Patent Application
20170149216
This application claims priority to DE 10 2015 120 254.9, filed on Nov. 23, 2015, which is hereby incorporated herein by reference in its entirety.
Corona ignition devices are generally known from EP 1 515 594 A2, DE 20 2014 101 756 U1, and DE 10 2009 059 649, for example.
For corona ignition devices, the dielectric strength of the insulator is of great importance. Bypasses, flashovers and parasitic partial discharges can lead to premature failure of a corona ignition device. The risk of flashovers and parasitic partial discharges can be reduced with an electrically conductive coating of the insulator. Such coatings can consist of metal or electrically conductive ceramic and provide a cavity-free contact face between insulator and electric earth, which reduces susceptibility to flashovers and partial discharges. However, the end of the coating is susceptible to flashovers, since field peaks can form there.
To counteract this problem, it is known from DE 20 2014 101 756 U1 to provide an undercut in the insulator so that the tubular face of the coating is turned over its end. In this way, the end of the coating is situated in a field-free space, namely, inside a space provided by the undercut. In the radial direction the end of the coating is placed above an empty space provided by the undercut and above another section of the coating covering the bottom of the undercut. Therefore, flashovers can be prevented there. However, a disadvantage of this solution is the complicated shape of the insulator, which results in very high manufacturing costs.
This disclosure teaches a way, in a corona ignition device, to reduce the risk of flashovers at the end of the electrically conductive coating of the insulator with a reasonable manufacturing outlay.
The insulator of a corona ignition device according to this disclosure has an annular shoulder, on which is situated the end of the electrically conductive coating that is remote from the combustion chamber. Any irregularities present on the end of the coating, in particular an irregular boundary, are largely insignificant for the electric field, since the area of electrically conductive coating is oriented radially at the end thereof so that a geometrical tangent extending coating points generally in the radial direction. In the axial direction, the end of the electrically conductive coating that is remote from the combustion chamber is well-defined and therefore the risk of flashovers is also correspondingly reduced. The end remote from the combustion chamber is the end that is further away from the at least one ignition tip than the other end.
The end of the electrically conductive coating is a ring-shaped line where a first surface of the insulator that is free from the electrically conductive coating borders on a second surface of the insulator that is covered by the electrically conductive coating. For example, a tubular section of the insulator that is free from the electrically conductive coating may border on a groove which is covered with the coating. One sidewall of the groove provides a shoulder, on which the end of the coating is arranged.
The annular shoulder may have an annular face that faces towards the at least one ignition tip and on which the end of the coating is situated. The tubular face of the coating is therefore widened at the end thereof, i.e., a tangential extension of the coating is oriented radially outwards.
A corona ignition device according to this disclosure can be produced with a method in which: an insulator having an annular shoulder is formed; a first section of the insulator that ends at the annular shoulder is provided with an electrically conductive coating, at least some of the annular face of the annular shoulder also being coated; a central electrode is inserted into the insulator; and the insulator is inserted into a holder such that the electrically conductive coating bears against the holder. With such a method it is not necessary to carry out the steps in exactly the same order as just stated. For example, the coating can be applied before or after the central electrode is inserted into the insulator.
In an advantageous refinement of this disclosure, the coating is applied continuously on both sides of the annular shoulder and then a section of the insulator that is remote from the combustion chamber is removed, for example, ground away, as far as the annular shoulder. In this manner, a well-defined end of the coating that largely prevents field peaks can be produced. In this case, the annular shoulder ends at the outer boundary thereof in a ground edge, i.e., an edge formed by grinding the insulator.
The above-mentioned aspects of exemplary embodiments will become more apparent and will be better understood by reference to the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:
The embodiments described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of this disclosure.
The corona ignition device shown in
The central electrode 3, together with the insulator body 2 and the holder 1, forms a capacitor, which is series-connected to a coil 4 connected to the central electrode 3. The coil 4 consists of wire, which is wound onto a coil body. This capacitor and the coil 4 are part of an electrical oscillating circuit, the excitation of which can be used to generate corona discharges at the ignition tips or ignition tip of the central electrode 3.
In the embodiment shown, the coil 4 is arranged in a metal housing, which is formed by the holder 1 and in which the insulator body 2 sits. The coil 4 may also be arranged outside such a housing and, for example, be connected to the central electrode 3 via a cable.
The insulator 2 of the corona ignition device is shown schematically in
The coating 2 forms a tubular face, which ends on an annular shoulder 6. The annular shoulder 6 may be provided by a groove, which can be seen in particular in
The holder 1 can bear against the full length of the cylindrical section covered by the coating 5. This cylindrical section is however preferably somewhat longer. A tapering section 2b of the insulator 2 adjoins the cylindrical section. The transition from the annular shoulder 6 to this tapering section is rounded. Field peaks can be reduced in this manner. The annular shoulder 6 has an edge 7 on its outer boundary. The electrically conductive coating 5 preferably ends at this edge of the annular shoulder.
Edge 7 on the outer boundary of the annular shoulder 6 can be a ground edge, that is, the insulator 2 can be ground on the side remote from the combustion chamber, facing away from the at least one ignition tip. Advantageous production is possible by initially applying the electrically conductive coating 5 to the insulator 2 beyond the annular shoulder 6. The coating 5 is then removed, for example by grinding or turning, on the side of the insulator 2 remote from the combustion chamber, thereby forming edge 7. In this manner, the coating terminates such that it is flush with the outside cylindrical surface of the insulator.
As shown in
While exemplary embodiments have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of this disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2015 120 254.9 | Nov 2015 | DE | national |
