Spark plug for internal combustion engine

Details Spark plug for internal combustion engine Spark plug for internal combustion engine

1997-09-19

2001-07-17

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Spark plugs

Particular electrode structure or spacing

C313S144000

Reexamination Certificate

active

06262522

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spark plug for an internal combustion engine and a noble metal chip for the electrodes of the spark plug.
2. Description of the Related Art
With regard to spark plugs for internal combustion engines, it is a continuing need to improve the lifetime (i.e., to improve the consumption resistance) and the performance (i.e., to improve the spark flyability and the ignitability). To this end, attempts have been made to use a noble metal chip, particularly of Pt, as a discharging element of the spark plug for an internal combustion engine.
Recently, there is an increasing need to further improve the lifetime and the performance. To this end, studies have been conducted to use a noble metal chip made of Ir having a melting point higher than that of Pt.
Although Ir advantageously has a melting point of 2454° C., which is much higher than that of Pt, it also has a disadvantage that the volatilization consumption is undesirably accelerated at elevated temperatures above 900° C.
To suppress the volatilization consumption of Ir, Japanese Unexamined Patent Publication (Kokai) No. 2-186579 proposed introduction of Al, Y or other elements having a strong affinity for oxygen and precipitation thereof to form an oxidation-protection film over the surface of an Ir electrode, thereby preventing the volatilization consumption of Ir.
However, the proposal had a drawback that the oxidation-protection film is composed of alumina, yttria, or other ceramics, which provides poor bond with the Ir noble metal and causes spalling thereof.
Japanese Unexamined Patent Publication (Kokai) No. 2-49388 proposed addition of Pt to Ir, but could not provide a satisfactory noble metal chip having a sufficiently improved consumption resistance and heat resistance at high temperatures.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a spark plug having a noble metal chip bonded to the discharging spot thereof and having an improved heat resistance and consumption resistance at high temperatures.
Another object of the present invention is to provide a noble metal chip for a spark plug, the chip having an improved heat resistance and consumption resistance at high temperatures.
To achieve the object according to the present invention, a spark plug has a noble metal chip bonded to the discharging spot thereof, the chip consisting of an Ir—Rh alloy containing Rh in a specified amount to cause enrichment and precipitation of Rh on the chip surface and the precipitated Rh forms an oxidation-protection film. Because Rh is a noble metal having a high melting point and forming a strong bond with the chip body of the Ir—Rh alloy, the oxidation-protection film of the present invention provides an improved consumption resistance and heat resistance at high temperatures.
The alloying of Ir with Rh advantageously provides a noble metal chip having an improved consumption resistance and heat resistance at high temperatures, so that the noble metal chip of the present invention, when used in the spark plug of an internal combustion engine, allows reduction in the electrode diameter, and thereby improves the performance of the spark plug for an internal combustion engine, particularly a reduced discharging voltage and an improved ignitability.


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Japanese Official Action dated Sep. 9, 1997.
Applicant's Comments with Reference Figures 1 and 2.
“High Temperature Behaviour of Iridium-Rhodium Alloys, Oxidation Resistance and Compatibility,” Platinum Metals Review, Apr. 1967, vol. 11, No. 2, pp. 53-55.

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