JPH06196247A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a spark plug for an internal combustion engine improving the withstand voltage. CONSTITUTION:The leg section 1a of an insulator 1 exposed in a combustion chamber is formed integrally with the main body 1 via a step section 1b. An insulator leg base section 1e facing a step section 3c provided on the inside of a housing 3 via a gap is provided on the leg section 1a of the insulator 1. The lower end section 1f of the insulator leg base section 1e is formed to the same thickness as the thickness of the insulator 1 at the junction section 1g with the step section 1b, and it is formed into a cylindrical shape. The insulator leg base section 1e is formed at the leg section 1a of the insulator 1, and the thickness of the insulator 1 facing the step section 3c is made thicker than that of the tapered leg section of a conventional insulator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for an internal combustion engine, and more particularly to a spark plug for an internal combustion engine having the shape of an insulator capable of withstanding a high voltage.

[0002]

2. Description of the Related Art In internal combustion engines currently used in automobiles and the like, further energy saving is demanded from the viewpoints of environmental problems and global resources, and fuel consumption is being reduced. As a means for this, high compression, lean burn with a lean air-fuel mixture and the like are performed. However, the ignition voltage of the spark plug must be improved by increasing the compression and lean burn the internal combustion engine. However, as the flying voltage rises, the sharp corner causes a sharp potential gradient between the insulator provided on the inner surface of the housing and having a sharp corner. for that reason,
At the portion of the insulator corresponding to this acute corner, the electrical insulation strength becomes insufficient, and a pinhole that short-circuits the housing and the center electrode is formed, causing a problem of electrical breakdown. When electrical breakdown is reached, a spark is generated between the center electrode and the housing through the insulator, and a spark in the spark gap cannot be expected, resulting in a mistake in ignition of the air-fuel mixture and a malfunction of the internal combustion engine. Directly connected to.

Therefore, there have been conventionally devised methods for improving the electric insulation resistance of the insulator. For example,
Japanese Unexamined Patent Publication No. 60-14781 discloses a stepped portion having an acute-angled corner portion provided on the inner surface of a housing for fixing an insulator, and the corner portion of the stepped portion is removed to change to a smooth round system. As a result, it is possible to suppress the generation of corona concentrated in this portion and avoid the generation of pinholes.

[0004]

However, in the above-mentioned prior art, the generation of corona is greatly affected not only by the shape but also by the surface condition thereof. For example, in the above method, when a machining burr exists on the surface of the shape, it is difficult to suppress the generation of pinholes due to corona concentration at the machining burr. Therefore, it is necessary to manage not only the shape of the step portion but also the surface roughness thereof. However, this step portion is on the inner surface of the housing, and it is difficult to check the control of the surface roughness, so that the quality varies.

Therefore, the present invention has been made in view of the above problems. Focusing on an insulator whose surface can be easily confirmed, the quality control is easy and the electric insulation strength is improved. A spark plug for an internal combustion engine is provided.

[0006]

According to the present invention, an insulator is formed by integrally forming a mother body and legs through a step, a center electrode contained in the insulator, and an outer periphery of the insulator. A housing provided, a ground electrode that is provided in the housing and forms a discharge gap with the center electrode, and a corner that is provided inside the housing and that faces the leg portion with a gap, A protruding step portion that abuts the step portion of the insulator and supports the insulator, and a leg portion of the insulator facing the corner portion, at a joint portion between the step portion and the leg portion. A spark plug for an internal combustion engine, comprising an insulator leg base having at least the wall thickness of the leg.

[0007]

In the present invention, the shape of the insulator leg portion facing the corner portion of the stepped portion of the housing is set to be equal to or larger than the wall thickness at the joint portion between the step portion and the leg portion of the insulator, The electrical insulation strength of the insulator legs facing the corners of the step is improved and pinholes are suppressed.

[0008]

As described above, according to the present invention, by providing the porcelain insulator leg base portion on the porcelain insulator leg portion facing the corner of the stepped portion of the housing, it is possible to improve the electric insulation strength. It has an excellent effect.

Further, since it is only necessary to change the shape of the porcelain insulator legs, it is easy to check the surface of the porcelain insulator, and there is an excellent effect that the quality is improved.

[0010]

The present invention will be described below based on the embodiments shown in the drawings. FIG. 1 is a sectional view of a spark plug for an internal combustion engine of the present invention.

Reference numeral 1 is an insulator made of alumina porcelain. In this insulator 1, a leg portion 1a exposed to a combustion chamber (not shown) is integrally formed with a mother body 1c via a taper-shaped step portion 1b. Further, a shaft hole 1d is provided in the axial direction, a center electrode 2 made of a nickel alloy is included on the combustion chamber side of the shaft hole 1d, and one end 2a thereof is exposed to the combustion chamber. On the other end 2b of the center electrode 2, a conductive glass seal layer 4 made of copper powder and low melting point glass is formed.
Is electrically connected to the center shaft 5 made of carbon steel. A cylindrical housing 3 is made of heat-resistant and corrosion-resistant metal, and the insulator 1 is fixed to the inside of the housing 3 via a ring-shaped hermetic packing 6 and a caulking ring 7. The housing 3 is provided with a screw portion 3a for fixing to a cylinder block of an internal combustion engine, and a ground electrode 8 made of a nickel-based alloy is provided, and a discharge gap G is formed with the one end 2a of the center electrode 2. is doing.

Here, FIG. 2 shows an essential part of the present invention. Reference numeral 3c denotes a ring-shaped housing step portion provided inside the housing 3, and this housing step portion 3c
Supports the insulator 1 inside the housing 3 by contacting the step portion 1b of the insulator 1 via the ring-shaped airtight packing 6. Here, the corner portion 3b on the combustion chamber side and the inner peripheral surface 3d of the housing step portion 3c face the insulator leg base portion 1e with a gap therebetween. Further, the lower end portion 1f of the insulator leg base portion 1e is provided with the housing step portion 3
It is provided at the same position with respect to the corner portion 3b on the combustion chamber side of c. The insulator foot base 1e is the insulator 1 at the joint 1g between the insulator leg 1a and the step 1b.
D1 and the thickness D2 of the insulator 1 at the lower end 1f of the insulator leg base 1e are substantially the same. Therefore, the insulator leg portion 1a of the present embodiment is
The cylindrical insulator leg base 1e having the same wall thickness is formed.

Next, the operation of the above configuration will be described. When a high voltage is applied to the spark plug having the above configuration, the potential gradient becomes steep in the gap between the corner portion 3b of the housing step portion 3c and the insulator leg base portion 1e facing the corner portion 3b, and local space destruction causes corona damage. Invites concentration. However, the spark plug of the present invention has a steep potential gradient,
By providing the insulator leg base 1e capable of improving the electrical insulation strength at the location where the corona is concentrated,
It suppresses the occurrence of pinholes.

The effect of the spark plug of the first embodiment of the present invention will be described with reference to FIG. The vertical axis is the insulator leg base 1
The breakdown voltage value at which a pinhole is formed at e, and the horizontal axis indicates the position of the lower end 1f of the insulator leg base 1e. As the spark plug of the present embodiment, a spark plug in which the lower end 1f of the insulator leg base 1e is changed is used. At this time, the lower end portion 1f has a positive side on the combustion chamber side when the position facing the corner portion 3b of the housing step portion 3c is set to 0 mm as a reference.
0.5mm, + 1.0mm, + 1.5mm, + 2.0mm, +
The thickness was 2.5 mm, +3.0 mm, and +3.5 mm, and the side opposite to the combustion chamber side was -0.5 mm. Further, as the spark plug of the conventional internal combustion engine, the one having the tapered insulator legs is adopted. The dimensions of the housing step portion 3c and the center electrode diameter were the same as those of the comparative example. The evaluation is performed by applying a high voltage to the spark plug while insulating the spark gap between the center electrode 2 and the ground electrode 8 and by changing the housing step 3c.
The breakdown voltage at which pinholes were generated in the insulator legs facing the corners 3b was defined as the electric insulation strength.

As a result, the lower end portion 1 of the insulator leg base portion 1e.
f is the corner 3 of the housing step 3c where corona is concentrated
It is necessary to at least face b in order to improve the electric strength.

Further, the effect is that the lower end portion 1f has a corner portion 3b.
The maximum value is +3.0 mm from the position facing to the combustion chamber side, and after that the effect does not increase so much. Regarding this cause, as a result of observing many spark plugs with pinholes, all pinholes were generated up to +3.0 mm, so even if the lower end 1f was set to +3.0 mm or more, pinholes were generated. This is because they are not much involved in suppressing

That is, in improving the electric insulation strength, the lower end portion 1f of the insulator leg base portion 1e is provided with the housing step portion 3a.
+3.0 mm from the position facing the corner 3b of c to the combustion chamber side
It has been found that is desirable.

Next, the influence on other characteristics by providing the insulator leg base 1e on the leg 1a of the insulator 1, particularly,
It was evaluated by the acceleration performance in low temperature smoke. Here, low-temperature smoldering means that carbon is generated due to incomplete combustion due to deterioration of atomization due to a rich air-fuel mixture and low temperature. Carbon has conductivity and adheres to the entire surface of the insulator leg portion, causing high voltage leakage. For this reason, a spark is sporadically generated between the housing and the insulator leg portion together with a spark in the spark gap. Flying between the housing and the insulator legs (hereinafter referred to as back flying) causes combustion delay and misfire, which causes poor acceleration.

FIG. 4 shows the result of the time from the idling to the rapid acceleration up to 2000 rpm in the above-mentioned smoldering plug of the sample. When the lower end portion 1f of the insulator leg base portion 1e is moved toward the combustion chamber side with respect to the corner portion 3b of the housing step portion 3c, the acceleration performance is deteriorated due to the backfire when it is larger than +1.5 mm. This is because the lower end 1f of the insulator leg base 1e moves to the combustion chamber side, so that the narrowed space formed between the insulator leg base 1e and the inner surface of the housing 3 extends to the combustion chamber side. This is because the carbon has become easier to accumulate.
Therefore, the deterioration of the acceleration performance due to the backfire is caused by the lower end 1 of the insulator leg base 1e with respect to the corner 3b of the step 3c.
If f is +1.5 mm or less, the effect is slight.

Therefore, from the effect of improving the electric insulation strength, the lower end portion 1f of the insulator leg base portion 1e is replaced by the housing step portion 3a.
+3.0 mm from the position facing the corner 3b of c to the combustion chamber side
However, it was found that 0 to +1.5 mm is preferable in consideration of the acceleration performance during smoking.

Further, in the embodiment of the present invention, the lower end portion 1f of the insulator leg base portion 1e is a corner portion 3b of the housing step portion 3c.
However, the present invention is not limited to this, and as shown in FIG. 5, the lower end 1f of the insulator leg base 1e is within +3.0 mm on the combustion chamber side. It should be provided at a distance.

Further, in the embodiment of the present invention, the thickness D2 of the insulator 1 at the lower end 1f of the insulator leg base 1e is
The thickness is almost the same as the thickness D1 of the insulator 1 at the joint portion 1g, but the present invention is not limited to this.
D2 may be thicker than D1.

[Brief description of drawings]

FIG. 1 is a half cross-sectional view showing a spark plug for an internal combustion engine according to the present invention.

FIG. 2 is a half sectional view showing a main part according to the present invention.

FIG. 3 is a relationship diagram showing a change in electrical insulation strength with respect to a shape range of an insulator leg base of the present invention.

FIG. 4 is a relationship diagram showing changes in arrival time during acceleration with respect to the shape range of the insulator leg base of the present invention in low temperature smoldering.

FIG. 5 is a half sectional view showing another embodiment of the present invention.

[Explanation of symbols]

 1 Insulator 1e Insulator leg base 2 Center electrode 3 Housing 3c Step 8 Ground electrode

Claims (2)

[Claims] 1. A ceramic insulator integrally formed with a mother body and legs via a step, a center electrode contained in the ceramic insulator, a housing provided on the outer periphery of the ceramic insulator, and the housing. A ground electrode that forms a discharge gap with the center electrode, a corner portion that is provided inside the housing and that faces the leg portion with a gap, and the step portion of the insulator. A protruding step portion that abuts and supports the insulator, and a leg portion of the insulator facing the corner portion has at least a wall thickness of the leg portion at a joint portion between the step portion and the leg portion. A spark plug for an internal combustion engine having an insulator leg base having the spark plug. 2. The lower end of the insulator leg base is set within 3.0 mm on the combustion chamber side from the position of the leg of the insulator facing the corner of the step. The spark plug for an internal combustion engine according to claim 1.