Ignition coil having improved thermal stress resistance

Abstract

 The present invention relates to an ignition coil apparatus housing several ignition coils and ignition coils provided with a coating with electrical conductive, resilient material properties. An ignition coil in question includes a magnetic core of a magnetically permeable material, a high-voltage winding and a low-voltage winding in order to allow generation of a high-voltage signal for being supplied to a spark plug of an internal combustion engine. The magnetic core has at least one axis (B', C', D', D"), coaxially to which each the high-voltage winding and the low-voltage winding are arranged. The low-voltage winding is in particular arranged outwardly to the high-voltage winding .The ignition coil is provided outwardly with the aforementioned coating to avoid or at least minimize mechanical stress resulting from thermal-mechanical elongation effects and to protect against potential internal discharges.

Description

[0001] The present invention relates generally to ignition coils for developing a spark firing voltage that is applied to one or more spark plugs of an internal combustion engine. In particular, the present invention relates to an improved protective coating relating to mechanical and electrical protective means of the ignition coils.

[0002] Ignition coils utilize primary and secondary windings and a magnetic circuit for generating high-voltage signals to be supplied to spark plugs for firing fuel-air mixtures in internal combustion engines. The magnetic circuit includes conventionally a magnetically permeable central core.

[0003] With reference to EP 1 229 619 there is disclosed an ignition coil and more particularly an ignition coil of "pencil" type, which incorporates several layers interposed within and applied upon the winding assembly. The several layers are configured to meet specific physical and material properties. Primarily, the layers in the from of release and encapsulating layers are configured to avoid or at least minimize internal mechanical stress resulting from curing of epoxy resin adhesives and adhesive effects between adjacent surfaces in order to ensure uniform shape of the windings.

[0004] Nevertheless, conventional teaching of ignition coil manufacturing does not specifically relate to thermal-mechanical stresses, which results from different thermal elongation coefficients of differing types of materials and internal discharge avoidance.

[0005] There is therefore a need to provide an improved ignition coil and ignition coil apparatus, respectively, which provide an improved thermal stress resistance and eliminates or at least minimizes one or more of the shortcomings as set forth above.

[0006] An object of the present invention is to solve one or more of the problems as set forth above.

[0007] An ignition coil according to a first aspect to the present invention overcomes shortcomings in the art by providing a coating with electrical conductive, resilient material properties. The ignition coil includes a magnetic core of a magnetically permeable material, a high-voltage winding and a low-voltage winding in order to allow generation of a high-voltage signal for being supplied to a spark plug of an internal combustion engine. The magnetic core has at least one axis (B', C', D', D"), coaxially to which each the high-voltage winding and the low-voltage winding are arranged. The ignition coil is provided with the aforementioned coating to avoid or at least minimize mechanical stress resulting from thermal-mechanical elongation effects and to protect against potential internal discharges. Preferably the coating is provided on the magnetic core or on a part thereof. More preferably the coating extends on an outward surface of the magnetic core which may contact other parts of the adjacent apparatus.

[0008] According to an embodiment of the present invention, the magnetic core comprises at least a magnetic core frame. The magnetic core frame serves to short-circuit magnetic flux induced by anyone of the high-voltage and/or low-voltage windings into the magnetic core by for instance the low-voltage signals supplied to the low-voltage winding. The electrical conductive, resilient coating covers at least partially outwardly facing surfaces of the magnetic core frame.

[0009] According to an embodiment of the present invention, the magnetic core comprises a central magnetic core with the axis (B', C'), coaxially to which the high-voltage winding (310) and the low-voltage winding (320) are arranged. The low-voltage winding (320) is arranged outwardly of the high-voltage winding (310). Preferably, the magnetic core corresponds essentially to a closed E-shaped magnetic core.

[0010] According to an embodiment of the present invention, the magnetic core frame comprises at least one the axis (D', D"), coaxially to which the high-voltage winding and the low-voltage winding are arranged. The both windings are space at a distance from each other and do not overlap in their cross-sections with each other.

[0011] According to an embodiment of the present invention, the magnetic core is composed of two magnetic core parts, which when combined form substantially a closed E-shaped magnetic core.

[0012] According to an embodiment of the present invention, the magnetic core parts may correspond essentially to E-shaped magnetic core parts with three legs having different lengths or with legs having at least partly the same lengths. Alternatively, the magnetic core parts may compirse a C-shaped magnetic core and a T-shaped magnetic core part which, when combined, form the closed E-shaped magnetic core.

[0013] According to an embodiment of the present invention, the magnetic core is composed of two magnetic core parts, which, when combined, form substantially an O-shaped magnetic core.

[0014] According to an embodiment of the present invention, the magnetic core parts correspond essentially to C-shaped magnetic core parts.

[0015] According to an embodiment of the present invention, the electrical conductive, resilient coating is composed of a resilient material including electrically conductive particles. Particularly the resilient material is made of a resilient polymer material such as an elastomeric material. More particularly the resilient material is made of polytetrafluorethylene material, polyamide material or polyester material. Advantageously, the resilient material is a soft resilient material such as rubber material, especially elastomeric materials, rubber material, silicon rubber material etc. The electrically conductive property is obtained by included particles which are in particular metallic particles, soot particles or graphite particles. Silver particles are for instance comprised by suitable metallic particles.

[0016] According to an embodiment of the present invention, the electrically conductive, resilient coating is applied to the ignition coil by injection molding, dipping or as an overmolded foam.

[0017] An ignition coil apparatus according to a second aspect of the present invention overcomes shortcomings in the art by providing a coating with an electrical conductive, resilient material properties, which coating is applied to the several ignition coils comprised by the ignition coil apparatus. Each ignition coil includes a magnetic core of a magnetically permeable material, a high-voltage winding and a low-voltage winding in order to allow generation of a high-voltage signal for being supplied to a spark plug of an internal combustion engine. The magnetic core of each ignition coil has at least one axis (B', C', D', D"), coaxially to which the high-voltage winding and the low-voltage winding are arranged. The several ignition coils comprised by the ignition coil apparatus are arranged in a rail and housed in a common enclosure. Each ignition coil is provided outwardly with a coating. As aforementioned each ignition coil is provided with the coating having electrical conductive, resilient properties. The electrical conductive, resilient coatings of adjacent ignition coils are in physical contact with each other such that mechanical stress resulting from thermal-mechanical elongation effects is avoided or at least minimized and the ignition coil apparatus is protected against potential internal discharges.

[0018] According to an embodiment of the present invention, the magnetic core comprises at least a magnetic core frame. The magnetic core frame serves to short-circuit magnetic flux induced by anyone of the high-voltage and/or low-voltage windings into the magnetic core by for instance the low-voltage signals supplied to the low-voltage winding. The electrical conductive, resilient coating covers at least partially outwardly facing surfaces of the magnetic core frame.

[0019] According to an embodiment of the present invention, the magnetic core comprises a central magnetic core with the axis (B', C'), coaxially to which the high-voltage winding (310) and the low-voltage winding (320) are arranged. The low-voltage winding (320) is arranged outwardly of the high-voltage winding (310). Preferably, the magnetic core corresponds essentially to a closed E-shaped magnetic core.

[0020] According to an embodiment of the present invention, the magnetic core frame comprises at least one the axis (D', D"), coaxially to which the high-voltage winding and the low-voltage winding are arranged. The both windings are space at a distance from each other and do not overlap in their cross-sections with each other.

[0021] According to an embodiment of the present invention, the magnetic core is composed of two magnetic core parts, which when combined form substantially a closed E-shaped magnetic core.

[0022] According to an embodiment of the present invention, the magnetic core parts may correspond essentially to E-shaped magnetic core parts with three legs having different lengths or with legs having at least partly the same lengths. Alternatively, the magnetic core parts may compirse a C-shaped magnetic core and a T-shaped magnetic core part which, when combined, form the closed E-shaped magnetic core.

[0023] According to an embodiment of the present invention, the magnetic core is composed of two magnetic core parts, which, when combined, form substantially an O-shaped magnetic core.

[0024] According to an embodiment of the present invention, the magnetic core parts correspond essentially to C-shaped magnetic core parts.

[0025] According to an embodiment of the present invention, the magnetic core is composed of two magnetic core parts. The both magnetic core parts each correspond to E-shaped magnetic cores, which have three legs with differing leg lengths.

[0026] According to an embodiment of the present invention, the electrical conductive, resilient coating is composed of a resilient material including electrically conductive particles. Particularly the resilient material is made of a resilient polymer material. More particularly resilient material is made of polytetrafluorethylene material, polyamide material or polyester material. Advantageously, the resilient material is a soft resilient material such as rubber material, especially elastomeric materials, rubber material, silicon rubber material etc. The electrically conductive particles are in particular metallic particles, soot particles or graphite particles. Silver particles are for instance suitable metallic particles.

[0027] According to an embodiment of the present invention, the electrical conductive, resilient coating is applied to the ignition coil by injection molding, dipping or as overmolded foam.

[0028] The present invention will now be described in detail with reference to the attached drawings, which are provided purely to furnish non-limiting examples, and in which:

Figure 1(a) to (d)

illustrate several sectional views of an ignition coil according to an embodiment of the present invention;

Figure 2

illustrates a sectional view of a magnetic core assembly according to an embodiment of the present invention;

Figure 3

illustrates a rail of four ignition coils enclosed within a common ignition coil enclosure according to an embodiment of the present invention;

Figure 4(a) and (b)

illustrate an alternative shaping of an ignition coil in different sectional views according to an embodiment of the present invention;

Fig. 4(c)

illustrates an alternative rail of four ignition coils enclosed within a common ignition coil enclosure according to an embodiment of the present invention; and

Figure 5(a) to (d)

illustrate several sectional views of alternative ignition coils and sectional views of corresponding magnetic core assemblies according to an embodiment of the present invention.

[0029] Referring now to the drawings wherein like reference numerals are used to identify identical components in the various drawings. With reference to the drawings, reference numeral 100 designates an ignition coil for motor vehicles, which is designated to be used on internal-combustion engines with spark ignition. The ignition coil comprises substantially coaxially arranged high-voltage and low-voltage windings arranged in turn coaxially with a high permeability magnetic core.

[0030] With reference to Fig. 1(a) to 1(d), Fig. 1(a) depicts a first sectional view of the ignition coil according to an embodiment of the invention in accordance with a first longitudinal plane, Fig. 1(b) depicts a second sectional view of the ignition coil according to an embodiment of the invention in accordance with a second longitudinal plane indicated in Fig. 1(a) with an axis B' and Fig. 1(c) depicts a transversal sectional view of the ignition coil according to an embodiment of the invention in accordance with a transversal plane indicated in Fig. 1(a) with an axis A'. Fig. 1(d) depicts a more detailed partly sectional view in accordance with the illustration shown in Fig. 1(b).

[0031] In general, the ignition coil illustrated in Fig. 1(a) to 1(d) according to the embodiment of the present invention is assembled on a closed E-shaped magnetic core, which comprises in principle a central magnetic core 200, which is provided for carrying at least a high-voltage winding 310 and a low-voltage winding 320, and a magnetic core frame 210 for conducting the magnetic flux induced into the central magnetic core 200. The magnetic flux is substantially enclosed within the central magnetic core 200 and the magnetic core frame 210. The magnetic core is preferably formed, in a way in itself known, from metal laminations composed of metal sheets and made of a material with high magnetic permeability such as silica iron. In accordance with the embodiment depicted in Fig. 1(a) to 1(d), the central magnetic core 200 and the magnetic core frame 210 have rectangular-shaped cross sections.

[0032] As aforementioned, the central magnetic core 200, which has a rectilinear axis, is provided with the high-voltage winding 310, which is arranged coaxially relative to the central magnetic core 200 and its rectilinear axis. The central magnetic core 200 is further provided with the low-voltage winding 320, which is arranged coaxially and outside relative to the high-voltage winding 310. The rectilinear axis of the central magnetic core 200 corresponds essentially to the axis B' and axis C', respectively, illustrated in Fig 1(a), 1(b) and 1(c). The high-voltage winding 310 and the low-voltage winding 320 are preferably made of insulated wires such as enameled copper wires.

[0033] As known by those skilled in the art, the design and assembly of the high-voltage winding 310 and the low-voltage winding 320 may vary. Reference shall be given to Fig. 1(d), which illustrates an example design and assembly of the windings 310 and 320 as a non-limiting example. In accordance with the embodiment illustrated in Fig. 1(d), the high-voltage winding 310 is supported by a first spool 330, onto which the high-voltage winding 310 is wound. Analogously, the low-voltage winding 320 is supported by a second spool 350, onto which the low-voltage winding 320 is wound. Such spool bodies may be made of injection-molded plastic materials, having thermoplastic or thermosetting material properties.

[0034] Moreover, the high-voltage winding 310 and the low-voltage winding 320 may be uncoupled, i.e. electrically and/or mechanically uncoupled. The uncoupling of the both windings 310 and 320 may be obtained by interposing at least one intermediate layer 340 anywhere between the high-voltage winding 310 and the low-voltage winding 320. For mechanical uncoupling, the intermediate layer 340 is configured to eliminate or at least minimize mechanical stress between the high-voltage winding 310 and the low-voltage winding 320, respectively. Several materials may be applicable for such an intermediate layer 340, comprising for instance polytetrafluorethylene, polyamide, polyester, silicone coatings, silicon rubber, and the like. It should be noted that other materials or a combination of materials might be applicable to obtain a mechanical uncoupling. In principle, a mechanical uncoupling is obtained by materials having low (chemical or physical) adhesion properties with an adjoining or resting surface such as the outer surface of the high-voltage winding 310 and the inner surface of the low-voltage winding 320, respectively.

[0035] For electrical uncoupling, the intermediate layer 340 is configured to insulate electrically between the high-voltage winding 310 and the low-voltage winding 320, respectively. A board number of materials are known in the art, which allow the design of an insulating layer 340 such as defined above. For instance, epoxy resin is applicable to obtain an intermediate layer 340 having electrically insulating properties.

[0036] It shall be noted that the high-voltage winding 310 and/or the low-voltage winding 320 may be designed as a self-supporting winding, respectively, such that there is no need for any spool 330 or 350 supporting the corresponding self-supporting winding 310 and/or 320. It should be also understood that even additional layers interposed between the central magnetic core 200, the high-voltage winding 310 and the low-voltage winding 320 may be provided. Moreover, one or more further layers may be arranged outside relative to the low-voltage layers. A detailed arrangement and design of such layers as aforementioned and the windings 310 and 320 is out of the scope of the present invention. A biasing magnet 230 may be included in the magnetic circuit and in particular in the central magnetic core 200 for magnetically biasing purpose.

[0037] With reference to Fig. 2, a possible two-part design of the closed E-shaped magnetic core according to an embodiment of the present invention is shown. The two-part design of the closed E-shaped magnetic core comprises a first E-shaped magnetic core part 120 and a second E-shaped magnetic core part 130. The both E-shaped magnetic core parts 120 and 130 correspond in such a way with each other that, when combining the E-shaped magnetic core parts 120 and 130, the closed E-shaped magnetic core is obtained.

[0038] The first E-shaped magnetic core part 120 and a second E-shaped magnetic core part 130 are designed differently; in particular, the central magnetic core 200 is substantially completely designed and arranged with the second E-shaped magnetic core part 130. This design of the central magnetic core 200 is advantageously, when considering the manufacturing of the ignition coil according to an embodiment of the present invention. One or more of the high-voltage and low voltage windings with or without spool bodies and/or layers may be pre-manufactured and then arranged onto the central magnetic core 200 such that the high-voltage winding 310 and/or low-voltage winding 320 conforms essentially coaxially with the rectilinear axis of the central magnetic core 200.

[0039] Conventionally, each ignition coil is associated with a spark plug, which is supplied with a high-voltage signal generated by the associated ignition coil. The high-voltage signal causes the spark plug to release a spark between electrodes separated by spark gap for firing a fuel-air mixture in the cylinder of the internal combustion engine, at which the spark plug is mounted. In a conventional internal combustion engine, each spark plug is typically provided with an ignition coil.

[0040] With reference to Fig. 3 a simplified schematic depiction of an ignition coil enclosure 400 enclosing several ignition coils such as of the type illustrated with reference to Fig. 1(a) to 1(d) and Fig. 2 is depicted. The illustrated number of four ignition coils is exemplary. It should be noted that alternatively each ignition coil might be provided with its own ignition coil enclosure enclosing only one ignition coil for example of the type illustrated with reference to Fig. 1(a) to 1(d) and Fig. 2.

[0041] The ignition coil enclosure 400 housing the several ignition coils is preferably filled with a dielectric material, preferably a dielectric polymer material such as a dielectric epoxy resin. The dielectric epoxy resin has preferably electrically insulating properties. Additionally, the dielectric epoxy resin used for filling the ignition coil enclosure 400 is likewise used for electrically insulating the components of the ignition coils against the ignition coil enclosure 400. For the sake of simplicity, the illustrated ignition coils are depicted for the way of illustration by the means of their magnetic cores omitting any winding configuration and arrangement, respectively, electrical connections etc. A connection rail 410 indulging several low-voltage connections connects the low-voltage windings of the ignition coils with a common low voltage connector 420. Each ignition coil is provided with a separate high-voltage connector 430, which is preferably configured to accept a high-voltage plug connecting the high-voltage windings of the ignition coils with the respective spark plugs of the internal combustion engine.

[0042] During lifetime of the ignition coils, the ignition coils and their ignition coil enclosure 400 is subjected to mechanical, thermal and/or mechanical-thermal stresses. The presence and appearance of mechanical, thermal and/or thermal-mechanical stresses, especially when the stresses appear regularly and/or frequently, the possibility of damages such as cracks, fractures etc rises, which can result in a loss of function of the ignition coils. Different physical mechanisms effect the aforementioned mechanical, thermal and/or mechanical-thermal stresses. Vibrations for instance caused by the combustion engine and/or the motor vehicle which is powered by the combustion engine and transferred from the outside of the ignition coil enclosure 400 may have shock effects on the components thereof.

[0043] But most serious is thermal-mechanical stress, which results from components having different thermal elongation coefficients and which is caused by changing temperatures driving thermal expansion at different extend. Typically, ignition coils are designed to be operable within a temperature range of approximately -40°C to 150°C. As aforementioned, the components comprised by the ignition coils and ignition coil enclosures, respectively, are made of different kind of materials including polymeric material such as thermoplastic and thermosetting polymers, enameled copper and silica iron. The thermal elongation coefficients of this selection of materials differ significantly, which cause inevitably mechanical stress at changing temperatures. In particular, such thermal-mechanical stresses are magnified in case several ignition coils are housed within a common enclosure such as depicted in Fig. 3.

[0044] In order to achieve acceptable levels of reliability and durability and acceptable lifetimes such stresses have to be avoided or at least minimized. Due to the fact that the different thermal elongation coefficients cannot be balanced and the selection of the different materials originates on the different electrical, mechanical and magnetic properties required to enable the functionality of the ignition coils, precautions have to be taken to at least minimize thermal-mechanical stresses occurring unavoidably.

[0045] Suitable measures concerning thermal-mechanical stresses within the winding arrangement have been described in detail with reference to Fig. 1(d). Nevertheless, measures have also to be taken with respect to the effect of thermal-mechanical stress between ignition coils and ignition coil enclosure 400. Therefore, the ignition coil 100 is provided with a resilient coating provided at least on the surfaces, which are adjacent to one or more adjoining ignition coils and/or to the inner surface of the ignition coil enclosure 400. Such a resilient coating is indicated in Fig. 1(a) to (c) with the means of the reference numeral 220. The resilient coating 220 of a sufficient thickness of for instance less than approximately 1 mm is able to compensate for mechanical expansions and dilatations due to changing temperature and differing thermal elongation coefficients. The resilient coating 220 deforms in accordance with the need of space required by the ignition coils and the space provided by the ignition coil enclosure 400.

[0046] A second serious problem is posed by dangerous potential internal discharges, which may occur potentially, and which may cause irreparable damages. Ignition coils such as those described with respect to Fig 1(a) to Fig. 1(d) are applied to generate high-voltage signals, which are supplied to sparks plugs to produce a spark to fire the fuel-air-mixture in the cylinders of an internal combustion engine. A low-voltage signal is fed into the low-voltage windings of an ignition coil to generate a high-voltage signal in the order of about several thousands of volts, particularly, in the order of about several ten thousands of volts and more particularly in the order of forty thousand volts. The presents of such high-voltage signals within ignition coils inherently implies the danger of internal discharges.

[0047] Conventionally, specific ground connections are provided within the ignition coil enclosure to divert such internal discharges to ground. The ground connections may be designed as one or more metallic pins inserted adjacent to an ignition coil or between each magnetic core of the ignition coils.

[0048] According to the present invention, the one or more ground connections are substituted by an electrically conductive coating provided at the outside surface of the ignition coil and the magnetic core of the ignition coil, respectively. With reference to the resilient coating 220 described in detail above, the electrically conductive coating and the resilient coating is preferably provided as a coating comprising both material properties, i.e. the coating 220 is an electrically conductive, resilient coating 220. Such an electrically conductive, resilient coating 220 serves to compensate for mechanical stress and to absorb mechanical shocks such that mechanical failure due to mechanical stress is avoid. The electrical conductivity of the electrically conductive, resilient coating 220 enables to divert potential dangerous internal discharges protecting against damages resulting from unintentional internal discharges.

[0049] The electrically conductive, resilient coating 220 can be composed of a resilient material, in particular a soft polymeric material. A broad number of possible polymeric materials are applicable such as polytetrafluorethylene, polyamide, polyester etc. Preferably, soft resilient materials are applicable, such as soft polymeric materials including for instance rubber material e.g. silicon rubber or any other material having resilient material properties. For electrical conductivity the resilient material is preferably filled with electrically conductive particles such as metallic particles, soot particles or graphite particles, wherein the metallic particles include in particular silver particles. The electrically conductive, resilient coating 220 is preferably applied by injection molding, by dipping or with the help of overmolded foam.

[0050] With reference to Fig. 1(a) to Fig. 2, at least one of the side surfaces, the button surfaces and the top surfaces, respectively, facing outside, are at least partly applied with the electrically conductive, resilient coating 220 having a thickness of about 1 mm and less. In more detail, at least part of the surfaces of the magnetic core frame 210, which surfaces facing outside and which surfaces are perpendicular to the cross-sectional view of the ignition coil shown in Fig. 1(a), are covered with the electrically conductive, resilient coating 220.

[0051] With reference to Fig. 3, the ignition coil rail comprising the four ignition coils illustrated each being arranged adjacent to each other. In detail, the ignition coils disposed in a rail are arranged such that the magnetic core frame of each ignition coil is in contact with the one or both adjacent magnetic cores of the one or both adjacent ignition coils. As aforementioned, at least the side surfaces, which surfaces are perpendicular to the cross-sectional view of the ignition coil shown in Fig. 1(a), are covered with the electrically conductive, resilient coating 220. This means that the electrically conductive, resilient coatings of the one or both adjacent magnetic cores of the one or both adjacent ignition coils are in physical contact with another.

[0052] On the one hand, the physical contact of the electrically conductive, resilient coatings serves to compensate for mechanical stress and to absorb mechanical shocks between adjacent ignition coils and magnetic (frame) cores, respectively. On the other hand, the physical contact of the electrically conductive, resilient coatings serves to divert potential dangerous internal discharges from one of the ignition coil to the other ignition coil protecting against damages resulting from unintentional internal discharges.

[0053] In summary, the present invention provides for advantages in the coil design, coil process and coil reliability. The electrically conductive, resilient coating allows to design ignition coils and ignition coil apparatus without constrains relating to electrical connections between magnetic cores for diverting internal discharges, which results in a simplified coil design. In parallel, the avoidance of electrical connections for diverting discharges simplifies the manufacturing process of ignition coils and ignition coil apparatus, excluding the need for expensive equipment necessary for the pin insertion between the magnetic cores serving as electrical connections for diverting internal discharges. Additionally, the presence of the electrically conductive, resilient coating between the magnetic cores within the ignition coils and ignition coil apparatus avoids, attenuates or at least minimizes mechanical stress and mechanical shocks. Conclusively, the components within the ignition coils and ignition coil apparatus and the number of production steps for manufacturing are reduced, which results in a reduced failure probability due to manufacturing or component failure. Consequently, the reliability of the ignition coils and ignition coil apparatus is increased which in parallel allows increasing the operation temperature range of the ignition coils and ignition coil apparatus.

[0054] With reference to Fig. 4(a) and 4(b) it should be noted that the aforementioned configuration of the ignition coil according to an embodiment illustrated with reference to Fig. 1(a) to Fig. 2 is also applicable with "pencil"-type shaped ignition coils. Fig. 4(a) depicts a first sectional view of the ignition coil according to an embodiment of the invention in accordance with a first longitudinal plane and Fig. 4(b) depicts a more detailed partly sectional view in accordance with the illustration shown in Fig. 4(a).

[0055] In general, the ignition coil illustrated in Fig. 4(a) and 4(b) according to embodiments of the present invention are assembled in a so-called pencil-type style which comprises in principle a longitudinal extending central magnetic core 200, which is provided for carrying at least a high-voltage winding 310 and a low-voltage winding 320. The magnetic flux is substantially enclosed within the central magnetic core 200 and a shielding layer 360. The central magnetic core 200 is preferably formed, in a way in itself known, from metal laminations composed of metal sheets and made of a material with high magnetic permeability such as silica iron. In accordance with the embodiment depicted in Fig. 4(a) and 4(b), the central magnetic core 200 may have a rectangular-shaped cross section, an elliptic-shaped cross section, a circular-shaped cross section and any other shape of the cross section.

[0056] The shield layer 360 is in general disposed radially outwardly relative to the windings 310 and 320 and in particular to the low-voltage windings 320. The shield layer 360 preferably comprises electrically conductive material and more preferably metallic material such as silicon steel or any other material. The shield layer may not provide only a protective barrier for the ignition coil but also provides for a magnetic path for conducting the magnetic flux of the magnetic circuit of the ignition coil in question. The shield may be composed of multiple individual sheets comparable with the lamella design of the central magnetic core 200.

[0057] As aforementioned, the central magnetic core 200, which has a rectilinear axis, is provided with the high-voltage winding 310, which is arranged coaxially relative to the central magnetic core 200 and its rectilinear axis. The central magnetic core 200 is further provided with the low-voltage winding 320, which is arranged coaxially and outside relative to the high-voltage winding 310. The rectilinear axis of the central magnetic core 200 corresponds essentially to axis C' illustrated in Fig 4(a) and 4(b). The high-voltage winding 310 and the low-voltage winding 320 are preferably made of insulated wires such as enameled copper wires.

[0058] As known by those skilled in the art, the design and assembly of the high-voltage winding 310 and the low-voltage winding 320 may vary. Reference shall be given to Fig. 4(b), which illustrates an example design and assembly of the windings 310 and 320 as a non-limiting example. In accordance with the embodiment illustrated in Fig. 4(b), the high-voltage winding 310 is supported by a first spool 330, onto which the high-voltage winding 310 is wound. Analogously, the low-voltage winding 320 is supported by a second spool 350, onto which the low-voltage winding 320 is wound. Such spool bodies may be made of injection-molded plastic materials, having thermoplastic or thermosetting material properties.

[0059] Moreover, the high-voltage winding 310 and the low-voltage winding 320 may be uncoupled, i.e. electrically and/or mechanically uncoupled. The uncoupling of the both windings 310 and 320 may be obtained by interposing at least one intermediate layer 340 anywhere between the high-voltage winding 310 and the low-voltage winding 320. For mechanical uncoupling, the intermediate layer 340 is configured to eliminate or at least minimize mechanical stress between the high-voltage winding 310 and the low-voltage winding 320, respectively. Several materials may be applicable for such an intermediate layer 340, comprising for instance polytetrafluorethylene, polyamide, polyester, silicone coatings, silicon rubber, and the like. It should be noted that other materials or a combination of materials might be applicable to obtain a mechanical uncoupling. In principle, a mechanical uncoupling is obtained by materials having low (chemical or physical) adhesion properties with an adjoining or resting surface such as the outer surface of the high-voltage winding 310 and the inner surface of the low-voltage winding 320, respectively.

[0060] For electrical uncoupling, the intermediate layer 340 is configured to insulate electrically between the high-voltage winding 310 and the low-voltage winding 320, respectively. A board number of materials are known in the art, which allow the design of an insulating layer 340 such as defined above. For instance, epoxy resin is applicable to obtain an intermediate layer 340 having electrically insulating properties.

[0061] It shall be noted that the high-voltage winding 310 and/or the low-voltage winding 320 may be designed as a self-supporting winding, respectively, such that there is no need for any spool 330 or 350 supporting the corresponding self-supporting winding 310 and/or 320. It should be also understood that even additional layers interposed between the central magnetic core 200, the high-voltage winding 310 and the low-voltage winding 320 may be provided. Moreover, one or more further layers may be arranged outside relative to the low-voltage layers. A detailed arrangement and design of such layers as aforementioned and the windings 310 and 320 is out of the scope of the present invention. A biasing magnet 230 may be included in the magnetic circuit and in particular in the central magnetic core 200 for magnetically biasing purpose in order to improve the performance of the magnetic circuit.

[0062] With reference to Fig. 4(c) simplified schematic depiction of an ignition coil enclosure 400 enclosing several ignition coils such as of the type illustrated with reference to Fig. 4(a) and 4(b) is depicted. The illustrated number of four ignition coils is exemplary. It should be noted that alternatively each ignition coil might be provided with its own ignition coil enclosure enclosing only one ignition coil for example of the type illustrated with reference to Fig. 4(a) and 4(b).

[0063] The ignition coil enclosure 400 housing the several ignition coils is preferably filled with a dielectric material, preferably a dielectric polymer material such as a dielectric epoxy resin. The dielectric epoxy resin has preferably electrically insulating properties. Additionally, the dielectric epoxy resin used for filling the ignition coil enclosure 400 is likewise used for electrically insulating the components of the ignition coils against the ignition coil enclosure 400. For the sake of simplicity, the illustrated ignition coils are depicted schematically as illustrated in Fig. 4(a) omitting details relating to winding arrangement, electrical connections etc. A connection rail 410 indulging several low-voltage connections connects the low-voltage windings of the ignition coils with a common low voltage connector 420.

[0064] Each ignition coil is provided with a separate high-voltage connector 430, which is preferably configured to accept a high-voltage plug connecting the high-voltage windings of the ignition coils with the respective spark plugs of the internal combustion engine.

[0065] On the basis of the description above those skilled in the art will appreciate that potential damaging effects such as thermal-mechanical stress, mechanical shocks and potential internal discharges described in detail above can also occur in conjunction with ignition coils and ignition coil apparatus illustrated with reference to Fig. 4(a) to 4(c). Analogous measures have also to be taken with respect to the effect of thermal-mechanical stress between ignition coils and ignition coil enclosure 400 and potential internal discharges. Therefore, the ignition coil 100 is provided with an electrically conductive, resilient coating 220 provided at least partly on surfaces, which are adjacent to one or more adjoining ignition coils and/or to the inner surface of the ignition coil enclosure 400. Such an electrically conductive, resilient coating 220 is indicated in Fig. 4(a) to 4(c) with the means of the reference numeral 220. The electrically conductive, resilient coating 220 of a sufficient thickness of for instance less than approximately 1 mm is able to compensate for mechanical expansions and dilatations due to changing temperature and differing thermal elongation coefficients. The electrically conductive, resilient coating 220 deforms in accordance with the need of space required by the ignition coils and the space provided by the ignition coil enclosure 400.

[0066] According to the present invention and in analogy with the description above, the one or more ground connections, which are typically provided for diverting discharges, are substituted by the electrically conductive, resilient coating 220 provided at least partly on the outside surfaces of the ignition coil and the magnetic core of the ignition coil, respectively. The electrical conductivity of the electrically conductive, resilient coating 220 enables to divert potential dangerous internal discharges protecting against damages resulting from unintentional internal discharges.

[0067] The electrically conductive, resilient coating 220 can be composed of a resilient material, in particular a soft polymeric material. A broad number of possible polymeric materials are applicable such as polytetrafluorethylene, polyamide, polyester etc. Preferably, soft resilient materials are applicable, such as soft polymeric materials including for instance rubber material e.g. silicon rubber or any other material having resilient material properties. For electrical conductivity the resilient material is preferably filled with electrically conductive particles such as metallic particles, soot particles or graphite particles, wherein the metallic particles include in particular silver particles. The electrically conductive, resilient coating 220 is preferably applied by injection molding, by dipping or with the help of overmolded foam.

[0068] With reference to Fig. 5(a) to (d) several alternative designs of ignition coils and their magnetic cores are presented for the way of illustration. Each alternative design is based on a two-part assembly of the magnetic core.

[0069] With reference to Fig. 5(a), the ignition coil presented therein is constituted on the basis of an alternative two-part design of a closed E-shaped magnetic core according to an embodiment of the present invention is shown. The two-part design of the closed E-shaped magnetic core comprises a first E-shaped magnetic core part 120 and a second E-shaped magnetic core part 130. In general, the both E-shaped magnetic core parts 120 and 130 correspond in such a way with each other that, when combining the E-shaped magnetic core parts 120 and 130, the closed E-shaped magnetic core as illustrated above with respect to Fig. 5(a) is obtained.

[0070] The first E-shaped magnetic core part 120 and a second E-shaped magnetic core part 130 correspond essentially to each other; in particular, the central magnetic core 200 is substantially designed and arranged with both the first E-shaped magnetic core part 120 and the second E-shaped magnetic core part 130.

[0071] One or more of the high-voltage windings 310 and low voltage windings 320 with or without spool bodies (not illustrated) and/or layers (not illustrated) may be pre-manufactured and then arranged onto the central magnetic core 200 such that the high-voltage winding 310 and/or low-voltage winding 320 conforms essentially coaxially with the rectilinear axis of the central magnetic core 200. The arrangement and purpose of intermediately arranged and additionally arranged spool bodies and layers have been discussed in detail with reference to Fig. 1(d). It shall be noted that the discussed principles apply likewise to the embodiment described with reference to Fig. 5(a).

[0072] With reference to Fig. 5(b), the ignition coil presented therein is constituted on the basis of an alternative two-part design of a closed E-shaped magnetic core according to an embodiment of the present invention is shown. The two-part design of the closed E-shaped magnetic core comprises a first O-shaped magnetic core part 120 and a second I-shaped magnetic core part 130. In general, the first O-shaped magnetic core part 120 and the second I-shaped magnetic core part 130 correspond in such a way with each other that, when combining the both magnetic core parts 120 and 130, the closed E-shaped magnetic core as illustrated above with respect to Fig. 5(b) is obtained.

[0073] The first O-shaped magnetic core part 120 corresponds substantially to the magnetic core frame 210, whereas the second I-shaped magnetic core part 130 correspond essentially to the magnetic central magnetic core 200.

[0074] One or more of the high-voltage windings 310 and low voltage windings 320 with or without spool bodies (not illustrated) and/or layers (not illustrated) may be pre-manufactured and then arranged onto the first magnetic central core part 130 such that the high-voltage winding 310 and/or low-voltage winding 320 conforms essentially coaxially with the rectilinear axis of the central magnetic core 200. The arrangement and purpose of intermediately arranged and additionally arranged spool bodies and layers have been discussed in detail with reference to Fig. 1(d). It shall be noted that the discussed principles apply likewise to the embodiment described with reference to Fig. 5(b).

[0075] With reference to Fig. 5(c), the ignition coil presented therein is constituted on the basis of an alternative two-part design of a closed E-shaped magnetic core according to an embodiment of the present invention is shown. The two-part design of the closed E-shaped magnetic core comprises a first T-shaped magnetic core part 120 and a second C-shaped magnetic core part 130 (and U-shaped magnetic core part 130, respectively). In general, the first T-shaped magnetic core part 120 and the second C-shaped magnetic core part 130 correspond in such a way with each other that, when combining both magnetic core parts 120 and 130, the closed E-shaped magnetic core as illustrated above with respect to Fig. 5(c) is obtained.

[0076] The first T-shaped magnetic core part 120 and a second I-shaped magnetic core part 130 correspond essentially to each other; in particular, the central magnetic core 200 is substantially designed and arranged with the first T-shaped magnetic core part 120.

[0077] One or more of the high-voltage windings 310 and low voltage windings 320 with or without spool bodies (not illustrated) and/or layers (not illustrated) may be pre-manufactured and then arranged onto the central magnetic core 200 such that the high-voltage winding 310 and/or low-voltage winding 320 conforms essentially coaxially with the rectilinear axis of the central magnetic core 200. The arrangement and purpose of intermediately arranged and additionally arranged spool bodies and layers have been discussed in detail with reference to Fig. 1(d). It shall be noted that the discussed principles apply likewise to the embodiment described with reference to Fig. 5(c).

[0078] With reference to Fig. 5(a) to 5(c), the central magnetic core 200 of the embodiment illustrated in the aforementioned figures has a rectilinear axis, which is depicted likewise as axis B'. The high-voltage winding 310, which is arranged coaxially relative to the central magnetic core 200 and its rectilinear axis B' is further provided with the low-voltage winding 320, which is arranged coaxially and outside relative to the high-voltage winding 310 (and central magnetic core 200 and its rectilinear axis B'). The high-voltage winding 310 and the low-voltage winding 320 are preferably made of insulated wires such as enameled copper wires.

[0079] With reference to Fig. 5(d), the ignition coil presented therein is constituted on the basis of an alternative two-part design of an O-shaped magnetic core according to an embodiment of the present invention is shown, which alternative two-part design differs from the aforementioned designs according to embodiments of the present invention. The two-part design of the O-shaped magnetic core comprises a first C-shaped magnetic core part 120 and a second C-shaped magnetic core part 130 (or first U-shaped magnetic core part 120 and a second U-shaped magnetic core part 130, respectively). In general, the both C-shaped magnetic core parts 120 and 130 correspond in such a way with each other that, when combining both C-shaped magnetic core parts 120 and 130, the (closed) O-shaped magnetic core as illustrated above with respect to Fig. 5(d) is obtained.

[0080] The first C-shaped magnetic core part 120 and the second C-shaped magnetic core part 130 correspond essentially to each other to from the O-shaped magnetic core, which corresponds essentially solely to the magnetic core frame 210 without central magnetic core 200.

[0081] One or more of the high-voltage windings 310 and low voltage windings 320 with or without spool bodies (not illustrated) and/or layers (not illustrated) may be pre-manufactured and then arranged onto the magnetic core frame 210 such that the high-voltage winding 310 and low-voltage winding 320 conform essentially coaxially with rectilinear axes of the magnetic core frame 210. The high-voltage winding 310 and low-voltage winding 320 are in particular arranged at different positions on the magnetic core frame 210. With reference to Fig. 5(d) two axes D' and D", which are substantially parallel to each other and which spaced at a predefined distance from each other, are illustrated. The arrangement and purpose of intermediately arranged and additionally arranged spool bodies and layers have been discussed in detail with reference to Fig. 1(d). It shall be noted that the discussed principles apply likewise to the embodiment described with reference to Fig. 5(d).

[0082] With reference to Fig. 5(a) to Fig. 5(d), at least one of the side surfaces, the button surfaces and the top surfaces, respectively, facing outside, are at least partly applied with a coating 220, in partciular the the electrically conductive, resilient coating 220, having a thickness of about 1 mm and less. In more detail, at least part of the surfaces of the magnetic core frame 210, which surfaces facing outside and which surfaces are perpendicular to the cross-sectional view of the ignition coil as shown illustratively with reference to Fig. 5(a) to Fig. 5(d), are covered with the electrically conductive, resilient coating 220.

[0083] It is to be understood that the above description is merely exemplary rather than limiting in nature, the invention being limited only by the appended claims. Various modifications and changes may be made thereto by one of ordinary skill in the art, which embody the principles of the invention and fall within the spirit and scope thereof.

Claims

1. Ignition coil (100) including a magnetic core of a magnetically permeable material, a high-voltage winding (310) and a low-voltage winding (320), wherein said magnetic core has at least one axis (B', C', D', D"), coaxially to which said high-voltage winding (310) and said low-voltage winding (320) are arranged, wherein said ignition coil is provided with a coating (220),
characterized in that
said coating (220) is electrically conductive and resilient

2. Ignition coil according to claim 1, characterized in that said magnetic core comprises a magnetic core frame (210), which serves to short-circuit magnetic flux induced by one of said high-voltage winding (310) and low-voltage winding (320), wherein said electrical conductive, resilient coating (220) covers at least partially outwardly facing surfaces of said magnetic core frame (210).

3. Ignition coil according to claim 1 or claim 2, characterized in that said magnetic core comprises a central magnetic core (200) with said axis (B', C') coaxially to which said high-voltage winding (310) and said low-voltage winding (320) are arranged, wherein said low-voltage winding (320) is arranged outwardly of said high-voltage winding (310).

4. Ignition coil according to claim 1 or claim 2, characterized in that said magnetic core frame (210), comprises at least one said axis (D', D") coaxially to which said high-voltage winding (310) and said low-voltage winding (320) are arranged, which are space at a distance from each other.

5. Ignition oil according to anyone of the claims 1 to 3, characterized in that said magnetic core is composed of two magnetic core parts, which when combined form substantially a closed E-shaped magnetic core.

6. Ignition oil according to claim 4, characterized in that said magnetic core parts correspond essentially to E-shaped magnetic core parts with three legs having different and/or equal lengths or a C-shaped magnetic core and a T-shaped magnetic core part.

7. Ignition oil according to anyone of the claims 1 to 3, characterized in that said magnetic core is composed of two magnetic core parts, which when combined form substantially an O-shaped magnetic core.

8. Ignition oil according to claim 6, characterized in that said magnetic core parts correspond essentially to C-shaped magnetic core parts.

9. Ignition coil according to anyone of the preceding claims, characterized in that said electrical conductive, resilient coating (220) is composed of a resilient material including electrically conductive particles, wherein said resilient material comprises a resilient polymer material.

10. Ignition coil according to anyone of the preceding claims, characterized in that said electrical conductive, resilient coating (220) is applied to the ignition coil by injection molding, dipping or as overmolded foam.

11. Ignition coil apparatus comprising several ignition coil (100),
wherein each ignition coil includes a magnetic core of a magnetically permeable material, a high-voltage winding (310) and a low-voltage winding (320), wherein said magnetic core has at least one axis (B', C', D', D"), coaxially to which said high-voltage winding (310) and said low-voltage winding (320) are arranged, wherein said ignition coil is provided with a coating (220),
wherein said several ignition coils of said ignition coil apparatus are arranged in a rail and housed in a common enclosure (400),
characterized in that
said coating (220) is an electrical conductive, resilient coating (220),
wherein said electrical conductive, resilient coatings (220) of adjacent ignition coils are in physical contact with each other.

12. Apparatus according to claim 11, characterized in that said magnetic core comprises a magnetic core frame (210), which serves to short-circuit magnetic flux induced by one of said high-voltage winding (310) and low voltage winding (320), wherein said electrical conductive, resilient coating (220) covers at least partially outwardly facing surfaces of said magnetic core frame (210).

13. Apparatus according to claim 11 or claim 12, characterized in that said magnetic core comprises a central magnetic core (200) with said axis (B', C') coaxially to which said high-voltage winding (310) and said low-voltage winding (320) are arranged, wherein said low-voltage winding (320) is arranged outwardly of said high-voltage winding (310).

14. Apparatus according to claim 11 or claim 12, characterized in that said magnetic core frame (210), comprises at least one said axis (D', D") coaxially to which said high-voltage winding (310) and said low-voltage winding (320) are arranged, which are space at a distance from each other.

15. Apparatus according to anyone of the claims 11 to 13, characterized in that said magnetic core is composed of two magnetic core parts, which when combined form substantially a closed E-shaped magnetic core.

16. Apparatus according to claim 15, characterized in that said magnetic core parts correspond essentially to E-shaped magnetic core parts with three legs having different and/or equal lengths or a C-shaped magnetic core and a T-shaped magnetic core part.

17. Apparatus according to anyone of the claims 11 to 13, characterized in that said magnetic core is composed of two magnetic core parts, which when combined form substantially an O-shaped magnetic core.

18. Apparatus according to claim 17, characterized in that said magnetic core parts correspond essentially to C-shaped magnetic core parts.

19. Apparatus according to anyone of the claims 11 to 18, characterized in that said electrical conductive, resilient coating (220) is composed of a resilient material including electrically conductive particles, wherein said resilient material comprises a resilient polymer material.

20. Apparatus according to anyone of the claims 11 to 19, characterized in that said electrical conductive, resilient coating (220) is applied to the ignition coil by injection molding, dipping or as an overmolded foam.

Drawing