The paper presents a numerical approach to determining the optimal vehicle control from the fuel conservation point of view. The method described is based on a mathematical model of vehicle dynamics and the optimal control theory. The model of vehicle consists of non-linear differential equations, engine efficiency map and road load curve. Some parameters of model were calculated on the basis of experimental data. The optimized control vector includes percentage of propelling torque, brake torque and gear ratio, considered as functions of time.
Because of mixed nature of the controls (continuous and discrete) the general optimal control problem is solved separately for steady state velocity and acceleration process, both for various values of road slope. An original algorithm based on the Minimum Principle was developed and described.
In the end the results obtained are discussed. The paper presents the fuel saving strategies in various conditions. They are compared with other vehicle control rules. The differences in fuel consumption among various strategies are significant (several tenth percents in the worst case: up-hill driving). Calculations were done for a bus equipped with Diesel engine.