JPH07272826A - Spark plug - Google Patents

Abstract

PURPOSE:To provide a spark plug having excellent exhausting characteristic against sparks and also possibly maximum durability by forming noble metal parts at the firing surface and front surface of the center electrode. CONSTITUTION:A foremost noble metal part 5 and a tail noble metal part 6 both chiefly containing platinum are provided at the peripheral surface 32 of the tip 31 of a center electrode 3. The noble metal part 5 is attached by welding to the peripheral surface 32 of the tip 31 of the center electrode 3 confronting the first aerial spark discharge gap G1, while the part 6 is attached by welding to the peripheral surface 32 of the tip 31 of the center electrode 3 confronting the foremost face 22 of an insulating material 21. The parts 5, 6 are arranged alongside the whole peripheral circumference of the center electrode 3 in a band form. The axial length T of the noble metal part 5 should preferably be between 0.5L<=T<=1.2L, where L is the outside electrode diameter in the plug long axis direction. The part 6 is positioned as protruding 0-0.2mm from the foremost surface 22 and intruding 0.4mm or more into the shaft hole 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the durability of a spark plug having a noble metal portion on the surface of the ignition portion of a center electrode.

[0002]

2. Description of the Related Art In a spark plug, a rod-shaped center electrode is fitted to an insulator having a shaft hole in a state where its tip portion projects from the tip surface of the insulator, and the insulator is fitted to a tubular metal shell. It has a complicated structure. An outer electrode is provided at the tip of the metallic shell, and a spark discharge gap is formed between the tip of the outer electrode and the outer peripheral surface of the tip (firing portion) of the center electrode. The center electrode or the outer electrode is made of a heat-resistant metal such as a nickel alloy, and a noble metal portion having excellent spark wear resistance such as platinum is provided on the surface of the center electrode facing the spark discharge gap or the surface of the outer electrode.

Further, in the spark plug, in addition to the first spark discharge gap between the tip of the outer electrode and the tip of the center electrode, a second spark is provided between the tip of the insulator and the tip of the outer electrode.
When the spark discharge gap is formed, when the tip of the insulator is contaminated with carbon or the like, the carbon is burned off by flying in the second spark discharge gap, so that insulation deterioration due to smoldering can be prevented. Furthermore, in a multi-pole spark plug in which multiple outer electrodes are provided at the tip of the metal shell, the spark consumption of only one center electrode is large, and therefore the circumference of the ignition part of the center electrode is reduced in order to reduce spark consumption of the center electrode. It is effective to improve the durability by providing a noble metal part on the.

[0004]

As shown in FIG. 2 (a), the center electrode of these spark plugs has the most frequent spark discharge S at the ignition surface of the first air spark discharge gap G1 when the insulation resistance is normal. 2B, the first air spark discharge gap G1 expands due to spark consumption. As the expansion of the first air spark discharge gap G1 progresses, as shown in FIG. 2C, the spark discharge S frequently occurs in the second air spark discharge gap G2. As shown in the figure, the center electrode 3 is consumed so as to be hollowed around the position of the tip surface 22 of the insulator 2. An object of the present invention is to provide a structure of a spark plug having a noble metal portion on the outer peripheral surface of the tip portion (ignition portion) of the center electrode, which has excellent spark wear resistance and maximum durability.

[0005]

According to the present invention, a rod-shaped center electrode and an insulator having a shaft hole for holding the center electrode are provided.
An outer side that forms a spark discharge gap between a tubular metal shell fitted onto the insulator and a tip of the center electrode that is provided at the tip of the metal shell and protrudes from the tip surface of the insulator. In a spark plug consisting of an electrode, on the surface of the center electrode, the noble metal portion on the front side in the portion facing the spark discharge gap,
A rear noble metal portion is provided at a portion facing the end of the shaft hole.

According to a second aspect of the present invention, the outer electrode is provided so as to project from the tip surface of the metal shell, the tip portion of the outer electrode is directed toward the center electrode, and the tip portion of the outer electrode and the center electrode are formed. The first air spark discharge gap G1 with the tip portion and the second air spark discharge gap G2 between the insulator surface of the outer electrode and the tip surface of the insulator are 0.4 mm. ≤ G2 ≤
G1 .ltoreq.1.5 mm. According to the configuration of claim 3, the front noble metal portion is formed at a position corresponding to the tip of the outer electrode, and the rear noble metal portion is 0 from the tip surface of the insulator.
It was formed at a position protruding by 0.4 mm to 0.2 mm and entering 0.4 mm or more. In the structure of claim 4, the diameter of the tip portion (ignition portion) of the center electrode is formed as small as 1.0 mm to 2.5 mm.

[0007]

According to the present invention, the ignition surface of the center electrode with the noble metal portion facing the first air-spark discharge gap G1 is provided.
Since it is formed on the surface of the center electrode that extends from the tip of the insulator to the inside of the shaft hole, erosion of the tip of the center electrode due to spark discharge can be most effectively prevented. As a result, spark consumption of the ignition part of the center electrode can be reduced to the minimum, and the durability of the spark plug can be improved. Further, since it is not necessary to cover the entire tip portion of the center electrode, the amount of precious metal is small and the cost can be reduced.

In the structure of claim 2, 0.4 mm≤G2≤
Since G1 ≤ 1.5 mm, the ignitability is high, the spark discharge required voltage can be in the practical range, the cleaning action of smoldering is high, and the decrease in the resistance value of the insulator can be reliably prevented. In the structure of claim 3, spark consumption of the sparking surface of the center electrode facing the first air spark discharge gap G1 and the second air spark discharge gap can be effectively reduced with a minimum of noble metal, and the durability of the spark plug is improved. Is improved. In the structure of claim 4, since the diameter of the ignition part of the center electrode is made small, the amount of precious metal used can be reduced, and the extinguishing action of the center electrode is reduced, so that the ignition performance can be improved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the tip of a two-pole spark plug 100 according to one embodiment of the present invention. Spark plug 10
0 is formed by fitting a rod-shaped insulator 2 provided with an axial hole 21 having a circular cross section into a cylindrical metal shell 1. The center electrode 3 is fitted into the shaft hole 21 in a state in which a tip portion 31 serving as a firing portion of the center electrode 3 projects from the tip surface 22 of the insulator 2. The tip end of the insulator 2 is a tapered leg long portion 23, and the tip end surface 22 is a flat surface.

An engine mounting screw 11 is provided on the outer periphery of the tip of the metal shell 1, and two outer electrodes 4, 4 are welded to the tip surface 12 so as to face each other. Each of the outer electrodes 4 is formed of a heat-resistant metal rod having a substantially rectangular cross section, the lower end of which is welded to the front end surface 12 of the metal shell 1 and the column portion 41 projecting in the axial direction and the upper end of the column portion 41. Firing part (tip part) 4 of the outer electrode 4 bent in the direction of the center electrode 3.
It consists of 2. Tip surface 43 of ignition part 42 of outer electrode 4
Is a cylindrical surface coaxial with the outer peripheral surface 32 of the tip portion 31 of the center electrode 3, and the outer peripheral surface 3 of the tip portion 31 is
A first air spark discharge gap G1 is formed between the first and second air sparks.

In this spark plug 100, the second air spark discharge gap G2 between the insulator ring surface 44 of the ignition part 42 of the outer electrode 4 and the leg long portion 23 of the insulator 2 and the tip surface 22. A second spark discharge gap consisting of a creeping spark discharge gap G3 along the surface of the is formed. In the second spark discharge gap, when soot or the like adheres to the surface of the tip of the insulator and the insulation resistance of the spark plug 100 decreases, a creeping discharge that causes sparks along the tip surface 22 is generated, and soot or the like is generated. It has the function of performing a burn-out cleaning action, preventing the insulation resistance of the spark plug 100 from lowering, and reducing the occurrence of flying mistakes.

On the outer peripheral surface 32 of the tip portion 31 of the center electrode 3, a front noble metal portion 5 and a rear noble metal portion 6 which are mainly made of platinum are provided. The front noble metal portion 5 is formed by welding to the outer peripheral surface 32 of the tip end portion 31 of the center electrode 3 facing the first air spark discharge gap G1, and the rear noble metal portion 6 is formed into the insulator axial hole 21. It is formed by welding to the outer peripheral surface 32 of the front end portion 31 of the center electrode 3 facing the front end surface 22. The front noble metal portion 5 and the rear noble metal portion 6 are formed in a strip shape along the entire circumference of the center electrode 3 in this embodiment. The axial length T of the noble metal portion 5 on the front side is preferably in the range of 0.5 L to 1.2 L with respect to the thickness L of the outer electrode in the axial direction of the plug. The rear precious metal part 6 has a tip surface 2
It is provided at a position projecting from 0 mm to 0.2 mm from 2 and entering the inside of the shaft hole 21 by 0.4 mm or more.

The numerical limitation of the formation position of the rear noble metal portion 6 is as follows.
The reason is as follows. A gap of about 0.1 mm is provided between the inner periphery of the tip of the shaft hole 21 and the outer periphery of the center electrode 3 to prevent the insulator 2 from being broken due to a difference in thermal expansion. If the amount of penetration into the inside of 21 is less than 0.4 mm, discharge sparks will enter through the gap and spark consumption of the center electrode 3 will easily start from inside the shaft hole 21. Further, if the protruding amount from the front end face 22 is smaller than 0 mm, the significance of providing the rear noble metal portion 6 is lost, and if it is larger than 0.2 mm, the effect is hardly increased. Further, the length T in the axial direction of the front side precious metal portion 5 is set to 0.5L to 1.2L, because if it is 0.5L or less, it is not possible to sufficiently cover the variation of the spark discharge generation position, and 1.2L. This is because the cost is increased and the effect is not increased even in the above case.

The front precious metal portion 5 and the rear precious metal portion 6 are
In this embodiment, as shown in FIG. 3A, a noble metal wire 50 made of platinum, iridium, a platinum nickel alloy or a platinum iridium alloy is brought into contact with the outer periphery of the center electrode 3,
As shown in (b), the tip portion 31 is melted by the laser beam R.
To the outer peripheral surface 32 of the. According to this laser fusion,
The bond strength between the noble metal and the base material of the center electrode is high, and the peeling resistance of the noble metal part can be improved as compared with the case where the noble metal part is formed by other methods such as electric resistance welding, cold forging, and inert gas shield welding.

The relationship between the first air spark discharge gap G1 and the second air spark discharge gap G2 is 0.4 mm≤G2≤G1≤
It is desirable to set it to 1.5 mm. The first air spark discharge gap G1 and the second air spark discharge gap G2 are 0.4 mm.
If it is smaller, the ignitability due to sparks is low, so the ignitability at a lean air-fuel ratio is reduced. Also, the first air spark discharge gap G
If 1 and the second air spark discharge gap G2 are larger than 1.5 mm, the required voltage required for spark discharge in the spark plug 100 becomes too high, which lowers the practicality. further,
If G2 ≤ G1, spark discharge easily occurs in the creeping spark discharge gap G3, the insulator has a high cleaning function, and the insulation resistance is prevented from lowering due to carbon contamination or the like.

Next, the performance of the spark plug of the present invention will be described. In FIG. 4, the diameter of the tip outer peripheral surface 31 is 2.0 mm.
The spark plug 100 having the center electrode 3 of
5000cc when mounted on a 0cc, 6-cylinder gasoline engine
The following shows the amount of expansion of the first air spark discharge gap G1 and the amount of expansion of the second air spark discharge gap G2 and the required voltage when a continuous durability test was conducted for 400 hours under the operating conditions of m × W · O · T.

FIG. 4A shows the tip 31 of the center electrode 3.
A) when the noble metal part is not provided, b) the front noble metal part 5
6 shows the amount of expansion of the spark discharge gap in the case where only the rear noble metal portion 6 is provided, in the case where only the rear precious metal portion 6 is provided, and in the case where both the front precious metal portion 5 and the rear precious metal portion 6 are provided. Figure 4 (b)
Shows the change in the spark discharge required voltage at 6 atmospheres and room temperature in the desktop test. As a result, it can be seen that the spark plug of the present invention has the smallest expansion amount of the spark discharge gap and the lowest required voltage.

FIG. 4C shows the air-fuel ratio A / F after the 400-hour durability test and the number of occurrences of ignition mistakes. Figure 4
(D) is a maximum of 1 in pattern operation (repetition of idling and low speed operation) of the pollution test at -10 ° C using the spark plug after 400 hours endurance test.
It indicates the number of cycles at which the insulation resistance becomes 10 megohms when 0 cycles are performed. From these test results, it is found that the spark plug 100 of the present invention including the center electrode 3 having the front noble metal portion 5 and the rear noble metal portion 6 according to the present invention maintains excellent ignition performance and stain resistance performance. Has been proven.

FIG. 5A shows the diameter of the tip portion 31 of the center electrode 3 and the spark discharge gap G1 after the 400-hour durability test.
5 and (b) are graphs showing the ignition limit, showing the ratio of the expansion amounts of G2 and G2 to those with and without the noble metal layer. As a result, the diameter of the tip portion 31 of the center electrode 3 is 1.0
When it is less than mm, there is no difference in the expansion ratio of the spark discharge gap between when there is no noble metal, and when it is more than 2.5 mm, the difference in ignition limit due to the thickness of the center electrode is small.

Further, in the multipolar spark plug, there is a problem that the ignition performance is deteriorated due to the extinction of a plurality of outer electrodes 4, so that it is made as thin as possible to reduce the extinction effect by the center electrode 3 and the extinction effect by the surface of the electrode It is desirable to make it small. Therefore, the diameter of the tip portion 31 of the center electrode 3 is set to 1.
When it is smaller than 0 mm, the durability of the center electrode 3 is reduced and the manufacturing becomes difficult in view of mechanical strength. Therefore, the diameter of the tip portion 31 of the center electrode 3 is 1.0 mm to 2.5 m.
Set to m.

FIG. 6 shows a spark plug having another structure according to the present invention. In (a), the noble metal portion was formed only on the surface of the center electrode 3 in the portion facing the firing surface of the outer electrode 4.
(B) is a multipolar spark plug having three outer electrodes 4. (C) is a spark plug having one outer electrode 4. (D) is a multipolar spark plug having two or more outer electrodes 4 having different heights. (E) is a semi-creeping spark plug in which the outer electrode 4 is formed in an annular body integral with the metal shell 1. (F) shows an air discharge spark plug in which the front side noble metal portion 5 is provided on the front end surface of the center electrode and the rear side noble metal portion 6 is formed at a position facing the front end surface of the shaft hole of the insulator.

(G) shows a two-pole spark plug in which the tip of the outer electrode is extended in the axial direction. (H) is the outer electrode 4
Shows the air discharge spark plug in which the front end portion 42 is formed in a flat plate shape, and the front side noble metal portion 5 has a cap shape. The effects of the present invention can be obtained with these (a) to (h) or spark plugs other than these.

[Brief description of drawings]

FIG. 1 is a perspective view of a tip portion of a spark plug of the present invention.

FIG. 2 is a sectional view of a tip portion of a conventional spark plug after an endurance test.

FIG. 3 is a process drawing of forming a noble metal portion on a center electrode.

FIG. 4 is a graph showing an engine test result of a spark plug.

FIG. 5 is a graph showing an engine test result of a spark plug.

FIG. 6 is a perspective view of a tip portion of a spark plug of another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Center electrode 4 Outer electrode 5 Front noble metal part 6 Rear noble metal part 12 Tip face 21 Shaft hole 22 Tip face 23 Leg long part (tip of insulator) 31 Tip part (firing part) 32 Outer periphery Surface 42 Tip part (firing part) 43 Tip surface 44 Insulator surface 100 Spark plug G1 1st air spark discharge gap G2 2nd air spark discharge gap G3 Creeping spark discharge gap

Claims (4)

[Claims] 1. A rod-shaped center electrode, an insulator having a shaft hole for holding the center electrode, a tubular metal shell fitted on the insulator, and a tip provided on the metal shell. A spark plug comprising an outer electrode that forms a spark discharge gap between the tip of the center electrode protruding from the tip surface of the insulator, and an outer electrode that faces the spark discharge gap on the surface of the center electrode. A spark plug, wherein a side precious metal portion is provided, and a rear precious metal portion is provided at a portion facing the end of the shaft hole. 2. The outer electrode according to claim 1, wherein the outer electrode is provided so as to project from a tip surface of the metal shell, the tip portion of the outer electrode is directed toward the center electrode, and the tip portion of the outer electrode and the center electrode are formed. The first air spark discharge gap G1 between the tip and the outer peripheral surface
And the second air spark discharge gap G2 between the insulator surface of the outer electrode and the tip of the insulator is 0.4 mm ≦
A spark plug characterized in that G2 ≤ G1 ≤ 1.5 mm. 3. The method according to claim 1, wherein
A position in which the front noble metal portion is formed at a position corresponding to the tip of the outer electrode, and the rear noble metal portion protrudes from the tip surface of the insulator by 0 mm to 0.2 mm and enters 0.4 mm or more inside. A spark plug characterized by being formed on. 4. The spark plug according to claim 1, wherein the center electrode has a tip portion having a diameter of 1.0 mm to 2.5 mm.