Dynamic Characteristics And Experimental Investigation Of Power Unit Vibration Isolation Systems

Power unit is the main vibration source of cars and ships, and the vibration level of them can be significantly reduced through effective vibration isolation of power unit. With extensive application of thin and light structures in cars and ships, installed foundation of power unit presents a certain degree of elasticity. The elastic characteristics of installed foundation become much apparent with high-speed and high-power development trend of power unit, and the error between prediction and engineering practice of isolation effect increases. Surrounding vibration coupling characteristics of power unit and elastic foundation, dynamic model of power unit vibration isolation system of elastic foundation was proposed in this thesis, and coupling characteristics of vibration isolation system were studied, comparing with rigid foundation structure model.According to vibration isolation problems of power unit, dynamic model of rigid foundation isolation system was established to make theoretical simulation and calculation of transmissibility. It was found that theoretical efficiency of vibration isolation couldn’t fit with actual condition well in high-frequency domain, which meant that the model was not exact when we regarded the foundation as a rigid one. Derivation of system transfer characteristic expressions was carried out by mechanical impedance and terminal parameter method, and influences of foundation parameters on vibration isolation efficiency were evaluated with transmissibility. Results show that the amount of transmissibility curve peak increases and the transmissibility become higher because of the elasticity of foundation; the system can be regarded as a rigid foundation if the equivalent mass and rigidity of lumped parameter foundation or the elastic modulus and thickness of flexible beam foundation are large enough.Dynamic model of power unit vibration isolation system of elastic foundation was established, and power flow equations were derived with combing substructure mobility method. Power flow was used as evaluation index to discuss the impact of different structural parameters on isolation effect. Firstly, the elastic foundation was simplified into lumped parameter model to analyze the impact of elastic foundation on power flow transmission:power flow transferred to foundation decreased with the increase of quality and rigidity of foundation; the foundation could be regarded as a rigid one when quality and rigidity of it were large enough. Then, the elastic foundation was simplified into a flexible beam model, and power flow characteristics under different structural parameters were discussed. Results show that even-order modals of foundation beams are not excited and the amount of wave crests in high-frequency domain decreases when isolators are arranged symmetrically; power flow transferred to foundation decreases with the increase of amount of vibration isolators and elasticity modulus of foundation beams and with the decrease of damping factor; in low-frequency domain, vibration isolation problems of vibration isolation system with flexible beam foundation can be solved by simplifying it as a lumped parameter foundation.According to the influence of installation conditions on power unit in engineering, dynamic model of inclined isolation system based on elastic foundation was proposed, a set of matrix formulations relating to dynamic parameters of vibration isolation system were derived, and power flow transmission expressions were presented. Transverse-roll coupled vibration characteristics of the system were studied deeply, effects of vibration isolation under decoupling conditions were discussed, influences of standing wave effect of isolators and second harmonics of power unit on power flow transmission were analyzed. It is founded that the system can be decoupled and its vibration energy transmission can be reduced significantly when structure parameters of mounts are reasonable; the power flow in high frequency increases significantly resulting from standing wave effect of isolators; the existence of second harmonics of power unit also make power flow increases.The installed foundation of power unit was simplified to a flexible clamped beam, its vibration characteristics under Euler and Timoshenko beam theory were analyzed, and the elastic properties of it were studied experimentally. Researches show that natural frequencies of Euler beam are lower than that of Timoshenko beam; in measuring process of vibration signal, some vibration modal will be missed if sensors are arranged on nodes or section lines of the system; natural frequency of the system decreases for influences of acceleration sensor’s quality; the accuracy can be improved slightly by increasing hitting points, but the process is fussy, so we should choose appropriate hitting points in engineering according to actual situation.