JPH10302929A - High-presure side connection device of ignition coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen spike noise entry when an ion current of an ignition plug is detected. SOLUTION: In an insulation resin made of high-pressure tower part 34, a high-pressure terminal 35 to which a high voltage of an ignition coil 29 is applied is provided, and a conductive spring 37 is mounted to this high-pressure terminal 35. A silicon-rubber made plug boot 39 is mounted to the high-presure tower part 34, this plug boot 39 is pushed to an insulator 25 of the ignition plug 22 and engaged therewith, and thereby the spring 37 is held with the spring being electrically contacted with a terminal 24 of the ignition plug 29. A clearance between a tip end of the plug boot 39 and a metal housing of the ignition plug 22 is set to 2 mm or less (preferably zero), an exposure area for the surface of the insulator 25 is smaller than conventional, thereby a charge quantity of an electrostatic charge of the surface of the insulator 25 is lessened, and electric discharge (spike noise) of electrostatic charge to a metal housing 26 from the surface of the insulator is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage side connection device for an ignition coil having an improved fitting structure between an insulator of a spark plug and a plug boot.

[0002]

2. Description of the Related Art An example of a conventional ignition coil high voltage side connection device will be described with reference to FIG. The high-voltage tower portion 2 of the ignition coil 1 is formed in a cylindrical shape from an insulating resin, and a high-voltage terminal 3 to which a high voltage of the ignition coil 1 is applied is provided therein. Spring 4 is mounted. A plug boot 5 made of silicon rubber or the like is mounted on the high-pressure tower portion 2. The plug boot 5 is pushed into and fitted to the insulator 7 of the ignition plug 6, thereby connecting the spring 4 to the terminal 8 of the ignition plug 6. To hold it.

[0003]

In recent years, in order to monitor the combustion state in a cylinder during operation of an engine, an ion current flowing through electrodes 9 and 10 of a spark plug 6 has been detected.
An ion current detection method for detecting misfire, knocking, preignition, and the like has been considered. This ion current detection method has an advantage that it is not necessary to provide another sensor because the ignition plug 6 can also be used as a sensor.

The normal ion current has a waveform as shown in FIG. 7 (a), but when a discharge of an electrostatic charge described later occurs, spike noise is mixed into the ion current as shown in FIG. 7 (b). As a result, knocking or the like may be erroneously detected due to the spike noise. Therefore, in order to increase the reliability of the ion current detection method, it is necessary to prevent spike noise from being mixed into the ion current to be detected.

[0005] As a cause of the spike noise, it is conceivable that electrostatic charges discharged on the surface of the insulator 7 of the ignition plug 6 are discharged. That is, in the conventional connection structure shown in FIG. 6 described above, the plug boot 5 is formed short so as to give priority to the attachment of the plug boot 5 to the insulator 7 of the ignition plug 6. There is a gap G of 2.5 mm or more between the metal plug 11 and the metal housing 11 of the ignition plug 6, and the insulator 7 is exposed. The gap G serves as an ionization space. At the time of spark discharge, corona discharge occurs on the surface of the insulator 7 exposed to the gap G, and the surface of the insulator 7 is charged with an electrostatic charge at the end of the discharge. When the amount of electrostatic charge on the surface of the insulator 7 increases, the electrostatic charge is discharged to the metal housing 11, and this discharge current (spike noise) is detected by being mixed with the ion current, which may lead to erroneous detection. Conceivable.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and therefore has as its object to effectively reduce the discharge of static charge from the insulator surface of the spark plug to the metal housing. It is an object of the present invention to provide a high-voltage side connection device for an ignition coil that can reduce spike noise mixed in when an ion current is detected.

[0007]

In order to attain the above object, according to the present invention, there is provided an ignition coil connecting device for a high pressure side of an ignition coil, wherein an insulator exposed portion between a tip of a plug boot and a metal housing of an ignition plug is provided. Is set to 2 mm or less. That is, conventionally, there is a gap of 2.5 mm or more between the tip of the plug boot and the metal housing of the spark plug, and the exposed area of the insulator is large. Discharge (spike noise) of electrostatic charges from the metal housing to the metal housing was likely to occur. On the other hand, in the present invention, the width of the insulator exposed portion between the tip of the plug boot and the metal housing of the spark plug is set to two.
By setting it to be equal to or less than mm, the exposed area of the insulator is made smaller (or made zero) than before, and the amount of electrostatic charge on the insulator surface is reduced. As a result, the discharge of static charges from the insulator surface to the metal housing can be effectively reduced, spike noise mixed in at the time of ion current detection can be reduced, and engine controllability by ion current detection can be improved. .

In this case, a configuration may be adopted in which the entire periphery of the tip end of the plug boot is in contact with the entire periphery of the metal housing of the spark plug. With this configuration, the entire surface of the insulator can be completely covered with the plug boot, which is an insulator, and the exposed area of the insulator can be reduced to zero. As a result, electrostatic charge on the insulator surface can be prevented, and discharge of electrostatic charge from the insulator surface to the metal housing can be prevented.

Further, the tip side portion of the plug boot may be formed in a shape which can be easily deformed. With this configuration, the plug boot can be easily pushed into the insulator of the ignition plug, so that the plug boot can be reliably pushed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment (1) of the present invention will be described below with reference to FIGS. As shown in FIG.
An ignition plug 22 is mounted on a cylinder head 21 of the engine by a mounting screw portion 23 for each cylinder. The ignition plug 22 includes a terminal 24, an insulator 25, a metal housing 26, a center electrode 27, a ground electrode 28, and the like.

On the other hand, the ignition coil 29 is constituted, for example, as a stick-type S-DLI ignition coil, in which a primary coil 41, a secondary coil 42, an iron core 43 and the like shown in the circuit diagram of FIG. ing. As shown in FIG. 2, the ignition coil 29 is inserted from the insertion hole 31 of the head cover 30 toward the ignition plug 22, and a bolt 33 is inserted from above into a bolt insertion portion 32 formed at the upper end of the ignition coil 29. Screw hole of head cover 30 (not shown)
The ignition coil 29 is fixed to the head cover 30 by tightening.

As shown in FIG. 1, a high-voltage tower section 34 is formed of an insulating resin in a lower part of the ignition coil 29, and a high-voltage tower section 34 in which a high voltage of the ignition coil 29 is applied is formed therein. A terminal 35 is buried by insert molding, and the inner diameter hollow portion 3 formed downward on the high voltage terminal 35 is formed.
6 is provided with a conductive spring 37 (corresponding to a high-pressure portion). In this case, the spring 37 is prevented from falling off by fitting the large-diameter portion 37a formed on the upper end of the spring 37 into the fall-off preventing groove 38 formed in the inner diameter cavity 36 of the high-voltage terminal 35.

A plug boot 39 made of an insulating elastic material such as silicon rubber is mounted on the high-pressure tower section 34 by press-fitting. The high-pressure tower section 34 has a plurality of retaining projections 4 at a portion where the plug boot 39 is press-fitted.
0 is formed, and the plug boot 39 is prevented from coming off by the engagement between each ridge portion 40 and the plug boot 39. The plug boot 39 is connected to the insulator 25 of the ignition plug 22.
The spring 37 is held in a state of being in electrical contact with the terminal 24 of the ignition plug 29 by being pushed into and fitted into the terminal.

Here, it should be noted that the plug boot 3
9 is formed to be longer than before. Thereby, the entire circumference of the tip of the plug boot 39 is
The entire surface of the insulator 25 is completely covered with the plug boot 39 so that the exposed area of the insulator 20 is zero. Alternatively, the clearance between the tip of the plug boot 39 and the metal housing 26 of the spark plug 22 (the width of the exposed portion of the insulator 25) may be set to 2 mm or less. The reason will be described later.

Next, the circuit configuration of the ignition system will be described with reference to FIG. One end of the primary coil 41 of the ignition coil 29 is connected to the battery 44, and the other end of the primary coil 41 is connected to the collector of the power transistor 45 of the igniter 52. One end of the secondary coil 42 is connected to the ignition plug 22, and the other end of the secondary coil 42 is connected to the ground via two Zener diodes 46 and 47. The two Zener diodes 46 and 47 are connected in series in opposite directions, a capacitor 48 is connected in parallel to one Zener diode 46, and a resistor 49 is connected in parallel to the other Zener diode 47. The potential Vin between the capacitor 48 and the resistor 49 is input to the inverting input terminal (-) of the inverting amplifier circuit 51 via the resistor 50 and is inverted and amplified, and the output signal Vout of the inverting amplifier circuit 51 is used as the ion current detection signal. Becomes

During operation of the engine, the power transistor 45 is turned on / off in synchronization with an ignition signal transmitted from an engine control circuit (not shown) to the igniter 52. When the power transistor 45 is turned on, a primary current flows from the battery 44 to the primary coil 41. Thereafter, when the power transistor 45 is turned off, the primary current of the primary coil 41 is cut off, and a high voltage is electromagnetically induced in the secondary coil 42. The electrodes 27 and 2 of the spark plug 22
A spark discharge occurs between eight. At this time, the discharge current flows from the ground electrode 28 of the spark plug 22 to the center electrode 27, and is charged through the secondary coil 42 to the capacitor 48.
It flows to the earth side via the Zener diodes 46 and 47.

On the other hand, the ion current flows in the direction opposite to the discharge current. That is, the ion current is applied to the center electrode 2
7 to the ground electrode 28, and furthermore, the resistance 4
9 to the capacitor 48. At this time, the resistor 49
The input potential Vin of the inverting amplifier circuit 51 changes according to the change of the ion current flowing through the inverting amplifier circuit 51, and a signal Vout corresponding to the ion current is output from the output terminal of the inverting amplifier circuit 51. An ion current is detected from the output signal Vout of the inverting amplifier circuit 51, and misfire, knocking, preignition, and the like are detected from the ion current.

The metal housing 26 of the ignition plug 22
Since the ground is the same as the ground electrode 28, if an electrostatic charge charged on the surface of the insulator 25 is discharged to the metal housing 26, the discharge current flows in the same direction as the above-described ion current. As a result, the discharge current is mixed with the ionic current and flows through the resistor 50, so that the input potential Vin of the inverting amplifier circuit 51 is affected by the discharge current and is discharged to the ionic current detection signal Vout output from the inverting amplifier circuit 51. Spike noise due to the current is mixed in (see FIG. 7B). This spike noise causes erroneous detection when knocking or the like is detected by the ion current. Therefore, in order to increase the reliability of the ion current detection method, it is necessary to minimize the occurrence of spike noise.

The main cause of the spike noise is the discharge of static charge from the surface of the insulator 25 to the metal housing 26. The discharge of the electrostatic charge is more likely to occur as the charge amount of the electrostatic charge charged on the surface of the insulator 25 increases. Therefore, in order to reduce spike noise, the charge amount of the electrostatic charge on the surface of the insulator 25 needs to be reduced. There is. The electrostatic charge on the surface of the insulator 25 is caused by the occurrence of corona discharge at the exposed portion of the insulator 25 between the plug boot 39 and the metal housing 26 during spark discharge. To reduce the clearance, the clearance between the tip of the plug boot 39 and the metal housing 26 (the insulator 25
It is effective to reduce the exposed portion), and by reducing this clearance, the frequency of occurrence of spike noise can be reduced.

The inventors of the present invention have conducted experiments on the relationship between the clearance between the tip of the plug boot 39 and the metal housing 26 and the frequency of occurrence of spike noise. The results shown in FIG. 4 were obtained. From this experimental result, it was confirmed that the smaller the clearance between the tip of the plug boot 39 and the metal housing 26, the more effectively the frequency of occurrence of spike noise was reduced.

In the configuration example shown in FIG. 1, the entire periphery of the tip of the plug boot 39 is brought into contact with the entire periphery of the metal housing 26 of the ignition plug 22, and the clearance between them is zero.
The frequency of occurrence of spike noise can be significantly reduced as compared with the conventional case (clearance is 2.5 mm or more),
The detection accuracy of the ion current can be improved.

However, the present invention is not limited to the case where the clearance between the tip of the plug boot 39 and the metal housing 26 is set to zero, and the clearance may be set to 2 mm or less. Even in this case, the frequency of occurrence of spike noise can be reduced as compared with the related art (the clearance is 2.5 mm or more).

By the way, in the configuration example of FIG. 1, the amount of pushing of the plug boot 39 into the insulator 25 of the ignition plug 22 is longer than the conventional one by 2.5 mm or more. If too long, plug boot 39
The workability at the time of pushing is reduced.

Therefore, in the embodiment (2) of the present invention shown in FIG. 5, the distal end portion 39a of the plug boot 39 is formed to be thin, so that the distal end portion 39a is formed in an easily deformable shape. . In this way, even if the amount of pushing the plug boot 39 into the insulator 25 becomes longer than before,
The pressing force (pressing force) of the plug boot 39 to the insulator 25 can be made approximately the same as that of the related art, and the workability at the time of pressing the plug boot 39 can be improved. And plug boots 3
9, the thin portion 39a on the tip side is easily compressed and deformed in the axial direction (vertical direction), so that the length of the plug boot 39 becomes longer than the actually required pushing amount due to the dimensional variation of each portion. In this case, the thin portion 39a on the distal end side of the plug boot 39 can be pressed against the metal housing 26 and easily compressed and deformed, and the electrical connection between the spring 37 and the terminal 24 of the ignition plug 22 can be reliably performed. it can.

In the above embodiment (2), the distal end portion 39a of the plug boot 39 is formed to be thin so that the distal end portion 39a can be easily deformed. By forming a plurality of concave grooves or slits (slits) extending vertically in the portion, the distal end portion may be formed into a shape that is easily deformed.

In the above embodiments, no other member is interposed between the tip of the plug boot 39 and the metal housing 26. However, a short cylindrical elastic member is press-fitted into the insulator 25 of the ignition plug 22 in advance. After fitting, the cylindrical elastic member is brought into contact with the metal housing 26, and the clearance between the cylindrical elastic member and the tip of the plug boot 39 is set to 2 mm.
The following (more preferably, zero) may be set. In short, the width of the exposed portion of the insulator 25 between the tip of the plug boot 39 and the metal housing 26 may be set to 2 mm or less (more preferably, zero).

In each of the above embodiments, the present invention is applied to a stick type ignition coil 29. As shown in Japanese Patent Publication No. 7-109810, an S-DLI type ignition other than the stick type is used. The present invention can be applied to a coil, and the present invention can also be applied to a system in which an ignition coil is connected to a high-pressure tower (a connection to a spark plug) by a high-voltage cord.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an ignition coil high-pressure side connection device according to an embodiment (1) of the present invention.

FIG. 2 is a longitudinal sectional view showing a mounting structure of an ignition coil to an engine.

FIG. 3 is an electric circuit diagram of an ignition system.

FIG. 4 is a diagram showing the relationship between the clearance between the tip of the plug boot and the metal housing and the frequency of occurrence of spike noise.

FIG. 5 is a longitudinal sectional view of an ignition coil high-pressure side connection device according to an embodiment (2) of the present invention.

FIG. 6 is a longitudinal sectional view showing an example of a conventional high-pressure side connection device for an ignition coil.

FIG. 7A is a waveform diagram of an ion current in a normal state, and FIG.
Is the waveform diagram of the ion current when noise occurs

[Explanation of symbols]

Reference numeral 22: spark plug, 24: terminal, 25: insulator, 26: metal housing, 27: center electrode, 28: ground electrode, 29
... Ignition coil, 34 ... High voltage tower, 35 ... High voltage terminal,
37: Spring (high pressure part), 39: Plug boot, 3
9a: thin portion, 41: primary coil, 42: secondary coil,
44 ... battery, 52 ... igniter.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Isao Goto 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (3)

[Claims] 1. A high-voltage portion to which a high voltage of an ignition coil is applied, and a plug boot made of an insulating elastic material. A high-voltage side connection device for the ignition coil that holds the spark plug electrically connected to the terminal of the ignition plug, wherein the width of the insulator exposed portion between the tip of the plug boot and the metal housing of the ignition plug is 2 mm or less. A high-pressure side connection device for an ignition coil, characterized in that: 2. The high-pressure side connection device for an ignition coil according to claim 1, wherein the entire periphery of the distal end of the plug boot abuts on the entire periphery of the metal housing of the ignition plug. 3. The high-pressure side connection device for an ignition coil according to claim 1, wherein a tip side portion of the plug boot is formed in a shape that can be easily deformed.