An Approach for Prediction of Motorcycle Engine Noise under Combustion Load

In this paper the approach to predict engine noise under combustion forces is presented. This Methodology is divided into three stages: 1. Multi body dynamic (MBD) Simulation to determine excitation forces 2. Vibration analysis of engine under combustion load 3. Acoustic analysis of engine to predict Sound Pressure Level (SPL). Important parts of motorcycle engine with single cylinder are considered as flexible bodies for MBD simulation. It is necessary to accurately model crankshaft ball bearing for capturing the accurate transmissibility of combustion forces from crankshaft to casings. In this work crankshaft ball bearing is modeled with 6×6 stiffness matrix. It provides coupling between radial, axial and tilting deflections of bearing and it also allows moment transfer from crankshaft to casing. It helps to predict the realistic forces at bearings. Forces predicted from MBD simulation are applied to engine FE model for carrying out vibration analysis. Predicted vibration response of engine at few locations is compared with test data. It was found that predicted response was in well agreement with test response. Vibration response of engine outer surface is used as an input to carry out acoustic analysis. Predicted SPL helped to identify the critical locations on engine responsible for high SPL. Hence, corrective actions can be implemented based on analysis results in early design stage by carrying out structural modifications.