The present thesis aims at evaluating the performance of a real-time implementable onboard energy management strategy (EMS) for Hybrid Electric Vehicles (HEVs), namely Equivalent Consumption Minimization Strategy (ECMS). A full hybrid heavy-duty vehicle with a 4,5L compression ignition engine has been chosen as reference vehicle. A P2 parallel hybrid architecture, with the electric machine located between the engine and the gearbox, has been simulated by means of a design optimization tool developed in MATLAB programming environment. The ECMS control strategy has first been implemented in the simulation tool following a detailed Equivalence Factors (EFs) calibration, then it has been tested on different driving scenarios and finally it has been compared with the Dynamic Programming (DP) global optimizer.