The determination of driving resistances plays an important role during the development of a vehicle and for its certification. Since 2017, the Worldwide harmonized Light-duty Test Procedure (WLTP) has been required for the type approval of new models. Aerodynamic drag and rolling resistance are particularly important here, since both directly influence the vehicle's consumption and cannot be recovered, even in electric vehicles. FKFS has specialized test benches and simulation methods for determining air resistance and rolling resistance, and has comprehensive expertise in optimizing these driving resistances.
Reducing rolling resistance is an important target regarding compliance with today's and future emissions standards and carbon dioxide limits.
At FKFS, the rolling resistance of passenger vehicle tires is studied using a rolling resistance measuring trailer. In addition, detailed full vehicle simulations are conducted to investigate the rolling resistance of the entire vehicle. This particularly takes into account the influence of real operational and environmental conditions on the tire temperatures and therefore on the tire rolling resistance. Especially for commercial vehicles, this kind of holistic consideration offers further potential to reduce the rolling resistance.
Optimizing a vehicle's aerodynamic drag is vital for compliance with current and future emission standards and CO2 limits. Unlike, for example, the energy expended for acceleration, the losses resulting from air resistance cannot be recovered. This is particularily important for electric vehicles, as high aerodynamic drag will irrevocaly reduce their range.
At FKFS, we are able to measure and optimize passenger vehicles' aerodynamic drag, not only on a 1:1 scale in our Aeroacoustic Wind Tunnel, but also on a 1:4/1:5 scale in our Model Wind Tunnel. To achieve the best possible accuracy, the moving floor beneath the vehicle and the rotation of the wheels present on the road are reproduced in our wind tunnels. In order to depict the naturally transient conditions on the road, both wind tunnels are equipped with the FKFS swing® system. It can be used, for example, to simulate a journey with gusting crosswinds.
FKFS also operates an Intel HPC cluster with more than 2000 CPU cores and the latest CFD software. This enables detailed insight into the flow field around the vehicle, allowing us to find new approaches in minimizing aerodynamic drag. By intelligently combining CFD and wind tunnel work, potential for improving aerodynamics – and consequently reducing CO2 as well as other emissions – can be identified efficiently.
Since September 1, 2018, all newly-sold vehicles must be certified according to the Worldwide harmonized Light-duty Test Procedure. This test procedure now not only takes all the special equipment of a vehicle into account, but the average and maximum speeds have also been increased compared with the predecessor cycle, the NEDC, to obtain more realistic consumptions for each vehicle. Both these points result in an increased air resistance component for the certified consumption of the vehicle.
FKFS uses a 1:1 scale aeroacoustic wind tunnel to determine a car's air resistance coefficient according to WLTP. This wind tunnel has been certified for WLTP requirements since 2017, by, for example, TÜV Nord. This enables us to efficiently determine the air resistance coefficients of all vehicle configurations required for certification.