JP2932403B2 - Spark plug for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug having a multi-pole outer electrode used in an internal combustion engine.

[0002]

Recently, in the spark plug for use in an internal combustion engine with the development of the internal combustion engine, in order to prevent the consumption Worn of the center electrode by the spark discharge, the spark section and the firing portion of the center electrode leading end tip A spark plug is known in which a noble metal tip is welded to an outer electrode disposed at a position opposite to the spark plug to improve spark erosion resistance due to spark discharge. The outer electrode protrudes into the room, and the outer electrode is likely to be broken by vibration generated by the internal combustion engine to which the spark plug is mounted, which may damage the internal combustion engine.

Further, 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 having a structure in which an outer electrode is arranged at a position opposite to a tip of a firing portion of a center electrode, the ignitability to an air-fuel mixture is reduced by lowering the firing position.

[0004] Therefore, on the side of the ignition portion at the tip of the center electrode,
There has been proposed an arrangement in which a plurality of outer electrodes are arranged so as to face each other, and a spark is emitted between a side surface of a firing portion of a center electrode and these outer electrodes to ignite an air-fuel mixture.

[0005]

However, in the above prior art, a plurality of outer electrodes are arranged on the side of the ignition portion at the tip of the center electrode so as to face each other, and the side of the ignition portion of the center electrode and these outer electrodes are arranged. Between the fires,
When the spark plug to adopt a structure to be ignite air-fuel mixture, but which must be multipolar in order to ensure the resistance vanishing耗性outer electrode. The spark discharge between the ignition part and a plurality of outer electrodes of the center electrode tip becomes a burden with respect to the firing portion of the center electrode, the spark discharge extinction of the firing portion of the same time the center electrode tip and the vanishing Worn outer electrode Wear also progresses remarkably, and even if the number of electrodes is increased in order to secure the durability of the outer electrode , the durability of the spark plug itself can not be secured . Further, when the outer electrode is multi-polarized, especially when the outer electrode has three or more electrodes, the cooling action is large, the ignitability to the air-fuel mixture is reduced, and gas exchange inside the ignition part is difficult to be performed, and smoldering by carbon is sufficiently performed. There is a problem that cannot be dealt with.

Therefore, the present invention is to improve the disadvantages of the above-mentioned conventional one. In order to increase the number of electrodes of the outer electrode, the durability of the spark plug itself is improved, and the spark plug is ignited to the air-fuel mixture. It is possible to sufficiently cope with carbon smolder.

[0007]

Means for Solving the Problems] Therefore, the double so as to be opposed to the side peripheral around the firing portion of <br/> tip of the center electrode
A number of outer electrodes are arranged, a spark discharge portion of a firing portion at the center electrode tip is covered with a noble metal, and a step is provided in the insulator of the center electrode to reduce the diameter of the tip, and
When the tip of the insulator is reduced in diameter, the step in the step is L1, the length from the inner bottom of the step to the opening end of the insulator is L2, the length of the reduced portion of the insulator tip is L3, When the thickness of the insulator whose diameter is increased is t, the diameter of the center electrode is d, and the inner bottom and the width of the step provided in the center electrode are G and F, respectively,
0.3 mm ≦ L1 ≦ 1 mm, L1 + 0.5 mm ≦ L2,
L2 ≦ L3, 0.1 mm ≦ G, F, 0.15 ≦ t / d ≦
0.45 is satisfied.

[0008]

With the above configuration, a plurality of outer electrodes are arranged so as to face each other around the ignition portion at the tip of the center electrode so as to be opposed to each other , and mixed with the ignition portion for a long time. Even if a spark discharge is performed to ignite the spark, the side circumference of the ignition portion at the tip of the center electrode facing the outer electrode that performs the spark is covered with a noble metal, so that it is possible to reduce the spark consumption due to the spark discharge. it can.

Further, the thickness of the insulator tip is reduced by reducing the diameter of the insulator tip, and furthermore, a step is provided on the center electrode in the shaft hole of the thinned insulator tip, whereby mixing is achieved. The heat generated by the ignition of the air is easily absorbed by the insulator to prevent carbon from adhering . At the same time, during the discharge between the center electrode step and the metal shell, the carbon adhering to the insulator is removed from the insulator surface and the inner wall of the insulator shaft hole by a spark discharge, and the mixture to the air-fuel mixture is removed. It is possible to cope with carbon smolder generated by ignition.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. (1) is a spark plug for an internal combustion engine according to an embodiment of the present invention. The spark plug (1) for an internal combustion engine has a center electrode (5) having a firing portion (5) at the tip of a shaft hole (3). An insulator (2) that holds 4) and seals one end of the resistor (9) and the terminal electrode (10) sandwiched by the conductive glass seal (8) in the shaft hole (3); The center electrode (4) is held on the side circumference (6) of the center electrode (4) held at the tip of the shaft hole (3) of the insulator (2). A metal shell (11) comprising a plurality of outer electrodes (12) at equal intervals along the side circumference (6) of (4), and further having a screw portion (13) on the side circumference for screwing when mounted on an internal combustion engine. )
It is composed of

The spark plug (1) for the internal combustion engine (1) has an insulator (2) and a peripheral portion (5) of a spark portion (5) at the tip of a center electrode (4) held at the tip of a shaft hole (3). 6) is, for example, Pt-20% Ir or Pt10
It is covered with a noble metal coating (7) made of a 40% Ni alloy or the like.

Also, an insulator (2) for the center electrode (4)
In the axial hole (3) within the co-when diameter of the tip of the center electrode (4) is provided a stepped portion (14), to reduce the diameter of the insulator (2) tip. At this time, the step in the step (14) is
1. L2 from the inner bottom portion (15) of the step portion (14) to the insulator opening end (16), L3 the length of the reduced diameter portion at the tip of the insulator (2), and the reduced diameter insulator (2) The thickness of the tip is t, the diameter of the center electrode (4) is d, and the inner bottom (15) and the step (14) of the step (14) provided on the center electrode (4 ).
Width each G, as a F a, 0.3 ≦ L1 ≦ 1mm, L1
+0.5 mm ≦ L2, L2 ≦ L3, 0.1 mm ≦ G,
F, satisfying 0.15 ≦ t / d ≦ 0.45.

Since the actual traveling example of the present invention has the above-described structure, the center electrode (4) is located at a position facing each other around the ignition portion (5) at the tip of the center electrode (4) or the center electrode (6). A plurality of outer electrodes (12) are arranged at equal intervals along the side circumference (6) of (4), and between the outer electrode (12) and the ignition portion (5) at the tip of the center electrode (4). in, it will row a spark discharge for igniting the air-fuel mixture over a long period of time. like this
Even so, the side circumference (6) of the ignition portion (5) at the tip of the center electrode (4) facing the plurality of outer electrodes (12) that perform the sparking is
Since it is covered with the noble metal coating portion (7), it is possible to reduce spark erosion due to spark discharge, and to make the center electrode (4) thinner, thereby improving ignitability.

Further, the insulator (2) of the center electrode (4)
L1, the step in the step (14) is L1, the distance from the inner bottom (15) of the step (14) to the insulator opening end (16) is L2, and the length of the portion of the insulator (2) having a reduced diameter at the tip. L3, the thickness of the tip of the reduced-diameter insulator (2) is t, the diameter of the center electrode (4) is d, the inner bottom (15) of the step (14) provided on the center electrode (4 ) and The width of the step (14) is G and F, respectively . In that case , 0.3 ≦ L1 ≦ 1 mm, L
1 + 0.5 mm ≦ L2, L2 ≦ L3, 0.1 mm ≦ G,
It stepped portions so as to satisfy F (14) is provided, also the tip of the center electrode (4) to co With smaller diameter, the insulator (2) satisfies 0.15 ≦ t / d ≦ 0.45 tips So as to reduce the diameter . As a result, the thickness of the center electrode (4) is reduced and the thickness t at the tip of the insulator (2) is reduced, so that heat generated by ignition of the air-fuel mixture is easily absorbed by the insulator (2). In addition, adhesion to the surface of the carbon insulator (2) caused by incomplete combustion of the air-fuel mixture is prevented by the self-cleaning action .
In addition , the shaft hole (3) at the tip of the thinned insulator (2)
By providing a step portion (14) on the side peripheral surface of the center electrode (4), even if carbon adheres to the inner wall of the shaft hole (3) at the tip of the insulator and the outer peripheral surface of the insulator, the insulation resistance is maintained. Due to the drop, a spark discharge occurs between the step (14) provided on the side peripheral surface of the center electrode (4) and the inner wall of the shaft hole (3).
When a spark discharge occurs, carbon attached to the inner wall of the insulator (2) can be removed by the spark discharge.
You. Therefore, it is possible to cope with poor ignition performance of the spark plug (1) to the air-fuel mixture, which is caused by carbon smolder generated by the ignition of the air-fuel mixture.

[0015] Incidentally, the side peripheral of the firing portion of the distal end of the axial hole (3) the center electrode held in the tip (4) of the insulator constituting the spark plug (1) for an internal combustion engine (2) (5) (6 The precious metal coating portion (7) covering ()) may be formed by a plastic working method. It may be by brazing.

Therefore, the embodiment of the present invention will be described mainly.
Two outer electrodes are provided in opposition to the tip side periphery of the electrodes;
= 0.3 mm, L2 = 1.0 mm, L3 = 2.5 mm,
F = 0.25 mm, G = 0.25 mm, d = 2.7 m
m, t = 0.9mm, this ● mark that was t / d = 0.33
Of the invention and, as a conventional example, a spark plug marked with a circle marked with two outer electrodes opposite to the periphery of the center electrode, and an L-shaped outer surface opposite to the tip surface of the center electrode. The comparison was made on a real machine using a spark plug marked X with an electrode. In this comparative test, the insulation resistance was measured in accordance with the number of cycles, with the choke closed at 3/4 and room temperature at room temperature, with 3 minutes of idling and 1 minute of stop as one cycle. As a result, the outer
A spark plug with multiple electrodes is a conventional multi-pole spark plug .
It was recognized that a decrease in insulation resistance could be suppressed as compared with the park plug (FIG. 3).

[0017]

As described above, according to the present invention, the side circumference of the firing portion of the center electrode leading end of the spark plug comprising a plurality of outer electrodes by coating the noble metal coating unit, reduces the consumption Worn ignition portion caused by spark discharge At the same time, in the shaft hole of the insulator whose tip is thinned, by providing a step on the center electrode having a reduced diameter, it is possible to prevent smoldering due to carbon generated due to incomplete combustion of the air-fuel mixture. So multipolar
The present invention has an excellent effect of improving the fouling resistance and durability of the spark plug for an internal combustion engine itself.

[Brief description of the drawings]

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

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

FIG. 3 is a result of a comparative test performed together with a conventional example by mounting on an actual machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spark plug for internal combustion engines 2 Insulator 3 Shaft hole 4 Center electrode 5 Firing part 6 Side circumference 7 Metal coating part 8 Conductive glass seal 9 Resistor 10 Terminal electrode 11 Metal shell 12 Outer electrode 13 Screw part 14 Step part 15 Inside Bottom 16 Insulator open end

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-249877 (JP, A) JP-A-61-61390 (JP, A) JP-A-61-230282 (JP, A) JP-A 64-64 27176 (JP, A) JP-A-2-181383 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01T 13/00-13/56

Claims (1)

(57) [Claims] 1. A around the firing portion of the tip of the center electrode as well as arranging a plurality of outer electrodes so as to face the side peripheral, a spark discharge portion of the firing portion of the center electrode tip and coated with precious metal, the central Provide a step in the electrode insulator
When the tip is reduced in diameter and the tip of the insulator is reduced, the step in the step is L1, the distance from the inner bottom of the step to the opening end of the insulator is L2, and the portion of the insulator tip is reduced in diameter. When the length of the insulator is L3, the thickness of the thinned insulator is t, the center electrode diameter is d, and the inner bottom and the width of the step provided on the center electrode are G and F, respectively, 0.3 mm ≤ L1 ≤ 1 mm, L1
+ 0.5mm ≦ L2, L2 ≦ L3, 0.1mm ≦ G,
F, a spark plug for an internal combustion engine that satisfies 0.15 ≦ t / d ≦ 0.45.