JPH0719152A - Misfire detecting device for gasoline engine - Google Patents

Abstract

PURPOSE:To provide a misfire detecting device capable of detecting misfire with excellent sensitivity in an ignition device with negative voltage applied to the center electrode of a spark plug. CONSTITUTION:During a fixed period immediately after the generation of spark discharge voltage, sensor output is held by a sample holding circuit 25, and the half of it is made the reference auxiliary value. The peak voltage after the termination of spark discharge is held by a peak holding circuit 2, and the three quarters of it is made the first reference value. The reference auxiliary value is added to the first reference value to obtain the second reference value, and a comparing circuit 28 outputs a high level during the time of the sensor output being larger than the second reference value. A misfire judging part 29 judges misfire in the case of the continuous time of the high level being long and judges ignition in the case of being short. Since the reference auxiliary value determined by the specifications of an ignition system is added to the first reference value to obtain the second reference value, the difference of the continuous time of the high level between the ignition time and the misfire time can be made large so as to enable the positive detection of misfire.

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 a gasoline engine, which detects the presence or absence of a misfire in a 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 differs depending on ignition or misfire in the gasoline engine.
As a result, the attenuation characteristic of the voltage generated in the spark plug after the completion 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. Therefore, there is one that detects a change in the voltage of the spark plug after completion of the spark discharge and detects the presence or absence of a misfire based on the attenuation characteristic of the voltage. In the conventional misfire detection device based on the voltage decay characteristic of this spark plug, as a method of detecting the voltage decay characteristic, the insulation coating of each plug cord that connects the distributor and each spark plug is used as a dielectric, and each plug is The voltage between the electrodes of the spark plug is obtained as the voltage signal of the sensor by the electrostatic capacity between the conductor provided at the center of the cord and the peak voltage information of the sensor after the spark discharge is stored and retained. (Hold), and then the misfire detection is determined based on the time until the voltage drops to a reference value determined at a predetermined rate (for example, 1/3) based on the stored and held peak voltage. .

[0003]

However, in an igniter in which a negative voltage is applied to the center electrode of the spark plug, the number of ions generated between the electrodes of the spark plug during ignition is small.
Since the equivalent resistance value between the electrodes is high and the difference in the voltage decay time between normal ignition and misfire is small, the sensitivity of misfire detection becomes low. Therefore, in an ignition device that applies a negative voltage to the center electrode of the spark plug, it is difficult to significantly improve the misfire detection rate with a device that determines misfire based on the voltage attenuation characteristic.

According to the present invention, in a misfire detecting device for a gasoline engine, even in an igniter in which a negative voltage is applied to the center electrode of a spark plug, misfire can be surely detected correctly, and an improvement in the misfire detection rate can be achieved. An object of the present invention is to provide a misfire detection device for a gasoline engine that can be used.

[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 generates a high voltage for spark discharge by interrupting a primary current. In a misfire detection device for a gasoline engine, which is provided with a voltage detection means for detecting a voltage, and detects a misfire state of the gasoline engine based on the detected voltage, a peak voltage of the detected voltage after the spark discharge in the spark plug is stored and retained. And a first voltage value setting means for setting a first reference value smaller than the peak voltage based on the peak voltage stored in the peak voltage storage means.
Reference value setting means, spark discharge voltage storage means for storing and holding the spark discharge voltage detected by the voltage detection means in a predetermined period after the start of spark discharge in the spark plug, and the spark discharge voltage storage means. And an auxiliary value setting means for setting a reference auxiliary value smaller than the spark discharge voltage based on the spark discharge voltage, and a second reference value is set by adding the first reference value and the reference auxiliary value. Second reference value setting means, voltage comparison means for comparing the second reference value with the detected voltage, and misfire determination means for determining misfire detection of the gasoline engine based on the comparison result of the voltage comparison means. The technical means consisting of.

[0006]

In the present invention, when the spark discharge is started by the ignition device, the detected voltage of the voltage detecting means is stored in the spark discharge voltage storage means as the spark discharge voltage, and the reference auxiliary value smaller than the spark discharge voltage is set. To be done. Further, when the spark discharge ends, the peak voltage of the voltage detected by the voltage detection means is stored in the peak voltage storage means after the spark discharge ends, and the first reference value smaller than this peak voltage is set, and the first reference value is set.
The reference value and the reference auxiliary value are added to set the second reference value. Here, the voltage detected during spark discharge is
The secondary auxiliary circuit of the ignition device, the voltage generated by the voltage drop due to the spark discharge current in the spark discharge between the spark discharge electrodes of the spark plug determined by the specifications of the ignition system such as the spark plug, and the reference auxiliary value is based on this voltage. Since the second reference value is determined, the first reference value is increased by the reference auxiliary value obtained regardless of the variation in the sensitivity of the voltage detecting means.

Therefore, by appropriately determining the first reference value and the reference auxiliary value, when the detected voltage is compared with the second reference value, in the case of normal ignition, the detected voltage is smaller than the second reference value. It is possible to shorten the decay time until it becomes less, and in the case of misfire, the decay time until the detection voltage becomes smaller than the second reference value is less likely to become shorter than that at the time of ignition. It is possible to increase the difference in the decay time between the time of fire and the time of misfire. As a result, the determination can be easily performed based on the decay time.

[0008]

According to the present invention, the second reference value for detecting the decay time of the voltage detecting means is set to the first reference value set from the peak voltage after the spark discharge is completed, and the predetermined reference value after the spark discharge is started. Since the reference auxiliary value set by the spark discharge voltage of time is added, the first reference value is equal to the reference auxiliary value determined according to the ignition specification of each ignition device regardless of the sensitivity of the voltage detecting means. Can be raised. Therefore, the time it takes for the detected voltage to decay to the reference value during normal ignition can be shortened compared to the time for the detected voltage to decay to the reference value during misfire. And the decay time of the detection voltage at the time of misfire can be increased.

As a result, since the number of ions generated between the electrodes of the spark plug at the time of ignition is high, the equivalent resistance value between the electrodes is high, and the difference in the decay time of the detected voltage between normal ignition and misfire tends to be small. Even in the case of an ignition device that applies a negative voltage to the center electrode of, since it is possible to reliably detect the difference in the decay time of the detected voltage at the time of ignition and misfire, without being affected by the variation of the voltage detection means as a sensor, Misfire can be easily detected based on the decay time of the detection voltage.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on the embodiments shown in the drawings. FIG. 1 shows one embodiment of a misfire device for a gasoline engine according to the present invention, which includes an ignition device 10 and a misfire detection 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, 42 is a signal generator, V is an in-vehicle power supply, 43 is a diode for preventing backflow, and a high voltage from the secondary circuit of the ignition coil 1 is applied to each spark plug 3. It

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, and 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).

The misfire detection circuit 20, as shown in FIG.
A zero potential setting circuit 20a that sets the potential of the output of the sensor 50 to zero potential according to the signal of the signal generator 42.
And an inverting circuit 2 for inverting the polarity of the output voltage of the sensor 50.
0b, and includes a peak voltage detection unit 21, a spark discharge voltage detection unit 24, an addition circuit 27, a comparison circuit 28, and a misfire determination unit 29.

The peak voltage detection unit 21 sets the peak hold circuit 22 set to reset in accordance with the ignition timing signal from the signal generator 42 and the peak voltage value peak-held by the peak hold circuit 22 to 3/4 thereof. Voltage dividing circuit 23 for dividing the voltage to a first reference value
Consists of. The peak hold circuit 22 ends the reset operation 200 microseconds after the ignition timing signal, and holds the peak value thereafter with a time constant of 50 microseconds. The spark discharge voltage detection unit 24 is a sensor that is transmitted through the zero potential setting circuit 20a and the inverting circuit 20b for a certain period (for example, 200 microseconds) immediately after the spark discharge voltage is generated according to the ignition timing signal from the signal generator 42. A sample and hold circuit 25 that samples and holds the output of 50, and a voltage dividing circuit 26 that sets 1/2 of the average value of the voltage sampled and held by the sample and hold circuit 25 as a reference auxiliary value.
Consists of.

The addition circuit 27 includes a first reference value set by the voltage division of the voltage division circuit 23 and the signal generator 4
The voltage divider circuit 26 divides the spark discharge voltage at a predetermined time immediately after the generation of the spark discharge voltage determined according to the ignition timing signal of No. 2 above.
Then, the second reference value is obtained by adding the reference auxiliary value set to ½ thereof.

The comparison circuit 28 compares the output of the sensor 50 transmitted through the inverting circuit 20b and the like with a second reference value, and outputs a signal corresponding to the result of comparison between the output of the sensor 50 and the second reference value. When the output of the sensor 50 is higher than the second reference value, a high level signal is sent from the comparison circuit 28 while the output of the sensor 50 becomes lower than the second reference value.
A low level signal is sent. Therefore, when the engine normally ignites, the output of the sensor 50 decreases at a high speed after the spark discharge is completed. Therefore, the high-level duration of the output of the comparison circuit 28 becomes short.
Since the output speed of the sensor 50 decreases slowly, the comparison circuit 28
The high-level duration of the output of is longer.

The misfire determination unit 29 measures the duration of the high level signal of the comparison circuit 28 by a microcomputer, determines that the duration is longer than a predetermined time as misfire, and determines that the duration is shorter than the predetermined time as normal ignition. judge.

Next, the operation of the misfire 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. When the transistor 41 is turned on and off by the ignition timing signal of the signal generator 42, a pulse current flows in the primary circuit of the ignition coil 1. Due to this intermittent pulse current, a secondary voltage is generated in the secondary coil of the ignition coil 1, and the spark plug 3 starts spark discharge due to the high voltage generated at the end of the pulse current, and then inductive discharge. This spark discharge lasts for a period of time according to the rotational speed of the gasoline engine, 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.
Kilovolt, 5 to 8 kilovolts at high speed operation) is boosted to a maximum value and then stepped down. The secondary voltage after the completion of the spark discharge indicates the charge charged in the electrostatic capacitance (usually 10 to 20 pF) between the discharge electrodes of the spark plug 3, and the secondary voltage after the pointed waveform including the maximum value has passed. In the case of normal ignition, the voltage waveform decreases rapidly as indicated by the solid line A, and in the case of misfire, as indicated by the solid line a, decreases gradually compared to the case of ignition.

On the other hand, in the misfire detection circuit 20 which detects misfire based on the secondary voltage which changes as described above, according to the ignition timing signal from the signal generator 42,
The output voltage of the sensor 50 is set to the zero potential by the zero potential setting circuit 20a immediately before the generation of the spark discharge voltage, and then the output of the sensor 50 is sampled and held by the sample hold circuit 25 in a predetermined period immediately after the generation of the spark discharge voltage. As a result, the output voltage determined by the specifications of the ignition system is held in the sample hold circuit 25 regardless of the variation in the sensitivity of the sensor 50, and a half of the output voltage is set as the reference auxiliary value.

On the other hand, after the spark discharge is completed, the peak voltage of the output voltage of the sensor 50 is peak-held by the peak-hold circuit 21, and as shown by broken lines B and b, respectively, is 3/4 of the peak-held output voltage. The value is set as the first reference value by the voltage dividing circuit 23, and the above reference auxiliary values are added to obtain the second reference values shown by the alternate long and short dash line C and the alternate long and short dash line c, respectively.

Here, in the comparison circuit 28, the sensor 50
The second reference value with which the output voltage of is compared is a value obtained by adding the reference auxiliary value to the first reference value set based on the peak voltage after the spark discharge is completed, and the reference auxiliary value is the ignition value. The first reference value determined based on the peak voltage is determined according to the specifications of the system and is 1/2 of the spark discharge voltage that appears regardless of the variation of the sensor 50. It can be raised by a certain amount.

The output signal of the comparison circuit 28 becomes high level until the output voltage of the sensor 50 becomes smaller than the second reference value, and becomes low level when the output voltage of the sensor 50 becomes smaller than the second reference value. Become a signal. Therefore, when the engine is normally ignited, the output voltage of the sensor 50 after the spark discharge is quickly attenuated to the second reference value or less, regardless of whether the engine is operating at low speed or high speed. As described above, the high-level duration of the output signal of the comparison circuit 28 becomes short, and at the time of misfire, as shown by the solid line d,
Since it takes time for the output voltage of the sensor 50 to decay to the second reference value or less, the high-level duration becomes long. Therefore, even if the difference between the decay times of the detected voltages at the time of ignition and at the time of misfire becomes small because a negative voltage is applied to the center electrode of the spark plug 3, in the present embodiment, the broken line E, Since the difference between the decay time at ignition and the decay time at misfire can be made larger than the high-level duration when only the first reference values shown by the broken line e are used as the reference, the misfire determination can be made. The unit 29 can easily detect the misfire based on the duration time when the output signal of the comparison circuit 28 is at the high level. The misfire determination unit 29 measures the duration of time when the output signal of the comparison circuit 28 is at a high level,
When the duration is short, it is determined that the ignition is normal, and when the high level continues for a predetermined time or longer, it is determined as the engine misfire state.

As described above, in the present embodiment, in the case of detecting the misfire based on the voltage between the electrodes due to the electrostatic capacity of the spark plug 3 after the spark discharge, in order to detect the attenuation characteristic of the detection voltage of the sensor 50. To the first reference value set based on the peak voltage after the end of the spark discharge, and the reference auxiliary value set based on the voltage during the spark discharge determined by the specifications of the ignition system of the ignition device 10. Since the added second reference value is used, the difference between the decay time of the detected voltage at ignition and the decay time of the detected voltage at misfire can be increased. Therefore, regardless of the polarity of the spark plug 3, even if a negative voltage is applied to the center electrode of the spark plug 3, misfire can be reliably detected.

[Brief description of drawings]

FIG. 1 is a configuration 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 misfire detection device of the present invention.

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

[Explanation of symbols]

 1 Ignition coil 3 Spark plug 10 Ignition device 20 Misfire detection circuit (gasoline engine misfire detection device) 50 Sensor (voltage detection means) 21 Peak hold circuit (peak voltage storage means) 23 Voltage dividing circuit (first reference value setting means) ) 25 sample hold circuit (spark discharge voltage storage means) 26 voltage dividing circuit (auxiliary value setting means) 27 addition circuit (second reference value setting means) 28 comparison circuit (voltage comparison means) 29 misfire determination section (misfire determination means) )

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location F02P 15/00 302 Z G01M 15/00 Z 7324-2G

Claims (1)

[Claims] 1. An ignition device in which an ignition 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, and voltage detection means for detecting a voltage between discharge electrodes of the ignition plug. Provided is a misfire detection device for a gasoline engine, which detects a misfire state of a gasoline engine based on the detected voltage, wherein peak voltage storage means for storing and retaining a peak voltage of the detected voltage after completion of spark discharge in the spark plug, First reference value setting means for setting a first reference value smaller than the peak voltage based on the peak voltage stored in the peak voltage storage means; and the voltage for a predetermined period after the spark discharge is started in the spark plug. Spark discharge voltage storage means for storing and holding the spark discharge voltage detected by the detection means, and the spark stored in the spark discharge voltage storage means Auxiliary value setting means for setting a reference auxiliary value smaller than the spark discharge voltage based on an electric voltage, and a second reference value for adding the first reference value and the reference auxiliary value to set a second reference value. Gasoline comprising reference value setting means, voltage comparing means for comparing the second reference value with the detected voltage, and misfire determining means for determining misfire detection of a gasoline engine based on the comparison result of the voltage comparing means. Engine misfire detection device.