Abstract: A principal operational variable of an internal combustion engine, for example the fuel-air mixture ratio, is controlled by superposition of three separate control steps. The basic setting of a control variable is obtained with a relatively coarse forward control, for example a carburetor in the case of fuel-air mixture control. Superimposed on this basic control is a refined forward control step which is based on the prevailing magnitudes of at least one operational variable, preferably the engine speed and the throttle valve position, and which applies a multiplicative correction to the basic setting of the fuel-air mixture. The third superimposed control step is a feedback control of the fuel-air mixture within the range of correction applied by the second control steps but based on still another engine variable, in particular the exhaust gas composition as sensed by an oxygen sensor (.lambda.-sensor). After comparison with the reference signal, the .lambda.

Abstract: Omission of a pulse in an otherwise regular pulse sequence, such as may be produced by omission of a tooth of a rotating gear that is used to generate a pulse sequence through a pick-up, is utilized after the manner of a special framing pulse, saving the complications of providing a framing pulse, especially in gasoline engine ignition timing. A counter is started with the beginning of every pulse of the sequence and is operated at a multiple of the sequence frequency. If the frequency varies, the count status when the next pulse arrives will vary slightly and this variation may be caused to change the initial condition for the beginning of each count cycle to keep the repetitive counting generally in step with the varying frequency.