초록 ▼

A twin spark ignition apparatus having two high-voltage (HV) outputs incorporates features for balancing load capacitance on each HV output. The ignition apparatus provides a first high-voltage (HV) connection configured for direct mounting on a first spark plug, and a second HV connection for coup

A twin spark ignition apparatus having two high-voltage (HV) outputs incorporates features for balancing load capacitance on each HV output. The ignition apparatus provides a first high-voltage (HV) connection configured for direct mounting on a first spark plug, and a second HV connection for coupling to a second spark plug by way of an HV cable. The HV cable would adds capacitance at the second HV output, as compared to a direct mount. Various structures are included to offset and balance the additional capacitance attributable to the HV cable so that the capacitance of the first HV connection and the second HV connection are balanced within a range. The voltage variation between the two HV outputs is reduced.

대표청구항 ▼

The invention claimed is: 1. An ignition apparatus comprising: a transformer assembly including a central core, a primary and a secondary winding, and an outer core, said central core being elongated and having a main axis, said primary and secondary windings being radially outwardly of said centra

The invention claimed is: 1. An ignition apparatus comprising: a transformer assembly including a central core, a primary and a secondary winding, and an outer core, said central core being elongated and having a main axis, said primary and secondary windings being radially outwardly of said central core; a case configured to house said transformer assembly, said case including a first high-voltage (HV) connection at a first end thereof configured for direct mounting on a first spark plug, said first HV connection having a first capacitance associated therewith when direct mounted to said first spark plug, said case further including a second HV connection at a second end thereof opposite said first end configured for connection to a second spark plug via a high-voltage distribution mechanism, said second HV connection having a second capacitance associated therewith when coupled to said second spark plug; a capacitance balancing structure disposed in said apparatus and arranged such that said first capacitance and said second capacitance are balanced within a predetermined range. 2. The apparatus of claim 1 further including a secondary spool having a winding surface configured to receive and retain said secondary winding wound in a progressive winding pattern, said capacitance balancing structure comprising said winding surface having a single-layer section at said first end of said case where said secondary winding is disposed in a single layer, said single-layer section of said winding surface having an axial extent selected such that said first and second capacitance are balanced within a predetermined range. 3. The apparatus of claim 2 wherein said secondary spool includes a spool axis substantially coaxial with said main axis of said central core, said primary winding being disposed radially outwardly of said central core, wherein said axial extent of said single-layer section of said secondary winding substantially overlaps said primary winding. 4. The apparatus of claim 1 wherein said predetermined range is +2.2 to-4 pF nominally centered about 48 pF. 5. The apparatus of claim 1 wherein said first HV connection comprises a first high-voltage (HV) tower having a first high-voltage (HV) terminal, a first tower housing, and a first high-voltage (HV) connector assembly, said apparatus further including a spark plug boot surrounding a portion of said tower housing and comprising electrical insulating material, and wherein said capacitance balancing structure comprises a shell of electrically conductive material around said spark plug boot configured to contact a base of said first spark plug, said base being electrically grounded. 6. The apparatus of claim 1 further including a secondary spool having a cylindrical body and extending along a spool axis, said spool further including a winding surface configured to receive and retain said secondary winding wound in a progressive winding pattern, said spool, said central core and said primary winding being coaxially arranged, and wherein said primary winding is disposed radially outwardly of said central core, and said secondary spool is disposed radially outwardly of said primary winding; said capacitance balancing structure comprising an axially-extending taper of said cylindrical body portion of said spool such that a radial secondary-to-primary winding distance decreases as an axial distance from said first end proximate said first HV connection decreases. 7. The apparatus of claim 1 wherein said case comprises electrically insulating material, said case further including a body portion coaxially extending and surrounding said pencil coil transformer assembly, said capacitance balancing structure comprising an electrically conductive coating disposed over a radially outermost surface of said body portion of said case, said electrically conductive coating being substantially continuous over a predetermined axial extent of said outermost surface proximate said first end of said case, said predetermined axial extent selected such that said first and second capacitance are balanced to within a predetermined range. 8. The apparatus of claim 7 wherein said predetermined axial extent comprises approximately the axially lowermost half of said case proximate said first end. 9. The apparatus of claim 8 wherein said outer core comprises a magnetically-permeable shield, said conductive coating being electrically coupled to said shield. 10. The apparatus of claim 8 wherein said electrically conductive coating comprises a base material and an additive material, said additive material being an electrically conductive material. 11. The apparatus of claim 10 wherein said base material is selected from the group of polymeric materials consisting essentially of paint, epoxy, polyester and polyurethane. 12. The apparatus of claim 10 wherein said additive material is selected from the group consisting essentially of carbon black, silver, aluminum and iron. 13. The apparatus of claim 8 wherein said electrically conductive coating is electroplated onto said outermost surface of said case. 14. The apparatus of claim 1 wherein said case comprises electrically insulating material, said case further including a body portion coaxially extending and surrounding said pencil coil transformer assembly, said capacitance balancing structure comprising electrically conductive traces disposed on a radially outermost surface of said body portion of said case, said electrically conductive traces covering an increasing percentage of the radially outermost surface of said case as a function of axial position, said function being defined such that said first capacitance and said second capacitance are balanced within a predetermined range, said coating being electrically grounded. 15. The apparatus of claim 14 further including a grounding connection between said conductive traces and a mounting bushing, said bushing being grounded. 16. The apparatus of claim 1 wherein said case comprises electrically insulating material, said case further including a body portion coaxially extending and surrounding said pencil coil transformer assembly, said case including a mounting bore having an electrically conductive mounting bushing, said bushing being grounded, said capacitance balancing structure comprising an electrically conductive trace in the form of a continuous spiral disposed over a radially outermost surface of said case, said spiral trace extending from said grounded bushing toward said first end of said case, said spiral trace having an increased number of turns per unit axial length as a departure distance from said bushing increases and an entry distance from the first HV end decreases, the rate of increase of the number of turns per unit axial length being selected such that said first capacitance and said second capacitance are balanced within a predetermined range.