Research On Acoustic Simulation For The Reduction Of Noise From Gearbox Cover Of Motorcycle

Noise has been generally regarded as one of the most important environment pollutions. The noise control became obliged with the more stringent statutory noise requirements. A majority of noise was radiated from its surface by vibration, especially the thin parts for example oil pan, air valve cover, gearbox cover etc., so the surface noise control is significant for vehicle noise control. The method based on numerical simulation is widely used for its reduction on expend and short development period. In this paper, the acoustic simulation was applied to improve the noise performance of gearbox cover on the motorcycle of 125-C with the low vibro-acoustic structure design.It is showed in the sound intensity experiment that the gearbox of motorcycle is one of the main noise sources between the frequency 1200Hz-1440Hz. The CAD model and finite element model was founded. The calculating modal analysis and experiment modal analysis were carried out to get the inherent frequency and vibrational shape and so on. The error between calculating results and measurement results was limited. It is satisfied for the calculation request.The surface vibration experiment was carried out at the engine speed of 7200r/min for getting the vibrational speed nearby the bolts. The speed can be the load of frequency response analysis. The boundary element model of gearbox cover was founded. The sound pressure and acoustic radiated power were calculated through the acoustic simulation. It is obviously that the radiated noise is biggest at 1260Hz. From the sound intensity chart by simulation, it can be seen that the radiated noise source is the joint of the smaller part of gearbox. Both the frequency and the position showed that radiated noise was closely related with the fourth inherent frequency and vibrational shape.In this paper, three kinds of design were selected which were the design of adding ribs, adding the thickness and combined with the two designs respectively. The characteristics of radiated noise field of each design were obtained with acoustic simulations. It can be seen that each design has good effect from the comparisons between the optimized designs and primary structure. The comparison between three kinds of design showed that adding the thickness was the most effective, and combined with two designs was worst. This conclusion indicated that the effect of acoustic optimization was closed related with the characteristics of structure and the result of combined with two effective optimizations might be negative. Based the principle of lowest acoustic radiated power, the design by adding the thickness was selected, and the total acoustic radiated power was reduced 3.52dB.