Nowadays, the engine charging practice is widely adopted in the automotive field in relation to the “downsizing” technology: the reduction of the displacement and the adoption of a higher boost pressure, through a charging system, allow shifting the engine operating point in a zone of higher efficiency for a given engine torque. On the other hand, given a certain displacement, a supercharger can be adopted to increase the performance of the engine.
The objective of this work is to provide a detailed analysis about the feasibility of the implementation of a charged engine to a motorbike, with main focus on the possibility to achieve a challenging performance target: in a first stage, several engine architectures (In-line, V-configuration, Boxer) together with different charging concepts (centrifugal or volumetric compressor, with mechanical or fluid-dynamic connection to the engine) have been analyzed from the point of view of packaging. In a second part, a V4 engine architecture has been selected for a patrol motorcycle application: the conceptual investigation of the base engine design has been carried out with the development target of lowest possible weight and size. Several concepts of crankcase, lubrication system and clutch, type and position of gearbox and timing belt have been analyzed. Once the best configuration has been selected, the specific performance requirements of the engine have been analyzed via 1D gas-exchange simulations and a charging strategy together with optimized valve timing, intake manifold and exhaust manifold have been found out. In a last step, the mechanical analysis of the crankshaft has been performed. The calculation of the cranktrain dynamics as well as the stress distribution under the most critical load conditions allowed to define the main web parameters with the aim of preventing fatigue failure of the crankshaft.