JPH06249121A - Combustion condition detecting device for gasoline engine - Google Patents

Abstract

PURPOSE:To enable adaption to a device to whose center electrode negative pressure is applied, while not limiting polarity of high voltage to an ignition plug of an ignition device. CONSTITUTION:A maximum value passage detector 21 detects the passage of the maximum value of a sensor 50 which senses voltage between both electrodes of an ignition plug, after spark discharge of the ignition plug. After a specified time, the voltage is memorized by a peak hold circuit 35. The voltage value smaller than the memorized voltage value and larger than its two thirds serves as a reference value, and thereby time is measured until the voltage between the electrodes gets smaller than the reference value. Initial change in relation to voltage attenuation is detected by the time to the time that the voltage is decreased to lower than the reference value which is set based on the voltage memorized the specified time after the passage of the maximum value. Even when negative voltage is applied to a center electrode, a combustion condition can be accurately detected.

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 end of the spark discharge depends on the ion density between the electrodes of the spark plug, and 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 detecting 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 memorized and held (hold), Is performed on the basis of the time until the voltage decreases to a reference value determined at a predetermined ratio (1/3) based on the stored and held voltage. Here, the peak voltage information needs to be stored and retained after the spark discharge is completed, but at the time when the spark discharge is completed, there is a delay corresponding to the rotation speed of the gasoline engine with respect to the ignition timing of the ignition device. With a peak hold circuit that operates by giving a delay time corresponding to the rotation speed from the ignition timing,
It stores and holds the peak voltage information.

[0003]

However, in the engine (engine) of the ignition device in which a negative voltage is applied to the center electrode of the spark plug, there are few ions generated between the electrodes of the spark plug when ignited. The equivalent resistance value between the electrodes of the spark plug becomes high, and when the conventional combustion state detection device that detects the decay time of the voltage is used as described above, the voltage of the voltage that seems to be determined by the ion density between the electrodes of the spark plug There is a problem that the decay time is difficult to appear properly depending on the combustion state depending on the engine, and the applicable engine is limited to the engine of the ignition device in which a positive voltage is applied to the center electrode of the spark plug.

According to the present invention, in a combustion state detecting device for a gasoline engine, the attenuation characteristic of the voltage of the spark plug which differs depending on the combustion state of the gasoline engine is accurately determined without limiting the polarity of the voltage applied to the spark plug. The purpose is to detect.

[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 a discharge electrode 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 two, and less than the storage voltage value stored and held in the voltage value storage means and greater than two-thirds of the storage voltage value. Reference value setting means for setting a voltage value as a reference value for detecting the voltage change, and comparison means for comparing the reference value with voltage information between the discharge electrodes thereafter, the maximum value passage detection means After the passage of the maximum value is detected by, the combustion state is detected based on the elapsed time until the voltage between the discharge electrodes of the spark plug becomes smaller than the reference value.

[0006]

In the gasoline engine, the voltage between the discharge electrodes after the spark discharge once rises to a maximum value and then drops. Particularly, in the ignition device in which a negative voltage is applied to the center electrode of the spark plug, the electrode temperature is lower than the temperature of the combustion gas and the density of ions and electrons is low even when the ignition is normally ignited. The equivalent resistance between the electrodes is high,
It was considered that the voltage change between the electrodes depending on the combustion state was unlikely to appear. However, the inventors of the present application have found that, as a result of the test and consideration, even in the ignition device in which a negative voltage is applied to the center electrode of the spark plug, the damping characteristic according to the combustion state is obtained at the initial stage of the voltage decay immediately after the end of the spark discharge. Was found to appear. This is because immediately after the spark discharge, there is a portion where the electrode temperature of the spark plug is locally high due to the spark discharge, which is considered to make it difficult for the density of ions and electrons in the vicinity thereof to become locally low. It is considered that this is because the electric charge charged between the electrodes is discharged. However, ions whose density is not low,
Since the electrons rapidly disappear as the electrode temperature drops, the time during which the combustion state can be detected is limited to a minute time immediately after the end of the spark discharge. In the present invention, the voltage change detection means for detecting the change in the voltage between the discharge electrodes of the spark plug, after the spark discharge, determines whether or not the maximum value of the voltage of the secondary circuit of the ignition coil has passed, 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 voltage value is detected. By setting a voltage value smaller than the stored and held voltage value and larger than two-thirds as a reference value, the voltage between the electrodes can be measured by measuring the elapsed time until the voltage between the electrodes decreases to the reference value. It is possible to detect the initial voltage attenuation characteristic when the voltage begins to attenuate. Further, even if the peak voltage noise due to the induced voltage from the ignition circuit is superposed 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. By properly setting the above-mentioned predetermined time until the memory is held after passing the maximum value based on the characteristics of the ignition coil or the like, it is possible to store and hold the correct voltage information between the electrodes immediately after passing the superimposed noise. it can.

[0007]

According to the present invention, the passage of the maximum value of the voltage waveform among the voltage information appearing between the discharge electrodes of the spark plug after the completion of the spark discharge is detected, and the voltage information is stored and retained after a predetermined time. 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 for setting the reference value for detecting the combustion state. The initial change in the voltage decay can be detected. Further, based on this storage voltage, a voltage value smaller than the storage voltage and larger than two-thirds of the storage voltage is set as a reference value, so that an initial change in voltage attenuation can be detected. Therefore, even in a gasoline engine using an ignition device in which a negative voltage is applied to the center electrode of the spark plug, the attenuation characteristic of the voltage according to the combustion state can be reliably detected, and the applicable gasoline engine is limited. Therefore, it is possible to detect the presence or absence of misfire and the combustion state of various engines. 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. By so doing, the voltage information is promptly stored and held at the time when it is delayed by the time when the noise may be superimposed, so that the voltage information to which the noise component is added is not stored and held. In this case, there is no delay in the memory retention of the voltage information suitable for setting the reference value for detecting the combustion state, and the subsequent memory information is promptly stored and retained before the change of the voltage information according to the combustion state appears. be able to.

[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.
Reference numeral 2 is a signal generator, V is a vehicle-mounted power source, and a high negative voltage is applied to each spark plug 3 from the secondary circuit of the ignition coil 1.

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 includes a maximum value passage detecting section 21, a voltage change detecting section 22, and
The combustion state detecting unit 23 is provided, and an inversion circuit 50a that inverts the polarity of the output of the sensor 50 is provided between the combustion state detection circuit 20 and the combustion state detection circuit 20. The maximum value passage detection unit 21 peak-holds the output of the sensor 50 transmitted via the inversion circuit 50a at a timing determined according to the ignition timing signal, and compares the output of the sensor 50 with the peak-held value. When the maximum value of the output of the sensor 50 has passed, the time when the maximum value of the output of the sensor 50 has passed is determined. Specifically, as shown in FIG. 2, a reset signal is issued according to the ignition timing signal from the peak hold circuit 31 and the signal generator 42, and the
A reset circuit 32 that releases the reset of the peak hold circuit 31 after s (microseconds) has elapsed, and a reset circuit 3
2 after the reset is released, the voltage held by the peak hold circuit 31 is divided (for example, 9/10) by the voltage dividing circuit 33, and the sensor 50 transmitted through the inverting circuit 50a.
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 detection unit 22 outputs the output of the sensor 50 transmitted through the inverting circuit 50a after a predetermined time after the maximum value passage detection unit 21 detects that the maximum value of the output of the sensor 50 has passed. Peak hold is performed as the voltage information for setting the reference voltage (reference value), and the sensor 5
When the output of 0 is reduced 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. Specifically, as shown in FIG. 2, the peak hold circuit 35 and a reset signal for the peak hold circuit 35 are issued in response to the ignition timing signal from the signal generator 42, and then the sensor 50 in the maximum value passage detection unit 21 is operated. A reset circuit 36 for canceling the reset of the peak hold circuit 35 when it is detected that the maximum value of the output of
The voltage held in the peak hold circuit 35 after a predetermined time T0 after the reset of 6 is released is divided (for example, 2/3 to 4/5) to be 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 circuit 37 and the output of the sensor 50 with the reference voltage which is the output of the voltage dividing circuit 37, the output of the sensor 50 becomes a predetermined value. It is composed of a comparison circuit 38 for discriminating when it has decreased.

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
The secondary voltage is generated in the secondary coil of the spark plug 3, and the spark plug 3 starts the spark discharge due to the high voltage generated at the end of the pulse current, and then the inductive discharge occurs. It lasts for a period of time depending on the rotation speed,
It ends with the reduction of the electrical energy of the ignition coil 1.

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 a of kilovolts, 5 to 8 kilovolts in high-speed operation, and then stepped down. The secondary voltage after 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 has the maximum value a.
The secondary voltage waveform after the passage of the pointed waveform including is rapidly decreased as shown by the solid line b in the case of normal ignition, and is shown in the case of ignition as shown by the solid line c 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 d, the value decreases later than in the case of normal ignition indicated by the solid line b.

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, the reset circuit 36 starts resetting the peak hold circuit 35, and 50 μs (microsecond) after that, the peak is reached. The reset of the hold circuit 31 is released. As a result, the peak hold circuit 31 peak-holds the voltage of the maximum value a 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 a, 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 a 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 e) 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 T1 of the signal sent from the comparison circuit 38 of the voltage change detection unit 22,
From the duration T1, determination of ignition or misfire and determination of 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. Even in the case where the ignition device 10 in which a negative voltage is applied to the center electrode of the ignition plug 3 is used to detect the change (attenuation state) of only the initial voltage change of the voltage decay of the voltage, the ignition is performed. The combustion state can be detected from the voltage change between the electrodes of the plug 3. In addition, since the voltage for setting the reference voltage for detecting the combustion state is held (memory retention) immediately after the time when noise due to the induced voltage of the ignition coil 1 may be included passes, accurate The combustion state can be detected. Therefore, the gasoline engine that can detect the combustion state is not limited,
It can be applied to various institutions.

[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) 37 Voltage dividing circuit (reference value setting 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 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. And a voltage value storage means, and a voltage value smaller than the storage voltage value stored and held in the voltage value storage means and larger than two-thirds of the storage voltage value. Reference value setting means as a reference value for detecting, and a comparison means for comparing the reference value and the voltage information between the discharge electrodes after that, the maximum value passage detection means to pass the maximum value. A combustion state detection device for a gasoline engine, which detects a combustion state based on an elapsed time until the voltage between the discharge electrodes of the spark plug becomes smaller than the reference value after the detection.