A spark ignition system for an internal combustion engine comprising:
- (A) a free running source of equally time-spaced pulses which periodically switch between logic "high" and logic "low" levels;
- (B) engine angular position sensing means for generating an engine timing signal characterized by the presence of a first logic level when the engine angular position is within a first angular range and by the presence of a second logic level when the engine angular position is within a second angular range which does not include said first angular range, said first engine angular position corresponding to at least a portion of an engine cylinder power stroke;
- (C) a triggerable source of intermittent high voltage pulses, said triggerable source having an output delivering a single high voltage single-polarity pulse each time it is triggered, said triggerable source comprising an ignition coil including a single-ended low voltage primary winding and a high voltage secondary winding;
- (D) trigger signal developing means having an input and an output, said trigger signal developing means output being connected to said triggerable source and adapted to trigger said triggerable source in response to the transition of a signal between logic "low" and logic "high" appearing at said input to said trigger signal developing means, said trigger signal developing means including an electronic switch disposed in series with said ignition coil primary winding and a d-c electrical power source such that, when said electronic switch is closed, current from said power source passes through said primary winding to generate a magnetic field and when said electronic switch is opened, the magnetic field collapses to induce a high voltage pulse in said secondary winding;
- (E) gating means responsive to the presence of said first logic level in said timing signal to pass said equally time-spaced pulses to said input of said trigger signal developing means and to the presence of said second logic level in said engine timing signal to prevent said equally time-spaced pulses from being applied to said input of said trigger signal developing means;
- (F) frequency determining means included in said free running source, said frequency determining means being set to establish the frequency of said equally time-spaced pulses to a frequency at which said ignition coil fully saturates during each period in which said electronic switch is closed such that said triggerable source delivers successive equal and full amplitude equally time-spaced high voltage pulses in response to successive equally time-spaced pulses applied to said gating means, all said pulses being of single and like polarity;
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- (G) high voltage distribution means for transferring a continuous train of equally time-spaced, full amplitude high voltage pulses generated by said triggerable source to a spark plug in the cylinder to be fired during the entire period when said engine angular position sensing means senses that the instantaneous engine angular position falls within said first angular range.