JP4873250B2 - Pre-ignition detection device for vehicle engine - Google Patents

Description

  The present invention relates to a pre-ignition detection device for a vehicle engine, and more particularly to a pre-ignition detection device for a vehicle engine that detects a pre-ignition intensity that is a magnitude of an effect of the pre-ignition on the engine based on detection of an ion current. .

2. Description of the Related Art Conventionally, in a spark ignition type internal combustion engine, a technique for detecting a precursor state of pre-ignition generation based on detection of an ion current flowing through ions existing in a combustion chamber has been proposed (see, for example, Patent Document 1). ).
In the ignition circuit for an internal combustion engine described in Patent Document 1, a spark plug is connected to one end of the secondary winding of the ignition coil, and a capacitor and an ion current detection circuit are connected to the other end of the secondary winding. . With this configuration, the ion current detection circuit of the ignition circuit can detect the ion current due to the electric charge discharged from the capacitor in accordance with the ion state in the cylinder.

  Then, the control device for the internal combustion engine of Patent Document 1 detects the peak generation time of the ion current based on the ion current detection signal received from the ignition circuit, and the peak generation time is advanced from a predetermined limit time. If so, it is determined that the pre-ignition is likely to occur.

JP 2006-46140 A

However, in the case of the configuration in which the ionic current is detected through the spark plug as in Patent Document 1, both the ionic current and the spark discharge current flow through the spark plug, and the ionic current is extremely small compared to the spark discharge current. During the ignition discharge, there is a problem that the ion current cannot be detected and the occurrence of pre-ignition cannot be detected. That is, in the configuration of Patent Document 1, the ion current cannot be detected during ignition discharge, and the ion current detection window is narrowed at least during the ignition discharge period.
In particular, in a high compression ratio type engine in an environment where pre-ignition is likely to occur, when the ignition discharge timing is set after the top dead center, the ionic current is caused by the occurrence of the pre-ignition or its precursor state. When the peak generation time is advanced, the ignition discharge period approaches or overlaps, and the detection accuracy of the ion current peak generation time decreases.

  The present invention has been made to solve such a problem, and in a pre-ignition detection device that detects the occurrence of pre-ignition of an engine based on the ionic current, the detection window of the ionic current is expanded to increase the pre-ignition. It is an object of the present invention to provide a pre-ignition detection device for a vehicle engine that can improve the detection accuracy of the pre-ignition intensity, which is the magnitude of the effect of the ignition on the engine.

In order to achieve the above object, the present invention provides an ignition plug disposed in an engine combustion chamber, an ignition circuit for igniting the ignition plug, and an ignition discharge timing of the ignition plug by controlling the ignition circuit. Ignition control means for controlling the ion current, ion current detection means for detecting the ion current flowing through the spark plug, and preignition detection for detecting the occurrence of preignition based on the ion current detected by the ion current detection means The ignition control means is configured to stop or delay the ignition discharge of the ignition plug by the ignition circuit based on the detection of the ion current by the ion current detection means before the ignition discharge by the ignition plug. The pre-ignition detection means is operated by the ion current detection means during the stop or delay period of the ignition discharge by the spark plug. Based on the detected ion current Te detects preignition strength preignition is the magnitude of the effect on the engine, ignition control means, the ion current detecting means detects an ion current before the ignition discharge by the spark plug Based on this, the ignition discharge timing of the spark plug is delayed until the exhaust stroke .

According to the present invention configured as described above, when an ionic current is detected via the spark plug before ignition discharge of the spark plug, the ignition discharge by the spark plug is stopped or retarded. Therefore, the ion current based on the pre-ignition can be detected without being disturbed by the ignition discharge current.
That is, the detection of the ion current before the ignition discharge of the spark plug means that pre-ignition has occurred and the ion concentration in the combustion chamber has increased. When the occurrence of pre-ignition is detected, the ion current detection window can be enlarged by stopping or delaying the ignition discharge. As a result, it is possible to reliably detect the ionic current by pre-ignition, and it is possible to accurately determine the degree of the adverse effect of the pre-ignition on the engine due to, for example, an increase in cylinder pressure or generation of impact sound. .

In addition , according to the present invention, by performing ignition discharge in the exhaust stroke, the ion current detection window can be secured over a long period from the normal ignition discharge timing to the exhaust stroke.

  Preferably, in the present invention, the ignition circuit has an ignition coil connected to the ignition plug, and the ignition control means extends the energization time to the ignition coil beyond the set time, thereby igniting the ignition discharge of the ignition plug. The timing is delayed, and when the ignition discharge timing delay of the spark plug exceeds a predetermined number of times, the energization time to the ignition coil is shortened from the set time.

  According to the present invention configured as described above, if the ignition discharge timing is frequently retarded, that is, if the energization time is extended, it is not preferable in terms of the reliability of the ignition coil. When the ignition occurs, the energization time to the ignition coil is shortened from the normal time. Thereby, the reliability of an ignition coil is securable. In addition, since the situation where pre-ignition frequently occurs is a state in which ignition is easy, the ignitability can be maintained even if the ignition discharge time is shortened. In this case, although ignition is performed, since the ignition discharge time is shortened, the detection window of the ion current is widened, and the determination accuracy of the pre-ignition can be improved.

  Preferably, in the present invention, a plurality of spark plugs are provided including at least the first and second spark plugs, and the ignition circuit is connected to each spark plug so as to be charged during ignition discharge. The ion current detecting means is configured to detect an ion current generated by discharging the electric charge charged in each capacitor, and the ignition control means is configured to detect the second ignition plug. The ignition discharge timing is controlled in phase so that the ignition discharge timing is retarded with respect to the ignition discharge timing of the first spark plug, and the second spark plug is detected by the ion current detecting means before the ignition discharge by the second spark plug. The ignition discharge of the second spark plug by the ignition circuit is stopped or delayed based on the detection of the ionic current flowing through the ignition circuit.

  According to the present invention configured as described above, a spark plug that is ignited and discharged on the retard side by performing phase difference ignition of a plurality of spark plugs has a wider ion current than an ignition plug that is ignited and discharged on the advance side. A detection window can be secured. Weak pre-ignition can be detected on the retard side than strong pre-ignition, but in the present invention, the occurrence of weak pre-ignition can be detected by adopting the phase difference ignition method.

Preferably, in the present invention, the pre-ignition detection means detects the pre-ignition intensity based on the generation time or peak value of the ion current detected by the ion current detection means.
According to the present invention configured as described above, it is possible to easily detect the magnitude of the pre-ignition action according to the peak generation time or peak value of the ion current.

  According to the pre-ignition detection device for a vehicle engine of the present invention, the pre-ignition which is the magnitude of the effect of the pre-ignition on the engine is expanded by expanding the detection window of the ion current for detecting the occurrence of the pre-ignition of the engine. Intensity detection accuracy can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. First, a pre-ignition detection device for a vehicle engine according to a first embodiment of the present invention will be described with reference to FIGS.
1 is a diagram showing a configuration of a vehicle engine, FIG. 2 is a configuration diagram of an ignition circuit, FIGS. 3 and 4 are graphs showing changes in engine cylinder pressure and ion current, and FIG. 5 is a flowchart of pre-ignition detection processing. 6 is a graph showing the pre-ignition determination region, FIG. 7 is a flowchart of the ion current detection process before ignition discharge, FIG. 8 is a flowchart of the calculation process of the generation evaluation time of the ion current, and FIG. 9 is a diagram showing the change of the ion current. FIG. 10 is a graph showing the relationship between the generation evaluation time of the ion current and the pre-ignition intensity, and FIG. 11 is a flowchart of the pre-ignition suppression control process.

First, a schematic configuration of the engine 1 of the present embodiment will be described with reference to FIGS. 1 and 2.
The engine 1 is an in-line multi-cylinder spark ignition direct gasoline engine. The engine 1 has an engine body including a cylinder block 2 and a cylinder head 3 fixed to the cylinder block 2. The upper end of the cylinder 4 that opens to the upper end surface of the cylinder block 2 is closed by the lower surface of the cylinder head 3.
A piston 5 is fitted into the cylinder 4 so as to be able to reciprocate. A combustion chamber 6 is defined between the upper surface of the piston 5 and a pent roof-type lower surface (ceiling surface) of the cylinder head 3. On the other hand, a crankshaft (not shown) is disposed in the crankcase below the piston 5, and is connected to the piston 5 by a connecting rod.

  A crank angle sensor 26 is provided in the crankcase below the cylinder block 2 of the engine 1. The crank angle sensor 26 detects the rotation angle (crank angle) of the crankshaft, and is provided on the outer peripheral portion of the rotor 27 attached so as to rotate integrally with the end portion of the crankshaft. It consists of an electromagnetic pickup coil that outputs a signal corresponding to the passage of the convex portion.

  Further, a water temperature sensor 28 for detecting the temperature state of the cooling water is provided on a water jacket (not shown) of the cylinder block 2. Further, an engine oil temperature sensor 29 is attached.

A plurality of spark plugs 7 are provided corresponding to each cylinder 4, and are attached to the cylinder head 3 so that the tip electrode of the spark plug 7 faces each combustion chamber 6. In addition, each spark plug 7 is connected to an ignition circuit 8.
In the present embodiment, a plurality of ignition circuits 8 are provided corresponding to the respective spark plugs 7. However, the present invention is not limited to this, and one or a plurality of ignition circuits 8 may be provided corresponding to the plurality of spark plugs 7.

As shown in FIG. 2, the ignition circuit 8 includes an igniter 8a composed of a power transistor, an ignition coil 8b composed of a primary winding and a secondary winding, a capacitor 8c connected to the ignition coil 8b, and a capacitor 8c. And an ion current detection circuit 8d connected between the ground potential. The ion current detection circuit 8d corresponds to the ion current detection means of the present invention.
The ignition circuit 8 corresponding to each cylinder 4 turns on the igniter 8a while energizing the ignition coil 8b while receiving a control signal for igniting and discharging the spark plug 7 from the PCM 30. When the ignition circuit 8 no longer receives a control signal after a predetermined energization time, the igniter 8a is turned off, whereby an ignition discharge current flows from the secondary winding of the ignition coil 8b, and the ignition plug 7 is ignited. .

  In the ignition circuit 8, the capacitor 8c is charged by this ignition discharge. The ionic current detection circuit 8d detects the current that flows when the charge of the capacitor 8c is discharged as an ionic current. The ignition circuit 8 outputs an ion current detection signal to the PCM 30.

Further, the cylinder head 3 is formed with two intake ports 9 and two exhaust ports 10 communicating with each combustion chamber 6. In addition, intake and exhaust valves (intake valve 11 and exhaust valve 12) that are opened and closed by rotation of a camshaft (not shown) are disposed at the port openings of the intake port 9 and the exhaust port 10, respectively.
One camshaft is provided on each of the intake side and the exhaust side, and is connected to the crankshaft by a common cam chain. The intake-side and exhaust-side camshafts rotate in synchronization with the rotation of the crankshaft, whereby the intake valve 11 and the exhaust valve 12 are opened and closed at predetermined timings, respectively.

  In addition, a variable valve timing mechanism 13 (hereinafter referred to as “VVT (Variable Valve Timing)”) capable of continuously changing the phase with respect to the rotation of the crankshaft within a predetermined angle range is attached to the camshaft on the intake side. Yes. The camshaft on the intake side can be changed by the VVT 13 so that the lift curve In of the intake valve 11 is advanced or retarded. Along with this, the overlap period with the lift curve Ex of the exhaust valve 12 changes, and the amount of burned gas remaining in the combustion chamber 6 (hereinafter referred to as “internal EGR”) can be changed.

An intake passage (intake manifold) 15 communicating with the intake port 9 is disposed on the intake side of the cylinder head 3. The intake passage 15 has a branch passage that branches toward each cylinder 4 and a forked passage that branches from the branch passage toward two intake ports 9 of each cylinder 4. One of the bifurcated passages is provided with a tumble swirl control valve (hereinafter referred to as “TSCV”) 14 for adjusting the strength of the intake air flow in the combustion chamber 6.
The intake passage 15 has an air cleaner 16 from the upstream side, an air flow sensor 17 for detecting the intake flow rate, and a throttle that throttles the intake passage 15 by an electric motor 18a between the upstream end of the intake passage 15 and the TSCV valve 14. A valve 18 is provided. In addition, an intake air temperature sensor 23 is provided in the vicinity of the air cleaner 16 in the intake passage 15.
Further, the cylinder head 3 is provided with a plurality of injectors 19 corresponding to the respective cylinders 4 for directly injecting fuel into the respective combustion chambers 6.

An exhaust passage (exhaust manifold) 20 for discharging burned gas (exhaust gas) from each combustion chamber 6 is disposed on the exhaust side of the cylinder head 3 so as to communicate with the exhaust port 10. Like the intake passage 15, the exhaust passage 20 has a branch passage and a bifurcated passage, and each bifurcated passage is connected to the exhaust port 10.
The exhaust passage 20 is provided with an oxygen concentration sensor (hereinafter referred to as “O ₂ sensor”) 21 for detecting the air-fuel ratio of the air-fuel mixture based on the oxygen concentration in the exhaust gas from the upstream side, and for purifying the exhaust gas. The catalytic converter 22 is disposed.

Further, one end of an exhaust gas recirculation passage 24 (hereinafter referred to as “EGR passage”) is branchedly connected to the exhaust passage 20 upstream of the O ₂ sensor 21. The other end of the EGR passage 24 communicates with the intake passage 15 on the downstream side of the throttle valve 18. The EGR passage 24 is provided with an electric flow control valve 25 (hereinafter referred to as “EGR valve”) whose opening degree can be adjusted, and exhaust gas (hereinafter referred to as “external”) that is recirculated through the EGR passage 24 by the EGR valve 25. EGR ")) can be adjusted.

As is well known, a PCM (Power-train Control Module) 30 includes a CPU, a ROM, a RAM, an I / O interface circuit, and the like. The PCM 30 includes an airflow sensor 17, an O ₂ sensor 21, a crank angle sensor 26, a water temperature sensor 28, an engine oil temperature sensor 29, an intake air temperature sensor 23, and a cam angle sensor that detects the rotation angle (rotation position) of the intake camshaft. 31, output signals of an accelerator opening sensor 32 for detecting the operation amount of the accelerator pedal, an engine speed sensor 33 for detecting the engine speed, an ignition circuit 8, and the like are input.

  The PCM 30 determines the operating state of the engine 1 based on the output signals from the sensors and the like, and controls the operation of the engine 1 according to this. That is, the PCM 30 outputs a signal for controlling the operation timing of the intake valve 11 to the VVT 13, and outputs a signal for controlling the intake flow rate to the throttle valve 18, and the combustion chamber to the TSCV 14 of each cylinder 4. 6 outputs a signal for controlling the strength of the intake air flow, outputs a pulse signal for controlling the fuel injection amount and the injection timing to the injector 19 of each cylinder 4, and provides an EGR passage to the EGR valve 25. 24 outputs a signal for controlling the amount of exhaust gas (external EGR) circulating to the intake system, and outputs a control signal for igniting and discharging the spark plug 7 to the ignition circuit 8 at a predetermined timing.

  Further, as will be described later, the PCM 30 detects the pre-ignition intensity that is the magnitude of the effect of the pre-ignition on the engine 1 and the occurrence of the pre-ignition on the engine 1 based on the ion current detection signal from the ignition circuit 8. . When the occurrence of pre-ignition is detected, the PCM 30 performs pre-ignition suppression control based on the pre-ignition intensity. Specifically, this control is control for suppressing the occurrence of pre-ignition due to control of the VVT 13 and the throttle valve 18 and the like. The PCM 30 corresponds to the ignition control means and the pre-ignition detection means of the present invention.

Next, an outline of pre-ignition detection according to the present embodiment will be described.
First, a case where the pre-ignition detection process of the present embodiment is not performed will be described with reference to FIG. FIG. 3 shows changes in in-cylinder pressure and ion current in a general compression stroke and expansion stroke.
In FIG. 3 and similar graphs thereafter, the alternate long and short dash line represents the change during normal combustion, and the solid line represents the change when pre-ignition occurs.

As indicated by the alternate long and short dash line in FIG. 3A, during normal combustion, the pressure in the cylinder 4 gradually increases in the compression stroke as the crank angle advances, and near the crank angle A ₁ (top dead center TDC). It becomes a peak (maximum value). The engine 1 of the present embodiment is a high compression ratio type engine, and the set period is set so that the spark plug 7 is ignited and discharged between the crank angles A _{2 and} A ₃ after the top dead center. This set period is determined in advance by the operating state of the engine 1. Due to this ignition discharge, the air-fuel mixture in the combustion chamber 6 is combusted and expanded to increase the in-cylinder pressure, reach a peak again at the crank angle A ₄ , and then the in-cylinder pressure gradually decreases.

Further, as indicated by the alternate long and short dash line in FIG. 3B, during normal combustion, the ionic current is substantially zero until ignition discharge is started at the crank angle A ₂ and increases after ignition discharge.
In the configuration of this embodiment, the ion plug 7 is used to detect the ion current. During the ignition discharge, a very large ignition discharge current is placed on the ion current, so that only the ion current cannot be detected. That is, the ionic current cannot be detected between the crank angles A _{2 and} A ₃ . However, only the ion current is illustrated in the graphs including the subsequent changes in ion current including FIG. 3 for easy understanding.

  In this example, the ion current has a peak immediately after the end of the ignition discharge. This peak is considered to be based on ions (radicals) existing on the flame surface that expands with the growth of the flame kernel after the mixture is ignited. Strongly influenced by fluid strength. That is, this peak becomes steeper as the initial combustion becomes active, and the peak advances.

The ionic current becomes a second peak substantially corresponding to the crank angle A _{4 at} which the in-cylinder pressure reaches a peak, and then gradually decreases to a substantially zero value. This second peak uses not only ions (radicals) generated by the combustion reaction itself, but also ions generated by thermal ionization of NOx present in the burned gas as the temperature of the combustion chamber 6 rises. it is conceivable that. This second peak appears at the crank angle position where the temperature of the combustion chamber 6 is highest, and becomes higher as the combustion as a whole increases, and decreases as it becomes slower.

On the other hand, as shown by the solid line in FIG. 3 (A), when pre-ignition occurs early after top dead center, the in-cylinder pressure is increased from the vicinity of the crank angle A ₅ before the start of ignition discharge (before crank angle A ₂ ). It becomes larger than the upward trend or normal combustion. In this example, the peak is reached at the crank angle A ₆ immediately after the end of the ignition discharge, and then gradually decreases.
Further, as shown by the solid line in FIG. 3B, when pre-ignition occurs, the ionic current starts to gradually increase from the zero value at the crank angle A ₅ before the start of ignition discharge, and during the ignition discharge (crank angle A ₂ -A ₃ between) to take the first peak, again becomes the second peak substantially corresponds to the crank angle a _6-cylinder pressure reaches a peak, then decreases. This second peak occurs at the crank angle position between the first peak and the second peak of the ionic current during normal combustion.

  As described above, when pre-ignition occurs, the ion current has one or two peaks during ignition discharge, but when the pre-ignition detection processing of the present embodiment is not performed, that is, in the prior art, Since the current could not be detected, there was a case where the pre-ignition could not be accurately evaluated.

Next, changes in the in-cylinder pressure and the ion current when the pre-ignition detection process in the present embodiment is applied will be described with reference to FIG.
As shown in FIGS. 4A and 4B, when pre-ignition occurs at a crank angle A ₅ before ignition discharge, the in-cylinder pressure starts to increase and the ionic current starts to increase from zero. In the present embodiment, when it is detected that the ion current has increased before ignition discharge, the ignition discharge at the set crank angle A ₂ -A ₃ is stopped or delayed. In FIG. 4B, the ignition discharge period is delayed to the crank angle A ₇ -A ₈ in the exhaust stroke after the expansion stroke that does not affect the ion current detection.

Thus, in the present embodiment, the occurrence of pre-ignition is determined based on the rise in ion current before ignition discharge. In this case, ignition discharge is not performed at the set ignition discharge timing (crank angle A ₂ -A ₃ ), but the air-fuel mixture in the combustion chamber 6 is combusted due to the occurrence of pre-ignition, and an ionic current is generated.
In this embodiment, the ignition discharge timing is delayed until the exhaust stroke, so that the ion current detection window is expanded between the crank angles A _{2 and} A ₃ . In other words, conventionally, the ionic current could not be detected at the ignition discharge timing at which the ionic current suddenly increased due to pre-ignition, but by delaying the ignition discharge timing as in the present embodiment, It is possible to detect a sudden rise in ion current due to ignition.

Next, the pre-ignition detection processing flow of the first embodiment will be described with reference to FIGS.
FIG. 5 is a main flow of the pre-ignition detection process of the PCM 30 and is executed for each engine cycle.
First, the PCM 30 updates the ignition discharge start delay data for the set number of cycles stored in the internal memory using the previous engine cycle data (step S11). The ignition discharge start delay data is data representing whether or not the ignition discharge start timing is delayed in each past engine cycle. The ignition discharge start delay data is initialized to data with no delay when the engine is started, but is updated every engine cycle. The set number of cycles is set based on the performance of the ignition coil 8b.

Next, the PCM 30 counts the number of ignition discharge delays in the ignition discharge start delay data for the set number of cycles (step S12), and calculates the ratio of the number of delays to the set number of cycles (step S13).
Then, the PCM 30 sets the ignition delay prohibition flag to “1” when the delay number ratio is larger than the allowable damage setting value, and sets it to “0” otherwise (step S14). The allowable breakage set value is set to limit the number of delays to protect the ignition coil 8b, and is determined based on the performance of the ignition coil 8b. In the ignition delay prohibition flag, “1” means prohibition of ignition discharge start delay, and “0” means allowance of ignition discharge start delay.

  Next, the PCM 30 determines whether or not the current operating state of the engine 1 is in the pre-ignition determination region based on the signal from the above-described sensor (step S15). The pre-ignition determination area is an operation area in which pre-ignition may occur. The PCM 30 holds the pre-ignition determination area as internal storage data in advance. The pre-ignition determination area is set with the engine speed, charging efficiency, engine water temperature, engine oil temperature, intake air temperature, octane number, etc. as parameters. Qualitatively, pre-ignition is more likely to occur when the engine speed is low (for example, up to about 1500 rpm), high filling efficiency, high engine water temperature, high engine oil temperature, high intake air temperature, and low octane number. An ignition determination area is set. For example, as shown in FIG. 6, when the horizontal axis is the engine speed and the vertical axis is the charging efficiency, the pre-ignition determination region is set to a region B with a low rotation and high load.

If the current operating state of the engine 1 is not in the pre-ignition determination region (step S15; No), the process returns to step S11 again.
On the other hand, when the current operating state of the engine 1 is in the pre-ignition determination region (step S15; Yes), the PCM 30 determines whether or not the ignition delay prohibition flag is “0” (step S16).

  When the ignition delay prohibition flag is not “0” (step S16; No), the PCM 30 sets the ignition discharge period to a length shorter than the normal setting period (step S17), and proceeds to step S21. In this case, since the ignition delay prohibition flag is “1”, it is evaluated that the pre-ignition frequently occurs within the latest set number of cycles. Therefore, the air-fuel mixture can be ignited even if the ignition discharge period is shortened. Easy. And the ion current detection window can be expanded by shortening the ignition discharge period. Further, the ignition discharge is performed at a normal ignition discharge start timing.

  The shortening of the ignition discharge period is achieved by shortening the transmission period of the control signal from the PCM 30 and making the conduction time of the igniter 8a shorter than the set length. Thereby, since the energization time of the ignition coil 8b is shortened, the ignition energy of the ignition coil 8b is reduced, and the duration (ignition discharge period) of the ignition discharge current from the ignition coil 8b is shortened. Moreover, since the energization time of the ignition coil 8b is shortened, damage to the ignition coil 8b can be prevented.

When the ignition delay prohibition flag is “0” (step S16; Yes), the PCM 30 detects an ion current in a specific period before the ignition discharge (step S18). That is, this processing flow is based on the ion current detection signal acquired from the ignition circuit 8 and during a specific period set between the top dead center and the start of ignition discharge (crank angle A ₁ -A ₂ ). This is a process for determining whether or not an error has occurred.

FIG. 7 shows the process of step S18. In the present embodiment, the PCM 30 acquires the ion current detection signal from the ignition circuit 8 during this specific period, and stores it as an ion signal pre-ignition determination value (step S18-1).
In this embodiment, the ion current value is adopted as the ion signal pre-ignition determination value. However, in addition to this, the integral value of the ion current detection signal and the rate of change of the ion current with respect to the crank angle are adopted. May be. Thereby, generation | occurrence | production of an ionic current is reliably detectable. The specific period may be a dwell period of the ignition coil 8b.

  Next, the PCM 30 determines whether or not an ionic current is significantly generated based on the ion signal pre-ignition determination value (step S19). In this process, it is determined whether or not the ion current that is the ion signal pre-ignition determination value is within a predetermined threshold range. If the ion current exceeds the predetermined threshold range, an ion current is generated (that is, the pre-ignition has occurred). If it does not exceed the predetermined threshold range, it is determined that no ionic current is generated (that is, pre-ignition is not generated). The threshold value is set according to the engine operating condition with reference to the magnitude of the ion current detected during normal combustion where pre-ignition has not occurred.

  For example, when the integral value of the ion current detection signal is adopted as the ion signal pre-ignition determination value, it can be determined that an ion current has occurred when a predetermined threshold value is exceeded. In addition, when the rate of change of the ion current with respect to the crank angle is adopted as the ion signal pre-ignition determination value, it is determined that the ion current is generated when the rate of change is within a certain threshold range for noise removal. it can.

When it is not determined that an ionic current is generated (step S19; No), the process proceeds to step S21.
On the other hand, when it is determined that an ionic current is generated (step S19; Yes), the PCM 30 performs a process of delaying the ignition discharge start timing to the exhaust stroke, and expands the ionic current detection window (step S20). As a result of this processing, the control signal output to the ignition circuit 8 is continued until the exhaust stroke without being cut off. Then, the output of the control signal is interrupted in the exhaust stroke, and the ignition discharge current is released.

If the ion current detection window is expanded due to the delay of the ignition discharge period, the ion current detection is not hindered by the ignition discharge, so that the pre-ignition intensity can be accurately detected in the subsequent processing steps.
Note that if the ignition coil 8b is energized for a long time in this delay process, the ignition coil 8b may be damaged. In this embodiment, the number of delays is limited in steps S11 to S14, S16, and S17. It is supposed to be.

Next, the PCM 30 detects the ion current based on the ion current detection signal from the ignition circuit 8 and stores it in the memory (step S21).
Based on this ion current detection, the PCM 30 calculates an ion current generation evaluation time that can be evaluated as a substantial generation time of the ion current (step S22). In this process, when the ignition discharge is performed during the original expansion stroke without expanding the ion current detection window, the generation evaluation timing of the ion current is calculated except for the ignition discharge timing. FIG. 8 shows a processing flow of step S22.

  As shown in FIG. 8, first, the PCM 30 takes in an ionic current in correspondence with the crank angle (step S22-1). When the ignition discharge is not performed, the ion current detection window into which the ion current is taken is, for example, a range of 180 ° (CA) from the top dead center, and when the ignition discharge is performed, the ion current detection window is a range excluding this period. At this time, smoothing processing (for example, moving average) of noise components such as ignition noise, combustion noise, and electromagnetic noise is performed.

And PCM30 detects the generation | occurrence | production evaluation time of an ionic current (step S22-2). In this case, the PCM 30 detects the peak of the ion current and stores the crank angle at that time.
In the present embodiment, the generation evaluation time of the ion current is made to correspond to the crank angle at which the ion current reaches a peak. However, the present invention is not limited to this, and the generation evaluation time of the ion current is set as shown in FIG. It may be set.
FIG. 9A shows an example in which the generation evaluation time of the ion current is set to a crank angle corresponding to a certain ratio of the integrated value of the ion current in the ion current detection window (or a certain section thereof). In the example of FIG. 9A, the crank angle corresponding to 50% of the integrated value is set as the generation evaluation time of the ion current, and the crank angles C ₁ (solid line) and C ₂ (two-dot chain line) are the ion current generation. Evaluation time.

FIG. 9B shows an example in which the ion current generation evaluation timing is set to the rising position of the ion current. In the example of FIG. 9B, the crank angle that has risen to 10% of the peak of the ionic current is set as the ionic current generation evaluation period, and the crank angles C ₃ (solid line) and C ₄ (two-dot chain line) are the ionic current. It is time to evaluate the occurrence of
Further, in the example of FIG. 9B, the rising position of the ion current is set, but it may be set to the falling position. Furthermore, in this embodiment, the generation evaluation time of the ionic current is used as the crank angle, but the present invention is not limited to this, and the generation evaluation time of the ionic current may be set as time (for example, time from top dead center).

Next, the PCM 30 calculates a pre-ignition intensity that is the magnitude of the effect of the pre-ignition on the engine 1 based on the generation evaluation time of the ionic current (step S23).
The pre-ignition intensity represents the degree to which the engine 1 is adversely affected or damaged, and is, for example, the magnitude of the maximum combustion pressure in the cylinder or the magnitude of sound generated in the cylinder 4. If the maximum combustion pressure in the cylinder is large, the engine 1 may be damaged, and the generation of sound leads to a decrease in merchantability.
FIG. 10 is experimental data showing the relationship between the generation evaluation time of the ion current and the pre-ignition intensity. FIG. 10 shows that the degree of influence of the pre-ignition intensity increases as the generation evaluation time of the ionic current advances more than that during normal combustion. Specifically, the earlier the pre-ignition occurs, the higher the maximum combustion pressure in the cylinder, causing knocking and increasing the knocking sound.

Then, the PCM 30 performs pre-ignition suppression processing according to the pre-ignition intensity (step S24). FIG. 11 shows the flow of this pre-ignition suppression process.
As shown in FIG. 11, first, the PCM 30 reads the pre-ignition intensity (step S25-1). Then, the PCM 30 determines whether or not the pre-ignition intensity exceeds a predetermined allowable limit value (step S25-2). Note that the allowable limit value is a value determined in consideration of merchantability and the like through experiments with the engine 1.

  When the preignition intensity exceeds a predetermined allowable limit value (step S25-2; Yes), the PCM 30 performs preignition suppression control (step S25-3). This pre-ignition suppression control includes control of the VVT 13, control of the throttle valve 18, and the like. The PCM 30 performs pre-ignition suppression control using one of these or a combination thereof. For example, the PCM 30 reduces the effective compression ratio by a predetermined amount by the VVT 13 or reduces the charging efficiency by reducing the throttle valve 18 (decreases the actual compression ratio), thereby setting the engine operating condition where pre-ignition is unlikely to occur. . In addition to these, the engine 1 may be configured to reduce the variable compression ratio.

  When the pre-ignition intensity does not exceed the predetermined allowable limit value (step S25-2; No), the PCM 30 gradually increases the control amount of the VVT 13 and the throttle valve 18 in the pre-ignition suppression control toward the normal set value. Return processing is performed (step S25-4). In other words, when the pre-ignition suppression control deviates from the normal set value, the control amount is gradually returned to the normal set value.

  After the pre-ignition suppression process, the PCM 30 determines whether or not the processes of steps S11 to S24 are performed again in the next cycle (step S25). If the process is performed again, the process returns to step S11. finish.

As described above, the pre-ignition detection device of the present embodiment is configured to delay the ignition discharge timing by determining that the pre-ignition has occurred when an increase in ion current is detected before the ignition discharge. Yes. As a result, the ion current detection window can be greatly enlarged, and the pre-ignition intensity can be reliably detected.
In this embodiment, in the delay process, the ignition discharge timing is delayed to the exhaust stroke, so that the combustion is not affected by the ignition discharge.
Furthermore, in this embodiment, since the energization time to the ignition coil 8b becomes longer due to the delay process, the ignition coil 8b may be damaged if the delay process is frequently performed. For this reason, in this embodiment, the ignition coil 8b is prevented from being damaged by limiting the number of delay processes.

  Further, in the present embodiment, when the delay process is limited, the ignition discharge period is shortened. When performing the delay processing, it is considered that the air-fuel mixture in the combustion chamber 6 is easily ignited. Therefore, even if the energization time to the ignition coil 8b is shortened to protect the ignition coil 8b, the air-fuel mixture is ignited. Can be achieved. Further, by shortening the ignition discharge period, the ion current detection window can be expanded and the detectability can be improved.

Next, a second embodiment of the present invention will be described based on FIG.
In the first embodiment, the process of delaying the ignition discharge is performed when the pre-ignition is detected. However, the present embodiment performs the process of stopping the ignition discharge when the pre-ignition is detected. It is. Note that, in the following embodiment, portions different from the above embodiment will be mainly described, and overlapping description will be omitted.

FIG. 12 is a flowchart of the pre-ignition detection process.
When the pre-ignition detection process starts, the PCM 30 performs steps S31, S32, and S33, which are the same processes as steps S15, S18, and S19 of the above embodiment.
If it is determined in step S33 that an ionic current is generated (step S33; Yes), the PCM 30 performs a process of stopping the ignition discharge (step S34). Thereby, the ion current detection window can be enlarged.
Subsequent processing steps S35 to S39 are the same as steps S21 to S25 of the above embodiment.

In the second embodiment, when the ionic current is detected before the ignition discharge is started, the ignition discharge is stopped. However, this also makes it possible to enlarge the ion current detection window and improve the detectability. Is possible.
Moreover, in 2nd Embodiment, it can avoid that the energization time of the ignition coil 8b becomes long by comprising so that ignition discharge may be stopped. As a result, the ignition coil 8b can be protected, and the process can be simplified because it is not necessary to perform the process for limiting the number of delay processes (steps S11 to S14, etc.).

Next, based on FIG. 13 thru | or FIG. 16, 3rd Embodiment of this invention is described.
The third embodiment is an example in which each cylinder 4 is provided with two spark plugs 7 capable of controlling the ignition discharge timing independently.
FIG. 13 is a diagram showing the arrangement of the spark plug, FIGS. 14 and 15 are graphs showing changes in the engine cylinder pressure and ion current, and FIG. 16 is a flowchart of the pre-ignition detection process.

  As shown in FIG. 13A, the lower surface (ceiling surface) of the cylinder head 3 is provided with two intake ports 9 and two exhaust ports 10 on the intake side and the exhaust side, respectively. Yes. A main spark plug 7a is provided on the lower surface of the cylinder head 3 at the center of the cylinder bore surrounded by these four openings, and an intake side edge beyond the openings of the two intake ports 9 from the main spark plug 7a. An auxiliary spark plug 7b is provided near the portion. Thus, it is desirable to dispose the main spark plug 7a and the sub spark plug 7b in the combustion chamber 6 apart from each other.

  Further, not only the arrangement of FIG. 13A but also the arrangement of FIGS. 13B to 13D, the main ignition plug 7a and the auxiliary ignition plug 7b are arranged apart from each other in the combustion chamber 6. can do. In FIG. 13B, the auxiliary spark plug 7b is disposed in the vicinity of the edge on the exhaust side. That is, they are arranged at symmetrical positions with the auxiliary spark plug 7b and the main spark plug 7a in FIG. In FIG. 13C, the auxiliary spark plug 7b is disposed in the vicinity of the edge portion that extends between the opening of the intake port 9 and the opening of the exhaust port 10 on one side from the main spark plug 7a. In FIG. 13D, the main spark plug 7a is disposed at the edge on the intake side and the sub spark plug 7b is disposed at the edge on the exhaust side across the center of the cylinder bore.

  The ignition circuit 8 shown in FIG. 2 is connected to each of the spark plugs 7a and 7b, and the PCM 30 can independently control the ignition discharge of the two spark plugs 7a and 7b. As will be described below, in the third embodiment, the PCM 30 controls the spark plugs 7a and 7b to be ignited and discharged simultaneously or with a phase difference when the current operating state of the engine 1 is not in the pre-ignition determination region. When the current operating state of the engine 1 is in the pre-ignition determination region, one ignition discharge timing is controlled to be delayed.

Next, an outline of pre-ignition detection according to the present embodiment will be described.
First, based on FIG. 14, a different part from FIG. 3 is demonstrated about the change of the general cylinder pressure and ion current when not performing the preignition detection process of this embodiment. The alternate long and short dash line in FIG. 14 represents a change during normal combustion, and the solid line represents a change when pre-ignition occurs.
The pressure change in the cylinder 4 shown in FIG. 14 (A) shows almost the same change as in FIG. 3 (A) both during normal combustion and when pre-ignition occurs. FIGS. 14B and 14C show changes in ion current detected through the main spark plug 7a and the sub spark plug 7b, respectively. The changes in these ion currents are almost the same as those in FIG. 3B both during normal combustion and when pre-ignition occurs.

Next, changes in the in-cylinder pressure and the ion current when the pre-ignition detection process in the present embodiment is applied will be described with reference to FIG. In the present embodiment, the pre-ignition detection process is performed when the current operating state of the engine 1 is in the pre-ignition determination region.
FIGS. 15A and 15B are the same as FIGS. 14A and 14B, respectively. As shown in FIG. 15B, the main spark plug 7a is ignited at the normal ignition discharge timing (crank angle A ₂ -A ₃ ). As shown in FIG. plug 7b ignition discharge is discontinued or ignition discharge timing is delayed crank angle a ₇ -A _8.

As described above, in the third embodiment, when the operating state of the engine 1 is in the pre-ignition determination region, the ignition discharge of the auxiliary ignition plug 7b is stopped or delayed, so that the auxiliary ignition plug is connected via the auxiliary ignition plug 7b. The ion current corresponding to the ion concentration around 7b can be continuously detected. That is, the detection window for detecting the ionic current via the auxiliary ignition plug 7b can be enlarged.
As shown in FIG. 15C, the peak of the ionic current appears at the crank angle A ₁₀ during the expansion stroke during normal combustion, but appears at the crank angle A ₉ that is advanced from the crank angle A ₁₀ when pre-ignition occurs.

That is, at the normal time, it is the crank angle A ₁₀ that the flame ignited by the main spark plug 7a propagates to the vicinity of the sub spark plug 7b. The ion current can be detected by the propagation of the flame.
On the other hand, when the preignition occurs, as well as self-ignition earlier than the ignition by the main ignition plug 7a, because the propagation speed of the flame is higher than during normal combustion, the flame at a crank angle A ₉ was advanced from the crank angle A ₁₀ Propagates in the vicinity of the auxiliary spark plug 7b.
As described above, when pre-ignition occurs, the peak of the ion current advanced from the normal time can be detected. The PCM 30 can determine the pre-ignition intensity by comparing the generation evaluation time of the ionic current at the time of pre-ignition with the generation evaluation time of the ionic current at the time of normal combustion that is previously stored as data. .

Next, the pre-ignition detection process flow of the third embodiment will be described with reference to FIG.
First, the PCM 30 performs the same step S51 as the process of step S15 in the above embodiment.
Next, when the current operating state of the engine 1 is in the pre-ignition determination region (step S51; Yes), the PCM 30 performs a process of stopping the ignition discharge of the auxiliary spark plug 7b or delaying the ignition discharge timing (step S52). . Thereby, the detection window of the ionic current detection via the auxiliary spark plug 7b can be enlarged.

Processes after step S52, that is, steps S53 to S57, are the same as steps S21 to S25 in the above embodiment. However, the ion current detected via the auxiliary spark plug 7b is used.
As described above, in the third embodiment, the sub-ignition plug 7b is specialized for ion current detection under an operating condition in which pre-ignition is likely to occur. Thereby, the ion current resulting from the pre-ignition can be detected reliably.

In the third embodiment, since the main spark plug 7a and the sub spark plug 7b are spaced apart from each other, it is possible to detect an enlarged difference in flame propagation between normal combustion and pre-ignition. It is possible to improve the detectability.
In the third embodiment, the sub-ignition plug 7b does not contribute to the ignition of the air-fuel mixture under operating conditions where pre-ignition is likely to occur, so that pre-ignition does not occur and only the main ignition plug 7a is ignited. A case occurs. For this reason, it is desirable to apply the third embodiment to the engine 1 that can tolerate performance degradation due to ignition only by the main spark plug 7a.

Next, based on FIG. 17 thru | or FIG. 19, 4th Embodiment of this invention is described.
As in the third embodiment, the fourth embodiment is an example in which two ignition plugs 7 capable of independently controlling the ignition discharge timing are arranged in each cylinder 4. However, the fourth embodiment employs a phase difference ignition method in which the ignition discharge timing of the auxiliary ignition plug 7b is retarded by a predetermined amount in advance of the main ignition plug 7a during normal combustion. And in 4th Embodiment, similarly to 1st Embodiment, when an ionic current is detected before ignition discharge, it is comprised so that the ignition discharge of the auxiliary spark plug 7b may be stopped or an ignition discharge timing may be delayed. Yes.
FIGS. 17 and 18 are graphs showing changes in engine cylinder pressure and ion current, and FIG. 19 is a flowchart of pre-ignition detection processing.

Next, an outline of pre-ignition detection according to the present embodiment will be described.
First, based on FIG. 17, a different part from FIG. 14 is demonstrated about the change of the general in-cylinder pressure and ion current when not performing the preignition detection process of this embodiment. The alternate long and short dash line in FIG. 17 represents a change during normal combustion, and the solid line represents a change when pre-ignition occurs.
The change in pressure in the cylinder 4 shown in FIG. 17A shows the same change as in FIG. 3A both during normal combustion and when pre-ignition occurs. FIG. 17B shows a change in ion current detected via the main spark plug 7a. This change in ion current is the same as that in FIG. 3B both during normal combustion and when pre-ignition occurs. It shows almost the same change.

FIG. 17C shows a change in the ionic current detected through the auxiliary ignition plug 7b. This change in the ionic current is affected by the ignition discharge in the auxiliary ignition plug 7b. In both normal combustion and pre-ignition occurrence, changes similar to those in FIG. 17B are shown.
As can be seen from FIGS. 17B and 17C, the ignition discharge timing (crank angle A ₁₁ -A ₁₂ ) of the auxiliary spark plug 7 b is greater than the ignition discharge timing (crank angle A ₂ -A ₃ ) of the main spark plug 7 a. ) Is shifted in the retarded direction.

Next, changes in the in-cylinder pressure and the ionic current in the compression stroke and the expansion stroke when the pre-ignition detection process in the present embodiment is applied will be described with reference to FIG.
In this case, FIGS. 18 (A), (B), and (C) are almost the same as FIGS. 15 (A), (B), and (C).
As described above, in the fourth embodiment, when the ionic current is detected before the ignition discharge of the auxiliary ignition plug 7b, the ignition discharge of the auxiliary ignition plug 7b is stopped or delayed as in the third embodiment. The detection window for detecting the ionic current through the auxiliary ignition plug 7b can be enlarged.

Next, the pre-ignition detection process flow of the fourth embodiment will be described with reference to FIG.
First, the PCM 30 performs the same step S51 as the process of step S15 in the above embodiment. Next, when the current operating state of the engine 1 is in the pre-ignition determination region (step S61; Yes), the PCM 30 performs a process of further shifting (shifting) the ignition phase of the auxiliary spark plug 7b (step). S62). As a result, the detection window for detecting the ionic current via the auxiliary ignition plug 7b is enlarged, and the detection sensitivity of the pre-ignition is improved. In this case, the ignition phase of the auxiliary spark plug 7b may be retarded and the ignition discharge period may be shortened.

Processes after step S52, that is, steps S63 to S70 are the same as steps S18 to S25 in the above embodiment. However, the ion current detected via the auxiliary spark plug 7b is used.
As described above, in the fourth embodiment, since the sub-ignition plug 7b is set with the ignition discharge timing later than the main ignition plug 7a in the normal state, the detection window before the discharge ignition of the first embodiment In comparison, it is possible to ensure a wide detection window before the ignition discharge of the auxiliary spark plug 7b. Thereby, the detection sensitivity of the ion current resulting from the pre-ignition before ignition discharge can be improved. That is, in the fourth embodiment, such pre-ignition can be detected even when the pre-ignition is weak and occurs at a later time.

Further, in the third embodiment, under the operating conditions where pre-ignition is likely to occur, the secondary ignition plug 7b is stopped from ignition or the ignition discharge timing is delayed, so that the secondary ignition plug is not necessarily generated even when pre-ignition does not occur. In 7b, the ignition discharge may not be performed at the normal ignition discharge timing, and the engine performance may be deteriorated.
On the other hand, in the fourth embodiment, the ignition of the auxiliary ignition plug 7b is stopped or the ignition discharge timing is delayed only when an ionic current is detected in a specific period before the ignition discharge of the auxiliary ignition plug 7b. Therefore, it is possible to suppress engine performance degradation.

The above embodiment may be modified as follows.
In the above embodiment, it is determined that the pre-ignition intensity is larger as the generation evaluation time of the ion current is advanced. However, the present invention is not limited to this, and it is determined that the pre-ignition intensity is larger as the ion current is larger. It may also be determined by a combination of these.

In the third and fourth embodiments, two spark plugs 7 have been described. However, the present invention is not limited to this, and a configuration including three or more spark plugs 7 may be used.
Further, in the third and fourth embodiments, when the delay process of the ignition discharge timing of the auxiliary spark plug 7b is frequently performed and the delay process is limited by the set number of times, the same as in the first embodiment. In addition, the ignition delay process of the auxiliary ignition plug 7b may be stopped and the energization time may be shortened. In this case, after the occurrence of pre-ignition is no longer detected by the pre-ignition suppression control, the ignition of the auxiliary spark plug 7b can be resumed after a predetermined period.

It is a figure showing the structure of the vehicle engine by 1st Embodiment of this invention. It is a block diagram of the ignition circuit by 1st Embodiment of this invention. 4 is a graph showing changes in engine cylinder pressure and ion current according to the first embodiment of the present invention. 4 is a graph showing changes in engine cylinder pressure and ion current according to the first embodiment of the present invention. It is a flowchart of the pre-ignition detection process by 1st Embodiment of this invention. It is a graph showing the pre-ignition determination area | region by 1st Embodiment of this invention. It is a flowchart of the ion current detection process before the ignition discharge by 1st Embodiment of this invention. It is a flowchart of the calculation process of the generation | occurrence | production evaluation time of the ionic current by 1st Embodiment of this invention. It is a figure showing the change of the ion current by 1st Embodiment of this invention. It is a graph which shows the relationship between the generation | occurrence | production evaluation timing of the ionic current and pre-ignition intensity | strength by 1st Embodiment of this invention. It is a flowchart of the pre-ignition suppression control process by 1st Embodiment of this invention. It is a flowchart of the pre-ignition detection process by 2nd Embodiment of this invention. It is a figure which shows arrangement | positioning of the ignition plug by 3rd Embodiment of this invention. It is a graph showing the change in the engine cylinder pressure and ion current by 3rd Embodiment of this invention. It is a graph showing the change in the engine cylinder pressure and ion current by 3rd Embodiment of this invention. It is a flowchart of the pre-ignition detection process by 3rd Embodiment of this invention. It is a graph showing the change of the engine cylinder pressure and ion current by 4th Embodiment of this invention. It is a graph showing the change of the engine cylinder pressure and ion current by 4th Embodiment of this invention. It is a flowchart of the pre-ignition detection process by 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder block 3 Cylinder head 4 Cylinder 6 Combustion chamber 7 Spark plug 8 Ignition circuit 8a Igniter 8b Ignition coil 8c Capacitor 8d Ion current detection circuit 9 Intake port 10 Exhaust port 11 Intake valve 12 Exhaust valve 13 Variable valve timing (VVT)
14 TSCV valve 15 Intake passage 17 Air flow sensor 18 Throttle valve 19 Injector 20 Exhaust passage 21 O ₂ sensor 23 Intake temperature sensor 24 Exhaust recirculation passage (EGR passage)
25 Flow control valve (EGR valve)
26 Crank angle sensor 28 Water temperature sensor 29 Engine oil temperature sensor 30 PCM
31 Cam angle sensor 32 Accelerator opening sensor 33 Engine speed sensor

Claims (4)

A spark plug disposed in the combustion chamber of the engine;
An ignition circuit for igniting and discharging the spark plug;
Ignition control means for controlling the ignition circuit to control the ignition discharge timing of the ignition plug;
Ionic current detection means for detecting ionic current flowing through the spark plug;
Pre-ignition detection means for detecting the occurrence of pre-ignition based on the ion current detected by the ion current detection means,
The ignition control means is configured to stop or delay the ignition discharge of the ignition plug by the ignition circuit based on the detection of the ion current by the ion current detection means before the ignition discharge by the ignition plug,
The pre-ignition detection means is a pre-ignition that is the magnitude of the effect of the pre-ignition on the engine based on the ion current detected by the ion current detection means during the stop or delay period of the ignition discharge by the spark plug. Detect the intensity ,
The ignition control means delays the ignition discharge timing of the ignition plug to the exhaust stroke based on the fact that the ion current detection means detects the ion current before the ignition discharge by the ignition plug . Engine pre-ignition detection device. The ignition circuit has an ignition coil connected to the spark plug;
The ignition control means delays the ignition discharge timing of the ignition plug by extending the energization time to the ignition coil from a set time, and the delay of the ignition discharge timing of the ignition plug becomes a predetermined number of times or more. The pre-ignition detection device for a vehicle engine according to claim 1 , wherein the energization time to the ignition coil is shorter than the set time. A plurality of spark plugs are provided including at least first and second spark plugs,
The ignition circuit has a plurality of capacitors connected to the respective spark plugs and provided so that electric charges are charged during ignition discharge,
The ion current detection means is configured to detect an ion current due to discharge of the electric charge charged in each capacitor,
The ignition control means controls the phase difference of the ignition discharge timing so that the ignition discharge timing of the second spark plug is retarded with respect to the ignition discharge timing of the first spark plug, and the ion current detection means Stopping or delaying the ignition discharge of the second spark plug by the ignition circuit based on the detection of the ion current flowing through the second spark plug before the ignition discharge by the second spark plug The pre-ignition detection device for a vehicle engine according to claim 1 or 2 . It said preignition detecting means, according to any one of claims 1 to 3, characterized in that detecting the preignition intensity based on timing or peak value occurs in the detected ion current by said ion current detecting means Pre-ignition detection device for vehicle engine.

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