Experimental Evaluation of Rotational Inertia and Tire Rolling Resistance for a Twin Roller Chassis Dynamometer

Chassis dynamometers are important equipment to perform vehicular experiments in the automotive industry. Usually, these equipments are used according to standard procedures for emissions, fuel consumption, and performance analyses. In this paper, an alternative procedure was developed to experimentally determine the dynamometer inertia and losses related to bearings and transmission systems. Furthermore, a study on the tires rolling resistance, considering a double tire-roller contact, was carried out. The experiments were performed in a 4x2 chassis dynamometer with four rollers, equipped with an eddy current brake (coupled to a transmission reducer of 2.5 instrumented with a 3000 Nm torque flange) and with a 30 CV AC electric motor (coupled to a planetary transmission with reduction of 4.43 and instrumented with a 500 Nm torque flange). The dynamometer was also instrumented with an encoder system for speed measurement. All data were acquired by NI/LabVIEW™ software and post-processed in Matlab™ and Excel™ interfaces. The initial experiments resulted in the overall dynamometer bench inertia and equivalent inertias of the braking and electric motorization systems. The secondary experiments provided equations to determine the losses of the braking and electrical motorization systems, the overall bench losses and the vehicle/bench total rolling resistance according to the vehicle speed. Finally, a simplified coast-down experiment was performed on the dynamometer, and the results were compared to a Matlab/Simulink™ model of a hypothetical vehicle with similar mass.