GB2328324A

GB2328324A - Ignition coil assembly with means for suppressing high frequency signals

Info

Publication number: GB2328324A
Application number: GB9812302A
Authority: GB
Inventors: Richard William Kautz; Mark Joseph Bartasius; Tamra Kim Green; Carl Rudolph Morganti; James Donald Mccoy
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 1997-06-09
Filing date: 1998-06-09
Publication date: 1999-02-17
Anticipated expiration: 2018-06-09
Also published as: GB9812302D0; GB2328324B

Abstract

An ignition coil assembly comprises an electrically conductive coil spring 26 with a ferromagnetic member 30 disposed within it. The spring 26 connects at one end to an ignition coil whilst the other end may be connected to a spark plug terminal. The spring 26 may be arranged to transmit electrical energy delivered by the ignition coil to a spark plug. The ferromagnetic member 30 may be a moulded cylindrical ferrite bead. The ferrite member may include an enlarged portion or spring clip arrangement to secure the member within the spring 26 in a spaced manner from either end of the said spring. The said spring 26 may be disposed within an elastomeric boot 24. The above ignition coil assembly may be used to provide a low impedance to low frequency signals and a high impedance for high frequency signals, thereby suppressing high frequency signals.

Description

IGNITION COIL ASSEMBLY The present invention relates generally to ignition systems for internal combustion engines and more specifically to ignition coil assemblies used in such ignition systems.

In ignition systems for internal combustion engines, one or more ignition coil assemblies are typically provided.

Each assembly typically has a "primary" coil and a "secondary" coil, these coils being magnetically coupled.

Relatively low-voltage electrical energy is switched through the primary coil, inducing higher voltage electrical energy in the secondary coil. This higher voltage is provided to an ignition device such as a spark plug. The higher-voltage energy breaks down an air gap in the spark plug, causing a spark which causes ignition in the engine.

The transient nature of the higher-voltage energy in the secondary circuit of an ignition coil tends to create electromagnetic fields which can be disruptive to electronic devices nearby. These fields are of considerably higher frequency than the frequency at which the spark energy is delivered to the engine.

In one known method of trying to reduce the electromagnetic fields, a resistor is placed in the spark plug boot, in contact with the top of the spark plug (that is, in series in the secondary circuit of the ignition coil). Such a resistor co-operates with the inductance already in the secondary circuit (or, in the case of a wirewound resistor, the resistor adds additional inductance) to filter the frequencies where electromagnetic fields are a concern. Although such a design may be generally effective in reducing electromagnetic fields, the design might not provide sufficient impedance at all frequencies where suppression is desired. Also, a resistor adds impedance not only in frequencies where suppression is desired, but also at lower frequencies, where spark energy is delivered. This reduces the amount of spark energy which is delivered.

Further, the resistor suppression design adds additional electrical connections between the spark plug and the secondary ignition coil, adding potential unreliability to the system.

Thus, a design which reduces the potential unreliability of a resistor while effectively reducing electromagnetic fields and not reducing delivered spark energy will provide advantages over the prior art.

The present invention provides an ignition coil assembly. The ignition coil assembly comprises a coil spring made of electrically conductive material, an electrical coil connected to deliver electrical energy from the ignition coil assembly via the coil spring and a ferromagnetic member disposed within the coil spring.

Devices according to the present invention effectively suppress emitted electromagnetic fields and reduce the unreliability of an added resistor. Further, devices according to the present invention can be less expensive than an added resistor. The present invention thus provides considerable advantages over alternative designs.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded view of an ignition coil assembly 10 according to one embodiment of the present invention; Figure 2 is a partial cross-sectional side view of the ignition coil assembly 10 of Figure 1; and Figures 3A and 3B are side and end views, respectively, of ferrite bead 30 of Figure 2 and a clip 32 designed to retain bead 30 within coil spring 26 of Figure 2.

Refer first to Figure 1, where one embodiment of the present invention is illustrated. Figure 1 illustrates an ignition coil assembly 10 for an internal combustion engine.

Ignition coil assembly 10 includes a moulded plastic housing 11. Disposed within housing 10 is a primary coil assembly 12, which is disposed within a secondary coil assembly 14.

Ignition coil assembly 10 further includes clip 16 and laminated ferromagnetic core sections 18 and 20. An electrical connector assembly 22 is also provided to enable connection of primary coil assembly 12 to appropriate vehicle wiring. Through appropriate switching of electrical power provided to primary coil assembly 12, higher voltage spark energy is induced in secondary coil assembly 14.

Ignition coil assembly 10 also includes an elastomeric boot 24, within which is disposed a metallic coil spring 26.

Boot 24 is designed to be pressed onto the body of a spark plug (not shown), with coil spring 26 then making the electrical connection between the conductive spark plug tip and secondary coil assembly 14. Coil spring 26 is compressed by the tip of the spark plug when boot 24 is pressed onto the body of the spark plug.

Ignition coil assembly 10 of Figure 1 is according to a "coil-per-plug" design, where one ignition coil assembly 10 is provided for each spark plug in the engine. If the reader requires more detail about the construction or use of such a "coil-per-plug" design, he is referred to U.S. Patent 5,333,593, the complete disclosure of which is hereby incorporated by reference.

Refer now additionally to Figure 2. Figure 2 is a partial cross-sectional side view of ignition coil 10 of Figure 1. Located within spring 26 is a moulded bead 30 of ferrite material (or other appropriate ferromagnetic material). Bead 30 increases the tendency of spring 26 to act as an inductor to the electrical energy delivered through secondary coil assembly 14 and spring 26 to the spark plug. The precise material and geometry of bead 30 can be selected such that the combination of spring 26 and bead 30 has the appropriate impedance versus frequency characteristic across frequencies of interest. In particular, it is desirable to have low impedance at the relatively lower frequencies (e.g., below 10kHz) where electrical spark energy is delivered to the spark plug, and higher impedance at the higher frequencies where electromagnetic fields of concern are generated.

Because bead 30 is not required to be in physical contact with either secondary coil assembly 14 or the spark plug to have the beneficial effect described here, bead 30 can be located away from the ends of spring 26.

Refer now additionally to Figure 3. If added retention for bead 30 is required in addition to retention provided by any contact of bead 30 with spring 26, a clip 32 can be provided. Clip 32 is preferably made of plastic and can be inserted in a groove in bead 30 after bead 30 is inserted into spring 26. Clip 32 would cooperate with spring 26 to retain bead 30 in place within spring 26. Clip 32 can also be replaced by a moulded-in area of increased radius which would similarly cooperate with spring 26.

Claims

1. An ignition coil assembly comprising: a coil spring (26) made of electrically conductive material; an electrical coil (14) connected to deliver electrical energy from said ignition coil assembly (10) via said coil spring (26); and a ferromagnetic member (30) disposed within said coil spring.

2. An ignition coil assembly as claimed in Claim 1, wherein said electrical coil is a secondary coil connected to deliver spark energy.

3. An ignition coil assembly as claimed in Claim 1, wherein said ferromagnetic member is substantially made of ferrite material.

4. An ignition coil assembly as claimed in Claim 1, wherein: said ferromagnetic member is generally cylindrical and includes a circumferential groove; and said ferromagnetic member includes a retainer disposed in said groove and retaining said ferromagnetic member within said coil spring.

5. An ignition coil assembly as claimed in Claim 1, wherein said ferromagnetic member is generally cylindrical in shape and has a radially-enlarged portion which cooperates with said coil spring to retain said ferromagnetic member within said coil spring.

6. An ignition coil assembly as claimed in Claim 4, wherein said coil spring has two ends and wherein said ferromagnetic member is spaced from both said ends.

7. An ignition coil assembly as claimed in Claim 5, wherein said coil spring has two ends and wherein said ferromagnetic member is spaced from both said ends.

8. An ignition coil assembly as claimed in Claim 2, further comprising an elastomeric boot in which said coil spring is disposed.

9. An ignition coil assembly as claimed in Claim 1, wherein said coil spring has two ends and wherein said ferromagnetic member is spaced from both said ends.

10. An ignition system comprising: an ignition coil assembly as claimed in Claim 1; and a spark plug having an electrically-conductive terminal, said terminal in physical contact with said spring.

11. An ignition system comprising: an ignition coil assembly as claimed in Claim 3; and a spark plug having an electrically-conductive terminal, said terminal in physical contact with said spring.

12. An ignition system comprising: an ignition coil assembly as claimed in Claim 9; and a spark plug having an electrically-conductive terminal, said terminal in physical contact with a said end of said spring.

13. An ignition coil assembly substantially as hereinbefore described with reference to the accompanying drawings.