PURPOSE: To prevent any trouble such as an accidental fire, etc., from being produced by stropping feedback control when detecting an idling state in the captioned method where ignition timing is periodically changed to a minimum lead angle value for obtaining the maximum torque.
CONSTITUTION: When operating an engine, a base lead angle value is estimated in an ignition setting circuit 21 from inlet pipe negative pressure PB and the number N of engine revolutions obtained from an intake air pressure sensor 14 and a turning angle sensor 7, and optimum ignition timing control is performed for leading and delaying the ignition timing at every four-ignition, etc., at every two revolution of the engine. Then, it is judged whether it is idling time where an idle switch 100 contained in a carburetor 2 is ON (throttle valve fully closed) or deceleration time where said inlet pipe negative pressure is over a prescribed value, and if NO, usual MBT (minimum lead angle yielding maximum torque) control is executed. On the contrary, if YES, MBT control is stopped taking an executed ignition timing value as the aforementioned baes lead angle value.
KOHAMA TOKIO
OOHAYASHI HIDEKI
IWATA TOSHIHARU
NIPPON DENSO CO