Mechanism of vehicular periodic operation for optimal fuel economy in free-driving scenarios

In addition to the fuel-efficient design of vehicles, eco-driving technologies can further reduce the fuel consumption and carbon emissions of road transportation. One of the major issues in eco-driving technologies is how to determine the fuel savings or fuel-optimised operating strategies of the power train. We examine the periodic operation of autonomous vehicles in free-driving scenarios with the purpose of maximising fuel economy. The design of such strategies can be considered to be an optimal control problem, which is proved by π-test to have singular arcs because of the S-shaped engine fueling rate. The optimal operations are solved numerically by using the Legendre pseudospectral method, and many are found to demonstrate periodic behaviours, that is, pulse and gliding. In periodic operation, the engine switches between the minimum break specific fuel consumption point and the idling point, while the vehicle speed oscillates between its upper and lower bounds. The formation of periodic operation, as well as some key properties, is analysed and presented.