Surface-gap spark plug for internal combustion engines

Details Surface-gap spark plug for internal combustion engines Surface-gap spark plug for internal combustion engines

1987-05-07

1989-01-17

Moore, David K.

Electric lamp and discharge devices

Spark plugs

Plural part insulating means

313131R, H01T 1338, H01T 1352

Patent

active

047989912

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a spark plug having a surface spark gap for internal combustion engines.
In contrast to spark plugs having air spark-gaps, such surface-gap spark plugs are distinguished by a substantially lower ignition voltage requirement with reference to the electrode spacing. However, the ignition spark must be very rich in energy, so that there is still sufficient energy for igniting the fuel mixture despite cooling of the slide path. The greater is the burning voltage after the ignition of the surface spark gap, the greater this energy is in a given ignition system. The burning voltage, in turn, is directly dependent on the magnitude of the surface spark gap, that is, on the length of the slide path formed between the electrodes on the surface of the insulating body on the combustion chamber side. Of course, a larger surface spark gap, in turn, requires a greater ignition voltage than a small one.


SUMMARY OF THE INVENTION

It is an object of the invention to provide a spark plug for internal combustion engines, which has the advantage that at a given ignition voltage the slide path length of the surface spark gap can be substantially increased. As a result of the suggested construction of the free surface of the insulating body on the combustion chamber side and the arrangement of a so-called rear electrode behind the surface, which rear electrode forms the cathode and has a constant or variable distance from this surface and an angle of inclination relative to this surface, as desired, even 90.degree., a surface charge is formed along the surface of the insulating body during the voltage increase at the spark plug as a result of the dielectric displacement. This surface charge, which is in proportion to the field intensity as well as the relative dielectric constants (relative permittivity) of the surface material of the insulating body, effects an ignition voltage which is greatly reduced relative to the pure gas discharge and is hardly dependent on the compression. At the ignition voltages which are made available by the ignition systems conventionally used in motor vehicles today, slide path lengths in the centimeter region can be bridged by the ignition sparks with the spark plugs according to the invention. Since the burning voltage also increases along with the possibly large slide path length, it is very easy to transmit energy which is predominantly supplied to the gaseous fuel-air mixture over the long distance of the surface spark gap. The shape of the surface of the insulating body and the electrodes is optional within the scope of the teaching according to the invention. At a representative ignition voltage, it is advisable to construct the surface in such a way that the greatest possible slide path length is achieved in order to achieve the highest possible burning voltage.
At presently available ignition voltages, the energy delivered to the combustible fuel mixture by the spark plug, according to the invention, is approximately ten times as great as in a conventional spark plug. Conversely, there is a much lower ignition voltage requirement in the spark plug, according to the invention, with identical energy transmission to the fuel-air mixture.
The spark plug, according to the invention, can be used for a slide glow discharge with a burning period of milliseconds, as well as for a slide disruptive discharge with a burning period of nanoseconds. The erosion occurring in the disruptive discharge as a result of the very hot ignition spark on the surface of the insulating body on the combustion chamber side can be distributed symmetrically along the circumference, since the individual slide paths in this construction are lengthened by means of the erosion and the ignition spark always jumps over at the shortest slide path. Additional protection against erosion can be achieved by means of the construction of the surface of the insulating body on the combustion chamber side.
Such erosion damage is prevented in the slide glow discharge. In the spark p

REFERENCES:
patent: 2657248 (1953-10-01), Smits
patent: 3046434 (1962-07-01), Schurecht
patent: 4695758 (1987-09-01), Nishida et al.

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