JPH0737675A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce discharge voltage in plus polarity by making the area of one end surface of an earth electrode to form a spark discharge space part smaller than the area of a jointing part with a subject metal fitting, and jointing a noble metal member to one end surface of the electrode. CONSTITUTION:In a spark discharge part 12 composed of a center electrode 3 and an earth electrode 10, a spark discharge gap part 14 is formed in one or more places out of a side surface part 8 on the tip of the electrode 3 and one end surface 13 as a discharge part of the electrode 10. The area of one end surface 13 to from the gap part 14 is made smaller than the area of a jointing part 15 with a subject metal fitting 9. A noble metal member 19 is jointed to one end surface 13. When the electrode 3 is put in plus polarity by using this simultaneous ignition system, discharge voltage in the electrode 10 can be restrained low, and the area of one end surface 13 to form the gap part 14 is made smaller than the area of the jointing part 15 with the subject metal fitting 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug mounted on an internal combustion engine, and more particularly to a DLI (Distributo).
The present invention relates to a structure of a spark discharge part of a spark plug which is used in a simultaneous ignition system accompanying the adoption of r-Less Ignition) or the like and in which a positive high voltage is applied to a ground electrode.

[0002]

2. Description of the Related Art Conventionally, in a spark plug mounted on an internal combustion engine of an automobile, a negative high voltage is connected to the center electrode of the spark plug and a ground is connected to the other ground electrode of negative polarity. With this polarity, the shape of the center electrode determines the level of the discharge voltage, and a shape with a strong electric field strength, for example, a shape with a reduced diameter, is a desirable shape. Further, also in the consumption of the center electrode and the ground electrode constituting the spark discharge part, the consumption of the center electrode with which the heavy gas atom cations collide is greater than that of the ground electrode with which the light mass electron collides, Therefore, in the improvement of the spark discharge part, measures for the center electrode, such as employing a noble metal for the center electrode, are the main measures.

Further, in recent years, in order to improve the degree of freedom of the structure of the internal combustion engine, the distributor is abolished, and the ignition advance angle is controlled by a cam position sensor or the like DLI (Di).
The mainstream of this is the stributor-Less Ignition), and along with this, a simultaneous ignition system in which two spark plugs are ignited by one ignition coil has come to be widely adopted. In this simultaneous ignition system, in addition to the conventional negative polarity, a positive high voltage is connected to the center electrode and the ground electrode is connected to the ground, so the shape of the ground electrode has a great influence on the discharge voltage, and its material has a great influence on electrode wear. Therefore, assuming that this case has a positive polarity, a spark plug used in a positive polarity simultaneous ignition system is, as shown in FIG. 9a, parallel to the tip surface (31) of the center electrode (30). A so-called parallel electrode shape in which a spark discharge gap (44) is formed between the opposing ground electrode (40) and the noble metal member (41), and only the amount of the noble metal of the ground electrode is increased, or the number of poles of the ground electrode. It has been proposed to employ a multi-pole spark plug with a large number of components.

[0004]

However, in the above conventional one, in the parallel electrode structure in which only the amount of the noble metal of the ground electrode is increased, the positive polarity is
No measures were taken to increase the electric field strength of the structure of the ground electrode, and the ground electrode is relatively thicker than the center electrode, so the electric field strength is low and the discharge voltage is high as shown in FIG. 9a. In the multi-pole spark plug in which the number of poles of the ground electrode is increased, the ground electrode surrounds the periphery of the center electrode, so the spark discharge gap occurs between the center electrode and the ground electrode. The growth of the flame kernel is hindered by the ground electrode, and the energy of the flame kernel is absorbed by the ground electrode, that is, the quenching action is relatively large, which may cause a decrease in ignitability.

Further, in the case of the positive polarity, the positive electrode of the gas atom having a heavy mass collides with the ground electrode serving as the negative electrode, and the ground electrode is exposed to the high temperature combustion gas, so that the temperature rises more severely than the central electrode. Therefore, there is a drawback that the consumption of the electrode is significantly increased.

Therefore, the present invention solves the drawbacks of the above-mentioned conventional ones, and eliminates the distributor and controls the ignition advance angle by a cam position sensor or the like.
In order to cope with the simultaneous ignition system that is adopted by LI etc. and generates positive and negative polarities, the discharge voltage in the positive polarity is lowered, and at the same time, a spark plug with low ignitability and low electrode consumption is proposed. is there.

[0007]

To this end, a spar having at least one spark discharge gap formed of one end face of a ground electrode facing the side face of the center electrode tip.
In the plug, the area of one end surface of the ground electrode forming the spark discharge gap is smaller than the area of the joint with the metal shell, and a noble metal member is joined to the one end surface of the ground electrode.

Further, the discharge end face of the side face of the center electrode forming the spark discharge gap is formed substantially parallel to the spark discharge end face of the noble metal member joined to one end face of the ground electrode, and the center electrode is also formed. The noble metal member is joined to the discharge end face of the side surface of the noble metal member, and the noble metal member is joined to one end face of the ground electrode forming the spark discharge gap, or the noble metal member is joined to the spark end face of the center electrode. Is formed on at least one of the spark discharge end faces of the formed noble metal member, and the ground electrode forming the spark discharge portion is a composite in which a good heat conductive metal is enclosed in a nickel alloy having corrosion resistance. It is a structure.

[0009]

With the above-mentioned structure, the spark plug having at least one spark discharge gap formed of one end surface of the ground electrode when facing the side surface of the tip of the center electrode is provided in the spark plug. Since the electric field strength difference with the ground electrode is small, the use of the simultaneous ignition system
In the case of a positive polarity, the discharge voltage at the ground electrode can be suppressed low, and the area of one end face of the ground electrode forming the spark discharge gap is made smaller than the area of the joint with the metal shell, for example, An edge effect is obtained by tapering the shape toward the center electrode direction, and the electric field strength of the ground electrode is enhanced. Further, by joining a noble metal member to one end surface of the ground electrode, an electrode associated with spark discharge can be obtained. It is possible to sufficiently prevent consumption.

When the center electrode has a negative polarity by using the simultaneous ignition system, the discharge end face of the side face of the center electrode forming the spark discharge gap is joined to one end face of the ground electrode. By forming a noble metal member on the discharge end face of the side surface portion of the center electrode while forming it substantially parallel to the spark discharge end face of the member, it is possible to prevent electrode consumption of the center electrode, and further By forming unevenness on at least one of the discharge surface of the noble metal member joined to one end face or the spark discharge end face of the noble metal member joined to the discharge end face of the side surface of the center electrode, it is possible to increase the electric field strength. The discharge voltage is further reduced, and the ground electrode that constitutes the spark discharge part is
By using a composite structure in which a good thermal conductive metal is enclosed in a ground electrode made of a corrosion-resistant nickel alloy, the temperature of the ground electrode, which easily rises in temperature compared to the center electrode, is sufficiently suppressed and the ground electrode itself is consumed. Can also be reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described with reference to the embodiments shown in FIGS. (1) is a spark plug for an internal combustion engine, which is an embodiment of the present invention. The spark plug (1) for an internal combustion engine projects at a tip and has a center electrode (3),
The terminal electrode (7) is held in the shaft hole (4) together with the resistor (6) sandwiched by the conductive glass seal (5) behind it,
Alternatively, at a position where the insulator (2) sealed or fixed and the side surface portion (8) at the tip of the center electrode (3) face each other,
A metal shell (9) having at least one discharge part for the ground electrode (10) and screwed with a screw part (11) screwed and fixed to a plug hole when mounted on the internal combustion engine itself. It is what is done.

Then, in the spark discharge part (12) composed of the center electrode (3) and the ground electrode (10),
At least one spark discharge gap portion (14) is formed by the side surface portion (8) at the tip of the center electrode (3) and one end surface (13) serving as a discharge portion of the ground electrode (10), and the spark discharge is generated. The area of the one end surface (13) of the ground electrode (10) forming the gap portion (14) is smaller than the area of the joint portion (15) with the metal shell (9), for example, in the direction of the one end surface (13) serving as the discharge portion. It is formed by pyramidal or conical taper toward, and a noble metal member (19) is joined to one end surface (13) of the ground electrode (10).
In addition, as the noble metal member (19), Pt, Ir, Pt
A noble metal member having excellent spark consumption resistance such as —Ir alloy, Ir-oxide-containing alloy, and Au alloy is desirable. In addition, the side surface (8) at the tip of the center electrode (3) is provided with a conical noble metal member (1
It may be formed in 6).

Further, according to the present invention, as shown in FIG. 3, the discharge end face (8 ') of the side surface portion (8) of the center electrode (3) forming the spark discharge gap portion (14) is connected to the ground electrode (10). Is formed substantially parallel to the spark discharge end face (19 ') of the noble metal member (19) joined to one end face (13) of the same, and the discharge end face (8) of the side surface part (8) of the center electrode (3) is formed. ') Is joined to a noble metal member (16), and further, the present invention is joined to one end face (13) of a ground electrode (10) forming a spark discharge gap (14) as shown in FIG. Spark discharge end face (19 ') of the noble metal member (19) or spark discharge end face (16') of the noble metal member (16) joined to the discharge end face (8 ') of the side surface part (8) of the center electrode (3). At least one of which is formed with concavities and convexities (17), for example, cross grooves, selections, and the like. Te, the spark discharge section (1
The ground electrode (10) constituting 2) is placed in a ground electrode (10) made of a nickel alloy such as Inconel 600 having corrosion resistance and having a good heat conductive metal (18) such as copper.
(Fig. 1).

Since the present invention has the above constitution, in the spark discharge part (12) composed of the center electrode (3) and the ground electrode (10), the side part (8) of the center electrode (3) is By forming at least one spark discharge gap portion (14) by the one end surface (13) of the ground electrode (10), the electric field strength difference between the center electrode (3) and the ground electrode (10) becomes small. By using the simultaneous ignition system, when the center electrode (3) has a positive polarity, the discharge voltage at the ground electrode (10) can be suppressed to a low level, and the spark discharge gap portion (14) can be suppressed.
The area of the one end surface (13) of the ground electrode (10) forming the metal is smaller than the area of the joint (15) with the metal shell (9), for example, in the direction of the one end surface (13) of the ground electrode (10). Since the edge effect is obtained by tapering toward the ground electrode, and the electric field strength of the ground electrode (10) is enhanced, spark discharge can be easily performed, and further, the ground electrode (10). One end face of (1
By joining the noble metal member (19) to 3), it is possible to sufficiently prevent electrode wear due to spark discharge.

Further, in the above simultaneous ignition system,
Since the center electrode (3) may have a negative polarity, the side surface part (3) of the center electrode (3) held in the shaft hole (4) of the insulator (2) forming the spark discharge gap (14) ( 8)
The discharge end face (8 ') of the ground electrode (10) on one end face (1
3) is formed substantially parallel to the spark discharge end face (19 ') of the noble metal member (19) joined to the same, and the noble metal is formed on the discharge end face (8') of the side surface part (8) of the center electrode (3). By joining the members (16) together, the electrode consumption of the center electrode (3) can be prevented (FIG. 3), and further,
The spark discharge end face (19 ') of the noble metal member (19) joined to one end face (13) of the ground electrode (10) forming the spark discharge gap (14), or the side face (8) of the center electrode (3). ) Noble metal member (1) joined to the discharge end face (8 ') of
By forming the unevenness (17) on at least one of the spark discharge end faces (16 ') of (6) (Fig. 4), the electric field strength of the discharge end faces (16') (19 ') of the noble metal members (16) (19). Therefore, the spark discharge can be easily performed between the spark discharge gaps (14).

And held by an insulator (2),
A composite structure in which the ground electrode (10) forming the spark discharge gap (14) together with the center electrode (3) is filled with a good heat conductive metal such as copper in the ground electrode (10) made of a corrosion-resistant nickel alloy. By so doing, it is possible to sufficiently suppress the temperature rise of the ground electrode (10) even if it receives heat from the combustion gas in the combustion chamber, and also reduce the wear of the ground electrode (10) itself. Is something that can be done.

Therefore, first, as shown in FIG. 5a, one spark discharge gap (14) is formed by the side surface portion (8) of the center electrode (3) and the ground electrode (109 of one end surface (13) of the present invention. Air-pressurized 6kgf / using spark plug
When the discharge voltage in the negative polarity and the positive polarity was measured under the condition of square cm, as shown in FIG. 5, as compared with the conventional parallel electrode shape shown in FIG. 9, the discharge voltage was almost the same regardless of the negative polarity and the positive polarity. Since it becomes constant, the discharge voltage can be suppressed low. The spark discharge gap (1) together with the center electrode (3) with respect to the joint area (15) of the joint (15) between the ground electrode (10) and the metal shell (9).
When the discharge voltage was measured with respect to the area ratio (100% to 20%) of the one end face (13) of the ground electrode (10) constituting 4), the spark discharge gap was measured together with the center electrode (3) as shown in FIG. Since the discharge voltage can be suppressed lower as the area ratio of the one end surface (13) of the ground electrode (10) forming the part (14) is smaller, it was confirmed that the spark discharge can be easily performed. .

Then, the discharge end surface (8 ') of the side surface portion (8) of the center electrode (3) held in the shaft hole (4) of the insulator (2) forming the spark discharge gap portion (14) is Noble metal member (1) joined to one end face (13) of the ground electrode (10)
The noble metal member (1) which is formed substantially parallel to the spark discharge end face (19 ') of 9) and is joined to one end face (13) of the ground electrode (10) forming the spark discharge gap (14).
9) of the spark discharge end face (19 ') or the discharge end face (8') of the side surface part (8) of the center electrode (3).
Spark discharge end face (16 ') of 8 mm precious metal member (16)
Cross groove (width 0.2 mm x depth 0.2
mm) unevenness (17) formed according to the present invention of FIG.
It was confirmed that the use of the cup plug can reduce the discharge voltage and easily cause the spark discharge as compared with the case where the unevenness (17) is not present as shown in FIG. 7.

Further, in the structure shown in FIG. 3, the ground electrode (1) forming the spark discharge gap (14) together with the center electrode (3).
0) has a composite structure in which a good thermal conductive metal such as a copper core (18) is enclosed in a ground electrode (10) made of a nickel alloy having corrosion resistance, and one in which the copper core (18) is not enclosed. At one end surface (13) of the ground electrode (10)
Noble metal member (1 mm in diameter x 0.7 mm in length) (1
9) and the spark plug gap amount in which the noble metal member (16) of Pt-Ir alloy was formed on the side surface portion (8) of the center electrode (3) was measured in a full-open high-speed durability test (5500 rpm). As shown in 8, the copper core (1
In the composite structure in which 8) is enclosed, heat is dissipated more efficiently than in the case where the copper core is not enclosed, so that the electrode temperature can be reduced and therefore the ground electrode can be restrained from being consumed.

[0020]

As described above, at least one spark discharge gap is formed by the side surface of the center electrode and one end face of the ground electrode, and the area of one end face of the ground electrode forming the spark discharge gap is reduced. By making it smaller than the joint area with the metal shell, and by joining a noble metal member to one end surface of the above ground electrode, the discharge voltage can be lowered even if it becomes a positive polarity by using the simultaneous ignition system. Improves the spark discharge property, and further forms the discharge end face of the side part of the center electrode that forms the spark discharge gap substantially parallel to the spark discharge end face of the noble metal member joined to one end face of the ground electrode. In addition, the noble metal member is integrally joined to the discharge end face of the side surface of the center electrode, and further, the spark discharge end face of the noble metal member joined to one end face of the ground electrode forming the spark discharge gap, or the center. By forming unevenness on at least one of the spark discharge end faces of the noble metal member joined to the discharge end face of the side surface of the pole, the ignition performance is improved due to the improvement of the spark discharge performance by reducing the discharge voltage, and It has an excellent effect that it can be used over a period of time.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a spark plug for an internal combustion engine that is an embodiment of the present invention.

FIG. 2 is an enlarged perspective view of a main part thereof.

FIG. 3 is an enlarged plan view of an essential part of a spark plug which is a second embodiment of the present invention.

FIG. 4 is an enlarged plan view of an essential part of a spark plug which is a third embodiment of the present invention.

FIG. 5 is a graph showing the relationship between the spark plug of the present invention used in an experiment and its discharge voltage in positive or negative polarity.

FIG. 6 shows the relationship between the ratio of the area of one end surface of the ground electrode to the area of the joint between the ground electrode and the metal shell and the discharge voltage.

FIG. 7 is a graph showing the relationship between the discharge voltage of the discharge end surface having irregularities and the discharge voltage of the other surface.

FIG. 8: Gap increase amount in a full-open high-speed durability test between a spark plug of this example having a composite structure in which a copper core, which is a metal having good thermal conductivity, is enclosed in a ground electrode, and a conventional one, in which a copper core is not enclosed. It shows the relationship of.

FIG. 9 is a graph showing a relationship between a conventional parallel-electrode-shaped spark plug and a discharge voltage of the spark plug.

[Explanation of symbols]

 1 Spark plug for internal combustion engine 2 Insulator 3 Center electrode 4 Shaft hole 5 Conductive glass seal 6 Resistor 7 Terminal electrode 8 Side part (of center electrode) 8'Discharge end face 9 Metal shell 10 Grounding electrode 11 Screw part 12 Spark discharge Part 13 One end face (of the ground electrode) 14 Spark discharge gap part 15 Joining part 16 Noble metal member 16 'Discharge end face 17 Unevenness 18 Copper core 19 Noble metal member 19' Discharge end face

Claims (4)

[Claims] 1. A spark plug having at least one spark discharge gap portion formed from one end surface of a ground electrode opposite to a side surface portion of a tip of a center electrode, the ground electrode forming the spark discharge gap portion. The spark plug for an internal combustion engine in which the area of one end surface of the ground electrode is smaller than the area of the joint with the metal shell, and a noble metal member is joined to the one end surface of the ground electrode. 2. A discharge end face of a side surface portion of a center electrode forming a spark discharge gap is formed substantially parallel to a spark discharge end face of a noble metal member joined to one end face of a ground electrode, and the center electrode is also provided. The spark plug for an internal combustion engine according to claim 1, wherein a noble metal member is joined to the discharge end surface of the side surface of the spark plug. 3. A spark discharge end face of a noble metal member joined to one end face of a ground electrode forming a spark discharge gap or at least one of a spark discharge end face of a noble metal member joined to a discharge end face of a side surface of a center electrode. The spark plug for an internal combustion engine according to claim 1 or 2, wherein the spark plug has irregularities formed therein. 4. The spark plug for an internal combustion engine according to claim 1, 2 or 3, wherein the ground electrode forming the spark discharge portion has a composite structure in which a highly heat conductive metal is enclosed in a corrosion resistant nickel alloy.