Ignition timing control apparatus

An electronic ignition control apparatus for a spark-ignition internal combustion engine having a crankshaft, a plurality of cylinders, and an equal plurality of pistons slidably mounted in respective cylinders and operatively connected to the crankshaft, said apparatus comprising:

• means for generating at least one condition signal which indicates the operating condition of the engine when the engine is running;
• means for generating a starting signal when the engine is in the starting condition;
• a crankshaft position sensor having a single pickup for detecting a plurality of angularly spaced predetermined crankshaft positions including at least a fixed firing position for each cylinder;
• means responsive to said single pickup for generating a crankshaft position signal when the crankshaft passes each predetermined position;
• means responsive to said at least one condition signal for calculating an optimum ignition timing value for said operating condition of the engine;
• means for selecting one of said crankshaft position signals from said single pickup occurring prior to the fixed firing position signal for each cylinder;
• means responsive to said calculated optimum ignition timing value and to the selected one of said crankshaft position signals occurring prior to the fixed firing position signal for each cylinder for producing a calculated ignition timing signal for each cylinder when the crankshaft passes through a position corresponding to the calculated optimum ignition value for the respective cylinder;
• means for selecting said calculated ignition timing signals for timing the sparks applied to the cylinders when the starting signal is absent and for selecting said fixed firing signals for timing the sparks applied to the cylinders when said starting signal is present.