Study On Low-frequency Vibration Isolator For Double-layer Vibration Isolation System Of Power Units

Diesel multiple unit(DMU)is the most economical and flexible solution for the speed increase of branch railway passenger car because of the comparable power and comfort to the electric train and excellent ability of arbitrary marshalling and flexible operation,and the low cost in initial stage.However,with the lightweight(materials and structures)and the increasingly stringent vibration control of DMU in various countries,the vibration isolation performance of the existing dual-layer vibration isolation system for internal combustion power pack needs to be significantly improved.The traditional rubber isolator is difficult to be further optimized.In order to develop a new type of low-frequency vibration isolator that significantly improves the vibration isolation performance of the system,the following works have been done:The test bench was built with reference to the double-layer vibration isolation system of a typical internal combustion power pack.A simulation model with the unit and frame of the test bench as soft bodies was established.The accuracy of the model was verified by modal tests.Through the analysis of frequency sweep characteristics,the influence of the three-way stiffness variation of the vibration isolator on the vibration isolation characteristics of the system was discussed.The analysis results showed that the horizontal stiffness variation of the vibration isolator has little effect on the vibration isolation performance of the system.The reduction of the horizontal stiffness mainly causes the frequency shift of the system vibration speed and the transmission force response in the low frequency band,and has basically no effect on the high frequency band;Reducing the vertical stiffness of the first and second isolators may increase the vibration intensity of the system's low frequency band(corresponding unit start-stop condition)to a certain extent,but it can effectively reduce the force transmissibility of the system's mid-to-high frequency band(corresponding to normal operation of the unit).On this basis,a new type of vibration isolator was proposed to have the characteristics of small vertical stiffness,large horizontal stiffness,and different lateral and longitudinal horizontal stiffness.Two optimization solutions for vibration isolator were proposed in combination with the actual structure of the engineering object: rubber spring combination vibration isolator,spring isolator and rubber stopper as displacement restrictor.The design ideas of the traditional rubber isolator and the limitations of the classical formulas were systematically analyzed.The Mooney Rivlin model parameters were fitted by the rubber uniaxial compression test,and the correctness of the simulation results of the rubber deformation characteristics were verified when the compression deformation was less than 25%.The effects of different slotting angles and width on the stiffness of the ring-shear type rubber isolators were analyzed,which provided a basis for the structural design of the newtype low-frequency isolators.This paper analyzes the problem that the new low-frequency vibration isolator may weaken the system's vibration isolation performance due to the effect of the spring standing wave.The dynamic model of the spring series rubber gasket was established by four-end parameter analysis method.The numerical solution of the relationship between the system transmission rate and the stiffness and the damping ratio of the rubber sheet was deduced.Theoretically,the effect of the standing wave of the spring can be effectively suppressed by connecting the rubber sheet with appropriate stiffness and damping ratio in series,which has been verified by experiments.Taking the vibration intensity and the reaction force of the secondary isolator as the evaluation index,the experimental comparison of the original vibration isolator scheme,the first-stage vibration isolator optimization scheme and the second-stage optimization scheme were conducted.It is verified that the new low-frequency vibration isolator solution with spring isolator and rubber stopper significantly improves the vibration isolation performance of the system.The above conclusions have practical engineering guidance value for optimizing the performance of the double-layer vibration isolation system for internal combustion vehicles,and also have certain reference value for the development of the double-layer vibration system of power machinery.And provide a research foundation for further study of variable stiffness actuators for semi-active control systems.