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Model Simplification and Observer Design of a Turbo Charged Engine

Tougher legislation and higher expectations on the comfort of the vehicles, forces the vehicle manufacturers to make progress. To manage the demands, it is crucial to correctly estimate the air mass-flow to the cylinders. To estimate the mass-flow, a mean value engine model (MVEM) could be used. Since the computational power in the controller system is limited, the original MVEM has to be modified. The purpose is to reduce the required sample frequency to run the model. Firstly, some of the states in the original model are reduced and replaced by statical equations. The objective of this is to replace states that have fast dynamics with statical expressions. The reduction in sample frequency required to simulate the model is though less than expected. Some equations in the original model are modified when large derivatives occur. By increasing the size of the regions where the modified equations are used, these large derivatives become smaller. Furthermore, a solver with high resolution for a part of the model, at the same time as a solver with lower sample frequency is used for the entire model, is implemented. The reduction in computational effort using these modifications does not fulfill the required demands. Therefore, three different observers are implemented. They are based on the model for the throttle and the volumetric efficiency in the original MVEM, to estimate the air mass-flow to the cylinders. Since the observers do not model the entire engine, the signals from the sensors are always used. This is not preferable during transients. The sample frequency to achieve a stable model is though acceptable.

Christofer Sundström


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Last updated: 2019-04-24