Experimental evaluation of magnetic suspension characteristics in a 5-axis active control type bearingless motor without a thrust disk for wide-gap condition

Bearingless motors are characterized by integration of electrical motors and magnetic bearings. These motors can realize magnetic suspension of rotor shafts without mechanical contacts. Recently, non-contact canned motor pumps without expendable parts by means of using these motors have been vigorously developed. In these pumps, the large magnetic gap length of about 5 mm or more is required of the bearingless motors, because fluid flows into the gap. It becomes difficult to generate sufficient suspension force for magnetic suspension, as the magnetic gap length is increased. Therefore, a novel structure of a 5-axis active control type bearingless motor which can generate the sufficient suspension force under wide-gap condition has been proposed by the principal authors. In general, thrust disks with large outside diameters are used in thrust magnetic bearings. However, in the canned motor pump application, rotational speed is limited to prevent cavitation caused by the large thrust disks. Accordingly, the proposed novel structure is equipped with a cylindrical rotor instead of the large thrust disk, and can generate sufficient suspension force in the axial direction, also. This paper introduces magnetic suspension characteristics of the proposed novel structure with experiments.