Abstract
Specific power output of modern HSDI diesel engine with common rail injection system has been increasing since it was applied to passenger car. With this market requirement and stringent emission / CO2 regulation, Variable Geometry Turbine (VGT) is almost essential component for HSDI diesel engine replacing Waist Gate Turbine (WGT) in order to increase intake air charging capability and to decrease pumping loss. This high air charging performance of VGT, however, needs precise and prompt control to prevent compressor surge which can damage VGT itself and cause abnormal noise especially if intake throttle flap is applied to increase EGR rate or for Diesel Particulate Filter (DPF) regeneration control. This study describes Engine Management System (EMS) control strategy to prevent compressor surge during abrupt deceleration using interactive control method between VGT, EGR, intake throttle flap and fuel injection control minimizing effect on emission and vehicle dynamic performance. For engine management system to recognize abrupt pedal-off phase, several engine and vehicle operation parameters were suggested as criteria and also maximum duration of pedal-off phase was decided. As indication of compressor surge during pedal-off phase, trace of intake air mass flow was evaluated under various intake throttle flap position, EGR valve opening and VGT vane position. Air mass flow of each case was evaluated by compressor characteristic map based on corrected air mass flow and compressor pressure ratio. To evaluate effect on emission of this new EMS control strategy to prevent compressor surge, emission test was carried out under New European Driving Cycle (NEDC).
Key words : Variable Geometry Turbine(VGT), Compressor Surge, Exhaust Gas Recirculation(EGR) Intake Throttle Flap, Engine Management System (EMS), High Speed Direct Injection (HSDI)