An electro-mechanical variable speed transmission (eVT) is proposed for hybrid electric vehicles. The transmission is comprised of a pair of planetary gear trains interconnected with two electric machines and clutches. With on-board energy storage devices, the transmission combines, in a compact unit, independent speed-ratio control and power regulation between the engine and drive wheels. It offers a highly integrated, efficient and low cost solution to hybrid electric vehicles.
Operating principles of the transmission were outlined. Virtual transmission and vehicle prototypes were built with EASY5. Simulations were conducted to evaluate its performance in context of a hybrid electric vehicle. Comparisons were made against non-hybrid vehicles equipped respectively with eVT and four-speed automatic transmission, and against the production hybrid vehicle Prius.
Results showed superior performance of the proposed eVT in hybrid vehicle. It improved vehicle acceleration and significantly reduced fuel consumptions comparing to the non-hybrid vehicles. The fuel economy improvements were 158% for FTP cycle and 92% for HWFET cycle over the non-hybrid vehicle with four speed automatic transmission.
Simulation indicated that the hybrid vehicle with eVT offers considerable technical advantages over Prius. It improved fuel economy and substantially decreased the power and torque demands on electric machines.
The peak torque of the electric machines for eVT was about 1/3 of the Prius, and peak power was about 2/3 of the Prius over various drive cycles.