Study of ironless permanent magnet devices being both a coupling and an axial bearing for naval propulsion

This paper describes the study of an original permanent magnet device. This device works as both a coupling and as an axial bearing. It can be particularly useful in naval propulsion application to transmit the torque without any contact between a motor axis and the propeller and to maintain the propeller in its axial position, compensating the axial force related to thrust. Two kinds of devices are studied for this type of specification. The first corresponds to the classical structure of cylindrical air-gap coupling. The second is an original structure where pairs of rings of axially magnetized magnets are stacked on each rotor. The computation of the behavior of the device (torque and axial force) is done using a semi-analytical method based on magnetic charge theory. This method allows a very fast calculation of the performances of the devices. This study shows the interest of the stacked structure for this type of application.