Digital-electronic engine ignition system

Abstract

The engine for which the system provides ignition control produces a basic signal giving the time lapse of a predetermined angle of crankshaft rotation. Leading and trailing edges of this basic signal produce control signals. During the interval between these two a first counter stepped by clock pulses produces a count proportional to engine speed down to a certain relatively low engine speed beyond which overflow of the counter holds the counter at its maximum value. The count so determined is utilized in an ROM as the engine speed parameter which together with other engine operation parameters produce the address that selects the appropriate number to control computed ignition timing. According to the engine speed range, a second counter is loaded either with the number provided by the ROM, or with a count number based on engine speed only and the second counter then counts down past thresholds provided by a second ROM to determine both the moment of closure of the electronic switch and the moment of opening. The closure interval is generally maintained constant, consistently so at low speeds, but at high speeds a minimum open interval of the electronic switch in the primary circuit of the ignition transformer overrides this requirement. In certain embodiments ignition timing is provided by the reaching of a threshold value of current in the primary winding, under certain limited conditions.