JPH1073069A - Ion current detecting spark plug and ion current detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain concentration of electric field in a gap so as to restrict generation of insulation breakage in the gap and generation of corona discharge near the gap by specifying the radial width of a gap between the projecting part of attaching metal fittings and the small diameter part of an insulation body. SOLUTION: Attaching metal fittings 31 provided with a screw part 31a for the purpose of being fixed to an engine block 100 include an insulation body 32 in its inside, and is fixed so that the one-end part 321 and the other end part 322 of the insulation body 32 may be exposed. Inside of the insulation body 32, a central electrode 33 is provided and fixed so that its one end part 331 may be exposed. In addition, a packing 36 is arranged between the projecting part 313 of the attaching metal fittings 31 and the stepped part 32b of the insulation body 32. In this case, a gap C having more than 0.5mm in its radial width W1 is formed between the projecting part 313 of the attaching metal fittings 31 and the small diameter part 324 of the insulation body 32. In addition, the upper limit of the width W1 of the gap C is so set as an axial overlapping size W3 between the projection part 313 of the attaching metal fittings 31 and the stepped part 32b may be more than 30% of the radial width W2 of the stepped part 32b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion current detecting spark plug capable of detecting an ion current and an ion current detecting device.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventional spark plug (hereinafter referred to as a spark plug) 3 for detecting ion current is used.
Has a cylindrical insulator 32 held inside a cylindrical mounting bracket 31, a center electrode 33 held inside the insulator 32, and one end 311 of the mounting bracket 31
A ground electrode 35 opposed to one end 331 of the center electrode 33 with a discharge gap 38 therebetween is fixed.

A stepped portion 32b is formed on the outer peripheral portion of the insulator 32 on the one end portion 321 side so as to form a small-diameter portion 324 further on one end portion 321 side than this portion. Have been. In the inner peripheral portion of the mounting bracket 31, a protruding portion 313 that protrudes radially from this portion toward the small-diameter portion 324 of the insulator 32 is formed in a portion near the stepped portion 32 b. .

[0004] One end 3 of the spark plug 3
The b side is inserted into the combustion chamber of the internal combustion engine, and a high voltage for discharge (approximately −10 kV to −35 kV) is applied between the mounting bracket 31 of the spark plug 3 and the center electrode 33, thereby causing spark discharge to the discharge gap 38. Is generated, and the air-fuel mixture in the combustion chamber burns. By the way, in the vicinity of the discharge gap 38, ions are generated due to the ionization effect accompanying the combustion, and the generation of the ions causes the center electrode 33 and the ground electrode 35 to generate ions.
It is known that an ionic current flows between (that is, the mounting bracket 31). In recent years, it has been studied to detect the state of combustion of the air-fuel mixture in the combustion chamber of the internal combustion engine by detecting the ion current with the ion current detecting means.

Normally, as shown in FIG. 5, when the ion current detecting means detects that the ion current detection waveform has risen by the rising height H for a predetermined time T or more, the air-fuel mixture burns. It is determined that there is. When the mixture is misfired, no ion current is generated because the ions are not generated, and the rising state is not detected. During preignition, the ions are generated before the discharge between the discharge gaps 38, and the rising state is detected before the discharge.

[0006]

By the way, a spike-like noise N is generated in the detection waveform of the ion current as shown in FIG. 5, which is detected by the above-mentioned ion current detecting means. It has been confirmed by the present inventor that the ion current detection means makes an erroneous detection due to the occurrence of the above. And, among the insulators 32 of the spark plug 3, the corona discharge that normally occurs from the protruding portion 313 to the one end 321 is a cause of the noise N.
The inventor has discovered that.

[0007] The contents of experiments and studies conducted by the present inventor on the relationship between the corona discharge and the noise N will be described below. First, in the conventional spark plug 3, the mounting bracket 3
A gap C having a very small width W ₁ (see FIG. 2, for example, about 0.4 mm) is formed in the radial direction between the one protrusion 313 and the small-diameter portion 324 of the insulator 32. As the reason, first, the projecting portion 313 of the mounting bracket 31 to securely hold the insulator 32, the protrusion 313 of the mounting bracket 31, overlap in the axial direction of the stepped portion 32b cash W ₃ ( This is because (see FIG. 2) is made as large as possible. Second
Further, in order to smoothly insert the insulator 32 into the mounting bracket 31, interference between the protruding portion 313 and the stepped portion 32b is avoided.

Since a high voltage of several tens of kV is applied between the mounting bracket 31 and the center electrode 33, a large electric field is formed between the mounting bracket 31 and the center electrode 33. Incidentally, the gap C formed between the mounting bracket 31 and the center electrode 33 is made of air having a smaller dielectric constant and dielectric strength than an insulating material. For this reason, an electric field larger than the dielectric strength is formed in the gap C, dielectric breakdown occurs in the gap C, and corona discharge occurs. Here, assuming that the dielectric constant of air is 1, the dielectric constant of the insulating material is about 9, and the dielectric strength of air is 2 at room temperature (about 20 ° C.).
３3 kV / mm, the dielectric strength of the insulating material is about 20 kV / mm
mm.

Here, the center electrode 33 is a cathode,
Since 1 is an anode, the insulator 32 is polarized positively on the inner surface side and negatively polarized on the outer surface side. As a result, the positive charge of the corona discharge generated in the gap C is
Is attracted to the vicinity of the outer surface on the one end 321 side, and accumulates. The accumulated charges move to the mounting bracket 31 due to some external factor. As a result, the plus charge flows between the center electrode 33 and the mounting bracket 31 in addition to the ion current, and appears as noise N in the waveform detected by the ion current detecting means.

When the accumulated positive charges continuously flow, a large number of noises N are generated in the detected waveform. When the large number of the noises N overlap, the detected waveform shows the rising state as described above. For example, when a large amount of noise N is generated when the air-fuel mixture is misfired, the detection unit erroneously detects that the air-fuel mixture is in a combustion state.

When the throttle of the engine is fully closed,
Since the amount of air and the amount of fuel supplied into the combustion chamber are small, the pressure in the combustion chamber is reduced, and corona discharge is more likely to occur. Therefore, the noise N occurs particularly frequently.
Therefore, when the throttle is fully closed, erroneous detection particularly by the ion current detecting means tends to occur frequently. The present invention has been made in view of the above problems, and has as its object to provide a spark plug that can suppress the occurrence of corona discharge.

[0012]

The corona discharge is caused by the protrusion (313) on one end (311) side of the mounting bracket (31) and the small-diameter portion (324) of the insulator (32). The present invention focuses on the fact that an electric field stronger than the dielectric strength of the gap (C) is formed in the gap (C) formed in the radial direction between the gaps (C). ) In the radial direction (W ₁ ) is made larger than in the prior art, thereby suppressing the concentration of the electric field in the gap (C), suppressing the occurrence of dielectric breakdown in the gap (C), and reducing the gap ( C) The generation of corona discharge in the vicinity is suppressed.

When the spark plug (3) of the present invention is applied to the ion current detection device (10), the spark plug (3) can suppress the occurrence of corona discharge. Charges can be prevented from flowing into the ion current circuit of the ion current detection device (10), and generation of noise (N) in the waveform detected by the ion current detection device (10) can be suppressed.

Specifically, a radial width (W ₁ ) of 0.5 mm or more is provided between the protrusion (313) of the mounting bracket (31) and the small-diameter portion (324) of the insulator (32). Is formed. According to this, it is possible to suppress occurrence of noise (N) in the detection waveform of the ion current detected by the ion current detection device (10) when the throttle is fully closed, in which noise (N) occurs particularly frequently. This has been confirmed by experiments described later.

Further, the radial width (W ₁ ) is set to 0.6.
It has been confirmed by experiments described below that the above-mentioned noise (N) can be prevented from being generated by setting the diameter to at least mm. The axial overlap (W ₃ ) between the protruding portion (313) of the mounting bracket (31) and the stepped portion (32b) of the insulator (32) is determined in the radial direction of the stepped portion (32b). If it is smaller than 30% of the width (W ₂ ), the mounting bracket (31) may not be able to hold the insulator (32) reliably. Therefore, the overlapping margin is (W _3), so that the radial width of the stepped portion (32b) (W ₂₎ of 30% or more. Note that the overlapping generations W ₃ that the above 0.6mm preferred.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. (First Embodiment) Regarding the spark plug of the present embodiment shown in FIGS. 1 and 2, the description of the same parts as those of the above-mentioned prior art will be omitted, and the current changes and supplementary explanations will be described below.

The mounting bracket 31 includes an engine block 100.
Screw part 31a for fixing the mounting bracket 3
An insulator 32 is fixed inside 1 such that one end 321 and the other end 322 thereof are exposed. A center electrode 33 is provided inside the insulator 32 at one end 3 thereof.
It is fixed so that 31 is exposed. The small-diameter portion 324 of the insulator 32 is formed so as to gradually decrease in diameter toward the one end 321. This allows
The gas volume G can be widened, and the heat resistance of the spark plug 3 can be improved. Also, one end 321 of the insulator 32,
By increasing the distance between the mounting bracket 31 and the one end 311, so-called side jumping can be suppressed.

The small-diameter portion 324 near the stepped portion 32b
The outer diameter of the are for example 6.9 mm, the width W ₂ in the radial direction of the stepped section 32b, for example a 1.1 mm. Also, of the gap C, the stepped portion 32b side in the width, i.e., the minimum width W _1, for example, 0.7mm gap C, and the above overlapping algebraic W ₃ for example 0.4 mm. Also, the axial width W ₄ of the protruding portions 313 for example, a 2.0 mm. The width W ₄ is 1.5 m in order to reliably support the insulator 32.
m or more.

A packing 36 made of a material having excellent heat resistance, for example, iron or copper is arranged between the protruding portion 313 of the mounting bracket 32 and the stepped portion 32b of the insulator 32. The heat-resistant temperature of the packing 36 is extremely high, that is, a temperature in the vicinity of the packing 36 during operation of the engine, for example, 300 ° C. or higher. The packing 36 includes a stepped portion 32 b of the insulator 32 and a protruding portion 313 of the mounting bracket 31.
It is configured in a shape that follows the shape of the gap between the sides.
The cross-sectional shape of the protrusion 313 is substantially trapezoidal.

In a portion of the outer peripheral portion of the insulator 32 which is disposed near the other end portion 312 of the mounting bracket 31, a small-diameter portion 323 is located closer to the other end portion 322 of the insulator 32 than this portion.
The stepped portion 32a is formed so as to constitute the above. The vicinity of the other end 312 of the mounting bracket 31 is bent inward along the stepped portion 32a over the entire circumference,
As a result, the insulator 32 is caulked and fixed to the mounting bracket 31.

FIG. 3 shows an ion current detecting device 10 to which the spark plug 3 of the present invention is applied. 3, the ignition coil 1 includes a primary winding 11 and a secondary winding 12, and a power transistor 2 and a vehicle-mounted power supply 8 are connected to the primary winding 11 in series. , The primary current generated in the primary winding 11 is interrupted. The spark plug 3 is connected in series to the secondary winding 12 and ignites an air-fuel mixture in a combustion chamber of an internal combustion engine (not shown) when a high voltage for discharge is applied.

A capacitor 4 is connected to the positive polarity side of the secondary winding 12, and a resistor 7 for converting an ion current into a voltage is connected between the capacitor 4 and the ground. The voltage generated at the resistor 7 is detected by the computer 6. The combustion state of the air-fuel mixture in the combustion chamber of the internal combustion engine can be detected based on the ion current detected by the computer 6.

The computer 6 controls the fuel injection amount and the ignition timing in accordance with the combustion state to maintain the optimum combustion state. Further, a constant voltage diode 5 is connected in parallel with the resistor 7 and the capacitor 4. The constant voltage diode 5 allows the charging voltage of the capacitor 4 to be set arbitrarily. The ignition coil 1, the power transistor 2, and the vehicle power supply 8
Constituting voltage supply means, capacitor 4, computer 6
The resistor 7 constitutes an ion current detecting means.

The ion current detecting device 10
At the ignition timing of the internal combustion engine, a negative high voltage for discharge (approximately −10 kV to −35 kV) is generated in the secondary winding 12, and a discharge current flows through a path indicated by a solid arrow in FIG. Discharge occurs between the discharge gaps 38. Further, the capacitor 4 is charged by the discharge current. At this time,
Ionization occurs with the combustion of the air-fuel mixture to generate ions. Here, since the capacitor 4 is charged, FIG.
The ion current flows through the path indicated by the middle dotted arrow, and the combustion of the air-fuel mixture can be confirmed by detecting the voltage generated at the resistor 7 by the generation of the ion current.

The width W _{1 of the} gap C according to the present invention will be described below.
The result of an experiment conducted on the relationship between the voltage waveform detected by the computer 6 and noise (indicated by N in FIG. 5) will be described. First, in the spark plug 3 described above, the width W _{1 of the} gap C is 0.1 mm, 0.2 m
m, 0.3mm, 0.4mm, 0.5mm, 0.6m
m, 0.7 mm, and 0.9 mm were prepared. In addition,
The width W ₂ in the radial direction of the stepped portion 32b is set to 1.1 mm, by changing the radial length of the projecting portion 313 of the mounting bracket 31, to form the above-mentioned dimensions of the spark plug 3, respectively.

Then, these spark plugs 3
The voltage generated in the resistor 7 when the cylinder was provided in an internal combustion engine of a 1800 cc vehicle and the throttle was fully closed (750 rotations) was detected by the ion current detection device 10 for 500 cycles. Then, the voltage waveform in which the occurrence of noise is confirmed even in one place is counted as the voltage waveform in which the noise has occurred, and the ratio of the voltage waveform in which the noise has occurred in the 500-cycle voltage waveform is expressed as the noise generation rate (%). ) To obtain the graph shown in FIG.

As a result, as can be seen from the above graph,
Width W of gap C₁With a spark plug 3 of 0.4mm or less
Means that the noise generation rate (%) is about 20% to 30%
The width W of the gap C₁Is 0.5 mm or more,
Noise generation rate is less than 5%, greatly reducing noise generation
It can be confirmed that it can be suppressed. Also, the width W of the gap C ₁
Is 0.6 mm or more, the noise generation rate is 0%.
It can be confirmed that generation of noise can be prevented.

In the above-described embodiment, the space where a corona discharge occurs is eliminated by a method of filling the gap C with a packing 36 made of iron or copper, and the noise N is reduced.
Although it is conceivable to prevent the occurrence of (see FIG. 5), in this method, a conductive packing 3 such as iron or copper is used.
There is a risk that the distance between the discharge gap 6 and the discharge gap 38 becomes short, and spark discharge is short-circuited to the packing 36.
On the other hand, according to the above embodiment, such a fear does not occur at all.

(Other Embodiments) In the above embodiment, the cross-sectional shape of the protrusion 313 is substantially trapezoidal.
The cross-sectional shape of 3 may be substantially triangular. According to this,
Thus, the radial width of the gap C can be increased, the concentration of the electric field in the gap C can be further suppressed, and the occurrence of corona discharge can be further suppressed.

In the above embodiment, the mounting bracket 3
By making the shape of the one protrusion 313 not a square shape but a rounded shape, this protrusion 313 is formed.
The concentration of the electric field formed in the nearby gap C can be further suppressed.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a spark plug according to a first embodiment and a prior art.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is a circuit diagram of the ion current detection device of the present embodiment.

FIG. 4 is a graph showing a relationship between a radial width W ₁ of a gap between a protrusion of a mounting bracket and a small diameter portion of an insulator, and a noise generation rate.

FIG. 5 is a graph showing a detection waveform of an ion current in the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 3 ... Spark plug, 31 ... Mounting bracket, 313 ... Projection part, 32 ... Insulator, 324 ... Small diameter part, 32b ... Stepped part,
33: center electrode, 35: ground electrode, 38: discharge gap, C: gap.

Claims (3)

[Claims] 1. A cylindrical mounting bracket (31), and both ends (321, 322) of said mounting bracket (31).
The cylindrical insulator (3) held inside the mounting bracket (31) so as to be exposed from both ends (311 and 312) of the cylindrical insulator (3).
2) a center electrode (33) held inside the insulator (32) so that one end (331) thereof is exposed from one end (321) of the insulator (32); A ground electrode (35) fixed to the one end (311) of the metal fitting (31) and facing the one end (331) of the center electrode (33) via a discharge gap (38).
An ion current detection spark plug used in an ion current detection device that detects an ion current flowing through the discharge gap (38), wherein the spark plug is provided on the one end (321) side of the insulator (32). A stepped portion (32b) is formed on the outer peripheral portion so as to form a small-diameter portion (324) closer to the one end (321) than this portion.
Is formed in a portion of the mounting bracket (31) near the stepped portion (32b) in a radial direction from this portion toward the small-diameter portion (324) of the insulator (32). And a protrusion (313) that is disposed so as to overlap with the stepped portion (32b) in the axial direction, and is formed between the protrusion (313) of the mounting bracket (31) and the insulating member. A gap (C) having a radial width (W ₁ ) of 0.5 mm or more is formed between the small-diameter portion (324) of the body (32) and the protrusion of the mounting bracket (31). The overlap (W ₃ ) in the axial direction between the portion (313) and the stepped portion (32b) is set to be 30% or more of the radial width (W ₂ ) of the stepped portion (32b). , the ion current detection, characterized in that the maximum width (W ₁₎ of the gap (C) is set Spark plug. 2. The width (W ₁ ) of the gap (C) is:
The spark plug for detecting an ion current according to claim 1, wherein the spark plug is at least 0.6 mm. 3. A spark plug (3) for detecting an ionic current according to claim 1 or 2, and a voltage supply means (1, 2, 8) for supplying a high voltage to the spark plug (3) for detecting an ionic current. Ion current detection means (4, 6, 7) for detecting an ion current flowing in the discharge gap (38) of the ion current detection spark plug (3). apparatus.