Modelling and control of a novel two-speed transmission for electric vehicles

Multiple speed transmissions adopted by electric vehicles (EVs) provide the probability of further improving the global efficiency of the drivetrain, as well as extending limited driving range for the fixed power storage. This paper proposes a novel two-speed transmission for an electric vehicle (EV), which is capable of realizing power-on gear shifting by operating the band brake to lock or unlock the one-way-clutch. The band brake controlled by the actuator provides a smooth and efficient gear shifting. To achieve power-on gear shifting, three alternative control strategies are proposed and applied in this novel two-speed transmission system. To verify the transient behaviour during the gear shifting, the EV powertrain equipped with the proposed two-speed transmission is undertaken. Firstly, a mathematical model is developed, including the electric motor, the proposed two-speed transmission, the vehicle, etc. Then, model-based alternative power-on gearshift strategies are developed, and a torque-based gearshift closed-loop controller with the desired speed trajectory is proposed. The vehicle jerk and the friction work are taken as the foremost metrics to evaluate the gearshift quality. The simulation results demonstrate that all strategies can achieve power-on gearshifts. The disadvantages and advantages of these strategies are exhibited clearly, which provides beneficial knowledge and reference to the researchers engaged in the development of the transmission controller.