Abstract: The period of conduction of an electronic interrupter of an ignition circuit is made shorter increasingly with falling engine speed in comparison to the duration of the period for which the switching path of the engine driven timing generator maintains its condition immediately before the ignition moment. During the time in which that condition is maintained immediately before changing at the ignition moment a capacitor (26) is provided with a first change (b) of its charge in a first direction and thereafter a second change (c) thereof is produced in the other direction. The switching of the electronic interrupter (7) into the conducting condition occurs when the charge of the capacitor reaches a threshold value during the second change of the charge. That threshold value is modifiable by a regulating value that depends at least in part on the engine speed.

Abstract: In addition to a first storage circuit in which a sawtooth wave is generated for comparing the ramp voltage with a threshold voltage that is caused to vary with engine conditions, particularly engine speed, for determining when the interruptor switch of the primary circuit of an ignition coil is closed to begin buildup of current therein, an auxiliary storage circuit is provided for generating an auxiliary signal within the duration of which the sawtooth wave of the main charging circuit must return to its starting condition, and another pulse signal present during all but an initial portion of the auxiliary signal for rapidly returning that sawtooth wave to its beginning a new beginning, thus making a longer part of the ignition cycle available for variation of the duration of the period during which the interruptor switch is closed to allow buildup of current in the ignition coil.

Abstract: The operation of the interrupting switch in the primary circuit of an ignition coil triggers a first timing circuit having a fixed interval or one sometimes modified by engine loading, at the end of which a timing interval signal is generated which lasts for a second interval. The latter is applied to switch a resistor across the timing wave generator to load down its output voltage. In this manner, an engine equipped with a simple ignition shift providing spark advance in the low speed region and then steady or slightly retarding timing thereafter, can be caused to provide a retarding priming shift that sets in at a medium speed, increases and then tapers off with higher speeds so as to cover a speed range in which the engine is particularly sensitive to engine knock and avoiding the inefficiencies which would be necessary if the simple ignition shift system had to be backed off to avoid intersecting the knock boundary.