Control strategy for a dual-mode electromechanical, infinitely variable transmission for hybrid electric vehicles

Abstract An operating strategy is proposed for a dual-mode electromechanical, infinitely variable transmission (EVT) hybrid electric vehicle (HEV). First, network analysis is performed to evaluate the dual-mode EVT efficiency with respect to the speed ratio. It is found from the network analysis that the EVT efficiency decreases when the power circulation occurs along the electric variator and the EVT should be operated in the speed ratio region that provides a relatively high system efficiency, which requires an operating strategy from the viewpoint of the overall powertrain efficiency rather than the internal combustion engine thermal efficiency. In order to develop the operating strategy of the dual-mode EVT, dynamic equations of the HEV powertrain including the EVT are obtained and the motor torque control algorithm is designed using inversion-based control. To evaluate the performance of the operating strategy, an HEV simulator is developed on the basis of the dynamic models of the HEV powertrain using Cruise and MATLAB/Simulink. The simulation results indicate that the operating strategy proposed in this study is able to operate the engine in the desired speed ratio range having a relatively high EVT efficiency, which provides improved fuel economy compared with conventional control. It is expected that the operating strategy based on the transmission efficiency can be used effectively in the design of the dual-mode EVT for HEV application.