Experimental Investigation of Oil Jet Cooling in Electrical Machines With Hairpin Windings

Oil jet cooling and hairpin windings have become popular in electrical machine design for modern electric vehicles. In recent years, these two technologies are often combined and can be found in many commercial products. The highly effective cooling capability of oil jets and the high thermal conductance of hairpin windings greatly benefit the machine performance metrics. However, published quantitative literature on this topic is relatively scarce. This article presents experimental results and practical insights of oil jet cooling on the end region of hairpin windings. Temperature distribution, heat transfer coefficient, and cooling efficiency are all investigated. Consistent temperature profiles are observed throughout the range of flow rates. Moreover, the effects of using different types of oil and inclination angles are researched as well. Analysis of variance indicates that these two factors affect various aspects of the oil jet cooling’s performance. Results are also compared against data obtained from previous studies on oil spray cooling. This study can help engineers implement oil jet cooling in machine designs with hairpin windings.