流体动力泵毕业论文外文翻译

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.流体动力泵泵的作用每个流体动力系统都使用一个或多个泵来维持液体正常的压力。带有压力的流体在流体动力系统的高压出口部分工作。于是这部分流体可用来推动油缸的活塞或者使液压马达的轴旋转。流体动力系统中泵的作用就是维持液体的压力以便于正常工作。某些系统采用100psi的低压或更低的压力工作。当输出功率需要很大时，就用1000psi的高压或更高的压力，所以我们发现每个现代流体动力系统至少用一个泵维持流体的压力。泵的类型流体动力系统中泵的类型包括：（1）旋转式泵；（2）往复式泵；（3）离心式泵简单的液压系统可以仅用一种类型的泵。选用泵的原则是泵的特性要最大限度地满足特别

51、的工作要求。泵的特性必须满足液压系统的要求，因此两种类型的泵连用的情况并非罕见。例如：离心泵可用于增压往复式泵的压力，而旋转泵可用来供应压力油以控制往复式的排量。旋转泵旋转泵应用于不同的设计中，在流体动力系统中极其常用。今天最常见的旋转泵是外齿轮泵、内齿轮泵、摆线转子泵、滑动叶片式泵和螺旋泵。每种类型的泵都有优点，适合于特定场合的应用。直齿齿轮泵，这种泵有两个啮合的齿轮在密封壳体内转动。第一个齿轮即主动轮的回转引起第二个齿轮及从动轮的回转。驱动轴通常连接到泵上面的齿轮上。当泵首次启动时，齿轮的旋转迫使空气离开壳体进入排油管。这样泵内空气运动使泵吸入口处形成了真空，于是外部油箱的液体在大气压的作

52、用下，由泵的入口进入，聚集在上下齿轮和泵壳之间，齿轮连续地旋转使液体流出泵的出口。直齿齿轮泵的压力的升高是由挤压啮合齿轮和腔体内的液体产生的。当齿轮脱开啮合时，腔内形成真空，使更多的液体被吸入泵内。直齿齿轮泵，当轴速不变时，输出流量恒定。只有一种方法即改变输入轴的转速，能调节这种直齿齿轮泵的排量。现代应用在流体动力系统的齿轮泵的压力可达3000psi。此为直齿齿轮泵的典型特性曲线。这些曲线表明了泵在不同速度下的流量和输入功率。当速度给定时，流量曲线接近于一条水平的直线。泵的流量随出口压力的升高而稍有降低，这是由于泵的出油口到吸油口地齿轮径向泄漏有所增加而造成的。渗漏有时定义为泄漏。泵出口压力的

53、增加也会使泄漏增加。表征泵的出口压力和流量之间关系曲线常叫水头流量曲线或泵的hq曲线；泵的输入功率和泵流量关系曲线叫做功率流量特性曲线或pq曲线。直齿齿轮泵的输入功率随输入速度和出口压力的增加而增加。随着齿轮泵速度的增加，流量也增加。于是在出口压力为120psi，转速为200rpm时，输入功率是5马力。在转速为600rpm时，输入功率是13马力。纵坐标压力为120psi，横坐标是200rpm和600rpm时，在hq曲线上可以读出相应的流量分别为40gpm和95gpm。这是直齿齿轮泵在粘度不变时的情况，随着流体粘度的增加（即流体变稠，不易流动），齿轮泵的流量降低。粘稠的流体在油泵高转速运转时，因

54、为这种流体在油泵中不能迅速进入泵体完全充满真空区，所以油流量受到限制，这就是流体动力泵系统中流体粘度的增大对旋转泵工作情况的影响。当流体粘度值为100ssu，出口压力为80psi时，泵流量为220gpm。当流体的粘度值为500ssu时，泵流量减少到150gpm。由功率特性曲线可知，泵输入功率也会增加。待添加的隐藏文字内容2滑动式叶片泵：这些泵有大量的叶片，叶片能在转子的槽内自由的滑进滑出。当驱动转子时，离心力、弹簧，或压力油使叶片伸出槽子，顶在泵壳体的内腔或凸轮环上。随着转子的旋转，叶片之间的流体经过吸油口时，完成吸油。流体顺着泵壳体到达排出口。在排出口，流体被排出，进入排油管。滑动式叶片泵中

55、的叶片安装在椭圆形的腔内，当转子开始旋转时，离心力使叶片伸出槽子。同时叶片又受到其底部腔内压力油的作用力，压力油来源于槽子端部的配流盘。吸油口通过a和a1口相通，他们位于直径的相对位置。同样两排油口位于类似的位置。油口这样配置，使叶片转子保持压力平衡，从而使轴承不受重载影响。当转子逆时针旋转时，从吸油管出来的流体进入a和a1口，聚集在叶片之间，沿周向流动后，通过b和b1口排出。这样设计的泵压力可达到2500psi。早期类型的泵必须分级才能达到这么大的压力，而现在用一级泵就能达到。在转子上应用均流压阀可以达到高压。转速通常限制在2500rpm以下，这是因为考虑到离心力和凸轮环表面叶片之间的磨损。每个槽内安装两个叶片可以控制其作用于壳体内部和凸轮环上的力。双叶片会产生更紧的密封，