JP2953227B2 - Spark plug for internal combustion engine - Google Patents

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 an insulator shape 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 called for from the viewpoint of environmental problems and global resources, and fuel consumption is being reduced. As means for achieving this, high compression, lean burn with a lean air-fuel mixture, and the like are performed. However, by increasing the compression and lean burn of the internal combustion engine, it is necessary to increase the spark voltage of the spark plug. However, as the sparking voltage rises, the potential gradient becomes steep due to the sharp corners between the insulator provided on the inner surface of the housing and having the sharp corners and the insulator. for that reason,
Insulators corresponding to the sharp corners have insufficient electrical insulation strength, pinholes for short-circuiting the housing and the center electrode are formed, and a problem of electrical breakdown occurs. If electrical breakdown occurs, sparks will occur between the center electrode and the housing via the insulator, and sparks in the spark gap cannot be expected. Directly connected to

[0003] For this reason, conventionally, there has been devised a method for improving the electrical insulation strength of an insulator. For example,
Japanese Patent Application Laid-Open No. Sho 60-14781 discloses that a step portion having an acute corner portion provided on an inner surface of a housing for fixing an insulator is removed to change the shape of the step portion into a smooth round shape. This makes it possible to suppress the occurrence of corona concentrated on this portion and to avoid the occurrence of pinholes.

[0004]

However, in the above-described conventional device, the occurrence of corona is greatly affected not only in the shape but also in the surface condition. For example, in the above method, when processing burrs are present on the surface of the shape, it is difficult to suppress the generation of pinholes due to the corona concentration at the processing burrs. Therefore, it is necessary to control the surface roughness in addition to the shape of the step. However, since this step is on the inner surface of the housing and it is difficult to confirm the management of the surface roughness, the quality is varied.

Accordingly, the present invention has been made in view of the above-mentioned problems, and focuses on an insulator which is easy to confirm on the surface of the insulator. The quality of the insulator is easily controlled and the electric insulation strength is improved. A spark plug for an internal combustion engine is provided.

[0006]

According to the present invention, there is provided an insulator in which a mother body and a leg are integrally formed via a step, a center electrode included in the insulator, and an outer periphery of the insulator. a housing provided, provided in the housing, said in
By facing the core electrode, discharge gap
A ground electrode forming a pump, provided inside the housing and in contact with the step of the insulator;
Opposed to the leg supporting the insulator via a gap
A protruding step having a corner, and
The insulator facing the corner provided on the combustion chamber side
The thickness of the leg has an insulator leg base having at least the thickness of the leg at the joint between the step and the leg of the insulator, and the insulator leg base has a thickness closer to the combustion chamber.
End faces the corner of the step portion on the combustion chamber side.
From the position of the legs of the insulator to the combustion chamber side.
A spark plug for an internal combustion engine, wherein the spark plug is set within 3.0 mm .

[0007]

According to the present invention, the shape of the legs of the insulator facing the corners of the steps of the housing is set to be greater than the thickness of the joint between the steps and the legs of the insulator, Insulator
The lower end of the base of the child leg faces the combustion chamber side corner of the step.
It was set within 3.0 mm from the leg position to the combustion chamber side.
Thus, the electrical insulation strength of the insulator legs facing the corners of the step is improved, and the occurrence of pinholes is suppressed.

[0008]

As described above, according to the present invention, the electrical insulation strength can be improved by providing the insulator leg base on the insulator leg facing the corner of the step portion of the housing. Has an excellent effect.

In addition, since only the shape of the insulator legs needs to be changed, it is easy to confirm the surface of the insulator, and there is also an excellent effect that the quality is improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in the drawings. FIG. 1 is a sectional view of a spark plug for an internal combustion engine according to the present invention.

Reference numeral 1 denotes an insulator made of alumina porcelain. In the insulator 1, a leg 1a exposed to a combustion chamber (not shown) is formed integrally with a base 1c via a tapered step 1b. Further, a shaft hole 1d is provided in the axial direction, and a center electrode 2 made of a nickel-based alloy is included in 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 provided.
Is electrically connected to the center shaft 5 made of carbon steel. Reference numeral 3 denotes a cylindrical housing made of a heat-resistant and corrosion-resistant metal. The insulator 1 is fixed inside 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 the internal combustion engine, a ground electrode 8 made of a nickel-based alloy is provided, and a discharge gap G is formed with one end 2a of the center electrode 2. doing.

FIG. 2 shows a main part according to the present invention. Reference numeral 3c denotes a ring-shaped housing step provided inside the housing 3, and this housing step 3c
The insulator 1 supports the insulator 1 inside the housing 3 by contacting with the step 1b of the insulator 1 via the ring-shaped airtight packing 6. Here, the combustion chamber side corner 3b and the inner peripheral surface 3d of the housing step 3c face the insulator leg base 1e via a gap. The lower end 1f of the insulator leg base 1e is connected to the housing step 3
c is provided at the same position with respect to the corner 3b on the combustion chamber side. The insulator leg base 1e is connected to the insulator 1g at the joint 1g between the insulator leg 1a and the step 1b.
Is substantially the same as the thickness D2 of the insulator 1 at the lower end 1f of the insulator leg base 1e. Therefore, the insulator leg 1a of the present embodiment includes:
This means that the cylindrical insulator leg bases 1e having the same thickness are formed.

Next, the operation of the above configuration will be described. When a high voltage is applied to the spark plug having the above-described configuration, the gap between the corner 3b of the housing step 3c and the insulator leg base 1e facing the corner 3b has a steep potential gradient. Invite concentration. However, the spark plug of the present invention has a steep potential gradient,
By providing an insulator leg base 1e capable of improving the electric insulation strength at a location where the corona is concentrated,
The occurrence of pinholes is suppressed.

Referring to FIG. 3, the effect of the spark plug according to the first embodiment of the present invention will be described. The vertical axis is the insulator leg base 1
The breakdown voltage 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 this embodiment, a spark plug in which the lower end 1f of the insulator leg base 1e is changed is used. At this time, when the position facing the corner 3b of the housing step 3c is set to 0 mm as a reference, the lower end portion 1f sets the combustion chamber side to +
0.5mm, + 1.0mm, + 1.5mm, + 2.0mm, +
2.5 mm, +3.0 mm and +3.5 mm, and -0.5 mm on the side opposite to the combustion chamber side. A conventional spark plug having a tapered insulator leg is used as the internal combustion engine spark plug. The dimensions of the housing step 3c and the diameter of the center electrode were the same as those of the comparative example. The evaluation was 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,
The breakdown voltage at which a pinhole is generated in the insulator leg facing the corner 3b of the insulator is defined as the electric insulation strength.

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

Also, the effect is that the lower end 1f has a corner 3b.
+3.0 mm from the position opposite to the combustion chamber to the combustion chamber side, after which the effect is not so high. Regarding the cause, as a result of observing a large number of spark plugs with pinholes, all pinholes were generated up to +3.0 mm. Therefore, pinholes were generated even if the lower end 1f was set to +3.0 mm or more. This is because they are not very involved in suppressing

That is, in order to improve the electric insulation strength, the lower end portion 1f of the insulator leg base 1e is connected to the housing stepped portion 3e.
+3.0 mm from the position facing the corner 3b of c to the combustion chamber side
Has been found to be desirable.

Next, the effect of providing the insulator leg base 1e on the leg 1a of the insulator 1 on other characteristics, particularly,
Evaluation was made based on the acceleration performance of low-temperature smoking. Here, low-temperature smoldering generates carbon due to incomplete combustion due to deterioration of atomization due to a rich mixture and low temperature. Carbon has conductivity and adheres to the entire surface of the insulator leg, causing high-voltage leakage. For this reason, sparks sporadically occur between the housing and the insulator legs together with the sparks in the spark gap. A spark between the housing and the legs of the insulator (hereinafter referred to as an inner spark) causes a combustion delay or misfire, which causes acceleration failure.

FIG. 4 shows the results of the time from the idling to the rapid acceleration to 2000 rpm in the above-described smoked plug of the sample. When the lower end 1f of the insulator leg base 1e is moved toward the combustion chamber with respect to the corner 3b of the housing step 3c, if it is larger than +1.5 mm, the acceleration performance is deteriorated due to deep sparks. This is because the lower end portion 1f of the insulator leg base 1e moves toward the combustion chamber, so that the narrowed space formed between the insulator leg base 1e and the inner surface of the housing 3 extends toward the combustion chamber. This has caused the carbon to accumulate more easily.
Accordingly, the deterioration of the acceleration performance due to the backfire is caused by the lower end portion 1e of the insulator leg base 1e with respect to the corner portion 3b of the step portion 3c.
If f is equal to or less than +1.5 mm, the effect is negligible.

Therefore, from the viewpoint of the effect of improving the electric insulation strength, the lower end portion 1f of the insulator leg base 1e is connected to the housing step 3
+3.0 mm from the position facing the corner 3b of c to the combustion chamber side
However, in consideration of the acceleration performance at the time of smoking, it has been found that it is preferable that the thickness be 0 to +1.5 mm.

Further, in the embodiment of the present invention, the lower end 1f of the insulator leg base 1e is connected to the corner 3b of the housing step 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 located within +3.0 mm of the combustion chamber side. What is necessary is just to be provided in the 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
Although the thickness is approximately the same as the thickness D1 of the insulator 1 at the joint 1g, the present invention is not limited to this.
D2 may be thicker than D1.

[Brief description of the drawings]

FIG. 1 is a half 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 electric insulation strength with respect to the shape range of the insulator leg base of the present invention.

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

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

[Description of Signs] 1 Insulator 1e Insulator leg base 2 Center electrode 3 Housing 3c Stepped portion 8 Ground electrode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-278684 (JP, A) JP-A-3-1474 (JP, A) Fully open 55-133587 (JP, U) Fully open 61 14490 (JP, U) Japanese Utility Model Showa 57-104481 (JP, U) Japanese Utility Model Showa 60-98290 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01T 13/20 H01T 13 / 36

Claims (1)

(57) [Claims] An insulator integrally formed with a base and legs via a step; a center electrode included in the insulator; a housing provided on an outer periphery of the insulator; and the housing. And is opposed to the center electrode.
Accordingly, a ground electrode forming a spark gap in the combustion chamber, provided inside the housing, the said insulator
The abutment with the step portion, which supports the insulator
A protruding shape having corners facing the legs and the gap
A step portion and a corner portion of the corner portion provided on the combustion chamber side.
That the thickness of the leg portion of the insulator has a insulator foot base having at least the thickness of the leg at the junction between the stepped portion and the leg portion of the insulator, the insulator leg base The end on the combustion chamber side of the
In front of the insulator facing the corner on the combustion chamber side of
Set within 3.0 mm from the position of the legs to the combustion chamber side
A spark plug for an internal combustion engine, comprising: