Digital feedback system

A feedback apparatus for controlling the air fuel ratio in an internal combustion engine comprising:

• a sensor means coupled to an exhaust system associated with the internal combustion engine for sensing the air-to-fuel ratio and providing a binary output indicative of the air fuel ratio being either rich or lean of stoichiometry;
• a revolution detecting means coupled to the internal combustion engine for sensing the revolution rate of the internal combustion engine;
• an inverter means coupled to said sensor means for inverting the state of the output of said sensor means;
• a delay register means coupled to said sensor means through said inverter means and said revolution detecting means for delaying the passage of inverted information as a function of the revolution rate;
• a logic means having two inputs, coupled to said sensor means and said delay register means and having an output node with a first output when the two inputs are the same and a second output when the two inputs are different;
• and
• a fuel control system for the air fuel mixture supplied to the internal combustion engine, said control system being coupled to the output of said logic means so that the control system causes no change in the air fuel ratio when said first output is received, and causes a change in the air fuel ratio when said second output is received, the direction of change being determined by the output of said inverter means.