Electric lamp and discharge devices – Spark plugs – Particular electrode structure or spacing
Reexamination Certificate
1998-07-09
2001-02-27
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Spark plugs
Particular electrode structure or spacing
C313S133000, C313S143000
Reexamination Certificate
active
06194819
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a spark plug and more particularly to a spark plug that operates at lower temperatures than conventional spark plugs.
BACKGROUND ART
Spark plugs that operate at high temperatures are commonly referred to as “hot plugs”. Hot plugs have a tendency to pre-ignite the fuel mixture in the combustion zone. Pre-ignition of the fuel mixture in the combustion zone, also known as engine knock, reduces engine performance and in some instances, causes damage to the engine.
Another drawback to hot plugs is that deposits from fuel and lubricant additives which haven't burned away, are melted by the hot plug to form a glaze which coats the nose portion of the plug insulator. When the glaze on the nose portion of the plug insulator gets hot, the plug is shorted out and engine misfire occurs. Engine misfire is accompanied by fuel and power loss.
The main reason spark plugs operate at high temperatures is that the ceramic insulator surrounding the center electrode becomes hot due to combustion gas temperatures. Further, ceramic materials are normally poor conductors of heat.
Various devices for removing heat from the firing end of a spark plug have been used. One such heat removal device is a heat pipe having a vaporizable medium. Heat at the firing end of the spark plug is absorbed by the vaporizable medium causing such medium to convert to a vapor. The change of state of the vaporizable medium extracts heat from the firing end of the plug. The vaporized medium moves to a cooler part of the heat pipe where it condenses and releases heat through another change of state. The use of a heat pipe is an added expense and is a less than desirable heat removal method for use in the market place.
Another device for removing heat from the firing end of a spark plug is a thermally conductive filler composition introduced between the center electrode and the spark plug insulator. Some of the thermally conductive filler compositions in use include silver, cermet, talc, and silicon. Filler materials serve as a seal between the electrode and the insulator but only provide moderate improvement in thermal conductivity.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In the present invention, a spark plug has a terminal end portion and a firing end portion disposed along a longitudinal axis. An annular metal shell is disposed about and along the longitudinal axis and has external threads located along the firing end portion. A firing end surface is located adjacent the external threads. A bore is defined within the annular metal shell and about the longitudinal axis. An electrical insulating material is received in the bore of the annular metal shell and is disposed along the longitudinal axis. The electrical insulating material has a first end surface facing the firing end portion and a second end surface facing the terminal end portion of the spark plug. The first end surface has at least one annular groove defined therein and about the longitudinal axis. An inner bore is defined within the electrical insulating material and about the longitudinal axis. An electrode is received in the inner bore of the electrical insulating material. The electrode extends along the longitudinal axis and is connected at a first end to the terminal end portion. The electrode has a second end terminating at the firing end portion.
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Atteberry Lonnie D.
Codina George
Krull Donald R.
Yap Steven
Caterpillar Inc.
Glastetter Calvin E.
Patel Ashok
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