| Commercial vehicles such as heavy trucks and large buses have high suspension natural frequency due to their performance requirements.When the vehicle is driving in a harsh working environment,factors such as uneven road surfaces and pits can cause frequent low frequency vibration problems in the cab.If the driver is exposed to such working environments for a long time,it will seriously affect their work efficiency,even worse,it will cause serious harm to their health.For this cabin vibration,Seat suspension is mainly used to isolate it to improve the ride comfort of the driver.Currently there are three types of seat suspension: passive seat suspension,active seat suspension,and semi-active seat suspension.Due to its limited stiffness and damping coefficients,passive seat suspension cannot effectively attenuate low-frequency vibration;Although the active seat suspension can well attenuate the low frequency vibration,but its cost is high and reliability is low;Semi-active seat suspension has the advantages of simple structure,high reliability,and similar damping effect to the active suspension,so it has a good application prospect in the field of vehicle vibration reduction.This paper takes the semi-active seat suspension based on magnetorheological fluid shock absorbers as the research object,studies and discusses the problems in its semi-active control,mainly including the following aspects:(1)The damping characteristics of the magnetorheological fluid damper are tested.Based on the experimental data,the hyperbolic tangent-polynomial model of the magnetorheological fluid damper is established.According to the established mathematical model,the inverse model is deduced.The model can calculate the required input current according to the expected damping force calculated by the control algorithm and the speed and acceleration values of the piston,so as to realize the application of the semi-active control algorithm to Seat control.(2)A sliding mode control algorithm based on the reference model is designed based on the adaptive simplification of the five-DOF "body-seat" model.Aiming at the“chatter” problem in sliding mode control,fuzzy control is adopted to optimize its approach law,so that the system can automatically adjust the approaching speed according to the distance between the moving point and the sliding surface during the control process.At the same time,in the design process of the approach law,the hyperbolic tangent function is selected to replace the symbolic function in the switch term of the approach law,which further reduces the "chattering" of the system.(3)The simulation model of semi-active seat suspension was established by using Matlab/Sinmulink,and the vibration reduction effects of semi-active seat suspension and passive seat suspension under different road surfaces and impact load are compared and analyzed to verify the effectiveness of the designed control algorithm.Through simulation,it is found that the semi-active seat suspension using the designed fuzzy sliding mode control algorithm can effectively improve the vibration reduction effect of the seat suspension,compared with the passive seat suspension.When the vehicle is driving on B-level road,C-level road,D-level road and under impact load,the RMS value of the vibration acceleration of the semi-active seat suspension decreases by 54.3%,54.8%,53.9% and 59.8%,respectively,compared with the passive seat suspension.Finally,by changing the load mass of the seat suspension,the robustness of the control algorithm is analyzed.Through simulation,it is found that the designed control algorithm still has good control effect and high robustness under different load masses. |
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