Electric Vehicles (EVs) with single-ratio gearbox provide high levels of smoothness, but using two-speed gearbox can provide significant benefits in terms of vehicle acceleration, max speed, and energy consumption. However, a smooth and seamless shifting is hard to be achieved due to the relatively large transmission ratio gap between two gears and the high speed characteristic of drive motor (DM). The purpose of this paper is to demonstrate a new seamless shifting control algorithm using DM torque for a novel multi-speed EV powertrain. First of all, a novel two-speed uninterrupted mechanical transmission, which consists of a planetary gear, a dry clutch and a band brake, is presented and modeled. In addition to clutch and band brake shift control strategies, new DM torque integration strategies are involved based on quick torque response feature of motors. According to the proposed algorithm, DM torque compensation in torque phase during upshift and less off-going clutch disengagement with DM torque compensation in inertia phase during downshift can both contribute to the uninterrupted output. To shorten the inertia phase time, the half-engagement of oncoming brake and reverse DM torque compensation are recommended. Simulation studies are taken to determine the shift transient behavior of the clutch, band brake and DM during two typical shifting conditions, power-on (when positive DM power is transmitted through the transmission when vehicles speed up or cruise) upshift and power-on downshift, which particularly demand uninterrupted output torque. The simulation results prove that the algorithm works effectively.

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