Simulation Research on Engine Torque Ripple Elimination Based on Engine Torque Observer by Using a Flywheel ISG
To be published on April 2, 2019 by SAE International in United States
This paper conducts simulation research on engine torque ripple elimination based on engine torque observer by using a flywheel ISG. Usually, the engine torque can be cancelled by using a passive method such as by installing a flywheel or torsional damper. However, failure problems arise in hybrid system because of different mechanical characters of engine and its co-axial ISG motor, which is an important issue in its high frequency domain. In my research group, we remove the flywheel and replace it with an ISG rotor, namely FISG (flywheel-ISG). Besides, the crank and FISG rotor are directly mechanically connected, which means no dampers or clutches are installed. If the engine torque ripples can be eliminated as the same level as flywheel and damper by FISG active torque compensation, the new generation of APU system can be more compact and economical. Simulation efforts are paid to verify its feasibility. Firstly, based on the experimental test bench, which is now under construction. A mechanical model was built based on LMS AMESim. Secondly, rigid and elastic crankshaft dynamic models are established respectively. Then, engine torque observers are built based on the crankshaft models, of which the inputs are in-cylinder pressure signals and the crankshaft angle position. Finally, the FISG control algorithm is designed and the engine torque ripple elimination algorithm is embedded. Simulation results show that by adding high frequency torque compensation by FISG, the torque ripples caused by engine can be significantly supressed. Compared with the elastic-model-based observer, the rigid but simpler one functions just as well, which shows great potential for on-line application.