Study, Development and Prototyping of a Novel Mild Hybrid Power Train for a City Car: Design of the Turbocharger

Within a large, state-funded, Italian National Project aimed to test the feasibility of an on-the-road prototype of a mild hybrid city vehicle, one of the tasks was to conceive, design and implement an innovative turbocharger that would allow for some energy recovery. The selected vehicle is propelled by a 3-cylinder, 998 cc turbocharged engine (the 66 kW Mitsubishi-Smart W451). The idea is to implement two types of energy recovery: one via the new turbocharger and one through a standard braking energy recovery (also known as KERS). The study of the former is the object of this paper. The proposed turbocharger configuration consists of mechanically separated, electrically coupled compressor and turbine, possibly mounting only slightly modified commercial equipment to reduce construction costs. This paper reports the results of the calculation of the behavior of the new turbocharging group across the entire engine operating range and describes the preliminary design of the unit. An accurate simulation of a mixed (urban and extra-urban) driving mission demonstrates that a net saving of about 5.6% can be attained by the installation of the novel turbocharger unit.