Electric lamp and discharge devices – Spark plugs – Non-conducting material in or adjacent gap
Patent
1988-12-07
1990-07-03
DeMeo, Palmer C.
Electric lamp and discharge devices
Spark plugs
Non-conducting material in or adjacent gap
313136, 313141, H01T 1320, H01T 1352
Patent
active
049394096
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a spark plug having a surface discharge gap. A spark plug with a surface discharge section for internal combustion engines is known, e.g. from the DE-OS 35 33 123, in which the insulation body is divided transversely and comprises an upper part on a connection side made of a material with a relatively low dielectric constant, and a lower part on a combustion chamber side made a material with a much higher dielectric constant. Such spark plugs are unobjectionable with respect to operation, but are relatively complicated to produce because of the divided insulator body.
SUMMARY OF THE INVENTION
In the spark plug according to the invention, the center electrode and the surface discharge section are made of an electrically non-conductive material and have electrically conductive films thereon has the advantage that it is simple to produce by means of thick-film technique, and the surface discharge films are highly effective and stable over a long period of time.
It is particularly advantageous that the electrically non-conductive ceramic consist of Al.sub.2 O.sub.3, and the electrically conductive film on the ceramic part consist of platinum or a platinum-Al.sub.2 O.sub.3 mixture with 60 to 85 percent by weight of platinum. The film of the surface discharge gap is produced from a platinum-Al.sub.2 O.sub.3 mixture with 10 to 40 percent by weight of platinum.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention both as to its construction and its method of operation, together with additional and advantages thereof, will be best understood from the following description with reference to an accompanying single FIGURE which shows schematically a partial cross-section of a spark plug according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The spark plug shown in the drawing, comprises a spark plug insulation body 1 made of aluminum oxide and comprising a bore 2 on a combustion chamber side. A T-shaped structural component part which is made e.g., of aluminum oxide and carries various surface coatings is located in the bore 2. The counter-electrode is indicated by a numeral 4. The structural component part 3 has a coating 5 within the spark plug body 1 and within the bore 2. The coating 5 projects a little beyond an end surface of the body 1. The coating 5 is electrically conductive and consists either of platinum or of a platinum-Al.sub.2 O.sub.3 mixture with 60 to 85 percent by weight of platinum and has a thickness of 5 to 15 .mu.m. The coating 6 on the structural component part 3 in the vicinity of the counter-electrode 4 consists of the same material, the coating 6 forming an electrical contact with the counter-electrode 4. The contact of the electrically conductive coating 5 within the spark plug insulation body 1 is effected with an electrically conductive glass 7 in the form of a molten glass mass located in an inner cavity of the spark plug insulation body, as known, e.g., from the US-PS 3 909 459.
The spark discharge film 8 between the coatings 5 and 6 consists of a platinum-Al.sub.2 O.sub.3 mixture with 10 to 40 percent by weight of platinum. After sintering the discharge film 8 has no intrinsic conductivity, since only individual islands of conductivity are formed which do not contact one another electrically, but provide for high displacement currents, which corresponds to a high dielectric constant. This coating 8 likewise has a thickness of 5 to 15 .mu.m.
In order to produce this spark plug, a T-shaped structural component part 3 made of aluminum oxide, is first produced and annealed at 1100.degree. to 1150.degree. C., but not yet sintered. The electrically conductive coatings 5 and 6 are then applied to this structural component part 3 by immersion or printing, and the surface discharge film 8 is then applied to it by printing or brushing on. The structural component part 3 with the coatings 5, 6 and 8 is then inserted into the bore 2 of the spark plug 1, which is also only annealed. The bore 2 has a diameter which just fit
REFERENCES:
patent: 4406968 (1983-09-01), Friese et al.
patent: 4414483 (1983-11-01), Nishio et al.
Friese Karl-Hermann
Grunwald Werner
Schmid Kurt
DeMeo Palmer C.
Robert & Bosch GmbH
Striker Michael J.
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