| The ride comfort of a motorcycle, which is one of the main performances of a motorcycle, is the performance that keeps within a minimum limit the vibration and impact to the driver and passengers during riding process, keeping cargo in good condition. As a core assembly, the frame bears the load. Its dynamic characteristic is a key factor for motorcycle ride comfort. This dissertation attempts to study the dynamic characteristics of the motorcycle frame through modern structural dynamics methods, to discover frame weakness, and find a way to improve its structure rationally, so as to improve the ride comfort of the motorcycle.Firstly, simplifying the frame of the 125cc motorcycle, the finite element model of the frame is established, which is submitted to FEA software for computational analysis. Based on the finite element model of frame, the finite element model is set up and computational modes are analyzed, where the engine is considered as a point and connected with frame with beam elements and Multiple Point Constraints. The experimental analyses of frame with and without engine are completed with LMS modal analysis testing system. The results show that computation modes is close to experimental modes, so these finite element models can be considered correct and accurate.Then, comparing the modal characteristic of the frame with and without engine, the result shows that the engine has great influence on the modal characteristic. The matching of frame with the excitations from engine and road are analyzed. Based on the analysis results, the frame is modified to improve modal characteristic. Computation modal analysis and experimental modal analysis of amended frame are completed. The modal characteristic of frame is improved obviously after modification.Finnaly, the road-test of ride comfort of origin motorcycle and modified motorcycle, are completed respectively. The comparison result shows that the vibration comfort is improved obviously after modification.
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