Coastdown Road Load Coefficients of Passenger Vehicles - Variation Analysis and its Correlation with Temperature

Road Load parameters (rolling resistance and aerodynamic drag) of a vehicle have strong impact on overall Vehicle Emissions and Fuel Economy. The road load coefficients are simulated on chassis dynamometer to carryout emission and fuel economy measurement and are hence required to be found beforehand. A realistic measure of road load parameters can be obtained by conducting a coastdown test. Coastdown test results are hugely impacted by various environmental parameters like ambient temperature, atmospheric pressure, wind speed etc. Though performed in standard boundary conditions, results of multiple tests performed on a vehicle vary from one another due to variations in the mentioned environmental parameters over and above standard test to test variation. This paper aims at studying the variation in test results due to ambient temperature as one of the parameters responsible. For this study, road load coefficients from more than 100 coastdown tests conducted on oval test track for almost 30 vehicles from multiple segments are considered. Through this study, an attempt has been made to build a correlation between ambient temperature and test results to analyze the test to test variation. This study can further be extended to predict the road load of a vehicle at different ambient temperature based on test results of the same vehicle in standard or known ambient temperature conditions.