【作者】 彭伟春；

【导师】 马文星；

【作者基本信息】 吉林大学 ， 机械设计及理论， 2004， 硕士

【摘要】 在世界工程机械市场，小型多功能液压挖掘机属产销量最大的工程机械产品之一。小挖的主要适应场合为：公路养护、园林绿化、小区建设、市政工程及农田建设等。其机动能力强、体积小，适合于各种土方量分散、作业范围狭窄的工况。由于我国目前正处于全面开展基础设施建设阶段，沿海地区正趋于基础建设逐步完善阶段，小挖应用的市场环境日益扩展并呈现可以预见的强劲后市，此时对小挖进行一些理论联系实际的研究显然具有重要的现实意义和长远的指导意义。国内小挖目前整体技术水平处于国际二十世纪八十年代末九十年代初水平，与国外先进技术的差距主要体现在整机匹配、微操作性能、维修性、可靠性及外观质量上，而优势仍主要建立在价格优势和服务优势上。国外小挖目前水平可以称之为渐趋完美、渐入佳境，其功能的可靠性，操作的流畅性和舒适性不必详述，即使其驾驶室内的美观与质感也几可与国产轿车蓖美。国外小挖目前的发展动向主要体现在：以一机多能为目标的多功能化；以提高操作性能为目标的智能化；以节能为目标的功率模式控制；以动态设计分析为基础的可靠性设计；以人为本的驾驶室设计；基于微电子技术的自动监控系统的发展。本文以HE39的研发、设计、制造及试验为基础，对小型多功能液压挖掘机进行了研究。HE39主要结构分为三大部分：工作装置、回转平台、底盘；工作装置通过转向头铰接于回转平台的前端；回转平台与底盘间通过回转支承联接；发动机后置于回转平台上；驾驶室置于回转平台的左前角；底盘前端装有推土铲；行走架上装橡胶履带；传动系统为总功率控制液压系统，其操纵方式为<WP=71>全液压先导式；电器系统兼有起动、照明、监控和自动报警功能。在挖掘参数上，HE39突出了挖掘深度的优势，符合国内市场用户的需求，因为在国内很多施工现场，对小挖的挖掘深度都有明确的要求。挖掘参数的设计涉及多方面的因素，其中主要有挖掘力、平衡重、轮距、底盘宽度以及工作装置自身的约束条件。其根本在于力矩的平衡。对斗杆油缸全行程理论挖掘力进行计算，得到的变化曲线符合实际工况的需要，在切入土壤时阻力逐渐增加，挖掘力也渐增，脱离土壤时阻力渐减，挖掘力渐减；最大挖掘力的大小与系统压力、斗杆缸缸径、各铰点力臂有关，可以根据设计的需要进行优化；在大多数情况下，系统压力、油缸缸径差别不大，故斗杆缸理论挖掘力的大小及变化曲线是否合理主要取决于铰点的设计。 对铲斗油缸全行程理论破碎力进行计算，得到的变化曲线符合实际工况的需要，铲斗在切入土壤的过程中受到的阻力渐增，铲斗的破碎力也渐增，铲斗在脱离土壤的过程中受到的阻力渐减，铲斗的破碎力也渐减；铲斗的最大破碎力与系统压力、铲斗缸缸径、各铰点力臂有关；通常系统压力及油缸缸径差距不大，所以要获得好的破碎力变化曲线，需要对铰点位置进行优化。HE39的动臂与斗杆均为箱形梁结构，分析的目的为以最轻的质量、最佳的可靠性获得最优良的工作性能。目前，有限元方法是研究梁结构的先进有效的方法。有限元方法是结构力学中用来求解大型框架及板壳等复杂弹性体结构的力学问题时一种实用有效的数值近似计算方法，其理论基础是弹性力学中的变分原理，因此，有限元方法是一种可靠的近似方法。又由于它是用数值方法进行计算，所以在实际应用中很有效。在应用有限元进行结构力学分析时，主要有单元的划分形式和单元结点的设置两个方面的内容。对于挖掘机工作装置这种以杆件为主的结构来说，选用梁单元为模型最为适合，在<WP=72>结点的设置上，取结点位移为变量进行求解，即位移法。以这种空间梁单元形式可以建立工作装置空间梁单元有限元模型。但这只是一种静态的分析。工作装置是一个空间连杆机构，且其受力状况瞬息都发生着变化，必须作为一个弹性整体结构来进行弹性动力分析即对此机构在一个运动周期内任一瞬间的运动着的变化结构进行分析，因此实际的情况要比静态结构分析复杂的多，必须从动力学的角度考虑。液压系统动态分析的主要内容是：分析高压系统中（管道或容腔）压力瞬态峰值与波动情况；求出控制机构和执行机构（如液压元件或负载）的响应速度；了解液压系统工作过程中各参数变量（如压力、速度、位移等）随时间变化的规律。通过对液压系统动态分析研究，了解系统动态品质参数变化，从而为系统的改进提供依据。随着液压技术向高速、大功率、大流量、高控制精度方向发展，液压传动与控制系统在启动、换向等过程常常出现震荡或液压冲击，或因外来干扰而出现速度或控制精度不稳定等动态品质问题，因此对液压系统进行动态设计或动态特性研究具有重要意义。本文的研究对象---HE39小型多功能液压挖掘机，采用的是目前较为流行的全功率控制系统，从理论的角度对整个系统进行动态特性分析是极其复杂的，从应用的角度来说也不是必要的。故本文针对HE39小型多功能液压挖掘机在样机试验过程中出现的具有普遍性的两种问题进行动态特性分析。即：斗杆缸低速爬行现象和动臂启停抖动过大现象。液压缸本身的动态特性分析说明液压缸的低速爬行是客观存在的。所以消除不是目标，目标应是改善。进一步?更多还原

【Abstract】 In the world engineering machine market, mini-excavator is one of engineering machine products which have the largest produce and sale quantity. Mini-excavators are mainly used in the following occasions: highway maintenance, park and garden forestation, subzone construction, city planning and agricultural built, etc. And it has strong mobile performance and small dimensions, which make it met the case having dispersive earthwork and narrow working space. At present, basic establishment is carrying on all-around in our country, so the market of mini-excavator is expending and the demand is growing very fast. Therefore the theory research relating to practice has important operation significance and long-term direction significance. There are still many differences between the homemade mini-excavators and the overseas, which are mainly incarnated as complete machine matching, microoperation performance, maintainability, and reliability and appearance quality. The homemade product has advantages in price and service. The overseas mini-excavators are developing towards perfect appearance, high reliability, and convenience and comfortable in operating. Now the homemade mini-excavators are developing towards multifunction, intelligence, energy saving, high reliability, humanized design and automatic supervisory control. Based on the research and development, design, manufacture and of the HE39 , this paper do some research on mini-excavator.. The primary structure of HE39 is composed of work device, revolving dial and chassis. The work device is articulated with the frontend of the revolving dial by swaying head. The revolving dial and the chassis are coupled by revolving <WP=75>bearing. The engine is post positioned on the revolving dial. The drivers cabin is situated at the left frontal corner of the revolving dial. The bulldozer shovel is installed on the frontend of chassis. The rubber pedrail is installed on the travel gallows. The transmission agent is a total power controlled hydraulic system whose manipulate mode is the type of entire hydraulic forerunner. Its electric appliance system has the function of start, lighting, monitor and control and automatic alarm. Considered the digging parameter, HE39 gives prominence to the digging depth, which satisfies the demand of home market user. The design of digging parameter refers to many factors, for example digging force, back balance, tread, chassis width and the self constraint condition of work device. After computed the total travel theoretical digging force, we get the changing curve which is accord with the demand of operating mode. The maximum digging force which can be optimized based on design needs relates to the system pressure, cylinder diameter of scoop arm and each the arm force of linkage point. In most conditions, the system pressure and the cylinder diameter hasn’t much difference, so the design of linkage point is the most important factor to the theoretical digging force and the changing curve. The moving arm and scoop arm of HE39 is trunk structure girder. When optimizing, obtaining best performance with less mass and higher reliability should be the goal. At present, the finite element method is effective method to study girder structure, which base on elasticity mechanics. For the working device of excavator consisted of many girders, it is reasonable to choose girder unit model, and find out the displacement of crunode. According to the content mentioned above, static analysis can be finished. Since the working device is a interspaced lever structure, and the applying force on it is changing along with time, it is necessary to analyze it as a <WP=76>elastic structure in a motion cycle. So the actual motion analysis is more complex than static structure one and the research must be based on dynamics.The main contents of hydraulic system analysis are: the analyses of the transient state pressure and its fluctuation in the high pressure system, seeking the response speed of the control mechanism and actuator (such as hydrauli更多还原