Numerical Analysis of Electrically Assisted Turbocharger Application on Hybrid Vehicle

Despite the continuous efficiency increase, traditional vehicles still dissipate large amounts of energy. While actual hybrid powertrains allow to recover kinetic energy during the braking phases, exhaust gas energy can be recovered through the electric turbo compound (ETC). A turbocharger (TC) match with an electric machine (EM) appears to be the best solution for passenger cars since it also permits turbo lag reduction with restricted system complexity increase. The goal of this paper is to investigate the TC electrification impact on fuel consumption, considering transient behavior during a whole drive cycle simulation. This is obtained coupling a detailed one-dimensional (1-D) engine model with vehicle dynamics and signal processing by means of sole GT-Suite software. A baseline engine refers to a 1.3 L, SI, 3-cylinder turbocharged engine while a class C vehicle is modelled. Powertrain hybridization is obtained by replacing the alternator with a bidirectional EM and then an electrically assisted turbocharger (EAT) is introduced. Two different sizing criteria are considered and compared both by steady-state and transient engine simulations and then by dynamic analysis through the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). The results obtained are in line with those reported by the scientific literature and by car manufacturers, demonstrating how the electrification of TCs requires accurate turbine sizing, depending on the main objective. However, although the need to compensate for performance penalty due to inertia increase by electric assistance, this technology proves to be self-sufficient in every driving condition. Results show improvements in terms of fuel consumption reduction and in terms of performances, thanks to turbo lag reduction. Moreover, the turbine increase allows us to use a stoichiometric mixture in every working condition, as it could be required by Euro7 directives on emissions.