介绍了液压自由活塞发动机的发展历程、工作原理、典型系统、研究现状及研发中的关键技术问题。

液压变压器是在恒压网络二次调节系统下发展起来的新型液压元件。介绍了液压变压器的技术背景及发展历程、液压变压器的节能思想及其特点，并对典型液压变压器的工作原理、研发中需要解决的关键技术问题、液压变压器的效率计算进行了阐述，同时介绍了液压变压器的国内外研究现状及其在液压系统中的应用。对液压变压器的应用前景进行了展望，指出经完善其关键技术，液压变压器必将会在未来的液压传动系统中扮演重要角色。

Sealing performance of the reciprocating seals on a larger diameter (100 mm in diameter) axial piston is theoretically invest igated. Based on the characterist ics of the clearance flow between the seal and the piston, reasonable boundary conditions for Navier-Stokes equations are determined and the equations are modified, so that the final equations can describe the real flow state of the clearance flow. Through combining the final equations with finite element method, the pressure distributions within the clearance field during the reciprocating motion of the piston and the leakage rate with the pressure are studied. The deflections of the seal which affect sealing performance are calculated as well. Sealing performance of piston seals using oil as the working liquid is compared with using water. It is concluded that the seal using water as the working liquid is under dry friction, which cannot be dealt with the theory of fluid mechanics. The seal structure is only acceptable using oil as the working liquid..

In this paper, experiments were carried out to study the friction and wear performance for the materials of piston and cylinder in a water hydraulic axial piston pump. The matching of 940 stainless steel circle with F102 engineering plastics block and 940 stainless steel circle with Al2O3 ceramic block were also studied. The wearing capacities were calculated by theoretical formulae based on the grinding crack widths. When pure water is used as hydraulic transmission medium, it is better to use ceramic with engineering plastics as matching materials for the piston and cylinder of water hydraulic axial piston pump. The experimental results have provided a theoretical basis for selecting the matching materials of piston and cylinder.

提出一种新型能量回馈式VVVF液压电磁速度控制系统，并对电梯上升和下降速度控制中的温度控制、电梯下行过程控制中的压力平衡、下降能量回收率等设计过程中的一系列问题进行了详细探讨和试验研究。试验结果表明，能量回馈式vvvF液压电梯同传统的阀控液压电梯相比具有控制性能优、节能效果显著等特点。