitor C4 occurs much slower than during the second phase of the second cycle.

Thus, during the charging and energy transfer phases of the second cycle (including the moments between t10 and t 15), the integrated voltage V _ int _ I _ ion has an increasing trend from the maximum negative value Vint _ max to a substantially zero value (e.g., about 0.7 volts) at a moment t13, which is reached at a moment t13 not far from the moment t12, and then remains equal to the substantially zero value (see fig. 2B).

The operation between the instants t15 and t20 of the second ignition cycle (third phase of ionization current measurement) is similar to the operation between the instants t5 and t10 of the first ignition cycle described above, so that the bias capacitor C6 is at least partially discharged by means of the ionization current I _ ion flowing through the secondary winding 2-2, and the integrating capacitor C4 is charged towards a negative value, so that a value proportional to the integration of the ionization current I _ ion is measured by means of detecting the integrated voltage signal V _ int _ I _ ion across the integrating capacitor C4.

At the moments comprised between t17 and t20, the ionization current I _ ion has a value substantially zero, since the activation of the spark plug 3 on the electrodes has been completed.

At time t20, the second ignition cycle ends and a third ignition cycle begins, in which misfire occurs.

Operation between times t20 and t22 of the third ignition cycle (first phase of charging energy) is similar to that previously described between times t10 and t12 of the second ignition cycle.

In particular, at the time t20, the control signal S _ ctrl has a rising edge and the local control unit 9 generates a combustion monitoring voltage S _ id carrying a voltage pulse I3 with a rising edge, which voltage pulse I3 is to be used by the electronic control unit 20 in a second cycle to detect the presence of correct combustion of the air-fuel mixture in the combustion chamber of the engine cylinder in which the spark plug 3 is installed.

In particular, the local control unit 9 receives an integrated voltage V _ int _ I _ ion representing a value proportional to the integrated measurement value of the ionization current I _ ion in the second ignition cycle and generates a combustion-monitoring voltage S _ id carrying a voltage pulse I3 having a length Δ T3, the length Δ T3 being proportional to the value of the integrated voltage V _ int _ I _ ion of the measurement phase of the ionization current I _ ion of the second ignition cycle.

Thus, at the instants comprised between T20 and T22, the local control unit 9 sends to the electronic control unit 20 a combustion monitoring voltage S _ id carrying a voltage pulse I3 having a length Δ T3; the electronic control unit 20 receives the combustion monitoring voltage S _ id, performs the comparison between the value of the time length Δ T3 and the ignition threshold value, detects that the value of the time length Δ T3 is greater than the value of the ignition threshold value, and thereby detects that no misfire of the air-fuel mixture occurs in the combustion chamber of the engine cylinder in which the ignition plug 3 is mounted in the second ignition cycle (i.e., that a proper spark occurs between the electrodes of the ignition plug 3 in the second cycle, that is, that a proper combustion of the air-fuel mixture occurs).

Operation between times t22 and t25 of the third ignition cycle (second energy transfer phase) is similar to that previously described between times t12 and t15 of the second ignition cycle.

In contrast, the operation between times t25 and t30 of the third ignition cycle (the third stage of ionization current measurement and integral measurement of ionization current) is different from the operation between times t15 and t20 of the second ignition cycle because in the third cycle, misfiring of the air-fuel mixture occurs in the combustion chamber of the engine cylinder to which the spark plug 3 is mounted.

In particular, at the instants comprised between t25 and t30 of the third cycle, the value of the ionization current I _ ion flowing through the secondary winding 2-2 is substantially zero, due to the misfiring of the air-fuel mixture and therefore the integrating capacitor C4 is not charged, but remains discharged at a value substantially zero; thus, during the third phase of the third cycle, an integrated voltage V _ int _ I _ ion is detected having a value substantially zero, i.e. in the third phase of the third cycle, the measured value of the integration of the ionization current I _ ion is approximately equal to zero.

At time t30, the third firing cycle ends and the fourth firing cycle begins, which is only partially shown in fig. 2C.

In particular, fig. 2C shows that at time t30, the control signal S _ ctrl has a rising edge and the local control unit 9 generates a combustion monitoring voltage S _ id carrying a voltage pulse I4 with a rising edge, which voltage pulse 14 is to be used by the electronic control unit 20 in a third cycle to detect the presence of a misfire of the air-fuel mixture in the combustion chamber of the engine cylinder on which the spark plug 3 is mounted.

In particular, the local control unit 9 receives the integrated voltage V _ int _ I _ ion having a value of approximately zero, since in the third ignition cycle the integrated measured value of the ionization current I _ ion is approximately equal to zero due to the misfire, the local control unit 9 generates a combustion monitoring voltage S _ id carrying a voltage pulse I4 having a very small length Δ T4.

Thus, at the instants comprised between T30 and T30.1, the local control unit 9 sends to the electronic control unit 20 a combustion monitoring voltage S _ id carrying a voltage pulse I4 having a very small length Δ T4; the electronic control unit 20 receives the combustion monitoring voltage S _ id, performs the comparison between the value of the time length Δ T4 and the ignition threshold value, detects that the value of the time length Δ T4 is smaller than the value of the ignition threshold value, and thereby detects that a misfire of the air-fuel mixture occurs in the combustion chamber of the engine cylinder in which the ignition plug 3 is mounted in the third ignition cycle (i.e., that a proper spark does not occur between the electrodes of the ignition plug 3 in the third cycle, that is, that a proper combustion of the air-fuel mixture does not occur).

It should be observed that for the purposes of the previous explanation of the operation of the invention, it is considered for the sake of simplicity that, in the case of correct combustion of the air-fuel mixture, the pulse length Δ T of the combustion monitoring voltage S _ id is proportional to the detected (absolute) value of the integrated voltage V _ int _ I _ ion, but more generally, the invention applies to the case in which the pulse length Δ T of the combustion monitoring voltage S _ id increases with an increase in the detected (absolute) value of the integrated voltage V _ int _ I _ ion.

It should also be observed that the drive unit 5 and the local control unit 9 can also be realized with a single electronic component that performs both the function of driving the drive unit 5 and the control function of the local control unit 9; in other words, the local control unit 9 may be incorporated within the drive unit 5 and vice versa.

It should be observed that fig. 2A-2C show the case where the combustion monitoring voltage S _ id carries time pulses I1, I2, I3, I4 representative of the presence or absence of a misfire in the previous cycle, i.e.:

the length of time Δ T1 of the first voltage pulse I1 lies within the first charging phase of the first cycle, but it represents that there is no misfire in cycles (not shown in fig. 2A-2C) preceding the first cycle (which is comprised between T1 and T10);

the length of time Δ T2 of the second voltage pulse I2 lies within the first charging phase of the second cycle, but it represents that there is no misfire for the first cycle comprised between T1 and T10;

the length of time Δ T3 of the third voltage pulse I3 lies within the first charging phase of the third cycle, but it represents that there is no misfire for the second cycle comprised between T10 and T20;

the length of time Δ T4 of the fourth voltage pulse I4 lies within the first charging phase of the fourth cycle, but it represents the presence of a misfire in the third cycle comprised between T20 and T30.

Alternatively, it is also possible to generate the combustion monitoring voltage S _ id such that it carries time pulses I1, I2, I3 representative of the presence or absence of a misfire in the same cycle, namely:

the length of time Δ T1 of the first voltage pulse I1 lies within the first charging phase of the first cycle and it represents that there is no misfire for the first cycle comprised between T1 and T10;

the length of time Δ T2 of the second voltage pulse I2 lies within the first charging phase of the second cycle and it represents that there is no misfire for the second cycle comprised between T10 and T20;

the length of time Δ T3 of the third voltage pulse I3 lies within the first charging phase of the third cycle and it represents the presence of a misfire in the third cycle comprised between T20 and T30.

Referring to fig. 3, an electronic ignition system 115 is shown in accordance with a variation of the present embodiment.

The ignition system 115 of fig. 3 differs from the ignition system of fig. 1A-1C in that it further comprises a current generator 11 controlled in dependence on the value of a current control signal S _ ctrl _ i generated by the local control unit 109 (similar to 9): in this way, the use of an additional connection between the local control unit 109 and the electronic control unit 20 to transmit the combustion monitoring signal S _ id can be avoided.

In particular, the current generator 11 is configured to generate a trigger current I _ cl having a value depending on the value of the current control signal S _ ctrl _ I, which in turn depends on the detected value of the integrated voltage V _ int _ I _ ion.

More particularly, in a variant of the invention, the presence or absence of misfire in the previous cycle is determined in each combustion cycle using the distance between the two edges of the pulse variation of the trigger current I _ cl (see pulses I5, I6, I7, I8 and the corresponding distances Δ T5, Δ T6, Δ T7, Δ T8 in fig. 4A-C), i.e. the distance between the two edges of the current pulse is proportional to the value of the integrated voltage signal V _ int _ I _ ion during the ionization current measurement phase of the previous cycle.

The local control unit 9 comprises a first input terminal adapted to receive the ignition signal Sac, comprises a second input terminal adapted to receive an integrated voltage signal V _ int _ I _ ion representing a measure of the integration of the ionization current I _ ion (measured by means of a voltage drop across an integrating capacitor C4 of the integrating circuit 7), and comprises an output terminal adapted to generate a current control signal S _ ctrl _ I to control the value of the trigger current I _ cl generated by the current generator 11, depending on the value of the ignition signal Sac and the detected value of the integrated voltage V _ int _ I _ ion.

Referring to fig. 4A-4C, trends of some of the signals of the electronic ignition system 115 of fig. 3 are shown.

Consider a situation where the distance between two edges of the change in the trigger current I _ cl of one cycle represents the presence or absence of a misfire of the previous cycle.

Specifically, it is assumed that correct combustion of the air-fuel mixture occurs in the first cycle included between t1 and t10, correct combustion occurs in the second cycle included between t10 and t20, and misfire occurs in the third cycle included between t20 and t30.

It can be observed that the values of the distances Δ T6 and Δ T7 between the two changing edges of the trigger current I _ cl in the second and third ignition cycles are much greater than the distance Δ T8 between the two changing edges of the trigger current I _ cl in the fourth cycle, because in the first and second cycles, proper ignition of the air-fuel mixture occurs, while in the third cycle, misfiring of the air-fuel mixture occurs.

It should be observed that for the purpose of explaining the invention, the case of misfire of the comburent combustible mixture (for example, air-fuel) in the combustion chamber of the cylinder in which the spark plug 3 is fitted is considered, but more generally, the invention applies to the case in which combustion of an insufficiently solid comburent combustible mixture occurs in the combustion chamber (i.e. insufficient sparking occurs between the electrodes of the spark plug 3); thus, the foregoing considerations regarding misfire apply in a similar manner to the case of insufficient combustion.

Referring to fig. 5, it shows the trend of the signals in the ignition system in the case of pre-ignition of the air-fuel mixture during the first phase of charging the primary winding 2-1 with energy: in this case, the ionization current I _ ion is also generated by the secondary winding 2-2 during the first phase of charging energy into the primary winding 2-1.

Fig. 5 shows an ignition cycle similar to that of fig. 2B, except that the ionization current I _ ion has an increasing trend from zero to a maximum value iinon _ max between times t10.2 and t12 of the first phase of charging energy into the primary winding 2-1, since pre-ignition of the air-fuel mixture takes place from time t 10.2; thus, during the first charging phase, the pre-charging of the integrating capacitor C4 takes place, so that the integrated signal V _ int _ I _ ion (i.e. the integrated value of the ionization current I _ ion) is zero between the instants t10 and t10.2, then at the instant t10.2 it starts to have a monotonous decreasing trend until it reaches a maximum negative value Vint _ max (for example equal to the zener voltage V _ DZ11 of the zener diode DZ11) at the instant t10.3 comprised between the instants t10.2 and t12.

Subsequently, in the second energy transfer phase, the integrated signal V _ int _ I _ ion has a tendency to increase rapidly towards the zero value due to the rapid discharge of the integrating capacitor C4, so that the integrated signal V _ int _ I _ ion remains at a substantially zero value (for example, equal to 0.7 volt) during the remaining time interval of the second energy transfer phase comprised between t12.1 and t 15.

Finally, in the third phase of the ionization current measurement (including the instants between t15 and t 20), the trend of the integrated signal V _ int _ I _ ion is similar to that of the second cycle of the embodiment of the invention of fig. 2B described previously, i.e. starting from instant t15, due to the charging of the integrating capacitor C4, it has a decreasing trend from a zero value until reaching the maximum negative value Vint _ max at instant t17, so that the integrated signal V _ int _ I _ ion has a substantially constant trend equal to Vint _ max for the remaining time interval of the third phase, including between t17 and t20.

In the event that no pre-ignition of the air-fuel mixture occurs in the combustion chamber during the charging phase, the integrating capacitor C4 maintains the state of charge substantially constant, i.e., a value of substantially zero (as shown in fig. 5) or equal to the value of the zener voltage V _ DZ11 of the diode DZ11 (as shown in fig. 2A).

The previous considerations for misfire related to the voltage pulses of fig. 2A-2C and the current pulses of fig. 4A-4C apply in a similar manner to pre-ignition, except that the voltage pulses or the current pulses are located at the end of the first phase of charging energy.

Thus, the voltage pulse carried from the monitoring signal S _ id (see I9 and I10 in fig. 5) is located in the last part of the ignition signal S _ ac, where it has a high value and is related to the presence or absence of pre-ignition in the previous cycle, and has the opposite meaning with respect to that of misfire detection, namely:

-if the length Δ T is less than the value of the pre-ignition threshold, indicating that no pre-ignition occurred in the previous cycle,

-if the length Δ T is greater than or equal to the value of the pre-ignition threshold, it indicates that pre-ignition occurred in the previous cycle.

Considering the example shown in fig. 5, the voltage pulse I9 in the second cycle has a length Δ T9 that is less than the value of the pre-ignition threshold, because no pre-ignition occurs in the first cycle, while the voltage pulse I10 in the third cycle has a length Δ T9 that is greater than the value of the pre-ignition threshold, because pre-ignition occurs in the second cycle.