Architectures for phase variation compensation in AFR control

To counteract the binary nature of an exhaust gas oxygen sensor and to improve the efficiency of a three way catalyst, the delivered fueling quantity is typically dithered around stoichiometry for gasoline internal combustion engines. Determining whether the switching sensor reads rich or lean because of the dithering or a disturbance is very difficult. This problem is often overcome by estimating the plant delay and tracking a reference signal. Without an accurate delay estimate, however, the benefits of this type of control architecture are limited. This paper compares two switching sensor based control architectures, phase lock loop and duty cycle control, for tracking a periodic reference air-to-fuel ratio signal while overcoming the uncertainty of a dynamic plant delay estimate.