EP1730754B1 - Transformer device for generating an ignition voltage for internal combustion engines - Google Patents

Description

The present invention relates to a transformation device according to the preamble of claim 1 for generating an ignition voltage for internal combustion engines. Such a transformation device has a primary winding to which a primary voltage can be applied, a secondary winding in which a secondary voltage is inducible, a ferromagnetic core arranged in the primary winding and the secondary winding, and an electrode facing one end of the ferromagnetic core, which is connected to the secondary winding and which is connectable to a spark gap.

Such a transformation device is for example from the DE 101 43 055 A1 known. In the transformation device described therein, the primary and the secondary winding, the ferromagnetic core and the electrode are housed in a housing and potted with potting compound. The housing is open at one end and can be plugged directly onto a spark plug, which is screwed into an engine block. As a result, a compact arrangement is provided in which the ignition voltage is generated exactly where it is needed, ie in the immediate vicinity of the spark plug. This has the advantage that high voltage leads to the spark gap and the associated EMC (electromagnetic compatibility) problem can be avoided. Further prior art is in the patents US 6 522 232 B2 . EP 1 284 488 A2 . EP 0 827 163 A2 . DE 101 02 342 A1 . US Pat. No. 6,191,674 B1 . GB 725 722 and US 2 107 973 disclosed.

Since such transformation devices are arranged in the engine block, typically in recesses in the cylinder head, they must necessarily be designed small and compact. The compactness of such transformation devices is becoming increasingly important as internal combustion engines for motor vehicles, especially for passenger cars and motor sports in relation to their performance are designed smaller and smaller. The generation of high secondary voltages in a confined space inevitably leads to strong electric fields within the transformation device. To avoid electrical breakdown between components with different electrical potential, they must be effectively isolated from each other.

In practice, the problem arises that the insulating materials age relatively quickly within the transformation device. The term "aging" is understood to mean the "irreversible, detrimental change in the operability of insulation systems" according to an IEC Directive for the Assessment and Labeling of Electrical Equipment Insulation Systems from 1953 (IEC 505).

A transformation device according to the preamble of claim 1 is known from DE 101 43 055 A1 ,

The invention has for its object to provide a transformation device in which the aging of the insulating materials is slowed down. This object is achieved according to a first aspect of the invention by the features of claim 1, as will be explained in more detail below. Advantageous developments are specified in the dependent claims.

In experimental investigations, the inventors have identified partial discharge phenomena in small, partly microscopic cavities as the main cause of the aging of the insulating materials. Such cavities in the insulating materials can occur in transformation devices of the type mentioned for different reasons. In casting materials may occur when using incomplete degassed casting resins or chemical side reactions cavities, so-called voids. Furthermore, gaps may arise at interfaces between different insulating materials, for example due to thermo-mechanical stress. Finally, in the case of high electrical load, so-called "electrical treeing" can produce elongated branched cavities parallel to the field direction.

The theory of partial discharge processes in cavities is for example in the Dissertationsschrift "Evaluation of partial discharges in gap-like insulating material defects" by Katrin Engel, University of Dortmund (1998 ) explained and described in detail. Characteristic of partial discharges in cavities is a gas discharge process, which interacts with the insulating material. The gas discharge process by concomitant charge carrier bombardment and UV radiation changes the surface of the insulating material by chemical decomposition and erosion, which ultimately leads to aging of the insulating material. The Telltladung is ignited by the presence of a so-called start-up electron, provided that the present electric field strength exceeds a threshold, the so-called Einsetzfeldstärke.

The invention is based on the finding that partial discharges and thus the aging of the insulating material can be suppressed if the electric field which is caused by the secondary voltage between the electrode and its opposite end of the ferromagnetic core is everywhere below the Einsetzfeldstärke for partial discharges. This is achieved in the present invention in that the electrode facing End of the ferromagnetic core has a continuously curved transition between lateral surface and end face.

According to the first feature of this solution, an edge between the lateral surface and the end surface, as is usual in known ferromagnetic cores, is avoided and thus a locally increased field strength in the region of such an edge, which is due to an increased charge carrier density in the edge region, also avoided , As a result, the probability of the occurrence of partial discharges in the region of the end of the ferromagnetic core is significantly reduced in practice, and the aging of the insulating material is significantly slowed down.

Preferably, moreover, the electrode is concave on its side facing the core. This causes an equalization and homogenization of the electric field between the ferromagnetic core and the electrode and thus also a reduction of the local field strengths, as will be explained in more detail below with reference to an embodiment.

It is emphasized that each of the two features is suitable for reducing the strength of the electric field between the electrode and the ferromagnetic core. Seen in this way, both features individually enable the solution of the problem. However, a particularly good result is obtained by combining both features.

The described in the characterizing part of the main claim end of the ferromagnetic core with continuous transition between lateral surface and end face can be obtained by a cylindrical or angular magnetic core is rounded at its end facing the electrode. This rounding of the end of a magnetic core is unusual in the prior art, since the core to avoid eddy currents from mutually electrically isolated layers, which would be torn apart during machining of the end of the core by turning or grinding. In that regard, there is a technical prejudice against this inventive embodiment of the ferromagnetic core. However, the inventors have been able to connect the layers of the ferromagnetic core so firmly together that a machining of the end of the ferromagnetic core without separation of the layers is possible.

In an advantageous development, the ends of the ferromagnetic core are formed by permanent magnets. In this case, the above-described continuously curved transition between the lateral surface and the end surface is achieved by suitably rounding off at least the permanent magnet on the side of the ferromagnetic core facing the electrode. Such rounded permanent magnets are also unusual, since permanent magnets are usually produced in a sintering process in extruded profiles and then broken in tablet form.

Preferably, the end face of the ferromagnetic core facing the electrode is convex. In this case, preferably the curvature of the convex end face increases with increasing distance from the central axis of the ferromagnetic core. Thus, the curvature of the convex face in the region of the central axis, i. in the region projecting farthest toward the electrode, thereby reducing the surface charge density from regions of greater curvature, and therefore also reducing the electric field strength in that region.

In an advantageous development, the electrode has a cup-shaped section, the opening of which faces the ferromagnetic core. Through the cup shape, the electric field between the electrode and the ferromagnetic On the one hand, the core is distributed over a larger spatial area and thus, to a certain extent, equalized, which reduces the field strength; on the other hand, the field strength is spatially homogenized, whereby the occurrence of locally increased field strengths is avoided. This effect of the cup-shaped portion of the electrode will be explained below with reference to an embodiment.

For the most homogeneous possible configuration of the field between the cup-shaped section and the ferromagnetic core, an arrangement would be ideal in which the inner surface of the cup-shaped section is parallel to the surface of the end facing the ferromagnetic core. In an advantageous development of this ideal arrangement is approximated insofar as the cup-shaped portion has a bottom portion which is arranged transversely to the central axis of the ferromagnetic core, and has a wall portion which surrounds a space located between the bottom portion and the end face of the ferromagnetic element, wherein the distance between each point on the ferromagnetic core facing part of the surface of the wall portion and the ferromagnetic core 0.5 to 2.5 times, preferably 0.75 to 1.8 times the distance between the bottom portion and the intersection of the end face with the central axis of the ferromagnetic core. By this arrangement, a sufficiently homogeneous field is generated for practical purposes, which contributes effectively to avoid partial discharges.

Preferably, the transformation device has a sleeve-shaped secondary winding carrier on which the secondary winding is arranged and which is closed at one end with the cup-shaped portion.

In known transformation devices, the gaps between the components of the transformation device with an electrically insulating Potting compound filled containing a synthetic resin and a filler. The filler has, inter alia, the function of adjusting the thermal expansion coefficient of the potting compound to the coefficient of thermal expansion of the components, for example the expansion coefficient of the metal of the electrode.

The probability of the occurrence of partial discharges in the insulating material, i. In this case, in the potting compound, according to a second aspect of the invention, it is substantially reduced that the dielectric constant of the filler is 0.5 to 1.5 times, preferably 0.8 to 1.25 times and particularly preferably 0.9 times to 1.2 times the dielectric constant of the synthetic resin.

The inventors have found that the spatial distribution of the filler in the potting compound is not necessarily or not everywhere homogeneous. For example, an increased filler concentration may occur on the surface of the secondary winding, while between the turns, the secondary winding is only the pure synthetic resin because the gaps between the turns of the secondary winding are too small for the filler particles to penetrate. In this example, the secondary winding effectively acts as a filter for the filler.

Since, in conventional casting compounds, the dielectric constant of the filler differs considerably from that of the synthetic resin, spatial fluctuations in the concentration of the filler lead to spatial variations in the dielectric constant of the casting compound. The spatial variations in the dielectric constant in turn lead to spatial fluctuation in the electric field that permeates the potting compound because the strength of the electric field is inversely proportional to the dielectric constant of the dielectric that interspersed.

The spatial variations in the electric field strength have a threefold negative effect on the aging behavior of the insulating material, i. the potting compound. First, they cause locally increased electric field strengths, which can lead to partial discharges in cavities. Second, mechanical forces occur at locations where the field strength also changes abruptly as a result of a sudden change in the dielectric constant. Since these forces are applied continuously during operation of the transformation device, they occupy the material in the longer term, and the composite of the material is gradually weakened, whereby gaps can occur, in which then partial discharges can take place.

Third, the inventors have found in experimental studies that the spatial variations in the electric field strength based on an inhomogeneous distribution of the filler not only cause the formation of cavities, but also significantly accelerate the growth of existing voids in the insulating material in practice. As already explained above, the insulating material is eroded by partial discharges in cavities. This erosion leads to a growth of the cavities, which is known for example as "electrical treeing". This growth takes place all the faster, the more often partial discharges occur in the cavity. If the electric field strength varies greatly due to an inhomogeneous distribution of fillers, locally increased field strengths occur, which can ignite partial discharges and accelerate the growth of the cavity.

In the case described here, it is aggravating that the spatial distribution of the fillers is of a statistical nature and is therefore not only inhomogeneous, but also microscopically disordered. The disorder or uncertainty of the distribution of filler concentration leads to a disorderly distribution locally excessive electric field strengths, which in turn leads to partial discharges in different sections of a propagating cavity and allows its growth in different directions. Due to the disordered distribution of locally increased field strengths, there are far more possibilities for the growth of cavities due to partial discharges than is the case, for example, with an elevation of the electric field occurring along a defined interface between two different dielectrics. Thus, the voids can spread easier and faster due to the Unordered field elevation.

In summary, the inventors have recognized that the spatial variations in the filler concentration are the cause of the formation of imperfections in the insulating material, the occurrence of partial discharges in existing defects and accelerated growth of defects, and thus accelerate the aging of the insulating material.

This cause of accelerated aging can be effectively suppressed in the manner described above by the adjustment of the dielectric constants of the filler and the synthetic resin. Namely, if the dielectric constants of the filler and the resin deviate only to the extent described, the dielectric constant of the potting compound as a whole is approximately homogeneous, even if the filler is not homogeneously distributed in the resin. Thus, even with inhomogeneous distribution of the filler partial discharges are avoided in the potting compound and suppresses the formation and growth of defects, whereby the aging of the potting compound is effectively delayed.

The described approximation of the dielectric constants of the filler and of the synthetic resin according to the second aspect of the invention thus contributes to the solution of the same problem as the features of claim 1 to do the first aspect of the invention. However, it is emphasized that the second aspect can also be realized independently of the first aspect.

The above-mentioned components whose interspaces are filled with the potting compound may include one or more of the following: a primary winding carrier, a secondary winding carrier, an electrode connected to a secondary winding and connectable to a spark gap, a ferromagnetic core and / or or a metal case.

If the components mentioned are made of plastic, the dielectric constant of the plastic in an advantageous development is 0.5 times to 1.5 times, preferably 0.8 times to 1.25 times, and particularly preferably 0.9 times to 1.2 times the dielectric constant of the potting compound. This avoids an excessive jump in the dielectric constant at the interface between the potting compound and the component along with the negative consequences described above.

In an advantageous development, the synthetic resin is an epoxy resin and the filler is quartz.

Another aspect of the invention is directed to the electromagnetic compatibility of the transformation device. The inventors have found in simulations and experimental EMC tests that the spark is the most important source of electromagnetic interference.

According to the third aspect of the invention, a conductive layer which is connected to the ground potential is arranged between the primary winding and the secondary winding. This prevents the interference caused by the spark by capacitive coupling between the secondary winding and the primary winding is transferred to the on-board network of a motor vehicle connected to the primary winding. As a result, interference of electronic control devices that are connected to the on-board network can be effectively avoided.

It is emphasized that the use of a conductive, connected to ground potential layer between the primary and the secondary winding in a transformation device is also possible and advantageous regardless of the above-described features of the transformation device. This feature also constitutes an essential and advantageous contribution to the prior art.

The conductive layer is preferably arranged directly adjacent to the primary winding. This has the consequence that the conductive layer is at a maximum distance from the secondary winding. Thereby, the strength of the electric field between the conductive layer and the secondary winding can be kept low.

The conductive layer may be formed by a film or applied to a substrate, in particular vapor-deposited or printed.

Preferably, the secondary winding is at least partially disposed within the primary winding. This arrangement, in which the secondary winding is inside and the primary winding outside, leads to a reduced electric field strength in the interior of the transformation device in comparison to the usual, inverted arrangement with the same diameter of the transformation device and contributes to the prevention of partial discharges.

The transformation device preferably has a sleeve-like primary winding carrier on which the primary winding is arranged. In a particularly preferred embodiment, the above-mentioned conductive layer is arranged on the outer circumferential surface of the primary winding carrier. The primary winding carrier then serves to space and isolate the conductive layer from the secondary winding. Preferably, the above-mentioned secondary winding carrier is disposed within the primary winding carrier and the space between the primary winding carrier and the secondary winding carrier filled with potting compound.

In an alternative embodiment, the turns of the primary winding may be connected by conductive baked enamel or conductive adhesive forming the conductive layer. Then no primary winding carrier is needed.

Fig.1

eine Längsschnittsansicht einer Primärwicklung und eines Primärwicklungsträgers im auseinandergenommenen Zustand,

Fig.2

eine Längsschnittsansicht der Primärwicklung und des Primärwicklungsträgers im zusammengesetzten Zustand,

Fig.3

eine perspektivische Ansicht der Primärwicklung und des Primärwicklungsträgers im zusammengesetzten Zustand,

Fig.4

eine Längsschnittsansicht einer Sekundärwicklung, eines Sekundärwicklungsträgers, eines ferromagnetischen Kernes, eines leitenden Stiftes und einer Elektrode im auseinandergenommenen Zustand,

Fig.5

eine Längsschnittsansicht der Komponenten von Fig.4 im zusammengesetzten Zustand,

Fig.6

eine perspektivische Ansicht der Komponenten von Fig.4 im zusammengesetzten Zustand,

Fig.7

eine Längsschnittsansicht einer Zündtransformationsvorrichtung nach einer Weiterbildung der Erfindung,

Fig.8

eine perspektivische Ansicht der Zündtransformationsvorrichtung von Fig.7,

Fig.9

eine schematische Darstellung des Verlaufes des elektrischen Feldes zwischen einer Elektrode und einem Ende eines ferromagnetischen Kernes nach dem Stand der Technik,

Fig.10

eine schematische Darstellung des Verlaufes des elektrischen Feldes zwischen einer Elektrode und einem ferromagnetischen Kern bei einem Ausführungsbeispiel der Erfindung,

Fig.11

eine schematische Darstellung eines radialen Schnittes durch einen Teil der Transformationsvorrichtung von Fig.7,

Fig.12

den Verlauf des elektrostatischen Potentials in radialer Richtung in dem in Fig.11 gezeigten Teil der Transformationsvorrichtung für zwei Vergussmassen mit unterschiedlichen Füllstoffen.

Fig.13

den der Fig.12 entsprechenden Verlauf des elektrischen Feldes,

Fig.14

eine schematische Darstellung des Störpfades eines durch einen Zündfunken hervorgerufenen Störimpulses bei einem Zündtransförmator nach dem Stand der Technik und

Fig.15

eine schematische Darstellung des Störpfades eines durch einen Zündfunken hervorgerufenen Störimpulses bei einem Zündtransformator gemäß einem Ausführungsbeispiel der Erfindung.

Further advantages and features will become apparent from the following description in which the invention with reference to an embodiment with reference to the accompanying drawings will be explained. Show:

Fig.1

a longitudinal sectional view of a primary winding and a primary winding carrier in the disassembled state,

Fig.2

a longitudinal sectional view of the primary winding and the primary winding carrier in the assembled state,

Figure 3

a perspective view of the primary winding and the primary winding carrier in the assembled state,

Figure 4

a longitudinal sectional view of a secondary winding, a secondary winding carrier, a ferromagnetic core, a conductive pin and an electrode in the disassembled state,

Figure 5

a longitudinal sectional view of the components of Figure 4 in the assembled state,

Figure 6

a perspective view of the components of Figure 4 in the assembled state,

Figure 7

FIG. 3 is a longitudinal sectional view of an ignition transformer according to an embodiment of the invention; FIG.

Figure 8

a perspective view of the Zündtransformationsvorrichtung of Figure 7 .

Figure 9

a schematic representation of the course of the electric field between an electrode and one end of a ferromagnetic core according to the prior art,

Figure 10

a schematic representation of the course of the electric field between an electrode and a ferromagnetic core in an embodiment of the invention,

Figure 11

a schematic representation of a radial section through a part of the transformation device of Figure 7 .

Figure 12

the course of the electrostatic potential in the radial direction in the in Figure 11 shown part of the transformation device for two potting compounds with different fillers.

Figure 13

the the Figure 12 corresponding course of the electric field,

Figure 14

a schematic representation of the Störpfades caused by a spark interference pulse in a Zündtransförmator according to the prior art and

Figure 15

a schematic representation of the Störpfades caused by a spark interference pulse in an ignition transformer according to an embodiment of the invention.

In Fig.1 are a primary winding carrier 10 and a primary winding 12 in the disassembled state shown in longitudinal section, and in Fig.2 the primary winding carrier 10 and the primary winding 12 are shown in the assembled state in longitudinal section. The primary winding carrier 10 is made of insulating plastic and has a sleeve-like shape with an approximately cylindrical cavity 14. At one end of the cavity 14 is an opening 16 whose diameter is reduced relative to the diameter of the cavity 14.

The peripheral surface of the primary winding carrier 10 is coated with a conductive layer 18 which is formed by a foil or vapor-deposited or printed on the primary winding carrier 10. The conductive layer 18 is connected to the ground potential in the fully assembled transformation device (see Figure 15 ). The primary winding 12 has two terminals 20 and 22 for applying a primary voltage. In Figure 3 are the Primary coil carrier 10 and the primary winding 12 in the assembled state shown in perspective.

In Figure 4 For example, a secondary winding carrier 24, a secondary winding 26, a ferromagnetic core 28, a conductive pin 30 and an electrode 32 in a disassembled state are shown in longitudinal section.

The secondary winding carrier 24, as well as the primary winding carrier 10 of the Fig.1 to 3 made of insulating plastic and is sleeve-shaped with a cylindrical cavity 34. The ferromagnetic core 28 consists of a cylindrical soft iron rod 36, which consists of a plurality of mutually electrically insulated blades, and permanent magnets 38 which are arranged at the ends of the soft iron rod 36. The permanent magnets 38 magnetize the soft iron bar 36 with a polarity opposite to the polarity of the magnetic field generated upon application of a primary voltage to the terminals 20, 22 of the primary winding 12.

By applying the primary voltage to the terminals 20, 22 of the primary winding 12, therefore, the soft iron rod 36 is magnetized against the polarization of the permanent magnet 38. When the primary voltage is interrupted to generate the ignition voltage, the soft iron core assumes its output magnetization and the secondary voltage required for ignition is induced in the secondary winding 26. Due to the premagnetization with the permanent magnets, the energy stored in the magnetic field is increased, which allows an increased charge flow over the spark gap.

The electrode 32 has a cup-shaped portion 40 having a bottom portion 42 and a wall portion 44, and a threaded portion 46. Über the threaded portion 46 can be made in a manner not shown here, an electrical connection with a spark plug.

In Figure 5 are the components of Figure 4 shown in the assembled state in longitudinal section. The ferromagnetic core 28 is disposed in the cavity 34 of the secondary winding carrier 24. One end of the secondary winding carrier 24 is closed with the cup-shaped portion 40 of the electrode 32. After insertion of the ferromagnetic core 28 in the cavity 34 of the secondary winding carrier 24, the cavity 34 is poured with insulating potting compound 48. So that no air is trapped during the pouring of the cavity 34 in the region of the cup-shaped portion 44 of the electrode 32, both in the cup-shaped portion 44 and in the secondary winding body 24 air outlet openings 47 and 49 (see FIG. 4 ), through which the air can escape during pouring.

The conductive pin 30 is conductively connected to one end of the secondary winding 26 and is for connection to the ground potential. The other end of the secondary winding 26 is connected to the electrode 32. Figure 6 shows the composite components of Figure 5 in a perspective view.

Figure 7 shows a longitudinal sectional view in which the secondary winding carrier 24 including the secondary winding 26 and electrode 32 in the cavity 14 of the primary winding carrier 10 (see Fig.1 and 2 ) is arranged. In this case, the threaded portion 46 of the electrode 32 through the opening 16 (see Fig.1 ) inserted in the primary winding carrier 10. The space between the primary winding carrier 10 and the secondary winding carrier 24 is filled with insulating potting compound 48.

Note that potting may be done in two independent steps: First, the cavity 34 of the secondary winding substrate 24 may be potted with the ferromagnetic core 28 therein, and then the cavity 14 of the primary winding substrate 10 with the secondary winding substrate 24 therein. In this two-step potting making it easier to avoid the formation of voids where the partial discharges that are responsible for aging can take place.

The transformation device with in the Fig.1 to 8 shown components is particularly resistant to aging, as will be explained in more detail below. In Figure 9 Figure 4 is a sectional view of an electrode 32 'and a ferromagnetic core 28' having a soft iron bar 36 'and a permanent magnet 38' as used in conventional prior art transformers. Between the electrode 32 'and its end facing the ferromagnetic core 28', which is formed by the permanent magnet 38 ', there is an electric field 50', which is shown schematically by field lines. The permanent magnet 38 'is cylindrical and thus has at the transition between its lateral surface 38 a' and its end face 38 b 'a sharp edge 38 c'. At this sharp edge, the charge carrier density is increased locally and therefore the field line density of the electric field 50 'is also increased. Thus, in the region of the edge 38c 'there is a relatively strong electric field. The intermediate region between the electrode 32 'and the ferromagnetic core 28' is provided with an insulating potting compound (in Figure 9 not shown) filled. The electric field strength in the region of the edge 38c 'is sufficiently large to ignite partial discharges in microscopic cavities in the potting compound, which contribute significantly to their aging.

The conventional arrangement of Figure 9 is in Figure 10 compared the arrangement according to a development of the invention. This is different in the essentially by two features of those of the prior art. First, the permanent magnet 38 (see also 4, 5 and 7 ), ie it has a continuously curved transition between a lateral surface region 38a and an end surface region 38b. Thus, the shape of the permanent magnet 38 or, more generally, the shape of the electrode 32 opposite end of the ferromagnetic core 28, an edge or tip and a local increase in field strength associated therewith is avoided. It can thus be achieved that the strength of a field 50 between the ferromagnetic core 28 and the electrode 32 remains everywhere below the so-called Einsetzfeldstärke for partial discharges.

On the other hand, the electrode 32 has a cup-shaped portion 40 having a bottom portion 42 and a wall portion 44. The wall portion 44 surrounds the space between the bottom portion 42 and the end surface of the permanent magnet 38th

As based on the field lines of the field 50 of Figure 10 can be seen, the cup-shaped shape of the electrode 32 leads to an equalization of the field 50, ie to an increase in the space filled by the field 50 and to a homogenization of the electric field. Equalizing the field deflects its average field strength, while homogenizing the field avoids local field strength increases. Thereby, the strength of the field 50 can be kept anywhere below the field strength for partial discharges.

An ideally homogeneous field 50 would result if the surface of the permanent magnet 38 and the inner surface of the cup-shaped portion 40 of the electrode 32 were parallel to each other. In the illustrated electrode 32, the distance between any point on the permanent magnet is 38 facing portion of the surface of the wall portion 44 and the ferromagnetic core 0.75 to 1.8 times the distance between the bottom portion 42 and the intersection between the end face 38b of the permanent magnet 38 and a central axis 51 of the ferromagnetic core 28. In a Such dimensioning of the cup-shaped portion 40 can achieve a sufficiently homogeneous distribution of the field 50 for the purpose of avoiding partial discharges.

In Figure 11 is a radial section through the secondary winding carrier 24, the secondary winding 26, filled with potting compound 48 between the secondary winding carrier 24 and primary winding support 10 and the primary winding carrier 10 is shown. The potting compound 48 consists of a synthetic resin and a filler. The filler has, inter alia, the function, the thermal expansion coefficient of the potting compound 48 that of the electrode 32 and the like. equalize. The secondary winding 26 is in Figure 11 only indicated schematically. In fact, it can comprise about 70 layers of wire with a diameter of only about 50 μm. With such a fine wire, the spaces between the individual turns are so narrow that the filler can not penetrate into the spaces between the individual turns. In the secondary winding 26 thus penetrates only the pure resin. In a region 48a radially adjoining the secondary winding 26, ie, the region between r ₁ and r ₂ in FIG Figure 11 Accordingly, there is an increased concentration of the filler. In the region 48b between r ₂ and r ₃ , the potting compound 48 has the usual concentration of the filler, and radially outside of r ₃ , the primary winding carrier 10 begins.

In Figure 12 is the radial course of the electrostatic potential along the section of Figure 11 , and in Figure 13 the corresponding radial course of the electric field strength shown. In both diagrams 12 and 13, a broken line 52 and 56, the course for a conventional potting compound at the filler has a much higher dielectric constant than the synthetic resin, and the solid lines 54 and 58, the course according to a development of the invention, in which the dielectric constants of the resin and the filler are almost identical. For radii <r ₁ , ie in the field shadow of the secondary winding 26, the secondary voltage is constantly present. Between r ₁ and r ₃ , ie in the space filled with the potting compound 48 between the secondary winding 26 and the primary winding carrier 10, the potential decreases with increasing radial distance from the secondary winding. If, as in the prior art, the filler has a different, ie usually higher, dielectric constant than the synthetic resin, a change in the dielectric constant of the potting compound 48 results at r ₂ , where the concentration of the filler in the potting compound 48 changes as a whole. This leads to a kink in the potential curve (see graph 52 in FIG Figure 12 ) or a jump in the electric field (see graph 56 in FIG Figure 13 ). This jump in the electric field strength at r ₂ leads to mechanical stresses and, in the event of prolonged stress, to cracks or crevices in which, in turn, the partial discharges decisive for the aging of the potting compound can take place.

To circumvent this problem, a filler whose dielectric constant is almost identical to that of the resin is used. For example, an epoxy resin is used for the resin and quartz for the filler. Then there is a smooth progression of the potential between r ₁ and r ₃ (see graph 54 in FIG Figure 12 ) or a progression of the electric field strength between r ₁ and r ₃ without jumps (see graph 58 in FIG Figure 13 ). As a result, the formation of gaps in the area of the filler concentration change is effectively avoided. Furthermore, the maximum field strength (s graph. At r ₃ 56) (see Fig. 58 graph at r ₃₎ compared to the prior art is reduced, whereby the occurrence of partial discharges is further complicated.

In the potential course of Figure 12 This results in another kink at r ₃ , associated with a jump in the electric field strength (see Figure 13 ), which is due to a different dielectric constant of the potting compound 48 and the material of the primary winding carrier 10. In a particularly advantageous development, the dielectric constant of the material of the primary winding carrier 10 and of the secondary winding carrier 24 is also adapted to that of the synthetic resin. As a result, a gap formation between the potting compound on the one hand and the winding carriers 10, 24 on the other hand effectively avoided.

The following are with reference to the Fig.14 and 15 explains the improved EMC properties of the transformation device. First, referring to Figure 14 a conventional Zündanordnung described. The conventional ignition arrangement of Figure 14 includes an outboard secondary winding 26 'and an internal primary winding 12'. The secondary winding 26 'is conductively connected to an electrode 32', which in turn is connected via a contact spring 60 to a spark plug 62. The transformation device and the spark plug 62 are housed together in a housing 69 connected to the ground potential. The spark plug 62 has a ground potential electrode 64 which forms one end of a spark gap.

The beginning of a spark 65 is a sudden decrease in the secondary voltage from a higher value, which is required for ionization of the spark gap, to a lower, so-called burning voltage, under which the flow of current takes place along the spark gap. This erratic voltage change, which takes place within a few nanoseconds, according to studies of the inventors, the main cause of EMC problems in igniters. In Figure 14 is a Störpfad 66 along which a glitch propagates, shown schematically. The Störpfad begins in the spark gap and passes via the spark plug 62, the contact spring 60 and the electrode 62 'to the secondary winding 26'. From this runs the Störpfad 66 due to a capacitive coupling between the secondary winding 26 'and the primary winding 12' through the primary winding 12 'and its terminal 20' in the on-board network 68 of the motor vehicle in which it can cause malfunction of electronic control devices. The interference pulse passes through the on-board network 68 to the ground potential and thus to the electrode 64 of the spark gap, so that the Störpfad 66 closes.

In Figure 15 an ignition device is shown with the transformation device according to an embodiment of the invention. The ignition device includes those associated with the Fig.1 to 8 described transformation device, which is housed here together with a spark plug 62 in a connected to ground potential metallic housing or boiler shell 69. The electrode 32 is connected to a terminal of the spark plug 62 via a connector 70 shown schematically. The voltage drop due to the generation of a spark 65 propagates as a glitch along a Störpfades 72 via the spark plug 62, the connector 70 and the electrode 32 to the secondary winding 26, which is arranged inside in the illustrated transformation device. Since a conductive layer 18 is disposed between the secondary winding 26 and the primary winding 18, which is connected to the boiler shell 64, ie the ground potential, there is no capacitive coupling between the secondary winding 26 and the primary winding 18 here. The interference pulse is thus not transmitted to the on-board network 68. Instead, it flows low impedance over the boiler shell 69 to the ground potential. Experiments and simulations by the inventors have shown that with the aid of the conductive layer 18, in fact, by far the greatest part of the disturbances can be prevented.

In an alternative embodiment (not shown), the conductive layer is formed by conductive adhesive or conductive baked enamel with which the turns of the primary winding (12) are connected and held together. Then no primary spool is needed.

LIST OF REFERENCE NUMBERS

10

Primary winding support

12

primary

14

cavity

16

Opening in the primary winding carrier 10th

18

conductive layer

20

Connection

22

Connection

24

Secondary winding support

26

secondary winding

28

ferromagnetic core

30

senior pen

32

electrode

34

cavity

36

Soft iron bar

38

permanent magnet

40

cup-shaped section

42

bottom section

44

wall section

46

connecting section

47

Air outlet opening

48

potting compound

49

Air outlet opening

50

electric field

51

Central axis of the ferromagnetic core

52

Potential course according to the prior art

54

Potential course according to a development of the invention

56

Course of the electric field strength in the prior art

58

Course of the electric field strength in a development of the invention

60

contact spring

62

spark plug

64

electrode

65

spark

66

Störpfad the state of the art

68

Board network

69

Metal housing or boiler shell

70

connector

72

Störpfad in a development of the invention

Claims (22)

1. A transformation device for generating an ignition voltage for internal combustion engines, comprising
   a primary winding (12) to which a primary voltage can be applied, a secondary winding (26) in which a secondary voltage can be induced,
   a ferromagnetic core (28) which is arranged in the primary winding (12) and the secondary winding (26), and
   an electrode (32) which is opposite to an end (38) of the ferromagnetic core (28), is connected to the secondary winding (26) and is connectable to a spark gap,
   wherein between said end (38) of the ferromagnetic core (28) and the electrode (32) an electric field (50) is caused by the secondary voltage,
   characterized in that said end (38) of the ferromagnetic core (28) has a continuously curved transition between a lateral surface (38a) and an end face (38b).
2. The transformation device according to claim 1, characterized in that the electrode (32) is formed in a concave manner on its side facing the ferromagnetic core (28).
3. The transformation device according to claim 1 or 2, characterized in that the ends of the ferromagnetic core (28) are formed by permanent magnets (38).
4. The transformation device according to one of the preceding claims, characterized in that the end face (38a) of the ferromagnetic core (38) opposite to the electrode (32) is convex.
5. The transformation device according to claim 4, characterized in that the curvature of the convex end face (38b) increases with increasing distance to the central axis (51) of the ferromagnetic core (28).
6. The transformation device according to one of the preceding claims, characterized in that the electrode (32) has a cup-shaped section (40), the opening of which faces the ferromagnetic core (28).
7. The transformation device according to claim 6, characterized in that the cup-shaped section (40) has a bottom section (42) which is arranged transversely to the central axis (51) of the ferromagnetic core (28),
   and a wall section (44) which surrounds a space present between the bottom section (42) and the end face (38a) of the ferromagnetic element (28),
   wherein the distance between each point on the part of the surface of the wall section (44) facing the ferromagnetic core (28) and the ferromagnetic core (28) is 0.5 times to 2.5 times, preferably 0.75 times to 1.8 times the distance between the bottom section (42) and the point of intersection between the end face (38a) and the central axis (51) of the ferromagnetic core (28).
8. The transformation device according to claim 6 or 7, characterized by a sleeve-shaped secondary winding carrier (24) on which the secondary winding (26) is arranged and which is closed on one end with the cup-shaped section (40).
9. The transformation device according to one of the preceding claims,
   in which intermediate spaces between components of the transformation device are filled with a casting compound (48) which includes a synthetic resin and a filling material,
   characterized in that the dielectric constant of the filling material is 0.5 times to 1.5 times, preferably 0.8 times to 1.25 times and particularly preferably 0.9 times to 1.2 times the dielectric constant of the synthetic resin.
10. The transformation device according to claim 9, characterized in that said components comprise one or more of the following parts: a primary winding carrier (10), a secondary winding carrier (24), the electrode (32) which is connected to the secondary winding (26) and is connectable to the spark gap, the ferromagnetic core (28) and a metal housing (69).
11. The transformation device according to claim 9 or 10, in which at least one of said components (10, 24) is made of plastic material, characterized in that the dielectric constant of the plastic material is 0.5 times to 1.5 times, preferably 0.8 times to 1.25 times and particularly preferably 0.9 times to 1.2 times the dielectric constant of the casting compound (48).
12. The transformation device according to one of the claims 9 to 11, characterized in that the filling material is suited to adapt the coefficient of thermal expansion of the casting compound to that of said components.
13. The transformation device according to one of the claims 9 to 12, characterized in that the synthetic resin is an epoxy resin.
14. The transformation device according to one of the claims 9 to 13, characterized in that the filling material is quartz.
15. The transformation device according to one of the preceding claims,
    characterized in that between the primary winding (12) and the secondary winding (26) a conductive layer (18) is arranged which is connected to ground potential.
16. The transformation device according to claim 15, characterized in that the conductive layer (18) is arranged directly adjacent to the primary winding (12).
17. The transformation device according to claim 15 or 16, characterized in that the conductive layer (18) is formed by a foil.
18. The transformation device according to claim 15 or 16, characterized in that the conductive layer (18) is evaporated or printed on a carrier material.
19. The transformation device according to one of the preceding claims, characterized in that the secondary winding (26) is arranged at least in part within the primary winding (12).
20. The transformation device according to one of the preceding claims, characterized in that the transformation device has a sleeve-like primary winding carrier (10) on which the primary winding (12) is arranged.
21. The transformation device according to claims 19, 20 and one of the claims 15 to 18, characterized in that the conductive layer (18) is arranged on the outer circumferential surface of the primary winding carrier (10).
22. The transformation device according to one of the claims 15 to 20, characterized in that the conductive layer is formed by conductive adhesive or conductive baking varnish with which the windings of the primary winding (12) are bonded.

Images