Research On Transient Characteristics And Control Strategies Of Magnetorheological Squeeze Mount

People's requirements for comfort of automobiles are constantly improving.Engine vibration is one of the sources of vehicle vibration.Effective isolation of the transmission of engine vibration to the body and the development of mounts with good isolation effect are hot issues in modern vehicle design.Magnetorheological fluid(MRF)is a kind of intelligent material with convenient control and fast response,which is suitable for intelligent structure and control.MRF based on squeeze mode will generate a large response force under very small squeeze displacement,which meets the requirement of engine vibration isolation.However,the dynamic response of MRF has complex nonlinearity and time delay.The squeeze transient characteristics of MRF and the optimization and control of engine mount structure based on it are urgent problems to be solved.Furthermore,the squeeze flow transient characteristics of MRF are studied theoretically and experimentally to complete the analysis and expression of the transient characteristics;the structure design and optimization of MR squeeze mount are carried out according to the transient characteristics,and the engine mount control strategy is studied based on the transient characteristics.The main work and conclusions are as follows:1.Experimental study on the squeeze flow transient characteristics of MRF:Firstly,a testing device for the squeeze dynamic characteristics of MRF is designed,and the MRF squeeze test is carried out.Then,the test data are processed to remove the influence of noise force on the test results.Finally,the squeeze transient characteristics of MRF are analyzed.The main conclusions are as follows:(1)The influence of inertia force increases with the increase of frequency,and as the inertia force increases with the increase of squeeze speed,the inertia force at the rising edge of squeeze speed is obviously larger than that at the falling edge;(2)The increase of excitation frequency and amplitude,and the decrease of current and initial gap will make MRF yield more easily.;(3)The system's hard-to-control coefficient is about 0.7 at low frequency and 0.5 at high frequency,and the system's time delay can not be ignored.Increasing the excitation frequency and decreasing the current or excitation amplitude will reduce the time delay of MR devices.2.Establishment of squeeze flow transient dynamic model of MRF:Establishment of squeeze flow transient dynamic model of MRF.Firstly,the double viscous constitutive model is used to express the yield of MRF,and the inertia term in Navier-Stokes equation is solved to obtain the time domain model of MRF extrusion;then,according to the theory of zero-pole cancellation,the time-domain model is compensated to obtain the squeeze flow transient model of MRF;finally,the model is validated and the squeeze transient characteristics of MRF can be expressed by the established model.3.Design and optimization of MR squeeze mount structure:Structure design and optimization of MR squeeze mount.Firstly,the structure of MR mount is designed;then,according to the squeeze transient characteristics of MRF,the inertia force,electromagnetic response time and the adjusting range of damping force are taken as the optimization objectives.MMFD optimization algorithm was used to optimize the structure parameters of MR squeeze mount.The optimization results show that the adjusting range of damping force increases by 16.3%,the influence of inertia force decreases by 1.7%,and the electromagnetic response time decreases by 20.7%;finally,the size of the main rubber is designed,and the model of MR squeeze mount is obtained.4.Research on semi-active control strategy of MR squeeze mount:Research on semi-active control strategy of MR squeeze mount.Firstly,according to the engine vibration model,the vibration generated in the engine working process is analyzed;then,according to the excitation of the engine,the dynamic model of the engine vibration isolation system is established;finally,based on the mount model established above,the LQR controller is designed,and compared with the PID control and the Fuzzy control.Compared with PID control and Fuzzy control,the LQR control mount reduces the engine vibration acceleration by 26.0% and 26.5% at low frequency,while the vibration acceleration transmitted to the frame at high frequency decreases by 25.2% and 24.5%,respectively.The significance of this study lies in:(1)revealing the transient characteristics of MRF squeeze flow,and establishing a transient model to express them;(2)Based on the transient characteristics,the semi-active engine mount is designed and optimized,and the semi-active control strategy is studied.