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附录A英文部分：The commonly used sources of power in hydraulic systems are pumps and accumulators . Similarly,accumulator connected to atmosphere will dischange oil at atmosphere pressure until it empty. only when connected to a system having resistance to flow can pressure be developed. Three types of pumps find use in fluid-power systems: 1,rotary,2,reciprocating,3,or piston-type,and 3,centrifugal pumps. Simple hydraulic system may use but one type of pump . The trend is to use pumps with the most satisfactory characteristics for the specific tasks involved . In 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 to supercharge a reciprocating pump , or a rotary pump may be used to supply pressurized oil for the contronls associated with a reversing variabledisplacement pumps . Most power systems require positive displacement pumps . At high pressure , reciprocating pumps are often preferred to rotary pumps . Rotary pumps These are built in many differnt designs and extremely popular in modern fluid power system . The most common rotay-pump designs used today are spurgear , internal gear ,generated rotor , sliding vane ,and screew pumps . Ehch type has advantages that make it most suitable for a given application . Gear pumps Gear pumps are the simplest type of fixed displacement hydraulic pump available . This type consists of two external gear , generally spur gear , within a closed-fitting housing . One of the gear is driven directly by the pump drive shaft . It ,in turn , then drives the second gear . Some designs utilize helical gears ,but the spur gear design predominates . Gear pumps operate on a very simple principle , illustration Fig.7.3 . As the gear teeth unmesh , the volume at the inlet port A expands , a partial vacuum on the suction side of the pump will be formed . Fluid from an external reservoir or tank is forced by atmospheric pressure into the pump inlet . The continuous action of the fluid being carried from the inlet to the discharge side B of the pump forces the fluid into the system . Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid as it is expellde from between the meshing gear teeth and the casing . Fluid from the discharge side is prevented from returing to the inlet side by the clearance between the gears and houseing . Vane pumps The vane pump ,illustration 7.4 , consists of a housing that is eccentric or offset with respect to the drive shaft axis . In some models this inside surface consists of a cam ring that can be rotated to shift the relationship between rotor are rectangular and extend radially from a center radius to the outside diameter of the rotor and from end to end . A rectangular vane that is essentially the same size as the slot is inserted in the slot and is free to slide in and out . As the rotor turns , the vanes thrust outward , and the vane tips track the inner surface of the housing , riding on a thin film of fluid . Two port or end plates that engage the end face of the ring provide axial retention . Centrifugal force generally contributes to outward thrust of the vane . As they ride along the eccentric housing surface , the vane move in and out of the rotor slots . The vane divide the area between the rotor and casing into a series of chambers .The sides of each chamber are formed by two adjacent vanes ,the port or end plates , the pump casing and the rotor . These chambers change in change in volume depending on their respective position about the shaft . As each chamber approaches the inlet port , its vanes move outward and its volume expands , causing fluid to flow into the expanded chamber . Fluid is then carried within the chamber around to the dischange port . As the chamber approaches the discharge port , its vanes are pushed inward ,the volume is reduced , and the fluid is forced out the discharge port . The variable-volume vane pump can be adjusted to discharge a different volume of fluid while running at constant speed , simply by shifting the cam ring with respect to the rotor .When the pump components are in position such that the individual chambers achieve their maximun volume as they reach the inlet port , the maximum volume of fluid will be moved . If the relationship between housing and rotor is changed such that the chambers achieve their minmum of zero volume as they reach the inlet port , the pump delivery will be reduced to zero . Since the vane pump housing or cam ring must be shifted to change the eccentricity and vary the output , variable-displacement vane pumps cannot have the closed end fit common to fixed-displacement vane pumps . Volumetric efficiency is in the range of 90% to 95% . These pumps retain their efficiency for a considerable length of time since compensation for wear between the vane ends and the housing is automatic .As these surfaces wear , the vanes move farther outward from their slots to maintain contact with the housing . Vane pump speed is limited by vane peripheral speed . High peripheral speed will cause cavitation in suction cavity . which results in pump damage and reduced flow . An imbalance of the vanes can cause the oil film between the vane tips and the cam ring to break down , resulting in metal-to-metal contact and subsequent increased wear and slipage . One metheod applied to eliminate high vane thrust loading is a dual-vane construction . In the dual-vane construction , two independent vanes are located in each rotor slot . Chambered edges along the sides and top of each vane from a channel that essentially force causes the vane to follow the contour of each pair of vanes . Centrifugal force causes the vane to follow the contour of the cam-shaped ring . There is just sufficient seal between the vanes and ring without destroying the thin oil film . Piston-type pump Two basic types of piston or reciprocating pumps are the radial piston and the axial typese , both are available as fixed or variable displacement models . Axial piston pumps may be further divided into in-line and bent axis types . All piston pumps operate by allowing oil to flow into a pumping cavity as a piston retreats and then forcing the oil out into another chamber as the piston advances . Design differences among pumps lie primarily in the methods of separating inlet from outlet oil . In-line piston pump The siplest typeof axial piston pump is the swash plate in-line design , illustration 7.5 .The cylinder are connected though piston shoes and a retracting ring , so that the shoes beat anainst an angled swash plate . As the block turns ,the piston shoes follow the swash plate ,causing the piston to reciprocate . The ports are arranged in the valve plate so that the pistons pass the inlet port as they are being pulled out and pass the outlet port as they are being forcing back in . The angle of the swash plate controls the delibery . Where the swash plate is fixed , the pump is of the constant-displacement type . In the variable-displacement , inline piston pump , the swash plate is moumted on a pivoted yoke . As the swash plate angle is increased , the cylinder stroke is increase , resulting in a greater flow . A pressure compensator control can position the yoke automatically to maintain a constant output pressure . Operation of he inline pump compensator control is shown schematically in Fig.7.6 .The control can position the yoke automatically in Fig.7.6 . The control consists of a compensator valve balanced between load pressure and the force of a spring , a yoke piston controlled by the compensator valve to move the yoke , and a yoke retun spring . With no outlet pressure , the yoke return spring moves the yoke to the full delibery position .As pressure builds up ,it acts against the end of the valve spool .When the pressure is high enough to overcome the valve spring , the spool is displaced and oil enters dis placement . If the pressure falls off , the spool moves back , oil is discharged from the piston to the inside of the pump case , and the spring returns the yoke to a greater angle . The compensator thus adjusts the pump output to whatever is required to develop and maintain the preset pressure . This prevents excess power losses bu relief valve operation at full pump volume during holding or clamping . There compensator thus adjusts the pump output to whatever is required to develop and maintain the preset pressure . This prevents excess power losses by relief valve operation at full pump volume during holding or clamping . There is a variation of the swash plate in-line pump . It is a design where the swash plate turns , but the cylinder barrel remains stationary . The plate is canted so that it wobbles as it turns . This action pushes the pistons in and out the stationary cylingder barrel . This type of in-line pump contains a separate inlet and outlet check valve for each piston since the pistons do not move past the inlet and outlet port . BENT-axis piston pump Illustration 7.7 show a bent-axial piston pump , which contatins a cylinder block assembly in which the pistons are equally spaced around the cylinder block axis . Cylinder bores are parallel to the axis . The cylinder block turns with the drive shaft , but at an offest angle . The piston rods are attaached to the drive shaft flange by ball joints . A universal link keys the cylinder block to the drive shaft to maintain alignment and assure that they turn together . The link does not transmit force except to accelerate and decceltate the cylinder block and to overcome resistance of the block revolving in oil filled housing . As the shaft roates , distance between any one piston and the valving surface changes continually . Each piston moves away from the valving surface during one half of the revolution and toward the valving surface during the other half . The inlet chamber is in line as the pistons move away , and the outletr chamber is in line as the pistons move closer , thus drawing liquiring in during one half of the inlet chamber as the pistons are moving away from the pintle . Thereforce , during rotation , pistons draw liquid into the cylinder bores as they pass the inlet side of the pinntle and force that liquid out of the bores as they pass the outlet side of the pintle . The displacement of this pump varies with the offset angle , the maximum angle being 30 degree ,the minimum zero . Fixed displacement models are usually avaiable with 23 degree angle .In the variable displacement construction a yoke with an external control is used to change the angle . With some contronls , the yoke can be moved over center to reverse the direction of flow from the pump . Pump/system interaction Frequently , hydraulic system designers choose off-the-shelf pumps with little cocern other than supplying sufficient flow at available input power . Early enphasis that positive displacement pumps supply only flow and that pressure is developed by the system suggests that , as a minmum , the pump should be chosem in light of several overall requirements and with system detailed design and the nature of the working fluid well in mind . Positive displacement pumps generate flow . In a fixed delivery pump , provisions must be made to dissipate flow or system pressure will rise until a rupture occurs . The usual means of accomplishing flow control is to place a relief valve inthe high pressure line . When the pressure rise above an established amoumt ,the relief valve will vent excess flow back to the reservoir . In such systems , pump flow and relief valve capacity must be carefully matched to assure proper venting . Flow from a high pressure line through a relief valve to a low pressure element is wasted hydraulic horsepower , which can be calculated from the following relationship : hp=PQ/1714 Where : Q = flow in gpm This wasted horsepower is converted to heat in the hydraulic system . If not properly removed , the heat can damage the fluid , elastomer seals , and other organic material in the system . Pressure-compensated variavle delivery pumps do not require a relief valve in the high pressure line . The pressure compensation feature eliminates the need for the relief valve . In nearly all working systems ,however , at least one is used on just-in-case basis . The use of a pressure compensator , while avoiding dependence on a relief valve , brings on its own problems . The actuator -spring-spool arrangement in the compensator is a dynamic , damped-mass-spring arrangement . However , when the system calls for a chang in axhieve their maxmum volume as they reach the inlet port , the maximum volume of fluid will ve moved . If the relationship between housing and rotor is changed such that the chambers achieve their minimum of zero volume as they reach the inlet port , the pump delivery will be reduced to zero . Since the vane pump housing or cam ring must be shifted to change the eccentricity and vary the output , variable-displacement vane pumps cannot have the closed end fit common to fixed-displacement pumps . Volumetric efficiency is the range of 90% to 95% . These pumps retain their efficiency for a considerable length of time since compensation for wear between the vane ends and the housing is automatic . As these surfaces wear , the vanes move farther outward from their slots to maintain contact with the housing . Vane pump speed is limited by vane peripheral speed . High peripheral speed will cause cavitation in suction cavity , which results in pump damage and reduced flow . An imbalance of the vanes can cause the oil film between the cane tips and the cam ring to break down , resulting in metal-to-metal contact and subsequent increased wear and slipage . One method applied to eliminate high vane thrust loading is a dual-vane construction . In the dual-vane construction , tow independent vanes are located in each totor slot chmbered edges along the sides and top of each vane from a channel that essentially balances the hydraulic pressure on the top and bottom of each pair of vanes . Centrifugal force cause the vane to follow the contour of the cam-shaped ring .There is just sufficient seal between the vanes and ring without destroying the thin oil film . 附录B中文部分：常用的液压系统的动力源是泵和蓄能器。一般情况下，一个蓄能器在正常的大气压力下，连续的向各系统中压入液压油，直至将所储存的能量全部用完为止。 只有当其连接的系统中，具有抗流压力时才能够得到补充。在液压系统和液力系统中，常使用液压泵有三种类型： 1、回转式， 2、往复式， 3、活塞式或者离心式。 简单液压系统一般使用的都是第一类液压泵。 目前的发展趋势是针对具体的工作任务和工况，选用最佳的液压泵类型。在符合特性和要求的液压泵中，找到两种不同类型的液压泵式很常见的。 例如，离心泵，往复泵都可以可对系统增压，旋转泵和变量液压泵联合使用也可以提供高压的液压油。 大部分动力系统还需要采取容积式液压泵泵。而在较高的体统压力下，往复泵往往要优于回转泵。 回转泵这些形式的液压泵因为具有许多不同的设计形式而极受欢迎，在现代流体动力系统。 最常见的旋转泵的设计形式，包括内部使用齿轮的、内部使用转子的、内部采用滑动叶片的和使用螺杆的。 其中，每一种类型都有其独特的优点，都有其最适合的一定的应用场合。 齿轮泵齿轮泵是可以提供的最简单的一种液压泵。 这一类型的液压泵一般包括两个外啮合的齿轮，一般是圆柱直齿轮，安装在一个密封的壳体里面。 其中一个齿轮由液压泵的传动轴直接驱动， 第一个齿轮然后再推动第二轮。还有一些设计中利用螺旋齿轮，但是一般以齿轮设计为主。 齿轮泵的动作的原理非常简单，如插图7.3 所示。 由于在齿轮的轮齿在脱开啮合时，进气道扩大， 液压泵将会形成局部真空的具有吸力的空腔。 流体在系统的压力下被从外部油箱或罐体中压入， 连续运动的液压油在液压泵的作用下，从真空的吸力空腔中被送入排出液压油的一侧B侧。直齿轮泵内的液压油被从脱开啮合的轮齿和套管之间不断的排出，这种挤压运动使得齿轮泵内的压力上升，从排油一侧来的液压油由于被阻止，不能返回进油一侧的轮齿的间隙和空腔。 叶片泵如插图7.4所示，叶片泵一般是由一个相通的腔体，是偏心或抵消对传动轴轴线。在一些模型内的表面设有一个凸轮环，一个可旋转移动的长方形的转子，转子的径向延长，从一个中心，半径为外径的转子，到末端结束。 上面是尺寸大小相同的插槽，矩形叶片一般插入到插槽中，并且可以自如的滑入和滑出。 当转子转动时，叶片被向外甩出， 而叶片尖端则贴紧其运动轨道空腔的内表面， 处于液压油的薄膜的上面。 两个油口或端板，向环形的端面提供轴向的存储。 通常离心有助于叶片的向外推出。当叶片处于偏心空腔的表面上时，叶片从转子的缝隙中甩出和甩。 叶片将套管和转子之间的区域分成一系列的小空腔。每一个小空腔都是由两个相邻叶片，油口或者端盘，液压泵壳体和转子形成。 这些空腔的容积的变化取决于他们相对于轴的相对位置。当每个厅内靠近进内气孔的时候，其叶片向外移动，其空腔的容积膨胀， 造成液压油流入扩大空腔。 流体随后被带入围绕着排油孔的空腔内。当这些空腔靠近排油孔时，叶片被甩入腔内，空腔的容积减小，液压油随即被压出排油孔。变量叶片泵，可以进行调整，以适应不同的流体排量，当在定常速度下运行时， 只需要改变把凸轮环相对于对转子的位置即可。当液压泵的部件的处于各自的空腔在靠近吸油孔时达到最大的位置的时候，流体的最大排量就将会改变。 如果腔体和转子的相对关系改变，则空腔在他们到达吸油孔的时候就达到了他们的最小容积零容积，此时，液压泵的排油量也减少到零。由于叶片泵的空腔或凸轮圈必须变化从而改变偏心率即改变输出量， 变量叶片泵没有相应于普通固定位移叶片泵的固定端， 容积效率范围是90%至95% 。 这些液压泵能够在一个相当长的时间里保持其效率，因为叶片两端和空腔之间摩擦补偿是自动的。 正是由于这些表面的摩擦， 才使得叶片泵的叶片能够向外面甩出同时又不会脱离插槽。叶片泵的速度一般要受到叶片圆周速度的限制。 过高的圆周速度将导致空腔内出现负压，从而导致液压泵损坏和流量减小。 一个不平衡的叶片将会引起叶片顶端和凸轮环之间的油膜的破坏，从而进一步导致金属和金属之间的直接接触，因而增加了磨损和叶片泵的动力传动损耗 。消除这种叶片泵的叶片的高推力负荷的方法之一就是采用双叶片结构。在双叶式结构中，每两个互相独立的叶片是分别设置在每个转子槽中的。腔室的边缘两旁和顶部叶片每一个渠道，基本上形成了一个十字状，每个一双叶片等高。 在离心力的作用下，使得叶片随着凸轮环的外部轮廓的变化而变化。 当叶片和凸轮环之间形成了足够大的间隙的时候，将会破坏油膜。 活塞式泵两种基本类型的活塞液压泵或者是往复式液压泵都是活塞径向和轴向类型的， 两者均可作为定量泵或可变排量泵模型。 其中，轴向柱塞泵，又可以进一步分为线性柱塞泵和弯曲轴型柱塞泵两种类型。 所有的活塞式液压泵的运行原理，都是通过液压油流入泵腔而推动活塞向后面移动，然后活塞再向前移动，从而将液压油排出，使得液压油进入泵的另一个腔室中。 不同的泵的设计差异泵主要在于活塞进入和推出从而将液压油分离的方法。直轴式柱塞泵最简单的轴向柱塞泵是将冲板进行线性化设计，如插图7。5 所示，气缸与活塞的回缩盘之间相连， 使移动的回缩盘成倾斜式。 当倾斜圆盘转动的时候，柱塞的端脚斜盘上运动，从而使得活塞杆不断的往复的运动，同时因为油口分别安排在阀板上，能够使活塞通过进气道，当它们运动到一定的位置时，通过油口将液压油推出排油口。 斜盘的倾斜角度决定了柱塞泵的排量。在这里，斜盘的位置是固定的，而泵的位移是恒定的。 在变量的线性柱塞泵中，逆止阀活塞泵，冲板是装在一个铰链的枷锁。 由于冲板角度的增大，气缸冲程增加，形成了更大的流量。 由于压力补偿控制位置的作用，自动保持恒定输出压力。 线性柱塞泵的运行原理就是如插图7.6所示 。 在图中，能够自动的控制枷锁的定位。 这种控制由一个补偿阀来平衡负载压力和系统的压力，枷锁
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