Experimental Investigation of a Novel Direct Rotor Cooling Method for an Interior Permanent Magnet Synchronous Machine

A measurement setup is designed and constructed to experimentally investigate the thermohydraulic performance of a novel direct rotor cooling method for an interior permanent magnet synchronous machine, where oil is pumped through weight saving channels of the rotor iron close to the magnets. The setup consist of a stationary rotor assembly where heat is dissipated in an aluminum sleeve surrounding the rotor outer surface. Measurements are performed for different oil inlet temperatures, flow rates and heat losses. It is shown that tangential temperature variations can be neglected and axial variations are as expected. The conductive resistance within the rotor assembly is similar for each measurement point as the differences are within the measurement uncertainty. The convective resistance decreases with an increasing flow rate, inlet temperature and heat dissipation. From correlations in scientific literature, it is expected that the convective resistance will further reduce with increasing rotational speed of the rotor. A comparison of these results to a standard hollow shaft cooling method shows a great potential of the novel direct rotor cooling method to further increase the power density of electric machines.