JPS6014781A - Ignition plug for internal combustion engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark plug (hereinafter referred to as "plug") for an internal combustion engine that has an improved internal voltage.

Currently, there is a strong emphasis on fuel efficiency of vehicles. High compression LL and lean combustion are being implemented as a means to save combustion.

Along with such high compression and leanness, the required voltage of internal combustion engines is increasing. As a result, the phenomenon that the electrical dielectric strength of the plug cannot withstand the required voltage has sporadically occurred. In other words, instead of sparks flying in a normal spark gap, the voltage causes electrical breakdown in the insulator, creating a pinhole, and sparks fly to the location of the pinhole. As a result, the spark does not come into contact with the air-fuel mixture, resulting in ignition errors and, in extreme cases, the engine stalls.

The inventor of the present invention investigated the cause of this problem and found that it was caused by a stepped portion protruding from/inside the metal housing to support the insulator.

In other words, the potential gradient between the corner of the stepped portion and the local part of the insulator opposite to the corner becomes steep, leading to concentration of corona discharge, and pinpoles are generated at the legs.

The present invention has been devised in view of the above points, and aims to reduce the occurrence of bottle holes by dispersing the corona discharge.

The present invention will be explained in detail below using specific examples. 1st
In the figures, 1 is an insulator made of alumina porcelain, and a shaft hole 1a is provided in the center.

Reference numeral 2 denotes a center shaft made of carbon steel, which is inserted into the upper part of the shaft hole la of the insulator l. 3 is a cylindrical housing; 1.
The insulator 1 is fixed to the inside of the housing 3 via a ring-shaped airtight packing 4 and a caulking ring 5. A screw portion 3a is provided for fixing to the cylinder block. 6 is a center electrode;
The base metal is made of nickel-chromium (Ni-Cr) alloy or Inconel 600 (trade name).

A ground electrode 7 is made of a heat-resistant alloy such as a low chromium alloy or a high chromium alloy as the base metal, like the center electrode. 8 is a conductive glass seal layer sealed in the shaft hole 1a of the insulator l, and is made of copper powder and low melting point glass.This seal Fi8 seals the center shaft 2 and the center electrode 6.
In addition to electrically connecting the two, the two are fixed in the shaft hole 1a of the insulator 1 so that they do not move.

Incidentally, main parts according to the present invention are shown in FIG. 2.

In the figure, reference numeral 3c denotes a ring-shaped stepped portion, which is used to airtightly support the insulator 1 inside the housing 3 via the packing 4, and is formed to protrude from the inside thereof. Here, the inner diameter surface 3d of the stepped portion 3c corresponds to the leg portion 1b of the insulator 1 exposed inside the combustion chamber of the internal combustion engine.
are opposed to each other with a small gap between them. The lower end of this inner diameter surface 3d is 3b.

The upper end is 3e, and especially the lower end 3b is shaped like a tuna with a radius of at least 0.3.

The present invention is characterized in that the lower end 3b of the inner diameter surface of the stepped portion 3c is rounded in order to improve the electrical dielectric strength of the plug. Generally speaking, the place where the electrical dielectric strength of the plug is the weakest is considered to be near the upper end 3e of the inner diameter surface, and especially on the center electrode side of the packing 4. However, the actual position where the pinhole is formed due to dielectric breakdown is on the leg side 1b facing the lower end 3b of the inner diameter surface. Therefore, in order to investigate the cause of this, we took photographs of the corona discharge on three days ago and found that
It was found that the particles were concentrated at the lower end 3b of the inner diameter surface. This state is shown in FIG. 51 ((h) is not shown. Point Y in FIG. 5(b) indicates the corona discharge at the lower end 3b of the inner diameter surface.

This is a plug type W16EX-Ll, applied voltage 24K
This is an example taken with V. Furthermore, when measuring the potential at point X of the leg 1b facing the lower end surface 3b of the tip of the corona, it was found that there was almost no voltage drop. As a result, it has become clear that the lower end surface 3b of the support portion 3C has the same meaning as if it were present on the leg surface. This revealed that the potential between the lower end surface 3b of the support portion 3C and the center electrode 6 had become extremely steep. A virtual equipotential surface in this case is shown in FIG. From this, the potential gradient at point X becomes steep, and the leg 1 facing the lower end surface 3b
It was possible to see the pin pole at point X in b. Therefore, as a countermeasure to this problem, it was decided to make the potential gradient gentler in order to reduce the occurrence of corona discharge. As a means for this, it was decided to increase the radius of the lower end surface 3b as shown in the example. In addition, as a result of a thorough investigation of this R, 0,
It was confirmed that the pinhole opening voltage gradually saturated at 3R or more. The results are shown in Figure 4. The plug tested here was based on Wl 6EX-U, and in order to reduce the pinhole generation voltage and make voltage measurement easier, the outer diameter of the center electrode was increased by +1.3 am, and the insulator wall thickness was increased. We conducted an experiment by thinning ζ.

By attaching a rounded shape with a radius of 0.3" to the lower end surface 3b as shown by line A in FIG. 4, the pinball's dielectric strength level is 30 KV or more, which is a considerably high voltage region.

When I took a photo of a model W16EX-U spark plug with such a rounded radius during corona discharge, the result was as shown in Figure ff16. As can be seen from FIG. 6, the corona discharge at the lower end surface 3b of the support portion 3C of the housing 3 is weaker than that shown in FIG. 5, and does not occur excessively throughout the year.

By the way, it is known to apply a coating agent containing silicone mail as a main component to the surface of the leg portion 1b of the insulator 1 in order to prevent a misfire due to adhesion of carbon to the leg portion 1b of the insulator 1. This is shown in FIG. Reference numeral 9 is a coating agent. The withstand voltage level of a pinhole in a spark plug treated with such a coating agent deteriorates by about 20% compared to a line as shown by line B in FIG. The reason for this is that corona tends to concentrate more easily. Figure 8 shows the modeled state of corona concentration. From this, it is effective to add a radius to the lower end 3b of the inner diameter surface even when a coating agent is present.

Further, in the case of FIG. 7 in which the coating agent is held in the space of the support portion 3C, the potential gradient becomes larger than in the case without the coating agent, and the breakdown voltage decreases, as shown in FIG. 8.

Therefore, the coating agent is applied to the leg portions 2b so as not to fill the support portions 3C.
Apply only to the surface of the support part 3 as shown in figure ff19.
It is necessary to hold space in C. Note that FIG. 9 shows an example including a platinum chip 10.

FIG. 10 shows another embodiment of the invention.

As described above, according to the present invention, concentration of corona discharge can be prevented, and therefore, the chance of pinholes occurring on the leg surface can be prevented without reducing.

[Brief explanation of drawings]

FIG. 1 is a half-sectional view showing an embodiment of the present invention, FIG. 2 is a cross-sectional view showing an enlarged main part of FIG. 1, and FIGS. 3 and 4 are characteristic diagrams for explaining the present invention. , FIG. 5 (al) and FIG. 6 (al is Ill of the present invention, and 1' 4iII
lfi IJl photo, Figure 5(b) *3 and m6 figure f
bl is a schematic diagram of FIG. 5+al, FIG. 6+a), FIG. 7 is a sectional view showing a conventional example, FIG. 8 is a characteristic diagram for explaining the present invention, and FIGS. 9 and 10 are diagrams of the present invention. FIG. 7 is a sectional view showing still another embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Insulator, ■b... Leg part, 3... Housing, 3b... Lower end surface, 3C... Support part, 6... Center electrode, 7... Ground electrode. Representative patent attorney Takashi Okabe 4th illustration 0.3R0, 6RO, 9R 4' 0~0.2R Figure 7 GH451J (a) (b) Knee, 1. No. 11111 II Procedural amendment (method) l Indication of the case 1982 Patent Application No. 122781 Name of the invention Relationship to the case of a person who repaired spark plugs for internal combustion engines 3 Patent applicant 1-chome Showacho, Kariya City, Aichi Prefecture Address 1 (426) Nippondenso Co., Ltd. Representative Toda Madodai 4th Director 1-5 Showa-cho, Kariya-shi, Aichi Prefecture 448 Date of amendment order Date of dispatch October 25, 1980 6. Details subject to amendment In the column for a brief explanation of the drawings in the book, Drawing 7, contents of the amendment (11, page 8, lines 6 to 8, 1, Figure 5 ta + and... schematic diagram,) have been changed to ``Figure 5 and 6. The figure is a schematic diagram for explaining the present invention.'' (2) Figure 5 (a) of the drawing is deleted. (3) Figure 5 of the drawing (bl is revised to Figure 5 as shown in the attached sheet) (4) Delete Figure 6 (a) of the drawings. (5) Correct Figure 6 (b) of the drawings to Figure 6 as shown in the attached sheet. Figure ■ Figure 6 Procedural Amendment 1 Display of the case 1982 Patent Application No. 122781, Name of the invention Person who corrects spark plugs for internal combustion engines 3 Relationship to the case Patent applicant 1-1 Showa-cho (426), Kariya-shi, Aichi Prefecture Representative of Nippondenso Co., Ltd. Toda Madodai 4th generation Masato 1-1 Showa-cho, Kariya-shi, Aichi Prefecture 448 5 Detailed description of the invention in the specification subject to the amendment 6 Contents of the amendment 418-

Claims (1)

[Claims] It comprises an insulator, a center electrode held on a leg of the insulator that is exposed inside a combustion chamber of an internal combustion engine, a metal housing fixed to the outer periphery of the insulator, and a ground electrode provided on the housing. , inside the housing, n;
1. A spark plug for an internal combustion engine, comprising a protruding step portion supporting an insulator, and a corner portion of the step portion facing the leg portion of the insulator with a slight gap therebetween. The corner portion of the stepped portion has a radius of at least 0.
．． A spark plug for internal combustion engines characterized by a 3m round shape.