Fuel economy potential for a power split type hybrid system with 4-speed transmission by adding parallel mode

In this study, fuel economy potential of a power split hybrid configuration with 4-speed was investigated by adding the parallel mode. First, system efficiency of the power split configuration with 4-speed was investigated using network analysis. From the network analysis results, it was found that the efficiency of the target hybrid system was improved by the added 4-speed gear steps, which provides four mechanical points. To maintain the system operation at the mechanical points, a new power split-parallel architecture was proposed by adding a brake at the MG1 shaft, which provides a parallel mode instead of the power split mode. To evaluate the fuel economy potential of the proposed power split-parallel configuration, backward simulations were performed using dynamic programming by considering the drivetrain losses. From the backward simulations, it was found that the fuel economy of power split-parallel configuration with 4-speed is improved.