Compact Normalized Description of Vehicle Traction Power for Simple Fuel Consumption Modeling

This is an extension of simple fuel consumption modeling toward HEV. Previous work showed that in urban driving the overhead of running an ICEV engine can use as much fuel as the traction work. The bidirectional character and high efficiency of electric motors enables HEVs to run as a BEV at negative and low traction powers, with no net input from the small battery. The ICE provides the net work at higher traction powers where it is most efficient. Whereas the network reduction is the total negative work times the system round-trip efficiency, the reduction in engine running time requires knowledge of the distribution of traction power levels. The traction power histogram, and the work histogram derived from it, provide the required drive cycle description. The traction power is normalized by vehicle mass, so that the drive trace component becomes invariant, and the road load component nearly invariant to vehicle mass. The resulting normalized time and work distributions form a generic compact description of a drive cycle. The round-trip efficiency of the electric powertrain then determines the large reductions in engine running time and work in urban driving. Good agreement is found with EPA data for the Toyota Camry ICEV and HEV. Additionally, as the power/weight is a largely a low order function of vehicle speed only, it provides a useful way to graphically synthesize performance requirements and vehicle capability in the same plot. The different tools are demonstrated in the analysis of a new regulatory drive test.