Electricity: circuit makers and breakers – Periodic – Contact breaker detail
Patent
1993-04-08
1995-05-16
Pellinen, A. D.
Electricity: circuit makers and breakers
Periodic
Contact breaker detail
200 19DR, H01H 1900, F02D 702
Patent
active
054162920
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an ignition distributor for internal combustion engines comprising a housing, in which a distributor rotor is rotatably mounted, which comprises a first electrode close to the axis of rotation of the rotor, a second electrode at that end of the rotor which is remote from its axis of rotation, and between said electrodes an electrical line connecting the electrodes,
and a distributor cap, which closes the housing and is provided on its inside surface with a plurality of peripherally spaced apart stationary electrodes, which cooperate with the second electrode of the distributor rotor, and comprises a center electrode, which is closely spaced from and defines a spark gap with the first electrode of the distributor rotor,
wherein one electrode of the pair consisting of the first electrode of the distributor rotor and the center electrode is pinlike.
PRIOR ART
Such an ignition distributor is known from DE-37 43 940 A1. In the known ignition distributor the first electrode of the distributor rotor defines a spark gap with the center electrode of the distributor cap and consists of a bushing, into which the pinlike center electrode protrudes. As is usual with spark gaps, the two electrodes consist of brass. To cause the spark discharge to occur under an arc voltage which is as low as possible, it is desired to minimize the effective distance between the two electrodes; that distance is typically 0.5 mm and should not exceed 1 mm.
Whereas the electrodes defining the arc gap are not subjected to mechanical wear, as are the otherwise usual sliding contacts between the distributor rotor and the center electrode of the distributor cap, the life of the electrodes defining the arc gap has not been satisfactory thus far.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an ignition distributor which is of the kind described first hereinbefore and in which the pair of electrodes comprising the center electrode of the distributor cap has a longer life.
That object is accomplished by an ignition distributor having the features stated in claim 1. Desirable further features of the invention are subject matters of the dependent claims.
In the search for the solution provided by the invention it has been found that a cause of the wear of the pair of center electrodes resides in that the two electrodes are not exactly coaxial to one another. As a result, the pinlike center electrode of the distributor cap is irregularly consumed around its periphery because the spark discharge takes place preferentially at the narrowest portion of the annular gap between the center electrode and the bushinglike electrode of the distributor rotor. Whereas it would be obvious to accomplish the object by measures by which the deviations from an exactly coaxial arrangement would be decreased, that approach has not been successful because it has been found, in the first place, that the observed deviations from an exactly coaxial arrangement are virtually inevitable owing to the design and arrangement of the ignition distributor and, in the second place, that even when the coaxial arrangement of the two electrodes is improved the wear of the electrodes will still be excessive and will result in an insufficient life. The inventors have then found that the wear of the electrodes is not only due to spark erosion but the electrode surface is also chemically attacked. There are believed to be different causes of the chemical attack. In the first place the spark discharge and the accompanying conversion of energy will result in an excitation of the ambient gas atmosphere and it is believed that this results in a formation of ozone and nitrogen oxides. Besides, the electrodes and the plastic surrounding them are subjected to considerable thermal stresses caused by the spark discharges so that components of the plastic are decomposed and released. These components comprise also chlorine-containing components of flame-retardant substances. It is believed that an aggressive gas mixture is formed, which
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Bahm Klaus
Behnke Horst
Michal Roland
Doduco GmbH and Co.
Durrwachter Eugen
Friedhofer Michael A.
Pellinen A. D.
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