关于比例排量阀和恒功率阀的阀口设计改进技术分析及试验效果

针对国外BOSCH公司的二种阀的基本结构原理,分析、研究、探讨,通过设计改进阀口,提高产品试验特性,得出了具有本国高新技术的产品,为后期比例排量阀、恒功率阀的设计、加工、试验奠定了基础。

1015柴油机停阀机变排量技术的性能仿真研究

本文在确定停缸策略、增压系统方案、喷油模型、计算工况的基础上建立了基于GT-POWER的1015柴油机停阀机变排量技术的仿真模型,计算结果表明采用该变排量技术可以提高1015柴油机在低负荷下的经济性,并且找出了该技术所对应的最佳工况范围,通过与原机模型的对比分析了其优缺点。

基于曲轴箱污染物排放控制的PCV阀特性参数匹配设计

为了改善曲轴箱污染物的排放性能实现曲轴箱的压力控制,开展PCV阀及曲轴箱通风系统和发动机匹配研究有明显现实的工程意义。以某款车用汽油发动机为研究对象,研究活塞漏气量、进气歧管压力等发动机参数与PCV阀匹配规律,优化设计PCV阀的性能参数并通过实测曲轴箱压力对PCV阀的工作性能进行试验验证。结果表明,依据发动机自身运行工况参数设计PCV阀可变压力-流量特性,可满足排放法规对曲轴箱压力的要求。

考虑阀片变形的阻尼可调减振器动特性研究

为预测阻尼可调减振器的性能,需要对阻尼可调减振器动特性进行研究。通过对标某款阻尼可调减振器,以其结构及工作原理为基础,考虑阀片环形节流缝隙对阀片载荷力的影响,构建出节流阀片力学模型,应用变形理论建立阀片曲面微分方程并设定边界条件,得到在载荷力P作用下阀片变形量与半径的关系式,在此基础上建立减振器复原-压缩行程的数学模型,并搭建减振器Simulink模型,仿真得到减振器动特性曲线,对比MTS849减振器实验台的测试结果表明,减振器动特性的试验曲线与仿真曲线大致重合,仿真模型误差在13%以内;可见在载荷力P情况下建立的数学模型精确可靠,同时通过数据对比可以得到减振器动特性的一般规律。

在《液压传动》课的教学中如何培养学生的创造思维能力

工程技术课程是动态发展的科学技术,它的深度和广度都在发展变化之中。比如《液压传动》和《互换性与技术测量》课程,从五十年代到现在,已经由简单机床和工程机械液压传动发展到液压CAD技术,由借鉴苏联公差标准,更新为应用国际标准。

Bubble counter based on photoelectric technique for leakage detection of cryogenic valves

In order to overcome the inconvenience of manual bubble counting, a bubble counter based on photoelectric technique aiming for automatically detecting and measuring minute gas leakage of cryogenic valves is proposed. Experiments have been conducted on a self-built apparatus, testing the performance with different gas inlet strategies (bottom gas-inlet strategy and side gas-inlet strategy) and the influence of gas pipe length (0, 1, 2, 4, 6, 8, 10 m) and leakage rate (around 10, 20, 30, 40 bubbles/min) on first bubble time and bubble rate. A buffer of 110 cm3 is inserted between leakage source and gas pipe to simulate the down- stream cavum adjacent to the valve clack. Based on analyzing the experimental data, experiential parameters have also been summarized to guide leakage detection and measurement for engineering applications. A practical system has already been suc- cessfully applied in a cryogenic testing apparatus for cryogenic valves.

Structure optimization and flow field simulation of plate type high speed on-off valve

There is a relatively complex flow state inside the high speed on-off valve,which often produces low pressure area and oil reflux in the high-speed opening and closing process of the spool,causing cavitation and vortex and other phenomena.These phenomena will affect the stability of the internal flow field of the plate valve and the flow characteristics of the high speed on-off valve.Aiming at the problems of small flow rate and instability of internal flow field,a new spool structure was designed.The flow field models of two-hole and three-hole plate spools with different openings were established,and software ANSYS Workbench was chosen to mesh the model.The standard k−εturbulence model was selected for numerical simulation using FLUENT software.The pressure distribution and velocity distribution under the same pressure and different opening degree were obtained.The structure and parameters of the optimization model were also obtained.The stability analysis of flow field under different pressure was carried out.The results demonstrate that the three-hole spool has a similar flow field change with the two-hole spool,but it does not create a low pressure zone,and the three-hole spool can work stably at 2 MPa or less.This method improves the appearance of low pressure area and oil backflow in the process of high speed opening and closing of spool.The stability of flow field and the flow rate of high speed switch valve are improved.Finally,the products designed in this paper are compared with existing hydraulic valve products.The results show that the three-hole plate type high speed on-off valve designed in this paper maintains the stability of the internal flow field under the condition of 200 Hz and large opening degree,and realizes the increase of flow rate.

Design of a New Type of Distribution Valve for Hydraulic Breaker and Analysis of Energy Consumption

Energy consumed by distribution valves causes an energy loss for the output energy of hydraulic breakers, which has a significant influence on its efficiency. A new type of distribution valve used for hydraulic breakers, de- signed to reduce energy consumption, is analyzed on the basis of the operating principle and energy loss of the current distribution valve. The new distribution valve adopts a cone valve and the optimization technique of unequal open de- gree for the valve port. Theoretical calculations and analyses have proven that the new distribution valve can reduce en- ergy loss by 9.0127J, or energy consumption by 31%, during an impact cycle and the efficiency of the hydraulic breaker can be raised by 4.5%. It has the following characteristics: little leakage, little pressure loss and low energy consump- tion.

Properties analysis of a large flow-rate safety valve test device

In order to solve the problem of property test of large flow-rate safety, the property parameter of safety valve test system was analyzed, and a device for property oflarge flow-rate safety valve test was designed.The device used accumulators as power source and a united function cylinder, which can realized the large flow-rate output for the test system.Analyzed the test data and made a particular research on the test device by testing different flow-rate safety valves;it verifies that the test device can be used tode-sign larger flow-rate safety valve test system and can make the flow-rate test and analysis and dynamic characteristics for the large-flow safety valve.

Numerical and experimental investigation of leakage behavior at null position of high-pressure electro-pneumatic servo valve

The high-pressure electro-pneumatic servo valve(HESV)is a core element of the high-pressure pneumatic servo system.The annular clearance and the rounded corner of the spool-sleeve can cause the leakage at null position,thereby affecting high-precision control and stability of the servo system.This paper investigates the effects of the clearance structure on leakage behavior at null position of the HESV.A numerical approach was employed to evaluate the effects,and then a mathematical model was established to obtain the variation law of leakage flow rate at null position.The results indicate that the leakage flow rate at null position varies linearly with supply pressure and rounded corner radius,and is nonlinear as a quadratic concave function with annular clearance.The leakage flow rate of the annular clearance and the rounded corner varies with the valve opening in an invariable−nonlinear−linear trend.A test rig system of leakage behavior at null position of the HESV was built to confirm the validity of the numerical model,which agrees well with the conducted experimental study.

Magnetic Field Effects on Quantum-Dot Spin Valves

We study the magnetic field effects on the spin-polarized transport of the quantum dot （QD） spin valve in the sequential tunneling regime. A set of generalized master equation is derived. Based on that, we discuss the collinear and noncollinear magnetic field effects, respectively. In the collinear magnetic field case, we find that the Zeeman splitting can induce a negative differential conductance （NDC）, which is quite different from the one found in previous studies. It has a critical polarization in the parallel arrangement and will disappear in the antiparallel configuration. In the noncollinear magnetic field case, the current shows two plateaus and their angular dependence is analyzed. Although sometimes the two current plateaus have similar angular dependence, their mechanisms are different. Our formalism is also suitable for calculating the transport in magnetic molecules, in which the spin splitting is induced not by a magnetic field but by the intrinsic magnetization.

Influence of Pre-injection Control Parameters on Main-injection Fuel Quantity for an Electronically Controlled Double-valve Fuel Injection System of Diesel Engine

A simulation model of an electronically controlled two solenoid valve fuel injection system for a diesel engine is established in the AMESim environment.The accuracy of the model is validated through comparison with experimental data.The influence of pre-injection control parameters on main-injection quantity under different control modes is analyzed.In the spill control valve mode,main-injection fuel quantity decreases gradually and then reaches a stable level because of the increase in multi-injection dwell time.In the needle control valve mode,main-injection fuel quantity increases with rising multi-injection dwell time;this effect becomes more obvious at high-speed revolutions and large main-injection pulse widths.Pre-injection pulse width has no obvious influence on main-injection quantity under the two control modes;the variation in main-injection quantity is in the range of 1 mm3.

液压伺服作动系统启动时抖动问题的研究

液压伺服作动系统启动抖动问题是液压伺服作动系统常见的故障,为了研究影响液压伺服作动系统启动抖动的主要因素,从液压伺服作动系统工作原理、结构组成、产品机理三个方面入手,根据分析出的影响环节,逐个进行验证、仿真分析、数据分析,探索液压伺服作动系统抖动的变化规律。拟采取控制滑阀间隙及伺服阀内漏量两种措施解决问题,并通过试验验证措施的有效性。

Long-term follow-up of quality of life in high-risk patients undergoing transcatheter aortic valve implantation for symptomatic aortic valve stenosis

Background Transcatheter aortic valve implantation （TAVI） has become the standard treatment for patients with severe symptomatic aortic stenosis （AS） considered at very high risk for surgical aortic valve replacement. The purpose of this sub-study was to evaluate long-term （〉 4 years） health-related quality of life （QoL） in octogenarians who underwent TAVI. Methods A single center observational registry in twenty patients who underwent frame analysis assessment ≥ 4 years after TAVI. Health-related QoL was evaluated, using the Short Form-36 （SF-36）, the EuroQoL-5D （EQ-5D） and the visual analogue score （EQ-VAS） questionnaires. Results The mean SF-36 subscale scores at follow-up were physical functioning 40.8 ± 26.3, role physical functioning 67.7 ± 34.9, vitality 54.6 ± 21.6, general health 52.1 ± 20.4, social functioning 63.8 ± 37.7, role emotional functioning 70.2 ± 36.0, mental health 73.2 ± 23.3 and bodily pain 80.9 ± 22.9. The mean EQ-VAS score 〉 4 years after TAVI was 64.7 ± 15.1. With respect to functional class, 80% of the patients were in NYHA class I/II at follow-up compared to 15% prior to TAVI. Conclusions This sub-study reports a significant improvement in functional class （NYHA） in a selected group of very elderly patients 〉 4 years after TAVI. Furthermore, all patients showed a satisfactory QoL despite their age and multiple comorbidities. In addition, our study reveals a lower QoL when compared with the general age matched Dutch population.

Numerical Study on Flow-induced Noise for a Steam Stop-valve Using Large Eddy Simulation

The noise induced by the fluctuant saturated steam flow under 250 °C in a stop-valve was numerically studied.The simulation was carried out using computational fluid dynamics（CFD） and ACTRAN.The acoustic field was investigated with Lighthill＇s acoustic analogy based on the properties of the flow field obtained using a large-eddy simulation that employs the LES-WALE dynamic model as the sub-grid-scale model.Firstly,the validation of mesh was well conducted,illustrating that two million elements were sufficient in this situation.Secondly,the treatment of the steam was deliberated,and conclusions indicate that when predicting the flow-induced noise of the stop-valve,the steam can be treated as incompressible gas at a low inlet velocity.Thirdly,the flow-induced noises under different inlet velocities were compared.The findings reveal it has remarkable influence on the flow-induced noises.Lastly,whether or not the heat preservation of the wall has influence on the noise was taken into account.The results show that heat preservation of the wall had little influence.

Dynamic characteristics of the high-flow water three-way valve

Operating principle of water three-way valve with high flow for individual hydraulic prop in coal was presented in this paper, its strict and precise mathematical model was established, its flow field was simulated numerically by software Fluent, and its dynamic characteristics were analyzed during the work process such as raising leg, loading and overflow, the influence of the related parameters on high-flow water three-way valve was determined. The results as follows： during the raising leg stage and early raising leg stage, when the damping ratio increases, the overshoot of system decreases and the setting time reduces, and the dynamic response performance has a significant improvement. During the loading stage and the overflow stage, the pressure in plunger chamber of single hydraulic prop, the output flow and the displacement of the high-flow water three-way valve decrease with the decreasing of the external load. The spring stiffness of the safety valve directs the flow and the spool＇s displacement of the safety valve, and it can be used to control the high-flow three-way valve＇s sensitivity.

Measurement of trace nitrate concentrations in seawater by ion chromatography with valve switching

An ion chromatographic method with a valve switching facility was developed to determine trace nitrate concentrations in seawater using two pumps, two different suppressors, and two columns. A carbohydrate membrane desalter was used to reduce the high concentrations of sodium salts in samples. In this method, trace nitrate was eluted from the concentrator column to the analytical columns, while the matrix fl owed to waste. Neither chemical pre-treatment nor sample dilution was required. In the optimized separation conditions, the method showed good linearity( R >0.99) in the 0.05 and 50 mg/L concentration range, and satisfactory repeatability(RSD<5%, n =6). The limit of detection for nitrate was 0.02 mg/L. Results showed that the valve switching system was suitable and practical for the determination of trace nitrate in seawater.

Geometry Modeling of an Electronic Expansion Valve Head

This paper proposed that the flow characteristic of electronic expansion valve should be adapted to the evaporator superheat gain to refrigerant flow rate under different working conditions. Two native methods of geometry modeling of electronic expansion valve head were introduced. By analysis of them, some shortcoming was detected and a universal modeling method of electronic expansion valve head was put forward. Through this model, the flow characteristic of EEV and the influence factors can be investigated more deeply.

Periods and Energy Dissipations of a Novel TLD Rectangular Tank with Angle-adjustable Baffles

A novel tuned liquid damper (TLD) rectangular tank with two angle-adjustable baffles was pre- sented.The numerical analysis was performed using the commercial code FLUENT.The standard kinetic energy and dissipation rate turbulent model was employed,which was solved using volume of fluid (VOF) method able to treat both the free surface motion and the viscous stresses over the rigid walls accurately.The relationship between the natural periods of water and the angles of its baffles was studied by numerical sim- ulating of a case,and the changes of energy dissipations were investigated.The natural periods and dampers of the novel TLD can be changed in a wide range by adjusting the baffles' angle,thus it is more effective in controlling the vibration of structures in a wide frequency range.

液压伺服柔驱机构设计及其刚度连续可调分析

为满足液压机械臂工作时输出高刚度,碰撞时变刚度实现柔顺性,让机器人在不同工作条件和场景下具有相应的柔顺性,设计了一种兼具阀控泄漏量和浮动位的液压伺服柔驱机构。首先,介绍该关节结构和变刚度原理;其次,利用Amesim建立其动态仿真模型,确定阀控泄漏量和浮动位半径范围;然后,利用MATLAB/Simulink建立其刚度仿真模型,分析单个因素与关节变刚度的关系;最后,基于MATLAB拟合关节刚度多元非线性回归方程,并通过程序实现刚度初始散点和拟合四维曲线对比图。仿真结果表明:在保证较好的动态特性时,该柔驱机构刚度能在较宽范围内连续可调。