Strength And Random Vibration Analysis Of SRV Motorcycle Frame

Motorcycle frame is the main support of motorcycle, will bear the static and dynamic loads. So it is rather important for both its strength and dynamic characteristic design. The dynamic characteristic of the frame will affect the ride comfort, the control stability and the security of the motorcycle, and the reliability of the components. And if the strength, especially the dynamic strength can't meet its requests, the frame may be destroyed.Because it is difficult to solve these aspects of design problems, the finite element method which has been widely used in the overseas motorcycle industry was adopted for the analysis and design of the motorcycle frame.A new style of Sport Recreation Vehicle (SRV) was researched in this paper. First, the CAD model of the frame was modified, and then its statics, modal and random response finite element analysis models were created, and at last were respectively calculated on the above three aspects.The statics analysis was carried on two situations. The results indicate that the frame's static strength and stiffness can both satisfy the requests. But its stress distributing is rather uneven, and its strength has much surplus, the structure can be optimized.Through the modal analysis, the first ten nature frequencies and nature mode shapes are gained. The mode shapes show that there mainly are torsion and bend distortions along the frame. As its first mode frequency is equal to the engine's second order inertia force frequency at the demarcated power, it will make the frame resonate, and to avoid it, we shall increase its first order nature frequency by structure modification.Based on GB7031-86 "Vehicle vibration—Describing method for road surface irregularity", the road's time power spectrum density functions under three conditionswere constructed in this paper, and the random response analysis was also carried on the three conditions. The analysis results contain the rider's response acceleration and displacement power spectrum density, and the frame's response root mean square (RMS) stress. The results indicate that the human body' vibration frequency is mainly concentrated beyond the frequency of 22Hz. Furthermore, the frame's dynamic stress mainly concentrate on its engine connected place, this is the weakest place of the structure.This paper directed a direction for frame optimization, and established the foundation for the following work.