Coordinated Model Based Thottle and Turbo Control

Abstract: Downsizing and turbocharging is one way to meet the high demands on fuel consumptionand performance on todays engines. The air-path system in a turbochargedspark ignited engine is a complex system and because the intake manifoldpressure is tightly connected with the engine torque a consistent and robustcontrol is needed. The control strategy utilizes two control loops, one wastegateactuator to control the intercooler pressure and one throttle actuator to controlthe intake manifold pressure. These pressures are coupled, making both actuatorsaffect both pressures. Because of the time delay and the dynamics in the actuatorsand the system dynamics between the wastegate and the intercooler pressure thecontroller overreacts causing a pressure overshoot and sometimes oscillations. Theoscillatory behavior is caused by both actuators trying to minimize their respectivecontrol error, affecting the others pressure. The delay in the system dynamicscauses the two controllers to enter a state where they counteract each other.A compensation strategy is suggested, which estimates the intercooler pressurederivative and uses that to predict the future intercooler pressure. The compensationstrategy shows good performance in simulations, reducing the overshoots andeliminating the oscillations.