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

a carbon fibre-reinforced composite material designed in principle for mounting key components, and simulated in SolidWorks to optimise for material thickness and structural stiffness, with some other covers of plastic for the front end,” Haavikko says. “And regarding the front suspension, both our lower and upper A-arms share the same geometry, allowing the camber and caster angle to remain constant for the entire travel of the front suspension. A-arm pivoting axles point inwards to reduce any variations in ski stance – that is, the distance between the skis – during front suspension travel. That is a very undesirable variation, also known as ‘scrub’, so minimising it was critical. “Having the A-arm pivoting axles point inwards also lowers the eSled’s point of contact with the ground and its centre of mass during shock absorption, more so than Bombardier’s configuration typically would. That means more efficient shock absorption, and thus improved rider comfort.” The exoskeleton has been designed with maximising strength-to-weight and optimising torsional stiffness as key targets. The former was vital to ensuring the eSled’s 270 kg gross weight, which is roughly equivalent to that of a conventional snowmobile. “The overall chassis is a combination of aluminium and composite,” Haavikko notes. “The composite structure is made in two parts by hand lay-up using a clay mould, and are then laminated together. We’re working on metal moulds that we’ll later use to produce the chassis pieces as sheet-moulded compounds [SMCs].” High-strength steel mould tooling will ensure the long-term surface quality of the parts being produced, and the SMC approach is being taken as it is a high strength, high quality, lightweight and cost-effective route to manufacturing parts for powersport-type applications such as snowmobiling, where optimising range is crucial. The riding ergonomics are also designed for greater freedom of movement, and hence comfort, thanks to the omission of mufflers, coverings and fairings. Haavikko adds that this makes it easier to use the banked turning system as well as carry out aggressive or ‘sporty’ manoeuvres, for anyone so inclined. Internal layout Beneath the composite and plastic outer covers of the eSled is an onboard charger and a fast DC charging inlet. These connect via high-voltage DC (typically from 120 to 310 V, configurable according to need) to a power distribution unit (PDU), a power measurement board and an isolation and insulation monitoring device, which together gauge, make safe and distribute the HV power to the battery modules. Energy stored in the battery is then again sent to the PDU to be distributed to the three-phase AC inverter for the motor, and to a 12 V DC-DC converter for powering low-voltage systems including a central VCU, a vehicle charge control unit (VCCU) and driver control and interfacing systems. Signals travel throughout the LV network of computers, control instruments and sensors for driving and charging by way of CAN bus, which links most of the powertrain save for an isolated, dedicated CAN bus running from the BMS to the battery cells and sensors. The weight distribution of the internal componentry has been highly centralised. The batteries – as ever, the heaviest single component in this EV – are mounted to the exoskeleton and positioned under the front of the seat, and the integrated motor-inverter drive unit is positioned beneath and slightly forward of the batteries. “Keeping the centre of mass central is really critical for making riding a predictable and low-stress affair,” Haavikko explains. “For added rider safety, this component layout keeps the batteries and drive units protected from impacts, as it’s the safest place for them to be during a crash. Obstacles come from the front, but after a jump it tends to land on its rear.” The drive unit sits slightly to the right of centre, and to the left are the onboard charger, DC-DC converter, VCU and VCCU. Snow-proo ing the powertrain Since there is little data for virtually recreating a lifetime spent in -40 º C near-blizzard conditions, let alone the Some key suppliers Connectors: Amphenol Cable harnesses: Amphenol Cable harnesses: Molex Cable harnesses: TE Cable harnesses: GEP Cable harnesses: Aptiv Coolant pumps: Bosch Cooling plates: Heatraplates VCU: Bosch Rexroth Aurora has invented a suspension system that greatly enhances rider comfort as well as range, partially by enabling weight reduction through better load support 24 Winter 2022 | E-Mobility Engineering