Hybrid Magnetic/Foil Bearing System for an Oil-Free Thrust Bearing Test Rig

Abstract

A novel, high-speed, high temperature, oil-free, foil thrust bearing test rig has been developed with a critical element being a double-acting, active magnetic thrust bearing. The magnetic thrust bearing is used to react against loads applied to the foil thrust bearing under test. The magnetic bearing has the capability of reacting against thrust loads of up to 2224 N (500 pounds) at speeds to 80,000 rpm, while the rotor is supported by foil journal bearings. Two issues that are especially challenging for this test rig are magnetic material selection and the electronic control system. The magnetic material selection is critical due to the high centrifugal stresses that occur at 80,000 rpm. The electronic control system must handle the non-linear variation in stiffness and damping that is seen by the magnetic thrust bearing as the foil thrust bearing is loaded, as well as maintain rotor system stability as the foil bearing is purposefully overloaded to the point of failure to discover maximum load and performance capabilities. This paper describes the design of the active magnetic thrust bearing, the material selection process, and the development of a digital signal processor based control system. Typical experimental data obtained during operation of the test rig will also be presented.