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Abstract |
Mean-value Observer for a Turbocharged SI-engine
For air/fuel control, where the cylinder air charge (CAC) estimation is based on
intake manifold pressure, it is essential to reduce the noise from measured
intake manifold pressure signals while at the same time keeping the phase delays
low during transients. Observers provide means of filtering without introducing
large delays and therefore an observer is developed with emphasis on CAC
estimation for air/fuel ratio control. It also enables model based diagnosis
opportunities. The observer is based on a nonlinear mean value engine model
including the intake and exhaust side together with turbine shaft speed.
The observer feedback gains are determined using an extended Kalman filter.
Systematic methods are presented to determine the covariance matrices for the
noise and as part of that a novel method is presented to determine the state
noise based on the model quality. Additional performance benefits are
demonstrated when the model is augmented with one state. The observer is
evaluated using real engine data with feedback from measured pressures in the
intake manifold and after the intercooler. It shows very good results for CAC
estimation as it suppresses intake manifold pressure noise without introducing
phase delays. It also provides an accurate estimate of turbocharger
speed. Therefore it is highly suitable for control and diagnosis in turbocharged
SI-engines.
Per Andersson and Lars Eriksson
IFAC Symposium on Advances in Automotive Control, 2004
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