Noise reduction of a fan motor with fluid dynamic bearings by utilizing magnetic pulling force

Abstract

We identified a noise source of a fan motor supported by fluid dynamic bearings for various mounting angles. We experimentally confirmed that the flying motion of the rotor increases the noise of the fan motor that utilizes fluid dynamic bearings. In order to predict the position of the air-oil interface according to mounting angle, we used the equilibrium equation of force as well as a volume equation that takes into consideration the groove area. In addition, the dynamic coefficients of the fluid dynamic bearings were calculated by solving the Reynolds and perturbation equations, and a stability analysis was carried out by calculating the critical mass using eigenvalue analysis. Furthermore, we investigated that the flying height according to increased mounting angle decreases the stability. As a result, an improved design using an unbalanced magnetic force to prevent the flying height was proposed and manufactured. Finally, we validated that the proposed design reduces noise of the fan motor by comparing the flying height and noise of convention model to those of the proposed model.