Optimal energy management for a mechanical-hybrid vehicle with cold start conditions

This paper presents the design of an optimal Energy Management Strategy (EMS) for a hybrid vehicle that starts with a cold powertrain. The cold start negatively affects the combustion and transmission efficiency of the powertrain, caused by the higher frictional losses due to increased hydrodynamic viscosity effects. The excess fuel consumption of the engine and the excess power loss of the transmission are modeled by static relations as a function of the lubrication oil temperature. The thermodynamics in the powertrain during the heating period of the powertrain is approximated by a first-order dynamic model. The main design criterion for the optimal EMS is the minimization of the overall fuel consumption over a pre-defined driving cycle. Dynamic programming is used to find the globally optimal solution for six representative driving cycles. The results show that the cold start has a significant impact on the fuel consumption of the hybrid vehicle, yet its influence on the optimal EMS is negligible.