Study On Noise Mechanism Of Motorcycle Engine

As one of the fundamental and effective ways of reducing motorcycle noise, the research on the motorcycle engine noise has got more motorcycle manufactures' attention. Based on the structural improvement, it not only control the engine noise from root, but also can improve the engine performance without adding the complexity to the engine.A motorcycle engine is studied in this paper based on tests and simulation analysis emphasizing on the knock noise's generating mechanism and impact factors.Combustion noise and the piston knock noise are separated by adopting sound pressure method. At the low rotate speed, the combustion noise is the primary noise, while at high rotate speed, the piston knock noise is the main noise. It has also been clear that the source of piston knock noise is the impact between piston and cylinder sleeve by the vibration acceleration of the engine's body surface.A multi grid body simulating model of connecting rod with 2 DOFs is established. The section of piston skirt and the separate definitionof contact strength is proposed. The impact force between piston and cylinder sleeve is mainly studied. Also the influence of piston impact force are discussed which including engine rotate speed, piston pin offset, clearance between piston and cylinder, piston mass and contact strength of piston surface.There will be several knocks during an engine work cycle since the knock occurs around the top dead center and the bottom dead center, also the impact of major thrust side is fierce when the piston is near the top dead center. It has been found that the impact force of major thrust side is stronger than that of minor thrust side. The generating process of piston knock noise is thoroughly analyzed by the study of piston motion state and knock process with the engine at the rated engine speed.An improve plan to decrease the piston impact force is brought forward based on the analysis of factors influencing the piston impact force. The impact force decreases to some extend after the improvement. It is proved that the improvement of piston structure is effective to decrease the impact force and the knock noise caused by the piston.