Co-Simulation Analysis of Transient Response and Control for Engines with Variable Valvetrains

Modern engines are becoming highly complex, with several strongly interactive subsystems variable cam phasers on both intake and exhaust, along with various kinds of variable valve lift mechanisms. Isolated component models may not yield adequate information to deal with system-level interactive issues, especially when it comes to transient behavior. In addition, massive amounts of expensive experimental work will be required for optimization. Recent computing speed improvements are beginning to permit the use of cosimulation to couple highly detailed and accurate submodels of the various engine components, each created using the most appropriate available simulation package. This paper describes such a system model using GT-Power to model the engine, AMESim to model cam phasers and the engine lubrication system, and Matlab/Simulink to model the engine controllers and the vehicle. The simulation has been applied to examine fast transient response to throttle tip-in and tip-out maneuvers. After verifying the accuracy of the simulation against measured vehicle responses, various cam phaser control strategies were examined for their response to demand for engine torque and residual gas dilution. It was found that simple, conventional phaser control strategies such as position command using steady-state-based tables and phase-rate-limiting cannot provide sufficiently accurate dilution control. In order to extract the full fuel economy and emissions benefit from variable valvetrain systems, more accurate model-based control of residual gas fraction that is effective during fast transients is required. An approach to model-based dilution control is described and demonstrated.

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