Modeling and Simulation of an Electric Vehicle with Independent Rear Motors to Estimate the Fuel Economy during EPA Drive Cycles

Abstract

The “Car of the Future†project converted a 2015 rear-wheel drive (RWD) Subaru BRZ into a hybrid electric vehicle (HEV) with an intermediate milestone of a battery electric vehicle (BEV). BEV architecture required removal of the conventional powertrain components, such as internal combustion engine, transmission and differential, introduced an electric axle and battery. This intermediate BEV step provided a point at which the vehicle could be evaluated in its all electric operation with the absence of what was once critical components including its original powertrain and powertrain electronics. This step also ensures the electric components are working properly before more complexity is added to the system in building HEV. In our previous work, BEV Vehicle Technical Specifications (VTS) or requirements were developed and an electric axle was appropriately sized and selected to meet these requirements. After selecting the electrical axle with independent rear motors that will meet BEV performance requirements, Environmental Protection Agency (EPA) fuel economy rating of the BEV should be assessed. This paper presents a drive cycle analysis of the BEV vehicle using the EPA Urban Dynamometer Driving Schedule (UDDS) and Highway Fuel Economy Test (HWFET) drive cycles by means of dynamic modeling and simulation. In this study, the power required at the wheels, the efficiency of each motor and the energy required at the selected electrical axle were determined. In addition, the city, highway and combined miles per gallon equivalent (MPGe) fuel economy were determined.