JPH0221486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-wire glow plug that is mainly installed in a diesel engine and preheats a sub-combustion chamber of an engine head.

In general, diesel engines have poor starting performance, especially at low temperatures, so a glow plug is attached to the auxiliary combustion chamber installed in the engine head, and when electricity is applied to the glow plug, it becomes red hot and burns part of the fuel injected into the engine. In recent years, there has been a tendency for fuel to be used as an afterglow for stabilizing combustion even after startup.

Ceramic glow plugs are known as this kind of glow plug, which uses a ceramic heater as a heating element, which is made by embedding a heating wire of a high-melting point metal in a ceramic combustion body, and one end of the heating wire of the heater is insulated from the mounting bracket. Single-wire ceramic glow plugs are often used, and have a structure in which the center shaft is connected to the side electrode terminal, and the other end is electrically connected to the mounting bracket to form the ground electrode, and is usually used in multi-cylinder engines. Each glow plug installed in each cylinder is connected in parallel to a power source.

By the way, it is necessary to control the heating of these multiple glow plugs according to the necessary heating conditions during startup and afterglow after startup.
In order to be able to control current flow without changing the power supply voltage, a two-wire glow plug with a structure that connects each glow plug to an external circuit and can be switched in parallel or series at will is needed, and its practical application and improvement are needed. is in progress.

As a conventional example of a two-wire ceramic glow plug using a ceramic heater as a heating element, one having a structure as shown in FIG. 1 is known. (Utility Model Application No. 58-119045) In other words, in the figure, the ceramic heater 1 serving as the heating element has the heating wire 2 buried in the ceramic sintered body, and is inserted through the opening at the end of the mounting bracket 3, and is inserted into the central part. The shoulder portion 1a of the large diameter portion formed in the mounting bracket 3 is connected to the tip side step seat 3a of the small diameter portion formed in the inner cavity of the tip portion of the mounting bracket 3.
At the same time, one end 2a of the heating wire is connected to the center shaft 4 serving as one terminal electrode at the rear end of the heater 1, and the other end 2b
is connected to an electrode tube 5 fitted on the outside of the rear end of the heater 1. The electrode tube 5 has its inner cavity filled with a heat-resistant insulating material 6 to seal and support the center shaft 4, and the mounting bracket 3 It protrudes from the rear end and is insulated from the mounting bracket 3 by an insulator 7 so as to serve as the other electrode. Note that 8 is a terminal plate fixed to the electrode tube 5.

However, the conventional structure as mentioned above has a complicated structure, such as having a step part with a different diameter from other parts in the inner cavity of the ceramic heater 1 and the mounting bracket 3, which leads to high costs. It had manufacturing defects such as a risk of analysis loss.

The present invention has been made in view of the above-mentioned circumstances, and has a reinforcing structure for the heater part, in which the central part of the ceramic heater is covered with a metal outer cylinder and is electrically insulatingly joined to the inner cavity of the metal outer cylinder. By doing so, the present invention aims to provide a two-wire ceramic glow plug that is easy to manufacture and assemble, has improved insulation of the electrode portion, and has a bonding strength sufficient for practical use.

The present invention will be explained below with reference to the drawings.

FIG. 2 is a longitudinal cross-sectional view showing the structure of the two-wire ceramic glow plug according to the present invention. The metal outer cylinder 12 is joined and held in the inner cavity of the distal end of the mounting bracket 13, and the joint between the ceramic heater 11 and the metal outer cylinder 13 is shown in an enlarged cross-section of part A surrounded by a circle in the figure. As shown in FIG. 3, glass powder is applied to the outer periphery of the ceramic heater 11 to form a baked glass layer _11-1 , and then the two are electrically insulated and joined by soldering _11-2 . It is something.

One end 14a of the heating wire 14 buried in the ceramic heater 11 is electrically connected to a cap 15 fitted to the rear end of the ceramic heater 11, and the lead wire welded to the cap 15 is connected to the center shaft. 17 to form one electrode, and the other end 14b of the heating wire 14 is electrically connected to a connecting fitting 18 fitted on the rear end side outer periphery of the ceramic heater 11 at a distance from the cap 15. The end portion 18b of the lead portion 18a protruding from the connecting fitting 18 is connected to an electrode tube 19 that is inserted into the outside of the center shaft 17 and seals the center shaft 17 in its inner cavity. It has a structure that constitutes the other electrode. Note that 20 is an insulator, 21 is a sleeve for fixing the electrode tube 19, and 22 is a terminal plate.

The two-wire ceramic glow plug of the present invention having such a structure is particularly strong because the ceramic heater serving as the heating element has a reinforced structure in which the central portion is covered with a metal outer cylinder, and it can be assembled into the mounting bracket. It is possible to prevent precipitation of the ceramic heater during assembly work, etc., and since the joint is brazed with a glass layer interposed around the outer periphery of the heater, it has sufficient joint strength and is electrically stable. Because it is insulated, the insulation between the electrode part and the mounting bracket at the rear end of the ceramic heater is strengthened, and the glass layer acts as a heat insulator, which has an effect on the rising characteristics of the ceramic heater. It is possible to provide a two-wire ceramic glow plug that is easy to manufacture and has improved durability and reliability by improving the conventional problems.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view showing a conventional example of a two-wire ceramic glow plug, Fig. 2 is a longitudinal sectional view of the two-wire ceramic glow plug of the present invention, and Fig. 3 is an enlarged sectional view of section A in Fig. 2. It is. 1, 11: Ceramic heater, 2, 14: Heat generating wire, 3, 13: Mounting bracket, 4, 17: Center shaft,
5, 19: Electrode tube, 11 _-1 : Glass layer, 1
_1-2 : Brazed, 12: Metal outer cylinder.

Claims (1)

[Claims] 1. On the heating element exposed at the tip of the mounting bracket,
A ceramic heater is used in which a heating wire of a high-melting point metal is embedded in ceramic powder and sintered, and both ends of the heating wire of the ceramic heater are insulated and led out from the rear end of the mounting bracket. In the two-wire ceramic glow plug, the ceramic heater is covered by a metal outer cylinder fitted on the outside at its center portion, and is joined and held in the inner cavity of the ceramic heater. A glass layer is formed, and the metal outer cylinder is soldered to the inner cavity of the metal outer cylinder through the glass layer to be electrically insulated, and the metal outer cylinder and the mounting bracket are connected. Features a two-wire ceramic glow plug.