JPH0159497B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates primarily to a ceramic glow plug that is installed in a diesel engine, and more particularly to a ceramic glow plug that has improved soldering between a ceramic heater and metal.

Diesel engines generally have poor startability at low temperatures, so glow plugs are installed in the auxiliary combustion chamber, main combustion chamber, etc. of the engine head to burn part of the fuel injected into the interior, improving engine startability. In recent years, glow plugs have been required to have rapid temperature rise characteristics in order to facilitate starting.

Glow plugs that achieve this purpose use a high-melting point metal such as tungsten (W) for the heating wire, which is embedded in a ceramic sintered body whose main component is silicon nitride (Si ₃ N ₄ ). Ceramic glow plugs are known that use a ceramic heater as the heating element, but this type of glow plug has good temperature raising efficiency because the heating element is not covered with a metal sheath like in conventional metal glow plugs. Since a high melting point metal wire is used for the heating wire, there is an advantage that there is little risk of melting even at high temperatures.

By the way, the heating element described above is directly exposed to a combustion chamber such as a swirl chamber, and the temperature rises rapidly, and the surface of the heating element is cooled by the injected fuel and swirling air, which may cause ceramic cracking due to thermal shock. Since there is a problem in that the ceramic heating element is susceptible to precipitation due to external force such as contact when installing the plug, the base part of the ceramic heating element is covered with a metal outer cylinder and the base part is covered with silver brazing.
The metal outer cylinder is inserted into the inner cavity of the metal fitting in which the engine mounting screws are arranged, and silver soldered in the same manner. However, in the case of joining the ceramic heater and the metal outer cylinder using silver brazing material, there were the following drawbacks. In other words, (a) silver brazing material is expensive at 60,000 yen/kg. (b) The metal materials that can be soldered with silver solder are limited. In other words, in the case of normal silver brazing, the brazing temperature is approximately 850℃, and the atmosphere is pure hydrogen or hydrogen.
Nitrogen decomposition gas is used. In such an atmosphere, a heating temperature cycle as shown in Figure 1 is passed, during which the metal is oxidized by a small amount of moisture in the atmospheric gas in the low temperature range, and reduced by hydrogen gas until the brazing temperature is reached. The metal surface is cleaned and brazed. Therefore, the oxides need to be reduced by the brazing temperature, but in the case of stainless steel, the reduction temperature of Cr and Mn oxides is 900 to 1000.
℃, so it cannot be used for silver brazing. For this reason, the material for the metal outer cylinder during silver brazing is limited to iron or Kobal, which has the drawback of poor oxidation resistance. Furthermore, (c) the silver solder material used to join the metal outer cylinder and the metal fittings must have a melting point approximately 200°C lower than the silver solder material used to join the ceramic heater and the metal outer cylinder. However, the silver solder material was limited to BAg1 or BAg7, which has a large amount of added silver, and had problems such as high cost.

The present invention was made in view of the above circumstances, and it uses heat-resistant and oxidation-resistant stainless steel material for the metal outer cylinder and metal cap, and also reduces manufacturing costs by making it possible to use inexpensive copper brazing material. The purpose is to provide a ceramic glow plug that achieves a large reduction in heat.

The ceramic glow plug of the present invention will be explained below based on the drawings.

Fig. 2 shows a longitudinal cross-sectional view of the ceramic glow plug of the present invention. In the figure, 1 is a ceramic heater serving as a heating element, for example, W, Mo, or W.
Exothermic wire 2 made by using a W alloy with Re, Co, Mo, Zr, etc. as a wire and bending it into a U-shape at the center.
Lead wires 3, 3' are welded to both ends of the heater, and these are embedded in a ceramic combustion body mainly composed of silicon nitride (Si ₃ N ₄ ). Preferably, this heater has a perfect circular shape. formed into a rod shape with
Further, as a manufacturing method thereof, Japanese Patent Application No. 194768/1988 filed by the present applicant can be suitably used.
This ceramic heater 1 is fitted into the inner wall of a metal outer cylinder 4 made of stainless steel (for example, SUS310S), and is held with its tip exposed appropriately from the tip of the metal outer cylinder 4. A lead wire 3 welded to one end of the heating wire 2 is exposed on the surface of the ceramic heater, and is electrically connected to the metal outer cylinder 4 by a copper solder material 5 together with a part of the ceramic heater. The cylinder 4 is inserted into the inner cavity of a metal fitting 6 provided with engine mounting screws and is soldered with a silver solder material 7 to form an electrode, while the lead wire 3' welded to the other end of the heating wire 2 is connected to the ceramic heater 1.
The metal cap 9 is exposed at the rear end and is electrically connected to the metal cap 9 with the lead rod 8 using the copper brazing material 5. It has a structure in which it is tightened and fixed with a nut 12 with an insulating interposition between it and becomes an electrode.

Copper brazing between the ceramic heater 1 and the metal outer cylinder 4, and between the heater and the metal cap 9 in the present invention is performed at a brazing temperature of 1100 to 1150°C, so even if stainless steel is used, the oxides are sufficiently removed. Copper brazing can be performed by reducing the effect. Since the metal outer cylinder made of stainless steel has heat resistance and oxidation resistance, the exposed dimension of the ceramic heater (approximately 5 to 10 mm) can be made as short as possible, and cracking, breakage, etc. of the ceramic can be effectively prevented. Can be done. Further, since the metal cap is joined at the same time as the soldering of the metal outer cylinder, manufacturing costs can be reduced. Furthermore, when copper brazing material is used, its melting point is approximately
Since the temperature is 1100°C, any silver solder material can be used for soldering the metal outer cylinder 4 and the metal fitting 6, especially low silver solder material (Ag
The cost can be greatly reduced because the added amount of molten metal is small and the melting point is high).

As shown in FIG. 3, the copper brazing of the present invention involves coating the brazed parts of the ceramic heater 1 with the metal outer cylinder 4 and the metal cap 9 in advance with a glass material mainly composed of ceramic and glass with good wettability. After forming the baked glass layer 13, copper brazing is performed at 1100-1150°C in a non-oxidizing atmosphere. After that, this metal outer cylinder was coated with a known flux, inserted into the inner cavity of the metal fitting 6, and heated in the atmosphere for 800 minutes using a silver solder.
Soldered at ~850℃.

Here, as a glass material mainly composed of the above-mentioned glass, the coefficient of thermal expansion is similar to that of ceramic sintered body.
2.0~5.0× ^10-6 /℃, and sintering temperature 1150~1350
It has been found that it is preferred to have a viscosity of 10 ⁴ P at °C. The glass material is mainly borosilicate glass or silicate glass, preferably 100 parts by weight of the glass powder, 1 to 10 parts by weight of calcium carbonate (CaCO ₃ ), SiO ₂ , CuO,
At least one ceramic powder such as TiO ₂ , SiC, TiC, Si ₃ N ₄ , TiNβ-spodumene, etc.
10 parts by weight is added thereto, an appropriate amount of an organic or inorganic binder is added thereto, and the mixture is kneaded. After applying this mixture to the soldered part of the ceramic heater,
It is baked at ℃ to form a glass layer.
If the coefficient of thermal expansion of the glass material is outside the above range, the coefficient of thermal expansion of the ceramic sintered body (3.0 to 3.5
10 ^-6 /℃), the adhesiveness deteriorates and it cannot be used for practical use. Furthermore, in order to improve the fluidity of the copper brazing material, the best conditions were to have a baking temperature of 1150 to 1350°C and a viscosity of 10 ⁴ P.

In addition, the copper brazing of the present invention is used not only for joining the ceramic heater and metal parts of ceramic glow plugs, but also for forming parts of the piston, pre-chamber, combustion chamber of cylinder head, etc. of engine parts that are subject to high temperatures. It can also be applied to joining ceramic members and metal members.

As can be understood from the above description, the ceramic glow plug of the present invention uses heat-resistant and oxidation-resistant stainless steel material for the metal outer cylinder and metal cap, and also uses a cheaper silver solder material instead of the conventional silver solder material. The cost can be greatly reduced by maintaining the bonding force using the metal outer cylinder, and the exposed dimensions of the ceramic heater can be shortened compared to the conventional material by using the material of the metal outer cylinder. It is possible to provide a ceramic glow plug that effectively prevents breakage of the heater portion and cracking due to thermal cycles during use and has excellent durability.

[Brief explanation of drawings]

Fig. 1 is a state diagram showing a heating temperature cycle for brazing, Fig. 2 is a longitudinal sectional view showing an embodiment of the ceramic glow plug of the present invention, and Fig. 3 is a diagram showing the ceramic heater, metal outer cylinder, and metal cap of the present invention. FIG. DESCRIPTION OF SYMBOLS 1...Ceramic heater, 2...Heating wire, 4...Metal outer cylinder, 5...Copper brazing material, 6...Metal fittings, 9...Metal cap, 13...Glass layer.

Claims (1)

[Claims] 1. A ceramic heater in which high-melting point metal wires are embedded and sintered in ceramic powder is brazed with a metal outer cylinder that fits into the inner cavity of a metal fitting provided with a metal cap for taking out the electrodes and an engine mounting screw. In the ceramic glow plug, the soldered portion of the ceramic heater has a thermal expansion coefficient of 2.0 to 5.0×
A glass material mainly composed of glass having a temperature of 10 ^-6 /℃ is applied and baked at a baking temperature of 1150 to 1350℃, and the ceramic heater and the metal cap and metal outer cylinder made of stainless steel are bonded with copper solder via this glass layer. Ceramic glow plug characterized by the fact that it is attached.