A High Efficiency Transmission Architecture for Electric Vehicles

A Dual Power Split Electronic Continuously Variable Transmission (DPS-ECVT) with an input-split, output coupled, split-power-path configuration is proposed for improving overall system efficiency and range for electric vehicles. By modulating the power split ratio between the mechanical (planetary gear meshes) and electrical (Motor Generator Units) driveline components, a continuous range of gear ratios operating at higher efficiency is obtained. The proposed concept leverages two power-split units that lead to significantly reduced power flow through the electrical drivelines (compared with single speed EV transmissions as well as single power-split E-CVTs) while providing the same overall ratio spread for transmission operation. A multi-layered optimization is performed, first an inner layer optimization on the operational control strategy to maximize the end-of-cycle SOC (State of Charge) of the battery for a given set of transmission design parameters, and then subsequently an outer layer optimization on the design parameters to maximize the overall efficiency over multiple configurations of the given architecture. The performance of the architecture is bench-marked using simulation models derived from a Chevy Bolt baseline that are simulated on the EPA highway (HWFET) and the urban (UDDS) driving cycles. An effective gain of 13.6 percent in the range is demonstrated. A stick-diagram schematic realization of the optimized configuration is also presented.