The automobile manufacturers are currently facing a double challenge. While they must meet tight vehicle emission regulations established by the authorities, they also have to achieve the current market demands, which look towards fuel efficient vehicles for city driving, but still delivering high performance for unproblematic highway cycles.
The purpose of this study is to evaluate the influence of different axle ratios in the conflicting fuel economy versus acceleration performance trade-off. The article will present the modeling and simulation of a four-wheel-drive light-duty vehicle with six-speed automatic transmission subjected to three drive cycles: the FTP-72 (Federal Test Procedure) cycle, the Highway Fuel Economy Test (HWFET) cycle, and the 0-100 km/h acceleration cycle.
The simulations were performed in MATLAB/Simulink® environment by using system modeling that incorporates powertrain components such as engine, transmission, torque converter, axle ratio, wheels, driveshaft, etc. The auto driver was implemented by the approximation of the commanded speed curves to the desired speed curves (driving cycles) using a controller subsystem.
The vehicle model results aim to analyze the improvements generated by the optimal differential ratio in the maximum reduction of fuel consumption while keeping a minimum performance threshold of 7 seconds for the 0-100 km/h acceleration drive cycle.