挖掘机液压系统设计

前言挖掘机的液压系统是挖掘机上重要的组成部分，它是挖掘机工作循环的的动力系统。挖掘机的工作条件恶劣，且动臂和底盘动作非常频繁，因此要求液压系统工作稳定，平均无故障时间长。因此，液压系统的性能优劣决定着挖掘机工作性能的高低。液压技术的发展直接关系挖掘机的发展，挖掘机与液压技术密不可分，二者相互促进。液压技术是现代挖掘机的技术基础，挖掘机的发展又促进了液压技术的提高。挖掘机的液压系统复杂，可以说目前液压传动的许多先进技术都体现在挖掘机上。挖掘机的液压系统都是由一些基本回路和辅助回路组成，它们包括限压回路、卸荷回路、缓冲回路、节流调速和节流限速回路、行走限速回路、支腿顺序回路、支腿锁止回路和先导阀操纵回路等，由它们构成具有各种功能的液压系统。随着科技的进步，挖掘机的液压系统将更加复杂，功能更加多样且便于操作控制，工作效率高，耗能少，先进的液压系统会使挖掘机在工程领域发挥更大的作用。1绪论11选题意义随着国民经济的快速发展，液压挖掘机在各种工程建设领域，特别是基础设施建设中所起的作用越来越明显，液压挖掘机作为一类快速、高效的施工机械愈来愈被人们所认识。据统计，2003年我国挖掘机总销售量突破6万台，其中国内挖掘机生产企业销量总和达到348万台，成为世界第一大挖掘机市场。挖掘机的发展与液压技术密不可分，二者相互促进，一方面，液压技术是现代挖掘机的技术基础，另一方面，挖掘机的发展又促进了液压技术的提高。挖掘机的液压系统复杂，其性能的优劣决定着挖掘工作性能的高低，可以说目前液压传动的许多先进技术都体现在挖掘机上。近年来，有关挖掘机液压系统方面的文献并不少见，但文献的内容大多针对某一专题进行研究，系统地论述现代液压挖掘机液压系统的论文却较少，因此研究挖掘机液压系统具有重要的现实意义和理论意义。12挖掘机及其液压技术概述挖掘机的发展史可追溯到19世纪三四十年代。美国实施西部大开发工程催生了以蒸汽机作为动力，模仿人体大臂、小臂和手腕构造，能行走和扭腰的挖掘机。随后的一百多年中，挖掘机并没有得到很大发展，其原因一是当时的工程主要是国土开发、大规模的筑路和整修场地等，平面作业较多，使铲土运输机械成为当时的主力机种，二是挖掘机作业装置动作多、运动范围大、采用多自由度机构，机械传动难以适应这些要求，而当时的液压技术还不成熟，不能大规模地应用到实际工业中。随着社会的不断进步，工程建设和施工形式逐渐向土木施工方向发展，同时液压技术也逐步得以完善，这些因素的变化反过来又促进挖掘机的不断更新换代。20世纪40年代有了在拖拉机上配装液压铲的悬挂式挖掘机，50年代初期和中期相继研制出拖式全回转液压挖掘机和履带式全液压挖掘机，60年代，当液压传动技术成为成熟的传动技术时，液压挖掘机进入了推广和蓬勃发展吉阶段，各国挖掘机制造厂和品种增加很快（见表11），产量猛增。19681970年间液压挖掘机产量已占挖掘机总产量的83，目前已接近100，所谓挖掘机在现代主要是指液压挖掘机，机械式挖掘机已很少见，液压传动技术为挖掘机的发展提供了强有力的技术支撑。表11液压挖掘机制造厂及型号增长情况TAB11HYDRAULICEXCAVATORFACTORYANDGROWTHCIRCUMSTANCE制造厂家产品型号国别19631966196919721963196619691972西德5171718123674106美国2814174194373法国587310262731意大利36811371842英国36993122228日本4131462844合计1849687232106212324液压传动是挖掘机的重要组成部分之一，目前常用的传动方式有机械传动、电力传动和流体传动。流体传动包括液体传动和气体传动，液体传动又分为液压传动和液力传动。所谓液压传动是指在密闭的回路中，利用液体的压力能来进行能量的转换、传递和分配的液体传动。在现代工业中液压传动技术几乎应用于所有机械设备的驱动、传动和控制，如操纵车辆转向和制动，控制和驱动飞机、机床、工程机械、农业机械、采矿机械、食品机械和医疗机械等1650年法国帕斯卡提出的封闭静止流体中压力传递的帕斯卡原理成为液压传动的理论基础，此后液压传动理论不断得以丰富和完善，如1686年牛顿揭示了粘性流体的内磨擦定律，18世纪建立了流体力学的两个重要方程连续性方程和伯努利方程。丰富的理论和实践的需要促进了液体应用技术和成果的不断涌现。1795年英国人约瑟夫步拉默发明了世界上第一台水压机；随后出现在英国的工业革命促进了液压技术的迅速发展；到1870年液压传动技术已经被用来驱动各种液压设备，如液压机、起重机、绞车、挤压机、剪切机和铆接机等；1900年，世界上出现了第一台轴向柱塞泵；1910年及1922年海勒肖及汉斯托马斯研制出用油作工作介质的径向柱塞泵；1926第一套由泵控制阀和执行元件组成的集成液压系统在美国诞生；1936年哈里威克斯又发明了先导式液流阀。第二次世界大战之后，美国麻省理工学院的布莱克本、李诗颖等人对液压伺服控制问题作了深入的研究，于1958年制造了喷嘴挡板型电液伺服阀；20世纪六十年代末，电液比例阀应运而生；70年代后期，德美等国相继研制成负载敏感泵及大功率电磁阀；近年来，为适应机电一体化、控制柔性化和计算机集中控制的要求，液压系统的研究已由手动控制转向数字控制和信号控制。目前液压技术的研究和发展动向主要体现在以下几个方面（1）提高效率，降低能耗。（2）提高技术性能和控制性能。（3）发展集成、复合、小型化、轻量化元件。（4）开展液压系统自动控制技术方面的研究与开发。（5）加强以提高安全性和环境保护为目的研究开发。（6）提高液压元件和系统的工作可靠性。（7）标准化和多样化。（8）开展液压系统设计理论和系统性能分析研究20。13国内外研究现状我国挖掘机生产起步较晚，从1954年抚顺挖掘机厂生产第一台机械式单斗挖掘机至今，大体经历了测绘仿制、自主研发和发展提高三个阶段。新中国成立初期，以测绘仿制前苏联20世纪3040年代的机械式单斗挖掘机为主，开始了我国的挖掘机生产历史，由于当时国家经济建设的需要，先后建立起十多家挖掘机生产厂，到20世纪80年代末，我国的中小型液压挖掘机已形成系列，但总的说来，我国的挖掘机生产批量小，产品质量不稳定，与国际先进水平相比，差距较大。改革开放以来，生产企业积极引进、消化、吸收国外先进技术，促进了我国挖掘机行业的发展，目前国产液压挖掘机的产品性能指标已达到20世纪80年代的国际水平，部分产品达到了90年代的水平。国外挖掘机生产历史较长，液压技术的不断成熟使挖掘机得到全面发展。德国是世界上较早开发研制挖掘机的国家，1954年和1955年德国的德马克和利渤海尔两家公司分别开发了全液压挖掘机；美国是继德国以后生产挖掘机历史最长、数量最大、品种最多和技术水平处于领先地位的国家；日本挖掘机制造业是在二次大战后发展起来的，其主要特点是在引进、消化先进技术的基础上，通过大胆创新发展起来的；韩国是液压挖掘机生产的后起之秀，20世纪70年代开始引进技术，由于产业政策支持，很快进入国际市场，并已挤入国际液压挖掘机的主要生产国之一。20世纪60年代，挖掘机进入成熟期，各国挖掘机制造商纷纷采用液压技术并与其它技术相结合，使产品的适应性得到较快发展，产品寿命和质量不断提高操纵更加舒适，产品更加节能。例如美国卡特彼勒公司1995年以后推出的300B系列液压挖掘机，采用一种命名为MAESTRO的系统，通过载荷传感液压装置，控制发动机的输出功率，实现与液压泵的严格匹配。MAESTRO控制面板在机型上安装两种功率模式和四种工况状态，允许用户自行决定功率工况模式。再如韩国现代公司生产的ROBEX4503型液压挖掘机，有四种功率模式，通过集成化的电子控制系统自动确定最佳的发动机转速和液压泵的输出参数，使得发动机、液压泵的速度及液压系统压力与实际工况相适应，从而获得最高的生产率和最佳的燃油消耗。此种技术在日本小松、日立建机、神钢、韩国大宇重工、德国的利渤海尔、英国的JCB等公司均得到普遍应用，代表了当代液压挖掘机的最高水平。14挖掘机发展趋势随着液压挖掘机的生产向大型化、微型化、多功能化、专用化和自动化方向发展，挖掘机对液压技术的要求不断提高并呈现如下特点（1）迅速发展全液压挖掘机并进一步改进液压系统。中、小型液压挖掘机的液压系统有向变量系统转变的明显趋势。因为变量系统在油泵工作过程中，压力减小时用增大流量来补偿，使液压泵功率保持恒定，亦即装有变量泵的液压挖掘机可经常性地充分利用油泵的最大功率；当外阻力增大时则减少流量（降低速度），使挖掘力成倍增加；采用三回路液压系统，产生三个互不成影响的独立工作运动，实现与回转机构的功率匹配，将第三泵在其他工作运动上接通，成为开式回路第二个独立的快速运动。液压技术在挖掘机上的普遍使用，为电子技术、自动控制技术在挖掘机上的应用与推广创造了条件，液压、电子和自动化技术日益结合，共同促进挖掘机的控制性能不断提高。挖掘机由简单的杠杆操纵发展到液压操纵、气压操纵、液压伺服操纵和电气控制、无线电遥控、电子计算机综合程序控制。在危险地区或水下作业采用无线电操纵，利用电子计算机控制接收器和激光导向相结合，实现了挖掘机作业操纵的完全自动化。20世纪70年代，为了节省能源消耗和减少对环境的污染，使挖掘机的操作更加轻便和安全作业，降低挖掘机噪音，改善驾驶员工作条件，电子和自动控制技术逐步应用在挖掘机上。随着对挖掘机的工作效率、节能环保、操作轻便、安全舒适、可靠耐用等方面性能要求的提高，机电一体化技术在挖掘机上得以广泛应用，并使其各种性能有了质的飞跃。20世纪80年代，以微电子技术为核心的高新技术，特别是微机、微处理器、传感器和检测仪表在挖掘机上的应用，推动了电子控制技术在挖掘机上应用和推广，并已成为挖掘机现代化的重要标志，亦即目前先进的挖掘机上设有发动机自动怠速及油门控制系统、功率优化系统、工作模式控制系统、监控系统等电控系统。所有这一切，都是挖掘机的全液压化奠定的基础并为挖掘机的全面发展创造了美好的前景。（2）重视采用新技术、新工艺、新结构，加快标准化、系列化、通用化发展速度。例如美国林肯贝尔特公司新C系列LS5800型液压挖掘机安装了全自动控制液压系统，可自动调节流量，避免了驱动功率的浪费，还安装了CAPS（计算机辅助功率系统），提高了挖掘机的作业功率，更好地发挥液压系统的功能；日本住友公司生产的FJ系列五种新型号挖掘机配有与液压回路连接的计算机辅助功率控制系统，利用精控模式选择系统，减少燃油、发动机功率和液压功率的消耗，并延长了零部件的使用寿命；德国奥加凯（OBUNDERTHEWORKINGPARTSOFTHEPERFORMANCEREQUIREMENTSANDMOVEMENTSOFTHEORDER,LISTINGPOSSIBLETOACHIEVETHEBASICCIRCUITITSHOULDBENOTEDATTHISTIMETOCHOOSEASUITABLESPEED,SPEEDEXCHANGEPROGRAMSTODETERMINESAFETYANDUNLOADING,AUTOMATICALLYGUARANTEETHECOMPLETIONOFTHEWORKCYCLEOFACTIONANDORDERANDRELIABLEHYDRAULICDRIVEPROGRAMMING,THENATIONALSTANDARDSHOULDBETHEOFFICIALGRAPHICSYMBOLMAPPINGDIAGRAMTAGGINGSHOULDMAPOUTTHECOMPONENTSOFTHEHYDRAULICMODELSPECIFICATIONS,ITSHOULDALSOBEACOMPONENTOFTHEIMPLEMENTATIONOFACTIONPLANSANDTHERECYCLINGOFELECTRICALCOMPONENTSINTHETABLEOFOPERATINGCYCLE3CALCULATIONOFTHEMAINHYDRAULICSYSTE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