【作者】 马万福；

【导师】 高文志；

【作者基本信息】 天津大学 ， 动力机械及工程， 2005， 硕士

【摘要】 机体作为内燃机的骨架,是内燃机噪声的主要辐射表面。内燃机的激励力大部分都是通过机体传递给其他附件及覆盖件的,所以机体表面振动将直接影响内燃机的振动和噪声。计算机技术的快速发展使得有限元分析方法在内燃机的减振降噪研究领域得到广泛应用,但是由于机体构造和所受的载荷很复杂,因此在内燃机设计阶段利用有限元方法预测机体的振动和辐射噪声大多停留在模态分析阶段,而利用机体有限元动力响应分析来预测机体的振动和辐射噪声的方法刚刚起步,因此本文以柴油机4102BZQ的机体为例,对此方法进行了详细的研究。首先,利用三维建模软件Pro/E建立了机体的有限元计算模型,总结了机体计算模型的简化方法;通过利用大型有限元分析软件ANSYS对4102BZQ机体进行了自由模态和约束模态分析计算,得出了机体在自由模态和约束模态的前十阶的固有频率和振型,分析了约束对机体的振型和固有频率的影响规律;通过增加机体裙部厚度、主轴承隔板厚度和筋板厚度,加大了机体裙部的刚度,提高了机体的固有频率。其次,根据4102BZQ机体的主要工况和各气缸压力曲线,计算了机体各缸活塞侧向力、主轴承载荷和螺栓轴向载荷;根据有限元动力响应分析载荷简化原则编制了载荷施加命令流程序,合理地对机体施加载荷,利用ANSYS对机体进行了有限元动力响应分析,得到机体各节点的位移响应和机体随时间变化的应力分布。然后经过对机体有限元动力响应分析结果的后处理,仔细分析了机体表面振动分布情况,分析了活塞侧向力、螺栓轴向力和主轴承载荷对机体表面振动的影响。同时将振动测试原理与有限元动力响应相结合,从而实现了对机体表面振动速度的频域分析。而且根据GB7184-87,利用机体的动力响应分析结果预测了整机的振动烈度。最后根据内燃机机体的表面噪声辐射原理提出了利用机体有限元动力响应预测机体表面辐射噪声的一种简单实用方法。文章最后分析了内燃机机体表面辐射噪声的预测结果与实测值产生误差的原因,并提出了对预测方法的改进措施。更多还原

【Abstract】 As the frame work of internal combustion engine, the cylinder block is the mainnoise radiation surface. Most of exciting forces of internal combustion engine istransported to the accessories by the cylinder block,so the vibration of the block willdirectly affect the vibration and noise of internal combustion engine. With the rapidprogress of computer technology, FEM is widely used in the field of vibrationanalysis and noise assessment of internal combustion engine. However, the predictionof vibration and noise of engine block in design stage is only limited to modalanalysis for such complicated structures and complex exciting forces of cylinderblock. And predicting the vibration and noise of a cylinder block by using finiteelement transient dynamic analysis just begins. The method is discussed in detail inthis article by analysis of the cylinder block of 4102BZQ. An FEM model of the cylinder block is built for simulating the dynamiccharacteristics of the real structure by powerful 3D soft PRO/E. The method ofsimplification of the cylinder block’s simulation is described. The FEM modalanalysis of the cylinder block both at free-free condition and at real constraintcondition is performed by universal FEM soft ANSYS. The first ten order modes andfrequencies of the cylinder block are obtained. The inherent relation between theconstraints and the natural frequencies of the cylinder block is analyzed. Byincreasing the thickness of cylinder block skirt, reinforced ribs and main boring plates,the stiffness of the block skirt is improved, and the natural frequencies are increased.In order to perform transient FEM analysis of the cylinder block, the loads andconstraints are accurately calculated. The exciting forces are appropriately applied onthe cylinder block by making command flow programs according to the FEM rulesand principles. Then the time-history displacement of the nodes on the cylinder blockand the stress status of the cylinder block at any time are obtained by performingtransient dynamic FEM analysis to the cylinder block.After the time-history post-processing of the results of the analysis, the vibrationstatus of the surfaces of the cylinder block can be obtained. The influences on thevibration of the cylinder block caused by the exciting forces are studied in the article.Meanwhile, by using the theories of mechanical vibration principles, the frequencydomain analysis on the vibration velocity of the cylinder block is illustrated.Furthermore, the vibration strength of engine is predicted on base of the result ofFEM analysis of the cylinder block according to GB7184-87.By studying the basic acoustic theories, a simple and appropriate method ofpredicting the surface radiant noise of the cylinder block is developed according to theresult of transient FEM analysis of the cylinder block. The comparison between thepredicted result with that of test validate that is feasible to predict the noise of internalcombustion engine if the exciting forces and constraints are accurately simulated.更多还原