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無錫太湖學(xué)院學(xué)士學(xué)位論文
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.
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 Blasé 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 Blasé 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 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 .
液壓與氣壓傳動的特點及發(fā)展應(yīng)用概況
1. 液壓傳動有以下優(yōu)點
1）在同等體積下，液壓裝置畢電氣裝置產(chǎn)生更高的動力。再同等功率下，液壓裝置體積小，重量輕，功率密度大，結(jié)構(gòu)緊湊。液壓馬達的體積和重量只有同等功率電動機的12%左右。
2）液壓裝置工作比較平穩(wěn)。由于重量輕、慣性小、反應(yīng)快，液壓裝置易于實現(xiàn)快速啟動、制動和頻繁的換向。
3）液壓裝置能在大范圍內(nèi)實現(xiàn)無級調(diào)速（調(diào)速范圍可達2000），它還可以在運行過程中進行調(diào)速。
4）液壓傳動易于自動化，它對液體壓力、流量或流動方向易于進行調(diào)節(jié)或控制。當(dāng)將液壓控制和電氣控制、電子控制或氣動控制結(jié)合起來使用時，整個傳動裝置能實現(xiàn)復(fù)雜的順序動作，也能方便的實現(xiàn)遠(yuǎn)程控制。
5）液壓裝置易于實現(xiàn)過載保護，這是電氣傳動裝置和機械傳動裝置無法辦到的。
6）由于液壓元件已經(jīng)實現(xiàn)了標(biāo)準(zhǔn)化、系列化和通用化，液壓系統(tǒng)的設(shè)計、制造和使用都比較方便。
7）用液壓傳動實現(xiàn)直線運動遠(yuǎn)比用機械傳動簡單。
2.液壓傳動的缺點
1）由于流體流動的阻力損失和泄露是不可避免的，所以液壓傳動在工作過程中常有較多的能量損失。
2）工作性能易受溫度變化的影響，因此不宜在很高或很低的溫度下工作。
3）為了減少泄漏，液壓元件的制造精度要求較高，因而價格較貴。
4）液壓傳動出現(xiàn)故障時不易找出原因。
3.氣壓傳動的優(yōu)點
1）空氣可以從大氣中取得，同時，用過的空氣可直接排放到大氣中去，處理方便，萬一空氣管路有泄漏，除引起部分功率損失外，不知產(chǎn)生不利于工作的嚴(yán)重影響，也不會污染環(huán)境。
2）空氣粘度很小，在管道中的壓力損失較小，因此壓縮空氣便于集中供應(yīng)和遠(yuǎn)距離輸送。
3）因壓縮空氣的工作壓力較低（一般為0.3~0.8Mpa），因此，對氣動元件的材料和制造精度上的要求較低。
4）氣動系統(tǒng)維護簡單，管道不易堵塞。
5）使用安全，并且便于實現(xiàn)過載保護。
4.氣壓傳動的缺點
1）由于空氣具有可壓縮的特性，因此運動速度的平穩(wěn)性不如液壓傳動。
2）因為工作壓力較低和結(jié)構(gòu)尺寸不宜過大，因而氣壓傳動裝置的總推力一般不可能很大。
3）傳動效率低。
總的說來，液壓與氣壓傳動的優(yōu)點是主要的，而它們的缺點通過技術(shù)進步和多年的不懈努力，已得到克服或得到了很大的改善。
雖然在17世紀(jì)中葉法國物理學(xué)家伯雷斯.帕斯卡提出了靜壓傳遞原理，但在18世紀(jì)末才開始找到應(yīng)用在液壓系統(tǒng)和其他現(xiàn)代裝備中合適的元件。從那以后，液壓技術(shù)得到迅速發(fā)展。
17、18世紀(jì)是液壓基礎(chǔ)理論的建立最興旺的時期。其中在17世紀(jì)初期，意大利數(shù)學(xué)和物理學(xué)家托里切利研究流體運動原理；17世紀(jì)后期艾沙克牛頓研究物體在流動的液體中的粘性和阻力問題；18世紀(jì)中葉是最關(guān)鍵的時期，主要的成就有丹萊爾.箔某里發(fā)展了流體能量傳遞原理，同時伯雷斯.帕斯卡建立并提出了靜壓傳遞原理。從此靜壓傳遞原理奠定了流體傳動（液壓、氣壓傳動）的理論基礎(chǔ)。
靜壓傳遞原理在18 世紀(jì)后期得到廣泛運用。世界上第一臺水壓機是在18 世紀(jì)末由英國制造的。
在上述理論基礎(chǔ)上，納維推倒流體運動方程，到了19世紀(jì)初期斯托克斯葉獨立發(fā)現(xiàn)相同的方程并進一步發(fā)展了納維的流體運動方程。
近代液壓氣壓傳動是有19 世紀(jì)崛起并蓬勃發(fā)展的石油工業(yè)推動起來的，最早實踐成功的液壓傳動裝置是艦艇上的炮塔轉(zhuǎn)位器，其后才在機床上應(yīng)用。第一次世界大戰(zhàn)引入基于液壓原理的新武器。在20 世紀(jì)30 年代初期和后期在大型工業(yè)自動化中引入液壓制動。1940年代開始使用拖拉機以增強農(nóng)機設(shè)備的機動性和效率。第二次世界大戰(zhàn)期間，由于軍事工業(yè)和裝備迫切需要反應(yīng)迅速、動作準(zhǔn)確、輸出功率大的液壓傳動及控制裝置，促使液壓技術(shù)迅速發(fā)展；戰(zhàn)后，液壓技術(shù)很快轉(zhuǎn)入民用工業(yè)。在機床、工程機械、冶金機械、塑料機械。農(nóng)林機械、汽車、船舶等行業(yè)得到大幅度的應(yīng)用和發(fā)展。近幾年液壓傳動應(yīng)用到大型挖掘機和建筑施工的設(shè)備中，所涉及的總的動力常常比最大型的航空系統(tǒng)所需的動力還高。
隨著液壓機械自動化程度的不斷提高，液壓、氣動元件應(yīng)用數(shù)量急劇增加，元件小型化、系統(tǒng)集成化是必然的發(fā)展趨勢。特別是近十年來，液壓和氣動技術(shù)與傳感技術(shù)、微電子技術(shù)密切結(jié)合，出現(xiàn)了許多諸如電液比例控制閥、數(shù)字閥、電液伺服液壓缸等機（液）電一體化元器件，使液壓技術(shù)在高壓高速大功率節(jié)能高低噪聲使用壽命長高度集成化等方面取得了重大進展。無疑，液壓元件和液壓系統(tǒng)的計算機輔助設(shè)計（CAD）計算機輔助試驗（CAT）和計算機實時控制也是當(dāng)前液壓和氣動技術(shù)的發(fā)展方向?，F(xiàn)今采用液壓傳動的程度已成為衡量一個國家工業(yè)水平的重要標(biāo)志之一。如發(fā)達國家生產(chǎn)的95%的工程機械、90%的數(shù)控加工中心、95%以上的自動生產(chǎn)線都采用了液壓傳動。
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