| Vehicle seat suspension system is used to support the drivers and passengers,mitigate the impact acting on the humans induced by the uneven road and reduce the vibration transmitted from the vehicle body,it provides a comfortable environment for the drivers and passengers and has a great significance for improving the vehicle ride comfort.It is well known that when the stiffness of the linear passive vehicle seat suspension is smaller,the natural frequency of the system is smaller,the isolation frequency band is larger and the vehicle ride comfort is better.However,the static displacement of the vehicle seat suspension system increases and the load bearing capacity decreases.In order to overcome the dilemma existing in the linear passive vehicle seat suspension system,this paper presents a nonlinear vibration isolator which has Quasi-Zero-Stiffness(QZS)and applies it to the vehicle seat vibration isolation to achieve low frequency and large isolation frequency band,and also improve the vehicle ride comfort.The main contents of this paper are summarized as follows:(1)The dynamic characteristic and isolation performance of the QZS vibration isolator considering the effect of overload and underload are studied.Firstly,the primary resonance of the QZS vibration isolator under harmonic excitation is obtained using Harmonic Balance Method(HBM),the jump phenomenon is considered and the stability of the primary resonance is analyzed using Floquet method.Secondly,the 1/2 subharmonic resonance of the QZS vibration isolator under harmonic excitation considering the effect of overload and underload is obtained using HBM,the phenomenon of period-doubling bifurcations and their development into chaotic motion are analyzed by numerical method.Thirdly,the force transmissibility and displacement transmissibility are proposed to evaluate the isolation performance of the QZS vibration isolator,the effects of the damping,excitation amplitude and system parameters on the transmissibility of the QZS vibration isolator are studied,and also compared with an equivalent linear vibration isolator.Finally,a QZS vibration isolator is designed and the experimental study is conducted.The displacement transmissibility of the QZS vibration isolator is obtained by applying the harmonic base excitation displacement to the loaded QZS vibration isolator and compared with an equivalent linear vibration isolator.(2)The dynamic characteristic and isolation performance of the QZS vibration isolator with time-delayed cubic velocity feedback control are studied.Firstly,the primary resonance of the controlled QZS vibration isolator is obtained using multiple scales method,the effects of damping,cubic velocity feedback gain and time delay on the primary resonance are studied.Secondly,The jump phenomenon analysis of the controlled QZS vibration isolator without and with time delay is investigated using Sylvester resultant method and Levenberg-Marquardt optimization method,respectively.The critical excitation amplitude which leads to no jump phenomenon and the jump frequencies are obtained,the critical surface of the parameters that leads to no jump phenomenon is also considered.The stability of the primary resonance is analyzed using Floquet method.Thirdly,the1/3 subharmonic resonance of the controlled QZS vibration isolator is obtained using multiple scales method.The effects of damping,cubic velocity feedback gain and time delay on the amplitude-frequency characteristic and existence region of the 1/3 subharmonic resonance are also studied.Finally,the force transmissibility is proposed to evaluate the isolation performance of the controlled QZS vibration isolator,the effects of damping,cubic velocity feedback gain and time delay on the force transmissibility are studied,and also compared with an equivalent linear vibration isolator.(3)The dynamic model of the QZS vibration isolator under shock excitation and random excitation is established,the dynamic characteristic and isolation performance are studied.The dynamic responses of the QZS vibration isolator under shock excitation and random excitation are obtained using approximate analytic method and compared with numerical method to verify its validity.The appropriate performance index is defined to evaluate the isolation performance of the QZS vibration isolator under shock excitation and random excitation,the effects of the system parameters on the isolation performance are studied,and also compared with an equivalent linear vibration isolator.(4)Three kinds of Two-degree-of-freedom(TDOF)QZS vibration isolator are designed,the dynamic characteristic and isolation performance are studied.Firstly,the dynamic response and isolation performance of the Single-degree-of-freedom(SDOF)QZS vibration isolator is compared with the equivalent SDOF linear vibration isolator.Secondly,the dynamic response and isolation performance of the SDOF linear vibration isolator is compared with the TDOF linear vibration isolator while ensuring that the static displacements of both vibration isolators are the same.Thirdly,the dynamic response and isolation performance of three kinds of TDOF QZS vibration isolators are analyzed,the primary resonance is obtained using HBM and the peak dynamic displacement is obtained using backbone curve analysis and energy balancing method.Four performance indexes are defined to evaluate the isolation performance of the TDOF QZS vibration isolators and compared withSDOF linear vibration isolator,SDOF QZS vibration isolator and TDOF linear vibration isolator.Finally,the best structural parameter sets for the TDOF QZS vibration isolators based on the four performance indexes are identified.In addition,the best vibration isolator from the six different vibration isolators according to the four performance indexes is discussed.(5)The dynamic characteristic of the vehicle-seat-human coupled model considering the QZS vibration isolator is studied.When the QZS vibration isolator is in the ideal state,it is that the actual mass of the passengers match the specific designed mass of the vehicle seat suspension,a vehicle-seat-human coupled model of eight-degree-of-freedom that considers the QZS vibration isolator is established,the dynamic characteristic of this coupled dynamic model subjected to three different road excitations(shock excitation,harmonic excitation and random excitation)is analyzed using numerical method,the effects of the system parameters on the dynamic characteristic are studied,and also compared with an equivalent linear passive vehicle seat suspension.When considering the changing mass of the passengers,it is that the QZS vibration isolator is in the overloaded or underloaded state,the mass of the passengers is designed as an uncertain parameter.In order to further improve the vehicle ride comfort,a constrained adaptive back-stepping controller law based on the Barrier Lyapunov Function(BLF)is presented,an active vehicle-seat-human coupled model of three-degree-of-freedom that considers the QZS vibration isolator is established,the dynamic characteristic of this active coupled dynamic model subjected to road shock excitation is analyzed using numerical method,the effect of the controller law is studied.In summary,the dynamic characteristic and isolation performance of the QZS vibration isolator are studied systematically in this paper,the QZS vibration isolator is applied to the vehicle seat vibration isolation,the dynamic characteristic of the vehicle-seat-human coupled model considering the QZS vibration isolator is studied,the research results can give guiding significance for designing QZS vibration isolator as vehicle seat suspension. |
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