42 May/June 2025 | E-Mobility Engineering E-motor cooling technology is evolving rapidly, as Peter Donaldson finds out Cool motive force Discussions on thermal management in electric vehicles (EVs) usually focus on the battery because of the risk and potential consequences of thermal runaway. However, keeping motors comfortable in terms of temperature is also crucial to the performance, reliability, efficiency and longevity of an EV’s powertrain. E-motors generate significant heat from resistive losses in the windings, hysteresis and eddy current losses in the stator and rotor cores, and friction in the bearings. Furthermore, power and torque outputs, duty cycles, environmental conditions and location within the vehicle can also combine to make the process of removal of unwanted heat surprisingly complex. Over the past five years, however, the landscape of e-motor cooling technologies has witnessed significant advances. Cool trends One of the most notable trends is the integration of multiple coolant circuits. Nathan Stephens, chief engineer and head of technology at Grayson Thermal Systems, emphasises that, “The drive to connect EV motor coolant circuits to other coolant loops such as those for power electronics and power distribution into a complete thermal management system is one of the most significant advancements for increasing efficiency and performance.” This integrated approach allows for intelligent heat management, where waste heat can be employed strategically for other purposes. Stephens highlights that such systems “can now harvest the heat generated from EV traction motors and redirect it to the inside of a vehicle to improve passenger comfort.” This reduces reliance on energy-intensive auxiliary heating systems such as heat pumps or electrical heaters, leading to improved energy efficiency and extended driving range, particularly in colder climates. Parker Lord has focused on enhancing heat transfer at the component level through innovative material science. Business development manager Eric Wyman, points to the significant impact of “end-winding potting with thermally conductive two-component pottants.” This technique involves encapsulating the motor’s end windings with a specialized material that exhibits high thermal conductivity, facilitating a more efficient pathway for dissipation of heat from the windings to the stator housing. Wyman explains that “ensuring efficient cooling of the motor can allow for smaller motors with higher output, saving weight and expense,” because effective thermal management permits higher power densities without exceeding critical temperature limits. This reduction in the size and weight of the motor directly contributes to improved vehicle efficiency and handling. Smaller fluid measures Sudhi Uppuluri, director of automotive and transportation industry strategy, simulation and testing at Siemens, notes progress in the sparing use of coolants: “One of the key advances that I’ve seen In this EDU dielectric oil cools the rotor and stator before passing through a heat exchanger where a water/glycol mix absorbs it and takes it to a radiator (Image courtesy of Valeo)
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