JPH0882417A - Ceramic glow plug incorporating tungsten carbide coil - Google Patents

Abstract

PURPOSE: To stabilize performance over a long time and prolong the life time of a glow plug by using a coil material of tungsten carbide as a heating material. CONSTITUTION: A heating coil 3 comprising tungsten carbide is buried in ceramic 4 of a glow plug. The heating coil 3 is buried more densely toward the bottom of the ceramic 4. The part buried densely forms a heater part (b). Tungsten carbide is very stable matter and is never modified even in the high temperature atmosphere of silicon nitride containing carbon. For this, the tungsten carbide is not modified even in a furnace using carbon as a base material, and hence electric resistance thereof is prevented from being changed. Hereby, performance stabilized over a long time is ensured, and hence the life time of the glow plug can be prolonged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug applied to a forced ignition system for a diesel engine which uses a low cetane number fuel as a main fuel.

[0002]

2. Description of the Related Art FIG. 2 shows the structure of a heater portion of a conventional ceramic glow plug. An electric conductor 01 communicating with an electric wire from a battery (not shown) is provided with a silver brazing a on an electric wire connecting terminal 02 inserted in an upper portion of a ceramic 04 portion. A heating coil 03 made of tungsten is embedded in the ceramic 04 of the glow plug.

Moreover, the coil is more densely embedded in the lower part of the ceramic 04. The densely embedded portion b is the heater portion of the glow plug. The heating coil 03 is brazed with silver to the auxiliary metal fitting 05 at an intermediate position c of the ceramic 04, and electrically communicates with the lower portion 06 of the glow plug body.

[0004]

To embed and harden the tungsten coil 03 in the ceramic 04, a furnace made of carbon is used. That is, a ceramic coil component is completed by placing a tungsten coil 03 in ceramics and molding it, and then storing it in a furnace in the first half of the year and baking it at a high temperature and high pressure. However, when the carbon component forming the furnace material enters the ceramic during firing, the carbon reacts with the tungsten of the coil material at a high temperature, and the tungsten (W) on the outer periphery of the coil is transformed into tungsten carbide (WC). However, a tungsten layer is retained in the center.

However, since there is a difference in thermal expansion between the tungsten and the tungsten carbide, cracks occur and the cross section gradually loses. In addition, the change in electric resistance due to this cross-section loss and the difference in specific electric resistance between the two materials of tungsten and tungsten carbide are added, and the electric resistance of the coil as a whole gradually increases, which has the drawback of shortening its life. are doing.

An object of the present invention is to provide a ceramic glow plug with a built-in tungsten carbide coil, which solves the above-mentioned problems of the conventional product and greatly extends the life of the glow plug itself.

[0007]

The ceramic glow plug with a built-in tungsten carbide coil of the present invention is characterized in that a tungsten carbide coil material is used as a heat generating material.

[0008]

The tungsten carbide used as the heat generating material in the present invention is an extremely stable substance and does not change in the high temperature atmosphere of silicon nitride containing carbon. Therefore, unlike tungsten which has been conventionally used as a heat generating material, it does not deteriorate even in a furnace made of carbon at the time of firing, and changes in electric resistance can be suppressed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a first embodiment of the present invention, in which an electric conductor 1 communicating with an electric wire from a battery (not shown) has a wire brazing a attached to an electric wire connecting terminal 2 inserted in an upper portion of a ceramic 4 portion. A heating coil 3 made of tungsten carbide is embedded in the ceramic 4 of the glow plug.

Moreover, the coil is more densely embedded in the lower part of the ceramic 4. This densely embedded portion is the heater portion b. The heating coil 3 is provided with silver brazing c on the auxiliary metal fitting 5 in the middle of the ceramic 4, and is electrically connected to the lower part of the glow plug body. 2 of the conventional example and FIG. 1 of the present invention are different only in that the coil 03 is made of tungsten in FIG. 2, whereas the coil material is made of tungsten carbide in FIG.

Next, the operation of the above embodiment will be described.
The tungsten carbide used as the coil material in the above examples is an extremely stable substance, and does not deteriorate even when fired in a furnace made of carbon. Therefore, in the present invention, all the problems of the conventional example are solved, and the life of the glow plug itself is significantly extended.

[0012]

In the ceramic glow plug with a built-in tungsten carbide coil of the present invention, since the coil material is changed from the conventional tungsten to tungsten carbide, the coil does not deteriorate during firing, and the change in electric resistance and the coil It is possible to provide a glow plug that has no defects and provides stable performance over the long term and has a long life.

[Brief description of drawings]

FIG. 1 is a sectional view of a glow plug heater section according to a first embodiment of the present invention.

FIG. 2 is a corresponding diagram of FIG. 1 of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric wire, 2 ... Terminal, 3 ... Coil, 4 ... (Glow plug) ceramic, 5 ... Auxiliary metal fitting, 6 ... Glow plug lower part, a ... Electric wire and terminal contact point, b ... Coil heater part , C ... Connection point between coil and auxiliary metal fittings.

Claims (1)

[Claims] 1. A ceramic glow plug containing a tungsten carbide coil, wherein a tungsten carbide coil material is used as a heat generating material.