Patent ID: 6973911

Claim:
A method for controlling, during a low speed, ignition timing of an ignition device for a capacitive discharge internal combustion engine, the ignition device including an ignition coil having an ignition plug connected to a secondary side, a generator coil in a high-voltage magneto generator driven by the internal combustion engine, a rechargeable capacitor provided on a primary side of said ignition coil and recharged by a forward voltage portion of an output voltage from said generator coil, and a dischargeable switching element for discharging electric charges of said rechargeable capacitor to a primary coil of said ignition coil by conduction, said method comprising the steps of: generating a cycle detection signal at an ignition timing calculation start point in time, at which said forward voltage portion has reached a preset cycle detection voltage as a voltage making continual ignition operations available, to calculate an RPM in accordance with the cycle detection signal, generating a peak voltage detection signal at a peak detection point in time at which a delayed reverse voltage portion of said output voltage has reached a peak voltage, and generating a start-up voltage detection signal at a start-up point in time at which said delayed reverse voltage portion has reached a start-up voltage, the start-up voltage being set to a value which allows for staying as close as possible to the top dead center of the internal combustion engine outside a kickback area and for being reliably detected after said peak detection point in time with said cycle detection signal having been output, in a low speed region of a lower limit speed or less or a lower limit of a speed region in which the engine rotates with stability, dividing the delayed reverse voltage portion at a time of the lower limit speed with respect to said start-up voltage at a division ratio determined by a preset advancement angle characteristic line and a tolerance range setting to obtain a constant voltage characteristic line indicative of angle/speed characteristics with each divided value being made constant in order to output an ignition signal to the dischargeable switching element at a point in time at which a value of said delayed reverse voltage portion matches a value on the constant voltage characteristic line within the tolerance range, and outputting the ignition signal to the dischargeable switching element at said start-up point in time at the time of a start-up.