DI Diesel engine with variable geometry turbocharger (VGT): A model based boost pressure control strategy

The use of a variable geometry turbocharger (VGT) is a very efficient technology to improve performance of passenger car direct injection (DI) Diesel engines. In order to take full advantage of the potential of VGT, without penalty on fuel consumption and driveability, electronic control of boost pressure is desirable. Standard control techniques (i.e. Proportional-Integral) do not assure a reliable VGT behaviour. This paper describes a new boost pressure control strategy developed to improve PI technique, and based on a simplified modelling of VGT operation. Several tests were carried out on engines to point out which physical quantities directly influence VGT dynamics, and to find out VGT operation modes (OMs). Simplified models for each OM were developed and model parameters were identified. Experimental tests provided a basis to design a control strategy able to meet general performance requirements. Since two different OMs were recovered, two separate governors were developed, each active under certain conditions. A switching logic was created to manage transitions between the two governors. Finally, the new control strategy was validated on the engine with good results.