Fore-aft oxygen storage control

This paper describes model-based, active control of an aftertreatment system for a spark ignition engine equipped with a three-way catalyst (TWC) and pre- and post-TWC oxygen sensors. A controller is designed to manage the oxygen storage level in the TWC in order to maximize the simultaneous conversion efficiencies of oxides of nitrogen, NO_x, unburned hydrocarbons, HC, and carbon monoxide, CO. Linear exhaust gas oxygen sensors (UEGOs) are used to measure pre- and post-catalyst A/F. The pre-catalyst A/F measurement is assumed to be biased in addition to being corrupted by zero-mean noise, while the post-catalyst measurement is assumed to be only corrupted by zero-mean noise. A series controller configuration is adopted. The upstream controller provides relatively rapid response to disturbances, while the downstream controller uses an extended Kalman filter (observer) to estimate the relative oxygen level. The estimated value of oxygen storage is then used to regulate the relative oxygen level of the TWC to 50%. The performance and robustness of the proposed control system in the face of noise and model uncertainty are evaluated through extensive simulations.