Numerical Study of Oil Jet Cooling in Electric Traction Motors with Hairpin Windings

Abstract

Hairpin winding technology, combined with direct oil jet impingement cooling, is a viable solution known to increase volumetric power density and efficiency in the next generation of traction motors. However, the coolant fluid interaction with the complex winding geometry has not yet been fully examined; specifically, with the use of high-fidelity CFD simulations. Thus, the present work investigates the radial and axial oil impinging jets in a hairpin winding motor using multi-phase simulation. The study first analyses power losses and temperature distribution of the motor under the Worldwide Harmonised Light Vehicle Test Procedure (WLTP). Next, the performance of axial and radial jet impingement is numerically analysed by considering the fluid flow. Finally, the two configurations are compared in terms of their oil film formation rate. The results indicate that the maximum power losses observed in typical driving conditions are considerably lower than the maximum losses predicted for the complete operational region of the motor. Moreover, the axial impinging jet shows a higher oil film formation rate compared to a radial jet impingement configuration within the examined conditions.