【作者】 林琼；

【导师】 郝志勇；

【作者基本信息】 浙江大学 ， 动力机械与工程， 2008， 博士

【摘要】 随着现代发动机数字化仿真分析研究的不断深入,迫切需要解决发动机系统中的摩擦学特性与动力学特性耦合的问题,这也是发动机振动噪声控制研究水平不断提高的技术需求。本文对发动机系统中的摩擦学行为与动力学行为的耦合特性进行了开拓性的研究,采用有限元,非线性有限元和柔性多体动力学的方法建立了一个包含多种摩擦学特性的发动机数字化虚拟样机,为发动机动力学系统的评估分析和优化设计提供了可靠的数据平台。文章首先系统地分析了发动机中存在的各种摩擦学现象,将摩擦行为分为两个研究系统:油膜动力润滑摩擦系统和干摩擦系统。将弹性流体动力学和摩擦学理论引入多体动力学仿真技术中,提出了一种针对曲轴系统与油膜动力润滑摩擦耦合的联合仿真技术。以一台车用四缸柴油机为例建立了曲轴轴系与流体动力润滑主轴承耦合的发动机虚拟样机,系统地得到了发动机主轴承载荷、轴心轨迹以及油膜最小厚度等数据。通过分析发现发动机曲轴系统的油膜动力润滑摩擦行为会对系统的动力学特性产生较大的影响,使用流体润滑耦合的多体动力学系统进行仿真分析能更真实地反映发动机的实际工作状况。因此,在动力学建模和仿真计算时应该考虑系统中的油膜动力润滑摩擦行为。发动机在运行时有些运动副不可避免地会出现干摩擦现象。本文针对发动机运行中的干摩擦问题,提出了一种车用金属材料干摩擦特性的试验分析方法。通过自主设计的金属干摩擦特性试验装置,测量得到了干摩擦迟滞特性曲线以及等效刚度与阻尼变化规律,并将试验数据和理论模型进行比较分析,验证了理论模型的正确性与不足。参照理论模型与试验装置建立了相应的非线性有限元分析模型,并将有限元仿真计算结果与试验及理论结果进行对比,发现有限元模型结果与试验结果以及理论计算结果具有较好的吻合程度,验证了有限元分析方法可以用于进行实际机械结构金属材料干摩擦表面的接触分析。最后,以活塞-缸套系统为研究对象,提出了采用非线性有限元技术与多体动力学仿真技术相结合的方法,建立了包含子系统干摩擦行为的发动机多体动力学模型,仿真结果指出考虑了非线性接触摩擦的活塞-缸套多体动力学系统更真实地反映了金属表面所受到的侧向力冲击载荷,其摩擦力数值也更能反映实际情况。本文建立了一个完备的包含摩擦学行为的发动机虚拟样机,对发动机油膜动力润滑摩擦和干摩擦问题进行了开拓性和基础性的研究,为发动机动力学分析和振动噪声控制的研究提供了可靠的数据平台,为发展和完善发动机数字化设计和仿真分析技术提供了重要的基础研究成果。更多还原

【Abstract】 With the development on the research of modern engine numerical simulation technology, the coupling behavior of friction characteristic and dynamic characteristic in engine is cried for solving, which is also demanded by the research of engine NVH control technology. The pioneering study on the coupling characteristic of engine’s friction behavior and dynamic behavior was performed in this thesis. An integrated engine numerical virtual prototype including several frictional characteristic was build. It’s comprised of finite element method, non-linear finite element method and multi-body dynamic method was proposed, which provide a reliable data-base for the optimization and evaluation of engine’s dynamic system.First, the dissertation systemically analyzed all kinds of the friction phenomenon in engine and then divided them into two research system: hydrodynamic lubrication friction system and dry friction system. A united simulation technology for the coupling behavior of the hydrodynamic lubrication friction system and crankshaft system was proposed, which introduced the EHD theory and friction theory into multi-body simulation technology. By building a virtual prototype of a four-cylinder diesel engine for vehicle which coupled with a crankshaft system and the bearing hydrodynamic lubrication, the main bearing force, the minimum thickness of the oil film and its working characteristic can be systematically obtained. The obtained simulation result indicated that the hydrodynamic lubrication friction behavior will greatly affect the system dynamic characteristic of engine. To build a more reliable engine virtual prototype should consider the friction behavior as well as the progress of the numerical simulation and design.Some of the engine’s moving parts always have some inevitable friction phenomenon when it’s was working. Aimed at these dry friction problems, a method on the test research of the metallic frictional characteristic was proposed. A test-bed of metal’s dry friction characteristic was build to gain the hysteresis curve, equivalent stiffness and damping. The compare between test data and theory data of hysteresis curve, equivalent stiffness and damping was made to validate the theory model. The corresponding NFEM model was build in MARC and the result of FEM model was consistent with the test and theory data which provide the reliable computation for the NVH simulation of engine and validate the feasibility of the non-linear finite element method for the metallic dry friction analysis of the practical mechanical structure.At last, taking the piston-linear system as example, an integrated method integrated with non-linear finite element method and multi-body dynamic simulation method was proposed to build an engine multi-body dynamic model which concluding the sub-system’s dry friction behavior. The simulation result indicated that the piston-linear multi-body dynamic system with non-linear contact friction behavior showed more reliable lateral impact load between metallic surfaces and the dry friction of piston-linear system brought a biggish force fluctuation in main bearings.The dissertation carried out the pioneer studies and basal research of the EHD and dry friction problem to build an engine virtual prototype with friction behavior.It provided a reliable data-base for the engine dynamical analysis and NVH control technology. It also developed the numerical simulation technology of engine, and achieves some valuable production.更多还原