Patent Application
20140211365
The invention relates to a corona ignition device comprising a housing, an insulator surrounded by the housing, an inner conductor leading through the insulator to an ignition tip, and a coil connected to the inner conductor. Corona ignition devices generally of this type are known from DE 10 2010 055 570 B3, U.S.2011/0305998 A1 and EP 1 662 626 A1.
If coils are exposed to jolting motions or vibrations, as occur in ignition devices, there is the risk that turns of the winding on the coil former will move. Both the function of the coil and also the service life thereof may be impaired as a result.
In order to fix wire turns on the coil former, coil windings can be sealed with synthetic resin or a silicone material. Here, it is problematic that even tiny bubbles impair the quality of the coil. In addition, thermal expansions of the sealing material may lead to the formation of cracks or splits and may thus lower the dielectric strength. Thermal expansions of the sealing material are a problem in particular with coils that are exposed to considerable temperature changes, as occur for example with ignition devices of internal combustion engines.
A further possibility for fixing wire turns on a coil former lies in providing the coil with a coating film, for example by dipping or spraying, or in winding adhesive tape around the coil, once the wire has been wound onto the coil former. Electrical properties of the coil, in particular the quality thereof, may be impaired, however, as a result.
In order to avoid undesirable movements of the wire turns on the coil former, it is also known to provide the coil former with a thread-like channel and to position the wire in this channel. This approach is very complex, however, in terms of manufacture.
A further possibility for fastening wire turns on a coil former is to apply an adhesive layer to the coil former. A problem here is that the adhesive has to be applied very uniformly in a thin layer. If, specifically, the adhesive layer thickness is too great, the wire sinks in the adhesive layer and the electrical properties of the coil are impaired, for example similarly to when fixing with a coating film applied by dipping or by spraying.
The present invention provides a cost-effective way in which turns of a winding can be fixed on a coil former without impairing the electrical properties of the coil of a corona ignition device.
In a coil of a corona ignition device according to this disclosure, the wire is adhesively bonded to the coil former. The adhesive is not applied as a thin layer to the entire coil former however, but instead is arranged in one or more indentations, over which the wire runs. The wire wound onto the coil former is therefore also not adhesively bonded over its entire length to the coil former, but only to the wire portions arranged above an indentation filled with adhesive. Between the portions adhesively bonded to the coil former, the wire has portions which are arranged loosely on the coil former. Indentations, for example grooves or blind bores, can be provided with low outlay in the lateral surface of a coil former and then filled with adhesive.
In order to effectively fix a wire winding on the coil former, it is not absolutely necessary for each individual turn to be adhesively bonded to the coil former. If the indentations are formed for example as blind bores in the coil former, these can be arranged at an axial distance from one another, with the result that only each second or third turn for example crosses one of the indentations and is thus adhesively bonded to the coil former. The wire winding is, however, naturally fixed better onto the coil former, the more wire turns are adhesively bonded to the coil former. At least half, particularly preferably at least ¾, in particular at least ⅘, for example at least 9/10 of the turns, or even all of the turns are therefore preferably adhesively bonded to the coil former, that is to say cross an indentation filled with adhesive.
In accordance with an advantageous refinement of this disclosure, the at least one indentation filled with adhesive is a groove, preferably a groove running in the longitudinal direction of the coil former. A groove can be produced in the coil former with low manufacturing outlay and filled very easily with adhesive. If the groove extends in the longitudinal direction over the entire winding surface of the coil former, such a groove may adhesively bond an accordingly high number of turns to the coil former, specifically in the ideal case all the turns of a coil.
The groove can extend in a straight line, parallel to the longitudinal axis of the coil former. It is also possible, however, to provide the groove at an incline to the longitudinal axis of the coil former or in a wavy manner on the lateral surface of the coil former. Any groove running transverse to the turns of the wire winding is suitable per se.
The coil former may have a plurality of grooves filled with adhesive, which are arranged side by side on the coil former. The grooves can run parallel to one another. Since a plurality of grooves, preferably 2 to 6 grooves, are arranged on the coil former, the individual turns of the wire winding can be adhesively bonded to the coil former at a corresponding number of portions and thus effectively fixed to the coil former.
Further details and advantages of this disclosure will be explained hereinafter on the basis of an illustrative embodiment with reference to the accompanying drawings, in which:
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 the present invention.
The coil illustrated in
As
The indentations can be formed arbitrarily per se. In the illustrated illustrative embodiment, the indentations are formed as grooves. These grooves run parallel to one another in the longitudinal direction of the coil former 1.
The indentations preferably widen towards their opening, that is to say towards the lateral surface of the coil former 1. The edges of the individual indentations are rounded. The electrical properties of the coil can thus be improved. In particular, the creation of field peaks, which increase the risk of voltage flashovers, can be avoided. The adhesive 3 may contain an electrically or magnetically effective filler, for example ferrite powder, ceramic powder and/or metal powder. The inductance of the coil and the quality thereof can thus be adapted or optimized.
The adhesive 3, for example, may be a thermoplastic adhesive or a curing adhesive. If an adhesive is used that expands as it cures, the indentations are not filled completely with adhesive, and therefore the wire 2 when wound onto the coil former 1 initially has no contact with the adhesive 3. As it cures, the adhesive 3 then expands, and therefore portions of the wire 2, which bridge over the indentations, come into contact with the adhesive 1 and are thus adhesively bonded to the coil former 1. It is also possible to use a curing adhesive of which the volume reduces as it cures. In this case, the indentations are filled completely with adhesive. Even when winding on the wire 2, wire portions that bridge over the indentations are then in contact with the adhesive 3. If the adhesive then cures and its volume reduces, portions of the wire 2 arranged above the indentations may deflect slightly into the indentations.
The coil former 1 may have a tapering end portion, which is surrounded by turns of the winding. A tapering end portion of the coil reduces the risk that field elevations are formed in the connection region of the coil and thus reduces the risk of voltage flashovers, for example with use of the coil in a corona ignition device. The indentations formed as grooves also extend in the tapering end portion. In this end portion too, the turns are thus adhesively bonded to the coil former 1.
The grooves may extend over the entire winding surface of the coil former 1, such that all turns of the coil are adhesively bonded to the coil former 1, that is to say adhesively bonded wire portions follow one another at a distance of less than one peripheral length of the coil former 1. In order to fix the wire winding on the coil former 1, it is sufficient however if only some of the turns are adhesively bonded to the coil former 1.
An embodiment of a corona ignition device with the coil 7 of
In the illustrated embodiment, the housing 4 consists of a plurality of parts, specifically a housing tube, in which a coil 7 is arranged, and a housing head 4a, which surrounds an insulator 9. The coil former 1 of the coil 7 may at one end carry a bushing, into which the inner conductor 10 of the corona ignition device can be inserted. The inner conductor 10 may thus be connected to the coil 7.
The housing head 4a in the illustrated embodiment comprises an outer thread for screwing into an engine block. An outer thread is not necessary however, since the corona ignition device can also be fastened to the engine block in a different way.
The inner conductor 10 leads through the insulator 9 to one or more ignition tips 11. The housing head 4a, together with the inner conductor 10 and the insulator 9, forms a capacitor. This capacitor is connected in series to the coil 7 and forms an electric resonating circuit therewith. By exciting this resonating circuit, a corona discharge can be produced starting from the ignition tips 11.
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 the invention 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 2013 100 925.5 | Jan 2013 | DE | national |
This Application claims priority to DE 10 2013 100 925.5, filed Jan. 30, 2013, the entire disclosure of which is hereby incorporated herein by reference in its entirety.
