| Crawler Crane is a mobile crane which is widely applied in harbor, hydroelectricity,railway, petrochemical industry and other big projects. At present, it is developing towardslarge tonnage. Because all the large crawler cranes are fully hydraulic cranes, the reliabilityof crawler cranes, to a large degree, is ascribed to the stability of the hydraulic system. Thefact that the hydraulic system and its components are mainly imported from foreigncountries, as well as the core technology, impedes the development of crawler crane industry.Therefore, it is of a great theoretical and practical value to conduct researches on thedynamic characteristics of hydraulic system of crawler cranes.In recent years, thanks to the development in integrated sensoring skills and skills ofcontrolling electro-hydraulic proportional system, electronic control skills of hydraulicsystem have been perfectly adopted in crawler cranes. Thanks to integrated electroniccontrol skills based on integrated circuit and micro-processor, crawler crane products haveachieved integrated control of multi-hydraulic system: by controlling handles, operators cancontrol travel drive, lifting, slewing and luffing systems. Since large-tonnage crawler cranesare expected to become highly automated and sophisticated, they pose a higher standard tothe dynamic characteristics of hydraulic system and designers have to improve hydraulicsystem in such aspects as feedback speed, inching, control and stability.Currently, at home, research on the dynamic characteristics of hydraulic system haslagged behind European and American counterparts, and most of enterprises still useempirical and analogical methods in exploring products. Compared with advanced foreignproducts, ours need improving in such aspects as stablility, inching, controllability. Thisdissertation, funded by the project——“Development of Design and ManagementPlatform of Hydraulic system of Mobile Crane”, employs AMESim（Advanced ModelingEnvironment for Simulations of engineering systems）software to explore HCD（Hydraulic Component Design）model of hydraulic lifting, travel, slewing systems and does a HDCModel-based research on the typical dynamic characteristics of hydraulic system oflarge-tonnage crawler crane. This dissertation is designed to provide theoretical guidance fordomestic designs of hydraulic system of large-tonnage crawler crane, and meanwhile tonarrow the gap at home and abroad.The content of this dissertation is as follows:1. It reviews development of large crawler cranes at home and abroad； It introduceslifting, travel drive and slewing hydraulic systems of large crawler crane respectively；illustrates in details the development of simulation at home and abroad and adopts AMEsimsimulation software.2. It elaborates the composition and the working theory of lifting system of certain largecrawler crane； It establishes dynamic models of pilot-operated counterbalance valve andvariable displacement motor, and points out the following factors can influence the stabilityof the system: the decrease of the diameter of inlet damping and flow area, the minimumdisplacement, the volume and so on. It employs AMESim simulation platform to deign HCDmodel of hydraulic lifting system； and throug modality analysis, it elaborates the reasons ofpressure fluctuation in falling working state；it points out that changes of several factors caneasily affect system stability: flow area form of counterbalance valve, the motordisplacement, the dynamic characteristics of counterbalance valve and cutoff valve； basedon simulation, it proposes several optimization schemes to improve the stability.3. The thesis introduces the composition and working theory of load sensor travelhydraulic system.； it deduces transfer function of load sensor system； and accordinglypoints out major factors to influence output power of load sensing pump； it explores HCDmodel of hydraulic traveling system； makes dynamic simulation analysis； points out thefact that load sensory skills, when used in hydraulic traveling system, usually result inengine failure because of power mismatch； it, based on simulation platform, proposes threeoptimization schemes: to change load sensing valve spring stiffness, to connect damping inseries between two travel multi-way valves’ load feedback interface, to limit multi-way valve flow shifting.4. The thesis introduces the composition and working theory of slewing system, andestablishes mathematical model of main components； It explores HCD simulation model ofhydraulic open slewing system； conducts a detailed study on how dynamic characteristicsof hydraulic slewing system are influenced by such factors as reversing valve form, springstiffness of slewing cushion valve, pressure relief pressure and etc. The findings ofsimulation analysis cover the following aspects: reversing valve, used in the flow area formwith bigger gradient in initial stage, contributes to relieve pressure fluctuation and bettercontrol speed； cushioning valve flow area form, with smaller gradient, helps to lessensystem pressure； proper cushioning spring stiffness can lessen pressure fluctuation ofsystem startup and direction-change and decreases braking time.5. It designs pilot schemes to test dynamic characteristics of hydraulic lifting, travel,slewing systems of large crawler crane； analyses how the system is influenced by thestructural parameter of key hydraulic components； and proves the validity of simulationanalysis and the feasibility of optimization schemes proposed by this dissertation. |
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