JPH06207575A - Combustion state detecting device for gasoline engine - Google Patents

Abstract

PURPOSE:To prevent the occurrence of the influence of noise and to detect the accurate combustion state of a gasoline engine, in detection of a voltage change between the electrodes of an ignition plug. CONSTITUTION:The passage of the maximum 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 maximum value passage detecting part 21 and after a lapse of a given time starting from the detection, reset of a peak hold circuit 35 is released. In noise of an ignition device, since the damping characteristics of the noise are decided according to the characteristics of an ignition coil, by properly setting a given time, the detected voltage of the sensor 50 is held right after damping of the noise. Since the reference voltage of a following voltage change is set based on the held voltage, an accurate voltage change is detectable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion state detecting device for a gasoline engine, which detects the combustion state of the gasoline engine based on a change in the voltage of the electric charge charged in the floating capacitance of the spark plug after the spark discharge is completed. Regarding

[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 generated in the spark plug after the spark discharge ends changes differently depending on the presence or absence of ignition or the combustion state. For this reason, there is a method in which a change in the voltage of the spark plug after the completion of the spark discharge is detected, and the combustion state is detected based on the attenuation characteristic of the voltage. In the conventional combustion state 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 the spark discharge is stored and held as a reference value (hold), The degree of subsequent voltage drop relative to this 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, as described above,
The spark plug peak voltage information after the spark discharge is
For those that hold memory, the ignition coil and ignition
Since the lug is connected, electrostatic in the ignition coil
The voltage induced by the ignition coil overlaps the regular voltage due to the capacity.
If the tatami mat becomes high, it will be ignited by the induced voltage.
Since peak noise appears in the coil voltage,
When the noise is stored in memory, the voltage of the ignition coil suddenly increases.
Erroneously detected as if the
To prevent backflow between the secondary coil of the il and the spark plug
If a diode of
If the effect limits the voltage drop, the
The voltage applied is too high to detect accurate attenuation characteristics.
There is a problem.

According to the present invention, in a combustion state detection device for a gasoline engine, the influence of noise of the ignition device is eliminated, and an accurate voltage change is detected, so that the voltage of the spark plug that varies depending on the combustion state of the gasoline engine is attenuated. The purpose is to accurately detect the characteristics.

[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 combustion state 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 combustion state of the gasoline engine is detected based on the voltage change. A maximum value passage detecting means for detecting passage of a maximum value of the voltage of the secondary circuit of the ignition coil, and the discharge of the ignition plug after a predetermined time after the passage of the maximum value is detected by the maximum value passage detecting means. Voltage value storage means for storing and holding voltage information between the electrodes, and detection of the voltage change set based on the voltage value stored and held in the voltage value storage means. And technical means, further comprising: a comparing means for comparing the voltage information between the reference value and then the discharge electrode.

[0006]

In the present invention, the voltage change detecting means for detecting the change in the voltage between the discharge electrodes of the spark plug determines whether or not the maximum value of the voltage of the secondary circuit of the ignition coil has passed after the completion of the spark discharge. Then, the voltage information between the discharge electrodes of the spark plug is stored and held after a predetermined time after the passage of the maximum value of the voltage is detected. Here, the voltage between the discharge electrodes after the spark discharge once rises and exhibits a maximum value, and then decreases, so the inter-electrode voltage is detected after a predetermined time after the passage of the maximum value is detected. The voltage information can be stored and held, and the combustion state can be detected based on the elapsed time until the voltage decreases to a reference value (for example, a predetermined ratio to this voltage information) set based on this voltage information. Further, even if the peak voltage noise due to the induced voltage from the ignition circuit is superimposed on the inter-electrode voltage, the peak shape of this noise generally appears uniquely due to the characteristics of the ignition coil of the ignition circuit. Immediately after passing the superimposed noise, by setting the above-mentioned predetermined time until the memory is stored after passing the maximum value, based on the characteristics of the ignition coil, etc.,
Correct voltage information between the electrodes can be stored and retained.

[0007]

According to the present invention, of the voltage information appearing between the discharge electrodes of the spark plug after the spark discharge is completed, the voltage information is promptly stored at a timing delayed by a time in which noise may be superimposed. Since the voltage information is held, the voltage information added with the noise component is not stored and held. In this case, since the passage of the maximum value of the voltage waveform is detected and the voltage information is stored and retained after a predetermined time, the voltage information suitable for setting the reference value for detecting the combustion state can be stored and retained. There is no delay, and it is possible to quickly store and hold the voltage information before a change in the voltage information according to the combustion state appears thereafter. Since the duration of noise is a minute time with respect to the change in the voltage between the electrodes, the above predetermined time is set so that the voltage information is stored and held immediately after the passage of time corresponding to the passage of the entire noise waveform. If so, the voltage information before being affected by the ion density of the gasoline engine can be correctly stored and held as the voltage information suitable as the reference value for detecting the combustion state. Therefore, the combustion state of the gasoline engine can be accurately detected.

[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 combustion state detecting device for a gasoline engine of the present invention, which comprises an ignition device 10, a combustion state detecting circuit 20 and a sensor 50. 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, 4 is a switching element.
2 is a signal generator, and V is an in-vehicle power supply.

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 maximum value passage detecting section 2 as shown in FIG.
1, a voltage change detection unit 22 and a combustion state detection unit 23. The maximum value passage detection unit 21 peak-holds the output of the sensor 50 at a timing determined according to the ignition timing signal, and detects when the output of the sensor 50 becomes smaller than the peak-held value by a predetermined value. The time when the maximum value of the output of the sensor 50 has passed is determined. In particular,
As shown in FIG. 2, a peak hold circuit 31, a reset circuit 32 that issues a reset signal in response to the ignition timing signal from the signal generator 42, and releases the reset of the peak hold circuit 31 after 50 μs (microseconds) has passed, The voltage dividing circuit 33 for dividing the voltage held in the peak hold circuit 31 after the reset of the reset circuit 32 is released (for example, 9/10), and the sensor 50.
Is compared with the output of the voltage dividing circuit 33, and when the output of the sensor 50 becomes smaller than the output of the voltage dividing circuit 33, the comparison circuit 34 for determining that the maximum value of the output of the sensor 50 has passed. Consists of.

The voltage change detector 22 sets a reference voltage (reference value) for the output of the sensor 50 after a predetermined time after the maximum value passage detector 21 detects that the maximum value of the output of the sensor 50 has passed. As the voltage information for this purpose, the peak hold is performed, and when the output of the sensor 50 decreases to a predetermined ratio with respect to the peak held voltage information, it is detected as the information of the attenuation speed of the output of the sensor 50. Specifically, as shown in FIG. 2, a peak hold circuit 35,
A reset signal for the peak hold circuit 35 is issued according to the ignition timing signal from the signal generator 42,
After that, in the above-described maximum value passage detection unit 21, the sensor 50
Circuit 3 that releases the reset of the peak hold circuit 35 when it is detected that the maximum value of the output of
6 and the voltage held in the peak hold circuit 35 after a predetermined time T0 after the reset circuit 36 is released from the reset voltage, the voltage is divided (for example, 2/3) and used as a reference voltage for detecting the combustion state. When the output of the sensor 50 becomes smaller than the output of the voltage dividing circuit 37 by comparing the output of the voltage dividing circuit 37 with the reference voltage which is the output of the voltage dividing circuit 37, the output of the sensor 50 becomes a predetermined value. And a comparison circuit 38 for discriminating when the decrease has occurred.

In the voltage change detection section 22, a predetermined time T0 after the passage of the maximum value 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 determines the time until the output of the sensor 50 decreases to a predetermined rate after it is detected that the maximum value has passed, that is, the duration of the signal appearing as the output of the comparison circuit 38. Detected by the microcomputer, according to the required time, ignition in each cylinder of the gasoline engine, discrimination of misfire, and detection of the combustion state at the time of ignition, the result, for example, air-fuel ratio control,
It is used in gasoline engine control such as fuel injection control.

Next, the operation of the combustion state detecting device of the present embodiment having the above construction will be explained together with the operation of the gasoline engine with reference to FIG. 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
In the secondary coil of No. 2, a secondary voltage is generated, and in the spark plug 3, spark discharge is started by the high voltage a generated at time t1 at the end of the pulse current, and then inductive discharge occurs,
This spark discharge lasts for a time T1 corresponding to the rotational speed of the gasoline engine, and ends at time t2 as the electric energy of the ignition coil 1 decreases.

After completion of the spark discharge, the secondary voltage starts to increase due to the electric energy remaining in the ignition coil 1, and a 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 maximum value b of kilovolts, 5 to 8 kilovolts in high-speed operation, and then stepped down. The secondary voltage after the completion of the spark discharge represents the electric charge charged in the electrostatic capacitance (usually 10 to 20 pF) between the discharge electrodes of the spark plug 3, and the maximum 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. For example, as shown by the broken line e, the value decreases later than the case of normal ignition indicated by the solid line c.

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 near the time t1, and the reset circuit 36 starts resetting the peak hold circuit 35 for 50 μs (microsecond). Second) and then the peak hold circuit 31
Cancel the reset of. As a result, the peak hold circuit 31 peak-holds the voltage of the maximum value b of the pointed waveform after the spark discharge ends, and when the detection voltage of the sensor 50 drops to the voltage of 9/10 of the maximum value b, the comparison circuit 34 A signal for canceling the reset of the peak hold circuit 35 is sent from the reset circuit 36 to the reset circuit 36.

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 changes according to the time constant of the peak hold operation. The detection voltage of the sensor 50 is held after a delay of a predetermined time T0 (for example, 10 microseconds). As a result, the peak hold circuit 35 sets the detected voltage of the sensor 50 immediately after the pointed waveform including the maximum value b after the spark discharge has passed, to the voltage information for setting the reference voltage for detecting the combustion state. Hold as.

The comparison circuit 38 determines whether or not the detection voltage of the sensor 50 becomes lower than the reference voltage (broken line f) divided by the voltage division circuit 37 according to the stored voltage information,
Only while the detection voltage of the sensor 50 is higher than the reference voltage, a signal indicating that (for example, a high level signal) is transmitted.
The combustion state detection circuit 23 detects the duration T2 of the signal sent from the comparison circuit 38 of the voltage change detection unit 22,
From the duration T2, the determination of ignition or misfire and the determination of the combustion state during ignition are performed. As described above, in this 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 combustion state is detected by the sensor 50 that detects the voltage between the electrodes. Of the voltages, the voltage for setting the reference voltage for detecting the combustion state is held (memorized) immediately after the time that may include noise due to the induced voltage of the ignition coil 1 passes, It is possible to accurately detect the combustion state.

[Brief description of drawings]

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

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

FIG. 3 is a time chart for explaining the operation of the combustion state detecting device 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 of gasoline engine) 21 Maximum value passage detection unit (maximum value passage detection means) 22 Voltage change detection unit (voltage change detection means) 35 Peak hold Circuit (voltage value storage / holding means) 38 Comparison circuit (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 combustion state detection device for a gasoline engine, which is provided with a voltage change detection means for detecting a voltage change, and detects the combustion state of the gasoline engine based on the voltage change, the voltage change detection means is a secondary circuit of the ignition coil. Maximum value passage detecting means for detecting the passage of the maximum value of the voltage, and voltage information between the discharge electrodes of the spark plug after a predetermined time after the passage of the maximum value is detected by the maximum value passage detecting means. Voltage value storage means, a reference value for detecting the voltage change set on the basis of the voltage value stored and held in the voltage value storage means, and a reference value after that. Combustion state detecting apparatus for a gasoline engine characterized by comprising a comparison means for comparing the voltage information between the discharge electrodes.