JPH0315093B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ceramic glow plug that is installed in a diesel engine primarily for starting.

[Conventional technology]

Generally, diesel engines have trouble starting at low temperatures, so a glow plug is installed in the subchamber in the engine head, and when electricity is applied to it, it becomes red hot and burns part of the fuel injected into the cabin, raising the temperature. Glow plugs are required to maintain rapid temperature rise characteristics during startup, and recently, afterglow plugs have been developed to stabilize combustion even after startup. It has become a tendency to be used for a long time as a
There is an increasing demand for improved durability of glow plugs.

As a rapid heating type glow plug that meets these demands, a ceramic glow plug is known that uses a ceramic heater as a heating element, which is made by embedding a heating wire made of a high-melting point metal such as tungsten in ceramic powder, molding it, and sintering it. A conventional example of this type of ceramic glow plug has a structure as shown in FIG. 3, a vertical cross-sectional view of its essential parts. (simply abbreviated as heater) 3 is held by soldering to the inner cavity of the metal outer cylinder 4 with its tip heating part 3 _-1 exposed, and at the same time a lead wire 2 _-1 is connected to one end of the heating wire coil 2. are electrically connected, and the metal outer cylinder 4 is further soldered to the mounting bracket 5 to form an electrode, and the lead wire 2 _-2 connected to the other end of the heating wire coil 2 is The rear end of the heater 3 is connected to a metal cap 6, and the rear end of the plug (not shown) is connected via a lead rod 7 welded to a central shaft 8, which is insulated from the mounting bracket and serves as an electrode terminal. be.

By the way, in terms of mechanical strength, it is generally preferable that the exposed length l of the heater tip exposed from the metal outer cylinder of a ceramic glow plug be as short as possible.
If the heating part _3-1 of the heater is inserted into the metal outer cylinder 4 in order to shorten the conventional structure as shown in the figure, the heat generation efficiency will be hindered, and the metal outer cylinder 4 in this inserted part The internal temperature rises excessively, melting the brazing material that joins the heater 3 and the metal outer cylinder 4, and changing the heat generation characteristics. The exposure length l was set so that the heat generating part 3 _-1 of the heater including the wire connection part 2 _-3 was exposed from the tip of the metal outer cylinder 4.

[Problem that the invention seeks to solve]

However, in the conventional ceramic glow plug having the above-mentioned structure, the inside of the tip heating part _3-1 of the heater 3 exposed from the metal outer cylinder 4 occupies a volume that is uneven in shape compared to other parts. Because the heating wire connection part _2-3 is buried, when this part is installed in the engine and receives a heat load from the high-temperature gas in the combustion chamber, a temperature difference with other parts will occur, causing the ceramic material and the heating wire to Later, it was discovered that the difference in thermal expansion coefficients between the coil and lead wire could cause internal thermal stress to become unbalanced, potentially damaging the ceramic, and that the higher the heat receiving temperature in the combustion chamber, the higher the probability of ceramic damage. found.

[Means and actions for solving problems]

The present invention has been made in order to provide a ceramic glow plug that solves the above-mentioned problems.The present invention has been made in order to provide a ceramic glow plug that solves the above-mentioned problems. , and in this part there is a small gap between the heater and the metal outer cylinder and no soldering is performed, and around the rear lead wire there is a step on the inner surface so that there is a large gap. It has a structure in which only the inside of the large gap is soldered, and this reduces the heat that the heater surface of the heating wire connection part receives from the high-temperature gas in the combustion chamber, and also achieves the same effect as described in the description of the prior art above. This is to prevent the melting of the brazing filler metal due to overheating of the heat-generating wire connection portion inside the metal outer cylinder.

〔Example〕

Embodiments of the ceramic glow plug of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal cross-sectional view showing the essential parts of an embodiment of the ceramic glow plug of the present invention, and FIG. 2 is an exploded view for explaining the assembly procedure of the heater and metal outer cylinder in FIG. 1.

In FIG. 1, the metal outer cylinder 4' fitted on the outside of the heater 3' of the ceramic glow plug 1' is
Heating coil 2 of heater 3' and lead wires 2 _-1 , 2
The lumen ₄ ' at the tip end covering the heating wire connecting part 2 _-3 which connects the -2 to the lumen 4' _-1 has a small diameter, and the large diameter lumen 4' which is soldered to the heater as shown in Fig. 2A _{. 2} is plated with Ni or Cu to improve the flow of the filler metal.

Note that if Inconel or the like is used as the material for the metal outer cylinder 4', the small diameter inner cavity 4' _-1 will be oxidized during soldering, so the leakage of the filler metal can be prevented; however, if other materials that are difficult to oxidize are used. It is desirable to apply a silver solder outflow prevention agent (stop-off, etc.) such as ceramic-containing resin to the inner surface of the small-diameter inner cavity 4' _-1 .

Further, the heater 3' is made of ceramic having a higher melting point and a coefficient of thermal expansion than the brazing filler metal on the outer periphery of the part of the metal outer cylinder 4' that is to be soldered to the large _-diameter inner cavity 4'-2. After coating the glass material 3' _-2 , as shown in Figure C, a metal outer cylinder 4' is fitted on the outside, and the outer periphery of the heating wire connection part _2-3 buried inside is connected to the tip of the metal outer cylinder 4'. The heater _3' is set so as to be covered by the inner cavity of the _small diameter part, and the heater 3' is assembled by soldering 4'-3 to the inner cavity 4' _{-2 of the large diameter part of the metal outer cylinder 4' in a furnace in an H 2} or _{N 2} atmosphere. It is something.

The rest of the structure of the ceramic glow plug of the present invention is the same as that of the conventional example shown in FIG. 3, so a description thereof will be omitted.

〔Effect of the invention〕

As can be understood from the above description, in the ceramic glow plug of the present invention, the outer periphery of the heating wire connection part buried inside the heater and occupying a non-uniformly shaped volume is covered with the tip of the metal outer cylinder. Therefore, the heat received from the high-temperature gas in the combustion chamber is alleviated, the imbalance of internal thermal stress occurring in this area is reduced, and damage to the ceramic can be prevented.

Furthermore, the inner cavity of the metal outer cylinder that surrounds the outer periphery of the heating wire connection part of the heater has a small diameter and is not soldered, so the brazing material does not melt out due to overheating and has stable heating performance. This invention solves the problems in the prior art glow plugs and provides a ceramic glow plug with improved durability.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view of the main parts of the ceramic glow plug according to the present invention, Fig. 2 is an exploded view for explaining the assembly procedure of the heater and metal outer cylinder in Fig. 1, and Fig. 3 is a preliminary view of the ceramic glow plug. FIG. 2 is a vertical cross-sectional view of a main part of a conventional example according to the technology. 1, 1': Ceramic glow plug, 2: Heat generating wire coil, 2 _-1 , 2 _-2 : Lead wire, 2 _-3 : Heat generating wire connection part, 3, 3': Heater, 3 _-1 : Heat generating part,
3'- ₂ : Glass material, 4,4': Metal outer cylinder, 4' _-1 :
Small diameter part lumen, 4'- ₂ : Large diameter part lumen, 4'- ₃ : Brazing, 5: Mounting bracket, l: Exposed length.

Claims (1)

[Claims] 1 A ceramic heater made by embedding a heating wire of a high melting point metal in ceramic powder and sintering it is fitted to the outside so that the heating part at the tip is exposed and the connecting part between the heating wire coil and the lead wire is covered from the outer periphery. In a ceramic glow plug, the metal outer cylinder is soldered to the inner cavity of a metal outer cylinder and the metal outer cylinder is soldered to the tip of a shaft hole of a mounting fitting, and the metal outer cylinder is connected to a heating wire coil in a ceramic heater. A step is provided on the inner surface so that there is a slight gap around the connecting portion between the lead wire and the lead wire, and a large gap is formed around the subsequent lead wire, and the soldering is performed only within the large gap. Ceramic glow plug.