Abstract
Up to recent, gearboxes for EVs are only single speed solutions and some technical solutions even aim at no gearbox at all, by having 2 or 4 direct drive in-wheel motors for each wheel. However, there is also a trend to design multi-speed gearboxes in order to overcome a number of technical and functional drawbacks of single motor EV solutions. This paper describes the analysis, design and control of a powershifting two-speed transmission for EVs. The study and prototyping pursued is based on static and dynamic vehicle performance and energy flow simulations. Efficiency maps of the battery, e-motor and gearbox are incorporated in the simulation models. Furthermore, the vehicle mass (incl. batteries, e-motor, inverter, etc.) is included to evaluate the vehicle launch and speed performance as a function of road inclination. Efficiency optimization of the entire drivetrain is performed through gear ratio design/selection as well as shifting strategy (when to shift). Finally, for compactness and light weight design purpose, it is chosen to use a unique combination of planetary gearsets and lower cost shifting elements instead of multiple gear stages as seen in manual transmissions or multiple wet-plate clutch as seen in automatic transmissions. One of the main challenges was to enable smooth control using this new combination of planetary gearsets and shifting elements.
KEYWORDS – EV gearbox, multispeed, drive range, efficiency, shift comfort