Dynamic Analysis On Two-Stage Vibration Isolation System Of Powertrain Based On Rigid-Flexible Coupling Model

Diesel motor cars are widely used in less-developed areas and regional transportation where passenger flow is rather small or the development of electrification is not suitable, for its low cost, flexibility, convenience and reliability. The powertrain (power package) was usually used as its power source. The vibration characteristics of the system with multiple vibration source, broadband and strong coupling. In order to reduce the vibration of the system and improve the riding comfortability, the two-stage vibration isolation system was usually used in the powertrain, and the optimization design was usually based on multi-rigid-body model, ignoring the effect of component flexibility on the vibration isolation performance of the system. In order to qualitatively analyze the influences of flexible intermediate frame on vibration isolation characteristics of two-stage vibration isolation system, explore the influences of isolator parameters changes (stiffness and damping) on the vibration isolation characteristics, solve the problem of excessive vibration of powertrain in start and stop conditions and the vibration problem of vehicle body floor caused by structural vibration, improve the traditional optimization design method with multi-rigid-body model, guide the optimization design of two-stage vibration isolation system, the multi-body system dynamic model considering the flexibility of the intermediate frame was established and the system dynamics analysis were done.First of all, the dynamic model of two-stage vibration isolation system containing subsystems was established, and the common evaluation indexes of vibration isolation performance and their advantages and disadvantages were summarized, and the traditional optimization design method of two-stage vibration isolation system was introduced. Then, a finite element model of intermediate frame was established by combination simulation of Hypermesh and ANSYS. The correctness of the finite element model was verified by contrasting calculated modes and experimental modes. On this basis, a dynamic model of rigid flexible coupling multi-body system considering flexibility of the intermediate frame and the dynamics model of multi-rigid-body system treating the intermediate frame as a rigid body were established in ADAMS. The correctness of multi-body system was verified through modal testing of powertrain. By calculating free vibration and forced vibration of the system, influences of the intermediate frame’s flexibility on inherent characteristics (mode frequency and vibration coupling energy) and response characteristics (vibration intensity of components, dynamic reaction force at the second stage vibration isolators and vibration level differences) of the system were analyzed. Influences of vibration isolator parameters changes on the vibration isolation characteristics of the system were analyzed comprehensively by changing the stiffness and damping of the vibration isolator. Combined with the phenomenon of excessive vibration during start and stop conditions of powertrain test and the problem of vehicle body floor vibration caused by structural vibration, and the insufficiencies of traditional optimization design method with multi-rigid-body model (parametric model), the damping strategy of the rigid flexible coupling system was discussed.Research results showed that flexibility of the intermediate frame can reduce the system’s natural frequency and the decoupling degree of the main modal direction, and make the amplitude response of the system appear "shift frequency" or "increase frequency" phenomenon, that there is mainly "shift frequency" the low frequency band and mainly "increase frequency" in the high frequency band, and two kinds of phenomena occur at the same time in the middle frequency band. Flexibility of the intermediate frame has little influence on the vibration intensity of the unit, but it will increase the vibration intensity of itself and accessory equipment in most working conditions, and it can increase the dynamic reaction force at the second stage vibration isolators, and reduce vertical vibration level differences of the first stage vibration isolators. Changes of stiffness and damping of vibration isolators will affect the displacement response spectrum at the second stage vibration isolators and the velocity response spectrum at the unit vibration intensity measurement point, and then affect the performance of the vibration isolation system. It can effectively restrain the vibration response of the unit at start and stop working conditions and can effectively suppress the structural vibration in the high frequency band with the vibration isolation scheme that large stiffness is adopted at start and stop working conditions and small stiffness is adopted at normal working conditions; besides, it’s also effective to use the vibration isolation scheme that large damping is adopted at start and stop working conditions and in low frequency band. It can significantly reduce the dynamic reaction force at the second stage vibration isolators and control the structural vibration by reducing the vertical stiffness of the first stage vibration isolators and the stiffness of the second stage vibration isolators in any direction. Besides, it also can reduce the displacement response at the second stage vibration isolators in the higher frequency band and effectively control structural vibration of the system by moderately reducing the damping of the first stage vibration isolators.Relevant conclusions have guidance in optimization design of two-stage vibration isolation system, mode matching of the system, vibration control of power unit in start and stop conditions, and structural vibration control of the system.