28 “For us, this was a good thing, as it meant the project represented an opportunity to work towards what we’d like to be a range of efficient e-motors from 30 kW [<60 V] to over 300 kW [800 V], all with scaled versions of the same active parts – stators, rotors and so on,” recounted Adrien Maier, project engineer at EREM. Meanwhile, the consortium identified a three-phase inverter solution that could ensure minimum performance expectations in the packaging constraints required. This is a 15 kg unit supplied by Punch Powertrain, measuring 328 x 298 x 134 mm and running on silicon carbide transistors. The powertrain development process started in Simcenter Amesim, Siemens’ vehicle system-level simulation software, first using the initial state of the pre-retrofit snow groomer with its diesel engine to set a series of references, and then using the snow groomer’s finalised architecture to define the specification for each powertrain system and component. This work was first performed by GCK Mobility, with tests and data acquisition on the initial vehicle, and then by IFPEN for further simulation and definition. Those simulations were used to set targets for the components to be developed, as well as to model for the optimal levels of energy management in the EV. Further industrial, environmental and cost constraints were added as inputs to design optimisations for the electric motor. Critical targets for the motor were that it could fit into a space of 390 mm in diameter by 360 mm in length, while providing 320 kW of shaft power and 850 Nm of torque, as well as running at speeds up to 8000 rpm. Additionally, the motor and inverter were to have a collective weight of less than 200 kg. Further key requirements were that the powertrain needed to be able to run off a 700-825 V DC power supply (per the battery bus), and safely deliver its performance targets in ambient temperatures, ranging from -25 C to 50 C, while also functioning at altitudes of up to 4000 m. This latter quality poses a safety challenge to higher-voltage powertrains due to the greater risk of partial discharge, a dielectric phenomenon in which some localised portion of insulation in a HV system environment is electrically stressed to the point that it breaks down. At high altitudes, the low air density enables air particles to travel longer distances before colliding with other particles, meaning they accelerate for longer periods and collide with much more kinetic energy than at lower altitudes with higher air densities. This facilitates higher rates of ionisation than at low altitudes, and those higher rates of ionisation directly lead to higher rates at which conductive paths can form across air gaps inside HV wire harnesses. More conductive paths mean more localised electrical stresses, resulting in more insulation ageing and partial discharges, making electrical safety a huge point of concern for the stator design. Lastly, the powertrain’s power efficiency was important for meeting targets on maximising the vehicle’s operating time, and thus limit the rate at which the battery cells and H2 tanks would be drained during operations. Subsequent development of the motor was predominantly undertaken by aforementioned project partners IFPEN and EREM, with their first feasibility investigations starting in early 2021. “We took significant design influence from the 400 V, 147 kW e-motor previously developed for the Lancia Delta, although a lot of work was needed to scale it up several times over to be big enough for the snow groomer,” Maier says. From late 2021, until the design freeze in March 2022, IFPEN focused on active part optimisations, as well as material and cooling system evaluations, while EREM concentrated on mechanical assembly designs, and evaluations of production and assembly methods. “Fortunately, EREM’s stator-winding research led to a satisfactory solution to the partial discharge problem, but it is important to note this aspect is insufficiently covered for full-scale, The motor provides up to 320 kW of shaft power, 850 Nm of torque and speeds of up to 8000 rpm (Image courtesy of IFPEN) May/June 2024 | E-Mobility Engineering
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