Engine timing control circuit having a single pick-up for both starting

Abstract

A single pick-up coupled to sense engine crankshaft position can be utilized for both starting and running of the engine in an electronic spark timing advance control system. During starting, pulses from the pick-up are coupled via a zero crossing detector to the output ignition stage to cause spark plug firing at an essentially constant firing angle at or just slightly in advance of piston top dead center position. During running, the pulses from the pick-up reset, via a reset circuit, an integrator circuit so that a sawtooth waveform representative of engine crankshaft rotational position is developed. A desired timing signal derived from one or more parameters useful in controlling the time of ignition firing is compared against the sawtooth reference waveform and when a predetermined relationship between the two is attained, the ignition is fired. Should this predetermined relationship not be attained during a cycle of the sawtooth, the reset signal from the reset circuit forces ignition firing. A frequency sensitive switch circuit senses approximate engine speed to selectively control ignition firing via the zero crossing detector during starting and via the desired timing signal during running. A safety feature permits the ignition to continue to fire from the zero crossing detector in the event that firing by the desired timing signal is impaired.