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 efficienttechnology 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 ofboost pressure is desirable. Standard control techniques (i.e.Proportional-Integral) do not assure a reliable VGT behaviour. This paperdescribes a new boost pressure control strategy developed to improve PItechnique, and based on a simplified modelling of VGT operation. Severaltests were carried out on engines to point out which physical quantitiesdirectly influence VGT dynamics, and to find out VGT operation modes (OMs).Simplified models for each OM were developed and model parameters wereidentified. Experimental tests provided a basis to design a control strategyable to meet general performance requirements. Since two different OMs wererecovered, two separate governors were developed, each active under certainconditions. A switching logic was created to manage transitions between thetwo governors. Finally, the new control strategy was validated on the enginewith good results.