流體動力泵 外文翻譯

1、Fluid Power PumpsPurpose of pumpsEvery fluidpower system uses one or more pumps to pressurize the hydraulic fluid. The fluid under pressure, in turn, performs work in the output section of the fluid-power system. Thus, the pressurized fluid may be used to move a piston in a cylinder or to turn the s

2、haft of a hydraulic motor.The purpose of a pump in a fluid-power system is to pressurize the fluid so that work may be performed. Some fluid-power systems use low ressures-100psi or less-to do work. Where a large work output is required, high pressures-1000pse or more-may be used. So we find that ev

3、ery modern fluid-power system uses at least one pimp to pressurize the fluid.Types of PumpsThere types of pumps find use in fluid-power systems：(1)rotary, (2)reciprocating, and(3)centrifugal pumps.Simple hydraulic systems may use but one type of pump. The trend is to use pumps with the most satisfac

4、tory characteristics for the specific tasks involvedIn matching the characteristics of the pump to the requirements of the hydraulic system, it is not unusual to find two types of pumps in series. For example, a centrifugal pump may be used to supercharge a reciprocating pump, or a rotary pump may b

5、e used to supply pressurized oil for the controls associated with a reversing variable-displacement reciprocating pumpRotary PumpsThese are built in many different designs and extremely popular in modern fluid-power system. The most common rotary-pump designs used today are spur-gear, internal-gear,

6、 generated-rotary, sliding-vane, and screw pump. Each type has advantages that make it most suitable for a given application.Spur-Gear Pumps. These pumps have two mating gears are turned in a closely fitted casing. Rotation of one gear, the driver, causes the second, or follower gear, to turn. The d

7、riving shaft is usually connected to the upper gear of the pump.When the pump is first started, rotation of gears forces air out the casing and into the discharge pipe. This removal of air from the pump casing produces a partial vacuum on the suction side of the pump inlet. Here the fluid is trapped

8、 between the teeth of the upper and lower gears and the pump casing. Continued rotation of the gears forces the fluid out of pump discharge.Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid as it is expelled from between the meshing gear teeth and casing. A vacuum is

9、 formed in the cavity between the teeth as unmeshed, causing more fluid to be drawn into the pump. A spur-gear pump is a constant-displacement unit; its discharge is constant at a given shaft speed. The only way the quantity of fluid discharge by a spur-gear pump of the type in Figure can be regulat

10、ed is by caring the shaft speed. Modern gear pumps used in fluid-power systems develop pressures up to about 3000psi.Figure shows the typical characteristic curves of a spur-gear rotary pump. These curves show the capacity and power input for a spur-gear pump at carious speeds. At any given speed th

11、e capacity characteristic is nearly a flat line. The slight decrease in capacity with rise in discharge pressure is caused by increased leakage across the gears, from the discharge to the suction side of the pump .Leakage in gear pumps is sometimes termed slip. Slip also increases with arise in pump

12、 discharge pressure. The curve showing the relation between pump discharge pressure and pup capacity is often termed the head-capacity or HQ curve. The relation between power input and pump capacity is the power-capacity or PQ curve.Power input to a spur-gear pump increase with both the operating sp

13、eed and discharge pressure. As the speed of a gear pump is increased, its discharge rate in gallons per minute also rises. Thus the horsepower input at a discharge pressure of 120pse is 5hp at 200rpm and about 13hp at 600rpm. The corresponding capacities at these speeds and this pressure are 40 and

14、95gpm, respectively, read on the 120psi ordinate where it crosses the 200-and 600-rpm HQ curves.Figure is based on spur-gear handing a fluid of constant viscosity, As the viscosity of the fluid handled increased, the capacity of a gear pump decreases. Thick, viscous fluids may limit pump capacity at

15、 higher speeds because the fluid cannot into the casing rapidly enough fill it completely. Figure shows the effect of increased fluid viscosity on the performance of rotary pump in a fluid-power system. At 80-psi discharge pressure the pump has a capacity of 220gpm when handing fluid having a viscos

16、ity of 100SSU viscosity. Capacity of this pump decreases to 150gpm when handing fluid having a viscosity of 500SSU. The power input to the pump also rises, as shown the power characteristics.Capacity of rotary pump is often expressed in gallons per revolution of the gear or other internal element. I

17、f the outlet of a positive-displacement rotary pump is completely closed, the discharge pressure will increase to the point where the pump driving motor stalls or some part of the pump casing or discharge pipe ruptures, because this danger of rupture exists systems are fitted with a pressure-relief

18、valve. This relief valve may be built as of the pump or it may be mounted in the discharge piping.These pumps have a number of vanes which are free to slide or out of slots in the pump rotor. When the rotor is turned by the pump driver, centrifugal force, springs, or pressurized fluid causes the van

19、es to move outward in their slots and bear against the inner bore of the pump casing or against a cam ring. As the rotor revolves, fluid flows in between the vanes when they pass the suction port. This fluid is carried around the pump casing until the discharge port is reached. Here the fluid is for

20、ced out of the casing and into the discharge pipe.In the sliding-vane pump in Figure the vanes in an oval-shaped bore. Centrifugal force starts the vanes out of their slots when the rotor begins turning. The vanes are held out by pressure which is bled into the cavities behind the vanes from a distr

21、ibuting ring at the end of the vane slots. Suction is through two ports A and A1, placed diametrically opposite each other. Two discharge ports are similarly placed. This arrangement of ports keeps the rotor in hydraulic balance, reliving the bearing of heavy loads. When the rotor turns counterclock

22、wise, fluid from the suction pipe comes into ports A and A1 is trapped between the vanes, and is carried around and discharged through ports Band B1Pumps of this design are built for pressures up to 2500psi. Earlier models required staging to attain pressures approximating those currently available

23、in one stage. Valving, used to equalize flow and pressure loads as roter sets are operated in series to attain high pressures. Speed of rotation is usually limited to less than 2500rpm because of centrifugal forces and subsequent wear at the contact point of vanes against the cam-ring surface. Figur

24、e shown that the characteristic curves of the pump when operating at 1200rpm and handing oil having a viscosity of 150SSU at 100F.Two vanes may be used in each slot to control the force against the interior of the casing or the cam ring. Dual vanes also provide a tighter seal, reducing the leakage f

25、rom the discharge side to the suction side of the pump. The opposed inlet and discharge port in this design provide hydraulic balance in the same way as the pump. Both these pumps are constant-displacement units.The delivery or capacity of a vane-type pump in gallons per minute cannot be changed wit

26、hout changing the speed of rotation unless a special design id used. Figure shoes a variable-capacity sliding-vane pump. It does not use dual suction and discharge ports. The rotor runs in the pressure-chamber ring, which can be adjusted so that it is off-center to the rotor. As the degree of off-ce

27、nter or eccentricity is changed, a variable volume of fluid is discharged. Figure shows that the vanes create a vacuum so that oil enters through 180 of shaft rotation. Discharge also takes place through 180 of rotation . There is a slight overlapping of the beginning of the fluid intake function an

28、d the beginning of the fluid discharge.Figure shows how maximum flow is available at minimum working pressure. As the flow decreases to aminimum valve, the pressure increases to the maximum. The pump delivers only that fluid neended to replace clearance floes resulting from the usual slide fit in ci

29、rcuit components.A relief valve is not essential with a variable-displacement-type pump of this design to protect pumping mechanism. Other conditions within the circuit may dictate the use of a safety or relief valve to prevent localized pressure build up beyond the usual working levels.For automati

30、c control of the discharge, an adjustable spring-loaded governor is design to protect pumping mechanism. Other conditions within the circuit may dictate the use of a safety or relief valve to prevent localized pressure build up beyond the usual working levels.For automatic control of the discharge,

31、an adjustable spring-loaded governor is used. This governor is arranged so that the pump discharge acts on a piston or inner surface of the ring whose movement is opposed by the spring. If the pump discharge pressure rises above that for which the by governor spring is set, the spring is compressed.

32、 This allows the pressure-chamber ring to move and take a position that is less off center with respect to the roter. The pump then delivers less fluid, and the pressure is established at the desired leval. The discharge pressure for units of this design varies between 100 and 2500psi.The characteri

33、stics of a variable-displacement-pump compensator are shown in Figure. Horsepower input values also shown so that the power input requirements can be accurately computed. Variable-volume vane pumps are capacity of multiple-pressure levels in apredetermined pattern. Two-pressure pump controls can pro

34、vide an efficient method of unloading a circuit and still hold sufficient pressure available for pilot circuits.The black area of the graph of Figure shoes a variable-volume pump maintaining a pressure of 100psi against a closed circuit. Wasted power is the result of pumping oil at 100psi through an

35、 unloading or relief valve to maintain a source of positive pilot pressure. Two-pressure-type controls include hydraulic, pilot-operated types and solenoid-controlled, pilot-operated types. The minus of Figure shoes the solenoid energized so that the pilot oil is diverted to the tank. Thus, the pilo

36、t oil obtained from the pump discharge cannot assist the governor spring. Minimum pressure will result. The plus Figure shows the solenoid energized so that oil assists compensator spring. The amount of assistance is determined by the small ball and spring, acting as a simple relief valve. This prov

37、ides the predetermined maximum operating pressure.Another type of two-pressure system employs what is termed a differential unloading governor. It is applied in a high-low or two-pump to a minimum deadhead pressure setting. Deadhead pressure refers to a specific pressure level established ad a resul

38、ting action and the resulting flow at deadhead condition are equal to the leakage in the system and pilot-control flow requirements. No major power movement occurs at this time, even though the hydraulic system may be providing a clamping or holding action while the pump is in deadhead position.The

39、governor is basically a hydraulically operated, two-pressure control with a differential piston that allows complete unloading when sufficient external pilot pressure is applied to pilot unload port.The minimum deadhead pressure setting is controlled by the main governor spring A. the maximum pressu

40、re is controlled by the relief-valve adjustment B. the operating pressure for the governor is generated by the large-volume pump and enters through orifice C.To use this device let us assume that the circuit require a maximum pressure of 1000psi, which will be supplied by a 5-gpm pump. It also needs

41、 s large flow (4gpm) at pressure up to 500psi; it continues to 1000psi at the reduced flow rate. A two-pumped system with an unloading governor on the 40-gpm pump will provide the needs.We can unload the 40-gpm pump at 500psi to a minimum pressure setting of 200psi (or another desired value), which

42、the 5-gpm pump takes the circuit up to 1000psi or more.Note in Figure that two sources of pilot pressure are required. One, the 40-gpm pump, provides pressure within the housing so that maximum pressure setting can be obtained. The setting of the spring, plus the pressure within the governor housing

43、, determines the maximum pressure capacity of the 40-gpm pump. The second pilot source is the circuit proper, which will go to 1000psi. This pilot line enters the governor through orifice D and acts on the unloading piston E. The area of piston E is 15 percent greater than the effective area of the

44、relief poppet F. The unloading differential built into this governor control is, therefore, approximately 15 percent. The governor will unload at 500psi and be activated at 15 percent below 500psi, or 425psi. By unloading, we mean zero flow output of the 40-gpm pump.As pressure in the circuit increa

45、se from zero to 500psi, the pressure within the governor housing also increases until the relief-valve setting is reached, at which time the relief valve cracks open, allowing flow to the tank.The pressure drop in the housing is a maximum additive value, allowing the pump to deadhead. Meanwhile, the

46、 system pressure continues to rise above 700psi, resulting in a greater force on the bottom of piston E than on the top. The piston then completely unseats poppet F, which results in a further pressure drop within the governor housing to zero pressure because of the full-open position of the relief

47、poppet F. Flow entering the housing through orifice C is directed to the tank pass the relief poppet without increasing the pressure in housing. The deadhead pressure of the 40-gpm pump then decreases to the lower set value. Thus, at the flow rate to the unloading governor, the 40-gpm pump goes to d

48、eadhead. The flow rate to the circuit decreases to 5gpm as the pressure to 1000psi. At 1000psi, the 5-gpm pump is also at its deadhead setting, thus only holding system pressure.The 40-gmp pump unloads its volume at 500psi. It requires a system pressure of 600psi to unload the 40-gpm pump to its min

49、imum pressure of 200psi. The 600-psi pilot supply enters through orifice D and acts on the differential piston E. The pumps volume is required to open popper F completely and allow the pressure within the housing to decrease to zero.As circuit pressure deceases, both pumps come back into service in

50、a similar pattern.流體動力泵泵的作用每個流體動力系統(tǒng)都使用一個或多個泵來維持液體正常的壓力。帶有壓力的流體在流體動力系統(tǒng)的高壓出口部分工作。于是這部分流體可用來推動油缸的活塞或者使液壓馬達的軸旋轉。流體動力系統(tǒng)中泵的作用就是維持液體的壓力以便于正常工作。某些系統(tǒng)采用100psi的低壓或更低的壓力工作。當輸出功率需要很大時，就用1000psi的高壓或更高的壓力，所以我們發(fā)現每個現代流體動力系統(tǒng)至少用一個泵維持流體的壓力。泵的類型流體動力系統(tǒng)中泵的類型包括：（1）旋轉式泵；（2）往復式泵；（3）離心式泵簡單的液壓系統(tǒng)可以僅用一種類型的泵。選用泵的原則是泵的特性要最大限度地滿足特別

51、的工作要求。泵的特性必須滿足液壓系統(tǒng)的要求，因此兩種類型的泵連用的情況并非罕見。例如：離心泵可用于增壓往復式泵的壓力，而旋轉泵可用來供應壓力油以控制往復式的排量。旋轉泵旋轉泵應用于不同的設計中，在流體動力系統(tǒng)中極其常用。今天最常見的旋轉泵是外齒輪泵、內齒輪泵、擺線轉子泵、滑動葉片式泵和螺旋泵。每種類型的泵都有優(yōu)點，適合于特定場合的應用。直齒齒輪泵，這種泵有兩個嚙合的齒輪在密封殼體內轉動。第一個齒輪即主動輪的回轉引起第二個齒輪及從動輪的回轉。驅動軸通常連接到泵上面的齒輪上。當泵首次啟動時，齒輪的旋轉迫使空氣離開殼體進入排油管。這樣泵內空氣運動使泵吸入口處形成了真空，于是外部油箱的液體在大氣壓的作

52、用下，由泵的入口進入，聚集在上下齒輪和泵殼之間，齒輪連續(xù)地旋轉使液體流出泵的出口。直齒齒輪泵的壓力的升高是由擠壓嚙合齒輪和腔體內的液體產生的。當齒輪脫開嚙合時，腔內形成真空，使更多的液體被吸入泵內。直齒齒輪泵，當軸速不變時，輸出流量恒定。只有一種方法即改變輸入軸的轉速，能調節(jié)這種直齒齒輪泵的排量?，F代應用在流體動力系統(tǒng)的齒輪泵的壓力可達3000psi。此為直齒齒輪泵的典型特性曲線。這些曲線表明了泵在不同速度下的流量和輸入功率。當速度給定時，流量曲線接近于一條水平的直線。泵的流量隨出口壓力的升高而稍有降低，這是由于泵的出油口到吸油口地齒輪徑向泄漏有所增加而造成的。滲漏有時定義為泄漏。泵出口壓力的

53、增加也會使泄漏增加。表征泵的出口壓力和流量之間關系曲線常叫水頭流量曲線或泵的HQ曲線；泵的輸入功率和泵流量關系曲線叫做功率流量特性曲線或PQ曲線。直齒齒輪泵的輸入功率隨輸入速度和出口壓力的增加而增加。隨著齒輪泵速度的增加，流量也增加。于是在出口壓力為120psi，轉速為200rpm時，輸入功率是5馬力。在轉速為600rpm時，輸入功率是13馬力?？v坐標壓力為120psi，橫坐標是200rpm和600rpm時，在HQ曲線上可以讀出相應的流量分別為40gpm和95gpm。這是直齒齒輪泵在粘度不變時的情況，隨著流體粘度的增加（即流體變稠，不易流動），齒輪泵的流量降低。粘稠的流體在油泵高轉速運轉時，因

54、為這種流體在油泵中不能迅速進入泵體完全充滿真空區(qū)，所以油流量受到限制，這就是流體動力泵系統(tǒng)中流體粘度的增大對旋轉泵工作情況的影響。當流體粘度值為100SSU，出口壓力為80psi時，泵流量為220gpm。當流體的粘度值為500SSU時，泵流量減少到150gpm。由功率特性曲線可知，泵輸入功率也會增加?；瑒邮饺~片泵：這些泵有大量的葉片，葉片能在轉子的槽內自由的滑進滑出。當驅動轉子時，離心力、彈簧，或壓力油使葉片伸出槽子，頂在泵殼體的內腔或凸輪環(huán)上。隨著轉子的旋轉，葉片之間的流體經過吸油口時，完成吸油。流體順著泵殼體到達排出口。在排出口，流體被排出，進入排油管?；瑒邮饺~片泵中的葉片安裝在橢圓形的腔

55、內，當轉子開始旋轉時，離心力使葉片伸出槽子。同時葉片又受到其底部腔內壓力油的作用力，壓力油來源于槽子端部的配流盤。吸油口通過A和A1口相通，他們位于直徑的相對位置。同樣兩排油口位于類似的位置。油口這樣配置，使葉片轉子保持壓力平衡，從而使軸承不受重載影響。當轉子逆時針旋轉時，從吸油管出來的流體進入A和A1口，聚集在葉片之間，沿周向流動后，通過B和B1口排出。這樣設計的泵壓力可達到2500psi。早期類型的泵必須分級才能達到這么大的壓力，而現在用一級泵就能達到。在轉子上應用均流壓閥可以達到高壓。轉速通常限制在2500rpm以下，這是因為考慮到離心力和凸輪環(huán)表面葉片之間的磨損。每個槽內安裝兩個葉片可

56、以控制其作用于殼體內部和凸輪環(huán)上的力。雙葉片會產生更緊的密封，能減少從排油口到吸油口之間的泄露。這種入口和出口相對應的設計也能維持液壓平衡。這些都是定量泵。不改變轉速就不能改變葉片泵的流量，除非油泵采用特殊設計?；瑒邮阶兞咳~片泵不僅能夠雙吸油口和排油口。轉子在壓力腔內轉動，轉子形成的偏心量是可調的。隨著偏心的程度或偏心率的變化，流體的流量也隨著變化。吸油區(qū)和壓油區(qū)的起始段稍有重疊。在最小的工作壓力下可以得到更大的流量。隨著壓力的升高，當流量減小到最小值，壓力增大到最大值，泵只需要提供補充回路中原件滑動配合間隙中泄露的流體。這種變量泵的設計可以保護管路，溢流閥不是必須的，其他回路中，為阻止局部壓

57、力超過正常水平，可用安全閥或溢流閥來控制。為了自動控制流量采用可變彈簧負載調節(jié)器。安裝這種調節(jié)器，泵出口壓力作用于活塞或定子內表面，壓縮彈璜產生的位移。如果泵的出口壓力高于調節(jié)器彈簧的設定值時，彈簧被壓縮。這種壓力環(huán)移動，減小相對于定子的偏心量，于是，繃得流量減小，得到所需的壓力，這種油泵設計的出口壓力在100psi和2500psi之間。此為變量泵補償器的特性，標出輸入功率值，可以準確計算所需的輸入功率。變量泵可以預設不同壓力值的變化規(guī)律。高低壓泵控制既能提供有效的卸載回路，也能為先導控制回路提供足夠的壓力。陰影區(qū)域為變量泵在被壓100psi壓力下的閉式回路。油液以100psi通過卸荷或溢流閥

58、排出，可以維持正常的控制回路壓力，這些是消耗的功率。兩級壓力控制回路包括：先導液壓控制和電磁控制。負號表示電磁鐵不帶電，先導控制油路回油箱。于是泵排出的控制油的力小于調節(jié)器彈簧力，所以得到最小壓力。正號為電磁鐵帶電，控制油的力大于調節(jié)器彈簧力。與簡單的溢流閥原理一樣，小球和彈簧決定控制力的大小。這樣預先設定最大工作壓力。另一種良機壓力系統(tǒng)使利用所謂的差動卸荷調節(jié)器。它應用于高低壓或雙泵回路中，調節(jié)器通過壓力傳感器自動卸載大流量泵以達到最小的空載壓力設定值?？蛰d壓力指的是由于變量泵控制機構工作所形成的特定壓力。泵的實際空載流量等于系統(tǒng)的泄漏量與控制流量之和。當泵空載時，即使液壓系統(tǒng)在提供夾緊或保

59、壓作用，也不會需要較大的功率。調節(jié)器是液壓操縱的，差動活塞帶有雙壓力控制，當外部控制壓力作用于控制卸荷口時，差動活塞允許完全卸荷?？蛰d壓力的最小設定值由調節(jié)器主彈簧A控制，最大壓力由溢流閥調節(jié)點B控制。調節(jié)器的操作壓力由大容積泵提供，從小孔C進入。為了說明如何使用這種裝置，假定回路需要1000psi的最大壓力，由一個5-gpm的泵來提供。在壓力達到500psi時，需要大流量，繼續(xù)上升到1000psi，流量減小。由流量為40-gpm的帶有卸荷調節(jié)器的泵組成的雙泵系統(tǒng)可滿足要求。我們可以把40-gpm的泵從500psi卸荷壓力調整至200psi最小設定壓力（或另一需求值），這樣5-gpm泵可以使回路達到1000psi或更高的壓力。雙泵系統(tǒng)控制的壓力源由一個40-gpm的泵提供調節(jié)器腔內的壓力，就可以達到最大設定壓力。彈簧設定壓力加上調節(jié)器腔內壓力共同決定了40-gpm泵的最大壓力。第二個控制源是個