Air/fuel ratio control responsive to catalyst window locator

A method of maintaining the conversion efficiency of a catalytic converter within a predetermined efficiency window, said catalytic converter being associated with a vehicle having an engine associated with an exhaust gas oxygen sensor and NOx sensor, the method comprising the steps of:

• determining a base fuel signal related to a quantity of air inducted into the engine by said exhaust gas oxygen sensor;
• iteratively perturbing said base fuel signal by a bias signal until said NOx sensor indicates a predetermined NOx value corresponding to a minimum desired NOx conversion efficiency level;
• and
• modifying said base fuel signal as a function of said bias signal corresponding to said predetermined exhaust gas NOx value to maintain the air/fuel ratio at a value corresponding to a maximum desired NOx conversion efficiency.

An air/fuel ratio control system for a vehicle including an internal combustion engine having an associated fuel delivery system and catalytic converter, the system comprising:

• an exhaust sensor for indicating an air/fuel ratio of exhaust gas exiting the engine;
• a NOx sensor for indicating the NOx conversion efficiency of said catalytic converter;
• and
• a controller including a processor and associated memory programmed to perform the following steps:
• provide a base fuel signal related to a quantity of air inducted into the engine;
• generate a bias signal for biasing said base fuel signal towards a leaner air/fuel ratio;
• monitor said NOx sensor to detect a minimum desired NOx conversion efficiency associated with said bias signal;
• modify said base fuel signal as a function of said bias signal to maintain the air/fuel ratio at a value corresponding to a maximum desired NOx conversion efficiency;
• and generate an actuation signal to cause said fuel delivery system to deliver said modified base fuel signal to said engine.

An air/fuel ratio control system for a vehicle including an internal combustion engine having an associated fuel delivery system and catalytic converter, the system comprising:

• an exhaust sensor for indicating an air/fuel ratio of exhaust gas exiting the engine;
• a NOx sensor for indicating the NOx conversion efficiency of said catalytic converter;
• a controller including a processor and associated memory programmed to perform the following steps:
• provide a base fuel signal related to a quantity of air inducted into the engine;
• generate a bias signal for biasing said base fuel signal towards a leaner air/fuel ratio;
• monitor said NOx sensor to detect a predefined NOx conversion efficiency associated with said bias signal;
• modify said base fuel signal as a function of said bias signal to maintain said catalytic converter within a desired efficiency range;
• and generate an actuation signal to cause said fuel delivery system to deliver said modified base fuel signal to said engine;
• and
• a counter for determining the delay since the last modification of said base fuel signal.