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..

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。

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.