JPH03257780A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent a treeing deterioration and a reduction of insulation by covering a part or the whole area of the position where an insulator and a main body metal are approached, with a semiconductor membrane belt. CONSTITUTION:This spark plug is composed of an insulator 2 which holds an ignition electrode 3 at the tip and consists of a nitride ceramics, and a main body metal 4 furnishing an outside electrode 5 arranged opposite to the ignition electrode 3, and a part or the whole area of the surface 6' of the position of the insulator 2 where the insulator 2 and the main body metal 4 are approached is covered by a semiconductor membrane belt 7. As a result, even though a spark discharge is carried out from the ignition electrode 3, the electric field by the spark discharge is strong enough, and a concentration of electric field following the spark discharge can be disturbed by covering the surface 6' of the position where a corona discharge is liable to generate with the semiconductor membrane belt 7, and the dissolution reaction of the insulator 2 generated by the corona discharge is suppressed. Consequently, a treeing deterioration by the electric field concentration is prevented, and the insulation property of the insulator 2 can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) This invention relates to an insulator for spark plaque used in internal combustion engines.

(Prior art) Conventionally, the insulator of spark plugs used in internal combustion engines is generally made of ceramic such as alumina in order to maintain insulation properties, but as internal combustion engines become more compressible, Insulators protruding into the combustion chamber are required to have higher thermal shock mechanical strength, so insulators made of nitrides have come to be used.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional device, if the insulator is made of ceramic made of nitride, it is installed between the internal combustion engine and the ignition part electrode and the outer electrode in the combustion chamber. When spark discharge occurs, there is a region where the electric field is strong and corona discharge is likely to occur in a region where the insulator and the metal shell are close to each other. In particular, corona discharge tends to occur near the packing surface, and this large amount of corona discharge causes the following decomposition reaction in the nitride insulator.

S 13N4-+3S i +2N2↑(gas)2A
IN →2AI+ N,, ↑(gas) Metal S1 or AI produced as a result of this decomposition reaction is generated on the insulator surface,
It will accumulate. At this time, the metal Si or Al that is generated and deposited on the insulator surface induces concentration of electric field on the insulator surface due to the presence of the electrode placed in the rear direction, and further decomposes the nitride ceramic that constitutes the insulator. This causes dendritic marks, that is, tree ink deterioration, along the direction of the electric field toward the ignition center electrode, accompanied by thinning.

Deterioration of the tree ink that occurs on the surface of the insulator and metals (for example, S
] or AI) connects with the surface of the metal shell, resulting in a decrease in the insulation properties of the insulator, which has the disadvantage of causing a misfire.

Therefore, the present invention is intended to improve the above-mentioned drawbacks of the conventional method, and is intended to prevent tree ink deterioration due to concentration of electric fields and ensure the insulation properties of the insulator.

(Means for Solving the Problem) To this end, the insulator is made of nitride, and a part or the entire surface of the insulator and the part of the insulator adjacent to the metal shell is covered with a semiconductor coating band (in particular, a semiconductor coating band). The surface resistance value of the band is 10 to 5000MΩ・C1n, and the material is 600MΩ・C1n.
Materials that are stable in the temperature range of °C, such as SnO,...S
(consisting of iC, NiO, etc.), and the gap (L) in the area close to the insulator and the metal shell is roughly O<
1 <2mm, or the nitride constituting the insulator is S
It shall consist of i3N4゜A I N, Sialon, etc.

(Function) With the above configuration, even if it is installed in an internal combustion engine and spark discharge is performed, the surface resistance value can be reduced by 10 to 10% on a part or the entire area of the insulator surface where the insulator and the metal shell are close to each other. 5
000MΩ・cm, and the material is made of a material that is stable in the temperature range of 600℃, such as SnO2, SjC, NiO, etc., and is covered with a semiconductor film band, so that it will not be affected by the heat generated in the combustion chamber. Moreover, since the semiconductor film band covering the surface of the insulator has a resistance value of IOMΩ・Cfn or more, it prevents the discharge of the ignition part electrode due to flashover from being obstructed, and the resistance value is 5000MΩ・cm or less. Since the surface resistance value does not approximate the surface resistance value of an insulator, electric field concentration can be reliably prevented, so that reliable spark discharge can be performed.

(Example) This invention will be further explained with reference to embodiments shown in the drawings.

(1) is a spark plug for internal combustion engine WrIrI which is an embodiment of this invention.
1) holds a firing part electrode (3) at the tip, and an insulator (2) made of nitride ceramic (for example, Si3N, AIN, Sialon, etc.) faces the firing part electrode (3). It consists of a metal shell (4) on which an outer electrode (5) is arranged.

and an insulator (2) with a firing part electrode (3) at its tip.
At the surface (6) of the insulator (2) and the metal shell (
4) close to [gap interval (L) is o<L<2mm]
A part or the entire surface (6゛) of the insulator (2) (indicated by the t4 line) is covered with a material that is thermally stable up to about 600°C, such as St]02, SiC, NiO, Zn
O, VO2, TiO2, sb, , o3, Cu2O, Ca
b, Coo, MnO, PbTiO2, BaTiO3,5
It is coated with a semiconductor coating band (7) made of rTiOt or the like, and the surface resistance value of this semiconductor coating band (7) is 10 to 5000 MΩ·cm.

Since this invention has the above configuration, even if it is attached to an internal combustion engine and a spark discharge is performed from the ignition part electrode (3), the electric field due to the spark discharge is strong and the insulator (2) is likely to cause corona discharge. ) and a part or entire area (shown by diagonal lines) of the surface (6') of the part of the insulator (2) that is close to the metal shell (4), especially where the metal shell (4) and the insulator (2) are close to each other. The electric field is strongly concentrated on the surface (6') of the part (where the gap distance (L) is O<L<2 mm), and the surface (6') of this part is covered with the semiconductor coating band (7). This prevents the concentration of electric field associated with spark discharge, suppresses the decomposition reaction of the insulator (2) made of nitride ceramic generated by corona discharge, and reduces the decomposition reaction of the insulator (2) caused by metal precipitation (dendritic marks). It is possible to prevent the deterioration of the insulation properties of the

In addition, when the surface resistance value of the semiconductor coating band (7) covering the surface (6') of the portion where the metal shell (4) and the insulator (2) are close to each other is 10 to 5000 MΩ''C1n, the value is 10
If it is less than MΩ, flashover will occur due to the semiconductor film band (7) covering the surface of the insulator (2),
It becomes impossible to secure a discharge voltage necessary for spark discharge between the ignition part electrode (3) and the outer electrode (5) disposed at a position facing each other, resulting in a misfire or the like.

On the other hand, the surface resistance value of the semiconductor coating band (7) was set to 5000MΩ・
cm or more, the properties of the semiconductor film band (7) approach those of the insulator (2), making it impossible to prevent the concentration of electric field accompanying spark discharge, and preventing metal precipitation (density) due to corona discharge. This results in the occurrence of scratches, treeing deterioration).

Further, the material of the semiconductor coating band (7) is
) The tip of the insulator (2) covered by the insulator (2) protrudes into the combustion chamber and is exposed to high-temperature combustion gas due to spark discharge generated within the combustion chamber, so it is a material that remains stable up to about 600℃. is preferred.

Therefore, the embodiment of this invention should be installed on the actual machine after operation (5
000rprnX%11.0. T50 h r ), and traces of treeing deterioration on the surface of the insulator (2) were observed.

In addition, the spark plug for internal combustion engine (1) installed in the actual machine
In the semiconductor film band (7) covering the surface of the insulator (2) made of nitride ceramic, 1 to 10% of 5
l) 203 is added to SnO2, an inorganic binder is added to the finely pulverized semiconductor powder after pre-firing, and various shapes [Fig. Gap (L) inside = 1.5 mm, L2 = 1.
8mm, L3=2.0mm, L4=2.2mm,
L 5 = 3.0 mm] was coated on the surface of the insulator (2) and further baked at 800°C for 1 hour (No. 1 to 5.7), 5iC (average particle size 1 .5
μm) with an appropriate amount of inorganic binder added, applied to the surface of the insulator (2) in various shapes, and then baked at 800°C for 1 hour (No. 6.9), and TlO2
, CoO2, BaTiO2 (No. 7)
．． 8) (Table).

As a result of the experiment, as shown in the table, it was found that all of the examples of the present invention can reliably and sufficiently suppress treeing deterioration.

(Effect of the invention) As described above, by covering part or the entire area of the insulator and the metal shell in close proximity with the semiconductor coating band,
It prevents the concentration of electric field caused by spark discharge and prevents treeing deterioration, which prevents deterioration of the insulation properties of nitride ceramics and prevents problems such as misfires when used on internal combustion 41I leapfrogs. It has an excellent effect of preventing

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view of a spark plug for an internal combustion engine which is an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of the main part thereof, and FIG.
Figures (A) to (E) are partially enlarged views showing the state of coating with the semiconductor coating band in the example, and Figure (F) is a conventional spark for internal combustion engine, which is a comparative example compared with the example in an actual machine test. FIG. 3 is a partially enlarged view of the plug. l...Spark plug for internal combustion engine 2...Insulator 3
...Ignition part electrode 4...Metal shell 5...Outer electrode diagram

Claims (4)

[Claims] (1). 1. A spark plug for an internal combustion engine, in which an insulator is made of nitride, and a part or the entire surface of a portion of the insulator adjacent to the insulator and the metal shell is covered with a semiconductor coating band. (2). Gap between the insulator and the metal shell (L)
The spark plug for an internal combustion engine according to claim 1, wherein 0<1<2 mm. (3). Nitride constituting the insulator is Si_3N_4, A
Claim (1).
Or (2). Spark plug for the internal combustion engine described. (4). Claim (1) wherein the surface resistance value of the semiconductor film band covering the surface of the insulator is 10 to 5000 MΩ·cm.
). ,(2). Or (3). , a spark plug for an internal combustion engine. (5). Claim (1): The material of the semiconductor coating band covering the surface of the insulator is a material that is stable in a temperature range of 600°C, such as SnO_2, SiC, NiO, etc. ,(2). ,(3). Or (4). Spark plug for the internal combustion engine described.