44 integration of motor cooling systems with the thermal management of other critical components, most notably the battery and the power electronics. This holistic approach presents both substantial benefits and considerable engineering challenges. Integration pros and cons Grayson Thermal Systems’ Stephens underscores the economic and weight advantages of integrating cooling circuits: “Integrating motor cooling with other circuits really makes a better cost/ weight trade, as there are fewer systems to control.” He points out that the non-constant nature of heat rejection from various components allows for system sizing based on average usage, optimising efficiency. However, a key challenge lies in accurately understanding diverse vehicle use cases to strike the right balance in system capacity, avoiding both undersizing and unnecessary oversizing. A fundamental hurdle in integration arises from the disparate temperature requirements of different components. As Stephens notes, “power electronics coolant can run at hotter temperatures of up to approximately 60 C; battery coolant requires colder temperatures of up to approximately 30 C.” This temperature differential prohibits direct connection of these circuits. Nevertheless, innovative integration strategies, such as Grayson’s chassis-mounted complete thermal management system (CTMS), do offer solutions. The CTMS intelligently manages heat transfer across power electronics, the traction motor, battery coolant, and cabin HVAC system, optimizing energy flow and reducing refrigerant usage, Stephens says. Parker Lord’s Wyman emphasises the synergistic benefits of including the motor in a shared cooling loop, particularly when utilizing potting techniques to connect end windings to a liquid-cooled housing. This integration “allows the motor to get maximum cooling from the same cooling system, which may reduce weight and complexity versus a non-integrated system,” he says. Uppuluri highlights the complexities of physical integration, especially the tightly packaged arrangement of the inverter, motor, and gearbox. Heat transfer occurs bidirectionally between these components, necessitating careful thermal management considerations. Furthermore, the heat extracted from the motor by the coolant needs to be managed effectively within the broader vehicle thermal architecture, the expert from Siemens says. He explains that the existence of multiple cooling systems with distinct temperature ranges in hybrid vehicles−a hot loop for the engine, a medium-temperature loop for the motor, and a very low-temperature loop for the battery−often mandates the integration of a chiller. While these loops operate at different temperatures, the capacity for strategic exchange of heat between them is crucial for overall system efficiency, such as warming a cold battery using waste heat from the motor or engine, he says. This necessitates sophisticated valving and control systems to direct heat flow based on operating conditions. “Thermal management has to be considered at vehicle level, encompassing the battery, e-motor and power electronics as well as the air conditioning needs for cabin comfort,” according to Valeo’s Herman. What she terms global optimisation yields several crucial benefits, including enhanced system efficiency and energy optimisation by ensuring all heat-generating components operate within their ideal temperature ranges, preventing wasteful overcooling or undercooling. Integrated thermal management also contributes to improved component lifespan and reliability by preventing hotspots and enabling predictive thermal control. Furthermore, combining cooling loops can lead to packaging and weight efficiencies by removing redundant parts and reducing space usage. During high-demand scenarios like fast charging or hard acceleration, an integrated approach avoids thermal bottlenecks that could limit performance or trigger safety shutdowns, she adds. However, achieving effective thermal system integration presents significant challenges. Conflicting thermal needs, with batteries preferring temperatures cooler than those suitable for Insight | Motor cooling May/June 2025 | E-Mobility Engineering The single-fan, 6 kW capacity CP-6082-100 module is part of a family of motor and power electronics cooling systems for electric bus and coach, off-highway, commercial and specialist vehicles (Image courtesy of Grayson Thermal Systems)
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