Feedforward A/F control in turbocharged gasoline engines with variable valve timing requires knowledge of exhaust manifold pressure, Pe. Physical conditions in the manifold make measurement costly, compelling manufacturers to implement some form of on-line estimation. Processor limitations and the calibration process, however, put constraints on estimator complexity. This paper assesses the feasibility of estimating Pe with an algorithm that is computationally efficient and relatively simple to calibrate. A traditional reduced order linear observer is found to perform well but has too many calibration parameters for practical implementation. Using the performance of the observer as a benchmark, static estimation is explored by parameterizing the equilibrium values of Pe with both the inputs and the outputs of the system. This nonlinear static estimate, combined with simple lead compensation, yields a practical observer implementation.

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