Fuel/air ratio feedback control with catalyst gain estimation for an internal combustion engine

A method for controlling an internal combustion engine, the method comprising:

• controlling air/fuel ratio of the engine using an inner feedback control loop based on a reference air/fuel ratio and feedback from an universal exhaust gas oxygen sensor positioned upstream relative to a catalyst;
• determining a catalyst gain based on the universal exhaust gas oxygen sensor and the heated exhaust gas oxygen sensor by modeling the catalyst as an integrator with an unknown gain and estimating the catalyst gain;
• and
• generating the reference air/fuel ratio in an outer feedback control loop based on feedback from a heated exhaust gas oxygen sensor and a sensor reference voltage to reduce any error therebetween, the heated exhaust gas oxygen sensor being positioned downstream relative to a first portion of the catalyst and upstream relative to a second portion of the catalyst.

A system for controlling a multiple cylinder internal combustion engine, the system comprising:

• a first exhaust gas sensor positioned downstream relative to the engine;
• a catalyst positioned downstream relative to the first exhaust gas sensor;
• a second exhaust gas sensor positioned downstream relative to the first exhaust gas sensor and downstream relative to at least a portion of the catalyst;
• and
• a controller in communication with the first and second exhaust gas sensors, the controller having an inner feedback control loop to control air/fuel ratio of the engine with feedback provided by the first exhaust gas sensor and an outer feedback control loop that modifies a reference air/fuel ratio provided to the inner feedback control loop based on feedback provided by the first and second exhaust gas sensors wherein the reference air/fuel ratio adapts to oxygen storage capacity of the catalyst by estimating a catalyst gain based on the first and second exhaust gas sensors and modifying a reference air/fuel ratio offset based on the catalyst gain.

A computer readable storage medium having stored data representing instructions executable by a computer to control an internal combustion engine having a first exhaust gas oxygen sensor, a catalyst positioned downstream from the first exhaust gas oxygen sensor, and a second exhaust gas oxygen sensor positioned downstream relative to at least a portion of the catalyst, the computer readable storage medium comprising:

• instructions for modeling the catalyst as an integrator and determining a catalyst gain based on signals from the first and second exhaust gas oxygen sensors;
• instructions for determining an adaptive gain based on the catalyst gain;
• instructions for determining a reference air/fuel ratio offset based on a difference between a reference voltage and the second exhaust gas oxygen sensor;
• instructions for modifying the air/fuel ratio offset based on the adaptive gain and a target air/fuel ratio to determine a reference air/fuel ratio;
• and
• instructions for generating a fueling command for the engine such that an engine air/fuel ratio approaches the reference air/fuel ratio.