JPH0272577A - Ignition plug of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent abrasion of an electrode, by continuously equipping a bottom wall at the end of a cylindrical insulator to cover the bottom inner side of an outer electrode upto a vicinity of an orifice thereof. CONSTITUTION:A bottom wall 4a is continuously equipped at the end of an insulator 4, an outlet 7 of approximately same diameter as that of an orifice 6 is provided in the center thereof, and a discharging space 8 is produced across a gap G between a center electrode 2 and an outer electrode 5. Since a volume produced by this gap G and the discharging space 8 must be arranged at a specified level determined by a voltage and a required plasma gas generating volume, the shape of the discharging space 8 is made flat in a large diameter by projecting the bottom wall 4a of the insulator 4 and the center electrode 2 in a large diameter is employed. Therefore an electric current density in the center electrode 2 is lowered and abrasion of the discharging surface may be reduced. Thereby the abrasion of both electrodes 2 and 5 may be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spark plug used for ignition of an internal combustion engine and ignited by a plasma jet.

(Prior Art) As shown in FIG. 4, this type of spark plug generally includes a center electrode a1, an insulator, an outer electrode C, a discharge space d1 surrounded by these, and an orifice f provided at the bottom e of the outer electrode. , which has a gap G between both electrodes, and the high-temperature plasma gas generated by the discharge between the two electrodes is ejected from the orifice f to ignite the air-fuel mixture (Japanese Patent Laid-Open No. 57-1
5378).

(Problems to be Solved by the Invention) In this spark plug, electrode wear tends to occur on the center electrode side, where positive ions enter, while on the other hand, on the outer electrode side, the electrode is exposed to high temperature plasma gas and combustion gas in the cylinder. Since the fuel is heated from the ground, oxidative wear is likely to occur due to the oxygen in the air-fuel mixture.

Therefore, it is an object of the present invention to prevent such electrode wear.

(Means for Solving the Problems) A means for solving the above problems of the present invention is to interpose a cylindrical insulator between the center electrode and a bottomed cylindrical outer electrode having an orifice at the bottom, and to In a spark plug for a plasma jet internal combustion engine in which a discharge space is formed between, a special feature ( Effect) With the above configuration, if the gap between both electrodes and the volume of the discharge space are set to constant values in order to generate a constant plasma gas, the discharge space will become flat, so the cross-sectional area of the center electrode will be reduced. The inner surface of the outer electrode is covered with an insulating bottom wall, so heating from the plasma gas in the discharge space is prevented. oxidative wear of the outer electrode is also reduced.

(Example) Hereinafter, an example will be described with reference to the drawings. Figures 1 and 2
In the figure, 1 is a spark plug, 2 is a center electrode, 3 is a terminal connected to the center electrode 2, 4 is an insulator, 5 is an outer electrode, 5a
is equipped with an orifice 6 in the center at the bottom integrated with the outer electrode,
There is a gap G between the picture electrodes 2.5. A bottom wall 4a is connected to the end of the insulator 4, and a lower outlet having a diameter substantially equal to that of the orifice 6 is provided at the center thereof, and a discharge space 8 is formed between the gap G.

This gap G and the volume of the discharge space 8 must be set to constant values determined by the voltage and the required amount of plasma gas generation, so by extending the bottom wall 4a of the insulator 4, the shape of the discharge space 8 can be changed. , it is flatter and has a larger diameter than the conventional one, and a large diameter one can be used as the center electrode 2.

This lowers the current density of the center electrode 2 and reduces wear on the discharge surface.

On the other hand, since the bottom portion 5a of the outer electrode 5 is covered by the bottom wall 4a, the amount of heat received from the plasma gas in the discharge space 8 is suppressed and does not reach a high temperature. Therefore, the amount of wear of the electrode 5 due to oxidation by oxygen in the air-fuel mixture is also reduced.

The orifice 6 of the plug shown in Figure 2 has a slightly smaller diameter than the open lower part of the insulator, but it may be the same diameter, or the orifice 6 can be made larger in diameter than the opening 7 as shown in Figure 3. However, there is no problem with discharge (the same effect is produced).

(Effects of the Invention) As described above, the present invention prevents the temperature of the outer electrode from increasing and reduces oxidative wear by covering the bottom of the outer electrode with the bottom wall of the insulator, and also reduces the oxidation wear due to the large diameter of the discharge space. By increasing the diameter of the center electrode, the wear of the discharge surface is reduced, and the wear of the picture electrode can be prevented by a simple means, resulting in excellent effects at low cost.

[Brief explanation of the drawing]

Figure 1 is a front view of an embodiment of the present invention, and Figure 2 is A of Figure 1.
FIG. 3 is a sectional view of a main part of a modified example, and FIG. 4 is a sectional view of a conventional example. 2... Center electrode 4... Insulator 4a... Bottom wall 5... External electrode 5a... Bottom part
6... Orifice diagram 2

Claims (1)

[Claims] In spark plugs for plasma jet internal combustion engines, a cylindrical insulator is interposed between a center electrode and a bottomed cylindrical outer electrode with an orifice at the bottom to form a discharge space between the two electrodes. A spark plug for an internal combustion engine, characterized in that a bottom wall covering the bottom inner surface of an outer electrode up to the vicinity of an orifice is connected to an end of a shaped insulator.