Experimental Technology and Management

开展–40℃系统级低温原理性实验室试验，探索民机5 000 psi压力体制高压液压系统低温特性规律，分析试验结果数据，针对试验中测试系统和机械系统中典型的失效风险进行分析，并提出相应的规避措施。同时，全面复盘试验过程和设计方案，从准确、高效、安全三个方面逐一进行分析，提出针对5 000 psi液压系统的低温性能研究应融合机理探索与试验验证，试验验证应通过仿真-试验协同优化、智能传感技术应用、材料工艺创新、实验室规范管理等多维手段进行。该文对民机液压系统低温试验具有指导作用，能够助力5 000 psi液压系统低温故障预测和热机理研究，对5 000 psi压力体制液压系统研发具有重要意义。

[Objective] The shift toward higher pressures has become a consensus in the development of modern civil aircraft hydraulic systems. However, increasing hydraulic system pressures from 3000 to 5000 psi introduces potential risks, such as elevated pressure surges, faster fluid flow rates, and rapid oil temperature rise. These challenges impose new demands on thermal and pressure control in hydraulic systems, necessitating theoretical and experimental analyses for their mitigation. Moreover, aircraft hydraulic systems operate in extreme low-temperature environments(-20 ℃ to-60 ℃), challenging the performance of seals, pipelines, pumps, and valves. Therefore, investigating the low-temperature characteristics of 5 000-psi high-pressure hydraulic systems is a critical step in advancing civil aircraft hydraulic technology. The reliability of low-temperature testing directly impacts aircraft system development. Conducting preliminary studies on low-temperature characteristics during early design stages to explore underlying mechanisms can help proactively mitigate risks. Currently, research on low-temperature testing for aviation hydraulic systems in China is in a gradual development and refinement phase, with some progress already achieved. However, there remains a lack of data and experience in laboratory-based extreme cold testing for 5000-psi hydraulic systems at the civil aircraft system level. Challenges such as complex control, high costs, and low efficiency persist, and related test rigs and methodologies still require continuous improvement. [Methods] System-level–low-temperature laboratory experiments at-40 ℃ were conducted to investigate the low-temperature behavior of civil aircraft 5,000-psi high-pressure hydraulic systems. By comprehensively reviewing the testing process, design solutions, and test data, this study identified typical failure risks in both testing systems(e.g., pressure, temperature, and flow sensor drift under cryogenic conditions) and mechanical systems(e.g., oil leakage in seals and abnormal output pressure fluctuations in constant-pressure variable-displacement pumps). Theoretical analyses were conducted from the perspectives of accuracy(e.g., low-temperature environment simulation, soaking time, and system reliability), efficiency(e.g., test conditions, sequence, procedure, and simulation), and safety(e.g., risks from increased oil viscosity, hydraulic water hammer, oil leakage, and component failure prevention). Corresponding mitigation measures were proposed, along with an optimized testing approach. [Results] During the low-temperature testing of the 5,000-psi hydraulic system for civil aircraft, the typical failure risks in the test system primarily involved faults in pressure, temperature, and flow sensors. The low-pressure circuit was susceptible to water hammer risks, requiring sensors with appropriate ranges based on specific needs. Additionally, the impact of water hammer effects on the pipeline system could not be overlooked. The uneven temperature distribution in the system required the careful placement and selection of temperature sensors. When choosing flow sensors, the influence of oil viscosity and flow instability must be considered. Meanwhile, the typical failure risks in the mechanical system mainly include the degradation of seal performance at low temperatures, leading to oil leakage, as well as increased friction in components due to higher oil viscosity at low temperatures. These factors might also affect the control of hydraulic components. The low-pressure circuit was susceptible to water hammer effects, which could not be overlooked. Nonuniform temperature distribution within the system necessitated the careful selection of temperature sensor placement. Fluid viscosity and instability had to be considered when selecting flow sensors. For the mechanical system, typical failure risks included seal failure at low temperatures, leading to fluid leakage. Moreover, increased oil viscosity affected hydraulic component control. [Conclusions] Optimizing low-temperature testing for 5,000-psi hydraulic systems requires integrating mechanistic analysis with experimental validation. This should be achieved through multidimensional approaches, including simulation testing, collaborative optimization, intelligent sensing technologies, innovative materials and processes, and standardized laboratory management. These measures are expected to enhance operational safety and system performance under extreme conditions while providing critical technical support for the independent development of hydraulic systems in China's civil aviation sector.