Multi-Objective Optimization of the Timing System on a Small 2-Wheeler Engine (SOHC): Methodology and Case Study 2014-32-0055

In recent years the 2-wheelers engines companies have been focused on increasing the overall engine efficiency, that can be achieved amongst other by engine down-speeding, engine down-sizing and by reducing the frictions; however, to maintain or improve vehicle performance, it is necessary to provide a corresponding increase in specific power.In accordance with these trends, the studied approaches and methodologies have been exploited, during the development of the new Piaggio small scooter engine.In this work a multi-objective analysis has been applied to the valve train system design, in order to optimize the engine performance in terms of friction reduction, power curve and timing system response. Along with this optimization methodology, a robust design has been studied to make the peak cranking compression pressure insensitive to the engine starting device working. These calculation methodologies have been followed using commercial software as GT-SUITE® code and the modeFRONTIER® platform for the multi-objective optimization analysis.The several configurations investigated have allowed to reach the desired trade-off between the appropriate and efficient valve train behavior and the engine performances.The global engine friction reduction has been obtained thanks to low resisting cam torque profiles, a specific valve springs set and a new compression releaser device (during engine starting phase).The results have been further validated by an experimental campaign carried out on the test bench for engine performance and on the specific cold test bench to evaluate friction losses.