1、2.0噸叉車工作裝置液壓系統(tǒng)設計（中壓）1 提升裝置的設計根據(jù)設計條件，要提升的負載為2100kg，因此提升裝置需承受的負載力為：N為減小提升裝置的液壓缸行程，通過加一個動滑輪和鏈條（繩），對裝置進行改進，如圖1所示。圖1 提升裝置示意圖由于鏈條固定在框架的一端，活塞桿的行程是叉車桿提升高度的一半，但同時，所需的力變?yōu)樵瓉淼膬杀叮ㄓ捎谒璧墓Ρ３殖Ｖ?，但是位移減半，于是負載變?yōu)樵瓉淼膬杀叮?。即提升液壓缸的負載力為2 Fl = 41200 N如果系統(tǒng)工作壓力為150bar，則對于差動連接的單作用液壓缸，提升液壓缸的活塞桿有效作用面積為 m2 m2 所以活塞桿直徑為d = 0.0592 m，查標準

2、（50、56、63系列），取 d = 0.063m。根據(jù)液壓缸的最大長徑比20：1，液壓缸的最大行程可達到1.26 m，即叉車桿的最大提升高度為2.52 m，能夠滿足設計要求的2 m提升高度。因此，提升液壓缸行程為1m，活塞桿和活塞直徑為63/90mm（速比2）、63/100mm（速比1.46），或63/125mm(速比1.33)。由機械設計手冊查的，前兩種非優(yōu)先選用者，則選擇63/125mm(速比1.33)型的液壓缸。因此活塞桿的有效作用面積為m2當工作壓力在允許范圍內時，提升裝置最大流量由裝置的最大速度決定。在該動滑輪系統(tǒng)中，提升液壓缸的活塞桿速度是叉車桿速度(已知為0.2m/s)的一半，

3、于是提升過程中液壓缸所需最大流量為： m3/s l/min2 系統(tǒng)工作壓力的確定系統(tǒng)最大壓力可以確定為大約在150bar左右，如果考慮壓力損失的話，可以再稍高一些。3 傾斜裝置的設計傾斜裝置所需的力取決于它到支點的距離，活塞桿與叉車體相連。因此傾斜液壓缸的尺寸取決于它的安裝位置。安裝位置越高，即距離支點越遠，所需的力越小。圖2 傾斜裝置示意圖假設r =0.5m，傾斜力矩給定為T =7500 N.m，因此傾斜裝置所需的作用力F為： N如果該作用力由兩個雙作用液壓缸提供，則每個液壓缸所需提供的力為7500N。如果工作壓力為150bar，則傾斜液壓缸環(huán)形面積Aa為：m2由于負載力矩的方向總是使叉車桿

4、回到垂直位置，所以傾斜裝置一直處于拉伸狀態(tài)，不會彎曲。假設活塞直徑D=40mm，環(huán)形面積給定，則活塞桿直徑可以用如下方法求出。 m為了保證環(huán)形面積大于所需值，活塞桿直徑必須小于該計算值，取m，則環(huán)形面積為：傾斜機構所需最大壓力為： Pa =98.0 bar而液壓缸工作壓力為150bar，因此有足夠的余量。傾斜系統(tǒng)所需的最大流量出現(xiàn)在傾斜液壓缸的伸出過程中，此時液壓缸無桿腔充滿液壓油，因此應按照活塞端部一側計算，活塞面積用如下公式計算：=12.610-4 m2傾斜裝置所需最大速度給定為2/s，先轉換成弧度制，然后再轉換成線速度：因此，兩個液壓缸在伸出過程中所需的流量為：= 0.43981 m3/

5、s = 2.6 l/min傾斜裝置需要走過的行程為：綜上，兩個傾斜液壓缸的可選尺寸為40/25mm/mm，行程為200mm。4 油路設計對于提升工作裝置，單作用液壓缸就能夠滿足工作要求，因為叉車體的重量能使叉車桿自動回到底部。液壓缸不必有低壓出口，高壓油可同時充滿活塞環(huán)形面和另一面（構成差動缸），由于活塞兩側面積的不同而產(chǎn)生提升力。為減少管道連接，可以通過在活塞上面鉆孔實現(xiàn)液壓缸兩側的連接。傾斜裝置通常采用兩個液壓缸驅動，以防止叉車桿發(fā)生扭曲變形。行走機械液壓系統(tǒng)中通常采用中位卸荷的多路換向閥（中路通）控制多個液壓缸的動作，如圖3所示。圖3 中位卸荷的多路換向閥（中路通）控制的液壓系統(tǒng)也可采用

6、另一種稍有不同的雙泵供油方案，先確定基本油路組成，然后再加入安全裝置，如圖4所示。注意前述大部分計算過程對所有油路設計方案都適用，包括引入中通多路換向閥的設計。提升和傾斜兩個裝置都需要通過比例控制閥來控制，比例閥由手動操縱桿和對中彈簧來操縱。液壓系統(tǒng)原理圖中還應增加液壓泵，油箱和兩個溢流閥以保證安全，溢流閥可以用于調節(jié)供油壓力的大小。由于提升和傾斜兩個工作裝置的流量差異很大但相對都比較小，因此采用兩個串聯(lián)齒輪泵比較合適。大齒輪泵給提升裝置供油，小齒輪泵給傾斜裝置供油。齒輪泵與中通比例換向閥相連，當系統(tǒng)不工作時，兩個泵處于卸荷狀態(tài)，這樣可以提高系統(tǒng)的效率。圖4 雙泵供油方案的液壓系統(tǒng)另外，用于提

7、升裝置的方向控制閥可選用標準的四通閥，其B口應該與油箱相連不應堵塞。這樣，當叉車桿處于下降狀態(tài)，泵卸荷時，液壓油可以直接流回油箱，有利于提高系統(tǒng)效率。基本油路確定后，油路還不能正常工作，因為沒有安全保護裝置，也沒有調節(jié)流量（為限制負載下降速度而流出液壓缸的流量）的裝置?？梢酝ㄟ^引入一個安全閥，從而在負載下落時限制負載下落速度來解決這個問題，也可以在每個進油路上加一個單向閥，防止油液倒流。 因為存在負值負載（與活塞運動方向相同的負載），所以傾斜系統(tǒng)的回路設計稍微有所不同。上述回路設計過程中，應對如下兩個問題加以注意：1環(huán)形面一側一直處于增壓狀態(tài)，有可能通過方向閥產(chǎn)生泄漏；2防止在活塞另一側產(chǎn)生氣

8、穴現(xiàn)象（設置防氣穴閥）。5 液壓閥的選擇提升系統(tǒng)中，所有液壓閥通過的流量至多為19l/min，所以閥的尺寸很小。如果采用的是串聯(lián)泵，則傾斜裝置子系統(tǒng)流過的流量至多為3 l/min。為考慮系統(tǒng)的壓力損失（管路和各方向閥造成的），液壓系統(tǒng)提供的壓力應比負載所需壓力高1520bar：溢流閥的調定壓力應高于供油壓力10%左右，即設成170bar比較合適。溢流閥的最大壓力值可能比170bar還高，甚至超過200bar。注意：與使用中通旁路式多路換向閥相比，使用標準方向閥可以節(jié)省成本。但是，使用標準方向閥需要多增加一個溢流閥和一個泵，即使用兩個溢流閥和一個串聯(lián)泵。5.1 提升系統(tǒng)液壓閥選擇由以上計算可知：

9、提升子系統(tǒng)最大流量為18.7L/min。選擇直動式溢流閥的型號為DBDS10P10，帶保護罩的調節(jié)螺栓，通徑10mm,板式閥，進油口最大壓力63MPa，出油口最大壓力31.5MPa。選擇單向閥的型號為RVP-10-1-0，通徑10mm,最大工作壓力31.5MPa，最大流量1815000L/min。選擇順序背壓閥的型號為BXY-Fg6/10，通徑10mm，最高工作壓力20MPa；選擇手動換向閥的型號為4WMM6，通徑為6mm,最高工作壓力：油口A、B、P為31.5MPa,油口T為16MPa，最大流量60L/min。5.2 傾斜系統(tǒng)液壓閥選擇由以上計算可知：傾斜子系統(tǒng)最大流量為2.6L/min。選

10、擇直動式溢流閥的型號為DBDH6P10，調節(jié)手柄，通徑6mm,板式閥，進油口最大壓力40MPa，出油口最大壓力31.5MPa。選擇單向閥的型號為RVP-6-1-0，通徑6mm,最大工作壓力31.5MPa，最大流量1815000L/min。選擇手動換向閥的型號為4WMM6，通徑為6mm,最高工作壓力：油口A、B、P為31.5MPa,油口T為16MPa，最大流量60L/min。6 液壓泵的參數(shù)確定 由于提升系統(tǒng)與傾斜系統(tǒng)的流量相差很大，并且都很小，所以本設計采用結構簡單、價格低廉的齒輪泵串聯(lián)滿足設計要求。提升：假定齒輪泵的容積效率為90%，電機轉速為1500r/m，則泵的排量為： cm3/rev從

11、Sauer-Danfoss目錄中可查出，SNP2系列有排量為10.8和14.4cm3/rev的泵。應選擇排量為14.4cm3/rev(與13.8更接近)的液壓泵SNP2/014或SEP2/014， 滿負載條件下（1500rpm，容積效率90%）的實際流量為： l/min大于所需值18.7 l/min，滿足設計要求。傾斜： cm3/rev第二個泵的排量為1.92 cm3/rev，可選擇SNP1/2.2，選擇的時候只需要檢驗其是否與SNP2/014型號的泵配對，以構成串聯(lián)泵。在Sauer-Danfoss目錄中，有一張表格顯示了哪些泵可以用來構成串聯(lián)泵，最后選定合適的組合為：SNP2/014+SNP

12、1/2.27 電動機功率在最大壓力下的流動功率為： kw上面的數(shù)值假定的是效率為100%時得到的。齒輪泵的效率（包括容積效率和機械效率）在8085%之間，所以所需的電機功率為： kw8 管路的尺寸通常的流體速度：排油管路：3m/s5m/s吸油管路：0.5m/s1.5m/s泵自身的初始吸油壓力限制在不超過0.33bar(10Hg)這些速度受油路和裝置工作條件，功率損失，熱和噪聲的產(chǎn)生以及振動的影響，會發(fā)生變化。假定吸油管路的速度為1m/s，排油管路的速度為5m/s。排油管路計算：最大流量為0.000312m3/s，則管道的最小橫截面積為： （管道直徑）與計算數(shù)值最接近的實際管子直徑為8或10mm

13、，所以：當選用8mm的管徑時，流速為v=6.2m/s當選用10mm的管徑時，流速為v=4.0m/s推薦選用管徑為10mm的管子吸油孔計算孔的橫截面積： （孔徑）與之最近的實際值為20mm9 功率損失估計提升/下降油路：當叉車桿處于閑置或負載下降時，泵在低壓下有18.7l/min的流量流回油箱。當負載上升時，大部分流量將進入液壓缸。當負載緩慢上升時，有相當一部分流量從安全閥流失，造成很大的能量損失。假定泵流量的90%通過安全閥流失，損失的功率為：導致油液溫度升高：由于這種情況只會偶爾發(fā)生，所以不必裝冷卻裝置。設計一個好的油箱（如鰭狀箱體）或鰭狀回路管道有助于改善對流熱量損失。請刪除以下內容，O(

14、_)O謝謝！The origin of taxation in the United States can be traced to the time when the colonists were heavily taxed by Great Britain on everything from tea to legal and business documents that were required by the Stamp Tax. The colonists disdain for this taxation without representation (so-called bec

15、ause the colonies had no voice in the establishment of the taxes) gave rise to revolts such as the Boston Tea Party. However, even after the Revolutionary War and the adoption of the U.S. Constitution, the main source of revenue for the newly created states was money received from customs and excise

16、 taxes on items such as carriages, sugar, whiskey, and snuff. Income tax first appeared in the United States in 1862, during the Civil War. At that time only about one percent of the population was required to pay the tax. A flat-rate income tax was imposed in 1867. The income tax was repealed in it

17、s entirety in 1872. Income tax was a rallying point for the Populist party in 1892, and had enough support two years later that Congress passed the Income Tax Act of 1894. The tax at that time was two percent on individual incomes in excess of $4,000, which meant that it reached only the wealthiest

18、members of the population. The Supreme Court struck down the tax, holding that it violated the constitutional requirement that direct taxes be apportioned among the states by population (pollock v. farmers loan & trust, 158 U.S. 601, 15 S. Ct. 912, 39 L. Ed. 1108 1895). After many years of debate an

19、d compromise, the sixteenth amendment to the Constitution was ratified in 1913, providing Congress with the power to lay and collect taxes on income without apportionment among the states. The objectives of the income tax were the equitable distribution of the tax burden and the raising of revenue.

20、Since 1913 the U.S. income tax system has become very complex. In 1913 the income tax laws were contained in eighteen pages of legislation; the explanation of the tax reform act of 1986 was more than thirteen hundred pages long (Pub. L. 99-514, Oct. 22, 1986, 100 Stat. 2085). Commerce Clearing House

21、, a publisher of tax information, released a version of the Internal Revenue Code in the early 1990s that was four times thicker than its version in 1953. Changes to the tax laws often reflect the times. The flat tax of 1913 was later replaced with a graduated tax. After the United States entered wo

22、rld war i, the War Revenue Act of 1917 imposed a maximum tax rate for individuals of 67 percent, compared with a rate of 13 percent in 1916. In 1924 Secretary of the Treasury Andrew W. Mellon, speaking to Congress about the high level of taxation, stated, The present system is a failure. It was an e

23、mergency measure, adopted under the pressure of war necessity and not to be counted upon as a permanent part of our revenue structure. The high rates put pressure on taxpayers to reduce their taxable income, tend to destroy individual initiative and enterprise, and seriously impede the development o

24、f productive business. Ways will always be found to avoid taxes so destructive in their nature, and the only way to save the situation is to put the taxes on a reasonable basis that will permit business to go on and industry to develop. Consequently, the Revenue Act of 1924 reduced the maximum indiv

25、idual tax rate to 43 percent (Revenue Acts, June 2, 1924, ch. 234, 43 Stat. 253). In 1926 the rate was further reduced to 25 percent. The Revenue Act of 1932 was the first tax law passed during the Great Depression (Revenue Acts, June 6, 1932, ch. 209, 47 Stat. 169). It increased the individual maxi

26、mum rate from 25 to 63 percent, and reduced personal exemptions from $1,500 to $1,000 for single persons, and from $3,500 to $2,500 for married couples. The national industrial recovery act of 1933 (NIRA), part of President franklin d. roosevelts new deal, imposed a five percent excise tax on divide

27、nd receipts, imposed a capital stock tax and an excess profits tax, and suspended all deductions for losses (June 16, 1933, ch. 90, 48 Stat. 195). The repeal in 1933 of the eighteenth amendment, which had prohibited the manufacture and sale of alcohol, brought in an estimated $90 million in new liqu

28、or taxes in 1934. The social security act of 1935 provided for a wage tax, half to be paid by the employee and half by the employer, to establish a federal retirement fund (Old Age Pension Act, Aug. 14, 1935, ch. 531, 49 Stat. 620). The Wealth Tax Act, also known as the Revenue Act of 1935, increase

29、d the maximum tax rate to 79 percent, the Revenue Acts of 1940 and 1941 increased it to 81 percent, the Revenue Act of 1942 raised it to 88 percent, and the Individual Income Tax Act of 1944 raised the individual maximum rate to 94 percent. The post-World War II Revenue Act of 1945 reduced the indiv

30、idual maximum tax from 94 percent to 91 percent. The Revenue Act of 1950, during the korean war, reduced it to 84.4 percent, but it was raised the next year to 92 percent (Revenue Act of 1950, Sept. 23, 1950, ch. 994, Stat. 906). It remained at this level until 1964, when it was reduced to 70 percen

31、t. The Revenue Act of 1954 revised the Internal Revenue Code of 1939, making major changes that were beneficial to the taxpayer, including providing for child care deductions (later changed to credits), an increase in the charitable contribution limit, a tax credit against taxable retirement income,

32、 employee deductions for business expenses, and liberalized depreciation deductions. From 1954 to 1962, the Internal Revenue Code was amended by 183 separate acts. In 1974 the employee retirement income security act (ERISA) created protections for employees whose employers promised specified pension

33、s or other retirement contributions (Pub. L. No. 93-406, Sept. 2, 1974, 88 Stat. 829). ERISA required that to be tax deductible, the employers plan contribution must meet certain minimum standards as to employee participation and vesting and employer funding. ERISA also approved the use of individua

34、l retirement accounts (IRAs) to encourage tax-deferred retirement savings by individuals. The Economic Recovery Tax Act of 1981 (ERTA) provided the largest tax cut up to that time, reducing the maximum individual rate from 70 percent to 50 percent (Pub. L. No. 97-34, Aug. 13, 1981, 95 Stat. 172). Th

35、e most sweeping tax changes since world war ii were enacted in the Tax Reform Act of 1986. This bill was signed into law by President ronald reagan and was designed to equalize the tax treatment of various assets, eliminate tax shelters, and lower marginal rates. Conservatives wanted the act to prov

36、ide a single, low tax rate that could be applied to everyone. Although this single, flat rate was not included in the final bill, tax rates were reduced to 15 percent on the first $17,850 of income for singles and $29,750 for married couples, and set at 28 to 33 percent on remaining income. Many ded

37、uctions were repealed, such as a deduction available to two-income married couples that had been used to avoid the marriage penalty (a greater tax liability incurred when two persons filed their income tax return as a married couple rather than as individuals). Although the personal exemption exclus

38、ion was increased, an exemption for elderly and blind persons who itemize deductions was repealed. In addition, a special capital gains rate was repealed, as was an investment tax credit that had been introduced in 1962 by President john f. kennedy. The Omnibus Budget Reconciliation Act of 1993, the

39、 first budget and tax act enacted during the Clinton administration, was vigorously debated, and passed with only the minimum number of necessary votes. This law provided for income tax rates of 15, 28, 31, 36, and 39.6 percent on varying levels of income and for the taxation of social security inco

40、me if the taxpayer receives other income over a certain level. In 2001 Congress enacted a major income tax cut at the urging of President george w. bush. Over the course of 11 years the law reduces marginal income tax rates across all levels of income. The 36 percent rate will be lowered to 33 perce

41、nt, the 31 percent rate to 28 percent, the 28 percent rate to 25 percent. In addition, a new bottom 10 percent rate was created. Since the early 1980s, a flat-rate tax system rather than the graduated bracketed method has been proposed. (The graduated bracketed method is the one that has been used s

42、ince graduated taxes were introduced: the percentage of tax differs based on the amount of taxable income.) The flat-rate system would impose one rate, such as 20 percent, on all income and would eliminate special deductions, credits, and exclusions. Despite firm support by some, the flat-rate tax h

43、as not been adopted in the United States. Regardless of the changes made by legislators since 1913, the basic formula for computing the amount of tax owed has remained basically the same. To determine the amount of income tax owed, certain deductions are taken from an individuals gross income to arrive at an adjusted gross income, from which additional deductions are taken to arrive at the taxable income. Once the amount of taxable income has been determined, tax rate charts determine the ex