Electronic ignition control apparatus

An electronic ignition control apparatus for an internal combustion engine having an output shaft rotated by a piston, an ignition coil adapted to generate a spark voltage upon deenergization thereof and a spark plug activated by the spark voltage to ignite the air-fuel mixture metered into a combustion chamber of said engine so as to operate said piston, the ignition control apparatus comprising:

• first detecting means for producing a reference signal indicative of a reference angular position of said output shaft;
• second detecting means for producing a series of electric angular signals respectively at a predetermined angular interval related to the reference signal;
• third detecting means for producing a first binary signal indicative of the operating condition of said engine;
• a pulse signal generator for producing a series of pulse signals at a predetermined frequency;
• first memory means for previously memorizing second and third binary signals respectively indicative of the starting and terminating points for calculation of a time necessary for rotation of a predetermined angle defined by integer times as large as said predetermined angular interval, said first memory means further memorizing a program for calculating an optimum spark advance angle of said engine based on a function describing a desired relationship among the operating condition of said engine, a rotational time of said output shaft and the spark advance angle, for determining a fourth binary signal indicative of an angular position defined by integer times as large as said predetermined angular interval at the advance angle side of the calculated advance angle, and for calculating a time defined by the difference between the calculated advance angle and the angular position defined by said fourth binary signal;
• second memory means for temporarily storing the second and third binary signals from said first memory means and storing the fourth binary signal and a fifth binary signal indicative of the time defined by the difference between the calculated advance angle and the angular position defined by the fourth binary signal;
• control means responsive to the pulse signals from said pulse signal generator and the electric angular signals from said second detecting means for producing a first control signal based on a first logic equation describing a relationship between the second binary signal and the first predetermined number of the pulse signals, for producing a second control signal based on a second logic equation describing a relationship between the third binary signal and the second predetermined number of the pulse signals and for producing a third control signal based on a third logic equation describing a relationship between the fourth binary signal and the third predetermined number of the pulse signals;
• calculation means responsive to the first control signal to start calculation of the number of the pulse signals and responsive to the second control signal to cease the calculation of the number of the pulse signals, said calculation means producing a sixth binary signal indicative of the calculated number of the pulse signals defining the actual rotation time of said output shaft;
• processing means for calculating the optimum spark advance angle from the function in dependence upon the first and sixth binary signals such that the fourth binary signal is determined in relation to the calculated spark advance angle to be stored in said second memory means, said processing means further determining an energization timing of said ignition coil in relation to the calculated advance angle and calculating the difference between the calculated spark advance angle and the angular position defined by the fourth binary signal such that the fifth binary signal is determined in relation to the calculated difference to be stored in said second memory means;
• and
• drive means responsive to the determined energization timing from said processing means to energize said ignition coil and responsive to the third control signal from said control means to start calculation of the value of the fifth binary signal from said second memory means to conduct deenergization of said ignition coil upon completing the calculation.