Research On Nonlinear Control Of Semi-Active Seat Suspension

Commercial vehicles have higher load-carrying capacity requirements.They generally have larger suspension stiffness.The cab vibration problem is very serious because of bad operating environment,large vehicle vibration and limited attenuation of road surface roughness by suspension with large stiffness.At present,the passive suspension seat is the most common way to attenuate the vibration transmitted from cab to driver.Different working environments require different parameters of seat suspension.Traditional passive suspension can not meet the requirements of various road conditions.The semi-active suspension with variable damping can adjust the damper value in real time according to the current motion state of the seat,so as to achieve the optimal suspension performance.Semi-active suspension system has many non-linear factors: non-linear damping,non-linear force of air spring,structural non-linearity and friction force.The above factors lead to strong non-linear factors of seat suspension system,and the control effect of simple linear semi-active suspension control method is limited.In order to obtain better performance of semi-active suspension seat,understanding semi-active suspension seat systematically,compiling a non-linear control algorithm for seat suspension system,verifying the effectiveness of the non-linear control algorithm in the actual semi-active seat suspension is very meaningful.In this paper,the following three aspects will be studied: semi-active seat suspension model and road excitation,sliding mode variable structure control algorithm development and equal proportion seat suspension experimental verification.the main work of this study are as follows:Firstly,four kinds of pavement excitation models are built.Establishment 6 DOF Vehicle Model Based on Commercial Truck Parameters,the vertical displacement response of the cab is the vertical displacement excitation of the seat suspension system when the model is stimulated by the road surface.Secondly,use shock absorber test bench to obtain the external dynamic characteristics of magnetorheological shock absorber.Using test data and least square principle to identify model parameters to built the damper model,then derive an accurate and efficient inverse model for real-time control based on the damper model.According to the structural characteristics of seats suspension,consider the change of damper angle during seat vibration,built the dynamic equation of seat suspension.Thirdly,introduce the basic principle and design method of sliding mode variable control,taking the Skyhook mothod as a reference model,established a sliding mode controller for seat suspension control,and verify the stability of controller.The simulation results are analyzed by three analysis methods: time domain response,frequency domain response and phase plane diagram.Under random road excitation,SMC algorithm can improve comfort by 11.39% and operation safety by 48.15%.In the case of bump pavement,SMC algorithm can improve the impact of the seat,and make the seat stable when restore to the steady state,reducing the sense of bump.SMC algorithm can improve comfort and operation safety under low and high frequency sinusoidal road excitation.SMC algorithm can also reduce the gain at the seat resonance frequency and change the seat resonance frequency away from the sensitive range of human body.At last,build a seat suspension test bench.Then,verify the control effect of SMC algorithm on semi-active seat suspension under random road,bump road and sinusoidal road excitation.The experimental results show that SMC algorithm can improve the comprehensive performance of seat suspension under three road conditions.The results of bench test and simulation are basically consistent,which can verifies the control effect of sliding mode controller in actual seat.