DD290304A5 - SPARK PLUG FOR COMBUSTION MOTORS - Google Patents

Abstract

The invention relates to a spark plug for combustion engines with high electrical Überschlagkraft. Such Zuendkerzen can be used in conjunction with electronic Hochleistungszuendanlagen particularly advantageous. The object of the invention is to increase the electrical breakdown strength while maintaining the main dimensions of the spark plug insulating body. The object of the invention is to reduce the formation of sliding discharges on the surface of the Zuendkerzenisolierkoerpers. The object is achieved by applying on one part of the spark plug insulating body an electrically conductive layer surrounded by a sufficiently electrically impact-resistant overlay, which gives the spark plug thus produced an overstrike resistance of at least 20 kV. high electrical breakdown strength; Reduction of the emergence of sliding discharges; Surface of Isolierkoerpers; electrically conductive layer; impact resistant edition}

Description

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Field of application of the invention

The invention relates to a spark plug for internal combustion engine with high electrical breakdown strength. The spark plugs according to the invention are used in particular in connection with electronic high-performance ignition systems.

Characteristic of the known technical solutions

Among other things, the recently developed ignition systems for igniting leaner fuel-air mixtures also led to an increase in the ignition voltage offer up to 35 kV. Thus, all components of the ignition system, including the spark plugs, increased demands placed on their high-voltage strength.

To increase the flashover strength of the spark plugs, various design changes have therefore been proposed and carried out.

- Increasing the length of the insulator shaft

- Introduction of a corrugation

- Increasing the number and modified form of corrugation

- Application of glazes with high surface resistance

However, these changes carried out are possible only in the framework established by the international standard dimensions under consideration of other elements of the ignition system, such as the spark plug, an increase in the flashover strength of the spark plugs is problematic because it η on the Keramikoberfliu to sliding discharges, which already at voltages that are much lower than the static breakdown voltage, based on the distance of the high voltage terminal to ground.

These creeping discharges, which occur at slant boundary layers, gradually grow on the ceramic surface, associated with high-frequency voltage breakdowns, and produce surface plasmas, so-called streamers and leaders, which then prematurely initiate complete flashover. In addition, these constant discharge processes on the ceramic surface lead to unwanted electromagnetic RF interference voltages.

With the application of the corrugation, the formation of sliding discharges on the insulating body could be reduced by the vorbundono way pre-extension and oinor changed Foldvertoilung. Nevertheless, it still comes to this surface discharge, in particular on the non-corrugated part of the insulator. This effect is favored by unfavorable conditions of use (moisture, pollution). In the case of the same length of foresight, with dome static rollover in the air, the rollover strength is limited to about half that tension. As the inventors have pointed out, the fold strength advance along the insulator core shaft is such that the untangled part provides only a minor contribution to the overcoverage. From the Standardlitoratur allgomoin is known, as in Hochspannungsdurchführungon the electric Feldvertoilung and thus the Gleiteinsatzspannung has been determined by the size ratios of the longitudinal and Quorkapazitäton, i. by the oborface shape, the geometry, the tube thickness or the dielectric constant of the material. Such changes are no longer feasible with Zündkerzon due to the general standardization.

ZIoI the invention

It is the object of the invention, while maintaining the Hauptmosungung the Zündkerzenisoliorkörpors, dio electrical proof strength increase.

Explanation of the essence of the invention Dio task dor invention is to reduce the formation of Gleitentladungen on the surface of Spark plug insulation and thus in increasing the electrical flashover. This object is achieved in that eino with a part of the spark plug insulating body shank

is applied sufficiently electrically Durchschlagsfosten edition surrounded electrically conductive layer, which gives the spark plug thus produced a flashover strength of at least 2OkV.

It is advantageous that the outer surface of the insulator body shaft, starting from the spark plug and with this

electrically conductively connected, in the direction of the high-voltage connection to a maximum of the first corrugation or up to the maximum

Half the total length of the insulator shaft with one, of a sufficiently electrically impact resistant pad

surrounded, electrically conductive layer is provided.

In this case, the electrically conductive layer may be a metal layer, a carbon layer, a conductive glass layer, a conductive layer

ceramic glaze or a thick film resistor paste.

Furthermore, it is advantageous that the electrically impact-resistant support has a ceramic thickness applied in a corresponding thickness Glaze or a Keramit he mass is covered with a conventional glaze. It is important that to avoid Feldstärkoüberhöhunghungon the completion of the electrically conductive layer for High-voltage connection towards bead-shaped, the insulating body annularly surrounding or arcuate and is

the electrically impact resistant pad at this point has the greatest strength.

The wall thickness of the ceramic between the inner bore and electrically conductive layer must be greater than 1 mm. The The strength of the electrically impact-resistant support is dimensioned so that the corresponding standard size is achieved. A further advantage is that the applied electrically conductive layer and the impact resistant pad or pads

such are that the spark plug has a rollover resistance of 20 to 4OkV.

By means of the invention, a change in the field strength distribution is achieved. Di? electric field components,

which act parallel to the surface and are causally responsible for the emergence of the sliding discharges are eliminated.

The electric field previously built up between the terminal pin and the housing is passed through the conductive layer which is thereon Potential as the housing is located, dismantled. The inventive solution, the electrical flashover of the spark plug at the same insulator length

and unchanged geometric dimensions significantly increased. In addition, sliding or corona discharges on the

Insulating body surface greatly reduced and thus a source of the formation of electromagnetic RF interference voltages

eliminated.

embodiment An example of the realization of the inventive solution is shown in Fig. 1. The insulating body 1, here in a sectional view, according to

the desired embodiment, the standard dimensions. Within the insulator shaft, there is the conductive layer 3 surrounding the inner bore 2cylindrically. The conductive layer may be of any desired design. It may be a metal layer that is vapor-deposited, splintered, sprayed, fused, or otherwise adhered by another coating method.

Also suitable are carbon films, conductive glasses, conductive glazes, thick film resistor pastes and the like. ä. The wall thickness of the ceramic between the inner bore 2 and the layer 3 is greater than 1 mm. This ensures that the Dielectric strength is significantly higher than the rollover resistance. To avoid larger field inhomogeneity ends

this electrically conductive layer 3 in the direction of the high voltage terminal as a bead 4, the insulator 2 annularly enclosing.

To produce an electrically conductive connection to the housing of the spark plug, the electrically conductive layer 3 has a

accessible outer conductive layer portion 5 within de * spark plug housing.

The electrically conductive layer surrounding the electrically conductive layer 3 is in the best case of the same

ceramic material as the rest of the insulating body and is therefore not separately identified. The ceramic mass can be applied by the plasma jet spraying method.

Due to the same electrical, thermal and mechanical parameters, good functional equations can be achieved. Outward

The thickness of the impact-resistant overlay ensures the standard dimensions and the outer dielectric strength.

It goes without saying that as durchschlagfoste edition also jode andoro geeignote ceramic with correspondingly high

use electrical breakdown resistance; wordon can.

The rollover resistance of a spark plug with an insulating body as shown in Fig. 1 increases proportionally to the total height of

electrically conductive layer 3.

However, this also increases the high-voltage requirements for the electrically impact-resistant surrounding this layer Edition, especially in the area of the bead 4, so that at the height of the layer 3 is an optimum. Dio Total Harmony the

Electrically loitfähigen layer 3 is chosen here so that it is about the height dos ungeriffelton part dos Isoliorkörperschaftendes.

Claims (8)

1. A spark plug for internal combustion engine, consisting essentially of a Koramischen insulator with integrated pin and center electrode, a housing with outer electrode and an electrically conductive Verbindungsungskitt, characterized in that on a part of the Zündkerzenisolierkörperschaftes with a sufficiently electrically impact-resistant overlay surrounded electrically conductive layer ( 3) is applied, which gives the spark plug thus produced a Überschlap.festigkeit of at least 2OkV. 2. Spark plug according to item 1, characterized in that the outer surface of the insulator body shaft, starting from the housing and electrically connected thereto, in the direction of the high voltage terminal to a maximum of the first corrugation or a maximum of half the total length of the insulator shaft with one of a sufficient electrically electrically impact-resistant layer surrounded electrically conductive layer (3) is provided. 3. Spark plug according to item 1, characterized in that the electrically conductive layer (3) is a metal layer, a carbon layer, a conductive glass layer, a conductive ceramic glaze or a thick-film resistor paste. 4. Spark plug according to item 1, characterized in that the electrically impact-resistant pad is applied in a corresponding thickness ceramic glaze or a ceramic mass, which is coated with a conventional glaze. 5. Spark plug according to item 1 and 2, characterized in that the conclusion of the electrically conductive layer (3) to the high voltage terminal towards bead-shaped (4), the insulating body (1) annularly enclosing or arcuate and the electrically durchschlagfesto edition at this point the greatest strength. 6. Spark plug according to item 1, characterized in that the wall thickness of the ceramic between the inner bore (2) and electrically conductive layer (3) is greater than 1 mm and the strength of the electrically impact resistant support is such that the corresponding standard dimension is achieved. 7. Spark plug according to item 1 and 2, characterized in that the applied electrically conductive layer (3) and the impact-resistant support are such that the spark plug has a rupture strength of 20 to 4OkV. 8. Spark plug according to item 4, characterized in that the applied electrically conductive layer (3) and the impact-resistant pads are such that the spark plug has a flashover strength of 20 to 4OkV.