JPH04262388A - Spark plug for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce spark exhaustion, prevent carbon attachment, and enhance the durability of a plug proper, by covering the side periphery of the spark generating part at the tip of a center electrode with a noble metal, and furnishing a stepped part at the center electrode which is made thinner. CONSTITUTION:Outside electrodes 12 positioned oppositely are installed at the side periphery centering on the spark generating part of a center electrode 4 at its foremost, and the spark discharge part of this spark generating part is covered with a noble metal 7. In the insulation 2 of the center electrode 4 a stepped part is provided to make the tip of the insulation 2 thinner. According to this configuration, the following conditions are satisfactorily met: that 0.3mm<=L1<=1mm, L1+0.5mm<=L2mm, L2<=L3, 0.1mm<=G, F, and 0.15<=t/d<=0.45, where L1 is level difference at the stepped part, L2 is from the inner bottom of the stepped part to the open end of insulation, L3 is length of the thinned portion at the tip of insulation, (t) is wall thickness of insulation 2, (d) is dia. of center electrode, and G, F are the inner bottom and width of the stepped part provided at the center electrode 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a center electrode of a spark plug used in an internal combustion engine.

0002

[Prior Art] In recent years, with the development of internal combustion engines, in spark plugs used in internal combustion engines, in order to prevent wear of the center electrode due to spark discharge, the ignition part at the tip of the center electrode and the tip of this ignition part are A spark plug is known in which noble metal tips are welded to outer electrodes placed in opposing positions to improve spark consumption resistance due to spark discharge, but in the case of this spark plug, the outer electrodes The outer electrode is likely to break due to vibrations generated by the internal combustion engine to which the spark plug is installed, and there is a risk of damage to the internal combustion engine.

Furthermore, a spark plug has been proposed in which the amount of protrusion of the outer electrode into the combustion chamber is reduced.
In a spark plug that employs a structure in which an outer electrode is disposed at a position opposite to the tip of the ignition portion of the center electrode, the ignition position is lowered, resulting in a decrease in the ability to ignite the air-fuel mixture.

[0004] Therefore, on the side of the firing part at the tip of the center electrode,
It has been proposed that a plurality of outer electrodes are arranged to face each other, and sparks are caused between the side surface of the ignition part of the center electrode and these outer electrodes to ignite the air-fuel mixture.

[0005]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional device, a plurality of outer electrodes are arranged to face each other on the side surface of the firing portion at the tip of the center electrode, and the side surface of the firing portion of the center electrode and these outer electrodes are arranged so as to face each other. with a flying fire between the
In the case of spark plugs that have a structure that attempts to ignite the air-fuel mixture, the outer electrode must have multiple poles in order to ensure wear resistance, but there is The spark discharge at the center electrode also places a burden on the firing part of the center electrode, and at the same time as the outer electrode wears out, the spark discharge wear of the firing part at the tip of the center electrode progresses significantly. However, it is not possible to ensure the durability of the spark plug itself,
Furthermore, as outer electrodes become multipolar, especially when the outer electrode has three or more electrodes, the cooling effect is large and the ignitability of the air-fuel mixture decreases, and gas exchange inside the ignition part becomes difficult, making it difficult to prevent smoldering due to carbon. The disadvantage is that it cannot be dealt with.

[0006] Therefore, the present invention aims to improve the drawbacks of the above-mentioned conventional spark plugs, and improves the durability of the spark plug itself in response to the multipolarization of the outer electrode.
This makes it possible to sufficiently deal with the smoldering caused by carbon that occurs when the air-fuel mixture is ignited.

[0007]

[Means for solving the problem] To this end, outer electrodes are arranged around the firing part at the tip of the center electrode at positions facing each other, and the spark discharge part of the firing part at the tip of the center electrode is made of precious metal. Similarly, when the tip of the insulator is made thinner, the difference in step at the step is L1, and the tip is made thinner by providing a step in the insulator of the center electrode. L2 up to the end of the body opening
, L3 is the length of the thinned part at the tip of the insulator, t is the thickness of the thinned insulator, d is the diameter of the center electrode, and is the inner bottom and width of the step provided on the center electrode. When G and F, 0.3mm≦L1≦1mm, L1+0.5mm≦L
2, L2≦L3, 0.1mm≦G,F, 0.15≦t/
This is achieved by satisfying d≦0.45.

[0008]

[Operation] With the above configuration, a plurality of outer electrodes are arranged around the firing part at the tip of the center electrode at positions facing each other around the firing part, and the outer electrodes are connected to the firing part at the tip of the central electrode for a long period of time. Even if a spark discharge is performed to ignite the air-fuel mixture, the side periphery of the ignition part at the tip of the center electrode, which faces the outer electrode that causes the sparks to fly, is coated with a precious metal, so that the spark consumption caused by the spark discharge is reduced. Can be done.

[0009] Furthermore, by reducing the diameter of the tip of the insulator, the thickness of the tip of the insulator is reduced, and furthermore, by providing a stepped portion in the center electrode in the shaft hole of the thinned tip of the insulator, mixing is improved. By making it easier for the insulator to absorb the heat generated by the ignition of air, it prevents the adhesion of carbon, and
Carbon adhering to the insulator is removed by spark discharge from the insulator surface and the inner wall of the insulator shaft hole during the discharge between the center electrode step and the metal shell, and carbon smoldering occurs due to ignition of the air-fuel mixture. can be dealt with.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further explained with reference to embodiments shown in the drawings. (1) is a spark plug for an internal combustion engine which is an embodiment of the present invention;
) holds a center electrode (4) having a firing part (5) at the tip of the shaft hole (3), and also has a conductive glass seal (8).
) and a terminal electrode (10) sandwiched between the resistor (9) and the terminal electrode (10
) an insulator (2) whose one end is sealed in the shaft hole (3), and a side periphery (6) of a center electrode (4) held at the tip of the shaft hole (3) of this insulator (2). A plurality of outer electrodes (12) are provided at positions facing each other or equally spaced along the side circumference (6) of the center electrode (4), with the center electrode (4) as the center, and The main body member (11) has a threaded portion (13) that is screwed into the main body when the main body is mounted on an internal combustion engine.

[0011] And, this spark plug for internal combustion engine (
The side periphery (6) of the firing part (5) at the tip of the center electrode (4) held at the tip of the shaft hole (3) of the insulator (2) constituting 1) is made of, for example, Pt-20% Ir or is Pt10~40%N
It is covered with a noble metal coating part (7) made of i-alloy or the like.

[0012] Also, the insulator (2) of the center electrode (4)
In the same way, when the tip of the center electrode (4) is made thinner while providing the step (14), the tip of the insulator (2) is made thinner, and at this time, the step at the step (14) is L1, Step part (
14) from the inner bottom (15) to the open end of the insulator (16) is L2, and the length of the thinned part at the tip of the insulator (2) is L.
3. The thickness of the tip of the thinned insulator (2) is t, the diameter of the center electrode (4) is d, and the step provided on the center electrode (2) is
The width of the inner bottom (15) and step (14) of
, F, 0.3≦L1≦1mm, L1+0.5
≦L2mm, L2≦L3, 0.1≦G, Fmm, 0.1
It satisfies 5≦t/d≦0.45.

[0013] Since the embodiment of the present invention has the above-mentioned configuration, the central electrode (4) is located at opposing positions on its side circumference (6) centering on the firing part (5) at the tip of the central electrode (4), or at positions opposite to each other;
A plurality of outer electrodes (1) are arranged at equal intervals along the side circumference (6) of the
2), and a spark discharge is performed between this outer electrode (12) and the ignition part (5) at the tip of the center electrode (4) for a long period of time to ignite the air-fuel mixture. , a center electrode (4) facing a plurality of outer electrodes (12) that generate sparks;
The side circumference (6) of the firing part (5) at the tip is covered with a noble metal coating part (7).
), it is possible to reduce spark consumption due to spark discharge, and also to ensure that 0.15≦t/
Since the center electrode (4) can be made thinner by setting d≦0.45, it is possible to improve the ignitability.

Furthermore, the insulator (2) of the center electrode (4)
In the step (14), the step (14) is L1, and the step (14) is L1.
14) from the inner bottom (15) to the open end of the insulator (16) is L2, and the length of the thinned part at the tip of the insulator (2) is L.
3. The thickness of the tip of the thinned insulator (2) is t, the diameter of the center electrode (4) is d, and the step provided on the center electrode (2) is
The width of the inner bottom (15) and step (14) of
, F, 0.3≦L1≦1mm, L1+0.5
The stepped portion (14) is provided so as to satisfy ≦L2mm, L2≦L3, 0.1≦G, Fmm, and the tip of the insulator (2) is similarly made thinner. 0.15
By reducing the diameter so that ≦t/d≦0.45 is satisfied, the diameter of the center electrode (4) is reduced, and the wall thickness t of the tip of the insulator (2) is reduced, and by ignition of the air-fuel mixture, The generated heat is easily absorbed into the insulator (2), and the self-cleaning action prevents adhesion to the surface of the carbon insulator (2) caused by incomplete combustion of the air-fuel mixture. By providing a step (14) on the side circumferential surface of the center electrode (4) in the shaft hole (3) at the tip of the insulator (2), the inner wall of the shaft hole (3) at the tip of the insulator and the outer periphery of the insulator are Even if carbon adheres to the surface, spark discharge will occur between the stepped portion (14) provided on the side peripheral surface of the center electrode (4) and the inner wall of the shaft hole (3) due to the decrease in insulation resistance. When electric discharge occurs, the carbon adhering to the inner wall of the insulator (2) can be removed by this spark discharge, and the air-fuel mixture of the spark plug (1) due to the smoldering of carbon generated by ignition of the air-fuel mixture. It is possible to deal with poor ignitability.

[0015] The side periphery (6) of the firing part (5) at the tip of the center electrode (4) held at the tip of the shaft hole (3) of the insulator (2) constituting the internal combustion engine spark plug (1) The precious metal coating part (7) covering the metal plate may be formed by plastic working. It may be joined by brazing.

[0016] Therefore, regarding the embodiment of the present invention, L1
=0.3mm, L2=1.0mm, L3=2.5mm,
F=0.25mm, G=0.25mm, d=2.7mm
, t = 0.9 mm, t/d = 0.33, and the spark plug of the present invention is marked with ●, and as a conventional example, the spark plug with ○ is provided with two outer electrodes arranged opposite to each other on the side circumference of the tip of the center electrode. A comparison was made in an actual machine using a spark plug and a spark plug marked with an "X" that has an L-shaped outer electrode placed opposite the tip of the center electrode. In addition, for this comparative test, 3 types of chalk were used.
/4 Closed, at room temperature, idling for 3 minutes → Stop 1
The insulation resistance was measured according to the number of cycles, with each minute being one cycle. As a result, it was found that the example of the present invention was able to suppress a decrease in insulation resistance compared to the conventional example (FIG. 3).

[0017]

[Effects of the Invention] As described above, by covering the side circumference of the firing part at the tip of the center electrode of a spark plug equipped with a plurality of outer electrodes with a noble metal coating, wear of the firing part due to spark discharge can be reduced and By providing a step in the thinner center electrode in the shaft hole of the thinner insulator, it is possible to prevent smoldering due to carbon that occurs due to incomplete combustion of the air-fuel mixture. This has an excellent effect of improving the durability of the engine spark plug itself.

[Brief explanation of the drawing]

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

FIG. 2 is an enlarged sectional view of the main part thereof.

FIG. 3 shows the results of a comparative test conducted with a conventional example installed on an actual machine.

[Explanation of symbols]

1 Spark plug for internal combustion engine 2 Insulator 3 Shaft hole 4 Center electrode 5　Ignition part 6 Side circumference 7 Metal coating part 8 Conductive glass seal 9 Resistor 10 Terminal electrode 11 Main metal fittings 12 Outer electrode 13 Thread part 14 Stepped section 15 Inner bottom 16 Open end of insulator

Claims (1)

[Claims] Claim 1: Disposing outer electrodes at positions facing each other around the firing part at the tip of the center electrode, and covering the spark discharge part of the firing part at the tip of the center electrode with a noble metal. Similarly, if the tip of the insulator is made thinner while providing a step in the insulator, the step at the step is L1, the distance from the inner bottom of the step to the open end of the insulator is L2, and the insulator is The length of the thinned part at the tip of the body is L3, the thickness of the thinned insulator is t, the diameter of the center electrode is d, the inner bottom and the width of the step provided on the center electrode are G, respectively. When F, 0.3mm≦L1≦1mm
, L1+0.5mm≦L2mm, L2≦L3, 0.1m
A spark plug for an internal combustion engine that satisfies m≦G, F, 0.15≦t/d≦0.45.