Individual Cylinder Air–Fuel Ratio Control Using Fourier Analysis

Based on Fourier analysis, a general concept for the cylinder imbalance control problem with a single air-fuel ratio (A/F) sensor is presented. First, a control-oriented engine model is developed that is applicable for arbitrary engine types. With the model, a controller is designed, and the corresponding multirate control system is investigated in terms of stability using eigenvalue analysis. Moreover, a robustness analysis with respect to parametric uncertainties in the phase information is conducted using Monte Carlo simulations. It turns out that a good match of the model at steady state is more important than a sophisticated controller design. The domain of stable operation is identified. A five-cylinder test-bench engine is used to validate the model, to investigate the controller performance during a driving cycle, and to validate the results from the robustness analysis.