Analysis and simulation of the gearshift methodology for a novel two-speed transmission system for electric powertrains with a central motor

Abstract

Electric vehicle powertrains traditionally consist of a central electric motor drive, a single-speed transmission and a differential. This electric powertrain layout, for use in either fully electric vehicles or through-the-road parallel hybrid electric vehicles, will be extensively adopted in the next few years, despite the ongoing research in electric vehicles with individually controlled motors. However, current research suggests that electric powertrains with a central electric motor drive can still be widely improved. For example, the installation of a seamless multiple-speed transmission instead of a single-speed transmission can cause an increase in the vehicle performance, together with an enhancement in the overall efficiency of the electric powertrain. These novel transmission systems for electric powertrains require a specific design, in order to be efficient, compact, easy and robust to control and cheap to manufacture. This article presents the mechanical layout and the control system of a novel two-speed transmission system designed by the present authors, with particular focus on the achievement of optimal gearshift dynamics. The torque characteristics of typical electric motor drives require a different actuation of the seamless gearshifts, in comparison with the equivalent operation for a dual-clutch transmission within a powertrain driven by an internal combustion engine.