Experimental Evaluation of Axial Multi-nozzle Impinging Oil Jets for End Winding Cooling in Electric Vehicle Hairpin Traction Motors

Impinging oil jet cooling and hairpin winding technologies are increasingly used in modern electric vehicle traction motors due to their potential for high thermal performance. While recent studies have shown that axial (parallel to the motor shaft) oil jets can improve winding coverage in single-nozzle configurations, the literature still predominantly focuses on radial (perpendicular to the motor shaft) impinging jet arrangements. This study presents an experimental investigation of axial multi-nozzle impinging oil jet cooling performance for hairpin windings. The research systematically analyses temperature distribution, heat transfer coefficients, cooling efficiency, and overall system performance across configurations ranging from 12 to 90 nozzles. The effects of nozzle diameter, array setup, and motor power losses on cooling effectiveness are also examined. Finally, the performance of the axial multi-nozzle impinging jet cooling system is compared with conventional water jacket and axial spray cooling systems. Results indicate that impinging jet cooling can nearly double the maximum current density achievable in the motor design compared to water jacket cooling systems, while providing thermal performance comparable to spray cooling systems at a lower pump power and pressure levels.