Ignition timing control system for internal combustion engines

Claim 1

An ignition timing control system for an internal combustion engine comprising: a knock detector for sensing vibrations of said engine; a knock detecting circuit for comparing an output signal of said knock detector with a predetermined threshold level and for generating a knock detection signal indicating when said output signal is above said predetermined threshold level; correction advance computing means, responsive to said knock detection signal, for computing an advance correction angle and generating an ignition advance correcting signal related thereto, said advance computing means comprising: counter means for counting said knock detection signal to determine the number n of knocks occurring within a predetermined number of engine ignitions; and comparator and computing means for (i) comparing the counted number n with upper and lower limits (a) and (b), respectively; (ii) producing said ignition advance correcting signal effective to retard ignition timing when n≧a; (iii) producing said ignition advance correcting signal effective to not alter ignition timing when b<n<a; and (iv) producing said ignition advance correcting signal effective to advance ignition timing when n≦b; ignition timing signal generating means for generating an ignition timing signal as corrected with said advance correction angle thereby to retard or advance the timing of ignition of said engine depending on the amount of knock; and means for supplying electric power to said correction advance computing means even after a key switch associated with said engine is turned off, thereby to maintain said correction advance computing means being to maintain said correction advance computing means being energized to memorize said advance correction angle corresponding to a knock condition just before the key switch is turned off.