外文翻譯--常用的液壓系統(tǒng)的動(dòng)力源是泵和蓄能器

附 錄 附錄 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 . 附錄 B 中文部分： 常用的 液壓系統(tǒng)的 動(dòng)力源 是 泵和蓄 能 器。 一般情況下， 一個(gè) 蓄能器在正常的大氣壓力下，連續(xù)的 向 各系統(tǒng)中壓入液壓 油 ， 直至 將所儲(chǔ)存的能量全部用完為止。 只有當(dāng) 其 連接 的 系統(tǒng) 中， 具有抗流壓力 時(shí) 才能 夠 得到 補(bǔ)充。 在液壓系統(tǒng)和液力系統(tǒng)中，常使用液壓泵有三種類型： 1、回轉(zhuǎn)式， 2、 往復(fù)式 ， 3、 活塞式 或者 離心 式。 簡(jiǎn)單液壓系統(tǒng) 一般使用的都是第一 類 液壓 泵 。 目前的 發(fā)展 趨勢(shì)是 針對(duì)具體的工作任務(wù)和工況，選用最佳的液壓泵類型。在符合特性和要求的液壓泵中，找到兩種不同類型的液壓泵式很常見的。 例如 ， 離心泵 ，往復(fù)泵都可以 可對(duì) 系統(tǒng) 增壓 ， 旋轉(zhuǎn)泵 和變量液壓泵聯(lián)合使用 也可以提供高壓的液壓油。 大部分 動(dòng)力 系統(tǒng)還需要采取 容積式液壓泵 泵 。而在較高的體統(tǒng)壓力下，往復(fù)泵往往 要優(yōu) 于回轉(zhuǎn)泵 。 回轉(zhuǎn)泵 這些 形式的液壓泵因?yàn)榫哂?許多不同的設(shè)計(jì) 形式 而極受歡迎 ， 在現(xiàn)代流體動(dòng)力系統(tǒng)。 最常見的旋轉(zhuǎn)泵的設(shè)計(jì) 形式，包括內(nèi)部使 用齒輪 的、 內(nèi)部 使用 轉(zhuǎn)子 的、內(nèi)部采用滑動(dòng)葉片的和使用 螺桿 的。 其中， 每一種類型都有 其獨(dú)特的優(yōu)點(diǎn)，都有其最適合的一定的應(yīng)用場(chǎng)合。 齒輪泵 齒輪泵是 可以提供的 最簡(jiǎn)單的一種液壓泵 。 這 一 類型 的液壓泵一般包括 兩個(gè)外 嚙合的 齒輪 ， 一般 是 圓柱 直 齒輪 ，安裝 在一個(gè) 密封的殼體里面。 其中 一個(gè) 齒輪 由液壓泵的傳動(dòng)軸直接驅(qū)動(dòng)， 第一個(gè)齒輪 然后再推動(dòng)第二輪 。還 有 一 些設(shè)計(jì) 中 利用螺旋齒輪 ， 但是 一般以 齒輪設(shè)計(jì)為主 。 齒輪泵的 動(dòng)作的原理 非常簡(jiǎn)單 ，如 插圖 7.3 所示。 由于 在齒輪的輪齒在脫開嚙合時(shí)， 進(jìn)氣道擴(kuò)大 ， 液壓泵將會(huì)形成 局部真空 的具有吸力的空腔。 流體 在系統(tǒng)的壓力下被 從外部 油箱 或罐體 中壓入， 連續(xù) 運(yùn)動(dòng) 的 液壓油在液壓泵的作用下，從真空的吸力空腔中被送入排出液壓油的一 側(cè) B側(cè)。 直 齒輪泵 內(nèi)的液壓油被從脫開嚙合的輪齒和套管之間不斷的排出，這種擠壓 運(yùn)動(dòng)使得齒輪泵內(nèi)的 壓力上升 ，從排油一側(cè)來的液壓油由于被 阻止 ，不能 返 回進(jìn) 油一 側(cè)的 輪齒的 間隙 和空腔。 葉片泵 如 插圖 7.4所示， 葉片泵 一般是由一個(gè)相通 的 腔體， 是偏心或抵消對(duì)傳動(dòng)軸軸線 。 在 一些 模型內(nèi) 的 表面設(shè)有一個(gè)凸輪環(huán) ，一個(gè) 可旋轉(zhuǎn) 移動(dòng)的長(zhǎng)方形的轉(zhuǎn)子，轉(zhuǎn)子的 徑向延長(zhǎng) ， 從一個(gè)中心 ， 半徑為外徑的轉(zhuǎn)子 ，到末端 結(jié)束 。 上 面 是 尺寸 大小相同的插槽 ， 矩形葉片 一般 插入到插槽中 ， 并且 可以自如的滑入和滑出。 當(dāng) 轉(zhuǎn)子 轉(zhuǎn)動(dòng)時(shí)， 葉片 被 向外 甩出， 而葉片 尖端則貼緊其運(yùn)動(dòng) 軌道 空腔的 內(nèi)表面 ， 處于液壓油的薄膜的上面。 兩個(gè) 油口 或 端 板 ，向 環(huán)形 的 端面提供軸向 的存儲(chǔ)。 通常 離心 有助于葉片的 向外推 出。當(dāng)葉片處于 偏心 空腔的 表面上 時(shí)，葉片 從轉(zhuǎn)子的縫隙中甩出和甩。 葉片 將套管和 轉(zhuǎn)子 之間的區(qū)域分成 一系列的 小空腔。每一個(gè)小空腔都是由 兩個(gè)相鄰葉 片，油口或者端盤，液壓 泵殼 體和轉(zhuǎn)子 形成。 這些 空腔的容積的 變化取決于 他們相對(duì)于軸的相對(duì)位置。 當(dāng) 每個(gè)廳內(nèi)靠近進(jìn) 內(nèi)氣孔的時(shí)候， 其葉片向外移動(dòng)，其 空腔的容積 膨脹， 造成 液壓油 流入擴(kuò)大 空腔。 流體 隨后被帶入圍繞著排油孔的空腔內(nèi)。當(dāng)這些空腔靠近排油孔時(shí)，葉片被甩入腔內(nèi)，空腔的容積減小，液壓油隨即被壓出排油孔。 變量 葉片泵 ， 可以 進(jìn)行 調(diào)整 ， 以 適應(yīng) 不同的流體 排量，當(dāng) 在 定常 速度下運(yùn)行時(shí)， 只 需 要 改變 把 凸輪環(huán) 相對(duì)于 對(duì)轉(zhuǎn)子 的位置即可。 當(dāng) 液壓 泵 的 部件的 處于各自的空腔在靠近吸油孔時(shí)達(dá)到最大的 位置 的時(shí)候，流體的最大排量就 將會(huì)改變。 如果腔體和轉(zhuǎn)子的相對(duì)關(guān)系改變，則空腔在他們到達(dá)吸油孔的時(shí)候就達(dá)到了他們的最小容積 零容積，此時(shí)，液壓泵的排油量也減少到零。 由于葉片泵 的空腔 或凸輪圈必須 變化從而 改變偏心率 即改變 輸出 量 ， 變 量 葉片泵 沒 有 相應(yīng)于 普通固定位移葉片泵 的固定端， 容積效率范圍是90%至 95% 。 這些 液壓泵能夠在一個(gè)相當(dāng)長(zhǎng)的時(shí)間里保持 其效率 ， 因?yàn)槿~片兩端和 空腔之間摩擦 補(bǔ)償是自動(dòng)的。 正是 由于這些表面的 摩擦 ， 才使得葉片泵的 葉片 能夠向外面甩出同時(shí)又不會(huì)脫離插槽。 葉片泵的速度 一般要受到 葉片圓周速度 的限制 。 過 高 的 圓周速度將導(dǎo)致空腔內(nèi) 出現(xiàn) 負(fù)壓 ，從而 導(dǎo)致 液壓 泵損壞和 流量減小 。 一個(gè) 不平衡 的葉片 將會(huì)引起葉片頂端和 凸輪環(huán) 之間的 油膜 的破壞 ， 從而進(jìn)一步 導(dǎo)致金屬 和 金屬 之間的直接 接觸，因而增加了磨損和 葉片泵的動(dòng)力傳動(dòng)損耗 。 消除這種葉片泵的葉片的高推力負(fù)荷的方法之一就是采用雙葉片結(jié)構(gòu)。 在雙葉式 結(jié)構(gòu)中 ， 每 兩個(gè) 互相 獨(dú)立的葉片是 分別設(shè)置 在每個(gè)轉(zhuǎn)子槽 中的 。腔 室的 邊緣兩旁和頂部葉片每一個(gè) 渠道， 基本上 形成了一個(gè) 十字 狀， 每個(gè)一雙葉片等高 。 在 離心力 的作用下，使得 葉片 隨著 凸輪 環(huán)的外部輪廓的變化而變化 。 當(dāng)葉片和凸輪環(huán)之間形成了足夠大的間隙的時(shí)候，將會(huì) 破壞油膜。 活塞式泵 兩種基本類型的活塞 液壓泵或者是 往復(fù) 式液壓泵都是 活塞徑向和軸向類型的 ， 兩者均可作為定 量泵 或可變排量 泵模型 。 其中， 軸向柱塞泵， 又可 以 進(jìn)一步分為 線性柱塞泵 和彎曲軸 型柱塞泵兩種類型 。 所有 的 活塞式 液壓泵的運(yùn)行原理 ， 都是通過液壓油 流入泵腔 而推動(dòng) 活塞 向后面移動(dòng) ，然后 活塞再向前移動(dòng)，從而將液壓油排出，使得液壓油進(jìn)入泵的另一個(gè)腔室中 。 不同的泵的 設(shè)計(jì)差異泵主要在于 活塞進(jìn)入和推出從而將液壓油 分離 的 方法 。 直軸式 柱塞泵 最簡(jiǎn)單的 軸向柱塞泵是 將 沖板 進(jìn)行線性化 設(shè)計(jì)， 如 插圖 7。 5 所示，氣缸 與活塞的回縮盤之間 相連 ， 使 移動(dòng)的回縮盤成 傾斜式。 當(dāng)傾斜圓盤轉(zhuǎn)動(dòng)的時(shí)候 ， 柱 塞 的端腳 斜盤 上運(yùn)動(dòng) ， 從而使得 活塞 桿不斷的往復(fù)的運(yùn)動(dòng)，同時(shí)因?yàn)橛?口分別安排在閥板 上 ， 能夠 使活塞通過進(jìn)氣道， 當(dāng)它們運(yùn)動(dòng)到一定的位置時(shí) ，通過 油 口 將液壓油推 出 排油 口。 斜盤的傾斜 角 度決定了柱塞泵的排量。在這里，斜盤的位置是 固定 的 ，而 泵的位移 是恒定的。 在變量 的線性柱塞泵中， 逆止閥活塞泵，沖板是裝在一個(gè)鉸鏈的枷鎖。 由于沖板角度的增大，氣缸 沖程增加， 形成 了更大的流量。 由于 壓力補(bǔ)償控制 位置 的 作用 ，自動(dòng)保持恒定輸出壓力。 線性柱塞泵的運(yùn)行原理就是如插圖 7.6所示 。 在圖中，能夠自動(dòng)的控制枷鎖 的定位 。 這種控制由 一個(gè)補(bǔ)償閥 來 平衡負(fù)載壓力和 系統(tǒng)的壓力 ，枷鎖活塞 由 補(bǔ)償閥 移動(dòng)另一個(gè) 枷鎖 來實(shí)現(xiàn)控制。 由于壓力無法卸載 ， 枷鎖回位彈簧的 推動(dòng) 枷鎖 直到臨界 的 位置 。 由于壓力 的 累積，它 的動(dòng)作是組織 閥芯 末端 。當(dāng)壓力高至足以克服閥 的 彈簧 力的時(shí)候 ，閥芯 就會(huì)變換位置，同時(shí)，液壓 油 也會(huì) 進(jìn)入 原來的空腔中。 假如壓力 下降 ，閥芯 向后移動(dòng) ， 液壓 油 被 活塞 排出而進(jìn)入液壓泵的管道 。系統(tǒng)就會(huì)使枷鎖回到一個(gè)更大的角度。 補(bǔ)償器調(diào)節(jié)泵的輸出量， 從而 達(dá)到任何要求達(dá)到的更高的壓力或