Vibration Mode Analysis And Suspension Parameter Optimization Of Motorcycle

The consumption demand of motorcycle is gradually changing from small displacement commuting to large displacement racing entertainment.The vibration problem that affects its handling stability and riding comfort is attracting more and more attention.In order to reduce the vibration of motorcycle and improve the performance of recreational motorcycle,it is of great theoretical significance and engineering value to study and design the suspension parameters which affect the vibration of motorcycle,and to coordinate and improve the vibration of motorcycle including out-of-plane and in-plane vibration.In this paper,the out-of-plane vibration instability of a motorcycle is analyzed by establishing a simulation model of human-vehicle-road system.The suspension parameters are optimized and matched to improve the out-of-plane and in-plane vibration simultaneously.The main work of this paper is as follows:Firstly,the human-vehicle-road dynamic system model of motorcycle driving environment is established.By combining experimental measurement and theoretical calculation,the actual vehicle parameters used for motorcycle parametric modeling are extracted,and the 13-dof dynamic model of the motorcycle is established by Bikesim parametric modeling tool.The 3D road model of the driving environment is established by using Fourier inversion method and the driver control model of the motorcycle is established by using PID roll Angle control method base on pre-viewing path following,so as to complete the construction of the human-vehicle-road system model of the motorcycle driving environment,and provide model support for the subsequent analysis of the motorcycle vibration mode.Then,taking the simulation model of human-vehicle-road system as the vibration analysis platform,the root locus method is used to analyze the out-of-plane vibration stability of the motorcycle under the condition of straight driving and steady steering.The results show that the swerving mode of the motorcycle is always stable in the straight driving condition,while the swinging mode is unstable in the low speed range(30km/h-90km/h)because of the negative mode damping.The critical stable speed is90km/h,and the critical speed is too high.In steady-state steering mode,the root trajectory trend of swing and roundabout swing modes is consistent with that of straight driving mode,but the stability is weaker.the sensitivity method based on experimental design is used to analyze the factors affecting the out-of-plane and in-plane vibration of the motorcycle.Finally,In order to improve the out-of-plane vibration and in-plane vibration of motorcycles,a joint automatic simulation optimization platform based on Isight,Bikesim and Matlab was built by means of self-programmed integration technology and modal tracking law,and the NSGA-Ⅱ is applied to solve the multi-objective optimization of out-of-plane and in-plane vibration of motorcycles.Since neither pareto optimal solution can achieve the simultaneous optimization of the optimization objective,the entropy weight method is used to determine the selection of pareto optimal solution to determine the final specific suspension design parameters.The optimization results show that when the motorcycle is traveling in a straight line at the speed of 60km/h,the real part of the characteristic root of the shimmy mode changes from 1.01 to-3.77,indicating that the shimmy mode changes from unstable to stable.At this time,although the real part of the characteristic root of the circuitous swing mode changes from-4.71 to-4.23,the real part of the characteristic root is still negative and in an acceptable stable region.The root-mean square of vertical and pitch acceleration of in-plane vibration decreased from 1.14m/s~2 and3.45rad/s~2 before optimization to 0.96m/s~2 and 3.16rad/s~2 after optimization,respectively.The vibration suppression rates of 15.7% and 8.4% were achieved,and the comprehensive driving performance of motorcycle was improved.In order to further verify the effect of the optimization parameters of the suspension at other speeds,the root tracks of out-of-plane vibration modes and in-plane vibration modes were studied.The results show that both the vibration modes are stable at the straight driving conditions and steady steering conditions.At the same time,theoretical analysis shows that the response of in-plane vibration vertical and pitch acceleration to road excitation is linear under different vehicle speeds,and the optimization parameters of the suspension can also reduce in-plane vibration at other vehicle speeds.The study of out-of-plane and In-plane vibration of motorcycle shows that the vibration reduction can be achieved by multi-objective optimization of the structural parameters and performance parameters of motorcycle suspension system,and the performance of medium-high speed motorcycle can be improved.It can be used as a reference for other types of motorcycles.