反击系数在低比转速叶轮几何参数优化中的应用

低比转速叶轮为产生较高的给定扬程,叶轮直径都相对较大。叶轮圆盘摩擦损失大约正比于叶轮直径的5次方．圆盘摩擦损失成为低比转速泵内损失的主要形式,也是这类泵效率甚低的基本原因。为改善这类泵的效率指标,曾提出了一以降低叶轮直径和圆盘摩擦损失为主要目标的优化模型。针对对这一数学模型的质疑,从叶轮的反击系数这一概念入手,论证了不可能通过叶轮几何尺寸优化同时把叶轮圆盘摩擦损失和叶轮出口冲击损失降低到最小值,由于在低比转速泵中前者占优势,因而降低这类泵的圆盘摩擦损失是提高这类泵效率的主要途径,从而在理论上论证了所讨论优化模型的正确性．     

Effect of angular speed on behavior of a V-belt drive system

For a V-belt drive system, the effect of angular speed on the three-dimensional frictional contact behaviors on the contact surfaces between the V-belt and pulley flange is studied in this work. To deal with the frictional contact phenomena for the V-belt drive system, an effective three-dimensional finite element procedure is developed herein. By this procedure, the deformation of the V-belt and the normal/tangential contact forces occurring on the contact surfaces can be estimated accurately. The friction angles of contact points along the edge of the V-belt cross section are also presented for various dynamic friction coefficients. From the computed results, it is found that smaller friction angles are obtained as dynamic friction coefficients get larger. The results achieved are very helpful for the estimation of operation efficiency of the V-belt drive system.     

Study on Starved Lubrication Performance of a Cycloid Drive

The lubrication performance of cycloid drives affects the dynamic characteristics, mechanical efficiency, and contact fatigue behavior. Starved lubrication performance of a cycloid gear drive is studied using a numerical thermo-starved elastohydrodynamic lubrication model. The parameter of the inlet oil film thickness is chosen to represent the starvation degree. Effects of the inlet film thickness on the central film thickness, friction coefficient, frictional power loss, starting position of the effective film thickness, and lubrication efficiency are investigated. The optimum inlet film thickness is defined and is calculated under different rolling–sliding ratios, speeds, and loads. Finally, the optimum inlet film thickness during the meshing process of a cycloid drive is calculated.     

相似通风机流道表面相对粗糙度对其流动效率的影响

讨论了相似通风机流道中流体流动摩擦损失计算公式。推出了不同的流道表面相对粗糙度情况下模型与实物流动效率之间的计算公式。     

Development of a new composite material for bits of supporting and centering devices

Research has been conducted on the development of a new composite material for bits of well-supporting and -centering devices. The highly durable composite makes it possible to reduce frictional energy losses on straightline wellbore sections while ensuring a highly destructive effect at wellbore sections that are being explored. High-carbon high-alloy cast irons reinforced with titanium carbide have been proposed as the composite matrix. It has been shown that the hardness of the new material is comparable to that of hard alloys, while the minimum power losses for sliding friction under abrasion are lower than for hard alloys and diamond-bearing materials.     

齿轮啮合过程摩擦功耗研究

A novel method for frictional power losses of a gear meshing was presented according to the basic theory of power and energy of the system. It was provided that the relative sliding of two disks existed during the disks rotating, frictional power losses will be caused by the frictional torque for each disk. Based on the above principle, the model for the friction power loss of the gears meshing was built. The frictional coefficient plays important role to the frictional power loss of gears and the time-varying coefficient was analyzed. Based on the system frictional power loss of the gears, the time-varying frictional power loss was calculated. The results indicate that the power loss in the double tooth meshing plays significantly role in the whole power losses. Finally, the results obtained from the new method were compared to the test results by Velex and it is shown that the model of frictional power loss is feasible.     

差动液粘调速器的结构机理

该装置用于大功率带式输送机的软起动，事先给出带式输送机起动时理想的速度、加速度曲线。通过压力、速度、功率等检测信号反馈，形成闭环控制回路，自动调节摩擦片间隙，改变输出转速和转矩，使实际起动曲线逼近理想曲线，从而实现动态可控起动。同样用调节摩擦片间隙的方法，精确控制多机驱动功率平衡和软制动，大大降低胶带动张力，使输送机起动及制动更加平稳，同时大幅度降低设备成本。该文重点阐述差动液粘调速器的结构、工作原理、传递力矩计算、分析摩擦传动特性、效率及发热等。     

质子交换膜燃料电池-四温位吸收式制冷机混合系统性能分析

建立质子交换膜燃料电池-四温位吸收式制冷机混合系统模型,该模型考虑包括燃料电池热力学和电化学不可逆性、吸收式制冷循环不可逆性在内的主要损失,导出系统总的输出功率和效率表达式,以及吸收式制冷循环的制冷量及制冷系数关系式。通过数值计算探讨混合电池系统的整体性能,分析不同运行工况参数对混合系统性能的影响规律,得出电流密度、输出功率、效率等重要参数的优化工作区间。系统对质子膜燃料电池的余热进行合理利用,使质子膜燃料电池混合系统总的输出功率以及效率都有了较大的提高。     

精密柔索传动张力的分析与测量

精密柔索传动是一种通过主、从动轮之间有适当预紧的传动介质实现的摩擦挠性传动方式,具有轻质、高效、简洁等特点,在轻量化光电侦察吊舱等系统中得到了广泛的应用。张力是精密柔索传动系统的一项关键设计参数,可以有效调控传动特性。但是,由于空间结构尺寸所限,现有的张力测量方法难以进行精确测量。本文提出了一种改进型三点弯曲张力测量方法。建立了张力对传动特性的灵敏度关系,推导了基于抗弯刚度的张力测量修正模型。为了验证修正模型的有效性,将精密柔索传动单元下两种不同规格的传动柔索应用在三种不同跨距下,进行张力测试。实验结果表明,修正模型下的张力偏差均值大幅度减小,张力偏差能够缩小到5 N以内,满足柔索传动系统的张力测量精度要求。     

Indirect Cutting Force Measurement Considering Frictional Behaviour in a Machining Centre Using Feed Motor Current

In machine tools, friction exists between the table and the guideways, and in ballscrews. In this paper, feed motor current is measured by a hall effect current sensor. It is used to calculate the motor torque which, in turn, is the frictional torque at steady state. Some frictional phenomena are studied in feed drive systems of a horizontal machining centre, such as the relationship between feedrate and frictional torque, the relationship between frictional torque and table feed position, and the slideway cover effects on frictional torque. Considering all these frictional phenomena, the relationship between the feed force and the feed motor current is obtained. Feed force can be estimated well from the feed motor current considering frictional behaviour. The relationship between the cutting force and the feed motor current is slightly different during up milling and down milling, because y(vertical) directional cutting force changes the frictional force.     

The efficiency of a hypoid axle—a thermally coupled lubrication model

The final drive unit in road vehicles, such as medium and heavy trucks, and four-wheel-drive and rear-wheel-drive passenger cars, usually consists of a hypoid or spiral bevel geared transmission and differential, housed in a self-contained, dip-lubricated axle. Such units are subjected to very variable duty—including extreme combinations of speed, gradient, applied torque and external temperature—and are typically cooled by natural and forced convection on the exterior surface. On the other hand, there are appreciable internal power losses due to gear friction and churning and to bearing and seal losses. These losses are highly dependent upon the lubrication regime of the internal components and hence to the thermal behaviour of the entire axle.In the present paper, we describe a thermally coupled model of axle lubrication. The torque and speed demand is first found from a specified duty (“drive cycle”) which includes terrain as well as speed-versus-time and external temperature data. The evolution of sump oil and component temperatures is followed, and increments of energy loss evaluated in each time-step. Elastohydrodynamic film thickness is determined for the hypoid gear set, using a development of Buckingham's method, and friction losses calculated using a simple oil rheological model based on tribometer (MTM) testing. Churning, seal and bearing (speed-dependent) losses are found using empirical algorithms. Energy losses over complete drive cycles for different lubricants are derived, enabling the relative fuel economy for different oils to be evaluated.Results show that (i) the bulk temperature rise of the axle is highly dependent on the specified vehicle duty and (ii) the efficiency can be strongly influenced by choices available to the lubricant formulator. Taken together, these findings suggest that specialist axle lubricant formulations for particular vehicle types and applications will be attractive as a route to optimum fuel economy.     

The solution of Reynolds equation under natural boundary conditions for hydrodynamic journal bearings

The solution of Reynolds equation for hydrodynamic pressures of the load-carrying lubricating layer in journal bearings is discussed.The accepted boundary conditions are shown to be helpful in explaining more accurately the physical meaning of the lubricant flow process and in assuming the boundary curvature for the load-carrying lubricant film in the convergent-divergent zone of the bearing clearance.New algorithms for determining the above curve boundary in the process of the numerical solution of a basic differential equation are suggested. The technique used for the theoretical study of the bearings made it possible to provide results of greater accuracy for their principal operating characteristics such as load-carrying capacity, frictional losses and lubricant consumption.     

A new tribometer for friction drives

Friction drives have great potentials in future small-sized machines for their unique features, such as no-noise operation and high position accuracy coupled with simpler design. One of the main challenges of a friction drive is to find suitable material pair for the driver and follower components such that there is no slip and/or wear at the frictional contact regions. In this paper, we present a new tribometer that can be used to study the performance of a material for friction drive applications. The design and fabrication of the apparatus are presented with initial test results conducted to investigate the power efficiency and wear performances of several polymer and metal samples. Our results show that for a fixed power transmission torque, there exists a critical pre-load between the drive components at which the wear and slip are maximum and the value of critical pre-load is independent of the material. Both wear and slip can be minimized to near-zero if an optimum pre-load, which is higher than the critical pre-load, is applied between the two components.     

注塑机电液控制系统能量效率对比研究

在同一注塑机上,对采用异步电动机驱动定量泵、变转速异步电动机驱动定量泵、异步电动机驱动变量泵、变转速异步电动机驱动变量泵、交流伺服电动机驱动定量泵,5种电液控制方案加工同一制品的能量效率进行理论分析和试验对比。建立不同控制回路电动机和液压泵功率传输数学模型,绘制出能量特性曲线,分析对比注塑机工作在保压和冷却工况下,液压系统和电动机驱动系统功率消耗。研究结果证实,在部分负载和空载工况,异步电动机驱动定量泵系统存在大的溢流、节流损失,效率低;在此基础上引入变转速控制,包络系统所需的流量,可减少电动机功率消耗,提高系统效率,能量效率与异步电动机驱动变量泵相当;异步电动机驱动变量泵系统,可完全消除液压系统的溢流损耗,但电动机仍存在较大的空转损耗,在此基础上引入变转速控制,使电动机输出功率与液压负载相匹配,可进一步提高能量利用率26.5%;研究也表明,采用交流伺服电动机驱动的定量泵系统能量效率最高,较异步电动机驱动的定量泵系统节能88%,并且结构简单、动态性能好。     

谐波齿轮传动扭转刚度的实验研究

通过逐次加载扭矩的方法测试谐波齿轮传动装置扭转刚度,所获得的扭转刚度曲线揭示出了摩擦效应对其正反加、卸载测量值准确性的影响。对研究谐波齿轮传动刚度具有指导意义。     

Operational reliability of free-wheel mechanisms in a pulsed variable-speed drive

The operational reliability of eccentric free-wheel mechanisms (of both frictional and nonfrictional types) in a pulsed variable-speed drive is studied by calculation and experiment. The grades of steel ensuring the longest life of such mechanisms in pulsed loading are determined.     

Determining the losses in kinematic pairs and mechanical transmissions on the basis of the amontons-coulomb law

Methods of calculating frictional losses in machines need to be modernized. Models are proposed for the energy calculation of multilink and branched kinematic chains.     

超声电机的预压力特性分析与优化

预压力是保证超声电机定转子摩擦驱动的关键因素,开展预压力特性分析及优化方法研究对于提升电机性能及使用寿命具有重要意义。本文通过仿真分析了预压力对接触角及驱动区占比的影响,实验测试了预压力变化时的速度波动规律,并绘制了在不同预压力和转矩下的速度与效率曲面;借助编码器与薄膜温度传感器获取了不同预压力条件下电机工作200 s的速度与定子界面温度的变化过程。综合上述分析结果,提出了一种面对不同应用场合的预压力优化准则,确定了预压力的理想工作区间。实验结果表明,伴随着预压力的增长,接触区与驱动区同步扩展,同时驱动区占比逐步减小,在一定程度上能减小速度波动,电机最大效率点逐渐向大转矩方向移动,且机械效率在某个预压力下存在最高值,而界面温升则呈现先增大、后减小再增大的趋势。根据所提出的优化准则确定出TRUM60A型超声电机预压力较为理想的工作区间为260~320 N,在该预压力范围内,超声电机既能较好地满足低速稳定、温升小的要求,又能使制动力矩和机械效率达到理想范围。     

NUMERICAL SIMULATION OF FLOW FIELD BETWEEN FRICTIONAL PAIRS IN HYDROVISCOUS DRIVE SURFACE

The flow field of the oil film between frictional pairs in the hydroviscous drive test rig is investigated. A three-dimensional Navier-Stokes（N-S） equation considering viscous force and inertial force rather than Reynolds equation or modified Reynolds equation is presented to model the flow field. Pressure and temperature distribution in radial and circumferential direction under three different conditions, i.e., isothermal, that considering viscosity-temperature characteristic as well as shear thinning non-Newtonian fluid are simulated, respectively, by utilizing the commercial computational fluid dynamics（CFD） software FLUENT. The results reveal that the grooves on the driven plate make the pressure, temperature distribution present periodic variation. The oil temperature and shear rate have important effects on the flow field between frictional pairs, and the oil temperature is more important parameter. The simulation results lay a theoretical foundation for the reasonable designs ofhydroviscous drive.     

机械控制式惯性压电旋转驱动器

以惯性压电旋转驱动器为研究对象,对比研究了非对称式惯性压电旋转驱动器和变摩擦力式惯性压电旋转驱动器的运动特性。分析了两种驱动器的工作原理,设计、制作了试验样机,搭建了测试系统并对两种压电旋转驱动器进行了对比试验测试。结果显示:在8Hz方波电信号的激励下,非对称式压电驱动器的旋转步距大于变摩擦力式旋转驱动器;当驱动电压为100V时,非对称式与变摩擦力式压电驱动器的回退率分别为73.19%、65.67%;在40V、8 Hz的方波激励下,非对称式与变摩擦式压电驱动器的线性度残差平方和与重复性标准差分别为0.031、0.069与0.011、0.063。试验结果表明:与变摩擦力式驱动器相比,非对称式驱动器的输出步距及回退率更大,具有较高的线性度和重复性。