Research On Nonlinear Vibration Isolation Method And Technology Of High-Static-Low-Dynamic Stiffness For Vehicle Seat

Vehicle seat suspension plays an important role in attenuating the whole-body vibration of the driver and improving the vehicle ride comfort.In a variety of excitations applied on the automobile,the low-frequency vibration is the most harmful to human health.Besides,it is also the most difficult to be isolated.As we all know,inherent contradiction between the natural frequency and the static deflection exists in the traditional linear seat suspension.As a result,it is not easy to isolate the low-frequency vibration without sacrificing the load bearing capacity.However,this contradiction can be well overcome by the nonlinear seat suspension with high static and low dynamic stiffness.The high-static-low-dynamic stiffness(HSLDS)seat suspension has the advantages of small static deflection and low natural frequency,exhibiting excellent low-frequency or even ultra-low-frequency vibration isolation performance.Therefore,a comprehensive investigation on the HSLDS seat suspension is of great theoretical and engineering significance for improving the vehicle ride comfort.The main points of this paper are summarized as follows:(1)A novel HSLDS seat suspension is designed based on the principle of combining the positive stiffness parallel with the negative one.The restoring force and stiffness characteristics of the seat suspension are first obtained by statics analysis and further verified using the software of ADAMS.Then,the steady-state response of the suspension system under harmonic base excitation is obtained using the harmonic balance method(HBM).The influence of structural parameters on the dynamic characteristics of the suspension system is analyzed subsequently.Besides,the condition of avoiding the jump phenomenon is also determined.At last,the displacement transmissibility of the HSLDS seat suspension is obtained with the initial isolation frequency also derived.The result shows that the HSLDS seat suspension possesses a more excellent low-frequency vibration isolation performance than that of the linear counterpart.It can even achieve the whole-frequency vibration isolation under certain conditions.(2)The influences of load deviation caused by the weight change of driver on the dynamic characteristics and vibration isolation performance of the HSLDS seat suspension are investigated from the point of view of the mass ratio.The steady-state response of the suspension system is obtained first using the HBM.The effects of load deviation on the dynamic characteristics and vibration transmissibility are investigated subsequently.Then,the 1/3 subharmonic resonance of the suspension system is obtained using the incremental harmonic balance method(IHBM).Parametric analysis on the 1/3 subharmonic resonance is also conducted.At last,the effects of load deviation on the shock isolation performance of the HSLDS seat suspension are analyzed.It is shown that the load deviation can make the suspension system exhibit the softening stiffness property and lead to a worse isolation performance in high frequencies than that of the linear seat suspension.Besides,lowering the excitation amplitude and increasing the damping are beneficial to the avoidance of 1/3 subharmonic resonance.Moreover,load deviation can also make the shock isolation performance worse.(3)A geometric nonlinear damping based on the designed seat suspension is proposed with the purpose of avoiding the unbounded response.The mathematical model of the nonlinear damping is developed first by statics analysis and the steady-state response is obtained using the averaging method.Then,the effects of nonlinear damping on the dynamic characteristics and the displacement transmissibility of the HSLDS seat suspension are investigated.At last,an equivalent damping ratio is defined in order to explain the effects of the nonlinear damping.It is shown that the nonlinear damping can eliminate the phenomenon of unbounded response essentially and lead to such a phenomenon that increasing the excitation amplitude can make the peak transmissibility lower.(4)A time-delayed cubic displacement feedback control is proposed in order to improve the isolation performance of the HSLDS seat suspension when the excitation amplitude is large.The steady-state response is obtained first using the multiple scales method.The effects of feedback gain and delay time on the dynamic characteristics and displacement transmissibility are investigated,which provides guidelines for the selection of feedback parameters.Then,an equivalent damping ratio is defined in order to explain the effects of vibration control of the proposed method.The result shows that choosing appropriate feedback parameters can reduce the transmissibility in resonant region effectively with the vibration isolation performance in high frequencies unaffected.(5)An eight degrees-of-freedom(DOF)of the car-seat-human coupled model is established for considering more realistic situations.This coupled model is comprised of a quarter car model,seat suspension with cushion and a lumped parameter model of the human body with four DOF.The responses of human body under harmonic base excitation,shock excitation and random excitation are obtained respectively using the Runge-Kutta method.Then the evaluation indexes of vibration isolation performance for the seat suspension under different excitations are defined.The results show that the HSLDS seat suspension can improve the vehicle ride comfort.The greater the stiffness ratio is,the better the isolation performance becomes.Besides,the isolation performance of the HSLDS seat suspension becomes worse when the load deviation happens.(6)A prototype of the HSLDS seat suspension is developed and the vibration test bench is established.The acceleration transmissibility of the seat suspension under harmonic base excitation is obtained by experiment.It is shown that the HSLDS seat suspension possesses lower resonant frequency and initial isolation frequency than those of the linear counterpart.In addition,increasing the stiffness ratio can improve the low-frequency vibration isolation performance of the HSLDS seat suspension.