A Nonlinear Dynamic Model for Three-Way Catalyst Control and Diagnosis

Increasingly tighter automotive emissions legislation not only demands advanced catalyst control for super ultra low emission vehicle (SULEV) requirements, but also a close monitoring of catalyst performance. In the present paper, a control-oriented model is proposed that uses a library of four nonlinear (NARMAX) dynamic models to predict the three-way catalyst (TWC) transient response. Each nonlinear model is optimised for use under a certain operating region. In order to identify the current operating region and select the appropriate local model for prediction, the rate of change of stored oxygen is monitored. A simplified chemical model, which is based on the dynamics of the fundamental chemical reactions that occur inside the catalyst, is used for this purpose. The developed catalyst model only requires knowledge of the upstream/downstream air-fuel ratio (AFR) and it could form the basis of an on-board catalyst monitoring and control system.