Emission control system for an internal combustion engine

A system for controlling the air/fuel mixture input to an internal combustion engine which comprises:

• a sensor mounted to the engine for sensing the level of an exhaust gas and producing an analog signal indicative of that level;
• means for producing a reference level signal indicative of the desired level of said exhaust gas;
• a comparator connected to receive the analog exhaust gas signal and the reference level signal and being operable to produce a first logic level output if the analog exhaust gas signal exceeds the reference level signal and produce a second logic level output if the analog exhaust gas signal is less than the reference level signal;
• a clock for producing clock pulses;
• a flip-flop connected to the comparator and the clock and being operable to store the state of the comparator output each time a clock pulse is received and to produce a corresponding direction signal at an output;
• a stepper motor mounted to the engine for controlling the air/fuel mixture;
• and
• a stepper motor control connected to the clock and the flip-flop and being operable to advance the stepper motor one step for each received clock pulse in the direction indicated by the state of the flip-flop.