An Electro-Mechanical Infinitely Variable Speed Transmission 2004-01-0354

An electro-mechanical infinitely variable transmission (eVT), comprising a pair of planetary trains interconnected with two electric machines and clutches, has been proposed. The transmission leverages the advantages of an output power-split configuration for low-speed operation and a compound power-split configuration for high-speed operation. It is capable of being operated in a number of operating modes including an eVT only mode and a hybrid mode when equipped with on-board energy storage devices. The transmission provides a compact, highly efficient and potentially low cost driveline solution for both conventional vehicles and hybrid electric vehicles.

A virtual transmission prototype was built in EASY5¹. A base vehicle model was also constructed in EASY5 environment with Ricardo Powertrain Library components. Performance of the proposed transmission was evaluated in context of the base vehicle for driveline efficiency, vehicle acceleration, vehicle fuel consumption and emissions under various driving cycles. Comparison with a conventional four-speed automatic transmission was made.

Results of the evaluation have demonstrated superior performance of the proposed eVT over conventional automatic transmissions. The eVT has a high efficiency of 92% over most of the speed conversion range. The infinite conversion range of the eVT enhances the vehicle's tractive effort, improving vehicle acceleration. It shortens the acceleration time by 7.5% from 0 to 60 mph, and 9.5% from 30 to 50 mph. The infinitely variable speed ratio along with the rapid speed-ratio-change capability of the electric system allows the transmission to significantly improve vehicle's fuel economy and reduce vehicle's emissions. Even under eVT only operation mode (for conventional vehicle application), 11% fuel savings for urban driving and 9% on highway driving are easily achievable. The reduction in Nox emission is predicted to be about 12% under urban drive cycles and 5% on highway.

The electro-mechanical eVT allows various degrees of hybridization to provide further gains in fuel economy and environmental acceptability.