Vehicle coast-down method as a tool for calculating total resistance for the purposes of type-approval fuel consumption

A coast-down test is carried out in cases when there is a need for the exact expression of the forces acting on a road vehicle during its coast-down. These forces act mainly against the vehicle’s movement due to air and tyre rolling resistance. Knowledge of the course of these forces throughout the vehicle’s movement range is also a requirement when measuring fuel consumption with a roller performance dynamometer. The reason is that this device has to load the rollers by force or performance corresponding to the given vehicle, while testing it during various driving cycles. For approval purposes, the requirements for this type of test are described in the applicable regulations, i.e., UNECE Regulations No. 83 and No. 101, or the newly developed Worldwide Harmonized Light Vehicles Test Procedure (WLTP). Slovak Technical Standard STN 30 0556 also contains detailed procedures for carrying out the test. The authors of this paper have taken into account both types of technical regulations in order to conduct coast-down tests on chosen vehicles. The results are usable in terms of measuring fuel consumption on a roller dynamometer. Furthermore, the vehicle’s economic performance in normal operation mode can be also assumed with these results.