Model-based design of a diesel hybrid power pack for off-highway applications: in this master thesis , a model of parallel hybrid electric power unit (P2 architecture) has been implemented for four different off-highway applications on their respective driving cycles chosen from the American Non Regulatory Non-Road EPA: a backhoe, a crawler, an excavator and an agricultural tractor. The heavy-duty diesel engine has been hybridized to reduce NOx emissions and fuel consumption. Energy recuperation potential or hydraulics circuits for loads were not considered. After having introduced the state of the art for heavy-duty diesel engines and the main technologies to reduce pollutant emissions, it has been focused on the modeling of ICE and air path in particular through the MVEM.