Control Oriented Modeling of Gasoline Engines: A New Paradigm.


The advent of hybrid, flex fuel and smart vehicles has highlighted the need of an engine model suitable for a unified control and diagnostic framework. However, this may require a new engine modeling paradigm, deviating from traditional control oriented models and converging to first principle based models. These new developments have motivated the authors to bridge the prevailing gap between the existing control oriented engine models and the stringent requirements put up by new power-train architectures. In existing literature Mean Value Engine Models (MVEMs) are developed under a few assumptions and analogies. There exists a variety of approaches for evaluating the brake torque, however structure of engine speed dynamics remains the same. Though such a structure captures the mean value profile but builds an abstraction wall between model and the actual system. The said wall completely hides the aspects of crankshaft angular speed fluctuations, dynamics of multi-cylinders and others beneath its shadow. Among others, comprehensive control and diagnostic unification and derivation of the basis for model based cylinder-to-cylinder control are most prominent limitations.

To fill in the gap a new modeling strategy is presented in this thesis. The strategy takes into account the considerations of multi-cylinders and spatial orientation, without compromising the structural simplicity. The torque production subsystem is modeled by joining the model of torque producing mechanism and a simple closed form analytical gasoline engine cylinder pressure model. Model of the torque producing mechanism is derived using Constrained Lagrangian Equation of Motion, and is simplified to a suitable form to be integrated in overall engine model. An analytical gasoline engine cylinder pressure model is taken from literature and extended for a four cylinder engine, then integrated to the model of torque producing mechanism. Following such a modeling strategy unlike existing literature in control oriented gasoline engine models, torque production subsystem is not replaced by a continuously operating volumetric pump. As a result, the model vividly describes the crankshaft angular speed fluctuations and the dynamics introduced by multi cylinders. The employed physical principles give the global envelope of validity to the model. Thus the model describes dynamics of the healthy system, as well as system under faulty conditions, comprehensively. The proposed model is tuned and successfully validated. Pattern of crankshaft angular speed fluctuation for misfire in one cylinder is simulated and found closely matching to an actual engine misfire data.

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