Overrun prevention ignition system with ignition angle retardation

Abstract

Our overrun prevention ignition system of the capacitor discharge type includes an ignition angle retarding circuit for retarding the ignition angle by an overlapping period between an ignition signal and a predetermined conduction period of a switching transistor associated with an ignition controlling thyristor. The ignition angle retarding circuit includes an ignition signal generating coil sharing a common core with a magneto and includes a capacitor which is charged by a portion of an ignition signal from the ignition signal generating coil. The capacitor discharges for a certain period upon commencement of the decay of the ignition signal to produce a supplemental ignition signal thereby to effectively lengthen the width of the ignition signal. A switching transistor connected to the gate of the ignition controlling thyristor is maintained conductive for a predetermined period of time irrespective of the engine speed to bypass the ignition signal during this period. When the engine rotational speed exceeds a normal speed region and the interval between successive ignition signals is shortened, the ignition signal overlaps with the predetermined conduction period of the switching transistor and the ignition angle is retarded by the overlapping period. Since the width of the ignition signal is effectively lengthened by the supplemental ignition signal, a large retardation angle can be obtained to ensure prevention of the overrun of the engine.