Low-Cost BLDC Claw-Pole Motor Design for Fan Applications with Reduced Cogging Torque and Balanced Axial Forces

The implementation of skewing to reduce the cogging torque of brushless permanent-magnet motors usually induces axial magnetic forces which can not only cause noise but also decrease the bearing system's lifetime. This paper proposes an unconventional outer-rotor BLDC claw-pole motor design for sub-fractional horsepower fan applications. Owing to the proposed V-shaped claw-poles, the cogging torque can be reduced through skewing but, at the same time, the axial magnetic forces are balanced. As opposed to other cogging torque reduction and axial force compensation techniques, the proposed design improvements can be included at no increase to the manufacturing cost since they can be implemented at the stage of punching and deep-drawing the stator steel sheet parts. This is essential for cost-driven automotive auxiliary drive applications such as LED headlight fans, sensor blowers, or seat ventilations. The proposed designs are investigated by means of 3-D finite element analyses and measurements using a rheometer. The findings show that the proposed claw-pole shapes can achieve both cogging torque reduction of about 50% and axial force compensation. This is illustrated for a 5500rpm 1W example case motor as part of a low-cost fan application.