Method and system to control ignition timing of an internal combustion

Abstract

The composition of exhaust gases from an IC engine is dependent on ignition timing; to control the composition, therefore, ignition timing is adjusted in accordance with sensed exhaust gas composition signals. To prevent abrupt change of ignition timing, as the exhaust gas composition signal changes upon change of exhaust gases between reducing and oxidizing state, a limit stage is included which limits the change of ignition timing between succeeding ignition events to a predetermined incremental crankshaft angle, for example 2.degree.. The ignition angle adjustment may be nonsymmetrical in adding and subtracting direction, and, in any event, is limited to a maximum adjustment angle beyond which undesirable or unsafe operating conditions of the engine might obtain. In a preferred digital form, the count number of an accumulator counter, the output signal of which determines the occurrence of an ignition event, is modified, in said incremental steps, to thereby control the timing of the ignition event.