Simulation and control of a through-the-road-parallel hybrid electric vehicle

In the last years, the research concerning hybrid electric vehicles (HEV) has been developing greatly because of some dangerous natural phenomena such as global warming, directly linked to vehicles exhaust emissions. The hybrid electric vehicles are characterized by an improved fuel economy thanks to extra degrees of freedom provided by battery energy storage and one or more electric machines which allow running a smaller combustion engine in a higher efficiency region. The aim of this thesis is to demonstrate the viability both in terms of fuel economy and performance of a powertrain downsizing when coupled with modern electrical traction motors. In this regard, at the beginning of this research work, the capability of the baseline conventional powertrain, represented by a front-wheel-drive Opel Insignia with a 2.0 l diesel engine, performed numerically. Successively, the electrification of the rear axle via an electric motor has allowed the implementation of through-the-road-parallel (TTRP) hybrid architecture. Different gearshift strategies and an energy management controller have been implemented. Indeed, to guarantee an additional improvement in terms of fuel economy a well-defined energy management strategy is required, the aim of all those strategies is to find the optimal power-split between the electrical and thermal source and these results can be achieved only through actions that the controller must take at each time instant. For this reason, the interest in energy management strategies has increased and a lot of different controllers have been proposed. However, this work focuses on the Adaptive-Equivalent Consumption minimization strategy (A-ECMS), used to analyse the behaviour of the hybrid vehicle. A-ECMS is characterized by a cost function that must be minimized at each time in order to reduce fuel consumption and it only depends on instantaneous variables. The whole powertrain has been implemented in Amesim while the control strategy in Simulink and the two software have been run in co-simulation. In this thesis, an upgrade of the strategy mentioned before is proposed, thus the controller gearbox efficiency has been considered in the A-ECMS, so the strategy manages to take into account also the power loss by the transmission and therefore can compensate this by raising engine operating points to higher efficiencies zone. Eventually, the results show that the through-the-road-parallel hybrid electric vehicles do manage to reduce total fuel consumption over standard drive cycles with respect to the baseline vehicle. Nevertheless, the real-time implementation of the energy management strategy requires a computational effort that seems to be too great at the present time.