Ignition coil core isolation

Details Ignition coil core isolation Ignition coil core isolation

2003-09-18

2004-09-21

Nguyen, Tuyen T. (Department: 2832)

Inductor devices

With outer casing or housing

C336S096000, C123S634000

Reexamination Certificate

active

06794974

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to internal combustion engine spark ignition systems, and in particular to an ignition coil module that contains a ferromagnetic core about which primary and secondary coils are coaxially disposed. The ignition coil module may be a type that mounts on an engine over, and in direct electric connection with, an engine-mounted spark plug, in the manner of modules referred to by various names such as pencil-coil modules or coil-on-plug modules.
2. Background Information
Known internal combustion engines comprise cylinder blocks containing individual cylinders that are closed at one end by an engine cylinder head that is attached to the engine block. In a spark-ignition engine, the cylinder head contains threaded spark plugs holes, each of which is open to a respective cylinder. A respective spark plug is threaded into the respective hole to close the respective hole. External to the respective cylinder, each spark plug comprises a central electric terminal that is available for electric connection with a mating terminal of a secondary of the spark-ignition system.
Known spark ignition systems comprise what are sometimes called coil-on-plug type ignition coil modules or pencil-coil modules. Any such module comprises both a wound primary coil and a wound secondary coil. At the proper time in the engine operating cycle for firing a particular spark plug, electric current flowing through the primary of the respective module is abruptly interrupted to induce a voltage in the secondary coil sufficiently high to create a spark across gapped electrodes of the spark plug that are disposed within combustion chamber space of the respective engine cylinder, igniting a combustible fuel-air mixture to power the engine.
Examples of coil-on-plug modules are found in various patents including U.S. Pat. Nos. 4,514,712; 5,128,646; 5,590,637; and 5,870,012; as well as in U.K. Patent Application GB 2,199,193A. A common characteristic of such modules is that the primary and secondary coils are disposed one within the other, concentric with a common axis that is coincident with the spark plug central terminal. The coils may be bobbin-mounted and encapsulated. Various arrangements for providing electric circuit continuity of the secondary coil to the spark plug terminal are shown.
In certain engines, the threaded spark plug mounting hole may be at the bottom of a bore, or well, that extends inward from an outer surface of a cylinder head. For any of various reasons, such bores may be relatively long and narrow, and it is for such bores that pencil-coil ignition modules are especially suited. U.S. Pat. No. 6,094,122 “MECHANICAL LOCKING CONNECTION FOR ELECTRIC TERMINALS”, pending U.S. patent application Ser. No. 09/391,571 “PENCIL IGNITION COIL ASSEMBLY MODULE ENVIRONMENTAL SHIELD”, and pending U.S. patent application Ser. No. 09/392,047 “PENCIL IGNITION COIL ASSEMBLY MODULE” disclose an example of such a module.
An advantage of a pencil-coil module is that when it is installed on an engine, the wiring that runs to it from a signal source need carry only primary coil current, because the entire secondary coil is contained within the module and is for the most part sheltered within the bore. However, for proper ignition system performance, primary and secondary coils must be sized to reliably deliver a secondary voltage sufficiently large to spark the plug. The primary and secondary coils are typically encased in respective encapsulations which must possess physical characteristics suitable for providing protection both for the harsh underhood environment where an ignition coil module is located and for the voltages that must necessarily be generated. Because of dimensional constraints imposed by the design of an engine on a pencil-coil module, it is believed that a module possessing an ability to achieve specified performance criteria within confined space would be valuable to an engine manufacturer. It is further believed that the pencil-coil module shown in U.S. Pat. No. 6,094,122 and the two referenced pending patent applications possesses such value, and that further improvements can increase the value of such a product.
SUMMARY OF THE INVENTION
The present invention relates to improvements in an ignition coil module, especially improvements in the ferromagnetic core of the module and the manner in which the core is associated with a bobbin within which the core is coaxially disposed. It is believed that improved efficiencies in the fabrication and performance of ignition coil modules will result from use of the inventive principles disclosed hereinafter. While the inventive improvements can provide particular benefit in a module like the pencil-coil module of U.S. Pat. No. 6,094,122, they may also enjoy application to other ignition coil modules.
The improvements can enable a core to be efficiently assembled into a bobbin and to attain precise coincidence of the core centerline to the bobbin centerline. Effectively encapsulating the core within the bobbin is also an aspect of the invention. The core and bobbin employ features relating one to the other in an assured dimensional relationship that allows encapsulant that is introduced into the open upper end of the bobbin to flow efficiently into the bobbin interior and fill clearance space that is intentionally provided between the outer surface of the core and the inner surface of the bobbin. This results in a construction that is believed more robust because of the improved thermal/mechanical isolation provided between dissimilar materials in the bobbin and the core. A substantial surface area of the core is spaced from the wall of the bobbin, and the intervening space filled by encapsulant. Because of that construction, it is believed that thermal and mechanical factors acting on the module while in use may have less of an effect on design intent than they would absent the present invention.
The construction also allows additional magnetic circuit elements, such as magnetic cylinders, to be associated with the core within the bobbin interior. A retainer associates with the open upper end of the bobbin to keep the core, including any additional magnetic circuit elements associated with the core within the bobbin, in place before encapsulant is introduced, yet the retainer possesses features that allow encapsulant to flow efficiently past it as the encapsulant is introduced into the bobbin. When an additional magnetic circuit element is placed over a core that has been inserted into the interior of a bobbin, the retainer may also serve to dimensionally center that additional magnetic circuit element to the centerline of the core.
The present invention relates to a pencil ignition coil assembly module that possesses an organization and arrangement of elements believed to render it well suited for meeting specified performance criteria within the confines of limited space. Moreover, it is believed that the inventive module is well suited for reliable and cost-effective mass production, thereby making it especially attractive for use in automotive vehicle internal combustion engines.
One general aspect of the invention relates to an ignition coil module having an imaginary longitudinal centerline and comprising a primary coil for conducting primary electric current, and a secondary coil that is electromagnetically coupled with the primary coil for delivering a spark plug firing voltage when primary current conducted by the primary coil abruptly changes. A bobbin comprising an imaginary centerline is disposed coincident with the module centerline and comprises a sidewall having an inner surface that laterally bounds a hollow interior space and an outer surface on which one of the coils is disposed. A ferromagnetic core is disposed within the interior space of the bobbin and has a longitudinal centerline coincident with the centerlines of both the module and the bobbin. The core comprises an outer surface having a confronting area which confronts and is spaced from a con

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