JP2000303940A - Combustion state detecting device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To high-precisely and accurately detect an ion current without depending upon voltage damping vibration and detect a combustion state based thereon. SOLUTION: A high voltage for ignition is generated at the secondary coil L2 of an ignition coil 4 by a spark discharge generating circuit 20 and an ignition plug 3 is caused to generate spark discharge. In this case, a spark discharge current i2 flows to the diode 13 for charge, the capacitor 11, and the diode 12 of an ion current detecting part 10, and the capacitor 11 is charged by the Zener voltage of a Zener diode 16 connected in parallel therewith. At a point of time when, after the start of spark discharge, a spark discharge continuance time calculated based on the operation state of an internal combustion engine elapses, spark discharge is forcibly shut off by a spark discharge shut off circuit 40. Further, at a point of time when a given waiting time elapses, the two ends of the diode 13 for charge are short-circuited by a switch 14 for discharge, a high voltage is applied on the ignition plug 3 from the capacitor 11. A flowing ion current i3 is outputted as a voltage Vio to a detecting circuit 8 at a resistor 15 for detecting a current from a resistor 15 for detecting a current connected in parallel to the diode 12 and converted into a signal for detecting a combustion state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state detecting device used for an internal combustion engine of an automobile or the like, and more particularly, to an ion current flowing after a spark discharge by a spark plug mounted on the internal combustion engine. The present invention relates to a combustion state detection device capable of detecting a combustion state of an internal combustion engine based on the information.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting a combustion state such as abnormal combustion such as knocking or pre-ignition occurring in an internal combustion engine or a misfire, a spark plug mounted on the internal combustion engine is used. There is known a method of detecting an ionic current flowing by ions existing in the vicinity of the electrode after the end of the spark discharge generated between the electrodes of the spark plug.

That is, in the cylinder of an internal combustion engine, ions are generated when the air-fuel mixture is burned (flame propagation), and the resistance value between the electrodes of the spark plug changes according to the amount of generated ions. The amount of this ion generated is
It varies depending on the combustion state of the internal combustion engine and, consequently, the operating state of the internal combustion engine. For this reason, after a high voltage for ignition is applied to the ignition plug by an ignition coil or the like (that is, after spark discharge of the ignition plug is completed), a voltage is externally applied to the ignition plug, and an ion current flowing thereby is reduced. By detecting, it is possible to detect a change in the resistance value between the electrodes of the spark plug (that is, a change in the combustion state).

Here, as a combustion state detecting device for an internal combustion engine using such an ion current detecting means, for example, Japanese Patent Application Laid-Open No. 10-159700 is disclosed by the same applicant. In this publication technique, first, after a certain time is passed through a primary coil of an ignition coil, a high voltage for ignition is generated in a secondary coil by interrupting a current flowing through the primary coil, and an electrode of a spark plug mounted on an internal combustion engine is generated. A spark discharge is generated in between. Next, after a predetermined time has elapsed since the start of the spark discharge, the spark discharge is forcibly cut off by re-energizing the primary coil. Then, after forcibly interrupting the spark discharge, a detection high voltage lower than the ignition high voltage necessary for generating the spark discharge and having the opposite polarity is applied to the ignition plug via the secondary coil. In addition, an ion current is generated between the electrodes, and detection information obtained by detecting the ion current is processed to determine whether knocking has occurred in the internal combustion engine.

In this publication, the spark discharge is maintained only for a predetermined time necessary and sufficient to burn the air-fuel mixture, and the spark discharge is forcibly cut off during the spark discharge to thereby reduce the combustion into the air-fuel mixture. Since the spark discharge duration can be shortened without any trouble, knocking occurs during spark discharge, especially when the internal combustion engine is under high rotation and high load, and this knocking cannot be detected by ion current. Probability can be reduced. In other words, knocking can be reliably detected by the ionic current even at the time of high rotation and high load where the spark discharge duration tends to be unnecessarily long.

[0006]

Here, in the combustion state detecting device of the internal combustion engine disclosed in the above publication, the ion current detecting section for detecting the ion current between the electrodes of the ignition plug is disclosed, for example, in Japanese Patent Laid-Open Publication No. In general, a capacitor widely used as a power source for detecting an ion current, which is widely known, for example, from Japanese Patent Application Laid-Open No. 4-191465, is applied. Hereinafter, this Japanese Patent Laid-Open Publication No. 4-191465 will be described with reference to FIG. In describing the ion current detection unit, an ignition device to be applied includes an ignition plug mounted for each cylinder (only one cylinder is shown in the figure) of the internal combustion engine, and a high voltage for ignition applied to the ignition plug. And a transistor for turning on and off the ignition signal.

First, on the ignition device 101 side, the transistor 104 is turned on by the ignition signal IG, a current flows through the primary coil L1 of the ignition coil 103 by the battery voltage Vb, and when the transistor 104 is turned off by the ignition signal IG, the current is reduced. The ignition is interrupted, a high voltage for ignition is generated in the secondary coil L2, and a spark discharge is generated between the electrodes of the ignition plug 102. At this time, a spark discharge current Isp flowing due to the spark discharge is transmitted through the secondary coil L2 to the capacitor 105 and the diode 107 on the ion current detection unit 100 side.
And a Zener voltage is generated in a Zener diode 108 connected in parallel to these current paths. Therefore, the capacitor 105 is charged with a voltage corresponding to the Zener voltage. After that, when the voltage (ignition high voltage) induced in the secondary coil L2 decreases and becomes lower than the Zener voltage, the detection high voltage corresponding to the electric charge charged in the capacitor 105 becomes the secondary coil L2.
The ion current Iio flows according to the amount of ions generated between the electrodes and applied to the ignition plug 102 via the electrode 2. When the ion current Iio flows through the resistor 106, the ion current Ii is applied to the voltage across the resistor 106.
The detection value Vio corresponding to o is output.

By the way, Japanese Patent Application Laid-Open No. H4-1914 is known.
No. 65, etc., an ion current detection unit 10 using a capacitor as an ion current detection power supply
0, in the secondary coil side circuit of the ignition device 101 combined with the ion current detection unit 100, the inductance of the secondary coil L2 of the ignition coil 103 and the capacitance between the electrodes of the ignition plug 102 Since a resonance circuit is formed by the above, voltage attenuation oscillation occurs after the spark discharge of the ignition plug 102 ends.

The current flowing during the voltage decay oscillation may be several times the ion current depending on the operating conditions of the internal combustion engine.
It can reach very large levels, dozens of times,
Moreover, the vibration may last as long as several ms. Therefore, as shown in FIG. 7, the vibration component may be superimposed on the ion current. That is, Japanese Unexamined Patent Application Publication No. Hei 10-159700 and the like,
When the ion current detection unit disclosed in Japanese Patent No. 1465 is applied, even if the spark discharge of the ignition plug is forcibly cut off in order to prevent knocking from ending during the spark discharge, the ion When a current flows, a noise component due to current attenuation oscillation may be superimposed on the ion current, and the ion current may not be accurately detected. As a result, the ion current may be detected in a state where the noise component is superimposed, and the combustion state of the internal combustion engine such as knocking or misfire may be erroneously detected using the ion current.

On the other hand, it is conceivable to detect when the voltage attenuation oscillation generated after forcibly interrupting the spark discharge has converged, but depending on the time of the oscillation, the electric charge charged in the capacitor is consumed. When the vibration converges, a high voltage for detection necessary for ion current detection cannot be obtained, which causes a problem that the ion current cannot be detected.

Further, the capacitance of the capacitor is increased,
It is also conceivable that more charge is stored in the capacitor during spark discharge at the spark plug. However, in this case, when the electric charge consumed by the ionic current is small, an unnecessary voltage is applied to the ignition plug to discharge due to the electric charge remaining in the capacitor,
This causes a new problem that electrode wear of the center electrode is accelerated. Furthermore, carbon deposit particles and liquid fuel are present (adhered) on the insulator surface of the spark plug.
In this case, particles move between the electrodes of the ignition plug due to the electric field generated between the electrodes of the ignition plug due to the application of the voltage.
Because of easy alignment, the spark plug is contaminated earlier (reducing the insulation resistance) and the life of the spark plug is further shortened.

In order to solve the above-mentioned problems, the present invention provides an accurate and accurate ion current without being affected by a voltage attenuation oscillation generated after forcibly interrupting a spark discharge caused by a spark plug. To detect abnormal combustion such as knocking or pre-ignition occurring in the internal combustion engine or misfire based on the detection of the ionic current, and to extend the life of the spark plug. It is an object of the present invention to provide a combustion state detection device for an internal combustion engine that can perform the operation.

[0013]

According to the first aspect of the present invention, there is provided an apparatus for detecting a combustion state of an internal combustion engine, the apparatus comprising: Energizing, generating a high voltage for ignition in the secondary coil of the ignition coil by interrupting the energizing current,
Spark discharge generating means for starting a spark discharge between the electrodes of the spark plug; and a spark discharge duration required for burning the air-fuel mixture by the spark discharge based on an operation state of the internal combustion engine after the start of the spark discharge of the spark plug. And a spark discharge interrupting means for forcibly interrupting the spark discharge in accordance with the timing at which the predetermined spark discharge duration time has elapsed, and a spark discharge interrupting means inserted in series in a current path including the ignition plug and the secondary coil. A capacitor, charging means for charging the capacitor to a predetermined high voltage for detection having a polarity lower than the predetermined high voltage for ignition and a reverse polarity by a spark discharge current flowing at the time of spark discharge of the spark plug; and After the spark discharge is forcibly cut off by the means, the high voltage for detection is applied to the secondary coil by the capacitor charged by the charging means. A current detection resistor for detecting an ion current flowing through the current path when applied to the ignition plug; and a combustion for detecting a combustion state of the internal combustion engine based on the ion current detected by the current detection resistor. A state detecting means, and a charging diode connected in series to the capacitor with a direction in which the spark discharge current flows as a forward direction, and for preventing discharge of a charge charged in the capacitor by the charging means. A discharge switch that short-circuits both ends of the charging diode to discharge the electric charge charged in the capacitor, and switching control means that operates the discharge switch at a timing at which the ionic current is to be detected. It is characterized by having.

In the combustion state detecting device for an internal combustion engine according to the present invention, first, a high ignition voltage generated in a secondary coil due to interruption of a current (primary current) flowing through the primary coil of the ignition coil is mounted on a cylinder of the internal combustion engine. When a spark discharge occurs between the electrodes and a spark discharge occurs between the electrodes, a spark discharge current (secondary current) is generated in a secondary coil side circuit of the ignition coil.
The current flows through a current path formed by the capacitor together with the spark plug and the secondary coil.

At this time, the charging means charges the capacitor to a predetermined high voltage for detection (lower than the high voltage for ignition and having the opposite polarity) by the generation of the spark discharge current. Since the spark discharge current is supplied to the capacitor via the charging diode, the spark is not discharged even if the ignition high voltage falls below the charging voltage of the capacitor (detection high voltage). That is, even if the high voltage for ignition causes a voltage attenuation oscillation after the interruption of the spark discharge, the charge charged in the capacitor does not leak to the spark plug due to the influence of the oscillation.

The switching control means activates a discharging switch for short-circuiting both ends of the capacitor at a timing at which the ion current is to be detected, so that the charged capacitor is charged with the detecting high voltage. Is applied to the spark plug via the secondary coil of the ignition coil. Thereby, together with the ignition coil and the spark plug,
The resistance between the electrodes of the spark plug (the amount of generated ions) in the current path formed by the capacitor and the current detection resistor
Will flow according to the current. When the ion current flows, the voltage at both ends of the current detection resistor is output to the combustion state detecting means, and the combustion state detecting means detects the combustion state based on the voltage at both ends (that is, the ion current). Is converted as a signal.

That is, a point to be noted in the combustion state detecting apparatus for an internal combustion engine according to the present invention is that only when the ion current is to be detected, the electric charge charged in the capacitor is released and the high voltage for detection is applied to the ignition plug. This is the point that is applied. From this, even if voltage discharge oscillation occurs in the secondary coil side circuit of the ignition coil immediately after the spark discharge by the ignition plug is forcibly cut off, the charge stored in the capacitor is not wasted. Thus, the capacitance of the capacitor can be set to a necessary and sufficient value.

Since it is possible to detect the ion current at a stage where the voltage attenuation oscillation has converged to some extent by avoiding such a large period of the voltage attenuation oscillation, the voltage attenuation oscillation is superimposed on the ion current. The ion current can be detected when the noise component has decreased. That is, the detection value output from the ion current detection unit becomes a detection value substantially corresponding to only the ion current, and a filter or the like for removing a noise component from the detection value obtained thereby can be omitted or simplified.

Furthermore, even if the ionic current flowing after spark discharge between the electrodes of the spark plug is small due to misfire of the internal combustion engine and the like, and the electric charge is left in the capacitor, the ignition can be performed if the discharge switch is opened. Unnecessary voltage is not applied to the plug. Thereby,
It is possible to suppress the consumption of the electrodes of the spark plug, and further to prevent the spark plug from being soiled (that is, to reduce the insulation resistance), and to extend the life of the spark plug.

In addition, according to the combustion state detecting apparatus for an internal combustion engine of the present invention, when a spark discharge is generated by the spark plug, the spark required to burn the air-fuel mixture by the spark discharge based on the operating state of the internal combustion engine. Means are provided for calculating a discharge duration time and forcibly interrupting a spark discharge by the spark plug according to a predetermined spark discharge duration time. That is, in the present invention, the means for forcibly interrupting the spark discharge (spark discharge interrupting means) is not performed by simply controlling the energization time to the primary coil of the ignition coil,
By controlling after calculating the spark discharge duration time of the spark discharge, unnecessary supply of spark energy to the spark plug is prevented.

For this reason, by ensuring a sufficient time for energizing the primary coil, the ignition high voltage generated in the secondary coil can be reliably changed to a high voltage for ignition capable of spark discharge under all operating conditions of the internal combustion engine. In this state, the spark energy supplied to the spark plug can be controlled. In particular, under an operating condition where spark energy may be small, such as when the internal combustion engine is under high rotation and high load, the spark plug is reliably discharged at a high ignition high voltage by shortening the spark discharge duration by shortening the spark discharge duration. In addition, excessive supply of spark energy to the ignition plug can be suppressed. Conversely, in an operating condition in which the air-fuel mixture is difficult to ignite, such as during low rotation, such as during idling, the air-fuel mixture can be reliably burned by increasing the spark discharge duration. That is,
According to the present invention, by controlling the spark discharge duration optimally, it is possible to suppress the supply of excessive spark energy between the electrodes of the spark plug, and as a result, it is possible to suppress the electrode consumption of the spark plug. Synergistic with the configuration of the ion current detection section, it is possible to further extend the life of the ignition plug.

Next, a second aspect of the present invention is the first aspect.
In the combustion state detection device for an internal combustion engine according to the above, by operating the discharging switch, both ends of the charging diode are short-circuited, and a current path formed when the electric charge charged in the capacitor is discharged. Of the current paths from the capacitor to the secondary coil,
At least one or more resistors are provided.

According to the combustion state detecting device for an internal combustion engine having the above-described structure, the capacitor and the capacitor are included in the current path formed when the high voltage for detection charged in the capacitor is discharged to the spark plug. A resistor provided between the current paths to the next coil functions to limit the magnitude of the ionic current flowing in the current path. This makes it possible to reduce the noise component superimposed by the voltage attenuation oscillation when detecting the ion current. When a resistor having an excessively large resistance value is used, even the ion current itself having a magnitude of about several tens to several hundreds μA generated between the electrodes of the ignition plug may be limited. Therefore, it can be said that an appropriate resistance value of the resistor of the present invention is up to about 1 MΩ.

[0024] The invention described in claim 3 is the first invention.
Alternatively, in the combustion state detecting device for an internal combustion engine according to claim 2, a Zener diode is connected in parallel to the current detecting resistor with a ground side as a cathode.

According to the ignition device for an internal combustion engine provided with the ion current detection unit having the above-described configuration, the Zener diode detects the ion current when the ion current is detected (when the ion current is flowing). Value (both ends voltage)
It functions to suppress the generation of a voltage value equal to or higher than the Zener voltage of the Zener diode itself. This makes it possible to further reduce the noise component superimposed on the voltage attenuation oscillation when detecting the ion current. The zener voltage of the zener diode is set near the maximum value of the ion current normally generated between the electrodes of the ignition plug (that is, the maximum of the voltage across the current detection resistor calculated from the maximum value of the ion current). By setting the value to (near the value), the Zener diode can function to suppress the generation of any noise component exceeding the maximum value of the normally generated ion current, so that the noise component is further reduced. The ion current can be detected in the form.

As the spark discharge interrupting means, for example, a switching element and a resistance element for current control are provided in parallel with the spark plug, and when the spark plug discharges the spark, the switching element is turned on to ignite the spark. A bypass path for the spark discharge current flowing through the secondary coil of the coil may be formed, and the voltage applied between the electrodes of the spark plug may be controlled to a voltage at which the spark plug does not spark discharge. However, in this case, it is necessary to use switching elements and resistance elements having high withstand voltage, which is not preferable in practice.

Therefore, in order to forcibly interrupt the spark discharge without causing such a problem, the spark discharge interrupting means may be replaced by a spark discharge interrupting means. After interrupting the current supplied to the primary coil, the power supply to the primary coil is restarted in accordance with the timing at which a predetermined spark discharge duration time has elapsed since the start of the spark discharge. It is conceivable that the discharge is forcibly cut off.

In order to operate the spark discharge interrupting means in such a configuration, for example, in a general full-transistor type ignition device, it is provided to switch between energizing and deenergizing the primary coil of the ignition coil. This can be realized by turning on a switching element including a semiconductor element such as a power transistor. In addition to the full transistor type ignition device, the ignition device includes:
Since an electric or mechanical switching means is provided for switching between energization and non-energization of the primary coil of the ignition coil, such a switching means or a switching element is provided in parallel with the switching means and made conductive. You may do so.

Next, in the combustion state detecting device for an internal combustion engine according to any one of claims 1 to 4,
As described in the fifth aspect, the present invention is more effective when used in an internal combustion engine which is a gas engine using gaseous fuel as fuel.

Since gaseous fuel has higher insulation than gasoline which is liquid fuel, the spark discharge voltage is relatively high. Therefore, in an ignition coil for a gas engine using a gaseous fuel, it is necessary to set the maximum ignition high voltage generating capability higher than that for a gasoline engine (for example, the maximum ignition voltage of an ignition coil for a gasoline engine). If the voltage generation capacity is 30 kV or more, that for a gas engine is set to 40 kV or more.) Therefore, in designing the ignition coil, it is necessary to increase the number of turns of the primary coil and the secondary coil. However, when the number of turns of the primary coil and the secondary coil in the ignition coil is increased, the inductance of the ignition coil is increased, and as a result, the voltage attenuation oscillation generated when the spark discharge by the ignition plug is forcibly cut off. However, it becomes larger than a gasoline engine. That is, when the ion current is detected in the gas engine, a large amount of noise components may be superimposed on the obtained ion current as compared with the gasoline engine. For this reason, if the combustion state detecting device for an internal combustion engine according to any one of claims 1 to 4 is applied to a gas engine (internal combustion engine) using a gaseous fuel, the above-described effect is more exerted. You can do it.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an overall configuration of an apparatus 1 for detecting a combustion state of an internal combustion engine according to an embodiment of the present invention.

First, the ignition device 2 side of the combustion state detecting device 1 for an internal combustion engine according to the present embodiment will be described with reference to FIG. The ignition device 2 according to the present embodiment includes a battery 7 that supplies electric energy for discharge (for example, a voltage of 12 V).
And an ignition plug 3 mounted on the internal combustion engine, an ignition coil 4 including a primary coil L1 and a secondary coil L2, an npn transistor 5 connected in series with the primary coil L1, and an electrode of the ignition plug 3. A spark discharge generating circuit 20 that drives the transistor 5 to generate a spark discharge between 3a and 3b, and a spark discharge cutoff circuit 40 that forcibly cuts off the spark discharge are provided. In order to control the spark discharge to the spark plug 3, the spark discharge generation circuit 20 and the spark discharge cutoff circuit 40 are controlled by the first command signal Sa and the second command signal S.
b (hereinafter simply referred to as “ECU”)
6).

The transistor 5 is a switching element composed of a semiconductor element for switching between energization and non-energization of the primary coil L1 of the ignition coil 4. The ignition device 2 of this embodiment is a full transistor type. It is. Further, the spark discharge generation circuit 20 and the spark discharge cutoff circuit 40 in the present embodiment correspond to the spark discharge generation means and the spark discharge cutoff means described in the claims, respectively.

Here, one end of the primary coil L 1 is connected to the positive electrode of the battery 7, and the other end is connected to the collector of the transistor 5. One end of the secondary coil L2 is connected to the center electrode 3a of the ignition plug 3, and the other end is
As described later, it is connected to a capacitor 11 serving as a power supply for generating an ion current. The ground electrode 3b of the spark plug 3 is grounded to the ground having the same potential as the negative electrode of the battery 7, and the base of the transistor 5 is connected to the spark discharge generating circuit 20.
The emitter is connected to the ground, and is connected to the spark discharge cutoff circuit 40.

In the spark discharge generating circuit 20, the emitter is connected to a power supply line Lv to which an output Vc from a constant voltage power supply (not shown) is supplied, and the emitter and the base are connected to each other by a resistor 21. A base connected to the ECU 6 via the resistor 22 and a collector connected to the base of the transistor 5 via the resistor 23
It is composed of an np-type transistor 24.

As a result, when the first command signal Sa output from the ECU 6 is at a low level, the transistor 24 in the spark discharge generating circuit 20 is turned on, and the transistor 5 from the power supply line Lv through the resistor 23 is turned on. A current through a current path that reaches the base of the. Then, the transistor 5 is turned on, and the current (primary current) i1 flows through the primary coil L1 from the positive side of the battery 7 to the negative side of the battery 7 through the primary coil L1 of the ignition coil 4 to the primary side. Flow.

When the first command signal Sa goes high while the primary current i1 is flowing through the primary coil L1, the transistor 24 in the spark discharge generating circuit 20 is turned off and reaches the base of the transistor 5. The current path is interrupted. As a result, the transistor 5 is turned off, and the supply of the primary current i1 to the primary coil L1 is cut off. Then, a high voltage for ignition is generated in the secondary coil L2, and the high voltage for ignition is applied to the center electrode 3a of the ignition plug 3 so that the electrodes 3a-3b of the ignition plug 3
A spark discharge occurs in between. The ignition coil 4 is configured to generate a negative ignition high voltage lower than the ground potential on the center electrode 3a side of the ignition plug 3 by cutting off the current supply to the primary coil L1. 3, a spark discharge current (secondary current) i2 flowing through the secondary coil L2 flows from the center electrode 3a of the ignition plug 3 to the ion current detection unit 10 via the secondary coil L2. Will be.

Next, the spark discharge cutoff circuit 40
Transistor 41 and npn transistor 42
And a pnp-type transistor 43. And
The base of the transistor 41 is connected to the ECU 6, the emitter is grounded, and the collector is the resistor 4
4 and to the base of the transistor 42 via a series circuit of a capacitor 45 and a resistor 46.

The base of the transistor 42 is grounded to the ground via a resistor 47, the emitter is directly grounded to the ground, and the collector is a resistor 48 and a resistor 49.
Is connected to the base of the transistor 43 via the series circuit of The other end of the capacitor 51 having one end grounded is connected to a connection point between the resistor 48 and the resistor 49 connecting the collector of the transistor 42 and the base of the transistor 43.

The emitter of the transistor 43 is connected to the power supply line Lv,
Connected to self base. The collector of the transistor 43 is grounded, and is connected to the base of the transistor 5 via a series circuit of the diode 53 and the resistor 23 described above. The diode 53 has a collector side of the transistor 43 as an anode and a resistor 23 side as a cathode.
3 and the resistor 23.

The spark discharge cutoff circuit 4 thus configured
0 means that the transistor 41 is turned on when the second command signal Sb output from the ECU 6 is at a high level,
The transistor 41 side of the capacitor 45 is grounded. In this state, since no signal is input to the base side of the transistor 42 via the capacitor 45, the base potential of the transistor 42 is held at the ground potential via the resistor 47, and the transistor 42 is turned off. . As a result, the capacitor 51 provided on the collector side of the transistor 42 is connected to the resistor 5 from the power supply line LV.
2 and the resistor 49, the power supply voltage Vc is applied, a predetermined amount of charge determined by the capacitance and the power supply voltage Vc is accumulated in the capacitor 51, and no current flows. Therefore, the transistor 43 is kept in the off state. You.

Next, when the second command signal Sb changes from the high level to the low level, the transistor 41 is turned off, and the power supply voltage Vc is applied to the transistor 41 side of the capacitor 45 via the resistor 44. Therefore, the capacitor 45 includes the resistor 44 and the capacitor 4
5, a current flows through the path of the resistor 46 and the resistor 47, and the base potential of the transistor 42 rises.
2 is turned on. The capacitor 45 is connected to the resistor 4
4. A high-pass filter (differential circuit) is formed together with the resistor 46 and the resistor 47.
Immediately turns off the transistor, and turns on the transistor 42 to turn on the transistor 42. However, when a predetermined charge is accumulated in the capacitor 45, the current stops flowing, and the transistor 42 is turned off again.

When the transistor 42 is temporarily turned on, the transistor 42
While the electric charge accumulated in the capacitor 51 is discharged,
From the power supply line LV to the resistor 52, the resistor 49, the resistor 4
8 and a current flows through a current path formed by the transistor 42,
The base potential of the transistor 43 decreases, and the transistor 43 is turned on.

When the transistor 43 is turned on, the power supply line Lv switches the transistor 4
3. The transistor 5 is turned on via the diode 53 and the resistor 23. Therefore, in the spark discharge cutoff circuit 40, when the second command signal Sb changes from the high level to the low level, the current (primary current) i1 flows through the primary coil L1 of the ignition coil 4. As a result, energization of the primary coil L1 of the ignition coil 4 is resumed, and the ignition plug 3
Is forcibly interrupted. Then, in the spark discharge cutoff circuit 40, the second command signal S
When b changes from the high level to the low level, the transistor 42 is turned off, and the capacitor 51 is supplied to the capacitor 51 with a predetermined time constant determined by the capacitance of the capacitor 51 and the resistance values of the resistors 52 and 49. When the charge of
The transistor 43 is turned off.

Next, the ion current detecting section 10 of the combustion state detecting device 1 for an internal combustion engine according to the present embodiment will be described. In the ion current detection unit 10 of the present embodiment, a capacitor 11 and a diode 12 are formed on a path (spark discharge current path) through which the spark discharge current i2 flows. A charging diode 13 is connected in series between the capacitor 11 and the secondary coil L2 of the ignition coil 4 with the direction in which the spark discharge current i2 flows as a forward direction. A discharging switch 14 that is short-circuited in accordance with a detection signal Sd input from outside is connected in parallel to the charging diode 13. Further, a current detecting resistor 15 is connected in parallel with the diode 12 between the capacitor 11 and the diode 12. A zener diode 16 is connected in parallel to a closed circuit including the capacitor 11, the current detection resistor 15, the diode 12, the charging diode 13, and the discharging switch 14. In the ion current detection unit 10, the secondary coil L2 of the ignition coil 4 is used.
The collector is connected to the connection end of the base and the emitter is grounded, and a ground signal S input from the outside to the base is provided.
According to g, a transistor 17 for grounding the connection end to the secondary coil L2 is provided. In this embodiment,
The Zener diode 16 corresponds to a charging unit described in the claims.

The ion current detecting unit 1 thus configured
0 indicates that the current (spark discharge current i2) can flow only from the connection end of the ignition coil 4 with the secondary coil L2 to the ground end when the discharge switch 14 is open. At this time, a current (spark discharge current i2) flows so as to pass through a spark discharge current path including the capacitor 11, the diode 12, and the charging diode 13, and at the same time, a direction in which the zener diode 13 generates the zener voltage Vz. Current will flow through the This allows
The capacitor 11 includes a charging diode 13 and a diode 1 based on the Zener voltage Vz of the Zener diode 13.
2, the voltage Vc (= Vz−) smaller by the forward voltage Vf.
2 × Vf).

As will be described later, when the spark discharge between the electrodes 3a and 3b of the spark plug 3 is forcibly cut off by the spark discharge cutoff circuit 40, the discharge switch 14 is closed by the detection signal Sd from the ECU 6. Can be As a result, both ends of the charging diode 13 are short-circuited, and at this time, it is possible to allow a current to flow from the ground end to the connection end with the secondary coil L2. The current i3 flows so as to pass through a path composed of the capacitor 11 and the discharging switch 14, and the voltage between both ends of the current detecting resistor 15 is in accordance with the magnitude of the current i3 flowing at this time.

When the current i3 flows as described above, a voltage (that is, a high voltage for detection) is applied to the ignition plug 3 via the secondary coil L2 of the ignition coil 4, and an ion current flows. At this time, the voltage Vp applied to the ignition plug 3
Is obtained by subtracting the voltage drop at the current detection resistor 15 from the charge voltage Vc of the capacitor 11 (Vp = Vc
−R × i3; where R is the resistance value of the current detection resistor 15). Here, the applied voltage Vp needs to be set to such an extent that the spark plug 3 does not discharge again (for example, about 1 kV), that is, the Zener voltage Vz of the Zener diode 16 is set based on the applied voltage Vp. There is a need. By setting the Zener voltage Vz near the maximum value of the ion current generated between the electrodes 3a and 3b of the ignition plug 3, the Zener diode 16
Accordingly, it is possible to suppress noise that exceeds the maximum value of the ion current.

When an ionic current flows between the electrodes 3a and 3b of the ignition plug 3, the current detecting resistor 1
5 is output to the detection circuit 8 as Vio. In the detection circuit 8, the voltage V
io is converted into an analog signal, read, converted into a detection signal Dio suitable for input to the ECU 6, and output to the ECU 6 in order to detect the combustion state of the internal combustion engine. In the present embodiment, the detection circuit 8 corresponds to a combustion state detecting means described in the claims.

FIG. 2 shows the first command signal Sa, the second command signal Sb, the potential Vp of the center electrode 3a of the ignition plug 3 and the high voltage 15 for current detection in the combustion state detecting device 1 of the internal combustion engine of the present embodiment. Vio (that is, the spark plug 3
Each state of the ion current i3) flowing between the electrodes 3a and 3b, the detection signal Sd for short-circuiting both ends of the charging diode by the discharging switch 14, and the ground signal Sg are shown in a time chart.

First, at time t1, the first command signal Sa is switched from high to low, and the spark discharge generating means 20 is turned on.
A current (primary current) i1 flows through the primary coil L1 of the ignition coil 4, and then, at time t2 when a preset energization time has elapsed, the first command signal Sa is switched from low to high level, When the application of the primary current i1 to the primary coil L1 is cut off, a negative high voltage for ignition is applied to the center electrode 3a of the spark plug 3, the potential Vp drops sharply, and the electrode 3a-
A spark discharge occurs between 3b. At this time, the spark discharge current i
2 is generated, via the secondary coil L2 of the ignition coil 4,
The current i2 flows to the ion current detection unit 10 side. still,
Regarding the spark discharge current i2 flowing during this spark discharge,
As described above, the Zener voltage Vz is generated in the Zener diode 16 and supplied to the capacitor 11 via the charging diode 13 so that the capacitor 11 is charged.

Then, at time t2, the first command signal Sa
Is inverted from low to high level to generate spark discharge in the ignition plug 3 and, at the same time, switch the second command signal Sb from low to high level. At this time, the spark discharge duration is calculated based on the operation state of the internal combustion engine, and then, at time t3 when a predetermined time based on the calculated value of the spark discharge duration has elapsed, the second command signal Sb is inverted from high to low level. Then, energization of the primary coil L1 of the ignition coil 4 is restarted by the spark discharge cutoff circuit 40, and the spark discharge is forcibly cut off.

At this time t3, when the spark discharge by the ignition plug 3 is forcibly cut off, the high voltage for ignition (potential Vp of the center electrode of the ignition plug) induced in the secondary coil L2 of the ignition coil 4 becomes the voltage. Start damped oscillation. Then, at time t4 when a predetermined time for this vibration to converge to some extent has elapsed, the detection signal Sd is switched from low to high. At this time, the discharging switch 14 is operated so that both ends of the charging diode 13 are short-circuited, and the discharge of the electric charge charged in the capacitor 11 is permitted. Generate. The detection period is desirably set to such a length that all the charges charged in the capacitor 11 are discharged when the ion current i3 flows normally.

Then, when the detection period of the ion current i3 ends, at time t5, the detection signal Sd switches from high to low level, and the discharging from the capacitor 11 is prevented by the charging diode 13. At the same time, the ground signal Sg switches from low to high level, and the transistor 17 causes the ion current detection unit 10
Since the connection end with the secondary coil L2 on the side is grounded, for example, a misfire or the like occurs and a sufficient ion current i3 does not flow, the electric charge remaining on the electrode of the ignition plug 3 is reliably discharged. (Time t5 to t6). Therefore, unnecessary voltage is not applied between the electrodes 3a and 3b of the ignition plug 3, and it is possible to suppress electrode consumption of the ignition plug 3. The switching of the transistor 17 to the conduction state (discharge of the remaining charge of the ignition plug 3) and the non-conduction state is performed after the detection signal Sd is switched to the low level, and the next spark discharge is performed. (The first command signal Sa switches from a high level to a low level).

Next, a series of ion current detection processing executed by the ECU 6 provided in the combustion state detection device 1 of the internal combustion engine will be described with reference to the flowchart shown in FIG. The ECU 6 is for comprehensively controlling the spark discharge timing, the fuel injection amount, the idle speed, and the like of the internal combustion engine. In addition to the ion current detection processing described below, the ECU 6 detects the ion current. Detection of misfire or the like (combustion state) based on the above, state detection processing for detecting various operating states such as intake pipe pressure (or intake air amount), rotation speed, throttle opening, cooling water temperature of the internal combustion engine, and furthermore, detection Signal output processing for outputting various signals for engine control, such as a first command signal Sa for spark discharge in accordance with the operating state.

In the control processing for the ignition control shown in FIG. 3, for example, the internal combustion engine is operated by the internal combustion engine based on a signal from a crank angle sensor for detecting a rotation angle (crank angle) of the internal combustion engine. Perform combustion and exhaust strokes 1
It is executed once per cycle.

As shown in FIG. 3, when the present process is started, first, in S110 (S is an abbreviation for step), the operating state of the engine detected in the separately executed operating state detection processing is read. In step S120, based on the read operation state, a spark discharge occurrence time ts, a spark discharge continuation time Tt, and a standby time Tw for the operation of the discharge switch are calculated. Incidentally, the spark discharge occurrence time ts is obtained, for example, by obtaining a control reference value using a map or a calculation formula using the intake air amount and the rotation speed of the internal combustion engine as parameters, and calculating the control reference value by using the cooling water temperature,
It is calculated by a procedure such as correcting based on the intake air temperature or the like. Further, the spark discharge duration time Tt is determined based on, for example, the rotational speed of the internal combustion engine and the throttle opening indicating the engine load under an operating condition where the spark energy required to burn the air-fuel mixture is large (when the internal combustion engine is rotating at a low speed). , Etc.) is calculated using a preset map or calculation formula so as to be long under an operating condition where the spark energy may be small (such as at high rotation and high load). Furthermore, the standby time Tw for the operation of the discharge switch is within the period in which the ion current can be detected, and the voltage attenuation oscillation generated in the secondary coil side circuit of the ignition coil 4 after the forcible cutoff of the spark discharge. The length is set so as to converge to some extent. The standby time Tw can be calculated by using a map or a calculation formula set in advance based on the spark discharge duration described above.

Next, in S130, based on the spark discharge timing ts calculated in S120, the spark discharge timing t
With respect to s, the energization start timing of the primary coil L1 that is earlier by the preset energization time of the primary coil L1 is determined, and when the energization start timing is reached (time t1 shown in FIG. 2), the first
The command signal Sa is changed from high to low level. still,
When the first command signal Sa is switched from the high level to the low level by the process of S130, the spark discharge generating circuit 20 turns on the transistor 5, so that the primary current i1 flows through the primary coil L1 of the ignition coil 4. Further, the energizing time of the primary coil L1 until the spark discharge occurrence time ts is determined by energizing the primary coil L1 so that the maximum spark energy required to burn the air-fuel mixture under all operating conditions of the internal combustion engine is supplied to the ignition coil 4. This is the time required for accumulation and is set in advance.

In S140, it is determined whether or not the spark discharge timing ts calculated in S120 has been reached based on the detection signal from the crank angle sensor. If the determination is negative, the same steps are repeated. The execution waits for the spark discharge occurrence time ts to elapse. When it is determined in S140 that the spark discharge occurrence time ts has been reached, the process proceeds to S150.

In S150, as shown in FIG.
The command signal Sa is inverted from low to high level, and at the same time, the second command signal Sb is inverted from low to high level. As a result, by the operation of the spark discharge generating circuit 20, the transistor 5 is turned off, the primary current i1 is cut off, a high voltage for ignition is generated in the secondary coil L2 of the ignition coil 4, and the spark discharge occurs in the spark plug 3. appear. Further, on the side of the spark discharge interrupting circuit 40, the transistor 41 is turned on, and the standby state is established in which the primary current i1 can be re-energized. In step S150, the spark discharge is generated in the spark plug 3 so that the spark discharge current i2 flowing at the time of the spark discharge causes the Zener diode 16 to generate the Zener voltage Vz and the charging diode 13
To start charging to a predetermined high voltage for detection.

Next, at S160, after the spark discharge occurrence time ts at S140, it is determined whether or not the spark discharge duration time Tt determined at S120 has elapsed. By repeating the steps, it waits for the spark discharge duration time Tt to elapse. Then, in S160, when it is determined that the spark discharge duration time Tt has elapsed (time t3 shown in FIG. 2), the flow shifts to S170, where the second command signal Sb is changed from high to low level, and Discharge is forcibly shut off.

When the spark discharge is forcibly cut off, the flow shifts to S180. In S180, S120
It is determined whether or not the standby time Tw set in has elapsed. Specifically, the determination may be made by measuring a predetermined elapsed time after the spark discharge (forcibly interrupting the spark discharge) using a timer built in the ECU 16. Then, when it is determined that the standby time Tw has elapsed (time t4 shown in FIG. 2), the process proceeds to S190, and the detection signal Sd is inverted from low to high level only during a predetermined detection period. Then, the discharge switch 14 is operated. By operating the discharge switch 14 in this manner, discharge from the capacitor 11 is permitted, and a high voltage for detection is applied to the ignition plug 3 via the secondary coil L2 of the ignition coil 4, and the ignition plug 3 An ion current i3 flows according to the amount of ions generated between the three electrodes 3a-3b. still,
During the standby time Tw, the detection signal Sd is kept at the low level and the discharge switch 14 is kept open, so that the electric charge charged in the capacitor 11 is not discharged.

Subsequently, the flow shifts to S200, during which the voltage Vio across the current detecting resistor 15 is output to the detection circuit 8 during the detection period (the detection signal Sd is at the high level). The Vio is AD-converted and output to the ECU 6 as a detection value Dio. Then, when the detection period ends (time t5 shown in FIG. 2), in S210, the ground signal Sg is output to turn on the transistor 17, thereby discharging the electric charge remaining in the ignition plug 3 and performing this processing. To end. The ion current i3 taken into the ECU 6
Is used, for example, to detect a combustion state such as abnormal combustion such as knocking or pre-ignition of the internal combustion engine or misfire.

As described above, in the combustion state detecting device 1 for an internal combustion engine of the present embodiment, the discharge of the electric charge charged in the capacitor 11 is permitted only during the detection period in which the ion current i3 is to be detected, and the ignition plug 10, a high voltage for detection is applied. Thus, even if the secondary coil side circuit of the ignition coil 4 causes a voltage attenuation oscillation after the spark discharge in the ignition plug 3 is forcibly cut off, the charged charge of the capacitor 11 is not wasted. , Thereby the capacitor 1
This makes it possible to set the capacitance of one to a necessary and sufficient size. Further, according to the present embodiment, the ion current i3 can be detected in a state where the voltage attenuation oscillation of the secondary coil side circuit has converged to some extent, and the detection accuracy of the ion current i3 is improved, and the ion current i3 is improved. The detected value Vio (Di) detected from the current detection resistor 15 in accordance with
From o), a filter circuit or the like for removing a noise component based on damped oscillation can be omitted or simplified.

Further, the ion current i3 flowing after the spark discharge due to the misfire of the internal combustion engine is small, and the capacitor 11
Even if the electric charge remains in the ignition plug 3, as long as the discharge switch 14 is opened and the transistor 17 is turned on, it is possible to reliably prevent an unnecessary voltage from being applied to the electrode of the ignition plug 3, As a result, the spark plug 3
Of the electrodes, and furthermore, the contamination of the spark plug 3 (reduction of insulation resistance) can be suppressed.

In addition, when the primary coil L1 of the ignition coil 4 is energized using the spark discharge cutoff circuit 40, as shown in FIG. 2, the potential Vp of the center electrode 3a of the ignition plug 3 is sufficiently low and the electrode 3a- 3b, the electric potential V of the center electrode 3a of the spark plug 3 is increased.
By increasing p, the spark discharge can be forcibly cut off. From this, in the present embodiment, the ECU 6
By controlling the switching timing of the first command signal Sa, not only the spark discharge timing of the spark plug 3 is controlled, but also by controlling the switching timing of the second command signal Sb, the end of the spark discharge by the spark plug 3 By controlling the timing, the spark energy supplied to the spark plug 3 for burning the air-fuel mixture can be minimized and the consumption of the electrode of the spark plug 3 can be suppressed. The service life can be further extended in synergy with the configuration of FIG.

Further, in the above-described embodiment, various aspects can be adopted. A combustion state detecting device for an internal combustion engine according to another embodiment of the above-described embodiment (see FIG. 1) is shown in FIGS. This will be described with reference to FIG.

First, the combustion state detecting device for an internal combustion engine according to the first alternative embodiment shown in FIG. 4 is different from the combustion state detecting device 1 for the internal combustion engine described in the above-described embodiment (see FIG. 1). A resistor 18 is provided between the current path of the capacitor 11 and the secondary coil L2 of the ignition coil 4 in the current path of the ion current i3 formed when the electric charge charged in the capacitor 11 is discharged. Things. By providing the resistor 18 in this manner, the discharge switch 14
Is activated and the ion current i3 flows through the current path formed when both ends of the charging diode 13 are short-circuited,
Since the function is performed so as to control the size of the ion current i3, it is possible to detect the ion current i3 in a form in which the noise component superimposed on the ion current is reduced. The resistance value of the resistor 18 shown in FIG. 4 is such that the ion current i3 having a magnitude of about several tens to several hundreds μA generated between the electrodes of the ignition plug 3 does not limit the rate of the ion current i3 itself. It is necessary to provide a resistor 18 having a value.

Next, a combustion state detecting device for an internal combustion engine according to a second embodiment shown in FIG. 5 is different from the combustion state detecting device 1 for an internal combustion engine described in the above embodiment (see FIG. 1).
Instead of the diode 12, a Zener diode 19 is connected in parallel to the current detection resistor 15 with the ground side as the cathode. By providing the Zener diode 19 in this manner, when the ion current i3 flows through a current path formed by short-circuiting both ends of the charging diode 13 with the discharge switch 14, the current detecting resistor 1
The voltage Vio obtained from 5 is detected in a form in which generation of a voltage value equal to or higher than the Zener voltage of the Zener diode 19 itself is suppressed. Thereby, Zener Aether 1
The zener voltage of 9 is set near the maximum value of the ion current normally generated between the electrodes of the ignition plug 3 (that is, the detection value Vio from the current detection resistor 15 calculated from the maximum value of the ion current i3). By setting the value near the maximum value, the Zener diode 19 functions to suppress all the generation of the noise component exceeding the maximum value of the ion current, so that the detection of the ion current with the noise component reduced can be performed. It becomes possible. Note that when spark discharge occurs in the ignition plug 3 and the discharge switch 14 is open,
It goes without saying that the Zener diode 19 functions so that the spark discharge current i2 flows from the connection end of the ignition coil 4 with the secondary coil L2 to the ground end.

In the present embodiment, the detection circuit 8
Constitutes a combustion state detecting means. However, the detection circuit 8 is incorporated in the ECU 6 without being provided separately from the ECU 6, or the ECU 6 can read the voltage Vio directly between both ends. By adopting a configuration for detecting the state, there is no problem even if the combustion state detecting means is configured.

Further, the combustion state detecting device of the internal combustion engine of the embodiment described above (including the different embodiments shown in FIGS. 4 and 5) is applied to a gas engine using gaseous fuel such as methane gas as fuel. , More effective.

Since the gaseous fuel generally has a higher insulating property than the gasoline which is a liquid fuel, the spark discharge voltage is relatively high. Therefore, it is necessary to increase the number of turns of the primary coil and the secondary coil. As a result, the inductance is increased, and as a result, the voltage attenuation oscillation generated when the spark discharge in the ignition plug is forcibly cut off becomes larger. That is, when performing detection using an ion current in a gas engine, it is conceivable that more noise components are superimposed on the obtained ion current than in a gasoline engine. Therefore, by applying the combustion state detecting device of the internal combustion engine of the above-described embodiment (including the different embodiments shown in FIGS. 4 and 5) to a gas engine (internal combustion engine) using gaseous fuel, the ignition plug is used. This is extremely effective because it is possible to accurately and accurately detect the ion current without being affected by the voltage attenuation oscillation generated after forcibly interrupting the spark discharge.

Further, since the gas engine uses gaseous fuel as fuel, there is almost no smoldering (carbon deposition on the insulator) on the spark plug, and as described above, the electrode wear of the spark plug is reduced. By applying the internal combustion engine combustion state detection device of the present embodiment having the effect of suppressing the above to a gas engine, the life of the ignition plug can be further extended.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of a combustion state detection device for an internal combustion engine of the present invention.

FIG. 2 is a waveform chart showing signals of respective units according to the embodiment of the present invention.

FIG. 3 is a flowchart illustrating an ion current detection process executed by an ECU.

FIG. 4 is an overall configuration diagram showing a first different embodiment of the present invention.

FIG. 5 is an overall configuration diagram showing a second different embodiment of the present invention.

FIG. 6 is an overall configuration diagram showing a conventional ion current detection unit.

FIG. 7 is a waveform diagram showing signals of respective sections showing a conventional ion current detection section.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 combustion state detection device of internal combustion engine 2 ignition device 3 spark plug 4 ignition coil 6 electronic control unit (ECU) 8 detection circuit (combustion state detection means) 10 ion current detection unit 11 capacitor 13 charging diode 14 discharge switch 15 current Detection resistor 16 Zener diode (charging means) 18 Resistor 19 Zener diode 20 Spark discharge generation circuit (spark discharge generation means) 40 Spark discharge cutoff circuit (spark discharge cutoff means) L1 Primary coil L2 Secondary coil

Claims (5)

[Claims] An electric current is supplied to a primary coil of an ignition coil for a certain period of time, and a high voltage for ignition is generated in a secondary coil of the ignition coil by interrupting the electric current to start a spark discharge between electrodes of an ignition plug. Spark discharge generating means, after the start of spark discharge of the spark plug, based on the operating state of the internal combustion engine, calculates the spark discharge duration required to burn the air-fuel mixture by the spark discharge, the predetermined spark discharge duration Spark discharge interrupting means for forcibly interrupting the spark discharge according to the elapsed timing; a capacitor inserted in series in a current path including the ignition plug and the secondary coil; Charging means for charging the capacitor to a high voltage for detection having a polarity lower than the predetermined high voltage for ignition and having the opposite polarity by a spark discharge current; After the spark discharge is forcibly cut off by the power cutoff means, the capacitor charged by the charging means flows through the current path when the high voltage for detection is applied to the secondary coil and the ignition plug. A current detection resistor for detecting an ion current; andcombustion state detection means for detecting a combustion state of the internal combustion engine based on the ion current detected by the current detection resistor. A charging diode connected in series to the capacitor with the direction being forward, and for preventing discharge of the electric charge charged to the capacitor by the charging means; and charging and discharging the capacitor by short-circuiting both ends of the charging diode. A discharge switch for discharging the charged electric charge, and the discharge switch at a timing at which the ion current is to be detected. Combustion state detecting system for an internal combustion engine, characterized in that it comprises a switching control means for actuating. 2. The device for detecting a combustion state of an internal combustion engine according to claim 1, wherein when the discharging switch is operated, electric charges charged in the capacitor by short-circuiting both ends of the charging diode. A device for detecting a combustion state of an internal combustion engine, wherein at least one or more resistors are provided between the current paths from the capacitor to the secondary coil in a current path at the time of discharging. apparatus. 3. The combustion state detection device for an internal combustion engine according to claim 1, wherein the Zener diode is connected in parallel to the current detection resistor with a ground side as a cathode. A combustion state detection device for an internal combustion engine, which is characterized in that: 4. The apparatus for detecting a combustion state of an internal combustion engine according to claim 1, wherein said spark discharge cut-off means includes means for controlling said spark discharge generating means to connect to a primary coil of said ignition coil. After interrupting the energizing current, the power supply to the primary coil is restarted in accordance with the timing at which a predetermined spark discharge duration time has elapsed since the start of the spark discharge, thereby forcing the spark discharge of the spark plug. A combustion state detection device for an internal combustion engine, characterized in that the combustion state is blocked. 5. The combustion state detecting device for an internal combustion engine according to claim 1, wherein the internal combustion engine is a gas engine using a gaseous fuel as a fuel. Engine combustion state detector.