Convective Heat Transfer Coefficients and Mechanical Loss Evaluation of Oil Splashing in Direct Cooled Electrically Excited Hairpin Motors

There in an increasing trend in the use of the direct oil cooling in electric motors for automotive because of the increasing demand of high power/torque density as well as overload capability. One of the most immediate solution is to fill the housing with some oil level and benefit of the heat transfer from the oil splashing. The mechanical losses coming from the rotor rotation are well known and they represent a significant challenge, especially at high speed and high oil level. Therefore, the derivation and prediction of these losses have not been properly investigated leading to a lack in the current literature. Moving Particles Simulation (MPS) method is used in Particleworks to calculate the mechanical losses caused by the oil viscosity and convective heat transfer coefficients (HTC) are extracted for a 250 kW Electrically Excited Synchronous Machine at different speeds and oil levels.