Spark ignition transformer with a non-linear secondary current characteristic
View Patent ↗An ignition transformer for use with a spark ignition system for an internal combustion engine includes a central core, a primary coil, a secondary coil, and a magnetic return. The central core defines a first end and a second end. The primary coil is used to vary magnetic energy into the central core in response to a primary current applied to the primary coil. The secondary coil is used to generate a secondary voltage in response to changes in the magnetic energy in the central core. The magnetic return defines a return-path to couple magnetic energy from the first end to the second end. A permeability value of the return-path is selected so the transformer has a secondary-current versus time-response characteristic that decays to fifty-percent (50%) of an initial secondary current when ten percent (10%) to twenty-five percent (25%) of a burn-time interval has passed.
1. An ignition transformer for use with a spark ignition system for an internal combustion engine, said transformer comprising:
a central core that defines a first end and a second end;
a primary coil wound about the central core, wherein the primary coil is used to vary magnetic energy into the central core in response to a primary current applied to the primary coil;
a secondary coil wound about the central core, wherein the secondary coil is used to generate a secondary voltage in response to changes in the magnetic energy in the central core; and
a magnetic return that defines a return-path to couple magnetic energy from the first end to the second end, wherein a permeability value of the return-path is selected so the transformer has a secondary-current versus time-response characteristic that decays to fifty-percent (50%) of an initial secondary current when ten percent (10%) to twenty-five percent (25%) of a burn-time interval has passed.
2. The transformer in accordance with claim 1 , wherein the burn-time time interval occurs while the secondary voltage is 1000 volts.
3. The transformer in accordance with claim 1 , wherein the magnetic return is formed of a material characterized by a relative-permeability value between 10 and 1500.
4. The transformer in accordance with claim 3 , wherein the material comprises iron.
5. The transformer in accordance with claim 1 , wherein the return-path includes an air-gap.
6. The transformer in accordance with claim 5 , wherein a core area to air-gap size ratio is between 250 and 1500 mm.