Closed loop air/fuel ratio controller with asymmetrical proportional term

An air/fuel mixture control system for an internal combustion engine having combustion space into which an air/fuel mixture is supplied to undergo combustion and having means defining an exhaust passage from the combustion space into which spent combustion gases are discharged and directed to the atmosphere comprising, in combination:

• an air/fuel mixture supply means effective to supply a mixture of fuel and air to the combustion space;
• sensor means effective to sense the oxidizing/reducing conditions at a predetermined point in the exhaust passage and hence, after a transport delay period dependent upon engine operating conditions, to the mixture supplied to the combustion space, the sensor means providing a sensor signal indicative of the sense of deviation of the air/fuel ratio of the mixture supplied to the combustion space from a predetermined ratio;
• a control circuit responsive to the sensor signal effective to generate a control signal;
• and
• means effective to control the air/fuel ratio of the mixture supplied by the air/fuel mixture supply means in accord with the instantaneous value of the control signal,
• the control circuit including an integrator responsive to the sensor signal effective to provide an asymmetrical integral term portion of the control signal to effect a shift in the average value of the control signal in one direction from the value producing the predetermined ratio by an amount dependent in part by the value of the transport delay and
• a proportional circuit effective to provide an asymmetrical proportional term portion of the control signal to effect a shift in the average value of the control signal in the direction opposite said one direction by an amount dependent in part upon the value of transport delay, the shift in the average value of the control signal being dominated by the asymmetrical integral term portion of the control signal at large values of the transport delay and the shift in the average value of the control signal being dominated by the asymmetrical proportional term portion of the control signal at small values of the transport delay so that the average value of the air/fuel ratio of the mixture supplied to the engine varies from the predetermined ratio in one sense changing to the opposite sense as the engine operating conditions change thereby varying the transport delay through the engine between high and low values to thereby effect a scheduled offset in the air/fuel ratio in accord with engine operating conditions.