The Oil Spray Cooling System of Automotive Traction Motors: The State of the Art

With growing interest in green technologies and sustainable transport, hybrid and pure electric powertrains are attracting a lot of attention. According to demanded metrics, such as lightweight and high-power density motors, these offer clear motivation to develop advanced thermal management methods and integrate them with conventional cooling approaches. The oil spray cooling method is one of the latest cooling methodologies integrated with the conventional cooling approaches. Therefore, this article provides a comprehensive study on the oil spray cooling approach for electrical motors utilized in electric vehicle (EV) traction application drives. The objective is to provide the reader with a picture of the state of the art regarding the opportunities, challenges, and offered solutions for the cooling requirements in EV motors. In addition, this article presents the guidelines for selecting the appropriate spray nozzles and coolants as well as estimating their performance, spray characteristics, and heat transfer coefficient (HTC) during the design period. Besides, various closed-loop systems of spray cooling approach, including refrigerants as a coolant, low viscosity liquid coolant with high boiling temperature, and high viscosity lubricant oil as a coolant, are discussed with the pros and cons of each system being compared. Moreover, real-life examples of this method, applied in the latest automotive traction motor prototypes, have been described and evaluated. Finally, the performance of different schemes is addressed.