Spark ignition timing control system for internal combustion engines

Abstract

An ignition timing control system for retarding the spark of a spark plug wherein the ignition timing is regulated to be practically constant while the engine speed is within a low range, but wherein the ignition timing is retarded in proportion to an increase in engine speed as the engine speed increases over a given speed. The system is applicable to capacitive discharge ignition systems and includes a control circuit for triggering the capacitive discharge system as a function of engine speed. The control circuit includes a pick-up coil for generating a voltage having an amplitude proportional to engine speed, and for providing a trigger signal at the peak of the voltage waveform when the voltage waveform is below a preset value. When the voltage waveform exceeds this value, as determined by a limit circuit, the trigger signal is generated as the voltage waveform falls from its peak and reaches the preset value. A zener diode may be used to set the limit or preset value, and several embodiments of suitable control circuits are illustrated.