JP2805322B2 - Spark plug for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spark plug used for an internal combustion engine.

(Prior Art) Conventionally, in a spark plug used for an internal combustion engine, a central electrode is made of Ni or Ni encapsulated with a Cu core having excellent heat conductivity.
It is generally made of Ni alloy, but in order to reduce the wear of the center electrode tip due to ignition, the tip of the center electrode is made of a noble metal with excellent wear resistance and corrosion resistance, such as Pt or Pt alloy. It has been proposed to join different chips.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional one, when the center electrode is made of Ni or Ni alloy encapsulating a Cu core having excellent thermal conductivity, it is difficult to use for a long time. Corrosion is likely to occur due to the heat generated by the ignition of the fuel and the material of the fuel, and it is difficult to maintain reliable ignition because of high spark consumption. Therefore, a tip made of Pt or Pt alloy having excellent spark erosion resistance and corrosion resistance has been joined to the tip of the center electrode, but the tip made of Pt or Pt alloy joined to the tip of the center electrode has been used. The diameter of the chip is superior to that of the center electrode made of Ni or Ni alloy of the same diameter, so that the surface is hardly oxidized because the corrosion resistance is excellent, and the initial discharge voltage becomes high, Depending on the power supply capability, this increase in the discharge voltage makes it impossible to ignite sufficiently, and has a drawback that normal combustion cannot be ensured. In view of the above, the present invention is intended to improve the drawbacks of the above-described prior art and to secure a reliable ignition performance by reducing the discharge voltage.

(Means for Solving the Problems) For that purpose, a tip of the center electrode and / or an outer electrode opposed to the tip of the center electrode are provided with:
The Ni plating or Ni alloy plating is used to join the Pt alloy chip coated on the entire circumference, and furthermore, the Pt alloy chip coated by Ni plating or Ni alloy plating is subjected to a diffusion treatment, A diffusion layer is provided between Pt or a Pt alloy and a plating layer.

(Effect) With the above configuration, at least the surface on the discharge side of the Pt alloy chip bonded and fixed to both or any one of the center electrode tip and the outer electrode facing the center electrode tip, It is coated by Ni plating or Ni alloy plating, this surface is oxidized in the initial stage, it is possible to lower the discharge voltage,
Furthermore, the diffusion strength is applied to Ni plating or Ni alloy plating to improve the bonding strength with Pt.Electroless plating is usually used for electroless plating which is usually used for Ni plating or Ni alloy plating. P added when plating
The formation of a low-melting-point layer due to (phosphorus) or B (boron) can be prevented.

(Example) The present invention will be further described with reference to an example shown in the drawings.
(1) is a spark plug for an internal combustion engine according to an embodiment of the present invention.
The terminal electrode (10) and the glass seal (11) are sealed together in the shaft hole (9) of the insulator (2) made of ceramic, and Ni, 90-95% of Si, Cr, Al And Ni with Mn added
A center electrode (3) made of an alloy or an alloy of Ni: 70 to 75%, Cr: 14 to 18%, and Fe: 7 to 10% (commonly known as INC600) is held at a position opposed to the center electrode (3). And a metal shell (7) having an outer electrode (8). And
Pt or Pt is applied to the tip of the center electrode (3) held by the insulator (2) or the outer electrode (8) provided at a position facing the center electrode (3), or both of them.
Ni plating or Ni with a thickness of 50 to 200 μm all around the alloy (12)
A Pt alloy chip (4) (especially Pt-10-30% Ir alloy, etc.) coated with a plating layer (5) made of alloy plating is joined and fixed by resistance welding or the like, and further, Pt or Pt alloy By performing a diffusion treatment on the Pt alloy chip (4), which is covered with a plating layer (5) made of Ni plating or Ni alloy plating on the outer periphery of (12),
Pt alloy chip plating layer (5) and Pt or Pt alloy (1
2) A diffusion layer (6) having a thickness of 10 to 30 μm is provided between them.

For this reason, since a plating layer (5) made of base metal Ni plating or Ni alloy plating exists on the surface of the Pt alloy chip (4), the surface of the plating layer (5) is formed by spark discharge. Since an oxide is generated, the initial discharge voltage can be reduced along with the generation of the oxide, and the Pt alloy (12) of the Pt alloy chip (4) is usually
Since the Pt alloy is a Pt-10 to 30% Ir alloy, the surface of the Pt alloy chip (4) itself has irregularities due to oxidation due to aging, so that the discharge voltage can be similarly reduced. That is, as shown in FIG. 4, a 4-cycle, 6-cylinder 2000CC engine using city gas 6C (H ₂ 50% or less) as a fuel with the spark gap of the plug being 0.5 mm,
The discharge voltage at the time of idling 1000-1100rpm was measured for many plugs. As a result, the discharge voltage of the conventional plug was reduced by using a Pt-Ir alloy tip (diameter 1.1φ x thickness 0.4mm) at the tip of the center electrode. While the plug was high and unstable, the Ni-plated plug of the present invention had a low discharge voltage and was extremely stable.

When the thickness of the plating layer (5) made of Ni plating or Ni alloy plating is 50 μm or less, the duration of the discharge voltage reduction effect is short, and when it is 200 μm or more, the distance between plug gaps is large. Since the discharge voltage is increased and the durability is remarkably reduced, 50 to 200 μm is appropriate, and the plating method is performed at 700 to 950 ° C. for 1 hour or more by heat treatment such as diffusion treatment. P (phosphorus) contained in electroless plating used for alloy plating
Alternatively, the function as an electrode material is deteriorated by B (boron), and a low melting point compound layer is diffused and formed at a grain boundary. In order to prevent this, an electrolytic plating is optimal.

(Effects of the Invention) As described above, it is possible to lower the discharge voltage by applying non-metal plating to the surface of the Pt alloy chip used for the ignition portion, and to ensure the ignitability at the initial stage. In addition, it has an excellent effect of improving the durability.

[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 of the first embodiment, and FIGS. FIG. 4 is an enlarged sectional view of a main part of the Pt alloy chip of the first embodiment and the second embodiment, and FIG. 4 is a graph showing a measurement result of a discharge voltage. 1 ... spark plug for internal combustion engine, 2 ... insulator, 3 ...
... Center electrode, 4 ... Pt alloy tip, 5 ... Plating layer, 6
... Diffusion layer, 7 ... Metal shell, 8 ... Outer electrode, 9 ...
Shaft hole, 10 ... Terminal electrode, 11 ... Glass seal

Claims (2)

(57) [Claims] 1. A method in which both or one of a front end of a center electrode and an outer electrode facing the front end of the center electrode is coated with Ni plating or Ni alloy plating having a thickness of 50 to 200 μm all around. Spark plug for internal combustion engines, made by joining Pt alloy tips. 2. A Pt alloy chip coated by Ni plating or Ni alloy plating is subjected to a diffusion treatment at 700 to 950 ° C. for 1 hour or more, so that a thickness between the Pt or Pt alloy and the plating layer is increased. Claim (1) wherein a diffusion layer of 10 to 30 µm is provided. The spark plug for an internal combustion engine according to the above.