System and method for adaptive control of air-to-fuel ratio

A method for controlling an air-fuel ratio for an internal combustion engine, the method comprising:

• receiving oxygen signals output from an oxygen sensor or NOx signals from a NOx sensor;
• determining a first air-fuel ratio command;
• adjusting, as a first adjustment, the first air-fuel ratio command to increase or decrease a commanded air-fuel ratio;
• controlling at least one of:
• an admission valve, an intake throttle valve, or an exhaust gas recirculation valve based on the first adjustment;
• determining a second air-fuel ratio command;
• adjusting, as a second adjustment, the second air-fuel ratio command increasing or decreasing the commanded air-fuel ratio, one of the first adjustment or the second adjustment increasing the commanded air-fuel ratio command, the other of the first adjustment or the second adjustment decreasing the commanded air-fuel ratio, the first adjustment and the second adjustment being generated to cause repeating variations in the air-fuel ratio via an algorithm that seeks an objective by making adjustments to commanded air-fuel ratios;
• and
• controlling at least one of:
• the admission valve, the intake throttle valve, or the exhaust gas recirculation valve based on the second air-fuel ratio command according to adjustments to the commanded air-fuel ratios that are associated with the objective.

A system for controlling an air-fuel ratio for an internal combustion engine, the system comprising:

• an internal combustion engine configured to combust fuel;
• a valve for providing fuel to the internal combustion engine;
• a catalyst connected to the internal combustion engine to receive exhaust formed by combustion of the fuel with the internal combustion engine;
• a sensor configured to detect oxygen or NOx present in the exhaust;
• and
• a controller configured to:
• generate commands for controlling the valve,
• receive signals output from the sensor,
• determine a desired air-fuel ratio, and
• adjust the desired air-fuel ratio by generating an adjusted air-fuel ratio command that is above or that is below the desired air-fuel ratio as part of an adaptive control strategy that generates fluctuations that change a magnitude and a sign of the adjusted air-fuel ratio command.