Unit-18-Fluid-and-Hydraulic-System-機電專業(yè)英語-圖文課件

1、Unit 18 Fluid and Hydraulic SystemContentsNew Words & Expressions Text & TranslationComplex Sentence AnalysisKey to ExercisesNew Words & Expressions hydraulic system 液壓系統(tǒng)prehistoric pri:histrik adj. 史前的，很久以前的harness h:nis v. 利用(風(fēng)等)作動力，治理，控制watermill w:tmil n. 水車，水磨hydraulic motor 液壓電動機mosaic mzeiik

2、n. 鑲嵌細(xì)工，馬賽克domestication dmestikein n. 家養(yǎng)，馴養(yǎng)displacement displeismnt n. 位移，轉(zhuǎn)移，置換New Words & Expressions layer lei n. 層，層次tangential tndenl adj. 切線的，切向的Newtonian njutnin adj. 牛頓的，牛頓學(xué)說的nonlinear nnlini adj. 非線性的，非直線的rotational ruteinl adj. 旋轉(zhuǎn)的，轉(zhuǎn)動的，循環(huán)的compressible kmpresibl adj. 可壓縮的，可壓榨的Pascals law 帕斯

3、卡定律pressurize preraiz v. 增壓，給加壓New Words & Expressions intake inteik n. 入口，進口，進入量tank tk n. 油箱，水箱，池塘.reservoir rezvw: n. 蓄水池，水箱，蓄能器atmospheric tmsferik adj. 大氣的，空氣的discharge dist:d n. 卸貨，出料，流出; vi. 卸下，放出preference prefrns n. 優(yōu)先選擇compact kmpkt adj. 緊湊的，緊密的，簡潔的New Words & Expressions diagrammatic daig

4、rmtik adj. 圖表的，概略的oil pressure pump 液壓泵hydraulic cylinder 液壓缸kinetic energy 動能hydrostatic driver 靜壓傳動variable-delivery pump 變量泵by no means 決不self-contained adj. 獨立的，配套的，整體的New Words & Expressions stimulate stimjuleit v. 促進，激勵hydraulics haidr:liks n. 水力學(xué)，液壓系統(tǒng)resilience rizilins n. 跳回，恢復(fù)力，回彈virtue v:t

5、u: n. 優(yōu)點，效力，功能detriment detrimnt n. 損害，不利regrind ri:graind v. 重磨Text & TranslationHydraulic power has a long history，which dates from mans prehistoric efforts to harness the energy in the world around him. The only sources readily available were the water and the windtwo free and moving streams. The

6、 watermill，the first hydraulic motor，was an early invention. One is pictured on a mosaic at the Great Palace in Byzantium，dating from the early fifth century. The Romans had built the mill. But the first record of a watermill dates back even further，to around 100 BC，and the origins may indeed have b

7、een much earlier. Text & TranslationThe domestication of grain began some 5 000 years before and some enterprising farmers may have become tired of pounding or grinding the grain by hand. Perhaps，in fact，the inventors were some farmers wives. Since they often drew the heavy jobs. Fluid is a flowing

8、substance；that is，its constituent particles may continuously change their positions relative to one another. Moreover，it offers no lasting resistance to the displacement，however great，of one layer over another. This means that，if the fluid is at rest，no shear force (that is a force tangential to the

9、 surface on which it acts) can exist in it. Text & TranslationFluid may be classified as Newtonian and non-Newtonian. 1In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate of angular deformation. In non-Newtonian fluid there is a nonlin

10、ear relation between the magnitude of applied shear stress and the rate of angular deformation. The flow of fluids may be classified in many ways，such as steady or non-steady，rotational or irrotational，compressible or incompressible，and viscous or no viscous. Text & Translation2All hydraulic systems

11、 depend on Pascals law，named after Braise Pascal，who discovered the law. This law states that pressurized fluid within a closed containersuch as cylinder or pipeexerts equal force on all of the surfaces of the container. In actual hydraulic systems，Pascals law defines the basis of the results which

12、are obtained from the system. Thus，the liquid is moved by a pump in the system. The intake of the pump is connected to a liquid source，usually called the tank or reservoir. Atmospheric pressure，pressing on the liquid in the reservoir，forces the liquid into the pump. When the pump operates，it forces

13、liquid from the tank into the discharge pipe at a proper pressure. Text & TranslationThe flow of the pressurized liquid discharged by the pump is controlled by valves. Three control functions are used in most hydraulic systems：control of the liquid pressure，control of the liquid flow rate，and contro

14、l of the direction of flow of the liquid. Hydraulic drives are used in preference to mechanical systems when power is to be transmitted between point too far apart for chains or belts；high torque at low speed is required；a very compact unit is needed；a smooth transmission，free of vibration，is requir

15、ed；easy control of speed and direction is necessary；and output speed is varied steplessly. Text & TranslationFig.18.1 gives a diagrammatic presentation of the components of a hydraulic installation. 3Electrically driven oil pressure pumps establish an oil flow for energy transmission，which is fed to

16、 hydraulic motors or hydraulic cylinders，converting it into mechanical energy. The control of the oil flow is by means of valves. The pressurized oil flow produces linear or rotary mechanical motion. The kinetic energy of the oil flow is comparatively low，and therefore the term hydrostatic driver is

17、 sometimes used. There is little difference in construction between hydraulic motors and pumps. Any pump may be used as a motor. The quantity of oil flowing at any given time may be various by means of regulating valves (as shown in Fig.181) or the use of variable delivery pumps. Text & TranslationF

18、ig. 18-1 Speed-control Methods for Hydraulic Motors Text & TranslationThe application of hydraulic power to the operation of machine tools is by no means new，though its adoption on such a wide scale as exists at present is comparatively recent. It was in fact the development of the modern self conta

19、ined pump unit that stimulated the growth of this form of machine tool operation. Hydraulic machine tool drive has a great number of advantages. One of them is that it can give infinitely variable speed control over wide ranges. In addition，they can change the direction of drive as easily as they ca

20、n vary the speed. As in many other types of machine，many complex mechanical linkages can be simplified or even wholly eliminated by the use of hydraulics. Text & TranslationThe flexibility and resilience of hydraulic power is another great virtue of this form of drive. Besides the smoothness of oper

21、ation thus obtained，a great improvement is usually found in the surface finish on the work and the tool can make heavier cuts without detriment and will last considerably longer without regrinding.Text & Translation水力的歷史由來已久，始于人類為利用它周圍的能源而做出的努力。容易利用的能源就是水和風(fēng)兩種自由的流動流體。第一臺液力裝置水車是最早的發(fā)明。從5世紀(jì)早期，水車圖畫就出現(xiàn)在大宮

22、殿的馬賽克上。磨粉機由羅馬人發(fā)明，而水磨機的歷史更早，可以追溯到大約公元前100 年。當(dāng)一些上進的農(nóng)場主厭惡由手工沖擊、研磨谷物時，谷物的家庭養(yǎng)殖已開始5000 多年。也許，真正的發(fā)明家是那些農(nóng)場主的妻子，因為她們經(jīng)常要干重的農(nóng)活。Text & Translation流體是可以流動的物體，也就是說，構(gòu)成物質(zhì)的粒子可以連續(xù)地改變它們之間的相對位置，而且，它提供流體層間流動非連續(xù)的阻力。這意味著流體在靜止時，在其內(nèi)部沒有剪切力(作用表面切向方向的受力)存在。流體可以分為牛頓流體或非牛頓流體。在牛頓流體中，流體層間作用的剪切力和角度變形總量的大小成線性關(guān)系。在非牛頓流體中，流體層間作用的剪切力和角度

23、變形總量的大小成非線性關(guān)系。Text & Translation流體的流動可按多種方式分類，如定常流或非定常流、有旋流或無旋流、可壓縮流或不可壓縮流以及黏性流或無黏性流。所有的液壓系統(tǒng)遵循于帕斯卡定律，命名是由Braise Pascal 而來的，是他發(fā)明了此定律。這條定律指出在密封容積內(nèi)壓縮的液體例如圓柱筒或管子在容積的各個不同面上作用著相等的力。Text & Translation在實際液壓系統(tǒng)中，帕斯卡定律是解釋從系統(tǒng)中獲得的各種結(jié)果的基礎(chǔ)。因此，泵使液體在系統(tǒng)中流動，泵的進口連接液流源，通常叫油槽或油箱。作用在油箱液面上的氣壓使流體進入油泵。當(dāng)油泵工作時，在適當(dāng)?shù)膲毫ψ饔孟拢捅闷仁沽黧w

24、從油箱流動到出口。由油泵泵出的壓縮液體通過各種閥門來控制。在大多數(shù)液壓系統(tǒng)中采用3種控制功能：(1) 液體壓力的控制；(2) 液體流速的控制；(3) 液體流動方向的控制。Text & Translation當(dāng)處于下列幾種情況時，液壓驅(qū)動被優(yōu)先使用。：(1) 對于鏈傳動和皮帶傳動來說，功率的傳遞位置太遠(yuǎn)。(2) 低速高轉(zhuǎn)矩的場合。(3) 很緊湊的結(jié)構(gòu)。(4) 要求傳動平穩(wěn)、避免振動的場合。(5) 速度和方向容易調(diào)節(jié)的場合。(6) 輸出速度無級可調(diào)的情況。Text & Translation如圖18-1 所示給出了液壓元件安裝的圖形布局。由電氣驅(qū)動的油泵供有傳遞能量用的油量，并可傳遞給液壓電動機或

25、油缸，從而將液壓能轉(zhuǎn)換成機械能。通過閥門控制油的流動，壓力油流產(chǎn)生線性的或旋轉(zhuǎn)的機械運動。油流的動能相對比較低，因此有時采用靜壓傳動。液壓電動機和液壓油缸之間幾乎不存在構(gòu)造上的不同。任一油泵可以被用作液壓電動機。在任一時間里的油流量可以通過調(diào)節(jié)閥門(如圖18-1所示)或采用變量泵來改變。Text & Translation圖18-1 液壓電動機的速度控制方法Text & Translation液壓傳動運用到機床的運行中絕不是新的，雖說現(xiàn)在的大規(guī)模采用出現(xiàn)不久。現(xiàn)代油泵的發(fā)展促進了這類機床運行的增多。機床的液壓驅(qū)動具有許多優(yōu)點。其中一個是液壓驅(qū)動在廣泛的范圍內(nèi)提供無限變化的速度。另外，它們能像改

26、變速度一樣容易來改變驅(qū)動的方向。像許多其他類型的機床一樣，許多復(fù)雜的機械裝置能夠被簡單化或者由于液壓驅(qū)動的使用完全取消。液壓驅(qū)動的另一個優(yōu)點是它的柔性和緩沖性。除了運行平穩(wěn)外，還發(fā)現(xiàn)了許多改進，如工件表面光潔度的改善，在不損壞刀具的前提下能加大刀具的負(fù)荷，并能在刃磨刀具的情況下工作更長時間。Complex Sentence Analysis1 Hydraulic power has a long history, which dates from mans prehistoric efforts to harness the energy in the world around him. 水力

27、的歷史由來已久，始于人類為利用其周圍的能源而做出的努力。 date from： 從什么時候開始 prehistoric efforts：很久以前的努力Complex Sentence Analysis2 In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate of angular deformation. 在牛頓流體中，流體層間作用的剪切力和角度變形總量的大小成線性關(guān)系。applied shear stresses：作

28、用的剪切應(yīng)力 the resulting rate：總的合率(量) Complex Sentence Analysis3 All hydraulic systems depend on Pascals law, named after Braise Pascal, who discovered the law. 所有的液壓系統(tǒng)遵循于帕斯卡定律，命名是由Braise Pascal 而來的，是他發(fā)明了此定律。 depend on：遵循于 named after：根據(jù)命名的,此句是過去分詞短語做定語修飾 Pascals law。 who discovered the law 是非限定性定語從句，修飾Braise Pascal Complex Sentence Analysis4 Electrically driven oil pressure pumps establish an oil flow for energy transmission, which is fed to hydraulic motors or hydraulic cylinders, converting it into mechanical energy. 由電氣驅(qū)動的液壓泵供有傳遞能量用的油量，并可傳遞給液壓電動機或液壓缸，從而將液壓能轉(zhuǎn)換成機械能。 which is fed t