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(s)peed 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 drive-train losses. From the backward simulations, it was found that the fuel economy of power split-parallel configuration with 4-speed is improved.