JPH0341951B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark plug used in an internal combustion engine, and more particularly to a spark plug of a type in which a spark gap protrudes near the center of a combustion chamber in order to improve engine combustion. Regarding improvements.

Conventionally, a protruding type spark plug with a protruding spark gap part has a gap 2 (commonly known as a gas volume) between the inner wall 1a of the mounting bracket 1 and the inner wall 1a of the mounting bracket 1, as shown in FIG. 1.5～
A firing leg 3a of the porcelain insulator 3 protruding by 3 mm was provided, and a spark gap 6 was formed between the tip 4a of the center electrode 4 exposed from the tip surface 3b of the firing leg and the opposing outer electrode 5. It is something. In such a configuration, by increasing the protrusion dimension E from the end surface 1b of the mounting bracket 1 to the tip surface 4b of the center electrode 4 to 6 to 15 mm, it is possible to ignite an easily combustible air-fuel mixture and shorten the combustion time. In addition, in order to further improve ignition performance, the size of the spark gap has been changed from the conventional one.
It is being considered to make the diameter larger than 0.7 to 0.8 mm.

However, it has been found that the protruding type spark plug causes the following problems because increasing the spark gap increases the required voltage, and when the electrodes are worn out, the spark gap widens and this tendency is further exacerbated. That is, the center electrode 4 and the outer electrode 5
In addition to the spark discharge at the regular spark gap 6 between the two, sideways discharge occurs at other parts, which has the disadvantage of significantly impairing the ignition function. The position where the horizontal discharge occurs is (a) the gap B between the tip side surface 3c of the firing leg 3a of the insulator 3 and the inner side surface 5a of the outer electrode 5, where sparks are likely to fly. This tendency is especially true when the engine has a lean mixture.
Or the required voltage is higher than that of a gasoline car.
This is more likely to occur in LPG vehicles.

(b) When carbon adheres to the surface of the insulator ignition leg and the insulation resistance decreases in the gap C between the body side 3d of the ignition leg 3a and the inner wall 1c of the end face of the mounting bracket 1, the surface of the ignition leg is Along the line, it becomes easy for sparks to fly in the gap C.

The discharges other than spark gap 6 that occur in these (a) and (b) contribute to the ignition of the air-fuel mixture, but both are located at positions that are significantly retracted from the protrusion dimension E, which is undesirable from the standpoint of ignitability. .

The present invention has been made in order to solve the above problems, and the gaps B and C are set according to the size of the spark gap A, and the protrusion dimension from the end face of the mounting bracket to the tip face of the ignition leg. By setting D by the protrusion dimension E to the tip surface of the center electrode, it is possible to suppress the phenomenon in which the spark jumps sideways outside of the spark gap, and to create a protruding type spark that has satisfactory ignition performance even when the spark jumps sideways. The purpose is to provide plugs.

The present invention will be explained in detail below with reference to embodiments of the drawings.

FIG. 2 is a sectional view of a main part of the ignition part of a protruding type spark plug showing an embodiment of the present invention, and the same parts as in the conventional FIG. 1 are designated by the same reference numerals. 1 is a mounting bracket, 3 is a porcelain insulator, and 4 is a center electrode.The insulator 3, with the tip of the center electrode 4 exposed and fixed, is arranged inside the inner cavity of the mounting bracket 1, and the firing leg 3a is It protrudes from the end face 1b of the mounting bracket and is sealed and fixed according to known specifications. Reference numeral 5 designates an outer electrode welded to the end surface 1b of the mounting bracket 1, and a spark plug in which a spark gap 6 is formed between the tip 5b of the inner side surface 5a of the electrode and the tip surface 4a of the center electrode 4. It is.

In the present invention, when the size of the spark gap is A, the gap B between the tip side surface 3c of the firing leg 3a and the inner side surface 5a of the outer electrode 5 is 1.2A or more, and the body side surface 3d of the firing leg 3a is The gap C between the inner wall 1c of the end face of the mounting bracket 1 is 1.3A or more, and the distance between the end face 1b of the mounting bracket 1 and the tip face 3b of the firing leg 1a is 1.3A or more.
The protrusion dimension D up to this point is set to be E/3 or more with respect to the protrusion dimension E of the tip surface 4a of the center electrode 4.

The reason for limiting to these dimensions is as follows. That is, as shown in Figures 3 and 4, the protrusion dimension E is 10 mm, D is 4 mm, and the spark gap A is
Gap B to spark gap A, representing 1.1mm.
C was changed, and the discharge characteristics of the discharge starting voltage at which the spark jumps sideways outside the spark gap were investigated. For this experiment, we prepared a large number of spark plugs whose insulation resistance had decreased to 10 MΩ or less due to carbon adhesion on the surface of the insulator ignition leg, and the test was carried out by attaching the plugs to a spark tester and testing them at room temperature. The discharge characteristics of gaps B and C were compared when a pressure of 4 kg/cm ² was applied to the plug firing area. Furthermore, in the diagram, X is the discharge voltage of a regular spark gap (0.8 mm), and Y is the discharge voltage when the spark gap A expands to 1.4 mm after long-term use, which is the maximum value that is generally considered to be the limit of the effective life. be. As a result, based on Y, which is the limit of the effective life, the gap B is 1.2 times or more the size of the spark gap A as shown in Figure 3, and C is also 1.3 times or more as shown in Figure 4. When set to , sideways discharge can be greatly reduced.

Figure 5 also shows that the protrusion dimension E is 10 mm, the spark gap A is 1.1 mm, the gap B is 1.1 mm or less, and C is A×
1.4mm, and the protrusion dimension D is E/5, respectively.
Assuming that the gap B and the spark gap are at the same potential as E/3, the gap that occurs simultaneously in both gap is changed to E/3, and B is changed to A x 1.3 mm among the above dimensions, and D is E/3.
Prepare a spark plug using spark plug 3 that discharges only with a spark gap. In the experiment, a 4-cycle, 6-cylinder 2000c.c. engine was operated at idling (650rpm), and the total concentration of C ₀ , CO ₂ , and HC in the exhaust, which correlates with the air-fuel ratio, and the number of ignition errors were measured. We investigated the relationship between As a result, as shown in the figure, it was confirmed that D is preferably at least E/3 or more, which is similar to when ignition is reliably ignited with only spark gap A. By limiting each dimension in this way, even if the plug is soiled, discharge in gaps B and C can be avoided, and even if discharge occurs in B, there is little effect on ignitability deterioration and the ignitability is excellent. It can be done.

FIG. 6 shows the ignition part of a protruding type spark plug according to another embodiment of the present invention, in which the tip 4a of the center electrode 4 is connected to the tip surface 3 of the ignition leg 3a of the insulator 3.
Hold the insulator exposed from b and attach it to the mounting bracket 1.
Similarly fixed within the lumen of. The tip edge 4c (FIG. 6A) or the tip side surface 4d of the center electrode 4
(FIG. 6B), the inner side surface 15a or tip surface 15 of the outer electrode 15 protrudes from the end surface 1b of the mounting bracket 1.
b are spark plugs in which spark gaps 16 are formed in opposition to each other. The dimensional conditions of the present invention described in FIG. 2 are also applied to such a spark plug, and the spark plug can be configured to advantageously prevent horizontal spark discharge.

FIG. 7 shows another embodiment of the present invention, in which the spark discharge surface forming the spark gap between the center electrode 4 and the outer electrode 5 in the protruding type spark plug of the present invention shown in FIG. It is made by bonding precious metal chips 17 and 18 such as P ₁ or its alloy, and by providing such precious metal chips, it is not only effective in maintenance-free, but also the spark gap is widened by reducing wear and tear on the spark gap. Therefore, it is possible to effectively prevent the horizontal discharge of sparks in this expanding spark gap. Further, the spark plug shown in FIG. 6 can be similarly provided with a noble metal chip.

As described above, in the protruding type spark plug of the present invention, the gaps B and C are set to B>1.2A and C>1.3A, respectively, based on the size of the spark gap, and the protrusion dimension D of the tip surface of the ignition leg is centered. By setting D>E/3 with respect to the protrusion dimension E to the tip surface of the electrode, it is possible to effectively prevent the phenomenon of sideways discharge of sparks other than the spark gap, and it is possible to obtain a spark plug with excellent ignitability. . Furthermore, spark discharge in the gap C along the insulator surface caused by carbon contamination is prevented, and even if sparks fly in the gap B instead, deterioration in ignitability can be greatly reduced.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the main part of the ignition part of a conventional protruding type spark plug, Fig. 2 is a sectional view of the main part of the ignition part of the protruding type spark plug showing an embodiment of the present invention, and Figs. The figures show the characteristics of the present invention. Figures 3 and 4 are graphs showing the relationship between the sizes of gaps B and C and the sideways discharge characteristics, and Figure 5 is the effect of ignitability on the protrusion dimension D. 6 and 7 are cross-sectional views of essential parts of the ignition part of a protruding type spark plug showing other embodiments of the present invention. 1... Mounting bracket, 1a... Inner wall, 1b... End surface, 3...
Insulator, 3a... firing leg, 3b... tip surface, 3c...
Tip side surface, 3d... body side surface, 4... center electrode, 4a
... Tip part, 4b... Tip surface, 5, 15... Outer electrode,
6, 16...Spark gap.

Claims (1)

[Claims] 1 A firing leg of a porcelain insulator that protrudes from the end face of the mounting bracket with a gap between it and the inner wall of the mounting bracket, a center electrode exposed from the tip of the firing leg, and a tip of the center electrode. In a protruding type spark plug that forms a spark gap between the opposing outer electrode, the size of the spark gap is A, the gap between the side surface of the tip of the firing leg and the outer electrode is B, and the inner wall of the end face of the mounting bracket. and the side surface of the body of the firing leg is C, the protrusion dimension between the end surface of the mounting bracket and the tip surface of the firing leg is D, and the protrusion dimension of the tip surface of the center electrode from the end surface of the mounting bracket is E. B＞1.2A,
C>1.3A, and the protrusion dimension of D is D>E/
A protruding type spark plug characterized by satisfying the following conditions.