Abstract: Apparatus and methods for providing a pre-determined axial thrust force profile for use in a rotating machine that includes a magnetically permeable rotor with first and second surfaces and a generally perpendicular shaft is disclosed. One or more bearings support the shaft and a coil induces flux in the rotor. First and second pole pieces disposed adjacent to the first and second surfaces define first and second gaps. A series magnetic circuit including the pole pieces, the gaps and the rotor carries flux generated by current flowing in the coil. Pole pieces and gaps provide substantially similar reluctance in both gaps. Magnetic saturation characteristics of a series magnetic circuit may provide a pre-determined axial force profile as a function of coil current. A first magnetic saturation characteristic may provide a maximum axial force at a first current magnitude. A second magnetic saturation characteristic may provide a lower axial force at a current greater than the first current.

Abstract: Apparatus and methods for providing a pre-determined axial thrust force profile for use in a rotating machine that includes a magnetically permeable rotor with first and second surfaces and a generally perpendicular shaft is disclosed. One or more bearings support the shaft and a coil induces flux in the rotor. First and second pole pieces disposed adjacent to the first and second surfaces define first and second gaps. A series magnetic circuit including the pole pieces, the gaps and the rotor carries flux generated by current flowing in the coil. Pole pieces and gaps provide substantially similar reluctance in both gaps. Magnetic saturation characteristics of a series magnetic circuit may provide a pre-determined axial force profile as a function of coil current. A first magnetic saturation characteristic may provide a maximum axial force at a first current magnitude. A second magnetic saturation characteristic may provide a lower axial force at a current greater than the first current.