Auxiliary Bearing Design and Rotor Drop Analysis of High Speed Motor Compressor/AMB System

This paper presents the auxiliary bearing design and rotor drop analysis of a single stage motor-compressor. The auxiliary bearing design consists of double row, ceramic ball bearings with cages and with high axial preload. The axial preload is provided by Bellville washers which also provide axial spring stiffness and damping. The auxiliary bearings are laterally mounted on tolerance ring wave springs which provide support stiffness and damping to help absorb the impacts due to the rotor drop. A nonlinear transient rotor dynamics and auxiliary bearing modeling code has been utilized to carry out the rotor drop analysis. The very large mathematical model includes all of the shaft degrees of freedom, the auxiliary bearing races and all of the balls, as well as the Bellville washers and the wave springs. The rotor orbits, the inner and outer race orbits and the ball displacements are all evaluated versus time during the drop. The orbits were found to simply oscillate in the bottom of the auxiliary bearings and do not go into large orbit whirls. Also, the auxiliary bearing maximum compressive stress levels were evaluated and found to be well below the material yield stresses indicating long auxiliary bearing life in terms of number of drops without damaging the auxiliary bearings.