JPS6172932A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To reduce the heating in the surface of a heater at a heat generating line connecting part received from hot temperature gas and to prevent the melting of brazing material caused by over-heated part of the heat generating line connection part in a metallic outer cylinder by a method wherein the outer circumference of the heat generating line connection part is covered by an extremity end part of the metallic outer cylinder to be fitted to the heater and an inner diameter of the extremity end part covering the heat generating line connection part of the metallic outer cylinder brazed to the heater is stepped to form a reduced diameter part and the reduced diameter part is not brazed to the heater. CONSTITUTION:A metallic outer cylinder 4' to be fitted to the outside part of the heater 3' of a ceramic glow plug 1' is made such that an inner cavity 4'-1 at the extremity end covering the heat generating connection line part 2-3 of the heater 3.. is made a small diameter part. In case that inconel etc. is used for a material quality of the metallic outer cylinder 4', the inner cavity 4'-1 at the inner diameter part is oxidized when brazed and a flowing-out of the brazing material can be prevented. However, in case of a material quality which is hard to be oxidized, the silver brazer flow preventive agent is coated over the inner surface of the inner cavity 4'1- at the reduced diameter part. The heater 3' has a glass material 3'-2 coated at an outer circumference of the brazed part and a metallic outer cylinder 4' is fitted and the outer circumference of the heat generating line connection part 2-3 is set to be cove6ed with the inner cavity of the reduced diameter part and the heater 3' is brazed to the inner cavity 4'-2 at its part 4'-3 and assembled together.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention mainly relates to a ceramic glow plug installed in a diesel engine (two ceramic glow plugs) for starting.

[Conventional technology]

In general, diesel engines have poor starting performance at low temperatures (2), so a glow plug is installed in the engine head (= subchamber, etc.), and this glow plug (2) is energized, becomes red hot, and burns part of the fuel injected into the room. Glow plugs are required to have a rapid temperature rise characteristic at the time of starting. There is a tendency for gloves to be used for long periods of time as an afterglow for stabilization, and there is an increasing demand for improved durability of gloves.

As a rapid heating glow plug that meets these demands,
Ceramic glow plugs are known that use 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, forming it, and sintering it.This type of ceramic glow plug The conventional example has a structure as shown in Fig. 3 (=longitudinal cross-sectional view of the main part thereof), and the ceramic globe 2g 1 is a ceramic heater (hereinafter simply referred to as heater) in which a heating wire coil 2 is embedded. 3 is attached to the metal outer cylinder 4 with its tip heating part 3-1 exposed.
At the same time, one end of the two heating wire coils 2 (the two connected lead wires 2-1 are electrically connected), and at the same time the two metal outer cylinders 4 are attached. The e-electrode is configured by brazing and electrically connecting to the metal fitting 5, and the lead wire 2-2 connected to the other end of the heating wire coil 2 is joined to the metal cap 5 at the rear end of the heater 3. The inner shaft 8 (=connected) is welded to this or is insulated from the mounting bracket at the rear end of the plug (not shown) and becomes an O electrode terminal via a dowel rod 1.

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. In order to shorten the conventional structure as shown in Figure 3, if the heat generating part 3-□ of the heater is inserted into the metal outer cylinder 4, the heat generation efficiency will be hindered, and the Conventionally, the temperature inside the tube 4 rises excessively, melting the brazing material that joins the heater 3 and the metal outer tube 4, and changing the heat generation characteristics. Heat generating part 3-1 of the heater including 2-8 (hereinafter simply referred to as heat generating line connection part) 2-8
The two exposure lengths l were set so that the metal outer cylinder 4 was exposed from the tip thereof.

[Problem that the invention seeks to solve]

However, the conventional ceramic glow plug having the above-mentioned structure has a volume inside the tip heating part 3-8 of the heater 3 exposed from the metal outer cylinder 4 (2. Since the heat generating wire connection part 2-8 is buried, when this part is installed in an engine and receives a heat load from the high temperature gas in the combustion chamber, a temperature difference with other parts will occur, and the ceramic material and the heat generating part will be heated. There is a problem that the internal thermal stress is unbalanced due to the difference in the coefficient of thermal expansion of the wire coil and the lead wire, which may damage the ceramic, and the higher the heat receiving temperature in the combustion chamber, the higher the probability of ceramic damage. It became clear after that.

[Means and operations for solving the problems] The present invention has been made to provide a ceramic glow plug that solves the above-mentioned problems. The outer periphery of the heat generating wire connection part is covered with the tip of the metal outer cylinder, and the second invention is the first invention (in addition, the inner cavity of the metal outer cylinder to be soldered to the heater is covered with the heat generating wire). The inner diameter of the tip part that covers the connection part is stepped to make it smaller, and this small diameter part is designed not to be soldered to the heater, so that the surface of the heater of the heating wire connection part can be placed inside the combustion chamber. This is designed to alleviate the heat received from the high-temperature gas and to prevent the melting of the brazing filler metal due to overheating of the heat-generating wire connection portion in the metal outer cylinder as described in the description of the prior art.

〔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 main part of an embodiment of the ceramic glow plug of the present invention (second invention), and Fig.
FIG. 3 is an exploded view for explaining the assembly procedure of the heater and the metal outer cylinder in the case. The relationship between the first invention and the second invention is as follows:
Since the structure of the first invention is the main part of the structure of the second invention, the structure of the first invention is based on the diagram of the second invention shown in FIG.
The present invention will also be described, and illustration thereof will be omitted.

In Fig. 1, the outer side of the heater 3' of the ceramic glow plug 1' (=metal outer cylinder 4' to be fitted is the outer side of the heater 3'
' heating wire coil 2 and lead wires 2-, . 2-, Inner cavity 4'- of the tip part that covers the heating wire connection part 2-3 to be fully connected
□ has a small diameter, and as shown in Fig. 2 ((a)), the large-diameter inner cavity 4'→ which is to be soldered to the heater is plated with N1 or Ou to improve the flow of the filler metal. administered.

If Inconel or the like is used as the material of the metal outer cylinder 4', the small diameter inner cavity 4'-1 will be oxidized during the soldering process, which will prevent the solder metal from flowing out. 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 a diceramic-containing resin to the inner surface 1 of the small-diameter inner cavity 4'-1.

Further, the heater 3' is connected to the large diameter inner cavity 4'-2 of the metal outer cylinder 4'.
After coating the outer periphery of the part to be soldered with the glass material 3'-2, which has a higher melting point than the brazing material and has a coefficient of thermal expansion similar to that of the ceramic material, as shown in Figure 2, As shown in Fig. 01, set the outside (sH2 or N) so that the outer periphery of the heating wire connection part 2-8, which is fitted with a two-metal outer cylinder 4' and buried inside, is covered with the inner cavity of the small diameter part of the tip.
The heater 3' is assembled into the large diameter inner cavity 4'-8 of the metal outer cylinder 4' by soldering 4'-gL in the furnace atmosphere.

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.

The first invention is a case in which the inner cavity of the metal outer cylinder shown in FIG. 1. In the ceramic glow plug of the second 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, which reduces the imbalance of thermal stress inside this part (2) and prevents damage to the ceramic.

In addition, in the second invention, the inner cavity of the metal outer cylinder surrounding the outer periphery of the heating wire connection part of the heater has a small diameter and is not soldered. This product solves the problems in the prior art of this kind of glow plug.

It can be provided as a ceramic glow plug with improved durability.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part of a ceramic glow plug according to the second aspect of 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.
The figure is a longitudinal cross-sectional view of a main part of a conventional example of a ceramic glove 2 according to the prior art. 1 , 1' : Ceramic globe lug, 2 : Heating wire coil, 2-, , 2-, : Lead wire, 2-□
:Heating wire connection part, 3.3': Heater, 3-, :,
Heat generating part, 3'-, glass material, 4.4': Metal outer cylinder, 4
/-8: Small diameter lumen, 4/-! :Large diameter lumen, 4/-,
: Brazing, 5: Mounting bracket, I! : Exposed Long Agent Patent Attorney Mamoru Takeuchi Figure 2

Claims (2)

[Claims] (1) A ceramic heater made by embedding a heat-generating wire of a high-melting point metal in ceramic powder and sintering it is soldered to the inner cavity of a metal outer cylinder fitted on the outside with the heat-generating part at the tip exposed. In addition, in a ceramic glow plug in which the metal outer cylinder is brazed to the tip of the shaft hole of the mounting bracket, the metal outer cylinder connects the connecting part between the heating wire coil and the lead wire in the ceramic heater at the outer periphery at its tip. A ceramic glow plug characterized in that it is formed so as to cover it. (2) A ceramic heater made by embedding a heat-generating wire of a high-melting point metal in ceramic powder and sintering it is soldered to the inner cavity of a metal outer cylinder fitted on the outside with the heat-generating part at the tip exposed. In addition, in the ceramic glow plug in which the metal outer cylinder is brazed to the tip of the shaft hole of the mounting bracket, the metal outer cylinder has a slight air gap around the connection between the heating wire coil and the lead wire in the ceramic heater. 1. A ceramic glow plug comprising: a ceramic glow plug having a step on the inner surface so as to have a large gap around the lead wire at the rear thereof, and soldering only within the large gap.