A Brief Discussion on Vehicle Coast-Down Comparative Analysis

Vehicle Fuel Economy and Emission measurements requires road load determination by standardized Coast-down test. Worldwide stablished standards for testing and calculation apply second order polynomial fit models to describe road load. The common approach on road load analysis and validation is by direct comparison of coefficients and corresponding parabolas. This paper discuss an alternative approach (currently used by the USA Environmental Protection Agency) for estimating road load energy loss on standard test driving profile. Combining simple physical concepts on Work with the road load model and the chassis dynamometer driving profile, equations are derived describing the energy loss as a function of road load coefficients on a fuel economy test. It results in a simpler, more robust evaluation for test-to-test and vehicle-to-vehicle road load comparison with direct physical meaning, a stronger correlation with fuel economy, and readily applicable to methodology and standards in place.