E-Mobility Engineering 016 l Aurora Powertrains eSled dossier l In Conversation: Thomas de Lange l Automated manufacturing focus l Torque sensing insight l Battery Show Europe 2022 report l Sodium batteries insight l User interfaces focus

Modularity and automation are done to make their job easier, not to suggest that untrained personnel should try their hand at HV engineering.” Between the cells and modules, the BMS measures the voltages, currents and temperatures of the cells via cell sensor/supervision circuits (CSCs). These are programmed as slaves to the master BMS and contain passive balancing circuitry to average out cell-level voltage discrepancies. Each module has a CSC board of its own, which communicates with the BMS using an isoSPI protocol. Temperature discrepancies meanwhile are, as discussed, handled via the BMS’ adjustments of the thermal management system. Typically, the BMS directs the foil resistors to increase the individual module temperatures until they are at roughly the same level, with perhaps a little emphasis on the outermost modules, as the central ones suffer a slightly higher heat concentration owing to their position. The BMS then adjusts the liquid circuit’s pump to balance the heat across all the modules at once or decrease the temperatures across the board, raising or lowering the pump’s power as needed. “During development, we installed sensors throughout the battery modules to measure voltages, currents, temperatures, charge and discharge rates, all to check and prove the results of our battery simulations,” Haavikko says. “We’ve used these and other extensive test data to develop some predictive mapping to proactively adjust the thermal management systems and prevent faults like overheating occurring, both in the battery pack via the BMS and in the rest of the powertrain via the VCU.” Vehicle control unit The VCU is an off-the-shelf Bosch Rexroth BODAS controller, specifically the RC10-10 series 31 model, without C, C++ and Qt. We’ve also written the drivers ourselves so that we can swap new components in as we please,” Autioniemi says. “We’ve designed the network architecture with three separate CAN buses in order to prevent errors through crosstalk between subsystems. One is for the drivetrain systems such as the inverter and motor, a second is for power distribution systems such as the BMS and the OBC, and the third is for the driver’s instruments and diagnostics.” Charging systems The VCCU uses a computer board of proprietary design. Its charging control software has been written from the ground up in C and C++, in compliance with all major EV charge controller standards including DIN 70121, ISO 15118-20, SAE J3068 and IEC 61851 (including Annex D support). It communicates with the OBC’s Electric Vehicle Supply Equipment standard interface using PWM, PLC or LIN-CP, the latter two having been selected for future-proofing purposes. “The VCCU is something we plan to launch as a standalone product in any hardware modifications. Aurora says it is very satisfied with its design and capabilities, especially its I/Os for controlling and monitoring the eSled’s powertrain subsystems, which Autioniemi explains are especially critical in making the snowmobile run smoothly and responsively. The controller has 20 power outputs, 10 of which can be current-controlled, nine low-power signal output pins and 46 multi-functional input pins. It also comes with four independent CAN bus interfaces, a LIN interface and two independent sensor voltage supplies. Standard-issue embedded features include I/O fault detection, program sequence monitoring and closed-loop control of PWM solenoid currents, meaning they do not depend on supply voltage and temperature levels. Via CAN, the VCU monitors incoming data from the BMS, VCCU, inverter, motor, onboard charger, the driver’s controls at the handlebars, their instrument cluster and the DC-DC converter, with the bulk of command outputs going to the first three of these. “We’ve programmed the VCU in Codesys, and lower-level controller boards for each of those subsystems in ;Oe Iattery connectors from module to module are made as Åat as possible to help shape the pack geometry as needed Winter 2022 | E-Mobility Engineering 29 Dossier | Aurora Powertrains eSled