JP3080199B2 - Spark plug insulation drop detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting insulation deterioration of a spark plug.

[0002]

2. Description of the Related Art In order to purify exhaust gas of an automobile engine and improve fuel efficiency, there is a demand for a device capable of detecting a combustion state of each cylinder of an engine and taking measures to prevent misfiring of all cylinders. For this purpose, it is necessary to prevent a misfire caused by smoldering due to a decrease in insulation of the spark plug and a misfire that is not normally ignited even if a spark discharge occurs. Conventionally, as a device for detecting a missed fire, a hole is made in the cylinder block to mount an optical sensor, or a pressure sensor is attached to the mounting seat of the spark plug.
Methods for measuring the ion current of an ignition circuit are known.

[0003]

In the conventional method, mounting the sensor is troublesome, and mounting the sensor on all the cylinders of the vehicle increases the mounting cost and requires maintenance work. SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug insulation deterioration detecting device capable of detecting insulation deterioration of a spark plug with a configuration that is easy to mount and maintain.

[0004]

According to the present invention, there is provided a spark plug insulation deterioration detecting apparatus comprising: an ignition coil; primary current interrupting means for interrupting an electric current flowing through a primary circuit thereof; and a series provided in a secondary circuit of the ignition coil. The ignition device of a gasoline engine includes a gap or a backflow prevention diode, and a spark plug mounted on the engine and connected in series to the series gap or the backflow prevention diode provided in the secondary circuit of the ignition coil. A voltage divider for detecting a secondary voltage charged in the electrostatic stray capacitance of the spark plug with the end of the spark discharge, and a secondary voltage detection circuit for detecting an attenuation characteristic of the divided secondary voltage An engine speed detection circuit, and a fuel cut operation performed at the time of deceleration of the engine. The insulation resistance of the lug consists of a discriminating circuit for discriminating a decreased.

[0005]

According to the present invention, no fuel is supplied into the cylinder in the fuel cut operation at the time of deceleration that occurs during the operation of the automobile, so that a misfire naturally occurs. In this case, when the insulation resistance of the spark plug is reduced, the discharge time of the electric charge of the secondary voltage charged in the electrostatic stray capacitance of the spark plug is short. For this reason, when the discharge time is equal to or less than a certain value, it is determined that the insulation resistance of the spark plug has decreased. According to the present invention, since the decrease in the insulation resistance of the spark plug can be detected only by the electronic circuit, mounting and maintenance are easy.

[0006]

1 shows an ignition device 100 for an internal combustion engine provided with an ignition coil 1, a power distribution device 2, and a spark plug 3. FIG. The primary circuit 11 of the ignition coil 1 is connected to the vehicle power supply V and the primary current interrupting means 4, and the secondary circuit 12 is connected to the spark plug 3 via the power distributor 2. The secondary circuit 12 between the rotor gap 21 of the distributor 2 and the spark discharge gap 31 of the spark plug 3 includes a voltage divider 5, a secondary voltage detection circuit 6, an engine speed detection circuit 7, and a discrimination circuit 8. Is attached.

The primary current interrupting means 4 includes a switch element 41
The signal generator 42 detects the crank angle and the throttle opening of the engine, and interrupts the primary current so that the spark discharge timing becomes the ignition advance angle adapted to the load and the rotation speed of the engine.

The voltage divider 5 uses a sensor 51 made of a conductor disposed so as to generate 1 pF (picofarad) capacitance between the voltage divider 5 and the high voltage lead of the secondary circuit 12. The secondary voltage generated in the secondary circuit 12 is divided to about 1/3000 using a capacitor having a capacitance of 3000 pF. In this case, a 1-megaohm resistor 53 forming a discharge circuit in the capacitor (52)
Are connected in parallel, the time constant of the voltage divider 5 becomes 9 ms (millisecond), and a relatively long decay time of 3 ms described later can be reliably determined. As a result, a high voltage waveform of up to about 30,000 volts is reduced to a level of 10 volts and input to the secondary voltage detection circuit 6.

The secondary voltage detection circuit 6, as shown in FIG.
A peak hold circuit 61 that receives the voltage divided by the voltage divider 5 and the output of the signal generator 42, a voltage divider 62 that divides the output voltage of the peak hold circuit 61, and a voltage divider 6
The voltage divider 2 compares the output of the voltage divider 5 with the output of the voltage divider 5 and generates a pulse output. The comparator 63 detects the duration of a voltage of a certain level or more in the divided secondary voltage waveform.
In this embodiment, the peak value of the secondary voltage for insulation reduction detection and the secondary voltage for ion density detection is peak-held,
The time until the level of each secondary voltage waveform drops to, for example, 2/3 of the peak hold level is output as a pulse.

A rotational speed detecting circuit 7 of the engine detects a crank angular speed (synonymous with a rotational speed), and determines a deceleration condition (predetermined) in which a deceleration of a predetermined value or more is performed and a fuel cut operation is performed. Output to Discrimination circuit 8
Is determined that the insulation resistance of the spark plug 3 is reduced due to smoldering when the duration is equal to or less than a set value obtained by an experiment or calculation in advance during a fuel cut operation performed during deceleration.

Further, by inserting a backflow prevention diode between the ignition coil 1 and the power distributor 2, the detection accuracy of the attenuation characteristic of the secondary voltage can be improved. When the center electrode of the spark plug 3 has a positive potential,
Compared to the case of minus, the spark plug during normal combustion
The electric resistance of the spark discharge gap is low. For this reason, since the ion current flows smoothly, it is desirable that the secondary voltage is set to a positive potential by connecting the ignition coil in the opposite direction to the normal state.

The operation of the present invention will be described with reference to FIG.
In a vehicle powered by a gasoline engine, during deceleration operation, so-called fuel cut is performed in which fuel injection to the cylinder is stopped in order to reduce harmful substances in exhaust gas and improve fuel efficiency. In this fuel cut operation, since no fuel is supplied into the cylinder, combustion naturally occurs in the cylinder and a misfire occurs,
The discharge time (decay time) of the electric charge charged in the electrostatic floating capacitance of the spark plug 3 becomes longer. However, when the insulation resistance of the spark plug 3 is reduced, the discharge time of the electric charge charged in the electrostatic stray capacitance of the spark plug 3 becomes as shown in FIG.
Short as shown. When the discharge time is equal to or less than a predetermined value, it is determined that the insulation resistance of the spark plug 3 has decreased.

The detection of the insulation resistance by this method is as follows.
Since the level is several tens of megaohms (MΩ), it is difficult to detect a decrease in insulation resistance to 10 MΩ or less, which is a criterion for determining smoldering, and particularly to a decrease in insulation resistance to 1 MΩ or less, which actually hinders engine operation. However, there is an advantage that a sign of smoldering of the spark plug 3 can be detected and an engine trouble due to smoldering can be prevented.

[Brief description of the drawings]

FIG. 1 is an ignition circuit diagram of a gasoline engine equipped with an insulation deterioration detecting device of the present invention.

FIG. 2 is a partial circuit diagram of the insulation deterioration detecting device of the present invention.

FIG. 3 is a characteristic graph of an insulation resistance value and a discharge time of a secondary voltage at the time of fuel cut.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ignition coil 2 Distributor 3 Spark plug 4 Primary current intermittent means 5 Voltage divider 6 Secondary voltage detection circuit 7 Rotation speed detection circuit 8 Discrimination circuit 9 Insulation drop detection device 11 Primary circuit 12 Secondary circuit

Continuation of front page (56) References JP-A-61-155662 (JP, A) JP-A-63-120864 (JP, A) JP-A-62-135668 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) F02P 17/12 F02P 15/00 G01M 15/00

Claims (1)

(57) [Claims] An ignition coil, a primary current interrupting means for interrupting an electric current flowing through a primary circuit thereof, a series gap or a backflow prevention diode provided in a secondary circuit of the ignition coil, and an ignition coil mounted on an engine . Provided in secondary circuit
Series gap or backflow prevention diode
It is attached to the ignition system of a gasoline engine having a spark plug connected in series, for detecting the secondary voltage charged in the electrostatic floating capacitance of the <br/> spark plug with the end of the spark discharge A voltage divider, a secondary voltage detection circuit for detecting an attenuation characteristic of the divided secondary voltage, a rotation speed detection circuit of the engine, and a fuel cut operation performed when the engine is decelerated, the secondary voltage of the secondary voltage insulation system for detecting decrease of the spark plug insulation resistance of the <br/> spark plug when the decay time is less than a predetermined value comprising a discrimination circuit for discriminating a decreased.