Research On Structural Acoustic Characteristics And Optimum Design Method For I.C.Engines

Centering on key theme of structural acoustic characteristics and optimization for internal combustion engine, the study on the low noise structure design, noise radio virtual prediction, assemblies'vibration behavior and acoustic characteristics wereperformed by using virtual design and experiment method.The acoustic characteristics of gear-cover were investigated by using the Discrete Calculation Method (DCM). The influence of the thickness of the part, rib, constraint condition and the position of exciting force on the radiation efficiency wasalso explained.Based on the analysis of the result from experiment and simulation, by application of modern optimal design methods, the design for reducing radiated noisefrom the structure of internal combustion engine was accomplished. According to the structure characteristic of the oil pan, gear cover, cylinder head cover, different optimal strategies were made based on HYPERWORKS/OPTISTRUCT software. By the method of shape optimization, topology optimization, topography optimization, the optimized design to lower the radiated noise of the surface were accomplished, and the radiated noise of the optimization was also evaluated by software simulation.Shape optimization was performed on a cylinder block of 4100QB diesel engine.The maximum of nature frequency related with the shirt of the cylinder block was obtained by optimizing twelve structure dimensions of the cylinder block with constrains of flexibility of the cylinder block, the point displacement, the weight of the cylinder block, meanwhile the sensitivity analysis of the block was carried out to illustrate the variables'effect on the response of the structure, and their contribution to the optimization was also discussed. Aim to reduce the radiated noise from engine, ladder frame was used on 4100QB diesel engine, the improvement of vibration was evaluated by the result of frequency response by MSC/NASTRAN software, and the radiated noise was also predicted by using SYSNOISE software.The vibration behavior and acoustic characteristics of the assemblies wereinvestigated by experiments. The effect of the assembling method, with Tap-Bolts or with Through-Bolts, and the value of the tightening torque were explained by the parameters, such as nature frequency, damping ration, frequency response function and sound radiated efficiency. To validate the results of software simulation,bench scale test was necessary. A research on the influence of multi-body dynamics modeling method on the bearing force simulation of an engine, including bench installation conditions, were presented. 4100QB diesel flexible multi-body dynamics model was built by employing the modal synthesis technique in the software Adams, the flexible engine cylinder blockcomponent include cylinder block, cylinder head, gear chamber, wheelhouse, and engine bracket, the flexible shaft component include the crankshaft, the flywheel and the connecting flange, and the other parts were treated as rigid bodies. By comparing the simulation results of different models, the effects of flexibility of cylinder block and crankshaft, installing method of engine, coupling flange, mounting stiffness and the elasticity of shaft coupling were discussed, and the simulation result was validated by the measuring engine block vibration acceleration.