Electronic ignition timing control system for internal combustion engine

Abstract

An electronic ignition timing control system comprises a plurality of double ignition coils each being connected to the spark plugs of each set of two cylinders in a multi-cylinder engine. In addition to a large number of teeth on the periphery of the engine ring gear, there is provided a reference tooth at a predetermined angular crankshaft position for a selected set of the cylinders. The reference angular positions for the other sets of the cylinders are calculated arithmetically. A circuit including read-only-memories determines a desired ignition angle in accordance with engine operating parameters to produce a binary code signal consisting of higher order bits and lower order bits. A first comparator starts to count the number of teeth on the ring gear at the time of the detection of a reference angular position to roughly determine the ignition timing, the first comparator producing an output signal when the count value thereof reaches that of the higher bits. A second comparator starts to count the number of clock pulses of fixed frequency in response to the output signal of the first comparator to finely determine the ignition timing, the second comparator producing an ignition signal when the count value thereof reaches a value corresponding to a fractional ignition angle represented by the lower order bits.