Experimental Feasibility Study of Conical Gas Foil Bearings for Oil-Free, High-Speed Motors

Abstract The increasing demand for oil-free air compressors in fuel cell systems has led to a growing interest in aerodynamic bearing technology. Gas foil bearings are a type of aerodynamic bearings characterized by a compliant foil structure known to enhance the damping properties of the bearings and increase their robustness with regards to manufacturing and alignment inaccuracies. Rotor systems supported by conventional gas foil bearings require at least two gas foil journal bearings and two gas foil thrust bearings. Conical gas foil bearings, with their ability to support both axial and radial loads, offer the advantage of fully supporting a rotor with only two bearings, effectively halving the number of required bearings. Despite their potential application in systems driven by electrical machines, no experimental investigations of conical gas foil bearings in such systems have been reported in publicly available literature. This study investigates the replacement of ball bearings with conical gas foil bearings in a high-speed synchronous motor, demonstrating their use under near-application conditions for the first time. To realize this replacement both the motor shaft and motor housing were modified. A part of this modification provides the ability to adjust the clearance of the conical gas foil bearings. The modified rotor system was successfully operated at rotational speeds exceeding 85,000 rpm. Throughout the operation the displacement of the shaft was monitored. The analysis of the frequency components of the occurring vibrations across different rotational speeds provides valuable insights into the rotor system’s performance and stability, confirming the feasibility of conical gas foil bearings for high-speed, oil-free applications.