正开口气动伺服阀控缸匀速运动时的负载特性

建立了正开口气动伺服阀控缸的数学模型,得出了保持气缸作匀速运动时,气动伺服阀位移量与气缸左右腔的压力关系,各阀口的流动状态,阀位移与负载力的关系。当负载匀速运动,阀在零位及其附近时,供气侧为亚音速流动,排气侧为超音速流动。为保持气缸作匀速运动,阀位移与负载力之间必须满足一定的关系条件。可以通过软件技术,实现气动伺服阀的阀位移和负载力的关系,从而达到匀速控制的目的。     

具有不均等负重合量的非对称气动伺服阀压力特性研究

研究了一种具有不均等负重合量及均等负重合量的新型非对称气动伺服阀的压力特性。该非对称气动伺服阀的下游节流口面积为上游节流口面积的两倍。伺服阀的压力特性及零位压力取决于下游和上游开口面积比例和阀的负重合量。具有均等负重合量的伺服阀在零位时泄漏流量最大;具有不均等负重合量的伺服阀在零位附近某处时泄漏流量最大。理论结果和试验结果十分吻合。     

车载高压气动减压阀压力场与速度场研究

分析了氢能源汽车输氢系统的70 MPa两级气动减压过程,取得了两级减压阀各阀腔内部的压力场和速度场分布规律.研究结果表明:两级气动减压阀组的阀腔压力分布可分为上游压力区、中间压力区和下游压力区;第一级减压阀和第二级减压阀的阀口处气体均为超音速流动状态,2个减压阀出口的封闭直角区域均存在低速涡流现象.可以通过计算流体动力学(CFD)方法得到流场分布的数据,为车载减压阀组和锥形阀芯的形状与结构设计提供理论依据.     

环形节流静压止推气体轴承承载力和刚度分析

为提高大型重载静压气体止推轴承承载力和刚度,应用FLUENT15. 0对直径150 mm的双排孔节流静压气体止推轴承进行模拟,分析供气压力和轴承间隙对止推轴承压力分布以及刚度和承载力的影响,对比分析轴承间隙内的压力变化和流动情况,并通过与文献实验值进行对比,验证了该方法的准确性。结果表明:随着供气压力的增大,轴承上相同位置处的气膜压力增大,刚度和承载力呈线性增加;随着轴承间隙的增加,气体流速出现了从亚音速向超音速的跨越,轴承间隙内气膜压力骤减,轴承的刚度先增大后减小,承载力一直减小,因此,应合理选择轴承间隙,以维持较高的承载力和轴承刚度,且同时避免超音速区域的出现。     

超声速流下多供气空圆盘静压止推气体轴承性能分析

应用Fluent软件对多供气节流小孔盘静压止推气体轴承进行三维流场的模拟计算,分析供气小孔数、气膜间隙和供气压力对圆盘静压止推气体轴承性能的影响,并和Reynolds方程解的结果进行比较,分析气膜内发生超音速流和不发生超音速时气膜内的压力分布和马赫数情况.结果表明,应用Fluent数值模拟可以很方便地处理节流小孔进入到气膜内区域的复杂流场流动;增加供气孔数、减小气膜间隙和降低供气压力能够避免多供气孔静压止推气体轴承气膜内发生超音速.     

可变节流高度气浮支承结构设计及静态性能分析

为研究节流高度的变化对气浮支承性能的影响,设计一种可变节流高度的气浮支承。建立气浮支承CFD模型,分析节流口直径、节流高度、均压腔深度和供气压力的变化对气浮支承静态性能的影响。研究结果表明:气浮支承的承载能力随节流口直径、节流高度、均压腔深度和供气压力增大而增大;节流高度、均压腔深度、供气压力的增大能提高气浮支承刚度,而节流口直径的增大会导致刚度的降低;气浮支承的体积流量随节流口直径、节流高度、均压腔深度和供气压力增大而增大。     

非对称高速气动伺服阀的研究

介绍了一种新型非对称气动伺服阀.该阀作为硬件补偿,实现了气动系统下降时间与上升时间相同的快速响应特性.研制成的非对称气动伺服阀阀芯,在正反方向同等的阀位移时,下游节流口的通流能力为上游节流口的两倍.试验结果表明,非对称伺服阀频率响应带宽达200 Hz,阶跃响应上升时间达1 ms.对称阀的名义流量范围为 191至-171 NL/min,非对称阀的名义流量范围扩大为 191至-337 NL/min.理论分析结论和实验结果相吻合.     

气体喷射压缩器变工况激波特性分析与试验

为了解不同操作压力下的激波特性,采用试验与数值分析相结合的方法,测得不同出口压力下(0.105,0.110,0.115,0.120,0.125,0.130,0.135 MPa)的喷射系数;采用FLUENT赫数分布;对试验值与仿真值进行对比分析,平均误差率为12.5%,验证了模型的准确性。结果表明:受操作工况的影响,压缩器喷嘴出口处和扩散器内出现了激波,且在工作压力和引射压力一定的情况下,喷嘴出口处的激波是不随出口压力的变化而改变的;压缩器出口压力为0.105～0.12 MPa激波,双激波使得流体由超音速减至亚音速时消耗了大量的能量,而单激波时消耗能量则较少;压力为0.135 MPa时,喷射器出现回流,不能正常工作;在出口压力为0.125 MPa,吸入口压力为0.074 MPa,当工作压力为0.4 MPa时,压缩器内部出现微弱激波,且工作压力越大,激波现象越严重。     

超音速真空喷射器性能试验和数值研究

对超音速空气喷射器的性能进行了试验和数值研究,得到了喷射器的喷射器系数,并分析了不同进气参数下的喷射器内部压力场和马赫场。结果表明,喷射系数的计算值和试验值吻合的较好,偏差小于5%;随着进气压力逐渐下降,引射驱动力减小,喷射系数降低。此外,高压气体在工作喷嘴出口的膨胀程度随进气压力降低而逐渐减弱,激波链出现的位置和强度也随之变化;进气压力降低使得高压气体在工作喷嘴的膨胀越充分,达到的马赫数越大,但是当进气压力降低为0.01MPa时,混合室的主体段由超音速或音速流动转变为亚音速流动,在混合室出口未形成激波。     

可倾瓦径向节流器静态特性的仿真分析

利用COMSOL仿真软件建立可倾瓦径向节流器气体流域仿真模型,在供气压力为0.3～0.6 MPa,气膜厚度为5～25μm条件下,研究可倾瓦径向节流器的结构参数和供气压力对节流器静态性能的影响,结果表明：均压槽能够明显提高节流器的承载能力;承载力和刚度随着供气压力的增大而增大;承载力随偏心率(0～0.9)、节流孔孔径(0.1～0.3 mm)的增大表现为先增大后减小,刚度表现为先减小后增大;气膜间隙较小时(5～10μm),槽长、槽深的增加可以明显提高承载力和刚度;槽宽(0.2～0.6 mm)对节流器承载力和刚度的影响效果不显著。     

A new, high precision, quick response pressure regulator for active control of pneumatic vibration isolation tables

Pressure regulators are important elements in pneumatic systems. Relief-type precision pressure regulators are commonly used to control the supply pressure to actively controlled pneumatic vibration isolators.Herein, a high precision, quick response pneumatic pressure regulator is proposed. This consists of an isothermal chamber, a servo valve, a pressure sensor, a quick response laminar flow sensor (QFS), and a pressure differential sensor (PD sensor) as developed by the authors. Slight changes of pressure in the chamber can be detected by the PD sensor and are fed back to the servo valve to maintain the pressure at a desired value. The performance of this regulator was confirmed experimentally in comparison with one available commercially. The regulator was then applied to the supply pressure regulation of an actively controlled pneumatic vibration isolation table. The superior performance of the regulator is clearly shown in the experimental results, especially in terms of avoiding effects from upstream or downstream disturbances.     

Application of variable area cavitating venturi as a dynamic flow controller

The variable area cavitating venturi is an effective means to throttle the mass flow rate of liquid. The mass flow rate is a function of the upstream pressure, the pintle stroke, the density and saturation pressure of the liquid, independent of the downstream pressure. In this paper, a variable area cavitating venturi is designed and four different sets of experiments are conducted to investigate the performance of the variable area cavitating venturi. In these experiments, the mass flow rates are examined under different pintle positions, upstream pressures, downstream pressures and dynamic motions of the pintle. The experimental results indicate that the mass flow rate is independent of the downstream pressure when the ratio of the downstream pressure to upstream pressure is less than 0.8. The mass flow rate is almost linearly dependent on the pintle stroke for a constant upstream pressure. The discharge coefficient is a function of the pintle stroke, whereas the upstream and downstream pressures have rare influence on the discharge coefficient. The variable area cavitating venturi can control and measure the mass flow rate dynamically by determining the pintle stroke and the upstream pressure.     

Using two servovalves to improve pneumatic force control in industrial cylinders

Pneumatic actuation systems present several advantages like low cost, high force/volume ratios, and the absence of significant heat or magnetic field generation. However, its use in complex control tasks is hindered by their highly nonlinear behavior. This drawback is caused not only by the nonlinear behavior of phenomena like friction but also by the large variation of some of the system proprieties with the system state. One of such proprieties is the fluidic stiffness of the actuator, which may suffer significant changes with the piston velocity when the pressure dynamics of both actuator chambers are coupled due to the use of only one servovalve. This dependency can be eliminated if the pressure (or pneumatic force) inside each chamber is independently controlled using two servovalves. In this paper, two pneumatic force allocation strategies are proposed and analyzed. In the first one, the stiffness of the actuator becomes independent of the pneumatic force reference. In the second one, the pneumatic forces are devised to avoid early pressure saturation of the cylinder chambers. Based on an experimental test rig, both strategies are compared against each other and against the use of only one servovalve.     

Metal woven wire cloth feeding system for gas bearings

The paper presents an experimental investigation of pneumatic resistances constructed using woven wire cloth. Tests were carried out on commercial Touraille stainless steel wire cloth featuring different mesh sizes.Two types of experiments were performed: (a) Mass flow rate through single resistances was measured with different upstream and downstream pressures and wire mesh sizes. (b) Pressure distribution and mass flow rate were measured on a pneumatic pad with a fine wire mesh feeding system. Two approaches of identification of the single resistances are discussed.Test results can be used as the basis for developing woven wire cloth pneumatic resistances whose conductance is equivalent to that of certain of the calibrated orifices normally used in gas bearings.     

微细电火花加工中电极损耗机理的研究

微细电火花加工中,因电极损耗引起的电极尺寸和形状的变化严重影响被加工工件的尺寸精度和形状精度。在实验基础上分析了电极损耗的变化过程,并借助有限元方法和电磁理论研究了产生电极损耗的机理。研究表明：电场集中是棱边损耗的根本原因,一定阶段后电极形状趋于稳定;击穿放电产生的超高频电流使电极横截面上的电流在边缘的集中是发生二次放电的主要根源。     

高压气动压力流量复合控制数字阀压力特性研究

气体的可压缩特性使得压力和流量可以通过同一个阀门进行控制,为此提出了一种高压气动压力和流量复合控制数字阀,该阀包括八个二级开关阀,通过控制器和压力传感器构成压力闭环反馈控制,二级阀阀口采用临界流喷嘴结构以减少压损。在介绍阀门结构和工作原理的基础上,对二级开关阀阀口面积的编码方案进行了研究,并利用仿真软件AMESim建立了系统模型。仿真结果表明,该复合控制阀能够实现快速准确且稳定的压力输出,气源压力为20 MPa的情况下,输出压力的范围为1~19 MPa,稳态偏差在±01 MPa 以内,具有较好的压力控制特性。     

Externally pressurized gas bearings: A comparison between two supply holes configurations

Radial vibration of a vertical rotor with externally pressurized gas bearings is analyzed. The time-dependent Reynolds equation is solved together with the journal equation of motion to obtain the response characteristics of the bearing system. The bearings are supplied with either one or two sets of supply orifices. Stiffness and flow rate are compared for both cases. Stability maps are obtained at different supply pressures and with different supply orifice diameters. The mass range from orbital stability to instability is studied as a function of supply hole downstream pressure level.