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http://dx.doi.org/10.9725/kts.2019.35.2.123

Rotor Coastdown and Acceleration Performances of High-speed Motors Supported on Ball Bearings and Gas Foil Bearings  

Mun, HyeongWook (Graduate School, Dept. of Mechanics and Design, Kookmin University)
Seo, JungHwa (Graduate School, Dept. of Mechanics and Design, Kookmin University)
Kim, TaeHo (School of Mechanical Engineering, Kookmin University)
Publication Information
Tribology and Lubricants / v.35, no.2, 2019 , pp. 123-131 More about this Journal
Abstract
This study characterizes the coastdown performances of two small electric motors supported on high-speed ball bearings (BBs) and gas foil bearings (GFBs), and it predicts their acceleration performances. The two motors have identical permanent magnetic rotors and mating stators. However, the shaft of the GFBs has a larger mass and polar/transverse moments of inertia than that of the BBs. Motor coastdown tests demonstrate that the rotor speed decreases linearly with the BBs and nonlinearly with the GFBs. A simple model for the BBs predicts a constant drag torque and linear decay of speed with time. The test data validate the model predictions. For the GFBs, the hydrodynamic lubrication model predictions reveal that the drag torque increases linearly with speed, and the speed decreases exponentially with time. The predictions agree very well with the test data in the speed range of 100-30 krpm. The boundary lubrication model predicts a constant drag torque and linear decay of speed with time. The predictions agree well with the test data below 15 krpm. Mixed lubrication occurs in the speed range of 30-15 krpm. Rotor acceleration performances are predicted based on the characteristics of deceleration performances. The GFBs require more time to reach 100,000 krpm than the BBs because of their larger shaft polar moment of inertia. However, predictions for the assumed identical polar moment of inertia reveal that the GFBs have a nearly identical acceleration performance to that of the BBs with a motor torque greater than $0.03N{\cdot}m$.
Keywords
high speed motor; gas foil bearing; ball bearing; coastdown; acceleration;
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