Design and Analysis of an Electrical Variable Transmission for a Series-Parallel Hybrid Electric Vehicle

This paper describes the mathematical modeling, analysis, and simulation results of a novel electrical variable transmission (EVT) for a series-parallel hybrid electric vehicle (SPHEV). The proposed EVT uses a two-degree-of-freedom (2-DOF) planetary gearset with four clutches to combine an engine and two electric machines with the vehicle. The topology of the planetary gearset is the same as that of conventional four-speed automatic transmissions. Therefore, the proposed EVT can be mass-produced and quite easily packaged. Nine operation modes can be realized. The properly arranged clutches more flexibly transmit power flow and avoid high spin losses for the engine and electric machines. Simulation under the New European Driving Cycle (NEDC) drive cycle shows that the fuel consumption of the proposed SPHEV is 5.62% lower than a benchmark vehicle, which uses two planetary gearsets and no clutches, indicating the fuel economy potential of this concept. The life cycle of the electric machines is expected to be extended, because the open or locked operations of the clutches allow efficient operation and, thus, might reduce the chance of overheating. Finally, the speed range of the electric machines is found to be smaller, compared with that used in the benchmark vehicle, which implies ease of manufacture, good sustainability, and low cost.