Based on the parallel mechanism theory, a new vibration-isolating platform is designed and its kinetic equation is deduced. Taylor expansion is used to approximately replace the elastic restoring force expression of vibration-isolating platform, and the error analysis is carried out. The dynamic-displacement equation of the vibration-isolating platform is studied by using the Duffing equation with only the nonlinear term. The dynamic characteristics of the vibration-isolating platform are studied, including amplitude-frequency response, jumping-up and jumping-down frequency, and displacement transfer rate under base excitation. The results show that the lower the excitation amplitude, the lower the initial vibration isolation frequency of the system. The influence of the platform damping ratio on displacement transfer rate is directly related to the jumping-down frequency Ω and the external excitation frequency. The vibration-isolating platform is ideally suited for high-frequency and small-amplitude vibrations.
In order to further extend the effective isolation range of the quasi-zero stiffness (QZS) platform, the vibration isolation performance of the chaotic interval is improved. For a class of self-design quasi-zero-stiffness (QZS) vibration isolation platform, starting with chaotic motion of the non-linear vibration isolation system, the jumping interval is eliminated by means of transient chaos phenomena. The control method of damping increase is proposed in combination with the application of the Von der Pol Plane, which can make the jumping-down frequency to be decreased below the external excitation frequency, thus the effective isolation range of vibration isolation platform can be extended, and a lower isolation frequency can be obtained. Research shows that, when the solution of the motion equation of the platform system falls to resonant branch led by certain initial conditions, the resonant amplitude response will jump to the nonresonant branch by transient damping increase control method, which the removal time is determined by the Von der Pol Plane, hence making the platform system obtain the ideal vibration isolation performance. The research results have a significant importance for improving the low frequency and ultra-low frequency vibration isolation effect of such platforms, which lays a foundation for the popularization and engineering application, and can also provide a reference for control of other nonlinear vibration system.
The paper explains a concept of a vehicle molecular spring suspension whose stiffness in middle stage can be as low as 13 N/mm. The design of this suspension spring on the basis of a hydrophobic nanoporous material is introduced. The test methods of determining the static and dynamic mechanical properties of the novel suspension spring are described. The rationality of experimental design and the accuracy of theoretical analysis is proved by the negligible error between experimental results and theoretical analysis. The vibration isolation test results show that the natural frequency of the suspension can be as low as 1.06 Hz.
Automotive suspension systems are important parts of vehicles and are vital for ride comfort, safety, and handling stability. Various active and semi-active suspension configurations have been developed and applied to high-end cars, but passive suspensions are still the most widely used type because of their lower cost, higher reliability, simpler structure, and lack of energy consumption. Consequently, it is meaningful to study a novel passive suspension based on a hydrophobic microporous material, whose working mechanism is illustrated using the Laplace capillary principle. A stiffness model is built based on hydrostatic principles, the primary resonance response of the nonlinear dynamic system is established using averaging, the performance of the passive suspension is simulated using MATLAB Simulink, and the ride comfort is assessed based on the weighted root-mean-square acceleration. The results show that the natural frequency, suspension deflection, and weighted root-mean-square acceleration of the new suspension meet the design objectives. In addition, for a given natural frequency, the suspension deflection of the studied suspension is less than that of a linear suspension, and the proposed low-pressure molecular-spring suspension offers a new choice when designing passive automotive suspensions.
A molecular spring isolator comprising ZIF-8 with hydrophobic micropores, water, and a cylinder/piston unit is introduced. Liquid water can be intruded into the micropores of ZIF-8 under critical pressure. In the meantime, mechanical energy is stored. And once the external pressure is withdrawn, spontaneous capillary evaporation will occur. The stored energy, meanwhile, is released. This behavior is similar to a coil spring. The Laplace–Washburn equation is used to describe the force equilibrium of a single water column in a micropore. After that, the result of water infiltrating a great deal of hydrophobic pores is revealed by theoretical analysis and an experiment. An averaging method is devoted to computing the primary resonance response and its accuracy is proved by the fourth-order Runge–Kutta method. Furthermore, the energy transmissibility is used to estimate its vibration isolation capability. Finally, a vibration isolation test indicated that the inherent frequency of the isolator is as low as 1.3 Hz.
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