JPS6030613Y2 - Two-wire ceramic glow plug - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a two-wire ceramic glow plug in which both terminals are installed insulated from an engine.

Conventionally, two-wire (both terminals insulated) glow plugs used in parallel or series connection in multi-cylinder diesel engines have a center electrode inserted into the center of a metal tube with a closed end inside a hollow mounting bracket. In addition, the center electrode and the bottom of the tube are connected by a heating wire, and the heat generating tube is electrically insulated and fitted. The inner circumferential surface of the metal fitting or
Applied to the outer surface of a metal tube to insulate it.

(b) Place a glass seal between the mounting bracket and the metal tube to insulate it.

In the case of (a), the ceramic coat peels off over time due to repeated heating and cooling, which tends to cause poor insulation between the mounting bracket and the heat generating tube, and in the case of (b), the glass seal There are problems in that there is a large difference in the coefficient of thermal expansion between the glass seal, the mounting hardware, and the metal tube material, making it difficult to set the glass sealing conditions, and fine cracks forming in the glass sealing layer, making it difficult to completely prevent airtight leakage.

The object of the present invention is to provide a two-wire glow plug that can prevent electrical short circuits and airtight leaks, which are the drawbacks of the two-wire glow plugs.

Next, the present invention will be explained based on the embodiment shown in the drawings.

1 is a hollow fixture made of a ceramic sintered body mainly made of silicon nitride and has a mounting screw 101 formed on the outer periphery; 2 is a rod-shaped ceramic heating element whose rear end is fitted and fixed to the tip IA of the fixture; There are ceramic rods 21 with high heat resistance and thermal shock resistance such as Si3N4 and SiC at both ends and 32
One end 31 is made of tungsten W or molybdenum Mo with one end 31 protruding from the center of the rear end surface and the other end 32 protruding from the periphery of the rear end surface.
It is formed by embedding a heat-resistant metal heating wire 3 mainly composed of.

To fix the ceramic fixture 1 and the ceramic heating element 2 and to seal the fitting surfaces, the inner peripheral wall of the ceramic fixture 1 and the outer peripheral wall of the intermediate portion of the ceramic heating element 2 may be metallized or made of nickel, copper, or titanium. This is accomplished by forming a metallized layer by vapor deposition or applying a baking paste, and applying a glass seal 5 to the annular gap 4 between the peripheral walls on which the metallized layer is formed.

Reference numeral 6 denotes a rod-shaped center electrode which is inserted in series with the heating element 2 at the center of the rear end of the fixture 1 and connected to one end 31 of the heat generating wire by brazing an electric wire 61; A cylindrical outer peripheral electrode is fitted to the rear end and connected to the other end 32 of the heating element 3 by brazing an electric wire 71, 8 is a terminal ring fixed to the rear end of the outer peripheral electrode 7, and 9 is the aforementioned This is an insulating ring that is interposed between the outer peripheral electrode 7 and the terminal ring 8 and holds the center electrode at the axis of the fixture 1.

Note that the metallized layer is formed on the inner circumferential wall of the fixture and the outer circumferential wall of the heating element in order to improve compatibility (wettability) with the glass seal and strengthen the adhesion force, and this metalized layer is extremely thin. Therefore, the influence of thermal expansion difference is small, and cracks do not occur in the glass seal. Also, since both the fixture and the heating element are made of ceramic, cracks due to thermal expansion difference can be suppressed, and they can be directly joined with a glass seal. It is possible to maintain airtightness and improve durability.

This glow plug is manufactured as follows.

The fixture 1 is manufactured by molding and sintering ceramic powder using a hot press, and the heating element 2 includes a heating wire 3 in the ceramic powder.
After burying it, it is fired and finished into a predetermined shape, and a central shaft that is the center electrode and a metal ring that is the outer electrode are placed at two places (the upper end surface of the ceramic) of the heating wire extraction part (electrode extraction part). are brazed or welded via electric wires, respectively.

Next, the inner circumferential wall surface of the fixture 1 and the outer circumferential wall (fitting surface) of the ceramic heating element 2 are coated with metal (Ni, Cu, Ti, etc.) by metallization, vapor deposition baking, paste application, etc., and then heat generation is performed. The body 2 is coaxially inserted into the fixture 1, and the annular gap between the metallized surface of the ceramic heating element 2 and the metallized surface of the fixture 1 is filled with a glass sealing material or a glass material for molding. After that, it is heated (400 to 600 degrees Celsius) to fix it.

Furthermore, the cylindrical outer peripheral electrode 7, the insulating ring 9, and the terminal ring 8 are assembled.

In the above embodiment, when the fixture 1 and the heating element 2 were fitted together, the inner circumferential wall surface of the former and the outer circumferential wall surface of the latter were respectively metallized, and then a glass seal was provided in the annular gap between them. Instead of this, a glass seal can be directly sealed between the inner circumferential wall surface of the fixture 1 and the heating element 2, and this can be used as another embodiment.

As described above, in the two-wire glow plug of the present invention, since the fixture 1 and the heating element 2 are both insulators, the fixture 1
There is no possibility of short-circuiting between the metallization, vapor deposition,
After performing metallization treatment such as applying baking paste, applying a glass seal improves the fit between the glass seal and the inner circumferential wall of the fixture 1 and the outer circumferential wall of the heating element 2. It is possible to reliably prevent "electrical short circuits" and "hermetic leakage" which were considered to be disadvantageous.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the two-wire glow plug of the present invention. 1... Mounting tool, 2... Heating element, 3...
...Heating wire, 5...Glass seal.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. A bar-shaped ceramic heating element, which has a heating wire embedded with the rear end visible and both terminals taken out, is coaxially fitted into a silicon nitride cylindrical fixture. A two-wire ceramic glow plug whose mating surfaces are sealed and fixed with a glass seal. 2. The two-wire ceramic glow plug according to claim 1, characterized in that a metallized layer is formed on the inner circumferential wall of the fixture and the outer circumferential wall of the heating element.