Alternative observers for SI engine air/fuel ratio control

In earlier work it has been shown that a nonlinear observer based on the use of the manifold pressure state equation and a nonlinear fuel film compensator can maintain accurate A/F ratio control during both steady state and transient operation. This observer may be called a manifold absolute pressure (MAP) observer because it is fundamentally dependent on the use of the manifold pressure state equation and a MAP sensor. It is in reality a constant gain extended Kalman filter. While this observer shows promise for some applications, it obviously cannot immediately be used with air mass flow sensors other than a MAP sensor. In this paper it is shown that it is possible to construct a family of alternative nonlinear observers which "naturally" allow the use of any given air mass flow related sensor or a combination of them for A/F ratio control. This new family of observers provides the SI engine control system designer with a variety of robust control systems which can easily be made redundant in order to satisfy newer engine emissions and diagnosis requirements and legislation.