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1、Unit 18 Fluid and Hydraulic SystemContentslNew Words & Expressions lText & TranslationlComplex Sentence AnalysislKey to ExercisesNew Words & Expressions lhydraulic system 液压系统lprehistoric pri:histrik adj. 史前的，很久以前的lharness h:nis v. 利用(风等)作动力，治理，控制lwatermill w:tmil n. 水车，水磨lhydraulic motor 液压电动机lmosa
2、ic mzeiik n. 镶嵌细工，马赛克ldomestication dmestikein n. 家养，驯养ldisplacement displeismnt n. 位移，转移，置换New Words & Expressions llayer lei n. 层，层次ltangential tndenl adj. 切线的，切向的lNewtonian njutnin adj. 牛顿的，牛顿学说的lnonlinear nnlini adj. 非线性的，非直线的lrotational ruteinl adj. 旋转的，转动的，循环的lcompressible kmpresibl adj. 可压缩的，
3、可压榨的lPascals law 帕斯卡定律lpressurize preraiz v. 增压，给加压New Words & Expressions lintake inteik n. 入口，进口，进入量ltank tk n. 油箱，水箱，池塘l.reservoir rezvw: n. 蓄水池，水箱，蓄能器latmospheric tmsferik adj. 大气的，空气的ldischarge dist:d n. 卸货，出料，流出; vi. 卸下，放出lpreference prefrns n. 优先选择lcompact kmpkt adj. 紧凑的，紧密的，简洁的New Words & Ex
4、pressions ldiagrammatic daigrmtik adj. 图表的，概略的loil pressure pump 液压泵lhydraulic cylinder 液压缸lkinetic energy 动能lhydrostatic driver 静压传动lvariable-delivery pump 变量泵lby no means 决不lself-contained adj. 独立的，配套的，整体的New Words & Expressions lstimulate stimjuleit v. 促进，激励lhydraulics haidr:liks n. 水力学，液压系统lresi
5、lience rizilins n. 跳回，恢复力，回弹lvirtue v:tu: n. 优点，效力，功能ldetriment detrimnt n. 损害，不利lregrind ri:graind v. 重磨Text & TranslationlHydraulic 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 an
6、d the windtwo free and moving streams. lThe 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 arou
7、nd 100 BC，and the origins may indeed have been much earlier. Text & TranslationlThe 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 of
8、ten drew the heavy jobs. lFluid is a flowing 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 s
9、hear force (that is a force tangential to the surface on which it acts) can exist in it. Text & TranslationlFluid 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 deforma
10、tion. In non-Newtonian fluid there is a nonlinear relation between the magnitude of applied shear stress and the rate of angular deformation. lThe 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 vi
11、scous. Text & Translationl2All hydraulic systems 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. lIn actual hydraulic systems，Pa
12、scals law defines the basis of the results which 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
13、 into the pump. When the pump operates，it forces liquid from the tank into the discharge pipe at a proper pressure. Text & TranslationlThe 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 p
14、ressure，control of the liquid flow rate，and control of the direction of flow of the liquid. lHydraulic 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 neede
15、d；a smooth transmission，free of vibration，is required；easy control of speed and direction is necessary；and output speed is varied steplessly. Text & TranslationlFig.18.1 gives a diagrammatic presentation of the components of a hydraulic installation. 3Electrically driven oil pressure pumps establish
16、 an oil flow for energy transmission，which is fed to 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 comparativ
17、ely low，and therefore the term hydrostatic driver is 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
18、 use of variable delivery pumps. Text & TranslationFig. 18-1 Speed-control Methods for Hydraulic Motors Text & TranslationlThe 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
19、 was in fact the development of the modern self contained pump unit that stimulated the growth of this form of machine tool operation. lHydraulic 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
20、can change the direction of drive as easily as they can 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 & TranslationlThe flexibility and resilience of hydraulic power is another great virtu
21、e of this form of drive. Besides the smoothness of operation 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 & Translationl水力的历史由来已久，始于人类为利用它周围的能源而做出的努力
22、。容易利用的能源就是水和风两种自由的流动流体。l第一台液力装置水车是最早的发明。从5世纪早期，水车图画就出现在大宫殿的马赛克上。磨粉机由罗马人发明，而水磨机的历史更早，可以追溯到大约公元前100 年。当一些上进的农场主厌恶由手工冲击、研磨谷物时，谷物的家庭养殖已开始5000 多年。也许，真正的发明家是那些农场主的妻子，因为她们经常要干重的农活。Text & Translationl流体是可以流动的物体，也就是说，构成物质的粒子可以连续地改变它们之间的相对位置，而且，它提供流体层间流动非连续的阻力。这意味着流体在静止时，在其内部没有剪切力(作用表面切向方向的受力)存在。l流体可以分为牛顿流体或非
23、牛顿流体。在牛顿流体中，流体层间作用的剪切力和角度变形总量的大小成线性关系。在非牛顿流体中，流体层间作用的剪切力和角度变形总量的大小成非线性关系。Text & Translationl流体的流动可按多种方式分类，如定常流或非定常流、有旋流或无旋流、可压缩流或不可压缩流以及黏性流或无黏性流。l所有的液压系统遵循于帕斯卡定律，命名是由Braise Pascal 而来的，是他发明了此定律。这条定律指出在密封容积内压缩的液体例如圆柱筒或管子在容积的各个不同面上作用着相等的力。Text & Translationl在实际液压系统中，帕斯卡定律是解释从系统中获得的各种结果的基础。因此，泵使液体在系统中流动
24、，泵的进口连接液流源，通常叫油槽或油箱。作用在油箱液面上的气压使流体进入油泵。当油泵工作时，在适当的压力作用下，油泵迫使流体从油箱流动到出口。l由油泵泵出的压缩液体通过各种阀门来控制。在大多数液压系统中采用3种控制功能：l(1) 液体压力的控制；l(2) 液体流速的控制；l(3) 液体流动方向的控制。Text & Translationl当处于下列几种情况时，液压驱动被优先使用。：l(1) 对于链传动和皮带传动来说，功率的传递位置太远。l(2) 低速高转矩的场合。l(3) 很紧凑的结构。l(4) 要求传动平稳、避免振动的场合。l(5) 速度和方向容易调节的场合。l(6) 输出速度无级可调的情况
25、。Text & Translationl如图18-1 所示给出了液压元件安装的图形布局。由电气驱动的油泵供有传递能量用的油量，并可传递给液压电动机或油缸，从而将液压能转换成机械能。通过阀门控制油的流动，压力油流产生线性的或旋转的机械运动。油流的动能相对比较低，因此有时采用静压传动。液压电动机和液压油缸之间几乎不存在构造上的不同。任一油泵可以被用作液压电动机。在任一时间里的油流量可以通过调节阀门(如图18-1所示)或采用变量泵来改变。Text & Translation图18-1 液压电动机的速度控制方法Text & Translationl液压传动运用到机床的运行中绝不是新的，虽说现在的大规模
26、采用出现不久。现代油泵的发展促进了这类机床运行的增多。l机床的液压驱动具有许多优点。其中一个是液压驱动在广泛的范围内提供无限变化的速度。另外，它们能像改变速度一样容易来改变驱动的方向。像许多其他类型的机床一样，许多复杂的机械装置能够被简单化或者由于液压驱动的使用完全取消。l液压驱动的另一个优点是它的柔性和缓冲性。除了运行平稳外，还发现了许多改进，如工件表面光洁度的改善，在不损坏刀具的前提下能加大刀具的负荷，并能在刃磨刀具的情况下工作更长时间。Complex Sentence Analysisl1 Hydraulic power has a long history, which dates f
27、rom mans prehistoric efforts to harness the energy in the world around him. 水力的历史由来已久，始于人类为利用其周围的能源而做出的努力。 l date from： 从什么时候开始l prehistoric efforts：很久以前的努力Complex Sentence Analysisl2 In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate
28、 of angular deformation. 在牛顿流体中，流体层间作用的剪切力和角度变形总量的大小成线性关系。lapplied shear stresses：作用的剪切应力l the resulting rate：总的合率(量) Complex Sentence Analysisl3 All hydraulic systems depend on Pascals law, named after Braise Pascal, who discovered the law. 所有的液压系统遵循于帕斯卡定律，命名是由Braise Pascal 而来的，是他发明了此定律。 l depend o
29、n：遵循于 l named after：根据命名的,此句是过去分词短语做定语修饰 Pascals law。l who discovered the law 是非限定性定语从句，修饰Braise Pascal Complex Sentence Analysisl4 Electrically driven oil pressure pumps establish an oil flow for energy transmission, which is fed to hydraulic motors or hydraulic cylinders, converting it into mechan
30、ical energy. 由电气驱动的液压泵供有传递能量用的油量，并可传递给液压电动机或液压缸，从而将液压能转换成机械能。 l which is fed to hydraulic motors or hydraulic cylinders 中的which 是指oil flow。l convertinto指“转换(形式)”的意思。Key to Exercisesl. Translate the following phrases into Chinese or English.l1. 液压电动机l2. shear forcel3. 牛顿流体l4. Pascals lawl5. 压缩的液体l6.
31、Closed containerl7. 液压泵l8. mechanical energyl9. 静压传动l10. variable-delivery pumpKey to Exercisesl. Mark the following statement with True (T) or False (F) according to the text.l1T l2. T l3. F l4. T l5. FKey to Exercisesl. Fill in the blanks with the suitable words or phrases given below.l1. an early
32、 inventionl2. the early fifth centuryl3. by the Romansl4. even furtherl5. become tired ofl6. in factKey to Exercisesl.Translate the Chinese parts given in the brackets into English.l1. The flow of fluids may be classified in many waysl2. All hydraulic systems depend on Pascals lawl3. In actual hydraulic systemsl4. Three control functions are used in most hydraulic systemsl5. The application of hydraulic power to the operation of machine tools is by no means newlThe end!
