3058 礦用液壓絞車設計2

3058 礦用液壓絞車設計2,液壓,絞車,設計 河南理工大學萬方科技學院本科畢業(yè)設計（論文）開題報告題目名稱 礦用液壓絞車設計學生姓名 張崴 專業(yè)班級 機制 08-3 班 學號 0828070083一、 選題的目的和意義：礦用液壓絞車是工業(yè)生產過程中一種常見的機械，具有悠久的發(fā)展歷史和比較成熟的設計制造技術。隨著絞車制造技術的不斷提高,加工材料的不斷改進以及電子控制技術的不斷發(fā)展，絞車在動力，節(jié)能和安全性等方面取得了很大的進步。目前，絞車正被廣泛的用于礦山，港口，工廠，建筑和海洋等諸多領域。通過本題目使我在礦用液壓絞車設計方面進行一次全面的系統(tǒng)的訓練，使我能綜合運用所學課程，系統(tǒng)地鞏固基本理論和專業(yè)知識，培養(yǎng)分析問題和解決問題的獨立工作能力；提高計算，繪圖，查閱文獻，使用規(guī)范手冊和編寫技術文件及計算機輔助設計計算等基本技能，掌握絞車設計原則，設計方法，步驟。樹立正確的設計思想及嚴謹負責，實事求是，刻苦鉆研，勇于創(chuàng)新的作風。為今后打下良好的基礎并能提高我的綜合運用知識和課本上的理論知識與實踐相結合的能力，同時也有助于以后在工作崗位能很快的適應工作環(huán)境。二、 國內外研究現(xiàn)狀簡述：礦用液壓絞車包括機械設備及拖動控制系統(tǒng)，是聯(lián)系地上和地下的重要途徑，是礦山生產的咽喉設備，其性能好壞直接關系到礦山的生產效率及安全性和可靠性，它的安全，可靠運行時整個礦井正常生產的必要條件，一旦發(fā)生故障，所造成的經(jīng)濟損失是巨大的。“運輸是礦井的動脈，提升是咽喉”形象的描述了礦井液壓絞車運輸系統(tǒng)的工作過程與重要作用。目前，國內對提升設備經(jīng)過多年的研究，近幾十年來發(fā)展的很快，尤其是提升設備的滾筒方式，制動方式和電力拖動，自動化控制等方面有了很大的改進，在提升設備的理論和實踐方面都取得了豐富的經(jīng)驗。我國的礦用提升機其調速原理經(jīng)歷了電阻調速，液壓調速，變頻調速及行星差動調速等幾次大的改進，目前國產提升機所采用的調速裝置主要有兩種類型：一是液壓傳動調速控制（液壓調速），其產品形式即為現(xiàn)有的液壓提升絞車；二是電控調速裝置（變頻調速），其產品形式即為現(xiàn)有的 JT 系列絞車。在過去的 20 年中，我國從德國共進口幾十套的大型礦用提升機，其電控配套裝置均為西門子公司的產品，其中十多套是為直流電動機配套的電流控制系統(tǒng)，其余均為變頻交流電氣傳動電控配套裝置。第一套是 1994 年為山西省常林主井提升機配套的，其調速性能非常理想，且節(jié)能效果相當明顯，它代表了世界礦用提升機的先進水平，也為我們指明了走節(jié)能和無級調速的路子。特別是隨著計算機技術的飛速發(fā)展，機電一體化技術和產品在世界范圍內得到了迅速發(fā)展和應用。先進采煤從采煤工作面，掘進工作面，到井下主煤流運輸及輔助運輸，到礦井提升及井下供電，排水等裝置，均具有建立在微處理器上的監(jiān)控和保護系統(tǒng)，其機電一體化的設備，性能，可靠性和功能等有大幅度提高。三、主要參考文獻與資料獲得情況：（1）王昆等主編，機械設計基礎課程設計，北京；高等教育出版社，1996（2） 《機械設計手冊》聯(lián)合編寫組編，機械設計手冊/上冊，化學工業(yè)出版社，1979（3）東北工學院《機械零件設計手冊》編寫組編，機械設計手冊（第二版）/中冊，冶金工業(yè)出版社，1982.1（4）郭奇亮等主編，機械零件課程設計，貴州人民出版社，1982.1（5）潘英編，礦山提升機械設計，徐州：中國礦業(yè)大學出版社，2000.12（6）濮良貴，紀明剛主編，機械設計（第七版） ，北京：高等教育出版社，2001（7）許灝，機械設計手冊，北京：機械工業(yè)出版社，1991（8）欒兆群，胡建明，孫曉兵編，礦用新型調度絞車的設計，煤炭機械，2001年第 9 期四、畢業(yè)設計（論文）進度安排（按周說明）：第 1 周：查詢相關資料，制定出詳細的實驗方案；第 2～5 周：進入工廠實習；第 6 周：確定畢業(yè)設計題目第 7～8 周：調研階段 從網(wǎng)上和圖書館查閱相關資料；第 9 周：完成開題報告 交指導老師檢查；第 10～12 周：開始編寫畢業(yè)論文 并完成初稿 交指導老師審查；第 13～14 周：整理說明書及圖紙，檢查錯誤處 確定畢業(yè)終稿；六、指導教師審批意見：（對選題的可行性、研究方法、進度安排作出評價，對是否開題作出決定）： 指導教師： （簽名）年 月 日 河南理工大學萬方科技學院本科畢業(yè)設計（論文）中期檢查表指導教師： 閆艷燕 職稱： 副教授 所在院（系）： 機械與動力工程學院 教研室（研究室）： 機制教研室 題 目 礦用液壓絞車設計學生姓名 張崴 專業(yè)班級 08 機制 3 班 學號 0828070083一、選題質量：（主要從以下四個方面填寫：1、選題是否符合專業(yè)培養(yǎng)目標，能否體現(xiàn)綜合訓練要求；2、題目難易程度；3、題目工作量；4、題目與生產、科研、經(jīng)濟、社會、文化及實驗室建設等實際的結合程度）該設計符合本科階段培養(yǎng)專業(yè)設計的能力，能夠很好的訓練學生的機械綜合能力，達到理論與實踐的結合，開拓視野，培養(yǎng)了學生創(chuàng)新的意識。本課題設計難度中等，符合本科階段要求，工作量大，需要同學認真查閱資料，扎實學好專業(yè)知識，與任課老師，相關的技術人員溝通，認真完成畢業(yè)論文。該題目是關于礦山方面的機械設計，對于將要從事礦山工作的學生來說，本次設計無疑是為學生深入了解礦山機械提供了一個很好的學習機會。希望學生在接下來的設計中認真查閱相關資料，本著嚴謹?shù)脑O計態(tài)度把接下來的設計搞好。從而為自己以后在工作中積累寶貴的經(jīng)驗。二、開題報告完成情況：確定了明確的課題設計方向；并對液壓絞車在使用中經(jīng)常出現(xiàn)的問題有一定的研究；已經(jīng)開始對課題進行設計草算，并有了突破性的進展，設計過程已經(jīng)快速地展開，確定了工作的內容和方法；同時，已完成了對相關資料的查閱，對課題有了總體的分析。開題報告順利完成。三、階段性成果：總體布置方案和主要結構參數(shù)已確定，并完成一些標準件的選型及和大多數(shù)零部件的設計計算工作。結構設計和校核工作正在進行中，英文翻譯工作即將結束，已開始初步草算和制作設計說明書的工作。四、存在主要問題：1.在液壓絞車傳動系統(tǒng)的設計上，專業(yè)性比較強設計的時候遇到了一定的阻力。2.由于液壓絞車的連續(xù)工作量比較大，從力學的角度考慮，要在連續(xù)工作量的要求內使液壓絞車的整體設計成本最經(jīng)濟，因此在設計時要綜合多方面的考慮。3.局部結構設計思路不清晰；設計內容不夠連貫，系統(tǒng)性不強；在整體結構及零部件結構上存在一定問題；4.獲得資料不夠充分，需要跟住實際的設計情況取得參考資料。5.在選用零件和確定結構工藝參數(shù)時缺少經(jīng)驗和參考五、指導教師對學生在畢業(yè)實習中，勞動、學習紀律及畢業(yè)設計（論文）進展等方面的評語指導教師： （簽名）年 月 日河南理工大學萬方科技學院本科畢業(yè)生論文１英文原文CIRCUIT DESINGSummaryThe selection of hydraulic components for use in a given application is determined by their ability to meet the required specification within the desired cost framework. A variety of components can be arranged to fulfil a given function by using different circuit configurations as the fluid power system designer has the freedom, within the constraints set by the preferences of the machine builder and/or the user, to select components of his choice.This freedom makes it difficult to summarise circuit on design however, the designer need to be able justify the circuit on the basis of technical considerations. This chapter therefore describes and, where applicable, evaluates variety of circuit options that can be used for the range of functions generally encountered in the application of fluid power systems.1. IntroductionTo a very large degree the main function of hydraulic circuits is to control the flow to one or several actuators as required by the application. There are, however, a variety of methods for controlling flow, some of which act indirectly by using pressure as the controlling parameter.The circuits discussed in this chapter include:· Directional control and valve configurations.河南理工大學萬方科技學院本科畢業(yè)生論文２· Velocity controls with constant supply pressure.· Velocity controls with load sensing.· Variable displacement pump controls.· Hydrostatic transmissions.· Load control.· Contamination control.2. Pressure and FlowHydraulic systems provide flow from the pump that is directed to one or more actuators(motors) at a pressure level that satisfies the highest demand. Where a single output is being driven the pump pressure will float to the level demanded by the load. However, even for such simple systems the method that is employed to provide variable flow needs to be evaluated in order to ensure that best efficiency is obtained. In circuits with multiple outputs this aspect can be more difficult to evaluate.For operation at pressures and flows that are lower than the required maximum values the efficiency of the system will depend on the type of pump being used (i.e. fixed or variable displacement). This can be represented diagrammatically as in Figure 1.For fixed displacement pump system it is clear from Figure 1 that excess pump flow will have to be returned to the reservoir so that the power required by the pump is greater than that being supplied to the load. The level of inefficiency incurred is dependent on the ratio between the pressure required by the load and that at the pump outlet which can be controlled at the maximum level by the relief valve or at lower pressures by 河南理工大學萬方科技學院本科畢業(yè)生論文３various types of bypass valves.Figure1 Flow and pressure varlotionFor variable displacement pumps the generation of excess flow can be avoided. However, the lever of pump pressure will depend on the method that is used for controlling the displacement but clearly there is scope for achieving much higher efficiencies than with fixed displacement pumps.Each of these control methods will require a particular circuit design employing components that have been described in the previous chapters.3. Directional controlValves used for controlling the direction of the flow can be put into fixed positions for this purpose but many types are frequently used in a continuously variable mode where they introduce a restriction into the flow path.河南理工大學萬方科技學院本科畢業(yè)生論文４3.1 Two position valvesA four-way valve with two positions for changing direction of the flow to and from an actuator is shown in Figure 2. For supply flow, Q, the actuator velocities will be:Extend UE=Q/Ap; Retract UR=Q/AAHere, the actuator areas are Ap for the piston and AA for the annulus or rod end the actuator. Hence,UR>UE as Ap>ARAny external forces (F) that are acting on the actuator rod must be in opposition to the direction motion. For reversing force applications it will be necessary to apply restrictor control which will be discussed later in the chapter. These forces will create a supply pressure that is= F/Ap or F/AAFigure2 Two position four-way valve河南理工大學萬方科技學院本科畢業(yè)生論文５Three-way valves are used in applications where only one side of the actuator needs a connection from the supply. A typical example for this is the operation of the lift mechanism on a fork lift truck, as shown in Figure 3 where the actuator is lowered under the action of the weight.Figure3 Two position three-way3.2 Three position valvesThree position valves have a third, central position that can be connected in different configurations. These variants are described.Closed Centre Valves (Figure 4)Closed centre valves block all of the four ports. This prevents the actuator from moving under the action of any forces on the actuator. The supply flow port is also blocked which may require some means of limiting the supply pressure supply pressure can be made by appropriate pump controls or by a relief valve.河南理工大學萬方科技學院本科畢業(yè)生論文６Figure4 Tandem Centre valves (Figgure5)Tandem centre valves block the actuator ports but the supply is returned to the tank at low pressure. If other valves are being supplied from the same source this type of valve may not be used-unless connected in series.Figure 5Open Centre Valves (Figure 6)Open centre valves connect all of the four ports to the tank so that the supply and the actuator pressure are at low presse. This allows the actuator to actuator to be free to be move under the action of any external forces.河南理工大學萬方科技學院本科畢業(yè)生論文７Figure6Where it is necessary to block the supply flow the configuration shown in Figure 7 can be used.Figure 74. Load holding valvesThe radial clearance between the valve and its housing of spool valves is carefully controlled in the manufacturing process to levels of around 2 micron. The leakage through this space, even at high pressures, is small but for applications where it is essential that the actuator remains in the selected position for long periods of time (e.g. crane jibs where any movement would be unacceptable) valves having metal-to-metal contact have to be used.Check valves usually employ metal-to-metal contact but they are only open in one direction under the action of the flow into the valve. For their use in actuator circuits it is necessary that they are open in both directions as required by the DCV. This function can be obtained from a Pilot Operated Check Valve that uses a control pressure to open the valve against reverse flow.河南理工大學萬方科技學院本科畢業(yè)生論文８Figure8 Pilot operated check valveFigure 8 shows a typical pilot operated check valve (POCV) where by a pilot pressure is applied onto the piston to force open the ball check valve to allow flow to pass from port 1to 2 when the check valve would normally be closed. The ratio of the piston and valve sent areas has to be chosen so that the available pilot pressure can provide sufficient force to open the valve against the pressure on port 1.The use of a POCV is shown in Figure 9 where the external force on the actuator is acting in the extend direction. With the DCV in the centre position the check valve will be closed because the pilot is connected to the tank return line that is at low pressure. Opening the DCV so as to extend the actuator causes the piston side pressure, now connected to the supply, to increase.河南理工大學萬方科技學院本科畢業(yè)生論文９Figure9 Actuotor Circuit using o POCVWhen this pressure reaches the level at which the check valve is opened against the pressure generated on the rod side of the actuator by the load force, the actuator will extend. The ratio of the pilot and ball seat diameters needs to be such that the pressure areas cause the POCV to be fully open against the annulus pressure. If the pilot pressure is insufficient to open the valve because of an intensified pressure at the check valve inlet from the actuator annulus and/or back pressure on the POCV outlet due to restriction in the DCV, oscillatory motion can result.5. Velocity controlThe velocity of actuators can be controlled by using a number of different methods. In principle the various methods can be employed for both linear and rotary actuators or motors but in some cases it may be necessary to refer to the manufacturer’s literature for guidance.河南理工大學萬方科技學院本科畢業(yè)生論文１０5.1 Meter-in controlMeter-in control refers to the use of a flow control at the inlet to an actuator for use with actuators against which the load is in opposition to the direction of movement.For a meter-in circuit that uses a simple adjustable restrictor valve selection of the DCV to create extension of the actuator will cause flow to pass through the restrictor into the piston end of the actuator. The required piston pressure, , will depend on the opposing force on the actuator rod. pWith a fixed displacement pump delivering a constant flow, excess flow from the pump will be returned to tank by the relief valve at its set pressure. Consequently, the available pressure drop. with this system the flow, and hence the actuator velocity variations are undesirable a pressure compensated flow control valve (PCFCV) can be used. This valve sill maintain a constant delivery flow providing that the pressure drop is greater than its minimum controlled level that is usually in the region of 10to 15 bar.河南理工大學萬方科技學院本科畢業(yè)生論文１１Figure10 Meter-in control Actuotor ExtensionFigure 10 shows a typical system in which the flow control is bypassed with a check valve for reverse operation of actuator. If the load force varies considerably during operation, there will be transient changes in actuator velocity at a level that depends on the mass of the load.For example, when the load force suddenly reduces, the piton pressure will reduce but at a rare that is dependent on the fluid volume and its compressibility and the mass of the load. During the period that the pressure is greater than the required new value, the actuator will accelerate and, as it does so the piston pressure will fall. The pressure can then fall below the new level and deceleration results and damped oscillations can occur.In some situations the mass of the load can be such as to cause problems of cavitation and overrunning because the pressure falls 河南理工大學萬方科技學院本科畢業(yè)生論文１２transiently to a level at which absorbed air is released. If the pressure falls low enough the fluid will vaporize. Both of these phenomena are referred to as cavitation and noisy operation, and damage to the components can be the result.A check valve having a spring cracking pressure that is high enough to suppress cavitation is sometimes used but this has the disadvantage if increasing the pump pressure and thus reducing the efficiency and increasing the heating effect on the fluid.5.2 Meter-out controlFigure12 meter-out controlFor overrunning load forces and/or those with a large mass, meter-out control is used where the actuator outlet flow during its extension passes through the restrictor or PCFCV as shown in the circuit of Figure 12.The flow control operates by controlling the actuator outlet pressure 河南理工大學萬方科技學院本科畢業(yè)生論文１３at the level required to oppose the forces exerted on the actuator by the load and by the piston pressure which is the same as that of the pump. This prevents cavitation from occurring during transient changes arising from load force variations or due to forces that act in the same direction as the movement (i.e. pulling forces).This system can, however, cause high annulus pressures to occur from the intensification of the piston pressure together with the pressure created by pulling forces. Further, when compared to meter-in, the rod and piston seals have to by capable of withstanding high pressures that may require a higher cost actuator to by used.5.3 Bleed-controlFor the fixed displacement pump system shown in Figure 13, excess flow is bled off from the supply so that the pump pressure is mow at the same level as that required at actuator piston.河南理工大學萬方科技學院本科畢業(yè)生論文１４Figure13 Bleed-off controlBleed-off control is therefore more efficient than meter-in and meter-out because of the lower pump pressure. However, as for meter-in, it cannot be used with pulling loads and it can also only be used to control one actuator at a time from the pump. This is in contrast to meter-in and meter-out where several actuators can be supplied by a single pump as shown in Figure14.河南理工大學萬方科技學院本科畢業(yè)生論文１５Figure14 Multiple Actuotor Circuit with Meter-in controlMeter-in and meter-out controls can be supplied from a variable displacement pump that is operated with a constant pressure control (pressure compensated) which reduces the power wastage that is inherent with a fixed displacement pump. This is demonstrated by making a comparison of the efficiencies as follows:For meter-in control the power efficiency,sPQ??For a pressure compensated pump the power efficiency,as sPsP?PsQ?Thus referring to Figure 1, the pump flow is always equal to that of the load, the pump is still capable of achieving the maximum demand, which is referred to as the ‘corner power’ of the pump. The fixed displacement pump operates at this rating continuously because of the use of the relief valve to control the flow to the actuator.The flow control methods described in this section are usually preset in a system that is being used on a continuous basis such as for a production machine (e.g. injection moulding) where possibly the operations are being carried out sequentially. It would normally be expected that the duration of, say, actuator movement is small in relation to the overall cycle time so that the power losses are relatively small. Where a continuously variable flow 河南理工大學萬方科技學院本科畢業(yè)生論文１６control is required alternative components and need to be considered.中文譯文河南理工大學萬方科技學院本科畢業(yè)生論文１７液壓回路設計概要具體應用中選擇液壓元件的型號主要取決于滿足要求的性能和理想的價格。液壓系統(tǒng)設計者有一定的自由選用各種元件構成不同的回路來實現(xiàn)制造商或者使用者所要求的特定功能。這種自由使得概括回路設計有些困難,因此設計者必須能證明回路在已考慮的技術范圍內,本章描述了多種回路形式在一般液壓系統(tǒng)的應用。1.緒論很大程度上,液壓回路的作用是控制流體按要求流向一個或幾個馬達。事實上有多種控制流體的方法,其中的一些直接以壓力作為控制參量.本章討論的回路包括:· 方向控制和控制閥的構造· 恒壓速率控制· 負載速率控制· 變量泵的控制· 液壓傳動· 負載控制· 綜合控制2.壓力與流量河南理工大學萬方科技學院本科畢業(yè)生論文１８由泵向液壓系統(tǒng)提供滿足最大需求的壓力和流量，供給一個或幾個執(zhí)行元件。單個輸出時，泵的壓力根據(jù)負載調整。所以對一些簡單系統(tǒng)按計算的需求提供流量的方法可以獲得最佳效率，多輸出時計算就較為困難。系統(tǒng)壓力和流量低于最大需求量時，泵的類型（定量泵或變量泵）決定系統(tǒng)效率。這從下圖 1 可以看出圖 1 壓力與流量圖中顯而易見，定量柱塞泵系統(tǒng)，因為多余的流量必須返回到油箱，因此泵需要的能量大于供給負載的能量，無用功的大小取決于負載所需的壓力和泵的出口壓力的比，泵的出口壓力可以用安全閥調制最大或用其他類型的旁通閥調到較低的壓力。變量柱塞泵就可以避免產生多余的流量，它的壓力可通過控制排量的方式調整，顯然它有可能達到比定量柱賽泵更高的效率。這些控制方法需要設計特殊的回路結構，前面章節(jié)已經(jīng)講過。河南理工大學萬方科技學院本科畢業(yè)生論文１９3.方向控制方向控制閥可以放在固定位置達到控制目的，但是多數(shù)類型經(jīng)常用在連續(xù)可變的模式，起到限流徑的作用。3.1二位閥二位四通閥控制流體進出執(zhí)行元件的方向如圖 2，進入流量為 Q 時，活塞移動的速度等于UE=Q/Ap； 返回時 UR=Q/AA這里，Ap 是無桿腔活塞面積，AA 是有桿腔有效面積，所以Ap>AA, AR>UE任何作用在活塞桿上的外力都有阻止活塞運動的趨勢，為克服此力，應進行節(jié)流控制，在后面的章節(jié)將會介紹?？朔枇π枰膲毫Φ扔冢紽/AA 或者 F/Ap圖 2 二位四通閥當執(zhí)行元件只有一端需要供壓時可以使用二位三通閥，典型的例子如起重機河南理工大學萬方科技學院本科畢業(yè)生論文２０的升降機構，如圖 3 所示，執(zhí)行元件在重力作用下下降。圖 3 二位三通閥3.2 三位閥三位閥第三個位置，中間位置有不同的構造，下面介紹不同的中位機能。中位關閉閥（圖 4）中位關閉閥關閉所有的四個端口，這樣就阻止執(zhí)行元件在任何力的作用下移動，供壓端口也被關閉，因此需要對系統(tǒng)壓力進行限制，可以通過對泵的適當調整或通過安全閥控制。河南理工大學萬方科技學院本科畢業(yè)生論文２１圖 4中位卸載閥（圖 5）中位卸載閥關閉執(zhí)行元件端口，接通供壓端口和油箱端口，使供壓系統(tǒng)以較低壓力卸載，當有其他壓力閥使用同一供壓源時，是不能使用中位卸載閥的，除非它們是串聯(lián)的。圖 5中位互通閥（圖 6）中位互通閥的四個端口同時連通到回油箱，使得供壓系統(tǒng)和執(zhí)行元件都處在較低壓力下，讓執(zhí)行元件可以在任何外力作用下自由移動。圖 6當需要關閉供壓端口時，結構如圖 7 所示河南理工大學萬方科技學院本科畢業(yè)生論文２２圖 74.單向閥在制造過程中單向閥的閥體和閥芯的徑向間隙可以精確的控制在 2微米的范圍，即使在高壓下，泄漏也很小，但卻是必要的，有時執(zhí)行元件要長時間處在一個位置（例如起重機臂的移動） ，金屬對金屬的接觸需要它潤滑。單向閥通常使用金屬對金屬接觸的結構，在流體壓力作用下只在一個方向開啟，在液壓回路中使用，有時換向閥要求要在兩個方向都能開啟，液控單向閥可以實現(xiàn)這種功能，它有能逆流開啟的控制壓力。圖 8 所示的時典型的液控單向閥（POCV） ，通過作用在活塞上的控制壓力打開球形閥，使流體從端口 1 流向端口 2，普通的單向閥此時是關閉的?；钊烷y的作用面積比要通過計算選擇，使控制壓力能產生足夠的力克服端口 1 的壓力，打開球形閥。河南理工大學萬方科技學院本科畢業(yè)生論文２３圖 8 液控單向閥液控單向閥的用處見圖 9 所示，外力作用在液壓缸的拉伸方向，換向閥處在中位時，控制壓力與回油箱連通，壓力較低，單向閥關閉。打開換向閥，以使液壓缸伸長，此時控制壓力接通到系統(tǒng)壓力，壓力升高。圖 9 液控單向閥的應用河南理工大學萬方科技學院本科畢業(yè)生論文２４當控制壓力達到一定水平克服有桿腔負載時，單向閥打開，液壓缸伸長?？刂茐毫颓蛐伍y直徑的關系應滿足：壓力作用有效面積能克服作用在有桿腔環(huán)狀面積上的壓力，使液控單向閥完全打開。如果從有桿腔進入單向閥入口的壓力較大，或者換向閥限制了單向閥出口的壓力，使控制壓力不足以打開單向閥，可能會引起單向閥的震動。5. 速度控制有多種方法控制執(zhí)行元件的速度，原則上這些方法既可以控制執(zhí)行元件的直線速度，又可以控制角速度，但是有些情況可能需要廠商的指導說明書。5.1 入口節(jié)流調速入口節(jié)流調速用在對執(zhí)行元件入口流量的控制，使執(zhí)行元件克服阻滯運動的負載。構建簡單的入口節(jié)流控制虧回路，需要簡單的可調式節(jié)流閥，通過換向閥的控制，讓流體經(jīng)過節(jié)流閥進入液壓缸的活塞，液壓缸活塞需要的壓力 Pp 取決于作用在活塞桿上的負載。使用定量柱塞泵提供恒定的流量，多余的流量經(jīng)溢流閥調定的壓力回到油箱，從而，讓使用壓力下降。這個系統(tǒng)中，流量和執(zhí)行元件的速度變化可通過帶有壓力補償?shù)墓?jié)流閥控制，當系統(tǒng)壓降大于其最小控制壓力（10～15 巴）時，這種節(jié)流閥能提供恒定的流量。圖 10 所示的是一個單向調速的入口節(jié)流控制系統(tǒng)，如果運行過程中負載變化頻繁，執(zhí)行元件的速度會隨著負載的變化而變化。河南理工大學萬方科技學院本科畢業(yè)生論文２５圖 10 入口節(jié)流調速系統(tǒng)例如，當負載突然變小時，作用在活塞上的壓力隨之減小，但是這要取決于流量，流體的可壓縮性和負載的慣性，這時系統(tǒng)壓力大于所需的壓力，液壓缸會加速運動，使壓力下降。形成新的系統(tǒng)壓力，最終減速并發(fā)生阻尼振動。有些情況下負載的慣性可能會引發(fā)氣穴現(xiàn)象和超壓。當壓力突然降到很低時，流體吸收的空氣被釋放出來，壓力足夠低時，還會引起流體蒸發(fā)，這就是氣穴現(xiàn)象，伴有噪聲，最終對系統(tǒng)造成損傷。單向閥產生背壓足以抑制氣穴現(xiàn)象，但是同時會使泵的壓力升高，系統(tǒng)效率下降還會影響流體的溫度。河南理工大學萬方科技學院本科畢業(yè)生論文２６5.2出口節(jié)流調速當負載或負載慣性過大時出口節(jié)流調速用來控制執(zhí)行元件的出口流量，出口流體經(jīng)過節(jié)流閥或調速閥的回路如圖 12圖 12 出口節(jié)流調速系統(tǒng)這種流量控制方法通過控制執(zhí)行元件的出口壓力，使其符合：作用在活塞上的壓力（泵的壓力）能克服負載。由于負載變化時，總有壓力作用在與運動相同的方向上（如拉力） ，避免了氣穴現(xiàn)象的產生。然而這種系統(tǒng)會引起有桿腔壓力和活塞桿拉力激烈的變化，與入口節(jié)流控制相比，活塞和活塞桿密封必須能承受高壓，可能導致執(zhí)行元件的使用成本升高。5.3 旁路節(jié)流調速河南理工大學萬方科技學院本科畢業(yè)生論文２７如圖 13 所示的旁路節(jié)流調速系統(tǒng)，多余的流量直接從系統(tǒng)流回油箱，因此系統(tǒng)壓力總是等于執(zhí)行元件所需壓力。圖 13 旁路節(jié)流調速因為泵壓力較低，與入口節(jié)流調速和出口節(jié)流調速相比，旁路節(jié)流調速系統(tǒng)有較高的效率。但是它不能用在拉伸負載上，而且單泵供壓時，每次只能控制一個執(zhí)行元件，出口和入口節(jié)流調速可以同時控制多個執(zhí)行元件，如圖 14 所示河南理工大學萬方科技學院本科畢業(yè)生論文２８圖 14 控制若干執(zhí)行元件的入口節(jié)流調速變量柱塞泵向入口與出口節(jié)流調速系統(tǒng)供壓時，可以提供一個恒定的壓力（有壓力補償作用） ，使系統(tǒng)功耗降低，這正是比定量泵的優(yōu)越之處。可以通過計算它們的效率來證明如下入口節(jié)流調速系統(tǒng)效率， sPQ??具有壓力補償系統(tǒng)的效率其中 sPsP?PsQ?參考圖 1，泵的流量總是等于負載所需的流量，而且仍然能夠達到最大所需值，定量泵要想連續(xù)這樣的話，就需要溢流閥不斷控制進入執(zhí)行元件的流量。本節(jié)介紹的幾種流量控制方法都是基于連續(xù)工作的系統(tǒng)，如專用機床（如注塑機）上可能需要控制的地方預先布置好的，是點控。通常人們期望執(zhí)行元件的工作時間與整個運行周期中的關聯(lián)較小，以降低功率損失，這就需要考慮調整系統(tǒng)結構實現(xiàn)無極調速。河南理工大學萬方科技學院本科畢業(yè)生論文２９致 謝此次畢業(yè)設計能如此順利的完成，完全得力于指導老師閆艷燕老師的充分指導。提出了許多寶貴的建議，改正了許多錯誤，使設計更加合理、完善。同時許多同學也給予了很多建議和幫助，院領導也提供了很多利于設計的條件，在此對老師、同學們還有院領導表示深切而誠摯的謝意！