Abstract
This paper proposes an optimal design of a middle motor integrated into a mid-drive unit for pedal electric cycles. This middle motor is an axial-flux permanent magnet brushless DC motor with a stator plate. Facing this plate is a rotor plate that acts as an eccentric component of a cycloidal reducer next to the stator. Both the middle motor and cycloidal reducer are easily installed on the same axle of the bike crankset. In the preliminary design, driving requirements are used to make the middle motor specifications. The numbers of stator slots and magnet poles on the rotor were chosen to achieve the best winding factor, and the winding layout was determined accordingly. A one-dimensional magnetic circuit model of the middle motor was built, and its shape was optimized utilizing a multifunctional optimization system tool. Finally, the resulting design was verified and refined by a finite element analysis. A prototype of the middle motor was fabricated with a stator made of a soft magnetic composite and integrated with a cycloidal reducer. Experimental results show that the motor has a sinusoidal back electromotive force. Additionally, it is easily controlled by sinusoidal currents with acceptable torque and speed curves.
Highlights
Electric bicycles (e-bikes) have gained increasing attention as a means of personal transportation and part of an urban lifestyle [1]
The present paper proposes an optimal design of an axial-flux permanent magnet (AFPM) middle motor in a mid-drive unit on a pedelec
The performance of PM motors has been improved by the wide use of the flux-weakening method to extend the motor speed range. This can be achieved by estimating the middle motor torque versus speed (TN) curve, based on the theory of maximum torque per ampere (MTPA) and the flux linkage method [13] by finite element (FE) analysis
Summary
Electric bicycles (e-bikes) have gained increasing attention as a means of personal transportation and part of an urban lifestyle [1]. The present paper proposes an optimal design of an axial-flux permanent magnet (AFPM) middle motor in a mid-drive unit on a pedelec.
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