JPH0322034B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark plug for internal combustion engines, and in particular to an improvement of a basic type spark plug in which a ground electrode is provided on the side of the exposed portion of the center electrode from the insulator (insulator). be.

A conventional spark plug of this type is disclosed in Japanese Patent Application Laid-open No. 121630/1983. This is a structure in which the tip of the center electrode is formed with a tapered surface symmetrical to its axis, and the tip of the ground electrode is opposed parallel to this tapered surface.

According to such a conventional spark plug, the tip of the ground electrode is parallel to and opposed to the tapered surface of the center electrode, so the air gap between the tapered surface and the tip of the ground electrode is caused by the existence of the tapered surface. The dimensions are the same within the range. Therefore, the spark discharge in the above air gap is not fixed at a specific location;
There will be various changes within the range of the tapered surface.

Therefore, the conventional structure has a problem in that the ignitability of the air-fuel mixture is poor.

In view of the above-mentioned problems of the conventional structure, the present invention has provided that the tip of the exposed portion of the center electrode is shaped like a truncated cone with an outer circumferential surface forming a conical surface, and the tip side of the ground electrode is opposed to the conical surface of the center electrode. and the angle formed between the tips of the ground electrode and the angle formed by the conical surface of the center electrode are set in a specific relationship, whereby the air gap between the conical surface of the center electrode and the tip of the ground electrode is It is characterized in that it becomes smaller toward the tip of the electrode, and with this configuration, the spark discharge position in the air gap is determined at a specific location, thereby improving ignition performance.

An embodiment according to the present invention is shown in FIG. 1 and will be described below. Reference numeral 1 denotes a center electrode made of a heat-resistant, corrosion-resistant, conductive base metal such as Ni or Ni-Cu. 2 is an insulator made of alumina porcelain, and a shaft hole 2a is provided in the center. 3 is the center shaft made of carbon steel, and the insulator 2
It is inserted into the upper part of the shaft hole 2a. 4 is a terminal made of brass or the like, which is screwed and fixed to the head of the center shaft 3. Reference numeral 5 denotes a cylindrical housing, which is made of heat-resistant, corrosion-resistant, and conductive metal. The insulator 2 is fixed to the inside of the housing 5 via a ring-shaped airtight packing 6 and a caulking ring 7. be.

The housing 5 is provided with a threaded portion 5a for fixing it to the engine block. Reference numeral 8 denotes a ground electrode made of a heat-resistant, corrosion-resistant, and conductive base metal, and is fixed to the lower end surface of the housing 5 by welding. Reference numeral 9 denotes a conductive glass sealing layer sealed inside the shaft hole 2a of the insulator 2, and is made of copper powder and low-melting point glass, and this sealing layer 9 electrically connects the center shaft 3 and the center electrode 1. At the same time, both are fixed to the shaft hole 2a of the insulator 2.

Next, the main part of the present invention will be explained with reference to FIG. The center electrode 1 has a cylindrical portion 11 exposed from the insulator 2, and a truncated conical portion 12 whose outer circumferential surface forms a conical surface 1a is formed at the tip of the cylindrical portion 11.
The ground electrode 8 is provided opposite to this conical surface 1a. The ground electrode 8 is vertically bonded and fixed to the lower end surface of the housing 6, and is connected to the conical surface 1 of the center electrode 1.
It has a configuration in which it is bent obliquely from the middle so that it is almost parallel to a.

The present invention has the greatest feature in that a specific relationship is established between the angle α formed by the conical surface 1a of the center electrode 1 and the angle β formed by the ground electrode 8 in FIG. The effect of each angle of β on the ignitability of the air-fuel mixture was determined through experiments.

The results are shown in FIG. 6 and will be explained. The experimental procedure was to keep the angle α constant at 60°, and install spark plugs with varying angle β to a 4-stroke, 4-cylinder, 1600 c.c. internal combustion engine, and perform idling operation (rotational speed 700 r.pm). Ta. Ignition performance was determined by looking at the air-fuel ratio of the mixture during idling operation. Note that the A dimension on the right side of Fig. 6 was 8.5 mm.

As is clear from the results shown in Figure 6, the angle β−
When the angle α is less than 2 degrees, the air-fuel ratio of the mixture that can be ignited is as low as about 12, indicating that ignition will not occur unless the mixture is quite rich. On the other hand, at 2° or higher, the air-fuel ratio of the mixture that can be ignited is around 15, indicating that even a lean mixture can be ignited.

This point will be explained using FIG. 3. FIG. 3a shows the case where the angle β minus the angle α is larger than 2°. As is clear from FIG. 3a, the air gap G between the conical surface 1a of the center electrode 1 and the tip of the ground electrode 8 becomes smaller as it approaches the tip of the center electrode A spark discharge will occur in part _G1 .
Since the gap G ₁ where this spark discharge occurs is close to the tip of the center electrode 1, it is also close to the center of the combustion chamber of the internal combustion engine, and after all, the gap G ₁ is located at a position where it can easily come into contact with the air-fuel mixture.

Therefore, the ignitability is good because the air-fuel mixture is easily exposed.

On the other hand, FIG. 3b shows a case where the angle β minus the angle α is smaller than 2°, that is, the tip of the ground electrode 8 is opposed in parallel to the conical surface 1a of the center electrode 1. According to this structure, the air gap _G1 is all the same within the range of the conical surface 1a of the center electrode 1. This means that the spark discharge position at the air gap G ₁ is not fixed, and the spark discharge position varies depending on the situation in the air-fuel mixture flow direction. For example, the spark discharge position may occur at the G ₂ position in the figure. be. At such a discharge position, the center electrode 1 and the ground electrode 8 prevent the air-fuel mixture from entering G ₂ , resulting in poor ignition performance. Furthermore, if the discharge position varies, the rotational speed of the internal combustion engine also varies and becomes unstable, resulting in, for example, idling failure.

On the other hand, FIG. 3c shows the case where the angle β minus the angle α is considerably large. In such a case, although the spark discharge location is determined as shown in FIG. The angle 8a will wear out between the two, causing the gap to widen and causing a misfire.

Therefore, as a result of consideration based on the above points, the angle β
- It was found that the difference in angle α is preferably between 2° and 20°.
Expressing this as an inequality, α+2°≦β≦α+20°. Although α is set constant at 60° in FIG. 6, it has been confirmed that there is no problem even if α is varied in various ways as long as the difference from β is within the above range.

On the other hand, in the embodiment described above, the tip of the ground electrode 8 is arranged to face the conical surface 1a of the center electrode 1. This relationship is schematically shown in FIG. 4a. Therefore, the discharge is concentrated at the part _G3 where the distance between the conical surface 1a and the ground electrode 8 is the shortest, and there is no variation in the discharge position. On the other hand, if a tapered surface x is used instead of the above-mentioned conical surface, it will be as shown in FIG. 4b because it is a flat surface. Therefore,
The distance between the tapered surface x and the ground electrode 8 is the same within the range of the tapered surface x, and the discharge position varies within this range.

Therefore, according to the present invention, the discharge position is set to the center electrode 8.
Since the discharge position is located at the tip of the internal combustion engine and the discharge position does not vary, the ignition of the air-fuel mixture is good, and stable engine operation is achieved without variations in the engine speed or breathing phenomenon.

The present invention is not limited to the above-described embodiments, and various modifications can be made as follows.

(1) As shown in Figures 5a and 5b, a groove 8b is provided on the spark discharge side of the ground electrode 8 from its tip to the part where it is fixed to the housing 5, and this groove 8b prevents the growth of the flame kernel. It may also be promoted.

(2) From the lower end of the housing 5 (the end where the ground electrode 8 is welded and fixed) to the conical surface 1a of the center electrode 1
By increasing the distance to the spark discharge portion, the spark discharge position can be brought closer to the center of the combustion chamber, and as a result, the ignitability of the air-fuel mixture can be further improved.

(3) The relationship among the angle α of the conical surface 1a of the truncated cone portion of the center electrode 1, the diameter D of the shaft portion of the center electrode 1, and the tip diameter d of the center electrode 1 (the tip diameter of the truncated cone portion) is set as follows. It's good to do that.

When 20゜<α≦40゜, d=0.5D~0.8D When 40゜<α≦80゜, d=0.3D~0.6D When 80゜<α≦120゜, d=0~0.4D A particularly desirable α is 90°.

As described in detail above, according to the present invention, the following effects are achieved.

(a) Since the spark discharge position is set closer to the tip of the center electrode, the spark from the spark discharge can easily come into contact with the air-fuel mixture, thus improving ignitability.

(b) Since the spark discharge position does not vary and is concentrated at a specific position, the ignition and combustion conditions of the air-fuel mixture are stabilized, and the engine speed can be stabilized.

[Brief explanation of drawings]

FIG. 1 is a half-sectional front view showing the overall configuration of an embodiment of the present invention, FIG. 2 a is a front view showing the main parts of FIG. 1, FIG. 2 b is a bottom view of FIG. 3a to 3c and FIGS. 4a and 4b are schematic diagrams for explaining the operation of the present invention, FIG. 5a is a front view showing another embodiment of the present invention, and FIG. A-A in diagram a
The cross-sectional view and FIG. 6 are graphs used to explain the operation of the present invention. 1... Center electrode, 1a... Conical surface, 8... Ground electrode.

Claims (1)

[Claims] 1. A center electrode in which a truncated cone-shaped part whose outer circumferential surface forms a conical surface is formed at the tip of a cylindrical part exposed from an insulator, and the tip side of the center electrode is bent in a direction along the conical surface of the center electrode. and ground electrodes disposed opposite to the conical surface with the conical surface as a boundary, the angle formed by the conical surface of the center electrode being α, and between the tips of the ground electrodes disposed opposite to each other. When the angle formed by is β, α+2゜≦β≦
An ignition plug for an internal combustion engine, in which an air gap between the conical surface of the center electrode and the tip of the ground electrode becomes smaller toward the tip of the center electrode, with a relationship of α+20°.