Diagnostics of Oxygen Sensors and Air-Fuel Ratio Adaptive Controls

Stringent emission regulations mandated by California air regulation board (CARB) require monitoring the upstream exhaust gas oxygen (UEGO) sensor for any possible malfunction causing the vehicle emissions to exceed standard thresholds. Six faults have been identified that may potentially cause the UEGO sensor performance to deteriorate and lead to instability of the air-fuel ratio (AFR) closed-loop control system. These malfunctions are either due to an additional delay or an additional lag in the transition of the sensor response from lean to rich or rich to lean. In this paper, a novel non-intrusive approach is developed to diagnose these faults using a combination of a statistical method and a system identification process. In the second part of this work, a control strategy is presented that utilizes the type, the direction and the magnitude of the fault present to update the gains of the controller for the closed-loop air-fuel ratio control system. The proposed strategy does not require modifying the controller structure and only adapts the baseline gains of the controller and delay compensator to match the actual system dynamics (in presence of fault). The proposed approach has been demonstrated on a vehicle (Mustang V6 3.7L) where different faults were induced, and the emissions associated with each fault were measured to show the improvement.