JPH04339176A - Misfire detecting device for spark ignition engine - Google Patents

Abstract

PURPOSE:To provide a misfire detecting device capable of detecting misfire of each cylinder with constitution of easy mounting and maintenance. CONSTITUTION:This is the misfire detecting device equipped in the ignition circuit of a gasoline engine provided with an ignition coil 1, a primary current interrupting means 4 to interrupt current in the primary circuit 11, series gaps 21 provided in the secondary circuit 12 of the ignition coil, and spark plugs 3 mounted on the engine, and it is constituted out of a charging means to charge to floating electrostatic capacity of the spark plug after spark discharge at the spark plug, a secondary voltage detecting circuit 6 to detect damping characteristic of the secondary voltage charged to the spark plug, and a misfire discriminating circuit 7 to discriminate misfire by the damping characteristic.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention utilizes the fact that the resistance value of the spark discharge gap of a spark plug differs when ignition occurs normally and when ignition error (misfire) occurs in a gasoline engine. This invention relates to a detection device.

0002

2. Description of the Related Art In response to demands for purifying the exhaust gas of automobile engines and improving fuel efficiency, there is a need for a device that can detect the ignition state of each cylinder of the engine and take measures to prevent misfires in all cylinders. As a misfire detection device, conventionally known methods include drilling a hole in the cylinder block and attaching a combustion light sensor, attaching a pressure sensor to the mounting seat of a spark plug, and measuring the ionic current of the ignition circuit.

0003

[Problems to be Solved by the Invention] In the conventional method, it is troublesome to install the sensor, high voltage diodes are required to detect the ion current, and installation costs are high when installed on all cylinders of the vehicle. There were disadvantages such as an increase in the amount of water and maintenance required. An object of the present invention is to provide a misfire detection device that is easy to install and maintain and is capable of detecting misfires in each cylinder.

0004

[Means for Solving the Problems] The misfire detection device of the present invention includes an ignition coil, a primary current intermittent means for intermittent current flowing through its primary circuit, and a series gap or backflow prevention device provided in the secondary circuit of the ignition coil. A misfire detection device installed in the ignition circuit of a gasoline engine, which includes a diode for use in the engine, and a spark plug installed in the engine, the charging means charging the stray capacitance of the spark plug after spark discharge at the spark plug. , a secondary voltage detection circuit that detects the attenuation characteristic of the secondary voltage charged in the spark plug, and a misfire discrimination circuit that determines a misfire based on the attenuation characteristic.

[0005]

According to the present invention, after spark discharge ends, the stray capacitance of the spark plug charges a secondary voltage for misfire detection. The attenuation characteristic of this charged charge differs depending on the presence or absence of ions generated by combustion in the spark discharge gap of the spark plug. Therefore, by detecting the attenuation characteristic of this secondary voltage and comparing it with the attenuation characteristic obtained by measurement or calculation in advance, it is possible to determine whether or not a misfire has occurred. Therefore, a combustion light sensor, a pressure sensor, and a high-pressure diode are not required, and a misfire detection device that is simple in structure, easy to attach to an engine, and highly practical can be obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an ignition system 100 for an internal combustion engine, which includes an ignition coil 1, a power distributor 2, and a spark plug 3. A primary circuit 11 of the ignition coil 1 is connected to an on-vehicle power supply V and a primary current interrupting means 4, and a secondary circuit 12 is connected to a spark plug 3 via the power distributor 2. Secondary circuit 12 between the rotor gap 21 of the power distributor 2 and the spark discharge gap 31 of the spark plug 3
A voltage divider 5, a secondary voltage detection circuit 6, and a misfire determination circuit 7 are connected to. In this embodiment, the primary current intermittent means 4 serves as a voltage generating means (functioning as an ion detection voltage or a misfire detection voltage) that charges the stray capacitance of the spark plug.

The primary current intermittent means 4 is composed of a switching element 41 and a signal generator 42, and detects the crank angle and throttle opening of the engine, and sets the spark discharge timing to an ignition advance angle adapted to the engine load and rotational speed. The primary current is intermittent.

In this embodiment, the voltage divider 5 is connected to the secondary circuit 1
Sensor 5 made of a conductor arranged to generate 1 pF (picofarad) capacitance between it and the high voltage lead of No. 2.
1 is used and 3000p is used as a low impedance element.
Using a capacitor 52 with a capacitance of F, the secondary voltage generated in the secondary circuit 12 is divided into about 1/3000. In this case, if a 3 megohm resistor 53 forming a discharge circuit is connected in parallel to the capacitor 52, the time constant of the voltage divider 5 will be 9 m.
s (milliseconds), and a relatively long decay time of 3 ms, which will be described later, can be reliably determined. As a result, the high voltage waveform with a maximum of around 30,000 volts is lowered to a level of 10 volts and input to the secondary voltage detection circuit 6.

The secondary voltage detection circuit 6 detects the duration of voltage above a certain level in the divided secondary voltage waveform, and the misfire determination circuit 7 determines that a misfire occurs when the duration exceeds a set value. do.

The operation will be explained with reference to FIG. The signal generator 42 outputs a pulse signal for intermittent primary current shown in (2), and a primary current as shown in (2) is generated in the primary circuit 11. Pulse waves a and c with a large width h are signals for generating spark discharge in the spark plug 3, and are delayed by a delay time i of about 0.5 to 1.5 ms after the end of these pulse waves a and c. Pulse waves b and d having a small width are signals for generating a spark plug capacitance charging voltage (ion detection voltage).

In the ignition circuit using the rotor gap 21 as a series gap, the proximity time between the rotor of the power distributor 2 and the side electrode changes depending on the engine rotation speed. Therefore, when the engine is operating at high speed, the width h and the delay time i are set short, and at 6000 rpm, the spark discharge duration is suitably about 0.5 to 0.7 ms.

[0012] Due to the above-mentioned interruption of the primary current, the secondary circuit 12
A secondary voltage shown in ■ is generated in the ignition coil 1. A spark discharge starts due to the high voltage p generated at the end of the pulse waves a and c, and a gentle voltage waveform q is subsequently generated due to the induced discharge. Next, in response to the rise of the pulse waves b and d, a positive waveform r is generated in the secondary circuit 12 due to a back electromotive force. Since electrical energy is accumulated in the ignition coil 1 when the primary coil is energized, the secondary voltage is boosted again after the energization is stopped, and a waveform s appears. The re-boosting level of this secondary voltage can be set as desired by the delay time i and the widths of the pulse waves b and d. In this invention, the level of the waveform s is set to 5 to 5 so that dielectric breakdown of the rotor gap 21 is possible and discharge is impossible when there are no burning fuel ions in the spark discharge gap 31 of the spark plug 3. It is set to 7 kilovolts.

[0013] As a result, between the rotor gap 21 of the power distributor 2 and the spark discharge gap 31 of the spark plug 3,
Mainly the capacitance of spark plug 3 (usually 10 to 20 pF)
As shown in (2), the secondary voltage charged in ) has a difference in decay time depending on whether it ignites normally or when it misfires. That is, when a misfire occurs, the secondary voltage waveform gradually decreases as shown in s1, and when ignition occurs normally and combustion occurs, the secondary voltage waveform rapidly attenuates as shown in s2. The secondary voltage detection circuit 6 detects the time when the secondary voltage is higher than the reference voltage v, as shown in (2), and outputs pulse waves t1 to t4 to the misfire determination circuit 7. The misfire determination circuit 7 determines that a misfire has occurred when this decay time is, for example, 3 ms or more.

[0014] In the above embodiment, the rotor gap 21 of the power distributor 2 is used as the series gap, but in a distributor-less igniter that does not include the power distributor 2, the reverse current that is normally inserted into the secondary voltage is used as the series gap. A prevention diode performs a similar function. Further, the ion detection voltage generating means may be provided separately from the primary current intermittent means. Note that when the center electrode of the spark plug 3 has a positive potential, the ionic current flows more smoothly than when the center electrode has a negative potential, so by connecting the ignition coil 1 in the opposite way than usual, the secondary voltage can be reduced. It is desirable to set it to a positive potential.

[Brief explanation of drawings]

FIG. 1 is an ignition circuit diagram of a gasoline engine equipped with a misfire detection device of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the misfire detection device.

[Explanation of symbols] 1 Ignition coil 2 Power distributor 3 Spark plug 4 Primary current intermittent means 5 Voltage divider 6 Secondary voltage detection circuit 7 Misfire detection circuit 11 Primary circuit 12 Secondary circuit 21 Rotor gap

Claims (1)

[Claims] Claim 1: An ignition coil, a primary current intermittent means for intermittent current flowing through its primary circuit, a series gap or backflow prevention diode provided in a secondary circuit of the ignition coil, and a spark plug installed in an engine. A misfire detection device installed in the ignition circuit of a gasoline engine equipped with a charging means for charging the stray capacitance of the spark plug after spark discharge at the spark plug, and a secondary voltage charged to the spark plug. A misfire detection device includes a secondary voltage detection circuit that detects the attenuation characteristic of a motor, and a misfire discrimination circuit that discriminates a misfire based on the attenuation characteristic.