JPH0783155A - Misfire detecting device of gasoline engine - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a misfire detection device that is easy to install and maintain and that can accurately detect a spark plug misfire. [Structure] A capacitance voltage divider 5 for detecting a secondary voltage charged in the electrostatic stray capacitance of a spark plug after a spark discharge, a secondary voltage detection circuit 6 for detecting a divided voltage waveform, and a secondary voltage. In a misfire detection device for a gasoline engine, which comprises a discrimination circuit for discriminating the presence or absence of misfire based on the attenuation characteristic of the waveform, and detecting the attenuation characteristic of the secondary voltage, the secondary voltage detection circuit 6 includes a voltage divider. And a discharge circuit 54 of No. 5 and a comparator 57 whose output terminal is connected to the voltage divider 5 via a backflow prevention diode D1 and whose inverting input terminal is connected to the voltage divider 5 so as to return the divided voltage to a zero point. 56
And an operational amplifier 53 for inputting the output of the voltage divider 5 via the discharge circuit 54 and the zero adjustment circuit 56.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misfire detection device for detecting a misfire (misfire) in a gasoline engine.

[0002]

2. Description of the Related Art In order to purify exhaust gas from an automobile engine and improve fuel efficiency, there is a demand for a device capable of detecting an ignition state of each cylinder of an engine and preventing misfire of all cylinders. Further, as a misfire detecting device, conventionally, a method of making a hole in a cylinder block and mounting a combustion light sensor, mounting an in-cylinder pressure sensor on a spark plug, and measuring an ionic current of an ignition circuit are known.

[0003]

However, in the above-mentioned conventional method, the mounting of the sensor is troublesome, or the high-voltage diode is necessary for detecting the ion current, and therefore when mounted on all cylinders of the vehicle. There were drawbacks such as increased mounting cost and time-consuming maintenance.
An object of the present invention is to provide a misfire detection device that is easily mounted and maintained and that can accurately detect a misfire of a spark plug.

[0004]

DISCLOSURE OF THE INVENTION A misfire detecting device according to the present invention includes a capacitance voltage divider for detecting a secondary voltage generated in a secondary circuit of an ignition circuit, and a divided secondary voltage waveform. A secondary voltage detection circuit for detecting, and a determination circuit for determining the presence or absence of misfire by the attenuation characteristic of the secondary voltage waveform, the attenuation characteristic of the secondary voltage charged in the electrostatic stray capacitance of the spark plug after spark discharge In a misfire detection device for a gasoline engine, which detects a misfire in the cylinder from the damping characteristic,
The secondary voltage detection circuit is a discharge circuit that discharges the divided voltage of the voltage divider, a zero-point adjustment circuit that returns the divided voltage that has swung in the opposite polarity beyond the zero point to a zero point, and a voltage divider of the voltage divider. Is provided with an interface consisting of an operational amplifier that receives as an input via the discharge circuit and the zero adjustment circuit,
The zero-point adjusting circuit is characterized in that the output terminal is connected to the voltage divider via a backflow prevention diode, and the inverting input terminal is composed of a voltage comparison circuit connected to the voltage divider.

[0005]

According to the present invention, a combustion light sensor, a pressure sensor, and a high-voltage diode are unnecessary, and a misfire detection device having a simple structure, excellent mountability on an engine, and high practicality can be obtained. Further, since the divided voltage of the voltage divider can be brought close to the zero point of the operational amplifier, the accuracy of misfire detection becomes high. further,
Since the zero adjustment circuit is composed of the voltage comparison circuit,
When the divided voltage of the voltage divider swings in the opposite polarity, the zero point can be quickly approached. Therefore, when a large voltage division ratio is set in the voltage divider, even if the deflection of the voltage waveform to the opposite polarity becomes large, the misfire can be detected accurately without being affected by it.

[0006]

SUMMARY OF THE INVENTION In a gasoline engine, a spark discharge of several kilovolts is generated by an inductive discharge following a high voltage of 15 kilovolts to 35 kilovolts by a capacity discharge in one spark discharge timing. In this invention, after the spark discharge is completed, the decay characteristics of the secondary voltage (secondary voltage for misfire detection) charged to the floating capacitance of the spark plug is analyzed, and when the decay is fast, the normal combustion occurs, and when it is late, Discriminates as a misfire.

Charging of the stray capacitance of the spark plug with the secondary voltage for detecting misfire is sufficiently performed by the electric energy remaining in the ignition coil after the completion of spark discharge when the engine is rotating at high speed. When the electric energy remaining in the ignition coil is small, such as when the engine rotates at low speed or when the power supply voltage drops, during or after the induction discharge period of spark discharge,
A primary current may be passed through the primary circuit of the ignition coil for a short time. When the re-energization is interrupted, the secondary voltage is boosted again, and the electrostatic stray capacitance of the spark plug can be charged with a secondary voltage for detecting misfire of several kilovolts. At this time, the level of the re-boosted secondary voltage is controlled by adjusting the re-energization time so that the series gap such as the rotor gap of the distributor can be destroyed (5 to 7 kilovolts).

The discharge time (attenuation characteristic) of the secondary voltage for detecting misfire of several kilovolts charged in the electrostatic stray capacitance of the spark plug differs depending on the presence or absence of ions generated by combustion in the spark discharge gap of the spark plug. . Therefore, the attenuation characteristic of the voltage waveform between the electrodes of the spark plug is
The misfire can be detected by measuring the misfire and the normal ignition in advance and storing them as data, and comparing them with the actual damping characteristics. That is, at the time of misfire, there are no ions between the electrodes of the spark plug, and the charged charges are less likely to be discharged through the ions, so the secondary voltage for misfire detection decays later than during normal ignition. Therefore, misfire can be detected because the decay time is longer than normal ignition.

In order to detect the secondary voltage for detecting the misfire, a secondary voltage sensor that produces a minute electrostatic capacitance between the secondary circuit of the ignition circuit and an electrostatic capacitance sufficiently larger than the secondary voltage sensor are used. It is convenient to use a capacitive voltage divider consisting of a capacitor with it. When using this capacitance voltage divider,
It is desirable to have a discharge circuit.

When the voltage dividing ratio of the voltage divider is reduced, the degree of reduction of the change in the secondary voltage waveform is also reduced. Therefore, when the secondary voltage for misfire detection is at a low level (and therefore the degree of change in the secondary voltage waveform is also small). Detection accuracy can be increased. That is, when the misfire detection secondary voltage is several kilovolts, it is desirable that the voltage division ratio be 1/1000 and the voltage can be divided into about several volts as an input to the operational amplifier of the secondary voltage detection circuit. Further, when the secondary voltage for detecting misfire is at a low level of about 1 kilovolt, if the voltage dividing ratio is set to about 1/500, the secondary voltage waveform attenuation characteristic between 0 and 2 volts will be detected. In order to improve the detection accuracy of the secondary voltage waveform attenuation characteristic, it is necessary to have a secondary voltage waveform of at least 1 volt or more. If this is less than several hundred millivolts, it becomes difficult to detect the secondary voltage waveform attenuation characteristic accurately. . However, if the voltage division ratio is small, the operational amplifier may be damaged by an excessive voltage when a high voltage voltage division during capacity discharge is input. Therefore, it is necessary to increase the voltage division ratio of the voltage divider in order to protect the operational amplifier from the excessive voltage. In this case, the reduction scale becomes large due to the large voltage division ratio, the secondary voltage level for detection becomes low, and even if the deflection to the reverse polarity occurs, in the present invention, the adjustment to the zero point should be performed promptly. Therefore, the accuracy of misfire detection can be improved even if the voltage division ratio of the voltage divider increases.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an ignition device for an internal combustion engine equipped with an ignition coil 1, a distributor 2 and a spark plug 3. The primary circuit 11 of the ignition coil 1 is connected to the vehicle-mounted power source V and the primary current disconnecting means 4, and the secondary circuit 12 is connected to the spark plug 3 via the distributor 2. Rotor gap 21 of distributor 2 and spark discharge gap 3 of spark plug 3
A misfire discriminating apparatus 1 including a voltage divider 5, a secondary voltage detecting circuit 6, and a misfire discriminating circuit 7 in a secondary circuit 12 between
00 is connected. In this embodiment, the primary current interrupting means 4 serves as a misfire detecting secondary voltage generating means for charging the floating capacitance of the spark plug.

The primary current interrupting means 4 comprises a switching element 41 and a signal generator 42, detects the crank angle and throttle opening of the engine, and the spark discharge timing becomes an ignition advance angle adapted to the load and the rotational speed of the engine. So that the primary current is intermittent. The voltage divider 5 has a secondary voltage sensor 51 arranged near the secondary circuit 12 of the ignition coil 1 and a capacitor 52 connected between the secondary voltage sensor 51 and the ground.

In this embodiment, the secondary voltage sensor 51 comprises a conductor arranged to create a 5 pF (picofarad) capacitance with the high voltage lead of the secondary circuit 12, and the capacitor 52 comprises 2500. The capacitance is about 5000 pF. Therefore, the voltage divider 5 includes the secondary circuit 12
The secondary voltage generated in 1 is divided into 1/500 to 1/1000. When the voltage division ratio is 1/1000, the secondary voltage due to capacitive discharge of 35 kV at maximum becomes 35 V, and the secondary voltage for misfire detection of several KV becomes several V and is input to the secondary voltage detection circuit 6.

When the voltage divider 5 based on the capacitance ratio is used as in the present invention, the divided voltage is charged in the voltage divider 5,
It is desirable to provide a discharge circuit for discharging the electric charge charged in the capacitor 52 with a predetermined time constant by the next ignition timing.

In this embodiment, the voltage dividing ratio is 1/1000, and the voltage dividing ratio between the voltage divider 5 and the ground is 1.2, as shown in FIG.
The discharge circuit 5 having a resistance R1 of mega ohm (MΩ)
4, the discharge time constant of the voltage divider 5 is set to 6 ms (millisecond). The decay time of the secondary voltage for misfire detection is
The maximum is 2 ms at the time of normal combustion, and it is sufficiently long at the time of misfire. Therefore, the discharge time constant cannot be set too short because the discharge time constant must include the decay time of 2 ms in order to reliably determine misfire.

The interface 50 includes an operational amplifier 53.
And a discharge circuit 54 provided between the output terminal of the voltage divider 5 and the input terminal of the operational amplifier 53, and the operational amplifier 53.
And a zero-point adjusting circuit 56 provided between the input terminal and the voltage divider 5. The partial pressure ratio is preferably small from the viewpoint of improving the accuracy of misfire detection, but it is not necessary to make it smaller than 1/500. If it is 1/3000, the accuracy of misfire detection starts to decrease. Therefore 1/500 to 1/3000
The range is preferably set to 1/500 to 1/1000.

When the electric charge stored in the floating capacitance of the spark plug 3 is not attenuated at the time of misfire and is discharged in the latter half of the exhaust stroke, the secondary voltage waveform is, for example, as shown in FIG. The secondary voltage for misfire detection lasts as long as 5 ms. In this case, the output voltage of the voltage divider 5 is lowered by the discharge by the discharge circuit 54 as shown in FIG. In this state, when the secondary voltage for misfire detection of the secondary circuit is stepped down to 0 volt as shown in (a), the secondary voltage waveform of the divided voltage has a reverse polarity (zero) from the zero point as shown in (b). It greatly sinks on the minus side. For this reason, the secondary voltage waveform at the next ignition timing is returned from the position where the zero point largely sinks to the opposite polarity, so that it becomes difficult for the operational amplifier 53 based on the zero point to detect the secondary voltage waveform.

Therefore, in the present invention, the zero-point adjusting circuit (which charges the capacitor 52) 56 of the voltage divider 5 is provided. The zero-point adjusting circuit 56 is composed of a voltage comparing circuit including a comparator 57 whose non-inverting input terminal is grounded in a single power source, and a backflow preventing diode D1 whose anode terminal is connected in series to the output terminal of the comparator 57. The inverting input terminal and the cathode of the backflow prevention diode D1 are both connected to the output of the voltage divider 5. The output terminal of the comparator 57 is a resistor R
A dedicated open-collector comparator IC connected to the power source through 2 was used. With this circuit configuration, when the output voltage of the voltage divider 5 swings from the zero point to the opposite polarity and sinks, the voltage of the opposite polarity is input to the inverting input terminal of the comparator 57, so that the output of the comparator 57 is output. The capacitor 52 of the voltage divider 5 which is inverted to the positive polarity and connected to the cathode of the backflow prevention diode D1 is charged with the time constant (0.01 ms) of the resistor R2.

As a result of the operation of the zero adjustment circuit 56, FIG.
As shown in (C), the reference level of the secondary voltage sunk on the minus side is restored to 0 volt by the next ignition timing. Therefore, it is possible to prevent a state where the starting point of the secondary voltage waveform starts from a position where the starting point of the secondary voltage waveform is largely depressed from the zero point to the opposite polarity, and the secondary voltage waveform having a low level can be accurately detected. The time constant of the zero-point adjusting circuit 56 is set to 0.1 ms or less, preferably 0.05 ms or less in order to surely return the voltage divider 5 to the zero point even during high-speed operation of the engine.

As shown in FIG. 4, the secondary voltage detection circuit 6 is
Interface 5 for shaping the output of voltage divider 5
0, the output of the interface 50 is input, and the peak hold circuit 61 is reset by the ON signal (inversion to high level) of the primary voltage of the signal generator 42, and its output is divided into, for example, 1/3. It is composed of a voltage dividing circuit 62 for compressing the voltage to obtain the reference voltage v, and a comparator 63 for comparing the voltage division of the voltage divider 5 with the reference voltage v, which is constant among the secondary voltage waveforms divided by the voltage divider 5. The duration t of the voltage above the level is detected.

The misfire discrimination circuit 7 compares the data obtained in advance by experiments or calculations with the duration t, and discriminates a misfire when the duration t of the spark discharge waveform is equal to or more than a set value.

The operation will be described with reference to FIG. A pulse signal for interrupting the primary current shown by the signal generator 42 is output, and a primary current such as is generated in the primary circuit 11. The pulse wave a having a large width h is a signal for generating a spark discharge in the spark plug 3, and has a small width delayed by a delay time i of about 0.5 to 1.5 ms after the end of the pulse wave a. The pulse wave b is a signal for generating a secondary voltage for detecting a misfire for charging the floating capacitance of the spark plug 3.

In the ignition circuit using the rotor gap 21 as the series gap, the proximity time between the rotor of the distributor 2 and the side electrode varies depending on the engine speed. Therefore, during high-speed operation of the engine, the pulse width h and the delay time i are set to be short and 6000
A suitable spark discharge duration of about 0.5 to 0.7 ms at rpm.

Due to the interruption of the primary current, the secondary circuit 12
The secondary voltage shown in is generated in the ignition coil 1. When the spark plug 3 normally discharges sparks and ignites and burns, the spark discharge starts due to the high voltage p generated at the end of the pulse wave a, followed by a gentle voltage waveform due to the induction discharge. q occurs.

Corresponding to the rise of the pulse wave b, a positive waveform r due to the back electromotive force is generated in the secondary circuit 12, and the spark discharge is interrupted while the spark discharge is continuing. After the power supply to the primary coil is stopped, the secondary voltage is boosted again and the waveform s appears. The re-boosting level of the secondary voltage can be set as desired by the delay time i and the width of the pulse wave b. In the present invention, the level of the waveform s is set so that the dielectric breakdown of the rotor gap 21 is possible, and the discharge is impossible when the burning fuel ions do not exist in the spark discharge gap 31 of the spark plug 3. Set to 7 kilovolts.

As a result, the secondary voltage waveform divided by the voltage divider 5 has a waveform as shown in FIG. The secondary voltage (the plug voltage) charged between the rotor gap 21 of the distributor 2 and the spark discharge gap 31 of the spark plug 3 mainly to the electrostatic capacitance of the spark plug 3 (usually 10 to 20 pF) is As shown in ,, there is a difference in the decay time between the case of normal ignition and the case of misfiring. In other words, when a misfire occurs, the voltage waveform gradually drops,
When normally ignited, it has a secondary voltage waveform that rapidly attenuates as in s ₁ .

The secondary voltage detection circuit 6 detects the decay time of the secondary voltage waveforms p and q at the time of spark discharge and s ₁ at the time of misfire detection as follows. The peak hold circuit 61 is
The peak value of each secondary voltage waveform divided by the voltage divider 5 is held, and the level of 1/3 of the peak hold value is used as the reference voltage v, and each secondary voltage waveform is compared with the reference voltage v. . That is, as shown in, the reference voltage v for detecting the ion current waveform for detecting misfire and the secondary voltage waveforms p, q and s ₁ are compared to detect the time of the secondary voltage equal to or higher than each reference voltage. , Pulse waves t ₁ and t ₂ are output to the misfire determination circuit 7. The misfire determination circuit 7 compares the width of the ignition secondary voltage waveform with a value equal to or higher than the set level and the width of each pulse waveform, which is the decay time of the detection secondary voltage, with data obtained in advance by experiment or calculation. , It is determined that a misfire has occurred when the time is longer than the set time.

In the above embodiment, the rotor gap 21 of the distributor 2 is used as the series gap. However, in a distributorless igniter that does not have a distributor, it is necessary to provide a backflow prevention diode in the secondary circuit. is there. Further, the voltage generating means for ion detection is
It may be provided separately from the primary current interrupting means. In addition, when the center electrode of the spark plug 3 has a positive potential, the ionic current flows more smoothly than when it has a negative potential. It is desirable to set it to a positive potential. Although the dedicated comparator IC is used as the voltage comparison circuit of the zero adjustment circuit in the above embodiment, an operational amplifier OP may be used as shown in FIG.
In this case, the resistor R3 is connected to the output terminal of the operational amplifier OP.
Is connected, and the anode side of the diode D1 is a resistor R3.
Are connected in series.

[Brief description of drawings]

FIG. 1 is an ignition circuit diagram of a spark ignition engine equipped with a misfire detection device of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of a zero adjustment circuit.

FIG. 3 is a waveform diagram for explaining the operation of the zero adjustment circuit of the misfire detection device.

FIG. 4 is a block diagram of a secondary voltage detection device.

FIG. 5 is a waveform diagram for explaining the operation of the misfire detection device.

FIG. 6 is a circuit diagram showing another embodiment of the zero adjustment circuit.

[Explanation of symbols]

 1 Ignition coil 2 Distributor 3 Spark plug 4 Primary current interrupting device 5 Voltage divider (capacitance voltage divider) 6 Secondary voltage detection circuit 7 Misfire determination circuit (determination circuit) 50 Interface 53 Operational amplifier 54 Discharge circuit 56 Zero adjustment circuit 57 Comparator (voltage comparison circuit) D1 Reverse current prevention diode R2 Resistor

Claims (1)

[Claims] 1. A capacitance voltage divider for detecting a secondary voltage generated in a secondary circuit of an ignition circuit, a secondary voltage detection circuit for detecting a divided secondary voltage waveform, and the secondary voltage detector. It consists of a judgment circuit that judges whether or not there is a misfire based on the attenuation characteristic of the voltage waveform.It detects the attenuation characteristic of the secondary voltage charged in the electrostatic stray capacitance of the spark plug after a spark discharge and detects the misfire in the cylinder from the attenuation characteristic. In the misfire detection device for a gasoline engine, the secondary voltage detection circuit returns the divided voltage oscillated in a reverse polarity beyond a zero point to a zero point with a discharge circuit that discharges the divided voltage of the voltage divider. An interface including a zero-point adjusting circuit and an operational amplifier that receives the voltage division of the voltage divider via the discharge circuit and the zero-point adjusting circuit is provided.
The zero-point adjusting circuit comprises a voltage comparison circuit having an output terminal connected to the voltage divider via a backflow prevention diode and an inverting input terminal connected to the voltage divider, and a misfire detecting device for a gasoline engine. .