Application of Nonlinear Transformations to A/F Ratio and Speed Control in an IC Engine 1999-01-0858

This paper presents the first application of the global feedback linearization method to an internal combustion (IC) engine. Through the application of this nonlinear control technique, the nonlinear coupled dynamics of the IC engine are globally linearized and decoupled. This represents a significant advance over previously published control approaches which rely on locally linearized dynamic models. With the IC engine dynamics globally linearized and decoupled, outer-loop controllers can be readily designed using simple linear tracking controller design methods, leading to very good dynamic response of three key IC engine outputs, air/fuel ratio, engine speed and manifold air pressure. In this paper, a standard IC engine model from the literature is first transformed to a controllable canonical form, required for the application of the global feedback linearization methods. With the IC engine model in controllable canonical form, necessary and sufficient conditions under which a dynamic system is globally feedback linearizable are verified for the IC engine model. Then, global feedback linearization techniques are directly applied to the internal combustion engine dynamic model. With this approach, the nonlinear coupled dynamics of the IC engine model are globally linearized and decoupled. With the nonlinear and coupled IC engine dynamics decoupled and globally linearized, linear control system design methods are readily applied to control air/fuel ratio, engine speed and manifold air pressure. This control approach is greatly simplified, since a controller for each of these variables can be designed without coupling effects from the other variables. Simulation results with the global linearizing feedback control and the outer-loop controls applied are given. In contrast to typical coupled responses of IC engines with other control approaches, the close-loop performance of the proposed method shows decoupled responses with very low error in the system outputs.