JPH0612680B2 - Spark plug - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an ignition plug mounted on a cylinder head of an internal combustion engine, and more particularly to an ignition plug having a ground electrode excellent in both corrosion resistance and thermal conductivity. .

[Technical Background of the Invention and Problems Thereof] A spark plug having a structure as shown in FIG. 1 has been conventionally known as a spark plug for an internal combustion engine. This spark plug has a tubular spark plug fitting 1 that serves as a fitting for an internal combustion engine, an L-shaped ground electrode 2 fixed to the lower end of the spark plug fitting 1 by butt welding or the like, and the spark plug fitting 1 It is composed of an insulator 4 fixedly attached to each other via O-rings 3a and 3b, and a center electrode 5 facing the ground electrode 2 provided at the tip of the insulator 4.

In recent years, from the viewpoint of exhaust gas regulation and energy saving, there is an increasing demand for a higher combustion rate of a gasoline engine, and as one of the means, a protruding spark plug is used.

That is, in a general spark plug, the length 1 of the center electrode 5 in FIG. 1 is set to about 4.5 mm, but in this protruding type spark plug, the length 1 of the center electrode 5 is 9.5.
The ignition spark is generated at a position away from the inner wall of the internal combustion engine. Therefore, the ground electrode that directly contacts the combustion gas of the protruding spark plug is subjected to severer thermal conditions than in the conventional spark plug. Therefore, if the ground electrode is made of a Ni-based low alloy such as Ni-2Cr-3Mn-2Si which has been used for the ground electrode of a general spark plug, abnormal corrosion 6 along the grain boundary will occur as shown in FIG. In particular, this abnormal corrosion 6 is likely to occur at the curved portion, so that the ground electrode may be damaged during use.

On the other hand, Cr, such as Inconel 600, which has good heat resistance and corrosion resistance
If the ground electrode is made of a Ni-based heat-resistant alloy containing 10% by weight or more, the problem of abnormal corrosion is solved, but since the thermal conductivity is less than half that of the alloy used for normal ground electrodes, There was a problem that the temperature became extremely high during use, and the ground electrode was prematurely worn and the ground electrode became a heat source to cause early ignition.

[Object of the Invention] The present invention has been made to solve such problems, and an object of the present invention is to provide an ignition plug having a ground electrode excellent in both corrosion resistance and thermal conductivity.

[Summary of the Invention] That is, in the spark plug of the present invention, the ground electrode fixed to the lower end of the spark plug fitting is provided with 10 wt% of Cr on the outer periphery of the core material made of a Ni-based low alloy or pure Ni having a total alloy element content of 10 wt% or less. It is characterized by comprising a clad material coated with a coating material made of a Ni-base heat-resistant alloy containing the above.

The Ni-based low alloy used in the present invention is Ni-2Cr-
3Mn-2Si, Ni-1Mn-1Si, industrial pure Ni
Ni-based low alloys having a total alloying element content of 10% by weight or less. This Ni-based low alloy is a part that particularly contributes to thermal conductivity. If the total amount of alloying elements is too large, the thermal conductivity will decrease and early wear and ignition of the ground electrode will occur. preferable.

Examples of the Ni-base heat-resistant alloy used in the present invention include Inconel 600, (Ni-16Cr-8Fe), and nichrome alloy (Ni-20Cr). Cr of this Ni-based heat-resistant alloy improves corrosion resistance in particular. If this amount is too small, the corrosion resistance decreases and abnormal corrosion occurs, so 10% by weight or more is preferable.

The ground electrode in the present invention usually has a width of 2.
It is molded to have a thickness of 2 to 3.0 mm and a thickness of 1.4 to 1.8 mm, and the ratio of the outer diameter of the core portion to the outer diameter of the coating portion is 1: 1.1.
Approximately 1: 1.6 is suitable.

The ground electrode in the present invention is manufactured, for example, as follows. That is, first, a pipe made of a Ni-based heat-resistant alloy,
Insert a Ni base alloy or pure Ni round bar slightly smaller than the inside diameter of this pipe, and after swaging and hot rolling, cold draw to the specified size and clad with the specified size and cross-sectional shape. Manufacture lumber. The composite rectangular wire thus obtained is cut into a certain length,
After welding to the spark plug fitting, an L-shaped bending process is performed.
At this time, in order to prevent the core material from being exposed from the tip portion of the ground electrode, it is desirable to crimp the tip or spray the Ni-base heat-resistant alloy onto the tip.

Embodiments of the Invention Next, embodiments of the present invention will be described.

Example 1 An Inconel 600 pipe having an outer diameter of 60 mm and an inner diameter of 50 mm was inserted with a Ni-2Cr-3Mn-2Si round bar having an outer diameter slightly smaller than the inner diameter of the pipe, and swaging and hot rolling. After processing, the material was cold drawn to produce a clad material having a width of 2.8 mm and a thickness of 1.6 mm. This is cut into a predetermined length (about 18 mm), then one end is welded to a spark plug metal fitting made of carbon steel, and then bending is performed so that the core 2a has a Ni base alloy and the outer peripheral portion 2b as shown in FIG.
To form a ground electrode 2 composed of a Ni-based heat-resistant alloy.
The structure of the other parts of the ground electrode is the same as that of the conventional ground electrode shown in FIG.

Attach this ground electrode to a high burn rate gasoline engine,
After continuous operation at 6000 rpm for 100 hours, no corrosion was found on the curved portion of the ground electrode. Although some corrosion was observed at the exposed tip of the core 2a of the ground electrode, no functional failure occurred.

Example 2 When the tip of the ground electrode obtained in Example 1 was caulked to form the shape shown in FIG. Only slight corrosion was observed.

Example 3 A ground electrode having the shape shown in FIG. 5 was obtained by coating the tip of the ground electrode obtained in Example 1 with Inconel 600 by thermal spraying. In the figure, reference numeral 3 indicates Inconel 600 that has been sprayed.

When this was used and a real machine test was conducted under the same conditions as in Example 1, no corrosion of the tip portion of the ground electrode occurred.

[Effects of the Invention] As described above, in the spark plug of the present invention, the outer peripheral portion of the ground electrode, which is subject to corrosion, is made of a Ni-base heat-resistant alloy having excellent corrosion resistance, and the core portion is made of Ni having good thermal conductivity. Since the base alloy or pure Ni is used, there is no risk of causing abnormal corrosion of the curved portion or early ignition, and stable characteristics can be obtained over a long period of time.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a conventional spark plug, and FIG. 2 is a vertical cross-sectional view showing a state after using a ground electrode made of a conventional metal,
3 to 5 are enlarged vertical sectional views of the ground electrode in the spark plug according to the embodiment of the present invention. 1 ... Spark plug metal fitting 2 ... Ground electrode 2a ... Core part 2b ... Outer peripheral part 4 ... Insulator 5 ... Center electrode 6 ... Abnormal corrosion

 ─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-55-163786 (JP, A) JP-B 38-9355 (JP, B1) JP-B 48-15531 (JP, B1) US Patent 2266318 (US) , A)

Claims (3)

[Claims] 1. A ground electrode comprising a core material made of a Ni-based low alloy or pure Ni having a total alloy element content of 10% by weight or less, and C on the outer periphery of the core material.
An ignition plug comprising a material coated with a coating material made of a Ni-base heat-resistant alloy containing 10% by weight or more of r. 2. The spark plug according to claim 1, wherein the tip of the ground electrode is covered with a Ni-base heat-resistant alloy containing 10% by weight or more of Cr. 3. The spark plug according to claim 1, wherein the spark plug is a protruding type.