High Efficiency Permanent Magnet Eddy Current Couplings

Abstract

Permanent magnet eddy current coupling (PMECCs) are electromagnetic devices which can transmit power from a motor to a load with no electrical or mechanical connections. Resulting in vibration isolation, low maintenance, and overload protection. However, PMECCs which have been considered exhibit relatively lower efficiencies due to their torque slip- speed characteristics. Consequently, their industrial applications as power transmission devices has been limited, and have mostly been employed in braking and damping applications. Therefore, in this thesis an investigation into the design and analysis of PMECCs for power transmission applications, where efficiency is a primary requirement, is undertaken. An example application considered in this thesis is limited-slip differentials for electric vehicles. PMECCs topologies described in the literature have mainly employed plain copper sheets as a conducting material. Although, these were simpler and more cost effective solutions, they suffered from relatively lower efficiencies. Therefore, it is shown, that employing squirrel cage conductors embedded in softmagnetic cores, results in significant improvement in efficiency, even when less conductive materials, such as Aluminium, are employed. 3- dimensional finite element analysis is employed to design and analyse the different topologies of PMECCs, such as radial, axial single- and double sided, topologies. Furthermore, the theoretical findings are validated on a prototype, which consists of a single-sided radial field PMECC, with one rotor equipped with 14 permanent magnet poles, and the other equipped with squirrel cage conductor having 17 bars embedded in slots.