JPH0313485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a ceramic glow plug that is attached to a diesel engine primarily for starting.

(Prior technology) In general, diesel engines are equipped with a glow plug in the auxiliary combustion chamber to improve startability, and the glow plug is energized to make the heater red-hot and burn a portion of the fuel injected into the engine to preheat the engine. Recently, ceramic glow plugs have come into use, which use ceramic heaters as heating elements, which are made by embedding heating wires of high-melting point metal in ceramic powder and sintering them. As a conventional example of this type of ceramic glow plug, FIG. 3 shows a partial vertical sectional view of a grounded type ceramic glow plug. In the figure, a ceramic heater 1 has a heating wire 2 embedded in a ceramic sintered body, which is soldered to the inner cavity of a metal outer cylinder 3.
One end 2-1 of the heating wire 2 is electrically connected to this, and the metal outer cylinder 3 is in contact with the inner cavity of the distal end of the mounting bracket 4 to serve as a side electrode, while the other end 2-2 of the heating wire 2 is It is connected to the tip of a center shaft 7 through a lead wire 6 welded to a metal cap 5 attached to the rear end of the ceramic heater 1. twisted and fixed,
An insulator 9 is interposed between the insulator 9 and the mounting fitting 4, and is tightened and fixed with a fixing nut 10 to form a side electrode.

In addition to the above-mentioned grounded ceramic glow plug, one end 2-1 of the heating wire 2 in FIG.
and a two-wire ceramic glow plug that is insulated from the mounting bracket 4 and taken out to the outside of the plug,
Alternatively, there are resistance-containing ceramic glow plugs in which a low antibody is interposed between the metal cap 5 and the center shaft 7, but in both cases, the ceramic heater is not made of metal, as in the case of the grounded ceramic glow plug shown in Fig. 3 above. The metal outer cylinder is soldered to the inner cavity of the cylinder, and the metal outer cylinder is further soldered to the inner cavity at the distal end of the fitting. Generally, a high melting point brazing filler metal is used for soldering between a ceramic heater and a metal outer cylinder, and a low temperature brazing filler metal is used for brazing between a metal outer cylinder and a mounting metal.

(Problems to be Solved by the Invention) In the case of the ceramic glow plug as described above, the brazed joint between the ceramic heater and the metal outer cylinder is exposed to the high temperature combustion gas of the engine, so it is necessary to prevent the brazing material from flowing out. Therefore, the soldered part between the metal outer cylinder and the mounting bracket is relatively low because it is not directly exposed to combustion gas, so this type of soldering is generally done at a low temperature. It is made with brazing material. Of course, a high-temperature brazing filler metal can also be used in this case, but even when using a high-temperature brazing filler metal, if the heating conditions are too rapid, thermal distortion will occur in the ceramic heater inside the metal outer cylinder, causing the ceramic to deteriorate. It may break.
Therefore, in order to prevent this, it is necessary to use a low-temperature brazing material and slowly heat the soldering material, which is inefficient. In addition, for soldering, a clearance is required between the metal outer cylinder and the mounting bracket for the brazing material to flow into, and for this reason, the metal outer cylinder tends to become eccentric and stick to the plug insertion hole when installed on the engine head. The ceramic heater will be damaged.

(Means and effects for solving the problems) The present invention has been made to solve the problems as described above. This is a ceramic glow plug with a structure in which the cylinder is press-fitted into the inner cavity at the tip of the fitting. This press-fitting can also be done by hot press-fitting, but in that case, it is necessary to surface paint the mounting bracket after press-fitting, which increases costs in terms of equipment and process, so cold press-fitting is preferable. This prevents thermal strain from occurring in the ceramic heater and prevents damage to the ceramic. However, in order to perform a good cold press fit, the hardness of the metal outer cylinder, the diameter difference between the outer diameter of the metal outer cylinder and the inner diameter of the mounting bracket, the surface accuracy of the press-fit parts of these metals, the press-fit length, etc. Appropriate settings are required, and if an appropriate lubricant is used in the press-fit portion, the reliability of the press-fit joint will be improved, especially in terms of airtightness.

(Embodiment) FIG. 1 is a partial vertical sectional view of a grounded ceramic glow plug as an embodiment of the ceramic glow plug according to the present invention. In the figure, a metal outer cylinder 3, into which the ceramic heater 1 is brazed, is joined to the inner cavity at the tip end of a mounting bracket 4 by cold press-fitting, and the rear end of the metal outer cylinder 3 is press-fitted into the inner cavity. The portion 3-1 is a chamfered portion provided to facilitate press-fitting during cold press-fitting. The structure of the other parts except for the above-mentioned parts is the same as that of the conventional example shown in FIG. 3, so a detailed explanation is omitted and the same parts are designated by the same reference numerals.

In the above-mentioned embodiment of the grounded ceramic glow plug, the metal outer cylinder is press-fitted into the inner cavity of the mounting bracket in the second step.
To explain with a diagram, a ceramic heater 1 is soldered to the inner cavity of a metal outer cylinder 3, and a center shaft 7 is soldered or welded to a metal cap 5 attached to the rear end of the ceramic heater 1 via a lead wire 6. A press-fitting part 3- is constructed, the tip of which is inserted into the receiving hole 11-1 formed in the pedestal 11, and press-fitted into the inner cavity of the tip of the mounting bracket 4 of the metal outer cylinder 3. Apply an appropriate lubricant to the outer periphery of the mounting bracket 2, insert the mounting bracket 4 from above, and press the upper end surface 4-1 of the mounting bracket with a press or the like so that the lower end surface 4-2 becomes the upper end surface 11- of the pedestal 11. 2
Press fit until the metal outer cylinder 3 contacts the mounting bracket 4.
It was joined to the lumen of the distal end. For the above cold press-fitting, the press-fitting length L, that is, the length of the press-fitting part 3-2 of the metal outer cylinder 3, should be 5 mm or more, the surface accuracy of the outer surface of the press-fitting part 3-2 should be 5 μm or less, and the mounting bracket The surface accuracy of the inner surface of the press-fitting part 4-3 in No. 4 is 10 μm or less, and the diameter difference (D ₂ - _{D 1} ) between the outer diameter D ₂ of the metal outer cylinder before press-fitting and the inner diameter D ₁ of the inner cavity at the tip of the mounting bracket is 0.05. ~0.25mm, and the press-fit introduction part 3-1 at the rear end of the metal outer cylinder 3 is chamfered by 0.2mm or more to facilitate press-fitting, the hardness of the metal outer cylinder 3 is 200MHV or more, and the mounting bracket is Although ordinary carbon steel was used for this purpose, free-cutting steel may also be used.

The reasons for limiting to the above values are (a) If the surface accuracy of the metal outer cylinder and mounting bracket is greater than the above, it will be difficult to maintain airtightness, and (b) press-fit diameter difference (D ₂ − D ₁ )
If it is smaller than the above size range, it will not be possible to obtain bonding strength and it will be difficult to maintain airtightness, and if it is too large, the ceramic heater will be damaged due to difficulty in press-fitting. (c) If the press-fitting length is less than 5 mm, bonding strength and metal The torsional strength of the outer cylinder is insufficient (d) Hardness of the metal outer cylinder is 200MHV
This is because if it is less than that, problems such as insufficient torsional strength will occur.

As a result of testing the ceramic glow plug constructed by cold press-fitting under the conditions described above, the airtightness was 40 kg/cm ² without any abnormality, the pull-out strength of the metal outer cylinder was over 300 kg, and the mounting bracket was fixed. The torsion strength when the metal outer cylinder is twisted is 100Kg.
- cm or more, and it was confirmed that the bonding strength was sufficient to withstand the conditions of use inside the combustion chamber of a diesel engine.

In addition, for two-wire ceramic glow plugs and resistor-containing ceramic glow plugs, assembly A
Although there is a slight difference in structure in the part shown in FIG.

(Effects of the Invention) As described above, in the ceramic glow plug according to the present invention, the metal outer cylinder is cold press-fitted into the inner cavity of the mounting fitting, so heat is not used to join the metal outer cylinder as in the conventional case. Ceramic does not undergo thermal distortion and will not be damaged. In addition, the joining time is approximately 1/3 that of conventional brazing, reducing work man-hours, eliminating the need to remove flux after joining, which was necessary with conventional brazing, and cleaning the seat surface when attaching to the engine head. This eliminates the need for finishing the soldered part at the tip of the mounting bracket and painting the surface of the mounting bracket, shortening the work process and increasing efficiency. moreover,
The amount of deflection of the ceramic heater relative to the metal fitting screw is about half that of the conventional one, and there are effects such as preventing damage to the ceramic heater due to contact with the plug insertion hole.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical sectional view of an embodiment of the ceramic glow plug according to the present invention, FIG. 2 is a diagram for explaining the manufacturing conditions of the embodiment of the ceramic glow plug according to the present invention, and FIG. 3 is a diagram of the conventional example. FIG. 2 is a partial vertical sectional view of a ceramic glow plug. 1: Ceramic heater, 3: Metal outer cylinder, 4: Mounting bracket.

Claims (1)

[Scope of Claims] 1. In a ceramic glow plug in which a metal outer cylinder with a ceramic heater fixed to the inner cavity is joined to a distal end lumen of a mounting bracket, the above-mentioned joint cools the metal outer cylinder to the distal end lumen of the mounting bracket. A ceramic glow plug characterized by being made by press-fitting. 2. The ceramic glow plug according to claim 1, wherein the cold press-fitting is performed under the following conditions. (a) The press-fit length is 5 mm or more (b) The surface accuracy of the press-fit part of the metal outer cylinder is 5 μm or less (c) The surface accuracy of the inner surface of the press-fit part of the mounting bracket is 10 μm or less (d) The outer diameter of the metal outer cylinder and the press-fit part of the mounting bracket The difference in diameter from the inner diameter is 0.05 to 0.25 mm.