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.

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。

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。