| 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.
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