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
2008
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Last updated: 2021-11-10
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