Vibration Comfort Based Optimal Design For The Rear Suspension System Of Mountain Bike

Taking three factors in designing rear suspension system of mountain bike as analysis objects, this paper builds a rider-bicycle multi-rigid-body dynamic model which views the rider as a five-rigid-body and takes the four-bar rear suspension into consideration. An efficient method to realize the rear suspension system optimization is developed to improve the vibration comfort. The main research achievements are shown as follow:1. Almost kinds of rear suspension system of mountain bike are analyzed and classified into three categories: one-hinge rocker-arm configuration, rocker-arm drove four-bar mechanism and connecting rod drove four-bar mechanism. The characteristics of the above rear suspension are studied and compared each other, based on the force ratio curve of the rear suspension, and the conclusion is drawn that: connecting rod drove four-bar mechanism has weaker rigidity, moreover the design parameters influencing the performance of the rear suspension system are pointed out to be: the length of the side link, the length of the connecting rod and the pivot position of the absorber and the frame. In addition, the parameters of rear suspension system are optimized, with the force ratio curve of the system as the cost function, the rod length and absorber position as design variables, the space of the practical configuration as limitation. Finally, the relatively better design parameters are acquired.2. The vibration performance is evaluated referring to the ISO2631-1 Mechanical Vibration and Shock-Evaluation of Human Exposure to Whole-body Vibration. According to this evaluation, the vibration experiment is performed, using the various absorbers vibration properties excited by different frequencies are analyzed, and the conclusion is drawn that: the same effect are got as the different absorber in some range of frequency.3. A multi-rigid-body dynamic model of mountain bike frame is set up, and its correctness is verified by the simulation. Then, the model of full bike is developed using the fore introduced bike frame, and a multi-rigid-body dynamic model of rider-bicycle is finished. A mathematical model, which concludes the relationship between the design variables of the rear suspension and targets of vibration comfort, is established with the help of stepwise regression analysis and BP neural network. It turns out to be that the vibration comfort result predicted based on mathematical model coincides with that simulated by multi-rigid-body dynamic model.4. By the calculation and analysis of regression equation, some revealed that: the vibration comfort gets worse with the increment of absorber stiffness and the length of side link, under the condition of the other parameters remained constant, but it will be better along with the length of connecting rod; when the absorber stiffness is constant, the longer side link connecting rod length and the shorter connecting rod length, the better vibration comfort; when the side link is constant, the shorter connecting rod length, the better vibration comfort, but the absorber stiffness is not sensitive to the vibration comfort; when the connecting rod is constant, the shorter side link length, the better vibration comfort, but the absorber stiffness is almost no influence on the vibration comfort.