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..