Abstract
Research and/or Engineering Questions/Objective
For the vehicle fuel economy test using a chassis dynamometer, road load force that occurs during drive on a real-world road must be simulated on the dynamometer. Currently, road load is measured and provided by the auto maker. However there is no method available for a third party to validate such road load. Hence this study is intended to look into methods for validating vehicle road load.
Methodology
In this study, various methods were explored to validate road load, including individual energy differences or combined energy differences depending on the fuel economy test mode and differences in road load in consideration of the speed range for on-board coast down. For the analysis of each method, author-defined road load has been used. In addition, to provide reference for the calculation of energy difference depending on fuel economy test mode, a constant was derived for each road load coefficient, which was subsequently used for the calculation of energy. Then the result from the calculation was compared with energy difference obtained using a different method.
Results
Results from the methods are as follows: For the same road load settings, comparison of individual fuel economy test mode reveals that there are energy differences of 14.9 % in the FTP-75 mode, 10.6 % in HWFET mode and 12.6 % in combined fuel economy test mode, respectively. This suggests that energy difference may vary depending on the method used for road load validation. Energy difference depending on the range of coast down speed was minimal while the difference in road load energy calculated using the constant of each road load coefficient and the energy difference taking into account the fuel economy test mode were found equivalent.
Limitations of this study
The lack of any globally accepted regulations regarding the method of validating road load and its tolerance requires further research in this area.
What does the paper offer that is new in the field including in comparison to other work by the authors?
This paper discusses methods of validating energy difference between road load provided by the auto maker and road load actually measured and compares how they are different.
Conclusions
Methods of validating road load were explored in terms of fuel economy test modes, coast-down speed and constant of road load coefficient. Results from the exploration can be used to validate road load provided by the auto maker in a more reliable manner.
Key Words : Coast down Test; Road Load; Energy Balance; Fuel Economy