【作者】 许勤；

【导师】 丁为民；

【作者基本信息】 南京农业大学 ， 农业机械化工程， 2009， 博士

【摘要】 液压冲击机械是实现工程作业机械化的重要机具之一,其发展和使用水平的高低,代表了一个国家工程作业机械化发展的程度。随着世界能源的普遍紧张和对工程建设中环保要求的提高,液压冲击设备已成为施工中不可缺少的主要机械。由于其独特的性能,现已在全球范围内逐步成为一个重要的新技术产业,在我国被列为“十一五”期间重点发展领域内的重点产品。液压冲击机械的核心——液压冲击器技术上属于精密部件,其性能决定了液压冲击机械的性能。世界上许多发达国家对提高液压冲击器的性能已从多方面开展研究,然而在我国研究工作并不顺利,随着《工程机械“十一五”发展规划》的实施,进一步开展对液压冲击器性能的研究是十分必要的。本文对液压冲击器的研究现状进行了论述,总结了目前研究中存在的问题,对液压冲击器的冲击性能及影响因素进行了较系统的理论分析,对试验设备进行了改进,在理论分析的基础上进行了试验,主要研究内容和结论如下：(1)分析影响液压冲击机械性能的因素,确定衡量冲击功能优劣的指标根据液压冲击机械的基本功能,分析比较了衡量冲击功能优劣的指标以及影响液压冲击器性能的因素,确定了冲击能、冲击频率、冲击功率或冲击效率是衡量冲击功能的主要性能指标。结果表明：在冲击器中除了结构对冲击功能造成影响外,液体的工作条件和冲击参数变化也会对冲击功能产生影响。(2)利用线性和非线性方法对液压冲击器运动进行分析在线性分析的基础上,为进一步研究液压冲击机械的性能,根据活塞和控制阀在运动过程中的位置,将整个机构运动划分成14个状态。对液压冲击器的运动规律进行非线性研究。在不失精确性的前提下,考虑到流量和压力的实际变化情况、油液的可压缩性等,提出了新的假设条件,将冲击器活塞作为研究对象,对液压冲击器的动态运动规律进行建模分析,为后续工作过程仿真和机构优化提供基础。在运动模型中,考虑了冲击器进出油口流量和压力的变化、内部结构对机构内部压力和流量造成的影响、换向阀和蓄能器实际工作状况等对冲击器流量和压力的影响,可较为准确地表达液压冲击器的运动特性。与此同时,还推导出对应于液压冲击器各工作状态时各工作腔工作压力、粘性阻力、液压卡紧力、泄漏量等计算公式；考虑到油液压力变化引起进口处高压油管容积变化对液压冲击器内部流量产生的补偿作用,给出了补偿流量计算表达式,根据试验进一步确定了公式中对应机型的压力流量系数；推导出每一运动阶段各管道间的压差计算式、活塞和控制阀各腔之间的压差计算式和阀在不同开口位置所造成的附加压差计算式和阀后腔压力计算式。(3)设计计算机测控系统,改进测试系统为了在线测试液压冲击器的结构参数和蓄能器等对冲击压力与流量波动变化的影响,对试验系统进行了改进；利用模块化思想和可靠性技术设计测控系统,建立了计算机辅助测控系统,使主要参数测试精度满足试验装置的要求。(4)利用光电位移微分法对液压冲击器压力与流量动态变化规律进行试验研究试验结果表明：实际工作中冲击压力随时间呈动态波动,其波动程度可用来说明活塞上实际压力的损耗程度；根据试验结果判断,冲击器工作压力的平均值仅为进口处压力的65%～75%左右。冲击器内部流量的波动程度随冲击压力的提高而增大,冲击器的冲击流量也随工作压力的提高以线性关系增大,说明流量是建立一定压力的必要条件。试验中发现,当流量满足冲击器所需的某一压力后,继续增大流量对冲击压力的进一步提高不再起作用,反而增加系统的发热量。冲击器后腔的压力损失是导致冲击器能量利用率下降的主要因素。(5)试验研究了影响液压冲击器冲击压力和流量变化的因素通过试验分析了进油管径尺寸、活塞尺寸、控制阀、蓄能器对液压冲击器冲击压力与流量波动的影响。试验表明：①进油管径对冲击压力和流量在一定频档和冲击压力下造成的压力损失,随着管径尺寸的减小而增大,但对流量的影响则相反；当压力和管径相同时,流量的变化程度会随冲击频率的增大而变小,但此时对压力的波动影响很小,可忽略不计；在同一频档下,后腔的压力损失随着管径尺寸的减小而变大。②既满足液压冲击器密封要求,又满足流量波动要求的活塞与缸体最佳配合间隙范围为：0.06mm～0.08mm,验证了理论上提出这一最佳值的正确性。③冲击行程对流量的影响较大,频档一定时,冲击活塞流量与冲击行程之间成三次方多项式关系,与压力的大小成近似线性关系。④蓄能器不同充氮压力与不同充氮体积的试验表明,HYD200型液压冲击器蓄能器充氮压力的取值一般在工作压力的40%～50%范围较为合适,冲击压力和冲击流量的波动程度会随着充氮体积的增大而减小。更多还原

【Abstract】 Hydraulic impactor is one of the important equipment for construction mechanization. Its development and application represent the developing level of a country’s construction mechanization. With the general insufficiency of world energy and rising environmental standard in engineering construction, hydraulic impactor has become indispensible major equipment in construction. Due to its unique properties, the machine has brought into being a prominent industry of new technology within the global scale, and it has been listed as key product in major development field of the "eleventh five-year" plan. Hydraulic impactor, core component of hydraulic impact machine, is precision instrument, and its performance determines that of the impact machine. Many developed countries in the world have researched from multiple aspects to promote the hydraulic impactor’s performance, yet in our country the research progress dose not go well. With the implementation of "the eleventh five-year plan for construction machinery industry", it is very important to carry out further researches on hydraulic impactor’s performance.This article has discussed the status quo of researches on hydraulic impactor, and summarized problems in current researches. Systematic theoretical analysis has been done on performance and influential factors of hydraulic impactor. Meanwhile we have improved the experimental equipment. On the bases of theoretical analysis we have made some test. Below is the main research content and results:(1)Analyze factors that affect performance of hydraulic impactor, and define indices to measure the quality of impact propertiesBased on fundamental functions of hydraulic impactor, we have analyzed indices to measure the impact property and factors that affect the impact properties after examination and comparison. And we put forward the idea that impact frequency has direct relationship with impact velocity, and indirect relationship with impact inflow. The results indicated that besides structure effects on impact power, working condition of liquid and variation of impact indices can also affect impact power.(2)Study the motion of hydraulic impactor with linear and nonlinear methodsBased on linear analysis, to further understand performance of hydraulic impactor, we divided the whole mechanism motion into 14 stages according to location of piston and control valve in the motion. Carry out nonlinear analysis of motion pattern of hydraulic impactor; without sacrificing precision, considering the actual changes of flow and pressure and compatibility of oil liquid, new hypothetical condition has been raised. The impact machine’ piston is the key research object, and dynamic movement regularities of hydraulic impactor have been analyzed, providing foundation for follow-up working process emulation and mechanism optimization. In the movement model, factors influencing impactor’s flow and pressure have been taken into account. The factors include: compatibility of oil liquid, changes in flow and pressure of impactor’entrance and exit, influence of inner structure on impactor’s flow and pressure, influence of redirection of reversing valve and accumulator’s working situation on impactor’s flow and pressure. Thus the model can indicate the motion properties of hydraulic impactor with precision. We gave out calculation formula of each working chamber’s working pressure, viscous resistance, hydraulic sticking force, leakage rate, etc. in response to hydraulic impactor’s specific working condition. Considering compensation of hydraulic impactor’s inner flow by changes in volumes of fuel injection pipe at the entrance caused by variation of oil liquid pressure, we gave out calculation expression of compensational flow, and determined pressure-flow coefficient in the expression with respect to this machine type. we deduced calculation formula for pressure difference between pipes and between chambers of piston and control valve, as well as additional pressure difference when valves have different opening position on each motion stage. We also deduced computational formula of pressure in valve back chamber.(3)Design computer control system, improve testing systemIn order to on-line test the influence of structural parameters of hydraulic impactor and accumulator etc. on change of impact pressure and flow fluctuation, we improved the trial system; we utilized Modularization Thinking and Reliability Technology to design the measurement and control system and constructed computer aided testing system, which are satisfied with the demands of test machine for main test parameter precision.(4)Experiment on dynamic change in pressure and flow of hydraulic impactor with photoelectric-displacement-differential methodThe experiment results indicated that:in actual working process, impact pressure exhibits dynamic fluctuation with time, and the fluctuation degree can explain consumption of actual pressure on piston. Judging from experimental result, average working pressure of impactor is only 65%-75% of pressure at the entrance. Fluctuation level of impactor’s inner flow would increase with the growing of impact pressure. Impact flow of the hydraulic impactor linearly increased with the increase of working pressure, which indicated that flow is necessary condition for forming pressure. Another conclusion was that when the flow was sufficient for certain pressure required by hydraulic impactor, continuing to increase flow would not further raise working pressure, but instead would increase heat production of the system. Pressure loss in back chamber of impactor is major factor that reduces impactor’s energy utilization efficiency.(5)Study factors that affect change of impact pressure and flow of hydraulic impactorWe did abundant experiments to analyze the extent of influence on hydraulic impactor’s impact pressure and flow by factors such as sucker’s diameter, dimension of piston’s relative motion, control valve and accumulator. The experiments suggest that:①Under certain frequency and impact pressure, pressure losses of impact pressure and flow caused by sucker’s diameter would increase with the shrinking of diameter dimension, contrarily to effects on flow; when pressure equals to pipe diameter, change degree of flow would decrease with the increase of impact frequency, but under such circumstances fluctuation effects on pressure is small, which can be ignored; meanwhile, under identical frequency, pressure losses in back chamber would increase with the decrease of pipe diameter.②We got the range of optimum fit clearance 0.06-0.08mm between piston and cylinder block, which meets both the sealing requirement the hydraulic impactor and the flow fluctuation demand. It proved the existence of optimum value raised through theoretical analysis, offering strong experimental evidence for future optimization of this machine type.③Results showed that striking journey has bigger influence on flow, and we analyzed the results from theoretical respect. We found that when the frequency is set, impact piston’s flow has cubic polynomial relationship with striking journey, yet has approximate linear relationship with pressure.④The experiment of nitrogen-charging volume and pressure of accumulator indicated their reasonable value range of Type HY200 hydraulic impactor were 40%～50% of work pressure. Fluctuation degree of impact pressure and flow in hydraulic impactor would fall with the expansion of nitrogen-charging volume.更多还原