An Experimental Methodology for Measuring Resistance Forces of Light-Duty Vehicles under Real-World Conditions and the Impact on Fuel Consumption

A vital element of any vehicle-certification test is the use of representative values for the vehicle resistance forces. In most certification procedures, including the WLTP recently adopted by the EU, the latter is achieved mainly through coast down tests. Subsequently, the resistance values measured are used for setting up the chassis-dyno resistances applied during the laboratory measurements. These reference values are obtained under controlled conditions, while a series of corrections are applied to make the test procedure more repeatable and reproducible. In real driving, the actual vehicle road loads are influenced by a series of factors leading to a divergence between the certified fuel consumption values, and the real-world ones. An approach of calculating representative road loads during on-road tests can help to obtain a more unobstructed view of vehicle efficiency and, when needed, confirm the officially declared road loads. This approach is also essential for validating simulations and achieving better estimates of the actual fuel consumption, a requirement introduced by the new policy adopted in the EU. In this study, a series of on-road experiments were conducted, under real-world conditions, on three vehicles, belonging to different vehicle body-categories, a supermini, a B segment cross-over city car, and a light-duty commercial vehicle. A wheel rim torque-measurement system (strain gauge torque sensors) was used to record the torque at the wheels accompanied by a wheel rotational-speed sensor. The present paper presents the results and investigates the capacity of such kind of tests to measure road loads with precision and accuracy. The calculated resistance forces are compared against the ones officially declared at type approval or measured via dedicated coast down tests. Results show satisfactory accuracy and repeatability, ranging within a ±3-7% range for the aerodynamic resistance, and point out margins for improvement. Simulation models are subsequently used to quantify the impact on real-world fuel consumption and CO₂ emissions. The road loads measured using the method lead to similar fuel consumption simulation results as the official road loads with deviations in total simulated CO₂ emissions remaining within ±6% of the measured values in the majority of the cases.