Variable geometry turbochargers are a well established technology for Diesel engine systems to optimize the energy recovery over a large operating range. More recently, Variable Geometry Compressors (VGC) systems are being considered as a further improvement of automotive turbochargers for their potential of providing a more direct control over the stability margin and the efficiency of the compressor. In particular, a direct control on the stability margin allows to size the compressor more aggressively to obtain better peak performances. When such an aggressive design is adopted the control of the VGC to prevent surging becomes essential and a reliable Surge Index (SI) estimator needs to be included in the control algorithm. This paper presents two estimator designs for an automotive Diesel engine equipped with a variable geometry compressor. The estimators aim at tracking the value of two important performance variables, namely the Surge Index and the compressor efficiency.
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