Ignition timing control apparatus for internal combustion engine

Claim 1

An ignition timing control apparatus for an internal combustion engine comprising: vibration acceleration sensing means for sensing knock signals of said engine; means responsive to the output of said sensing means for deriving said knock signals including a bandpass filter connected to said sensing means to pass therethrough only a frequency component inherent in the knocks, a noise level detector for converting the output of said bandpass filter into a DC voltage with a predetermined amplification, said DC voltage being higher than the noise component while lower than the knock component of the filtered output, and a comparator for comparing the outputs of said filter and said noise level detector to derive said knock signals; means responsive to the output of said knock signal deriving means for determining whether the current ignition timing characteristic is required to be changed over including a pulse generator connected to said comparator to generate one pulse per the occurrence of knock during one ignition and a counter connected to said pulse generator to count the output pulses of said pulse generator and to provide a logic signal indicating the presence of a predetermined knock occurrence rate per a predetermined time interval defined by a timer; means responsive to the output of said determining means for setting a reference ignition timing characteristic including a flip-flop set by said logic signal from said counter, a reference ignition timing signal generator, the ignition timing characteristic of which is set for a high-octane rating fuel, an ignition timing phase-shifter for shifting the timing of said reference ignition timing signal of said generator by a preset fixed value dependent upon the output of said flip-flop to control the ignition timing of an ignition coil; and means for overriding the output of said determining means when said engine lies in predetermined operating regions to fix the ignition timing corresponding to said predetermined operating regions including operating region sensing means for said engine comprising an engine speed sensor, an intake air pressure sensor and an overriding circuit responsive to said operating region sensing means connected between said flip-flop and said ignition timing phase-shifter, said overriding circuit comprising and AND gate, one input of which is connected to said flip-flop, a first OR gate, one input of which is connected to said engine speed sensor and the other input of which is connected to said pressure sensor, and a second OR gate, one input of which is connected to the output of said AND gate and the other of which is connected to said pressure sensor, the output of said first OR gate being connected to the other input of said AND gate, and the output of said second OR gate being connected to said phase-shifter.