JPH06207576A - Misfire detecting device for gasoline engine - Google Patents

Abstract

PURPOSE:To perform reliable detection of the misfire of a gasoline engine even in instantaneous brake during the occurrence of a misfire, in detection of a voltage change between the electrodes of an ignition plug. CONSTITUTION:The passage of the peak value of a sensor 50 to detect a voltage between the electrodes of an ignition plug after spark discharge of the ignition plug is detected by a peak value passage detecting part 21. By releasing reset of a peak hold circuit 35 after a lapse of a given time starting from the detection, the output of the sensor 50 is held, a peak value held by a peak hold circuit 31 is compared with a voltage value held by the peak hold circuit 35. In a case of instantaneous brake during the occurrence of a misfire, since a voltage after the passage of a peak value is remarkably reduced compared with that during ignition, instantaneous brake during the occurrence of a misfire is detectable. Further, since, during the occurrence of a normal misfire, a voltage is slowly reduced, decision is practicable by means of a comparing circuit 38 based on the voltage of the peak hold circuit 35.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misfire of a gasoline engine, which detects ignition or misfire of the gasoline engine based on a change in voltage of electric charge charged in a floating capacitance of a spark plug after completion of spark discharge. Regarding a detection device.

[0002]

2. Description of the Related Art In a gasoline engine, an electromotive force is generated in a secondary circuit of an ignition coil even after completion of spark discharge, and a floating capacitance of a spark plug is charged with a voltage corresponding to the electromotive force. Here, the ion density between the electrodes of the spark plug varies depending on the combustion state such as ignition or misfire in the gasoline engine, and when ignited, varies depending on the combustion state. As a result, the attenuation characteristic of the voltage of the spark plug after the completion of the spark discharge shows different changes depending on the presence or absence of ignition or the combustion state. Therefore, there is a method in which a change in the voltage of the spark plug after completion of the spark discharge is detected and ignition or misfire is determined based on the attenuation characteristic of the voltage.
In the conventional misfire detection device based on the voltage decay characteristic of the spark plug, as a method of detecting the voltage decay characteristic, the peak voltage information of the spark plug after completion of the spark discharge is stored and held as a reference value. The degree of subsequent voltage drop relative to the reference value is detected. Here, the peak voltage information serving as the reference value needs to be stored and retained after the spark discharge ends, but at the time when the spark discharge ends, there is a delay corresponding to the rotation speed of the gasoline engine with respect to the ignition timing of the ignition device. Therefore, the peak voltage information is stored and held by a peak hold circuit or the like that operates by being given a delay time corresponding to the rotation speed from the ignition timing.

[0003]

However, in a gasoline engine, even when a misfire occurs, the electric charge charged in the floating capacity of the spark plug is instantly discharged through the plug gap (discharge gap). As a result, the voltage between the electrodes may drop (breakdown). In such a case, the voltage sharply drops, so that the conventional misfire detection device cannot judge the correct misfire detection because it is determined that the voltage attenuation characteristic is large.

According to the present invention, in a misfire detecting device for a gasoline engine, misfire can be surely detected even when a sudden voltage drop occurs in a voltage between electrodes of a spark plug at the time of misfire. The purpose is to correctly identify ignition or misfire.

[0005]

SUMMARY OF THE INVENTION The present invention provides an ignition device in which a spark plug is connected to a secondary circuit of an ignition coil that produces a high voltage for spark discharge by interrupting a primary current. In the misfire detection device for a gasoline engine, wherein the voltage change detection means for detecting a voltage change between the discharge electrodes of the spark plug is provided, and the ignition or misfire of the gasoline engine is discriminated based on the voltage change. Is a peak value storage means for storing and holding the peak value of the voltage of the secondary circuit of the ignition coil; a peak value passage detecting means for detecting passage of the peak value; and a peak value passage detecting means. According to the voltage value storage means for storing and holding the voltage information between the discharge electrodes of the spark plug after a predetermined time after the passage of the peak value is detected, and the voltage value storage means stored and held in the peak value storage means. First voltage comparison means for comparing the initial value with the voltage value stored in the voltage value storage means, and detection of the voltage change set based on the voltage value stored and held in the voltage value storage means The technical means includes a second voltage comparing means for comparing the reference value for the voltage and the voltage information between the discharge electrodes thereafter.

[0006]

According to the present invention, the voltage change detecting means for detecting the change in the voltage between the discharge electrodes of the spark plug uses the peak value storage means to store the peak value of the voltage of the secondary circuit of the ignition coil after the spark discharge is completed. It is stored and retained, and it is determined by the peak value passing detection means whether or not the peak value has passed. Further, after a predetermined time after the passage of the peak value of the voltage is detected, the voltage information between the discharge electrodes of the spark plug is stored and held in the voltage value storage means. Here, in general, the voltage between the discharge electrodes after a spark discharge once rises to a peak value and then decreases, and the rate of decrease is fast at ignition and moderate at misfire. In the second voltage comparison means, when the voltage after a predetermined time after passing the value falls below a reference value (for example, a predetermined ratio to this voltage information) set based on the stored voltage information, If detected, ignition or misfire can be discriminated based on the elapsed time required until then. On the other hand, the voltage between the discharge electrodes after the spark discharge may drop sharply after passing the peak value even at the time of misfire. In this case, the voltage that drastically drops is lower than the voltage at the time of ignition, so the voltage stored after the peak value passage is detected by the first voltage comparison means is
By comparing with the peak value, it can be detected as a rapid voltage drop (breakdown) at the time of misfire. Therefore, in the present invention, ignition and misfire can be discriminated based on the comparison result of the second voltage comparison means, and further, the misfire when the voltage between the electrodes of the spark plug sharply decreases. Can be detected based on the comparison result of the first voltage comparison means.

[0007]

According to the present invention, the peak value of the voltage appearing between the discharge electrodes of the spark plug after the end of the spark discharge is stored and held, and the voltage after a predetermined time after the passage of the spark discharge is stored and held. By comparing the voltage with the peak value, it is possible to reliably detect the misfire even when the voltage sharply drops at the time of misfire of the gasoline engine. Further, since the voltage after the peak value has passed is memorized and the ignition and the misfire are discriminated based on the characteristic of the voltage drop thereafter, the normal ignition or the misfire can be discriminated accurately.
Therefore, even if the change in the voltage of the spark plug is not normal, it is possible to accurately detect the ignition or misfire of the gasoline engine.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on the embodiments shown in the drawings. FIG. 1 shows an embodiment of a misfire detection device for a gasoline engine according to the present invention, which comprises an ignition device 10, a combustion state detection circuit 20 and a sensor 50 for determining ignition or misfire and detecting the combustion state. In the ignition device 10, 1 is an ignition coil, 2 is a distributor, 3 is a spark plug having the number of cylinders, 41 is a transistor of a switching element, 42 is a signal generator, and V is a vehicle-mounted power source.

The sensor 50 for detecting the voltage between the electrodes of each spark plug 3 uses the insulating coating of each plug cord connecting the distributor 2 and each spark plug 3 as a dielectric, and the center of each plug cord. A sensor capacitor 51 formed by an electrostatic capacity between the conductor and a conductor provided corresponding to the conductor, and for connecting the sensor capacitor 51 in series and dividing the voltage between the electrodes of the ignition plug 3. A capacitor 52 for forming a voltage dividing circuit, and a capacitor 52
And a resistor 53 connected in parallel with the capacitor 52 for discharging the.

Here, each of the capacitors 51 has an electrostatic capacity of, for example, 1 pF, and the capacitor 52 has an electrostatic capacity of 3000 pF. The voltage dividing circuit composed of these capacitors 51 and 52 is used. The voltage between the electrodes of the spark plug 3 is divided into 1/3000, and a high voltage of up to 30,000 volts is converted to the order of 10 volts. Further, the resistor 53 has a resistance value of 3 M ohms, whereby the time constant of the discharging circuit of the capacitor 52 is set to 9 ms (millisecond).

As shown in FIG. 2, the combustion state detecting circuit 20 provided at the latter stage of the sensor 50 has a peak value passage detecting section 2 as shown in FIG.
1, a voltage change detection unit 22 and a combustion state detection unit 23. When the peak value passage detection unit 21 peak-holds the output of the sensor 50 at a time determined according to the ignition timing signal and the output of the sensor 50 becomes smaller than the peak-held value by a predetermined value. Is determined as the time when the peak value of the output of the sensor 50 has passed.

Specifically, a peak hold circuit 31,
A reset signal is issued in response to the ignition timing signal from the signal generator 42, and the reset of the peak hold circuit 31 is released after 50 μs (microseconds) has passed, and to the peak hold circuit 31 after the reset circuit 32 is released. The output of the sensor 50 is smaller than the output of the voltage dividing circuit 33 by comparing the output of the voltage dividing circuit 33 with the output of the voltage dividing circuit 33 that divides the voltage held (for example, 9/10). And a comparison circuit 34 for determining that the peak value of the output of the sensor 50 has passed.

The voltage change detection unit 22 sets the output of the sensor 50 to a reference voltage (reference value) after a predetermined time after the peak value passage detection unit 21 detects that the peak value of the output of the sensor 50 has passed. Peak hold is performed as voltage information for setting, and when the output of the sensor 50 decreases to a predetermined ratio with respect to the peak-held voltage information, it is detected and used as the information of the attenuation speed of the output of the sensor 50. Also,
In order to correctly determine the ignition or the misfire, the breakdown of the output of the sensor 50 at the time of the misfire is detected and used as the auxiliary information of the attenuation speed information of the output of the sensor 50.

Specifically, a peak hold circuit 35 for peak-holding the output of the sensor 50 and a reset signal for the peak hold circuit 35 are issued in response to an ignition timing signal from a signal generator 42 to detect the peak value passage. The reset circuit 36 that releases the reset of the peak hold circuit 35 when the peak value of the output of the sensor 50 is detected in the unit 21 and the reset circuit 3
After the reset of 6 is released, the peak hold circuit 35
A voltage dividing circuit 37 which divides the voltage held at (2/3) into a reference voltage for detecting a combustion state,
The output of the sensor 50 is compared with the reference voltage which is the output of the voltage dividing circuit 37, and the time when the output of the sensor 50 becomes smaller than the output of the voltage dividing circuit 37 is defined as the time when the output of the sensor 50 has decreased by a predetermined amount. After a peak value of the output of the sensor 50 is detected by the peak value passage detection unit 21 in accordance with the output signals of the comparison circuit 38 for determining and the comparison circuit 34, a predetermined time is passed. The connection circuit between the peak hold circuit 31 and the voltage dividing circuit 40 described below is opened only for (for example, 3 to 4 ms), and the transmission of the voltage held in the peak hold circuit 31 to the voltage dividing circuit 40 is stopped. Switch circuit 39, a comparison circuit 41 that compares the voltage held by the peak hold circuit 35 with the voltage divided by the voltage dividing circuit 40, and outputs the logical sum of the comparison circuit 38 and the comparison circuit 41. Consisting of circuit 42.

In the comparison circuit 38, is the detected voltage of the sensor 50 lower than the reference voltage (broken line f in FIG. 3) divided by the voltage dividing circuit 37 according to the voltage information stored in the peak hold circuit 35? Whether or not it is determined, and only when the detected voltage of the sensor 50 is higher than the reference voltage, a signal indicating that (for example, a high level signal) is transmitted. In addition, the comparison circuit 41
Is the voltage V1 obtained by dividing the peak value b held by the peak hold circuit 31 after the discharge time by the voltage dividing circuit 40 and the peak hold circuit 35 immediately after the passage of the peak waveform including the peak value b. Compare the held voltage V2,
When the voltage V2 becomes lower than the voltage V1 due to the breakdown, a signal serving as information indicating misfire is transmitted. Here, in the signal detected by the combustion state detection circuit 23 described later, when the duration of the high level signal is long, it is determined as misfire, and when it is short, it is determined as ignition. Therefore, at the time of misfire in breakdown, the comparison circuit 41
In order to output a high-level signal that indicates a misfire and lasts for a long time, the voltage dividing circuit 40 is provided with a capacitor 4 charged by the voltage of the held peak value b.
0a is provided, the voltage V1
Is higher than the voltage V2 for a certain period of time or longer.

In the voltage change detector 22, a predetermined time T0 after the peak value has passed, which is the timing at which the voltage of the sensor 50 is held by the peak hold circuit 35.
In the present embodiment, for example, 10 μs (microsecond) is set according to the time constant required for the peak hold circuit 35 to perform the peak hold operation after the reset release signal is applied to the peak hold circuit 35 by the reset circuit 36. It is set. As a result, there is no need to separately provide a timing circuit for timing the predetermined time T0, so that the circuit configuration is simplified and an inexpensive device can be obtained.
It should be noted that this predetermined time T0 is the time required for the noise to disappear when the noise induced by the ignition coil 1 is superimposed on the voltage of the secondary circuit of the ignition coil 1 detected by the sensor 50. , Is set based on the noise persistence characteristic of the ignition coil 1.

The combustion state detection unit 23 detects the time until the output of the sensor 50 decreases to a predetermined rate after it is detected that the peak value has passed, that is, the signal appearing as the output of the OR circuit 42 by the microcomputer. According to the required time, the ignition and misfire in each cylinder of the gasoline engine are discriminated, and the combustion state at the time of ignition is detected.The result is, for example, the gasoline for air-fuel ratio control, fuel injection control, etc. It is used in engine control.

Next, the operation of the combustion state detecting device of the present embodiment having the above-mentioned structure will be described with reference to FIG. 3 together with the operation of the gasoline engine. Signal generator 42
Transistor 41 is turned on by the ignition timing signal of
When turned off, a pulse current flows through the primary circuit of the ignition coil 1. Due to this intermittent pulse current, the ignition coil 1
A secondary voltage is generated in the secondary coil of the spark plug 3, and spark discharge starts at the spark plug 3 due to the high voltage a generated at the end of the pulse current, and then inductive discharge occurs. Of the ignition coil 1 is continued for a time corresponding to the rotation speed thereof and ends when the electric energy of the ignition coil 1 is reduced.

After completion of the spark discharge, the secondary voltage starts to be boosted by the electric energy remaining in the ignition coil 1, and the high voltage (2 to 3 in low speed operation) according to the rotational speed of the gasoline engine is started.
The voltage is boosted to a peak value b of kilovolts, 5 to 8 kilovolts at high speed operation, and then stepped down. The secondary voltage after the completion of the spark discharge indicates the electric charge charged in the electrostatic capacitance (usually 10 to 20 pF) between the discharge electrodes of the spark plug 3, and the peak value b
The secondary voltage waveform after the passage of the pointed waveform including is rapidly decreased as shown by the solid line c in the case of normal ignition, and in the case of ignition as shown by the solid line d in the case of misfire. Compared with the above, it decreases gradually. In the case of ignition, a difference occurs in the discharge state of the charged charge of the ignition plug 3 depending on the ion density generated between the discharge electrodes of the ignition plug 3 due to combustion, and the ignition is performed in a lean air-fuel ratio state. Etc., will decrease later than in the case of normal ignition.

On the other hand, in the combustion state detecting device 20 for detecting the combustion state based on the secondary voltage changing as described above,
In response to the ignition timing signal from the signal generator 42, the reset circuit 32 starts resetting the peak hold circuit 31, and the reset circuit 36 starts resetting the peak hold circuit 35. As a result,
The peak hold circuit 31 peak-holds the voltage of the peak value b of the peak waveform after the end of the spark discharge, and resets from the comparison circuit 34 when the detection voltage of the sensor 50 drops to the voltage of 9/10 of the peak value b. To circuit 36 Peak hold circuit 35
A signal is sent to release the reset. At this time, the switch circuit 39 opens the connection circuit between the peak hold circuit 31 and the voltage dividing circuit 40 according to the output of the comparison circuit 34, and the voltage of the peak value b held by the peak holding circuit 31 is divided. It is prevented from being transmitted to the circuit 40.

The reset circuit 36 releases the reset of the peak hold circuit 35 in response to the reset release signal of the comparison circuit 34, and the peak hold circuit 35 receives the reset release signal and predetermined by the time constant of the peak hold operation. The detection voltage of the sensor 50 is held after a delay of time T0 (for example, 10 microseconds). As a result, the peak hold circuit 35 uses the detection voltage of the sensor 50 immediately after the pointed waveform including the peak value b after the spark discharge has passed and the reference voltage for detecting the combustion state or the detection of misfire. Hold as voltage information for setting.

In the comparison circuit 38 and the comparison circuit 41, the detection voltage of the sensor 50 is compared with the outputs of the voltage dividing circuits 37 and 40, and a signal corresponding to the comparison result is transmitted. Since the OR circuit 42 is provided at the subsequent stage of the comparison circuit 38 and the comparison circuit 41, the voltage change detection unit 22 is provided at the time of ignition.
Sends a high-level signal that lasts for a relatively short time to the combustion state detection circuit 23. At the time of misfire, the comparator circuit 38 in the case of a normal misfire, and the comparator circuit 41 in the case of a misfire at breakdown, respectively. A high level signal that lasts for a long time is sent from the voltage change detection unit 22 to the combustion state detection circuit 23.

The combustion state detection circuit 23 detects the duration of the signal sent from the OR circuit 42 of the voltage change detection unit 22, and determines the ignition or misfire and the combustion state at the ignition based on the duration. To do. As described above, in the present invention, immediately after detecting the passage of the peak-shaped waveform including the peak value after the end of the spark discharge, the voltage is held, and it is compared with the peak value to break down the misfire. Therefore, misfire can be accurately detected. Further, in the present embodiment, in the case where the combustion state is detected based on the voltage between the electrodes due to the electrostatic capacity of the spark plug 3 after the spark discharge is completed, the voltage detected by the sensor 50 that detects the voltage between the electrodes Of these, the voltage for setting the reference voltage for detecting the combustion state is held (memory retention) immediately after the time when noise that may be included in the induction voltage of the ignition coil 1 may be included, so that accurate The combustion state can be detected.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an ignition device to which a misfire detection device of the present invention is applied.

FIG. 2 is a block diagram showing a configuration of a combustion state detection device having a misfire detection device of the present invention.

FIG. 3 is a time chart for explaining the operation of the combustion state detection device of the embodiment of the present invention.

[Explanation of symbols]

1 Ignition coil 3 Spark plug 10 Ignition device 20 Combustion state detection circuit (combustion state detection device for gasoline engine) 21 Peak value passage detection unit (peak value passage detection means) 22 Voltage change detection unit (voltage change detection means) 31 Peak hold circuit (peak value storage means) 35 Peak hold circuit (voltage value storage means) 38 Comparison circuit (first voltage comparison means) 41 Comparison circuit (second voltage comparison means)

Claims (1)

[Claims] 1. An ignition device in which a spark plug is connected to a secondary circuit of an ignition coil that generates a high voltage for spark discharge by intermittently supplying a primary current to an ignition device between discharge electrodes of the spark plug after completion of spark discharge in the spark plug. In the misfire detection device for a gasoline engine, which is provided with a voltage change detection means for detecting a voltage change of the gasoline engine, and which determines the ignition or the misfire of the gasoline engine based on the voltage change, the voltage change detection means is a secondary of the ignition coil. A peak value storage means for storing and holding a peak value of the voltage of the circuit, a peak value passage detecting means for detecting passage of the peak value, and a peak value passage detecting means for detecting passage of the peak value. Voltage value storage means for storing and holding voltage information between the discharge electrodes of the spark plug after the detected predetermined time, and the peak value and the voltage value storage stored and held in the peak value storage means First voltage comparison means for comparing the voltage value stored in the stage, a reference value for detecting the voltage change set based on the voltage value stored and held in the voltage value storage means, and thereafter And a second voltage comparison means for comparing the information on the voltage between the discharge electrodes with the second misfiring detection device for a gasoline engine.