Objectives and Results

Development and validation of heat transfer models for the oil spray cooling of electrical machines for hybrid electric vehicles (HEV) and battery electric vehicles (BEV).

Contents and Approach

In electrical machines, the end windings are only poorly connected to a cooling jacket, which results in an uneven heat dissipation and thus in "hot spots". Compared to traditional air cooling approaches, oil spray cooling offers an improvement in heat dissipation of 150% - 400%. This results in an even heat dissipation and prevents the formation of "hot spots" and thus punctual material fatigue.  To determine the heat transfer coefficients from the oil spray to the end windings, various influencing parameters (number of nozzles, arrangement, volume flow, ...) are investigated. The resulting knowledge of the heat transfer coefficients is then transferred into a thermal model of an electric motor in order to be able to model an electric motor with oil spray cooling.