JPH0612681B2 - Creepage discharge plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a creeping discharge in which creeping discharge of a creeping discharge type plug used in an internal combustion engine is caused by adhesion of a conductive substance such as carbon, and creeping discharge with improved ignitability. Regarding mold plugs.

(Prior Art) At present, in a high-power engine such as an outboard motor and a racing engine, as shown in FIG. 6, as a measure for preventing engine damage and porcelain cracking of an insulator caused by overheating associated with preignition of a spark plug. As shown in the drawing, the insulator 12 is housed and fixed by contacting the tip step surface 11b of the inner cavity 11a of the metal shell 11 and faces the tip peripheral edge 13b of the center electrode 13 held in the shaft hole of the insulator 12. A full creeping discharge type plug is used in which an annular creeping discharge gap 17 is formed along the insulator ignition part end face 12e between the metal shell and the inner wall 11d of the ignition part.

(Problems to be solved by the invention) However, since such a creeping discharge type plug has a very short insulating path due to its structure, it is liable to cause smoldering and fouling due to the adhesion of carbon etc. Therefore, the most important issue was to improve the point of poor ignitability due to poor contact with the mixed gas.

Therefore, the present invention is to provide a creeping discharge plug that has the original characteristics of the creeping discharge plug that the temperature on the ignition part side does not rise, and that has improved stain resistance and ignitability.

(Means for Solving the Problem) The present invention provides a hemispherical or mortar-shaped recess on the end face of an ignition part of an insulator, and the tip of the center electrode is arranged at the bottom of this recess to form a creeping discharge gap. When formed, the diameter A of the tip of the center electrode, the depth B of the recess, and the diameter C of the opening of the recess are 0.2 mm <A1.8 mm, B> 0.5 mm, C
It is set in the range of> 1.5 Amm, and further, an annular flat surface which is horizontal in the axial direction is formed on the outer periphery of the recess of the insulator ignition part. Further, the material of the tip of the center electrode is platinum-based metal or its alloy, or the platinum-based material is fixed to the insulator by co-firing.

(Operation) According to the present invention, a recess is formed in the end face of the insulator firing portion as in the above-described structure, and the outer diameter of the center electrode tip portion disposed at the bottom of this recess is thinner than usual (2.0 to 2.6 mm). .2-1.8 mm
Since the circumference length is shortened by the above, the cleaning effect of the carbon adhering to the inner wall of the recess is increased by the discharge energy of the sparks, and the stain resistance can be improved. Also, by arranging the depth and opening diameter of the specific size recess formed on the end face of the insulator ignition part and the center electrode on the bottom of the recess, sparks jump along the recess with the inner wall of the metal shell tip. Therefore, ignitability can be improved.In particular, by forming an annular flat surface on the outer periphery of the recess, sparks are accelerated along the inclined surface, making it easier to jump on the flat surface and forming an air gap. It has an effect that can be further improved. Further, a platinum-based electrode material is useful for the end of the thin center electrode from the viewpoint of durability, and it is also desirable to co-fire and integrate this platinum-based electrode material with an insulator from the viewpoint of wear resistance and manufacturing cost. It is a good idea.

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

1 and 2 show a creeping discharge type plug showing an embodiment of the present invention, in which 1 is a metal shell having an engine mounting screw at its tip, 2 is an insulator made of high alumina, etc., and 3 is The center electrode is inserted into the shaft hole of the insulator 2, and the resistor 5 is sandwiched between the conductive glass seal members 4 and integrally sealed with the terminal electrode 6.

The plug of the present invention abuts on the tip step seat surface 1b of the inner cavity 1a of the metal shell 1 to accommodate the stepped portion 2a of the insulator 2 and to press the upper end peripheral edge 1c of the metal shell 1 by a known caulking method. It is fastened and fixed. This insulator 2 has a small diameter hole 2b and an intermediate hole 2 through which the small diameter tip portion 3a of the center electrode 3 is inserted at the tip.
c and a large diameter hole 2d for sealing the sealing material, and a mortar-shaped recess 2f is formed in the central portion of the end face 2e of the ignition portion of the small diameter hole 2b. Is provided with a horizontal annular flat surface 2g. The center electrode tip portion 3a is arranged on the bottom portion 2h of the recess so as to be the same as or slightly protrudes from the bottom surface, and the tip peripheral edge 3b of the center electrode tip portion 3a and the ground electrode of the metal shell 1 are formed. The creeping discharge gap 7 passing through the recess is formed between the plug and the tip inner wall 1d. The center electrode tip portion 3a preferably has a diameter A of 0.2 to 1.8 mm from the viewpoint of stain resistance, and a diameter of 0.2 mm or less is disadvantageous in terms of wear resistance. Getting worse.
The depth B of the recess is preferably 0.5 mm or more, and the diameter C of the opening of the recess is preferably 1.5 A (0.3 mm) or more.
If it is less than mm, the ignitability is poor and the opening diameter is 1.5
If it is less than Amm, the ignitability also deteriorates. Further flat surface 2
When the size of g is 0.3 mm or more, sparks jump from the flat surface of the insulator, so that the ignitability can be further improved.

FIG. 3 shows another embodiment of the present invention, which is characterized in that the recess 2i has a hemispherical shape. Further, in the embodiment of the present invention, the tip 3a of the center electrode 3 has a low electrode temperature.
Although an alloy material can be used, a platinum-based material 8 made of Pt, Ir, Pd, Ru or an alloy thereof having excellent wear resistance as shown in FIG. It is useful that the above is joined to the tip 3a of the center electrode 3, and in particular, the wire of the platinum-based material is embedded in the unfired small diameter hole 2b of the insulator and then fixed by co-firing. Then, the intermediate electrode 9 may be joined to the tip electrode and similarly sealed by the sealing material.
In this case, since the processing and joining of the electrodes are simplified,
There is an advantage that the manufacturing cost can be reduced, and further, the temperature at the tip of the center electrode is lowered by being integrated with the insulator, so that the wear resistance is further reduced.

Next, the plug performance when the creeping discharge type plug shown in FIG. 2 of the present invention is used will be shown.

First, FIG. 4 shows the resistance of the plug when the diameter A of the center electrode tip is varied by setting the recess depth B of the insulator to 1.5 mm, the diameter C of the opening to 3.0 mm and the flat surface D to 0.8 mm. Show the relationship of fouling. The fouling resistance test was evaluated by the time until the engine malfunctioned during continuous idle operation at room temperature of -10 ° C and a rich air-fuel ratio. As a result, it was found that the smaller the diameter A of the tip of the center electrode, the less likely it is that the engine will malfunction, and that if the diameter A exceeds 1.8 mm, it will rapidly deteriorate.

FIG. 5 shows the ignitability relationship when the center electrode tip diameter A is 0.8 mm, the flat surface width D is 0.8 mm, and the recess depth B and the opening diameter C are variable. The ignitability test evaluated the ignitability by the low temperature startability at room temperature-20 ° C. In the figure, X indicates that the engine did not start, Δ indicates that the combustion was unstable due to intermittent combustion, and ○ indicates that the engine started well. As a result, it was found that the depth B of the recess needs to be 0.5 mm or more for starting, and the diameter C of the opening of the recess needs to be 1.5 times or more the diameter A of the center electrode tip.

(Effects of the Invention) As described above, in the creeping discharge plug of the present invention, the diameter A of the tip of the center electrode provided on the bottom of the recess is 0.2 to 1 by providing the recess on the end face of the ignition part of the insulator. By reducing the thickness to 8 mm, the stain resistance is improved and the depth B of the recess is 0.5.
mm or more and the diameter C of its opening is 1.5 A (0.3 mm)
By doing the above, the ignitability can be improved,
In particular, by forming an annular flat surface on the outer periphery of the recess of the insulator ignition portion, the ignitability can be further improved, and the creeping discharge type plug can have excellent performance not heretofore available.

[Brief description of drawings]

FIGS. 1 and 2 are creeping discharge type plugs showing an embodiment of the present invention, wherein FIG. 1 is a sectional view of an essential part of the plug, and FIG. 2 is an enlarged sectional view of an ignition part of FIG. FIG. 3 is an enlarged cross-sectional view of the ignition part showing another embodiment of the present invention, FIG. 4 is a graph showing the effect of stain resistance of the present invention, and FIG. 5 shows the effect of ignitability of the present invention. Explanatory drawing and FIG. 6 are enlarged sectional views of the ignition part of the conventional creeping discharge type plug. DESCRIPTION OF SYMBOLS 1 ... Metal shell, 1a ... Lumen, 1b ... Tip step seat surface 1f ... Tip inner wall, 2 ... Insulator, 2e ... Firing part end surface 2f, 2i ... Recess, 2g ... Flat surface, 2h ... Bottom part 3 ... Center electrode, 3a ... Tip part, 3b ... Tip peripheral edge 7 ... Creeping discharge gap

Claims (3)

[Claims] Claim: What is claimed is: 1. An insulator that abuts against a stepped seating surface of an inner cavity of a metal shell is housed and fixed, and an inner wall of the metal shell opposite to a tip peripheral edge of a center electrode held in a shaft hole of the insulator. In a creeping discharge type plug formed by forming an annular creeping discharge gap along the surface of an insulator between them, a hemispherical or mortar-shaped recess is provided on the end face of the ignition part of the insulator, and the center electrode is provided at the bottom of this recess. When the tip end portion is provided and the diameter A of the tip end portion of the center electrode, the depth B of the depression, and the diameter of the opening portion of the depression are C, 0.2 mm <A <1.8 mm, B> 0.5 mm, C>
A creeping discharge type plug which is set to 1.5 Amm and further has an annular flat surface which is horizontal in the axial direction formed on the outer periphery of the recess of the insulator ignition part. 2. The material of the tip of the center electrode is Pt, Pd,
The creeping discharge type plug according to claim 1, which is made of Ir, Ru or an alloy material thereof. 3. The creeping discharge type plug according to claim 1, wherein the tip of the center electrode is fixed to the insulator by co-firing.