| Due to the advantages of low operation cost,flexible grouping,good environmental compatibility,good power performance and comfort,diesel vehicles have been widely used in recent years.Modern diesel vehicles generally adopt power dispersion mode.In this way,the main power source of diesel vehicles comes from the powertrain arranged under the bus body.During the operation of the diesel vehicle,the excitation source and frequency of the powertrain are complex,which will cause strong vibration of the power system and seriously endanger the life and safety of the mechanical equipment.At the same time,the dynamic reaction transmitted to the body will reduce the ride comfort of the passengers.Therefore,the vibration control of the powertrain has become a key factor restricting the development of the diesel vehicle.In the case that the traditional passive rubber isolator has been unable to further improve the vibration isolation performance of the system,the vibration isolation system of “ low stiffness spring isolator in parallel with parameter adjustable damper “ is the most promising technical scheme for engineering application.The key technical problem is to develop the parameter adjustable damper with low-frequency large damping and high-frequency small damping characteristics.In order to solve the key technical problems,this paper intends to use the finite element method to explore the factors and internal mechanism that affect the low and high frequency characteristics of magnetorheological damper with adjustable parameters.On this basis,the optimization design and application research of magnetorheological damper are carried out.The research work has certain theoretical significance and engineering application value.Firstly,MAXWELL and FLUENT are used to establish a multi-physics coupling model which can be used to analyze the broadband characteristics of magnetorheological damper,and the correctness of the simulation model is verified.Based on the model,the reasons for the different characteristics of the damper at low and high frequencies are explored,and the pressure distribution law in the damping channel is analyzed to provide reference for determining the structural factors affecting the performance of the damper.Then,based on the multi-physics coupling model,the single-factor analysis of the structural parameters of the damper is carried out,and the key parameters that significantly affect the damping performance of the damper are determined as the optimization design variables.The damping ratio at low and high frequencies is determined as the test index for response surface analysis.Then,combined with the vibration characteristics of the powertrain double-layer vibration isolation system of the diesel vehicle,the low-frequency damping coefficient required by the system is taken as the constraint condition for the damper optimization,and the maximum low-frequency damping ratio is taken as the optimization objective to optimize the parameters of the damper.At the same time,combined with the low and high frequency characteristics of diesel vehicle powertrain,the damper structure is improved to further improve the damping ratio.Finally,the“ low stiffness spring isolator parallel parameter adjustable damper “ vibration isolation system with two optimized dampers and the conventional rubber vibration isolation system are applied to the double-layer vibration isolation experimental platform of the power unit for vibration isolation performance comparison test.The results show that the multi-physical field coupling model which can describe the broadband vibration characteristics of magnetorheological damper is established,and the simulation model is verified according to the experimental data.It is found that the error is less than 6% at low frequency and less than 2% at high frequency,which can be used to complete the follow-up work.From the perspective of magnetorheological fluid flow,it is found that the viscosity changes greatly under low frequency conditions,and the viscosity is small and stable in a period of time,resulting in a rectangular indicator diagram.At high frequency,the viscosity is small,and the magnetorheological fluid changes with the motion law of the piston,resulting in a circular indicator diagram.The pressure distribution in the damping channel accounts for 80% ～ 95% of the pressure distribution in the whole damper,so it is necessary to select the length of the damping channel as an important structural parameter for optimization design.Through single factor analysis,it is determined that piston diameter,piston rod diameter,damping gap,effective damping channel and coil length are the key parameters affecting the low and high frequency damping ratio of damper,which should be used as optimization design variables.The Box-behnken test design was carried out on the selected design variables,and the low and high frequency damping ratio was determined as the test index.The response surface analysis was carried out.According to the test index of low and high frequency damping ratio,the significance degree of each factor was quantitatively analyzed : effective damping channel > piston rod diameter > coil channel length >piston diameter > damping gap.The influence degree of interaction between the two factors on the index is : damping gap-piston rod diameter > damping gap-coil channel length > damping gap-effective damping channel > piston diameter-damping gap >piston rod diameter-piston rod diameter.With the low-frequency damping coefficient of 15.88 N.s/mm required by the studied internal combustion powertrain as the constraint condition and the maximum damping ratio of damper at low and high frequencies as the optimization objective,the quadratic response surface model constructed by the optimization objective was optimized and trial-produced.The test results show that the low frequency damping coefficient of the optimized magnetorheological damper is 2.32 times higher than that of the original damper,and the low and high frequency damping ratio is 6.1.In order to further improve the damping ratio,the structural optimization of the damper is carried out.The test results show that the low frequency damping coefficient of the variable stiffness magnetorheological damper after structural optimization meets the matching damping range of the system,the high frequency damping is reduced by 76 %,and the low and high frequency damping ratio is 34.6.The parameter optimization and structural optimization of magnetorheological dampers are combined with low stiffness isolators to form different vibration isolation schemes,which are applied to the double-layer vibration isolation experimental platform for vibration isolation performance comparison test.The experimental results show that the variable stiffness magnetorheological damper vibration isolation scheme can effectively attenuate the vibration velocity of the unit and make the unit in good working condition.Compared with the conventional vibration isolation system,the dynamic response of the parameter optimized magnetorheological damper scheme is reduced by 4.3%-37.6%,while the variable stiffness piston magnetorheological damper vibration isolation scheme can further reduce the dynamic response by 3.8%-35.3%.The vibration velocity and dynamic response show that the vibration isolation scheme composed of variable stiffness piston magnetorheological damper and low stiffness spring damper can improve the system stability and vibration isolation performance in the whole speed range.The research results of this paper are to establish a multi-physical field coupling model of magnetorheological damper with wide frequency excitation range,explain the internal mechanism of magnetorheological damper with different characteristics under low and high frequency conditions,and optimize the design of magnetorheological damper,which has certain theoretical significance and engineering application value.It can not only promote the development of “ low stiffness isolator parallel adjustable damping shock absorber “ composite vibration isolation system of diesel vehicle powertrain,but also provide new research ideas for vibration control of the same type of power machinery. |
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