Ignition timing control method

Claim 1

An ignition timing control method for an internal combustion engine having at least one cylinder and a crankshaft, comprising the steps of: detecting a parameter which affects the ignition timing of the operating engine; generating at least one electrical signal which indicates the value of the detected parameter; and calculating, in response to said generated electrical signal, a spark advance angle which represents an optimum ignition timing at the value of said detected parameter, wherein the improvement comprises: selecting one reference crank angle position from a plurality of different reference crank angle positions for each cylinder, said selected reference crank angle position depending on the value of said calculated spark advance angle; calculating the difference angle between said selected reference crank angle position and the crank angle position corresponding to the calculated spark advance angle; sensing when the crankshaft rotates through the selected reference crank angle position; calculating an ignition control value which represents a period of time required by the crankshaft to rotate through said calculated difference angle; and producing an ignition spark in response to said ignition control value when said period of time has elapsed after the crankshaft rotates past said sensed selected reference crank angle position.