Keep cool | Engineer Live

Electrifying heavy duty vehicles with a new high-voltage electrically driven fan.

Cooling strategies are still needed in electric vehicles (EVs), as although the internal combustion engine (ICE) has been replaced with an electric drivetrain, there are still several other systems that require cooling, such as the high-voltage battery, inverters and traction motors. Depending on whether it’s a battery EV (BEV) or a hydrogen-powered fuel cell electric vehicle, higher performance electric commercial vehicles need even more cooling capacity and airflow for the size of the braking resistors. Electric Motor Gearbox

BorgWarner’s eFan is a high-voltage cooling fan for electric commercial vehicles, consisting of a large diameter open or ring fan, an electric motor to drive the fan, and an inverter to convert direct current from the battery to the alternating current required to power the motor.

Five fan variants provide high-voltage options for both the low- and high-power vehicle segments. The top model – eFan 40 – is rated at 40kW to drive fans with diameters from 650-864mm. This is a high-torque machine that uses an axial flux motor as the power source. For lower demand applications, there are four smaller models – eFan 5, 10, 15 and 20 – rated at 5, 10, 15, and 20kW respectively. BorgWarner’s aerodynamic optimisation efforts reduced the torque requirement for these models, so they are driven by centrifugal flow motors.

Using these fans as a starting point, multi-dimensional numerical optimisation was used to fine-tune the fan geometry, and computational fluid dynamics (CFD) to validate the design in conditions simulating a typical customer installation. After CFD, a finite element analysis was carried out to check the fatigue strength. Fan acoustics were assessed by testing prototypes and using computer-aided aeroacoustics simulations. When the fan design was completed, the CFD calculations from the optimisation process were used to specify the electric motor and the inverter.

Essentially, the eFan replicates the function of the engine-driven main cooling fan in an ICE vehicle.

New cooling strategies play a vital role in developing high-voltage EVs, but until now, there was no complete 800V motor and inverter portfolio on the market that met the service life requirements of a heavy-duty electric commercial vehicle.

eFan 40, the most powerful in the range, is particularly effective in vehicles that use multiple radiators sandwiched together. This heat exchanger arrangement harnesses the dynamic pressure developed by forward motion of the vehicle, but at standstill or low speed the throttling effect of the radiators chokes the cooling airflow. Despite its compact size, the eFan 40 overcomes the high static pressure to replace or supplement the airflow, even in a tight installation space.

Safety heads the list of OEM requirements when adopting a new product. Each OEM has its own criteria regarding protection of high-voltage power electronics installations, so the inverter concept developed for the eFan needed to meet their functional safety standards in all driving situations, including a vehicle crash. BorgWarner achieved this by designing an inverter that can either be integrated into the motor or mounted externally or separately.

The eFan makes it easier to electrify heavy-duty vehicles that otherwise couldn’t be cooled cost-effectively throughout a long service life – it’s helping to remove fossil fuel-burning ICEs ad their harmful exhaust gases from road freight transport in favour of CO2-neutral powertrains.

The fans are designed for high aerodynamic efficiency, reducing drag to save battery power, increase vehicle range, and lower the use of resources needed to recharge the battery. The optimised aerodynamics also minimise sound pressure levels to reduce noise pollution.

Reducing energy consumption and achieving cost savings in the manufacturing process was another focus when the company designed the eFan. For the eFan 40’s axial flux motor, costs were reduced by introducing new manufacturing processes for its rotor. For eFan 5 through to eFan 20, the scalability and modularity of the centrifugal flow motor sees many identical or similar components used in each model to optimise material usage, such as copper windings, stator laminations and rare earth magnets.

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