Gear Ratio Variation Concept Influence on Energy Efficiency Optimization of Light Vehicles

The growing concern regarding global warming pushes the contribution of all emitting sources to mitigate greenhouse gases. The significant light passenger vehicle fleet deserves continued attention, both in the implementation of more efficient new technologies and in the optimization of conventional technologies, which are still widely used. The vehicle’s energy efficiency is directly influenced by the coupling of the internal combustion engine to the transmission system. Engines have a restricted operation region of maximum efficiency that must be adequately explored by the transmission system in the different conditions of vehicle use. Thus, this paper analyzes and quantifies the sensitivity of the vehicle’s energy efficiency of two distinct engine technologies, naturally aspirated and turbocharged, coupled to an automatic transmission system with six discrete or continuously variable gears. Experimental data on the overall efficiency of the engines and the transmission concepts, discrete or continuously variable, are used in a 1D mathematical model of a vehicle, developed to numerically simulate the fuel consumption of the four possible engine and transmission configurations as a function of the vehicle category and driving cycles. Initial results indicate an advantage of around 2% in continuously varying the transmission ratio when compared to the configuration with discrete gears, which represents a significant gain in fuel consumption.