内容简介：: 无锡太湖学院学士学位论文 - 1 -The Features and Development History and Application of Hydraulic and Pneumatic Transmission 1. The advantages of hydraulic transmission 1) A hydraulic system can produce higher power than electrical equipment under the same volume. The hydraulic equipment system has smaller volume, light, high power consistency and compact configuration at a given power. The volume and weight of a hydraulic motor are about 12% of an electric motor.2) Hydraulic equipment has a good working stability. It is because of light , less inertia , quick response : the hydraulic equipment can realize celerity start-up , brake and frequent change in motion direction .3) The hydraulic transmission can reach a wide range of speed regulation (with the range of 1:2000), and the speed can also be regulated during the work processing.4) The hydraulic transmission can easily realize automation and the pressure; flow rate and the flow direction can be regulated and controlled. If we combine it with electric, electron or pneumatic control systems, a more complex transmission system with remote control can be realized.5) The hydraulic system can protect from over-load easily, which cannot be done by electricity or machine equipment.6) Because of standardization, series, and all-purpose application; the hydraulic system is easier in design, fabrication and application.7) The hydraulic system is easier than machine equipment in doing line motion.2. The shortages of hydraulic transmission 1) Leak. Oil leaks are inevitable because of the loss in fluid flow resistance. So more energy loss exists in a hydraulic transmission.2) Working temperature. The working temperature has strong effect on the working property of a hydraulic system because of the viscosity-temperature character of hydraulic oil . It is suitable for working in a proper temperature.3) Cost. The cost is high because of the needs in high precision fabricate for hydraulic elements.4) It is difficult to find the reasons of fault.3. The advantages of pneumatic transmission. 无锡太湖学院学士学位论文 - 2 -1) The air can be obtained and expelled from the atmosphere. It cannot bring pollution to the environment.2) It is of low viscosity and lower pressure loss in pipes. The pressure air is convenient for convergence supply and remote transportation.3) It is of low working pressure (usually 0.3-0.8MP a). Avowers material and fabricate precision is required for the pneumatic transmission elements.4) The pneumatic transmission has a simple servicing .The air pipe is not easy to be jammed.5) Safety. The pneumatic system can protect from over-load easily.4. The short comes of pneumatic transmission 1) It is because of air compressibility. The working stabilities for pneumatic transmission system are poorer than those of hydraulic transmission system.2) Because of lower working pressure and small size in configuration, the push force of pneumatic transmission is usually very lower.3) Lower transmission efficiency.To sum up, the strong-points of hydraulic and pneumatic transmission have taken the main advantages, and the shortages have been overcome and improved by technical renovation.The fundamental law underlying the whole science of hydraulics was discovered by Blas Pascal ,a French physicist ,in the seventeenth century .But it was not until the end of the 18 century that man found ways to make the snugly fitting parts required in hydraulic systems and other modern equipment .Since then progress has been rapid .Hydraulic transmission has been experiencing the process as below.The 17th and 18th centuries were a productive period in the development of hydraulic theory . Torricelli studied fluid motion in the early 17th century .Late in that century, Sir Isaac Newton conducted studies on viscosity and the resistance of submerged bodies in a moving fluid .The key achievements of the period occurred in the middle of the 18th century when Daniel Bullion developed the theory of transmission of energy in fluid streams and Blas Pascal, at about the same time, established the principle of hydrostatic pressure transmission.This principle was first used in the latter part of the 18th century .The first hydraulic pressure machine was manufactured by England in the late 18th century .The fundamentals of fluid theory were established by the above work and refinements were 无锡太湖学院学士学位论文 - 3 -added by Nervier who derived the mathematics of motion in liquids including equations for fluid flow with friction .This was early in the 19th century .It was followed by the work of Stokes ,who independently discovered the same equations and further extended the work of Nervier .Recently hydraulic and pneumatic pressure transmission technology has been developed with a large scale patriotic industry in the 19th century ,and the barbette displace was the first one successful using hydraulic equipment ,and then hydraulic machine tool .In World War I many new machines based on the principles of hydraulics had been used .The great automotive industry introduced hydraulic brakes in the early thirties and hydraulic transmissions in the late thirties .The tractor industry began using hydraulics in 1940 to increase the flexibility and utility of farm equipment .In World War II because of the demand transmission and control equipments in fast reaction ,precision action and high output powers boosted development in hydraulic theology .After the War ,the hydraulic development turned into civil industry ,such as machine tool ,engineering ,metallurgy ,plastic machine ,farm machine ,vehicle and watercraft .In more recent years ,the role of leadership in hydraulic power application has been taken over largely by some of the large earthmoving and construction equipment manufacturers .The total power involved is often greater than that required in even the largest aircraft systems .With the development of higher automation of hydraulic machines and increasing use of hydraulic and pneumatic elements ,the scaled elements and integrated hydraulic system with miniaturization is inevitable .Especially in recent years hydraulic and pneumatic transmission is combined closely with the sensor and micro-electricity technology .It has been emerging amounts of new valves such as hydraulic-electricity proportional valves ,digital valves ,hydraulic and electro-hydraulic servo cylinders and the integrative elements ,which will lead the hydraulic and pneumatic technology to the development of higher pressure ,higher speed ,larger power ,lower energy wastage and noise ,longevity and high integration .Computer aided design (CAD ) and test (CAT ) and practical control technology used in hydraulic and pneumatic system will be the trend .Nowadays the application of hydraulic transmission system has become one of the important indications of industry level for a country .In developed countries ,95%of engineering machine ,90%of numerical control center and more than 95%of automation assembly lines use the hydraulic transmission system . 无锡太湖学院学士学位论文 - 4 -液压与气压传动的特点及发展应用概况1. 液压传动有以下优点1）在同等体积下，液压装置毕电气装置产生更高的动力。再同等功率下，液压装置体积小，重量轻，功率密度大，结构紧凑。液压马达的体积和重量只有同等功率电动机的 12%左右。2）液压装置工作比较平稳。由于重量轻、惯性小、反应快，液压装置易于实现快速启动、制动和频繁的换向。3）液压装置能在大范围内实现无级调速（调速范围可达 2000），它还可以在运行过程中进行调速。4）液压传动易于自动化，它对液体压力、流量或流动方向易于进行调节或控制。当将液压控制和电气控制、电子控制或气动控制结合起来使用时，整个传动装置能实现复杂的顺序动作，也能方便的实现远程控制。5）液压装置易于实现过载保护，这是电气传动装置和机械传动装置无法办到的。6）由于液压元件已经实现了标准化、系列化和通用化，液压系统的设计、制造和使用都比较方便。7）用液压传动实现直线运动远比用机械传动简单。2.液压传动的缺点1）由于流体流动的阻力损失和泄露是不可避免的，所以液压传动在工作过程中常有较多的能量损失。2）工作性能易受温度变化的影响，因此不宜在很高或很低的温度下工作。3）为了减少泄漏，液压元件的制造精度要求较高，因而价格较贵。4）液压传动出现故障时不易找出原因。3.气压传动的优点1）空气可以从大气中取得，同时，用过的空气可直接排放到大气中去，处理方便，万一空气管路有泄漏，除引起部分功率损失外，不知产生不利于工作的严重影响，也不会污染环境。2）空气粘度很小，在管道中的压力损失较小，因此压缩空气便于集中供应和远距离输送。3）因压缩空气的工作压力较低（一般为 0.30.8Mpa），因此，对气动元件的材料和制造精度上的要求较低。4）气动系统维护简单，管道不易堵塞。无锡太湖学院学士学位论文 - 5 -5）使用安全，并且便于实现过载保护。4.气压传动的缺点1）由于空气具有可压缩的特性，因此运动速度的平稳性不如液压传动。2）因为工作压力较低和结构尺寸不宜过大，因而气压传动装置的总推力一般不可能很大。3）传动效率低。总的说来，液压与气压传动的优点是主要的，而它们的缺点通过技术进步和多年的不懈努力，已得到克服或得到了很大的改善。虽然在 17 世纪中叶法国物理学家伯雷斯.帕斯卡提出了静压传递原理，但在18 世纪末才开始找到应用在液压系统和其他现代装备中合适的元件。从那以后，液压技术得到迅速发展。17、18 世纪是液压基础理论的建立最兴旺的时期。其中在 17 世纪初期，意大利数学

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