E-Mobility Engineering 017 l ECE Doosan electric excavators dossier l In Conversation: Matt Faulks l Battery testing focus l Battery Show North America 2022 report l Ariel Hipercar digest l Cathode materials insight l Thermal management focus

is therefore becoming an increasingly complex energy management issue, but the fundamental functions of an EV depend on it.” A significant advance in heat transfer materials that also affects battery pack architecture is the development of dielectric fluids that are in direct contact with the cells and their electrical connections. One specialist we consulted says a battery pack with cells immersed in a dielectric but thermally conductive fluid can keep cell temperatures within an optimal range more effectively than indirect cooling using conventional fluids, even with rapid charging and exuberant driving. He adds that this also protects the cells from degradation, helping to enable fast charging and longer battery service life. “We have also shown that dielectric thermal management fluids are effective at preventing thermal propagation should a single cell go into thermal runaway,” he says. Architectural e ects The growing demands of thermal management are affecting the way the architectures of powertrain subsystems and of vehicles as a whole are designed. The fluids specialist notes that efforts to maximise power and energy density have led to the need for aggressive thermal management. He says EV traction inverters and power converters for example are designed with wide-bandgap semiconductors that operate at high temperatures, while the effort to increase range is pushing the adoption of higher energy densities in cell chemistries as well as battery pack design. “As a consequence, heat generation increases, and removing that extra heat becomes more challenging,” he explains. “Traction battery designs that maximise active material content, such as cell- to-pack, need direct cooling to ensure minimum thermal gradients. Traction motors designed to maximise the direct exposure of coil windings to the cooling media achieve significant improvements in power density.” The expert from our vehicle electrification specialist says that perhaps the biggest change comes in the form of subsystems integration. Customers are looking at how they can save by combining functions that have similar thermal management needs, such as charging and power conversion, into integrated power modules, for example. As this trend strengthens, powertrain developers are moving towards solutions in which the e-drive, inverter and onboard charger are integrated into a so- called smart box, the thermal interface materials specialist notes. “The main aim is to combine various functionalities at the controller and power level in comprehensive designs for lighter and more efficient operation,” he says. This both dovetails with and promotes the integration of previously separate powertrain cooling and air-conditioning circuits into unified thermal management systems. This seemingly ever-closer integration raises the question of how early in an EV’s design process its thermal management system should be considered in detail. The automotive powertrain specialist emphasises that because of the strong influence that thermal management has on the performance and service life of system components, as well as the required overall energy efficiency, it must be taken into account early in vehicle development. The fluids specialist emphasises that this should happen right at the start. “If the fluid is considered as a component in the same way as, say, a pump or a manifold, then a much more optimised design is possible,” he says. “Through this kind of co-engineering approach, any potential synergies that exist between the fluid and hardware can be readily exploited.” Faced with the different heat generation rates associated with components that find themselves packaged in close proximity, EV developers are ambient temperature – is lower. At the same time, while the heat input into the cooling system is less than that of a diesel engine, for example, the difference is not as great as might be assumed.” Electric motors, power electronics including inverters, and transmissions also generate waste heat and add to the number of components that need cooling. Further, the powertrain specialist notes, the collected heat must be used carefully in EVs, for example through the use of heat pumps in cold weather to avoid immediate loss of range. He adds that keeping battery temperatures within a narrow window to avoid loss of performance and even material damage is a challenge that can also apply to motors and power electronics. “As a result, conventional cooling systems are no longer sufficient,” he says. “Coupling the refrigerant circuit of the air-conditioning system to the overall thermal management of the drivetrain is therefore absolutely necessary. That applies all the more to situations that cause increased thermal stress, such as charging at very high rates.” He continues by saying that many components must be actively heated when cold, but the waste heat from the exhaust gases from an IC engine are missing, so heating processes consume energy. “Thermal management A two-sided IGBT chip cooler, an example of a thermal management component designed for compactness, enabling designers to make the most of available volume (Courtesy of Dana) January/February 2023 | E-Mobility Engineering 65 Focus | Thermal management