Abstract
A low cogging torque and torque ripple are the most important qualities for electric power steering (EPS) motors. Therefore, various design methods are employed to obtain EPS motors with these qualities. In this study, a novel design method for the pole shape was developed by adopting a cycloid curve to realize the desired qualities of EPS motors without reducing the torque. An evaluation index ( $\delta q$ ) was used to design the pole shape of the magnet and to compare the pole shape between the proposed method and the conventional method. The proposed and conventional methods were applied to existing machine designs, and their performances were compared using a finite-element analysis (FEA). The results of the FEA and prototype tests indicated an improved motor performance for the proposed method.
Highlights
Electric machines are widely used for a variety of applications
Park et al.: Magnet Shape Design and Verification for surface permanent magnet synchronous machine (SPMSM) of electric power steering (EPS) System Using Cycloid Curve electric motor, cycloids have been applied to magnetic gears, having the function of increasing the torque using an electromagnetic force instead of a mechanical contact, as in the case of a conventional speed reducer [14]–[16]
The cogging torque and torque ripple are the key qualities of a motor for enhancing the control precision and driving sensibility of vehicles, robots, and other devices
Summary
Electric machines are widely used for a variety of applications. Owing to its high efficiency and torque density, the permanent magnet (PM) motor is commonly applied to electric power steering (EPS) systems [1], [2]. The second method involves applying a pole-shape design of a magnet in an SPM and a rotor core in an internal PM. This method reduces the back electromotive force (EMF) by implementing an air-gap flux wave as a sinusoidal wave [10]–[13]. Park et al.: Magnet Shape Design and Verification for SPMSM of EPS System Using Cycloid Curve electric motor, cycloids have been applied to magnetic gears, having the function of increasing the torque using an electromagnetic force instead of a mechanical contact, as in the case of a conventional speed reducer [14]–[16]. The motor performance, including the cogging torque and torque ripple, was compared for cycloid and conventional curves. A cycloid curve can be classified into six types, as shown in Table 1, according to the position of the tracing point on the rolling wheel [17]
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