Rotordynamics of a Rotor Supported by Foil Bearings Under Various Housing Excitation

Abstract

Abstract Proton Exchange Membrane (PEM) Fuel cell Systems (FCS) are rapidly growing technology in the field of electric cars, buses, and trucks. In such applications, a motor-driven oil-free air compressor is one of the most critical auxiliary subsystems for the FCSs. Foil bearings are the perfect choice as oil-free bearings for FCS compressors due to high rotordynamics stability and shock-resistance. The platform of a motor-driven oil-free compressor can also be used as an electric turbocharger for traditional internal combustion engines. All electromechanical subsystems for electric vehicles must satisfy vibration endurance requirements following ISO 16750-3:2012, characterized by certain g-loading at specific frequencies. FCS air compressors also follow the same ISO 16750 standard. For the compressor to satisfy ISO 16750 requirement, detailed rotordynamics simulations with externally excited compressor housing under certain g-loading are essential to design the foil bearings considering the static and dynamic loads to the bearing and rotordynamics stability. The main objectives of the current research are 1) to develop a six degree of freedom (6-DOF) dynamic model of the rotor supported by foil bearings under external excitation to the compressor housing, 2) to simulate linear and non-linear rotordynamics of the compressor rotor supported by two radial foil bearings, and 3) to provide appropriate design guideline such as bump stiffness and axial length of the foil bearings. The simulations show that the rotor is stable for both under single frequency excitation and simultaneous excitations of all the frequencies in ISO 17650 standard. 4-DOF modal analyses were applied to identify natural mode of the system under the housing excitation.