Motorcycle engines are operated at an extremely broad range of revolutions, from 1000 min-1 to 10000 min-1 or more. Ideally, the natural frequency of each part should never match the engine excitation frequency at any point over that entire range of revolution speeds, but practically, there are times when resonance cannot be avoided because the range is so broad, and therefore the vibration amplitude at resonance must be kept low. For this reason, it is important to grasp not only the resonance frequency but also the vibration amplitude at that point. This may be achieved by two methods, measurement and analysis. The direct measurement of vibration is generally difficult because the motorcycle muffler system has a complex shape and in addition it gets very high temperature when the engine is operating.
For this reason, with the aim of being able to predict muffler vibration at the design stage, we carried out a vibration test and FEM (finite element method) analysis. First, we carried out an experimental modal analysis of the muffler attached to the motorcycle and obtained the natural frequency and the vibration mode. The vibration amplitude at resonance when the engine was operating was measured with a Laser Doppler Vibrometer.
Secondary, the muffler system was modeled with 3D (three-dimensional) beam elements to analyze by FEM. Boundary conditions were determined by applying actually measured data. Thirdly, the FEM model was corrected by comparing calculated results with experimentally obtained data. In this way, we studied the FEM modeling technology required to predict vibration of motorcycle muffler system.