Optimal Design of a Middle Motor for a Pedal Electric Cycle

摘要

This paper proposes a novel design of a middle motor for pedal electric cycles. This middle motor is an axial-flux permanent magnet synchronous motor with a stator plate, facing which is a rotor as part of a cycloidal reducer next to the stator. The whole set of the middle motor and cycloidal reducer is easily installed along the same axle of the crankset of bike. In the preliminary design, driving requirements are used to make specifications of the middle motor. The numbers of stator slots and magnet poles on rotor are then chosen for the best winding factor so that the winding layout is determined accordingly. One-dimensional magnetic circuit model of the middle motor is built and its shape is optimized by using a multifunctional optimization system tool. Finally, the resulting design is verified and refined by the finite element analysis. A prototype middle motor is fabricated and integrated with a cycloidal reducer. Experimental results show that the motor has sinusoidal back electromotive force and is easily controlled by sinusoidal currents. The torque and speed curve as well as an efficiency map are estimated by the finite element analysis. The average driving efficiency of the pedelec driven by the proposed middle motor is estimated at 71.3% based on the driving cycle ECE-40 with a reduced speed limit of 25 km/hr.