Research On Coupling Vibration Mechansim And Vibration Isolation Optimization Of Pow Unit-vehicle System

Diesel multiple unit(DMU)is the most economical and flexible solution for the speed increase of branch railway passenger car because of the equal power and comfort performance to the electric multiple unit and excellent ability of arbitrary marshalling and flexible operation,and low cost in initial stage.In our coutry with vast territory and numerous railway branch lines,DMU will become the best tool for incresing train speed and occupying passenger transport markets of branch line,and has wide development space and application prospect.As the power source of the DMU,the internal combustion power pack is the main excitation source of DMU and usually hanging at the bottom of the vehicle body in the form of two-stage vibration isolation.The weighs of power pack is more than 3t and take a larger proportion in the whole body,this will greatly reduce the car body stiffness and increase the elastic coupling of power pack and velhicle body,and result in strong coupling vibration and radiated noise of carbody which serious affect the passenger ride comfort of the DMU.Therefore,by breaking the traditional modeling and design method of ordinary two-stage vibration isolation system,this paper aim at the vibration isolaition design of two-stsge vibration isolation power unit-DMU vehicle system and is devoted to modeling the quantitative vibration transmission model and corresponding simplified theoretical model of two-stage power unit-DMU vehicle flexible vibration isolation system with passive subsystem,flexible frame and vehicle body,illustrating various mechanics behavior existing in the flexible vibration isolation system,providing corresponding optimization strategy and algorithm for two-stsge power unit-DMU vehicle flexible vibration isolation system to achive an optimized vibration level.(1)In order to illuminate the coupling mechanism of subsystem and two-stage vibration isolation main system,a there-degree-of-freedom simplified theoretical model and a 18-degree-of-freedom multiple rigid body dynamics moded are established for the vibration analysis of it.Then,the dimensionless natural frequency,amplitude and energy decoupling degrees of the two-stage vibration isolation system is prospoed and a comprehensive transmission rate which can be applied to multi-point and multidirectional coupling system is also presented.Finally the effects of subsystem parameters on inherent characteristics and vibration isolation characteristics of the two-stage vibration isolation main system are studied based on these.Rsults show that,the subsystem has great effect on inherent characteristics and vibration islation performance of the two-stage vibration isolation system,a relative large mass and appropriate stiffness and damping means means both excellent low frequency and high frequency vibration isolation of the two-stage vibration isolation system.(2)Aiming at there is no effective vibration isolation design method for the two-stage vibration isolation system with subsystem at present,the idea that using the subsystem as a vibration absorber is introduce in the vibration isolation design of power unit two-stage vibration isolation system.A six-degreee-of freedom dynamics model is established for illustrating the vibration absorber mechanism of a multiple degree of freedom absorber applied on the multidimensional coupled two-stage vibration isolation system.A two-stage optimization strategy is presented to the vibration isolation optimization design of the power unit two-stage vibration isolation system,in which the first and second isolator stiffness was firstly obtained by optimizing the main system,secondly the subsystem is used as an absorber of the main system and its isolator stiffness is optimized according to H? criterion and the effective of this method is verified by experiment.Finally,an experiment of isolation permance of the power unit is conducted to verify the method.Rsults show that,the vibration absorbing can reduce the energy inputed into the two stage vibration isolation system and transfer the the energy from the main system to itself by coulping with the modal of the main system in the derection which is applied exciting force and the optimization area of it's mass and moment of ratio includes the condition that the the two of the are small;the optimized power unit has excellent vibration isolation performance in both conventional condition and shutdown codition.(3)In order to clarify the rigid-flexible problem exist in the two-stage vibration isolation power unit-vehicle body flexible vibration isolation system,a vibration energy index that can comprehensive reflect the rigid motion and elastic vibration intensity of flexible structure is presented and a thin-walled box beam is proposed to represent the bending and twisting coupled charecteristics of vehicle body.The vehicle body and suspended equipment rigid-flexible coupled system simplified theoretical model is establish and the frequency response function is proposed analytically.The effect of the masss,installation position and isolator parameters of suspended equipment on the vibration performance of system is studied,and the coupled vibration mechanism is illuminated.Then,a rigid-flexible coupled two-stage vibration isolation system simplified theoretical model is established and the analytical solution of natural frequency,mode shape function and frequency response function of the system is proposed.The effect of the frist and second isolator parameters on vibration isolation characteristics of the system and the rigid-flexible coupled characterstic between substructures of the two-stage vibration isolation system are illuminated.Results show that,the flexibility of the frame and vehicle body greatly reduce the high frequency vibration isolation performance of the system and also increase the displacement amplitude of rigid motion modals.(4)Aiming at the problem of the complex modeling and huge computing quantity in the vibration analysis of two-stage vibration isolation power unit-vehicle flexible vibration system,a computationally efficient method for the vibration transmission model of two-stage power unit-vehicle flexible vibration isolation system based on frequency response function synthesis is presented.Then,the power flow transmission characteristics in each layer and the relationship between the power flow and isolator parameters is analyzed.Finally,the rigid-flexible coupled characterstic in the flexible vibration isolation system is illuminated.Results show that,modelling method have features of low computational complexity and clear logic,and can be applied in vibration isolation optimazition of this complex flexible vibration isolation system.(5)According to the problem of the low speed and poor convergence in the optimization of two-stage vibration isolation power unit-vehicle flexible vibration isolation system result of the numerous variables and objectives,a hybrid multi-objective genetic algorithm based on a reference point method comparison operator and local search operator is presented.Then,a two-stage optimaztion method for the vibration isolation optimal design for the two-stage power unit-vehicle flexible vibration isolation system base on the optimization goal and variable reduction is put forward.Rsults show that,the genetic algorithm and two-stage optimaztion method have good convergence and diversity at the same time,and the optimization efficiency is also excellent.All vibration performance indicators are promoted greatly after,and the whole vehicle system has excellent vibration level both in normal and start/stop operating condition of the engine.