“eFan system supports our customers transitioning to electrified commercial vehicles”

AutoRevista.- Could you describe the BorgWarner eFan and how it was developed?

Ralf Christmann.-. The eFan is a high-voltage cooling fan for electric commercial vehicles. It consists 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 light truck and heavy-duty truck segments. The top model – eFan 40 – is rated at 40kW to drive fans with diameters from 650 to 864mm. This is a high-torque eFan 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. Our aerodynamic optimization efforts reduced the torque requirement for these models, so they’re driven by a radial flux permanent magnet synchronous motor.

Higher voltage electric fans have featured in our development program for several years. Using these fans as a starting point, we used multi-dimensional numerical optimization to fine-tune the fan geometry, and computational fluid dynamics to validate the design in conditions simulating a typical customer installation. After CFD, we carried out a finite element analysis to check the fatigue strength.

Fan acoustics were assessed by testing prototypes and using computer-aided aeroacoustics simulations. When the fan design was completed, we used the CFD calculations from the optimization process to specify the electric motor and the inverter.

AR.- Why is a powerful fan needed for an electric vehicle when there’s no internal combustion engine to cool?

R.C.- The eFan replicates the function of the engine-driven main cooling fan in an internal combustion engined vehicle. The fan is still needed in an eCV because despite replacing the engine with an electric drivetrain, there are several other systems that require cooling, such as the high-voltage battery, inverters and traction motors and if installed the braking resistors.

Depending on whether it’s a battery electric vehicle or a hydrogen-powered fuel cell electric vehicle, higher performance eCVs need even more cooling capacity and airflow to cater for the size of the braking resistors or fuel cell modules used.

Higher performance eCVs need even more cooling capacity and airflow to cater for the size of the braking resistors or fuel cell modules used

AR.- What challenges did you face when designing this product, and how did you overcome them?

R.C.- The high-voltage eFan demands a lot of power to operate it – anywhere from 5kW for a light truck, up to 40kW for a heavy-duty vehicle – which depletes battery capacity. As this is directly related to the distance the vehicle can travel, we had to find ways to minimize energy wastage and optimize fan performance and e-motor and inverter efficiencies in a limited package in the front of the truck. A large fan and electrical motor also create noise, which must be within limits defined by noise emissions legislation. This is even more important because the whole electrified propulsion system is running on very low noise levels overall.

We used computational fluid dynamics and computer-aided aeroacoustics to design a fan impeller with high aerodynamic efficiency

We met both of these challenges by using computational fluid dynamics and computer-aided aeroacoustics to design a fan impeller with high aerodynamic efficiency – this has less frictional drag, saving energy. More efficient airflow allowed us to reduce the rotational speed and power consumption of the electric motor to a level at which it develops sufficient torque to drive the fan but minimizes sound pressure levels.

AR.- What problems does the eFan address for customers?

R.C.- New cooling strategies play a vital role in developing high-voltage electric vehicles – 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 eCV.

The 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 in the high-voltage range. 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. We achieved this by designing an inverter that can either be integrated into the e-motor housing or mounted externally.

AR.- How does the eFan support BorgWarner’s sustainability goals?

R.C.- 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 internal combustion engines and their harmful exhaust gases from road freight transport in favor 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 optimized aerodynamics also minimize sound pressure levels to reduce noise pollution.

Reducing energy consumption and achieving cost savings in the manufacturing process was another focus when we 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 radial flux e-motor sees many identical or similar components used in each model to optimize material usage, such as copper windings, stator laminations and rare earth magnets.

AR.- What is the future potential for the eFan?

R.C.- The eFan system supports our customers transitioning to electrified commercial vehicles, helping them comply with CO2 emissions targets. Ahead of series production, it has already been selected by leading commercial vehicle manufacturers for their battery-electric and hydrogen-powered fuel cell long-distance road transport vehicles, in both the European and North American markets. Other major manufacturers are also keen to adopt the new technology.

eFan also supports BorgWarner’s own e-growth goals

Production is expected to commence in late 2024 with initial volumes of over 3,000, rising to nearly 74,000 by 2031. Our acquisition of Drivetek AG last December further enhances BorgWarner’s inverter expertise and capabilities to support projected eFan business growth.

eFan also supports BorgWarner’s own e-growth goals – we aim to generate more than 25 percent of total revenue from electric vehicles by 2025, grow to 45 percent electric vehicle revenue by 2030, and be carbon neutral in our operations by 2035.

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Interview published in AutoRevista 2.384