JPH07119605A - Misfire detecting device for gasoline engine - Google Patents

Abstract

PURPOSE:To surely detect a misfire even when an instantaneous breakdown is generated at the time of the misfire. CONSTITUTION:Between completion of ignition spark discharge and next ignition spark discharge, a voltage charged to a floating capacity between electrodes G of an ignition plug P is detected, and when the voltage between the electrodes G is higher than a specified value, a misfire is detected. The electric charge between the electrodes G discharges a large quantity at the time of ignition, while a little quantity at the time of misfire. Since the electric charge, discharged when a voltage to be charged between electrodes G of the ignition plug P after the completion of ignition spark discharge is instantaneously broken down, is limited to a charge CA in the vicinity of the electrodes G, an electric charge CB affected by a self-inductance L is not discharged and remains. Consequently, after the completion of ignition spark discharge, the electric charge CB in accordance with ignition or misfire is detected as a voltage between the electrodes G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a misfire in a gasoline engine based on the voltage of the electric charge charged in the floating capacitance between the discharge electrodes of the spark plug after the spark discharge has ended. Regarding a detection device.

[0002]

2. Description of the Related Art As a misfire detection device for a gasoline engine,
After the spark discharge, the voltage due to the residual energy of the secondary circuit of the ignition coil is charged to the floating capacitance between the discharge electrodes of the spark plug, and the charging voltage at this time is ignited or ignited by the ion density between the electrodes of the spark plug. Utilizing the fact that it changes depending on the misfire, the change in the charging voltage after the end of spark discharge,
For example, there is one that detects a misfire based on the damping characteristic.

In such a conventional device, the insulating coating of each plug cord connecting the distributor to each spark plug is used as a dielectric, and the static insulation between the conductor provided at the center conductor of each plug cord is established. The voltage between the electrodes of the spark plug is obtained as a voltage signal by the capacitance, and a voltage divider is configured with a capacitor connected in series, and the voltage division signal is detected as a sensor signal. It decays in a short time, and it takes longer for a misfire than for an ignition. Therefore, after the spark discharge ends, the sensor signal is peak-held, the reference value is determined based on that value, the sensor signal is compared with this reference value, and the time when the sensor signal exceeds the reference value is short. Is determined as ignition,
If the sensor signal exceeds the reference value for a long time, it is determined as misfire.

[0004]

However, when an instantaneous breakdown occurs at the time of misfire, the inter-electrode voltage after the spark discharge is drastically reduced, so that the above-mentioned sensor signal is below the reference value. The time over is shortened. As a result, the conventional misfire detection device has a problem in that if an instantaneous breakdown occurs during misfire, it cannot be distinguished from that during ignition, and misfire cannot be discriminated by the attenuation characteristics of the sensor signal.

It is an object of the present invention to provide a misfire detecting device for a gasoline engine which can surely discriminate misfire even when an instantaneous breakdown occurs at the time of misfire.

[0006]

According to a first aspect of the present invention, an ignition plug is connected to a secondary circuit of an ignition coil that generates a high voltage for spark discharge by intermittently flowing a primary current, and the ignition coil and the ignition plug are connected to each other. An ignition device provided with a backflow prevention means between the two is provided with voltage detection means for detecting a voltage between the discharge electrodes of the spark plug, and a misfire state of a gasoline engine for detecting a misfire state of the gasoline engine based on the detected voltage. In the detection device, the voltage between the discharge electrodes charged to the stray capacitance of the spark plug is extracted between the end of the spark discharge for ignition and the next spark discharge for ignition, and the extracted voltage between the discharge electrodes is It is a technical means to provide a misfire determination means for determining a misfire when it is higher than a predetermined value.

According to a second aspect of the present invention, in the first aspect of the present invention, the misfire determination means applies a high voltage to the spark plug between the end of the spark discharge for ignition and the next spark discharge for non-ignition. And a voltage difference for detecting the difference between the detection voltage of the voltage detection means immediately before the voltage application by the discharge voltage application means and the detection voltage of the voltage detection means immediately after the start of the spark discharge by the voltage application. The technical means is to provide a detection means and detect misfire based on the voltage difference detected by the voltage difference detection means.

According to a third aspect of the present invention, in the first aspect, the voltage detecting means includes a high voltage side capacitor having a dielectric as an insulating coating of a high voltage cable for transmitting the high voltage of the ignition coil to the spark plug, and the high voltage. A voltage divider consisting of a low-voltage side capacitor connected in series with a side-side capacitor, and a resistor for discharging the low-voltage side capacitor with a predetermined time constant. Discharge voltage applying means for generating a non-ignition spark discharge by applying a high voltage to the spark plug before the spark discharge for ignition, and the charge of the low-voltage side capacitor immediately before the voltage is applied by the discharge voltage applying means. It comprises zero potential setting means for discharging and comparing means for comparing whether or not the output voltage of the voltage divider after the spark discharge by the discharge voltage applying means is higher than a fixed value, Misfire determination means, the technical means that the above fixed value of the duration of the voltage divider output voltage after the start spark discharge by the discharge voltage applying means is determined that a misfire is shorter than the predetermined time.

According to a fourth aspect, in the third aspect, the comparing means compares whether or not the detection voltage of the voltage detecting means immediately after the spark discharge for ignition is higher than a predetermined value, and the misfire determining means. The technical means comprises a second misfire determination means for determining a misfire when the detected voltage of the voltage detection means immediately after the ignition spark discharge is higher than the predetermined value for a predetermined time or more. To do.

[0010]

[Action]

<Operation of Claim 1> In a gasoline engine, when a misfire occurs, electric charge is charged between the electrodes of the spark plug after the spark discharge for ignition is completed, and the potential thereof becomes high. The charge between the electrodes is discharged and the potential drops. The inventor of the present application has found that the discharge time of this instantaneous breakdown is very short and is in the nanosecond order.

As a result, for example, in FIG. 1, the electric charge discharged in the instantaneous breakdown at the time of misfire is limited to the electric charge charged in the electrostatic capacitance C _A of the portion of the ignition plug P which is close to the discharge electrode G, The electric charge of the electrostatic capacitance C _B at a portion apart from the discharge electrode G, which is affected by the self-inductance L of the high-voltage cable with respect to the discharge time of the very short instantaneous breakdown, for example, the electric charge of the high-voltage cable, is instantaneous. It does not discharge during breakdown and remains on the cable etc. Therefore, the voltage between the electrodes of the spark plug G is temporarily reduced by the instantaneous breakdown, and the voltage at the point A in FIG. 1 is, as shown in FIG. Since the electric charge of the electrostatic capacitance C _B is charged again between the electrodes of the spark plug P, the potential between the electrodes rises, and the voltage becomes higher than that at the time of ignition. Therefore, when the voltage between the electrodes G of the spark plug P is detected by the voltage detector after a predetermined time has elapsed after the spark discharge for ignition is completed, if the voltage is high, whether or not there is an instantaneous breakdown. Regardless of the above, it can be determined that a misfire has occurred, and if the voltage is low, it can be determined that an ignition has occurred. The voltage at point B is also shown in FIG.

<About the operation of claim 2> In claim 2, between the end of the spark discharge and the next spark discharge for ignition,
A high voltage is applied to the spark plug by the discharge voltage applying means. When non-ignition spark discharge is generated by the application of this high voltage, the inter-electrode voltage immediately after the start of the spark discharge is substantially constant regardless of the inter-electrode voltage immediately before the voltage application of the discharge voltage applying means. According to the present invention, the difference between the voltage detected by the voltage detection means immediately before the voltage application by the discharge voltage application means and the voltage detected by the voltage detection means immediately after the start of the discharge by the voltage application is detected, so that the inter-electrode voltage is detected. As the sensor, for example, one that detects the capacitance between the secondary circuit of the ignition coil and the high voltage cable is used, and even if the zero potential is likely to become unstable, the absolute value of the potential of the sensor is used. Since the misfire can be detected from the voltage difference before and after the non-ignition spark discharge that appears regardless of the above, the misfire can be reliably detected.

<Regarding the operation of claim 3> In claim 3, between the end of the spark discharge and the next spark discharge for ignition,
When a high voltage is applied to the spark plug by the discharge voltage applying means to generate non-ignition spark discharge, the inter-electrode voltage after the spark discharge is started by the discharge voltage applying means is 1 kV regardless of the voltage immediately before the spark discharge is started. It becomes almost constant value less than. Further, the electric charge of the low-voltage side capacitor of the voltage divider by the capacitor for detecting the inter-electrode voltage is discharged by the zero potential setting means immediately before the voltage application by the discharge voltage applying means.

The voltage between the electrodes of the spark plug is
Regardless of the presence of the instantaneous breakdown, a high voltage of several kV is reached immediately before the voltage is applied by the discharge voltage applying means, but the output of the voltage divider for this high voltage is set by the zero potential setting means immediately before the voltage is applied. Since the potential is set to zero potential, the output voltage of the voltage divider after the end of the discharge due to the voltage application of the discharge voltage applying means decreases to around zero volt. For this reason,
At the time of misfire, the output voltage of the voltage divider does not greatly exceed the fixed value of the misfire determination means regardless of the presence of the instantaneous breakdown. On the other hand, at the time of ignition, the voltage between electrodes of the spark plug after the end of the spark discharge for ignition is lower than that at the time of misfire,
Since the output of the voltage divider showing the low voltage is only set to zero potential, the output voltage of the voltage divider after the spark discharge by the voltage application of the discharge voltage applying means becomes a higher voltage than that at the time of misfire, and the misfire judgment is made. It is higher than the fixed value of the means.
Therefore, the misfire determination means compares the output voltage of the voltage divider detected after the start of non-ignition spark discharge with a fixed value, and ignites when the output voltage is higher than the fixed value for a long time, and instantaneously when the output voltage is shorter than the fixed value. It can be identified as a misfire including breakdown.

<Regarding the operation of claim 4> In claim 4, as in the conventional case, the inter-electrode voltage of the spark plug after the completion of the spark discharge for ignition is detected, and whether the voltage becomes lower than a predetermined value or not. Is compared by the comparison means. The decay time of the output of the voltage divider after the spark discharge for ignition is short when ignited, long when the misfire does not cause instantaneous breakdown, and short when the misfire involves instantaneous breakdown. Become. Therefore, the second misfire determination means can detect the misfire as before when the misfire is not accompanied by the instantaneous breakdown.
Then, the comparing means determines whether or not the inter-electrode voltage after starting the non-ignition spark discharge is higher than the fixed value in the misfire determining means.

As described in the action of claim 3, the output voltage of the voltage divider showing the inter-electrode voltage is not ignited when it is set to the zero potential by the zero potential setting means immediately before the voltage is applied by the discharge voltage applying means. The voltage after the start of the spark discharge becomes very low in the case of misfire and becomes high in the case of ignition. Therefore, the fixed value for comparing the inter-electrode voltage after starting the non-ignition spark discharge becomes a low value, and the predetermined value of the comparison means for examining the attenuation of the output of the voltage divider after the end of the spark discharge for ignition (for example, , A predetermined ratio with respect to the peak voltage). As a result, the two comparison results obtained by the comparison means are time-divided between the end of the spark discharge for ignition and the detection time after the start of the non-ignition spark discharge, so that the comparison means can be used for the two types of discrimination. You can

[0017]

【The invention's effect】

<Claim 1> According to claim 1 of the present invention, the electric charge discharged in the instantaneous breakdown at the time of misfire is limited to the electric charge charged in the portion in the vicinity of the discharge electrodes of the spark plug. The electric charge of the part apart from the discharge electrode that is affected by the self-inductance for a short discharge time (nanosecond order), for example, the electric charge of a high-voltage cable or the like, does not discharge in the instantaneous breakdown and remains in the cable or the like. Therefore, after the spark discharge for ignition is completed, after a certain time from the time when the discharge of the instantaneous breakdown is completed until the electric charge of the cable is charged again between the electrodes of the spark plug, When the voltage between the electrodes is detected, if the voltage is high, it is possible to determine that a misfire has occurred regardless of the presence or absence of an instantaneous breakdown, If pressure is low, it can be determined that the ignition.

<Regarding Claim 2> In Claim 2, a high voltage is applied to the spark plug to generate non-ignition spark discharge, so that the inter-electrode voltage immediately after the start of the spark discharge by the discharge voltage applying means, It can be made almost constant regardless of the inter-electrode voltage immediately before the voltage is applied, and can be detected as a voltage difference immediately before the voltage is applied by the discharge voltage applying means and immediately after the non-ignition spark discharge is started. Therefore, when the voltage by the discharge voltage applying means is not applied, it is easy to detect the inter-electrode voltage after the end of the spark discharge for ignition, which is difficult to detect because it appears to be small, by comparing it with that immediately after the start of the spark discharge for non-ignition. can do. Therefore, in a sensor or other configuration for detecting the inter-electrode voltage, high accuracy regarding the absolute value is not required, and for example, a sensor for detecting the capacitance between the ignition coil and the high-voltage cable of the secondary circuit of the ignition coil. Even if a sensor whose zero potential is apt to become unstable can be detected as the voltage difference before and after discharge regardless of the absolute value of the potential, the voltage detection circuit etc. Can be configured.

<Regarding Claim 3> In Claim 3, the electric charge of the low-voltage side capacitor of the voltage divider by the capacitor for detecting the inter-electrode voltage is discharged by the zero potential setting means immediately before the voltage is applied by the discharge voltage applying means. Thus, at the time of misfire, the output of the voltage divider corresponding to the inter-electrode voltage of the spark plug, which has reached several kV immediately before the voltage is applied by the discharge voltage applying means, can be set to zero potential. As a result,
The output voltage of the voltage divider after the end of non-ignition spark discharge is always very low at the time of misfire regardless of the presence of the instantaneous breakdown, so it is possible to reliably detect the misfire even in the case of the instantaneous breakdown. .

<Regarding Claim 4> In Claim 4, in addition to conventional misfire detection, misfire can be reliably detected even during misfire accompanied by an instantaneous breakdown. Further, in the conventional misfire detection device, a comparison means for determining the attenuation of the inter-electrode voltage of the spark plug after completion of the spark discharge is used to determine whether the inter-electrode voltage after completion of the spark discharge is higher than a predetermined value for examining the attenuation. Since it can also be used to determine whether or not the misfire is detected, the accuracy of misfire detection can be improved without complicating the circuit configuration of the stage subsequent to the voltage divider. Therefore, it is possible to provide a misfire detection device that is inexpensive and has excellent detection accuracy.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on the embodiments shown in the drawings. FIG. 3 shows an embodiment of a misfire detection device for a gasoline engine of the present invention, which comprises a bipolar DLI type ignition device 10 mounted on a two-cylinder engine, a misfire detection circuit 20, and sensors 50, 50a. In the ignition device 10, 1
Is an ignition coil, 2 and 3 are ignition plugs of the number of cylinders, 41 is a transistor of a switching element for connecting and disconnecting the primary current of the ignition coil 1, 42 is a signal generator, and an engine control unit (EC) for controlling the two-cylinder engine E
U) It is provided in 100. The spark plug 2,
3 is connected to the positive and negative secondary voltage terminals of the secondary coil 11 of the ignition coil 1, V is an in-vehicle power supply, and 43 and 44 are backflow prevention diodes.

The sensors 50 and 50a for detecting the voltage between the electrodes of the spark plugs 2 and 3 are insulation coatings of plug cords that connect the secondary coil 11 of the ignition coil 1 and the spark plugs 2 and 3, respectively. As a dielectric, the high-voltage side capacitors 51, 51a formed by the capacitance between the conductor and the conductor provided at the center of the plug cord.
And low-voltage side capacitors 52, 52a connected in series with the high-voltage side capacitors 51, 51a to form a voltage divider for dividing the voltage between the electrodes of the ignition plugs 2, 3. A resistor 53 in parallel with the low-voltage side capacitors 52, 52a for discharging the capacitors 52, 52a,
53a is connected.

Here, the high voltage side capacitors 51, 51a
Has a capacitance of, for example, 1 pF, and the low-voltage side capacitors 52 and 52a have a capacitance of 3000.
pF, these high voltage side capacitors 51,
The voltage divider composed of 51a and the low-voltage side capacitors 52 and 52a reduces the inter-electrode voltage of the spark plugs 2 and 3 to 1/300.
Divided to zero, high voltages up to 30,000 volts are converted to the 10 volt order. The resistors 53 and 53a are
Before the start of the next spark discharge, the low-voltage side capacitors 52, 52
It is provided to discharge a, and is set to a resistance value of 2 M ohms, for example, to set the discharge time constant to 6 mS (millisecond).

Next, a first embodiment of the misfire detection circuit 20 is shown in FIG.
It will be described based on. The misfire detection circuit 20 detects the voltage between the electrodes of each of the spark plugs 2 and 3 after the spark discharge for ignition is detected, and detects the decay time thereof, thereby detecting a case where the decay time is long as a misfire. Ignition is determined when the ignition is short, and sparks for ignition are added so that the misfire can be detected even when a momentary breakdown occurs when the misfire shortens the decay time even when the misfire occurs. Each spark plug 2 at a predetermined timing after the end of discharge,
The inter-electrode voltage of 3 is detected, and when the voltage value is equal to or higher than a predetermined value, it is detected as misfire.

In particular, here, in order to facilitate discrimination of misfire based on the voltage value between the electrodes after completion of ignition spark discharge, ignition of the ignition plug 2 performed in response to an ignition timing signal of the signal generator 41. By using the non-ignition spark discharge for the spark plug 2 that occurs at the same time when the spark discharge for the ignition plug 3 is generated in the ignition coil 1 between the spark discharge and the spark discharge for the next ignition, this non-ignition spark discharge is used. The voltage between the electrodes of the spark plug 2 is detected after the end of the spark discharge for ignition. Similarly, for the spark plug 3, for non-ignition of the spark plug 3 that occurs at the same time when spark spark discharge for the spark plug 2 occurs between the spark spark discharge for ignition and the spark discharge for the next ignition. The spark discharge is used to detect the inter-electrode voltage of the spark plug 3 after the end of the non-ignition spark discharge.

Therefore, the misfire detection circuit 20 includes zero reset circuits 21 and 21a corresponding to the output signals of the sensors 50 and 50a, and voltage detection circuits 22 and 22a.
And peak hold circuits 23 and 23a, reference voltage circuits 24 and 24a, and comparison circuits 25 and 25a.

The zero reset circuits 21 and 21a respond to the timing signal of the engine control unit (ECU) 100, immediately before the voltage application for non-ignition spark discharge to the respective spark plugs 2 and 3, and to the respective sensors 50, The low voltage side capacitors 52, 52a of 50a are discharged, and the sensor 5
The output voltages of 0 and 50a are set to zero potential.

The voltage detection circuits 22 and 22a are connected to the respective sensors 50 which are transmitted through the zero reset circuits 21 and 21a.
It is composed of an amplifier circuit such as an operational amplifier for amplifying the output voltage of 50a to a processable voltage value, and detects the output voltage value of each sensor 50, 50a. However, in the sensor 50a for detecting the inter-electrode voltage of the spark plug 3 connected to the negative polarity side of the secondary coil 11 of the ignition coil 1, since the detected voltage has a negative polarity, the voltage on the sensor 50a side is reduced. Detection circuit 22
An inverting circuit (not shown) for inverting the polarity of the signal is provided on the input side of a.

The peak hold circuits 23 and 23a are configured to output the peak voltage of the output voltage value of the voltage detection circuits 22 and 22a in accordance with the timing signal of the signal generator 41 after the spark discharge for ignition of each of the spark plugs 2 and 3 is completed. Hold.

The reference voltage circuits 24 and 24a are provided with a peak hold circuit 2 for detecting a misfire which has been conventionally performed.
Based on the peak voltage value held at 3, 23a,
A variable reference voltage for detecting the decay time of the inter-electrode voltage after the end of the spark discharge for ignition is set, and the spark spark discharge for one ignition and the spark discharge for the next ignition are set for each spark plug 2, 3. Has a fixed reference value that serves as a reference for comparing the inter-electrode voltage value after completion of the non-ignition spark discharge generated by applying the voltage for non-ignition spark discharge, and this fixed reference value is variable. It is also used as the lowest limit value of the reference voltage. Therefore, the higher value of the variable reference voltage and the fixed reference value becomes the reference voltage in the reference voltage circuits 24 and 24a.

The comparison circuits 25 and 25a output the output voltages of the voltage detection circuits 22 and 22a as the outputs of the sensors 50 and 50a after the ignition spark discharge and the non-ignition spark discharge in the respective spark plugs 2 and 3 are completed. Reference voltage circuit 24, 2
4a, the voltage detection circuit 22,
When the output voltage of 22a is higher than the reference voltage, a high level signal is sent out, and when it is low, a low level signal is sent out. As a result, after the spark discharge for ignition, in the case of ignition, the output voltage of the voltage detection circuits 22 and 22a decays rapidly, so that the high-level duration becomes short, and in the case of misfire other than instantaneous breakdown, Is the voltage detection circuit 22, 2
Since the decay of the output voltage of 2a is slow, the high-level duration becomes long.

After the non-ignition spark discharge is completed, in the case of ignition, the voltage between the electrodes when the zero potential is set is low, so that the voltage detection circuit 22 according to the output voltage of the sensors 50 and 50a thereafter. , 22a becomes high, and as a result, in the comparison circuits 25, 25a, the voltage detection circuits 22, 2,
It takes longer for the output voltage of 2a to be higher than the fixed reference value.
On the other hand, in the case of misfire, the inter-electrode voltage when the zero potential is set is high, so that the subsequent sensors 50, 50a
Output voltage of the voltage detection circuits 22 and 22a becomes lower than the output voltage of the voltage detection circuit, and as a result, in the comparison circuits 25 and 25a, the time when the output voltage of the voltage detection circuits 22 and 22a is higher than the fixed reference value is short, or The output voltage of the circuits 22 and 22a becomes lower than the fixed reference value.

In the engine control unit (ECU) 100, it is judged whether or not there is a misfire in each cylinder from the timing of the high level signals of the output signals from the respective comparison circuits 25 and 25a of the misfire detection circuit 20, and, for example, The driver is informed of this by storing it in the engine computer or by lighting a lamp or the like.

Next, the operation of the misfire detection device of the present embodiment having the above construction will be described together with the operation of the two-cylinder 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 circuit 11 of the ignition coil 1, and the spark plug 2 starts spark discharge for ignition due to the high voltage generated at the end of the pulse current of the primary circuit. Then, inductive discharge occurs and ends with the reduction of the electric energy of the ignition coil 1. When the ignition spark discharge of the ignition plug 2 occurs, the non-ignition spark discharge occurs in the ignition plug 3. Similarly, when spark discharge for ignition is generated in the spark plug 3, spark discharge for non-ignition is generated in the spark plug 2.

In the misfire detection circuit 20, each spark plug 2,
Sensors 50, 5 in response to the ignition timing signal to
After the detection voltage of 0a is peak-held after the spark discharge is completed, the variable reference voltage is determined based on it, and the output voltage of the sensor 50, 50a is compared with the variable reference voltage to change the output voltage of the sensor 50, 50a. While the voltage is higher than the reference voltage, a high level output signal is sent. Therefore, the decay time can be detected by measuring the high level output signal in the engine control unit (ECU) 100, and the misfire can be detected by the decay time.

On the other hand, after the spark discharge for ignition of the spark plug 2 is completed and before the next spark discharge for ignition is performed,
A voltage for non-ignition spark discharge is applied to the spark plug 2 at the timing of applying a voltage for spark spark discharge to the spark plug 3, and immediately before the voltage application, the zero reset circuit 21 in the misfire detection circuit 20. Thus, the output of the sensor 50 is set to zero potential. At this time, the voltage between the electrodes of the ignition plug 2 is high in the case of misfire and low in the case of ignition, and after the end of non-ignition spark discharge, the voltage detection circuit 22
The output of the sensor 50 detected at the time of ignition becomes high at the time of ignition, and after the end of the spark discharge for non-ignition, there are almost no ions between the electrodes, so the decay time becomes longer, but in the case of misfire, an instantaneous breakdown occurs. It will be low, including when it occurs, which will reduce the decay time. Similar results are obtained with the spark plug 3.

Therefore, the output signals of the comparison circuits 25 and 25a have a high-level time in the case of ignition and a high-level time in the case of misfire, including the case of instantaneous breakdown. It gets shorter.

In the engine control unit (ECU) 100, the determination is reversed based on the output signals of the comparison circuits 25 and 25a depending on the timing of the end of the spark discharge for ignition or the end of the spark discharge for non-ignition. Two types of misfire detection can be performed.

Next, the misfire detection circuit 20A of the second embodiment of the misfire detection device for a gasoline engine according to the present invention will be described with reference to FIG. In this embodiment, a high voltage having the same polarity as the high voltage for ignition is applied to the spark plugs 2 and 3 by the ignition coil 1 between the end of the spark discharge and the next spark discharge for ignition. The non-ignition spark discharge is generated by the application of this high voltage, and the voltage between the electrodes of the spark plugs 2, 3 immediately after the start of the spark discharge is substantially constant regardless of the voltage between the electrodes immediately before the voltage application. As a result, the misfire detection circuit 20A is provided with only the voltage detection circuits 22 and 22a that detect the output voltages of the sensors 50 and 50a, and the engine control unit (EC
U) At 100, process the output signal as follows.

That is, the engine control unit (EC
U) 100, the output voltage of each sensor 50, 50a detected immediately before the voltage application for non-ignition spark discharge and each sensor 5 detected immediately after the start of the non-ignition spark discharge.
The inter-electrode voltage between the spark discharges is detected from the voltage difference with the output voltage of 0, 50a, and when the value is equal to or higher than a predetermined voltage, it is determined as misfire, and when it is less than the predetermined voltage, it is determined as ignition.

As described above, in this embodiment, the misfire detection circuit 20A uses the output voltage of each sensor 50, 50a immediately before the voltage application for non-ignition spark discharge and the non-ignition spark discharge accompanying the voltage application. Since the voltage difference between the output voltage of each sensor 50, 50a immediately after the start is detected, and the capacitance between the high voltage cable of the secondary circuit 11 of the ignition coil 1 is detected, the zero potential is not detected. Each sensor 50, 50 that becomes stable
Even if a is used, the misfire can be detected from the voltage difference before and after the non-ignition spark discharge that appears regardless of the absolute values of the potentials of the sensors 50 and 50a, so that the misfire can be reliably detected. As described above, according to the present invention, even in the case of a misfire that causes an instantaneous breakdown, the misfire can be reliably detected.

In the above embodiment, the voltage between the electrodes of the spark plugs 2 and 3 is detected by using the sensor of the voltage divider of the capacitor. However, the voltage dividing circuit of the resistor having excellent insulation is formed. The sensor may be used.

[Brief description of drawings]

FIG. 1 is a circuit diagram for explaining the principle of a misfire detection device of the present invention.

FIG. 2 is a characteristic diagram showing an inter-electrode voltage in the circuit diagram of FIG.

FIG. 3 is a configuration diagram showing an ignition device to which the misfire detection device of the present invention is applied.

FIG. 4 is a block diagram showing a first embodiment of the misfire detection circuit of the present invention.

FIG. 5 is a waveform diagram for explaining the operation of the first embodiment of the misfire detection circuit of the present invention.

FIG. 6 is a block diagram showing a second embodiment of the misfire detection circuit of the present invention.

[Explanation of symbols]

1 Ignition coil 11 Secondary coil (secondary circuit) 2, 3 Spark plug 10 Ignition device (discharge voltage application means) 20 Misfire detection circuit (misfire detection device) 21, 21a Zero reset circuit (zero potential setting means) 22, 22a Voltage detection circuit 25, 25a Comparison circuit (comparison means) 43, 44 Backflow prevention diode (backflow prevention means) 51, 51a High voltage side capacitor, 52, 52a Low voltage side capacitor, 53, 53a Resistor 100 Engine control unit ( Misfire determination means, second misfire determination means, voltage difference detection means)

Claims (4)

[Claims] 1. An ignition device comprising a spark plug connected to a secondary circuit of an ignition coil for generating a high voltage for spark discharge due to an interruption of a primary current, and a backflow preventing means provided between the ignition coil and the ignition plug. , A gasoline engine misfire detection device for detecting a voltage between the discharge electrodes of the spark plug and detecting a misfire state of the gasoline engine on the basis of the detected voltage. The voltage between the discharge electrodes that is charged in the floating capacitance of the spark plug is extracted before the spark discharge for ignition, and a misfire determination is made when the extracted voltage between the discharge electrodes is higher than a predetermined value. A misfire detection device for a gasoline engine, which is provided with a means. 2. A discharge voltage applying means for applying a high voltage to the spark plug to generate a non-ignition spark discharge between the end of the spark discharge for ignition and the spark discharge for the next ignition. A voltage difference detection means for detecting a difference between the detection voltage of the voltage detection means immediately before the voltage application by the discharge voltage application means and the detection voltage of the voltage detection means immediately after the start of the spark discharge by the voltage application, The misfire detecting device for a gasoline engine according to claim 1, wherein the misfire is detected based on the voltage difference detected by the difference detecting means. 3. The high voltage side capacitor having a dielectric as an insulating coating of a high voltage cable for transmitting the high voltage of the ignition coil to the spark plug, and the low voltage connected in series with the high voltage side capacitor. A voltage divider composed of a voltage side capacitor, and a resistor for discharging the low voltage side capacitor with a predetermined time constant, the misfire determination means, from after the end of the spark discharge for ignition until the next spark discharge for ignition. Discharge voltage applying means for applying a high voltage to the spark plug to generate non-ignition spark discharge, and zero potential setting means for discharging the electric charge of the low voltage side capacitor immediately before the voltage is applied by the discharge voltage applying means. Comparing means for comparing whether or not the output voltage of the voltage divider after the spark discharge is started by the discharge voltage applying means is higher than a fixed value, and the misfire determining means is the discharge voltage The misfire detection device for a gasoline engine according to claim 1, wherein a misfire is determined when a duration of the output voltage of the voltage divider which is equal to or more than the fixed value after the spark discharge by the pressure applying means is shorter than a predetermined time. . 4. The comparing means compares whether or not the detected voltage of the voltage detecting means immediately after the end of the spark discharge for ignition is higher than a predetermined value, and the misfire determining means determines the end of the spark discharge for ignition. 4. The misfire of a gasoline engine according to claim 3, further comprising a second misfire determination means for determining a misfire when a voltage detected by the voltage detection means immediately after that is higher than the predetermined value for a predetermined time or longer. Detection device.