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。

研究了发动机一泵和泵一负载两个环节实现局部功率匹配的原理和方法，分析了现有液压挖掘机两个环节之间不能实现功率匹配与协调的原因，提出了液压挖掘机全局功率匹配与协调的原理与方法。并给出了实现方案。这项研究对于设计液压挖掘机新型节能控制系统，提高生产效率，具有较大意义；对于其他行走工程机械也具有参考和借鉴作用。

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..

This paper discusses and analyses the speed control of variable voltage variable frequency (VVVF) hydraulic elevator. The computational models of the control system are established. Numerical simulations are carried out with the SIMULINK of MATLAB. PID control law is adopted in experiments because the PID control algorithm is simple in operation, and is characteristic of good computer real-time control. It also possesses good adaptability when the parameters of the controlled object are changed. Experiments are also carried out for the upward and downward running speed of the VVVF hydraulic elevator. Computational simulations coincide with experimental results in general. The results of both simulations and experiments show that serious flutter occurs at the start-up of the VVVF hydraulic elevator, and there is an oscillating phenomenon in the system. During the start-up of the VVVF hydraulic elevator, the system absorbs elastic energy when static friction is changed to dynamic friction. This results in the oscillations after starting.

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。

非全周开口滑阀是液压阀的基本结构形式之一，其阀口是在阀芯凸肩圆周上均布若干不同形状的节流槽，用于获得不同流量控制特性。随着阀口开度变化，阀口节流面的位置、形状和射流角都会随之变化，因而传统理论计算方法无法准确计算压力流量、液动力特性等。采用计算流体动力学（CFD）方法，针对两种典型节流槽形式的滑阀进行了三维流场仿真分析研究，获得了不同流动方向下阀口全行程压力流量和液动力特性，并与试验测量结果进行了比较，两者吻合良好；分析比较了流场计算和理论公式计算结果。研究发现在特定的阀口开度范围内，液动力会使阀口趋于开大。此项研究对于非全周开口滑阀压力流量、液动力等性能预测以及减小阀驱动力具有重要意义。

纯水液压利用过滤后的自然水作为液压系统的压力工作介质，可以避免环境污染和火灾危险，具有价格低廉、清洁卫生等优点。阐述了水介质特性引起的润滑与密封、摩擦与磨损和腐蚀与气蚀等关键技术问题。介绍了陶瓷/陶瓷和增强塑料/不锈钢在水中的摩擦学特性研究结果，确定了陶瓷材料与增强塑料在水中的主要磨损机理。通过盐雾试验评价了热处理工艺对不锈钢腐蚀特征的影响。提出了在纯水液压泵中气蚀初生伴随着低频压力脉动现象。

A novel structure floatation cyclone with natural inlet air has been designed, and its structural characteristics and floatation principle have been analyzed. Simulations of the velocity and pressure distributions within the flow field of the floatation cyclone have been carried out using Navier Stokes equations and fluid mechanics of two-phase. Based on the flow characteristics of the coal-water slurry, reasonable boundary conditions are decided and the equations are modified, so that the final equations can describe the real flow state of the flow field of the floatation cyclone. The boundary surface position between float coal and tailings is determined and there is an air cylinder in the central region of the floatation cyclone. The research reveals the floatation mechanism of the floatation cyclone. The floatation results can be greatly improved by regulating the structural dimensions of cyclone. The experimental results show that the floatation cyclone is very effective for the floatation of fine coal grains.