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

coolant, making contact with as much of the cells’ surface area as possible to maximise heat transfer. This provides almost as much contact area as immersion cooling, but without the extra expense of a dielectric coolant and the mass of the extra liquid. “And because of the way the modules are built up we’re able to control their temperature equally,” he says. Heat on track Enabling the Hipercar’s battery to stand up to track use is a thermal management issue that also affects the whole powertrain. “You see it in any form of track environment; anyone who takes an EV on track knows they don’t do many laps before they tell you to stop,” Dowson notes. “You are balancing the size, weight and thermal management of the system for a track application, in particular for the battery,” he says. “If you want it to give ultimate performance you might want to preheat it to get the cells up to a good operating temperature to minimise the internal resistance, then you need to maintain the temperature within a narrow window.” PTC heaters in the thermal management circuit heat the coolant to bring the cells up to temperature, using valving to bypass the radiators so that heat is not rejected unnecessarily, he explains. The size, number and location of heat exchangers, however, are Ariel’s responsibility as the vehicle integrator. “We gave them a heat rejection target,” Dowson says. “We have also given them some guidance because it is something we have a lot of experience of across the group.” Designed to operate over an ambient temperature range of -20 to +45 ºC, the thermal management system is a multi- circuit heated and cooled water-glycol system that serves the cabin’s HVAC, battery pack, power electronics and drivetrain. Eight separate cooling circuits serve 10 systems. In building the battery, Cosworth takes advantage of the CSM technology’s modularity to shape the pack to meet the vehicle’s weight distribution requirements. “All the modules can be built in any length, so when there are shapes with which we have to conform we can adjust the lengths of the modules and stack them up,” Dowson explains. “With Ariel, because they were developing the chassis from scratch, we were able to put all the modules on a flat baseplate. Then we just needed a raised section in the middle, which would traditionally be a transmission tunnel, to carry all the electrical distribution systems, contactors, fusing and so on.” While minimising battery weight was extremely important, so was keeping the vehicle within the target price range, so Cosworth mostly avoided exotic materials. “We just have to do more simulation and finite element analysis on the construction of the system to ensure we have the right stiffness and weight balance,” Dowson says. “We use a little composite material in there, but we try to minimise that.” The battery casing is made from HyLight, a material based on a patented bonded aluminium composite but over the years that the vehicle has been in development we have seen an improvement in the power/energy balance of cells anyway,” he explains. The battery is built from cylindrical 21700-format lithium iron phosphate cells, which represent a conservative choice. “Through our cooling system and management of the battery we can extract the maximum performance from a fairly production-ready cell,” Dowson says. “Obviously we needed to end up with something that is not too exotic, otherwise the price point would be too high.” Initially, Cosworth made two versions of the battery, one with 18650 cells and the other with 21700s, eventually choosing the latter as it emerged that the format offers a better power/energy balance. The 62.5 kWh pack uses Cosworth’s Cylindrical Scalable Module (CSM) technology and provides a nominal voltage of 690 V, a maximum of 800 V and supplies a peak current of 1450 A. CSM modules contain a carrier that holds the cells and what Dowson describes as a conduit cooling system in the form of a soft-walled tube that conforms to the shape of each cell from two sides as it fills with liquid The Cat Gen range extender is a catalytic gas turbine generator with “negligible” emissions running on petrol. Future versions are slated to burn hydrogen (Courtesy of Ariel Motor) January/February 2023 | E-Mobility Engineering 53 Digest | Ariel Hipercar