JPH08222351A - Spark plug for internal combustion engine and its manufacture - Google Patents

Abstract

PURPOSE: To provide a spark plug that is excellent in the wear resistance of its center electrode end, has long life and is low-cost, for use in an internal combustion engine, and a method for manufacturing the same. CONSTITUTION: This spark plug for an internal combustion engine comprises an insulator 4, a center electrode 2, a housing 5, and a plurality of ground electrodes 31, 32. The spark plug has spark gaps G between each ground electrode 31, 32 and the center electrode 2. The center electrode 2 has a tapered portion 21 and noble-metal chips 211, 212 placed on those surfaces of the tapered portion 21 opposite to the discharge portions 310, 320 of the ground electrodes 31, 32. Each of the noble-metal chips 211, 212 is a platinum alloy composed of 10 to 30wt.% Ir, 2 to 10wt.% Ni and the rest Pt. The noble-metal chips 211, 212 have their respective upper ends exposed to the end face 200 of the center electrode 2.

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 and a method for manufacturing the spark plug.

[0002]

2. Description of the Related Art In an internal combustion engine used in an automobile or the like, fuel consumption reduction is strongly promoted from a global standpoint against environmental problems or global resource problems. As a concrete means, particularly in a gasoline engine, it has been dealt with by high compression, lean burn by lean mixture, and the like. When lean burn is performed, the discharge voltage required for spark discharge of the spark plug increases and the ignition performance of the air-fuel mixture tends to decrease.

This discharge voltage is further increased due to an increase in the spark gap due to the consumption of the electrodes, and the withstand voltage margin in the ignition system is reduced, and spark discharge is likely to occur in a place other than the spark gap portion. In this case, unnecessary damage is given to the internal combustion engine. In addition, a decrease in the ignition performance of the air-fuel mixture causes deterioration of the comfort of engine operation in lean air-fuel mixture combustion.

In order to avoid such problems of electrode consumption and ignition performance, a spark plug in which a noble metal tip having excellent wear resistance is arranged at the discharge part constituting the spark gap in the center electrode of the spark plug is proposed. (For example, JP-A-5-129063).

[0005]

However, the above-mentioned conventional spark plug for an internal combustion engine has the following problems.
That is, the above-mentioned conventional noble metal tip is mounted at a position away from the tip of the center electrode. In the case of spark discharge, it often starts between the strong electric field portion at the tip of the center electrode and the ground electrode. However, since the above-mentioned noble metal tip is not provided at the tip of the center electrode and the wear resistance to spark discharge is inferior, it is consumed early.

Further, as the discharge voltage rises, the oxidation of the joint between the Ni-based alloy forming the center electrode and the noble metal tip becomes remarkable, and the jointability deteriorates, and the noble metal tip is easily peeled or dropped. Become. Therefore, the discharge voltage rises due to electrode wear, which shortens the life of the spark plug.

As a measure against this, for example, Japanese Patent Laid-Open No. 6-188
As disclosed in Japanese Patent Laid-Open No. 062, there has been proposed a spark plug in which a noble metal tip is disposed on the entire tip of the center electrode. Further, an example in which a columnar or prismatic platinum rod exposed at the tip of the center electrode is attached is shown in the embodiment of Japanese Patent Laid-Open No. 5-129063. According to these spark plugs, the effect of suppressing electrode consumption is high, but the amount of precious metal required is large, which leads to a significant increase in cost and is not preferable.

The present invention has been made in view of the above-mentioned problems of the prior art, and is an internal combustion engine which has a high ignitability, an excellent wear resistance of the tip of the center electrode, a long life, and a low cost. A spark plug for a vehicle and a method for manufacturing the same are provided.

[0009]

According to the present invention, an insulator having a through hole, a center electrode held in the through hole, a housing holding the insulator, and a plurality of ground electrodes provided in the housing are provided. In a spark plug for an internal combustion engine in which a spark gap is formed between each ground electrode and the center electrode, the center electrode has a small-diameter portion having a diameter smaller than that of the body portion at its tip. At the same time, a noble metal tip is provided on the surface of the small-diameter portion facing the discharge part of the ground electrode, the noble metal tip being 10 to 30% by weight of iridium, 2 to 10% by weight of nickel,
A spark plug for an internal combustion engine, characterized in that it is a platinum alloy consisting of the balance platinum and the upper end of the noble metal tip is exposed at the tip surface of the center electrode.

What is most noticeable in the present invention is that the noble metal tip disposed on the small-diameter portion of the center electrode is composed of 10 to 30% by weight of iridium and 2 to 10% of nickel.
It is a platinum alloy consisting of wt% and the balance platinum, and the upper end of the noble metal tip is exposed on the tip surface of the center electrode.

Generally, a method of reducing the diameter of the center electrode is effective as a means for improving the ignition performance for a lean mixture, but in this case, the discharge part located at the tip of the center electrode is fine. Since it is a diameter, it becomes hot and wear is accelerated,
The life as a spark plug is shortened. Therefore, in the present invention, the upper end of the noble metal tip is exposed to the tip end surface of the center electrode while maintaining high ignitability, that is, in order to secure wear resistance in the center electrode having a small diameter. There are features.

The fact that the upper end of the noble metal tip is exposed at the tip surface of the center electrode means the following. That is, it means that the tip portion of the center electrode on the surface of the ground electrode facing the discharge portion is composed of a noble metal tip (see FIG. 3).

Further, in the above-mentioned noble metal tip, alloying iridium (Ir) and platinum (Pt) compensates for the defects of the two and obtains one having excellent wear resistance, workability and high strength. . That is, Pt has a high melting point,
Excellent wear resistance and workability, but low strength, cracks,
Cracks are likely to occur. On the other hand, Ir is a high melting point material like Pt, but has high hardness and poor workability. By alloying these, low strength, which is a drawback of Pt, and I
The low workability, which is a drawback of r, is compensated.

Here, the content of Ir is 10 to 30% by weight. When it is less than 10% by weight, there is a problem that sufficient strength cannot be obtained, and when it exceeds 30% by weight, there is a problem that workability is deteriorated.

The Pt-Ir alloy is excellent in wear resistance and the like, but has a smaller coefficient of thermal expansion than the Ni-based alloy forming the center electrode. In order to reduce the difference in thermal expansion coefficient between the Pt-Ir alloy and the Ni-based alloy, it is effective to add Ni to the Pt-Ir alloy. Here, the Ni content is 2
10 to 10% by weight. If the Ni content is less than 2% by weight, the effect of adding Ni is not sufficiently exerted, while if it exceeds 10% by weight, the wear resistance is deteriorated.

Further, it is preferable that the noble metal tip has a flat shape. As a result, the precious metal tip and the center electrode can be joined easily and reliably. In addition, the area contributing to discharge can be made larger than that of the same amount of non-flat metal tip.

Next, as a method of manufacturing the above spark plug for an internal combustion engine, an insulator having a through hole, a center electrode held in the through hole, a housing holding the insulator, and a housing provided in the housing are provided. A plurality of ground electrodes, each of which has a spark gap between the ground electrode and the center electrode, and the center electrode has a small-diameter portion having a diameter smaller than that of the body portion at its tip. With
A method for manufacturing a spark plug for an internal combustion engine, wherein a noble metal tip is provided on a surface of the small-diameter portion facing the discharge portion of the ground electrode, wherein a side surface of the small-diameter portion of the center electrode is provided. A method for manufacturing a spark plug for an internal combustion engine, which comprises exposing the upper end of the noble metal tip to the tip surface of the center electrode by removing the tip of the center electrode after joining the noble metal tip. .

Conventionally, as a method of exposing the upper end of the noble metal tip to the center electrode tip surface, there is a method of arranging the noble metal tip so as to match the center electrode tip surface and performing welding or the like. In this method, since the tip diameter of the center electrode is small, the heat capacity is small and the weld becomes very hot. Therefore, the weld at the tip of the center electrode melts out, causing not only burrs but also deformation. As a result, there is a problem that reliable joining cannot be performed.

What is most noticeable in the manufacturing method according to the present invention is that the noble metal tip is removed after the noble metal tip is bonded to the side surface of the small-diameter shaped portion of the center electrode. The upper end of the chip is exposed at the tip surface of the center electrode.

As a method of joining the above-mentioned noble metal tip to the small-diameter portion of the center electrode, there are methods such as resistance welding and laser welding. The noble metal tip is preferably flat. This allows easy and reliable bonding to the center electrode.

As a method of removing the tip portion of the center electrode, for example, a method of removing the tip portion of the center electrode by cutting or polishing and exposing the top end of the noble metal tip to the tip surface of the center electrode is used.

[0022]

In the spark plug for an internal combustion engine according to the present invention, the noble metal tip having the above specific composition is arranged in the small-diameter portion of the center electrode. The upper end of the noble metal tip is exposed at the tip of the center electrode. for that reason,
Even when spark discharge occurs from the tip of the center electrode, which is the strong electric field during spark discharge, the discharge is from the above noble metal tip.

Therefore, in the spark plug of the present invention, the electrode consumption amount of the center electrode is greatly reduced and the service life is extended as compared with the conventional one. Since the above-mentioned noble metal tip only needs to be provided on the discharge part of the center electrode, it is low in cost.

Further, in the method for manufacturing a spark plug for an internal combustion engine of the present invention, the tip of the center electrode is removed after the noble metal tip is bonded to the side surface of the small diameter portion of the center electrode. Therefore, the upper end of the noble metal tip can be easily exposed at the tip surface of the center electrode. Therefore, the excellent spark plug can be easily obtained.

Therefore, according to the present invention, there is provided a spark plug for an internal combustion engine, which is excellent in wear resistance of the center electrode tip portion while ensuring high ignition performance, has a long life, and is low in cost, and a manufacturing method thereof. can do.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A spark plug for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIGS. 1 to 3, the spark plug 10 for an internal combustion engine of this example includes an insulator 4 having a through hole 41 and the through hole 41.
A center electrode 2 held by the housing, a housing 5 holding the above-mentioned insulator 4, and two ground electrodes 31 and 32 provided in the housing 5, respectively.
A spark gap G is formed between 1, 32 and the center electrode 2.

As shown in FIGS. 1 to 3, the center electrode 2 has a small diameter portion 2 having a diameter smaller than that of the body portion 24 at its tip.
One. The ground electrode 3 in the small-diameter portion 21
Noble metal chips 211, 212 are provided on the surfaces of the 1, 32 facing the discharge parts 310, 320. The noble metal chips 211 and 212 are platinum alloys composed of 10 to 30% by weight of iridium, 2 to 10% by weight of nickel, and the balance platinum. The upper ends of the noble metal chips 211 and 212 are exposed at the tip surface 200 of the center electrode 2 as shown in FIG.

In manufacturing the spark plug 10, as shown in FIG.
Of the noble metal tip 21 on the side surface of the small-diameter shaped portion 21 of
After joining 1 and 212, the tip of the center electrode 2 is removed as shown in FIG. As a result, the upper ends of the noble metal chips 211 and 212 are exposed at the tip surface 200 of the center electrode 2. In addition, the precious metal tip 21
1,212, long diameter 1.5mm, short diameter 1.1m
An elliptical plate with m and a thickness of 0.4 mm was used.

In this example, before joining the precious metal chips 211 and 212, a flat flat portion is formed in advance on the side surface of the small-diameter portion 21, and the precious metal chips 211 and 212 are formed on the flat portion. Joined. Also, precious metal tip 2
The small-diameter portion 21 in which 11 and 212 are joined is formed into a substantially cylindrical shape by rolling, and thereafter, as shown in FIG. 4B, the tip of the small-diameter portion 21 is cut to form the noble metal tip 211. , 212 the upper end of the center electrode 2
Exposed to 00. At this time, the precious metal chips 211, 21
For No. 2, about 1/3 of the major axis was removed from the upper end.

As the center electrode 2, a Ni-base heat-resistant alloy (trademark: Inconel 600) was used. As the ground electrodes 31 and 32, a Ni-base heat-resistant alloy containing 90% by weight or more of Ni was used. Also, the spark gap G between the center electrode 2 and the ground electrodes 31, 32 is
It was set to 1.1 mm. The heat value of the spark plug 10 was set to # 20.

Next, the spark plug 1 for an internal combustion engine of this example
The oxidation resistance and the bondability of the joint surface between the noble metal chips 211 and 212 and the center electrode 2 at 0 were evaluated together with the comparative example. In the evaluation, the small-diameter portion 21 of the center electrode 2
The diameter D (hereinafter referred to as the center electrode diameter D) of 1.
0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0
mm, and N of the noble metal chips 211 and 212
The i content was changed in 2% by weight from 0 to 10% by weight. Further, Ir was fixed at 20% by weight. The Ni content of 0 is for comparison.

The evaluation test was carried out with a water-cooled 4 cylinder of 6 cylinders 2000 cc.
Using a cycle water-cooled gasoline engine, a 1-minute operation at 5000 rpm at full load and a 1-minute holding in an idling state at 650 rpm were alternately repeated, and a total of 50 hours of operation were performed. As the evaluation method, the oxidation rate of the joint surface of the center electrode of the spark plug used in the above test with the precious metal tip was determined.

As shown in FIG. 5, the above-mentioned oxidation rate of the joint surface is
What is the sum of the depth A of the upper portion 81 and the depth B of the lower portion 82 of the oxidation crack (the black-painted portions 81 and 82) with respect to the joint length C between the noble metal tip 211 and the center electrode 2. It is expressed by occupying the ratio of. That is, it is expressed by the equation of the oxidation rate of the bonding surface (%) = (A + B) / C × 100.

The evaluation results are shown in FIG. In FIG. 6, the horizontal axis represents the center electrode diameter D (mm), the vertical axis represents the noble metal tip 211,
Taking the Ni content (wt%) of 212, the results of three-stage evaluation of good joint, slight oxidation crack, and large oxidation crack were shown. It should be noted that good bonding means that the bonding surface oxidation rate is less than 20%,
Minor oxidation cracks indicate that the bonding surface oxidation rate is 20% or more and less than 40%, and large oxidation cracks indicate that the bonding surface oxidation rate is 40% or more.

As is known from FIG. 6, when the Ni content is 0, which is out of the range of the present invention, the oxidation cracks are large (bonding surface oxidation rate is 40% or more) when the center electrode diameter D is 2.5 mm or more. ), The center electrode diameter D is 1.5 mm, 2.
Oxidation cracks are slight when 0 mm (Oxidation rate of joint surface 20-40
% By weight).

On the other hand, when the Ni content was within the range of the present invention, the bonding surface oxidation rate was 20% or less and the bonding was good when the center electrode diameter D was 2.5 mm or less. If the above-mentioned bonding surface oxidation rate is less than 20%,
It has been confirmed that when used in the market, the above-mentioned noble metal chip-to-center electrode bondability problems do not occur at all.

Further, in order to evaluate the exposure effect of the upper end of the noble metal tip on the tip surface of the center electrode, as shown in FIG. 7, the tip surface 200 of the center electrode 2 and the noble metal tips 211, 212 are shown.
The wearability was evaluated by changing the distance L from the upper end surface of the. In the evaluation, the center electrode diameter D is 2.0 mm, the noble metal chips 211 and 212 are made of a platinum alloy having a Ni content of 5 wt% and Ir of 20 wt% and a residual Pt of 1.5 mm.
A flat elliptical plate with m, a short diameter of 1.1 mm and a thickness of 0.4 mm was used.

The evaluation test was carried out using a water-cooled 4 cylinder with 6 cylinders and 2000 cc.
5 at full load using a cycle gasoline engine
It was operated at 000 rpm for 100 hours and the consumability was observed. The required voltage across the discharge gap of this 100-hour operation product was measured to quantify the amount of consumption. The required voltage was measured in the gasoline engine at idling 650 rpm. The result is shown in FIG. As shown in FIG. 8, it can be seen that the required voltage (consumption amount) of the durable product is kept low if the noble metal tip is exposed at the tip of the center electrode.

As explained above, iridium 10 to 3
By exposing a noble metal tip made of platinum alloy of 0 wt%, nickel 2-10 wt%, and the balance Pt to the tip surface of the small diameter part of the center electrode, high ignitability is maintained, wear resistance is excellent, and life is long. A low-cost spark plug for an internal combustion engine and a method for manufacturing the spark plug can be provided.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional side view of a spark plug according to an embodiment.

FIG. 2 is a bottom view of the spark plug of the embodiment.

FIG. 3 is an explanatory view of a joined state of the noble metal tip in the example.

FIG. 4 is an explanatory view of a method of manufacturing the center electrode in the example.

FIG. 5 is an explanatory diagram of a bonding surface oxidation rate of a bonding surface of a noble metal tip in an example.

FIG. 6 is an explanatory view of a bondability evaluation result in the example.

FIG. 7 is an explanatory view of a joined state of the noble metal tip of the consumableness evaluation test in the example.

FIG. 8 is an explanatory view of the results of consumability evaluation in the example.

[Explanation of symbols]

 10,12. ． ． Spark plug, 2,7. ． ． Center electrode, 21, 71. ． ． Small-diameter portion, 211, 212, 711, 712. ． ． Noble metal tip, 31, 32. ． ． Ground electrode, 310, 320. ． ． Discharge unit, 4. ． ． Insulator, 5. ． ． Housing, 81, 82. ． ． Oxidation cracks,

Claims (3)

[Claims] 1. An insulator having a through hole, a center electrode held in the through hole, a housing holding the insulator, and a plurality of ground electrodes provided in the housing, each of which is grounded. In a spark plug for an internal combustion engine, wherein a spark gap is formed between the electrode and the center electrode, the center electrode has a small-diameter shaped portion having a diameter smaller than that of a body portion at the tip, A noble metal tip is provided on the surface of the shaped portion facing the discharge part of the ground electrode, and the noble metal tip is made of iridium 10 to 10.
A spark plug for an internal combustion engine, which is a platinum alloy consisting of 30% by weight, nickel 2 to 10% by weight, and the balance platinum, wherein an upper end of the noble metal tip is exposed at a tip surface of the center electrode. 2. The spark plug for an internal combustion engine according to claim 1, wherein the noble metal tip has a flat shape. 3. An insulator having a through hole, a center electrode held in the through hole, a housing holding the insulator, and a plurality of ground electrodes provided in the housing, each of which is grounded. There is a spark gap between the electrode and the center electrode, and the center electrode has a small-diameter shape portion having a diameter smaller than that of the body portion at its tip,
A method for manufacturing a spark plug for an internal combustion engine, wherein a noble metal tip is provided on a surface of the small-diameter portion facing the discharge portion of the ground electrode, wherein a side surface of the small-diameter portion of the center electrode is provided. A method for manufacturing a spark plug for an internal combustion engine, which comprises exposing the upper end of the noble metal tip to the tip surface of the center electrode by removing the tip portion of the center electrode after joining the noble metal tip.