JPH09129356A - Spark plug for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug for an internal combustion engine, which has a trapezoidal, wedge-shaped grounding electrode that can enhance ignitability and lower the required voltage even in a high-compression engine and a lean-burn engine. SOLUTION: This plug has a cylindrical principal metal fitting 1, an insulator 2 with an axial hole 21 fitted over the principal metal fitting 1, a center electrode 3 fitted into the axial hole 21 in the insulator 2, and a grounding electrode 4 projected form the end of the principal metal fitting 1 and having its end 41 curved in the direction of the center electrode 3, with a spark gap G formed between the side face of the center electrode 3 at the end 41 and the end face of the center electrode 3. The end 41 of the grounding electrode 4 on the center electrode 3 side has a trapezoidal part in the form of a trapezoid whose cross section decreases in width toward the end 31 of the center electrode 3, and serves as a tapered wedge-shaped part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for an internal combustion engine having an improved structure of a ground electrode ignition part.

[0002]

2. Description of the Related Art In Japanese Examined Patent Publication No. 59-36390, a central electrode side portion of a ground electrode is formed in a trapezoidal shape whose width decreases toward the central electrode side to improve ignition performance and required discharge voltage. A spark plug with a trapezoidal ground electrode has been proposed. Further, there is known a spark plug with a wedge-shaped ground electrode in which the tip end portion of the ground electrode is formed in a wedge shape having a tapered width to improve ignition performance.

[0003]

In high-compression engines and lean-burn engines that have been put into practical use in recent years, the ignitability due to spark discharge is lowered and the required discharge voltage is high. Therefore, the conventional trapezoidal ground electrode and wedge-shaped ground electrode have problems such as insufficient ignitability and increased required voltage.

An object of the present invention is to provide a spark plug for an internal combustion engine equipped with a trapezoidal / wedge-shaped ground electrode which can sufficiently improve the ignitability and reduce the required voltage even in a high compression engine or a lean burn engine. .

[0005]

According to the present invention, there is provided a tubular metal shell, an insulator with a shaft hole fitted in the metal shell, and a center electrode fitted in the shaft hole of the insulator. A ground electrode having a tip portion bent at the tip of the metal shell and having a tip portion bent in the direction of the center electrode; and a surface of the tip portion of the ground electrode on the side of the center electrode and a tip surface of the center electrode. In a spark plug for an internal combustion engine in which a spark discharge gap is formed between the tip ends of the ground electrodes, the cross-section has a trapezoidal portion whose width decreases toward the tip side of the center electrode, and the width is tapered. It is characterized by being a wedge-shaped wedge portion.

According to the second aspect of the invention, the wedge-shaped portion of the ground electrode has a taper angle α = 30 ° to 40 °, the width A of the ground electrode base and the width a of the ground electrode tip are a / A = 1/3. ~ 1 /
2. Taper angle β = 60 ° of trapezoidal section of tip section
120 °, the thickness B of the ground electrode and the thickness b of the trapezoidal portion are b / B = 1/2 to 2/3.
In the structure according to claim 3, a noble metal tip is welded to the surface of the tip of the ground electrode on the side of the center electrode. Claim 4
In the configuration described in (1), the diameter of the tip surface of the center electrode is 1.
It is characterized by being 2 mm or less.

[0007]

The ignitability can be improved by the synergistic action of forming the tip of the ground electrode into a structure in which the wedge shape and the trapezoidal cross section are combined. Since the ignitability can be maintained even if the spark discharge gap is made small, the spark discharge gap can be made small to reduce the required discharge voltage. The structure of the tip portion of the ground electrode has a large effect of reducing the flame extinguishing action because the volume of the tip portion of the ground electrode can be reduced. Further, since the effect of disturbing the air flow in the combustion chamber is small, it is advantageous in improving the ignitability, and the taper structure is also advantageous in strength. Further, as in claim 4, by combining the ground electrode with a center electrode having a small diameter (preferably a diameter of 1.2 mm or less), the ignitability can be further improved.

Therefore, when mounted on a high-compression engine or a lean-burn engine, the strong ignition property enables smooth operation. Since the sparking surface of the ground electrode becomes narrower and spark consumption increases, it is desirable to weld the precious metal tip to the sparking surface of the ground electrode to prevent spark consumption. In this case, since the ground electrode has a narrow ignition surface, the amount of precious metal used can be reduced.

[0009]

1 and 2 show a tip portion of a spark plug for an internal combustion engine according to the present invention. The spark plug includes a tubular metal shell 1 and an insulator 2 fitted in the metal shell 1 with a shaft hole 21. The center electrode 3 is fitted in the shaft hole 21 with the tip 31 protruding from the tip surface 22 of the insulator 2.

A modified hexagonal columnar ground electrode 4 is welded to the tip portion 11 of the metal shell 1 and the tip portion 41 is bent toward the center electrode 3 side. The ground electrode 4 has a trapezoidal portion having a trapezoidal cross section in which both angles on the side of the center electrode 3 of the base material having a rectangular cross section with a width A and a thickness B are deleted by an inclined surface with a taper angle β. The trapezoidal portion is the tip 4 of the ground electrode 4.
You may form only in one.

The ground electrode 4 is made of a heat-resistant nickel alloy, and the tip portion 41 is bent so as to be orthogonal to the extension line of the center line of the center electrode 3. The tip portion 41 is a wedge-shaped wedge portion whose width is tapered at a taper angle α. A surface 42 of the tip end portion 41 of the wedge-shaped / trapezoidal ground electrode 4 on the center electrode side forms a spark gap (spark discharge gap) G with the tip end surface of the center electrode 3. Center electrode side surface 42 (ignition surface)
A noble metal 5 such as platinum Pt, platinum iridium Pt-Ir, platinum nickel Pt-Ni, or Pt-Ir-Ni is welded to the.

The tip portion 31 of the center electrode 3 is formed by molding the tip portion of the center electrode base material to form a truncated cone portion 32 having a taper angle of about 90 degrees.
And a truncated cone portion 33 having a taper angle of about 30 degrees are provided, and a noble metal 6 such as platinum Pt, platinum iridium Pt-Ir, platinum nickel Pt-Ni, or Pt-Ir-Ni is welded to the end face of the truncated cone portion 33. . The truncated cone portion 33 may have a columnar shape.

The noble metals 5 and 6 are joined by melting the noble metals 5 and 6 and the electrode base material by laser beam irradiation, resistance welding or the like. Precious metals 5 and 6
Reduces spark consumption of the ignition part of the center electrode 3 and the ignition part of the ground electrode 4 and prolongs the life of the spark plug.
In the present invention, since the tip portion 41 of the ground electrode 4 is wedge-shaped / trapezoidal, the area of the ignition surface of the ground electrode 4 can be reduced, so that the amount of the precious metal 5 used can be reduced.

The wedge-shaped / trapezoidal structure of the tip 41 of the ground electrode 4 has a taper angle α = 30 ° to 40 °, and the width A of the base of the ground electrode 4 and the width a of the tip of the ground electrode 4 are a / A = 1/3
Set to 1/2, taper angle of cross section β = 60 ° to 1
20 °, the thickness B of the ground electrode 4 and the thickness b of the trapezoidal portion are b /
B is set to 1/2 to 2/3.

The above numerical limitation is based on the performance evaluation test results of a large number of test products, and is based on the following reasons. If the taper angle α of the wedge portion is too small, the portion having a small width is applied to the bent portion, and the strength is reduced. On the other hand, if it is too large, the volume of the tip portion 41 of the ground electrode 4 becomes large and the reduction of the flame-extinguishing effect becomes insufficient. If the width a of the tip of the ground electrode 4 is too small, spark consumption is increased, and if it is too large, reduction of the above-mentioned flame-extinguishing effect is insufficient.

The taper angle β of the trapezoidal portion and the ratio of the thickness b of the trapezoidal portion to the thickness B of the ground electrode 4 are mechanical strength,
While maintaining spark wear resistance, improving the anti-flame prevention effect,
In order to realize reduction of the required voltage required for spark discharge, it is necessary to be within the above range.

FIG. 3A shows the wedge-shaped / trapezoidal spark plug of the present invention, the trapezoidal spark plug for comparison, and the general-shaped spark plug whose ground electrode has a rectangular cross section according to the present invention shown in FIG. 3C. The result of having evaluated ignitability is shown. Spark gap G is 0.75mm
Set to. Engine operating conditions are 700 rpm x
(-530 mmHg), ignition timing is 10 ° BTD
C, and the ignition limit air-fuel ratio A / F was measured.

From the graph shown in FIG. 3A, the wedge-shaped trapezoidal spark plug of the present invention is a trapezoidal spark plug,
Alternatively, it has been proved that the ignition limit air-fuel ratio A / F can be made larger than that of a spark plug having a general shape, and that it has good ignitability even in a lean burn engine.

FIG. 3B shows the measurement result of the ignition limit air-fuel ratio A / F when the spark gap G is changed from 0.75 to 1.05 mm. From these measurement results, the wedge-shaped / trapezoidal spark plug of the present invention shows that even if the spark gap G is reduced to 0.75, the ignition limit air-fuel ratio A /
F remains large. Therefore, even if the spark gap is small, the ignition limit air-fuel ratio A / F does not decrease. As a result, the spark gap G can be reduced and the required discharge voltage can be lowered while maintaining the ignitability.

[Brief description of the drawings]

FIG. 1 is a perspective view of a tip portion of a spark plug for an internal combustion engine.

FIG. 2 is a three-view drawing of a tip portion of a ground electrode.

FIG. 3 is a graph of ignitability test data of a spark plug for an internal combustion engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Center electrode 4 Ground electrode 5 and 6 Noble metal 11 Tip of metal shell 31 Tip of center electrode 41 Tip of ground electrode

Claims (4)

[Claims] 1. A tubular metal shell, an insulator with a shaft hole fitted in the metal shell, a center electrode fitted in the shaft hole of the insulator, and a projection at the tip of the metal shell. And a ground electrode whose tip portion is bent toward the center electrode, and a spark discharge gap is formed between the center electrode side surface of the tip portion of the ground electrode and the center electrode tip surface. In a spark plug for an internal combustion engine, the tip portion of the ground electrode has a trapezoidal portion whose cross-section has a width that decreases toward the tip side of the center electrode, and is a wedge-shaped wedge portion having a tapered width. A spark plug for an internal combustion engine, which is characterized in that 2. The wedge portion according to claim 1, wherein the wedge portion has a taper angle α = 30 ° to 40 °, and the width A of the base portion and the width a of the tip of the wedge portion are a / A = 1/3 to 1 / 2, the trapezoidal portion has a taper angle β = 60 ° to 120 °, and the thickness B of the ground electrode and the thickness b of the trapezoidal portion are b / B = 1 /
A spark plug for an internal combustion engine, which is 2 to 2/3. 3. The spark plug for an internal combustion engine according to claim 1, wherein a noble metal tip is welded to a surface of the tip of the ground electrode on the side of the center electrode. 4. The spark plug for an internal combustion engine according to claim 1, wherein a diameter of a tip surface of the center electrode is 1.2 mm or less.