JPH02291691A - Ignition plug - Google Patents

Abstract

PURPOSE:To ensure improved smoldering resistance of an ignition plug by carrying out metal plating or formation treatment at a point opposing the outer surface of a porcelain insulator which retains a central electrode within the inner surface of a main fitting which retains a grounding pole. CONSTITUTION:A porcelain insulator 1 retains a central electrode 2 at its tip and is fixedly contained in the containing hole 4 of an iron-made main fitting 3 which retains a grounding electrode 6. A clearance 5 is formed between the outer peripheral surface 1a of the porcelain insulator 1 and the inner peripheral surface 3a of the main fitting 3. Metal plating of 5mum or more in thickness with the use of chromium, zinc, gold, etc., or formation treatment such as phosphate treatment and chromate treatment, or both of metal plating and formation treatment are carried out on the inner peripheral surface 3a. This arrangement suppresses the elution of an Fe ion catalyst which graphitizes carbon adhering to the inner peripheral surface 3a at 500-600 deg.C, contributing to improved smoldering resistance of a plug and its increased durability.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a spark plug for an internal combustion engine.

[Conventional technology]

For example, carbon is produced due to incomplete combustion of fuel when the engine is operated at low temperatures, and this carbon adheres to the porcelain insulator of the spark plug. When the carbon attached to the porcelain insulator becomes conductive, the insulation resistance between the electrodes decreases, making it impossible to generate a normal spark between the electrodes, resulting in so-called smoldering.

As a countermeasure against this, for example, Japanese Patent Application Laid-Open No. 61-7583 has a ceramic insulator that holds a center electrode, a metal shell that houses and fixes the ceramic insulator inside, and a metal shell that faces the outer surface of the ceramic insulator. A spark plug is disclosed in which the inner surface of the metal shell is covered with an insulating partition wall.

Furthermore, for example, Japanese Patent Application Laid-Open No. 63-168985 has a ceramic insulator that holds a center electrode, and a main metal fitting that houses and fixes the ceramic insulator inside. A spark plug is disclosed in which a coating layer made of a silicone compound that is solid at room temperature is formed on the exposed surface of the leg and on the inner surface of the metal shell opposite to the surface of the leg.

[Problem to be solved by the invention]

However, the former type of spark plug has a problem in that it is difficult to manufacture because it is necessary to cover the inner surface of the metal shell with an insulating partition wall to prevent it from peeling off. On the other hand, the latter spark plug has a problem in that the coating layer evaporates at high temperatures, resulting in poor smoldering resistance.

Furthermore, none of the conventional spark plugs prevents carbon adhering to the porcelain insulator from becoming conductive, which is the essential cause of smoldering.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, in a spark plug in which a porcelain insulator holding a center electrode is housed and fixed in a metal shell holding a ground electrode, and the ground electrode and the center electrode are disposed facing each other, engine combustion The inner surface of the metal shell facing the outer surface of the porcelain insulator on the chamber side is subjected to metal plating, chemical conversion treatment, or a combination of metal plating and chemical conversion treatment.

[For production]

The inner surface of the metal shell facing the outer surface of the porcelain insulator on the engine combustion chamber side has been subjected to metal plating, chemical conversion treatment, or a combination of metal plating and chemical conversion treatment, which has a catalytic effect on the conversion of carbon from the metal shell to graphite. Iron elution can be suppressed.

〔Example〕

FIG. 1 shows the portion of the spark plug located within the combustion chamber of the engine. Referring to FIG. 1, reference numeral 1 indicates a porcelain insulator, and 2 indicates a center electrode made of nickel chromium that is projected from the tip of the porcelain insulator. A substantially cylindrical storage hole 4 is formed in the iron main metal fitting 3, and the porcelain insulator 1 is stored and fixed in the storage hole 4.

The ceramic insulator 1 has a conical shape that tapers toward the tip, and therefore a gap 5 is formed between the outer peripheral surface 1a of the ceramic insulator 1 and the inner peripheral surface 3a of the metal shell 3. An L-shaped ground electrode 6 made of nickel chrome is held at the tip of the metal shell 3, and this ground electrode 6 is disposed facing the center electrode 2. Nickel plating 7 having a film thickness of 5 mm or more is applied on the inner circumferential surface 3 a of the metal shell 3 located in the gap 5 . This plating 7 is easily applied by electroless plating or electroplating performed by inserting an electrode into the metal shell 3.

Next, the mechanism by which smoldering occurs will be explained.

For example, carbon is generated due to incomplete combustion of fuel when the engine is operated at low temperature, and this carbon adheres to the outer periphery 1a of the porcelain insulator 1 of the spark plug. This deposited carbon contains not only carbon but also a large amount of hydrocarbon polycondensation compounds and oxygenated compounds, and therefore has poor electrical conductivity. Therefore, it is a high resistance material.

Further, when this deposited carbon is heated to about 1000° C., dehydrogenation progresses, and the carbonization rate increases and the conductivity becomes somewhat higher, but it exhibits a significantly higher resistance value than graphite. The transformation into graphite, which has electrical conductivity, does not proceed until the temperature reaches about 2000°C or higher.

However, the temperature at which carbon graphitizes decreases in the presence of impurities, and especially in the presence of Fe ions, the temperature at which carbon graphitizes decreases.
It was found that the temperature decreased to about 0 to 600°C. Therefore,
If Fe ions are present, graphite will be produced even during low load and low speed operation, and smoldering will occur during short period of engine operation. As shown in Fig. 2, Fe ions are eluted from the iron main metal fitting 3 into acidic water (about pfl2 to 5) generated in the engine combustion chamber, and the eluted F
It was found that e-ions adhered to the outer peripheral surface 1a of the ceramic insulator 1. It has also been found that carbon adhering to the outer peripheral surface of the ceramic insulator 1 comes into contact with Fe ions to promote graphitization of carbon.

In this embodiment, since the nickel plating 7 is applied on the inner peripheral surface 3a of the metal shell 3, there is no fear that Fe ions will be eluted into acidic water and adhere to the outer periphery 1a of the ceramic insulator 1.

Although nickel ions are eluted from the nickel plating 7 in the acidic water, the amount eluted is extremely small, and the promotion of graphitization is significantly reduced. That is, in the present invention, by taking measures against the essential factors of smoldering resistance,
Smolder resistance can be improved. Furthermore, since the plating is difficult to evaporate even in a high-temperature atmosphere, and because it is less likely to be eluted into acidic water and disappear even after a long period of time, the durability of the smoldering resistance can be improved.

In this embodiment, nickel is used for plating, but chromium, zinc, gold, etc. may be used for plating, or alloys may be used for plating. Further, elution of Fe ions into acidic water may be suppressed by performing a chemical conversion treatment such as phosphate treatment or chromate treatment on the inner circumferential surface 3a of the metal shell 3 to form a protective film. In this case as well, similar to metal plating, measures can be taken against the essential factors of smoldering resistance, and smoldering resistance can be improved. In addition, the protective coating is difficult to evaporate even in high-temperature snow surroundings, and is less likely to elute into acidic water, making it difficult for the protective coating to disappear even after a long period of time, making it possible to improve the durability of smoldering resistance. can. Further, the inner circumferential surface 3a of the metal shell 3 may be subjected to a treatment using a combination of metal plating and chemical conversion treatment, such as zinc chromate treatment.

〔Effect of the invention〕

The inner surface of the metal shell facing the outer surface of the porcelain insulator on the engine combustion chamber side is treated with metal plating, chemical conversion treatment, or a combination of both to suppress the elution of iron, which has a catalytic effect on the conversion of carbon to graphite. , the smoldering resistance and the durability of the smoldering resistance of a spark plug can be improved with a simple structure.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the main part of the spark plug, and FIG. 2 is a diagram showing the elution state of Fe ions. 1... Porcelain insulator, 2... Center electrode, 3... Metal shell, 6... Ground electrode, 7... Nickel plating.

Claims (1)

[Claims] In a spark plug in which a porcelain insulator holding a center electrode is housed and fixed in a metal shell holding a ground electrode, and the ground electrode and the center electrode are arranged facing each other, the ignition plug faces the outer surface of the porcelain insulator on the engine combustion chamber side. A spark plug in which the inner surface of the metal shell is subjected to metal plating, chemical conversion treatment, or a combination of metal plating and chemical conversion treatment.