毕业论文-2.0吨叉车工作装置液压系统设计说明书(中压).doc

2.0吨叉车工作装置液压系统设计（中压）1 提升装置的设计根据设计条件，要提升的负载为2100kg，因此提升装置需承受的负载力为：n为减小提升装置的液压缸行程，通过加一个动滑轮和链条（绳），对装置进行改进，如图1所示。图1 提升装置示意图由于链条固定在框架的一端，活塞杆的行程是叉车杆提升高度的一半，但同时，所需的力变为原来的两倍（由于所需的功保持常值，但是位移减半，于是负载变为原来的两倍）。即提升液压缸的负载力为2 fl = 41200 n如果系统工作压力为150bar，则对于差动连接的单作用液压缸，提升液压缸的活塞杆有效作用面积为 m2 m2 所以活塞杆直径为d = 0.0592 m，查标准（50、56、63系列），取 d = 0.063m。根据液压缸的最大长径比20：1，液压缸的最大行程可达到1.26 m，即叉车杆的最大提升高度为2.52 m，能够满足设计要求的2 m提升高度。因此，提升液压缸行程为1m，活塞杆和活塞直径为63/90mm（速比2）、63/100mm（速比1.46），或63/125mm(速比1.33)。由机械设计手册查的，前两种非优先选用者，则选择63/125mm(速比1.33)型的液压缸。因此活塞杆的有效作用面积为m2当工作压力在允许范围内时，提升装置最大流量由装置的最大速度决定。在该动滑轮系统中，提升液压缸的活塞杆速度是叉车杆速度(已知为0.2m/s)的一半，于是提升过程中液压缸所需最大流量为： m3/s l/min2 系统工作压力的确定系统最大压力可以确定为大约在150bar左右，如果考虑压力损失的话，可以再稍高一些。3 倾斜装置的设计倾斜装置所需的力取决于它到支点的距离，活塞杆与叉车体相连。因此倾斜液压缸的尺寸取决于它的安装位置。安装位置越高，即距离支点越远，所需的力越小。图2 倾斜装置示意图假设r =0.5m，倾斜力矩给定为t =7500 n.m，因此倾斜装置所需的作用力f为： n如果该作用力由两个双作用液压缸提供，则每个液压缸所需提供的力为7500n。如果工作压力为150bar，则倾斜液压缸环形面积aa为：m2由于负载力矩的方向总是使叉车杆回到垂直位置，所以倾斜装置一直处于拉伸状态，不会弯曲。假设活塞直径d=40mm，环形面积给定，则活塞杆直径可以用如下方法求出。 m为了保证环形面积大于所需值，活塞杆直径必须小于该计算值，取m，则环形面积为：倾斜机构所需最大压力为： pa =98.0 bar而液压缸工作压力为150bar，因此有足够的余量。倾斜系统所需的最大流量出现在倾斜液压缸的伸出过程中，此时液压缸无杆腔充满液压油，因此应按照活塞端部一侧计算，活塞面积用如下公式计算：=12.610-4 m2倾斜装置所需最大速度给定为2/s，先转换成弧度制，然后再转换成线速度：因此，两个液压缸在伸出过程中所需的流量为：= 0.43981 m3/s = 2.6 l/min倾斜装置需要走过的行程为：综上，两个倾斜液压缸的可选尺寸为40/25mm/mm，行程为200mm。4 油路设计对于提升工作装置，单作用液压缸就能够满足工作要求，因为叉车体的重量能使叉车杆自动回到底部。液压缸不必有低压出口，高压油可同时充满活塞环形面和另一面（构成差动缸），由于活塞两侧面积的不同而产生提升力。为减少管道连接，可以通过在活塞上面钻孔实现液压缸两侧的连接。倾斜装置通常采用两个液压缸驱动，以防止叉车杆发生扭曲变形。行走机械液压系统中通常采用中位卸荷的多路换向阀（中路通）控制多个液压缸的动作，如图3所示。图3 中位卸荷的多路换向阀（中路通）控制的液压系统也可采用另一种稍有不同的双泵供油方案，先确定基本油路组成，然后再加入安全装置，如图4所示。注意前述大部分计算过程对所有油路设计方案都适用，包括引入中通多路换向阀的设计。提升和倾斜两个装置都需要通过比例控制阀来控制，比例阀由手动操纵杆和对中弹簧来操纵。液压系统原理图中还应增加液压泵，油箱和两个溢流阀以保证安全，溢流阀可以用于调节供油压力的大小。由于提升和倾斜两个工作装置的流量差异很大但相对都比较小，因此采用两个串联齿轮泵比较合适。大齿轮泵给提升装置供油，小齿轮泵给倾斜装置供油。齿轮泵与中通比例换向阀相连，当系统不工作时，两个泵处于卸荷状态，这样可以提高系统的效率。图4 双泵供油方案的液压系统另外，用于提升装置的方向控制阀可选用标准的四通阀，其b口应该与油箱相连不应堵塞。这样，当叉车杆处于下降状态，泵卸荷时，液压油可以直接流回油箱，有利于提高系统效率。基本油路确定后，油路还不能正常工作，因为没有安全保护装置，也没有调节流量（为限制负载下降速度而流出液压缸的流量）的装置。可以通过引入一个安全阀，从而在负载下落时限制负载下落速度来解决这个问题，也可以在每个进油路上加一个单向阀，防止油液倒流。 因为存在负值负载（与活塞运动方向相同的负载），所以倾斜系统的回路设计稍微有所不同。上述回路设计过程中，应对如下两个问题加以注意：1环形面一侧一直处于增压状态，有可能通过方向阀产生泄漏；2防止在活塞另一侧产生气穴现象（设置防气穴阀）。5 液压阀的选择提升系统中，所有液压阀通过的流量至多为19l/min，所以阀的尺寸很小。如果采用的是串联泵，则倾斜装置子系统流过的流量至多为3 l/min。为考虑系统的压力损失（管路和各方向阀造成的），液压系统提供的压力应比负载所需压力高1520bar：溢流阀的调定压力应高于供油压力10%左右，即设成170bar比较合适。溢流阀的最大压力值可能比170bar还高，甚至超过200bar。注意：与使用中通旁路式多路换向阀相比，使用标准方向阀可以节省成本。但是，使用标准方向阀需要多增加一个溢流阀和一个泵，即使用两个溢流阀和一个串联泵。5.1 提升系统液压阀选择由以上计算可知：提升子系统最大流量为18.7l/min。选择直动式溢流阀的型号为dbds10p10，带保护罩的调节螺栓，通径10mm,板式阀，进油口最大压力63mpa，出油口最大压力31.5mpa。选择单向阀的型号为rvp-10-1-0，通径10mm,最大工作压力31.5mpa，最大流量1815000l/min。选择顺序背压阀的型号为bxy-fg6/10，通径10mm，最高工作压力20mpa；选择手动换向阀的型号为4wmm6，通径为6mm,最高工作压力：油口a、b、p为31.5mpa,油口t为16mpa，最大流量60l/min。5.2 倾斜系统液压阀选择由以上计算可知：倾斜子系统最大流量为2.6l/min。选择直动式溢流阀的型号为dbdh6p10，调节手柄，通径6mm,板式阀，进油口最大压力40mpa，出油口最大压力31.5mpa。选择单向阀的型号为rvp-6-1-0，通径6mm,最大工作压力31.5mpa，最大流量1815000l/min。选择手动换向阀的型号为4wmm6，通径为6mm,最高工作压力：油口a、b、p为31.5mpa,油口t为16mpa，最大流量60l/min。6 液压泵的参数确定 由于提升系统与倾斜系统的流量相差很大，并且都很小，所以本设计采用结构简单、价格低廉的齿轮泵串联满足设计要求。提升：假定齿轮泵的容积效率为90%，电机转速为1500r/m，则泵的排量为： cm3/rev从sauer-danfoss目录中可查出，snp2系列有排量为10.8和14.4cm3/rev的泵。应选择排量为14.4cm3/rev(与13.8更接近)的液压泵snp2/014或sep2/014， 满负载条件下（1500rpm，容积效率90%）的实际流量为： l/min大于所需值18.7 l/min，满足设计要求。倾斜： cm3/rev第二个泵的排量为1.92 cm3/rev，可选择snp1/2.2，选择的时候只需要检验其是否与snp2/014型号的泵配对，以构成串联泵。在sauer-danfoss目录中，有一张表格显示了哪些泵可以用来构成串联泵，最后选定合适的组合为：snp2/014+snp1/2.27 电动机功率在最大压力下的流动功率为： kw上面的数值假定的是效率为100%时得到的。齿轮泵的效率（包括容积效率和机械效率）在8085%之间，所以所需的电机功率为： kw8 管路的尺寸通常的流体速度：排油管路：3m/s5m/s吸油管路：0.5m/s1.5m/s泵自身的初始吸油压力限制在不超过0.33bar(10hg)这些速度受油路和装置工作条件，功率损失，热和噪声的产生以及振动的影响，会发生变化。假定吸油管路的速度为1m/s，排油管路的速度为5m/s。排油管路计算：最大流量为0.000312m3/s，则管道的最小横截面积为： （管道直径）与计算数值最接近的实际管子直径为8或10mm，所以：当选用8mm的管径时，流速为v=6.2m/s当选用10mm的管径时，流速为v=4.0m/s推荐选用管径为10mm的管子吸油孔计算孔的横截面积： （孔径）与之最近的实际值为20mm9 功率损失估计提升/下降油路：当叉车杆处于闲置或负载下降时，泵在低压下有18.7l/min的流量流回油箱。当负载上升时，大部分流量将进入液压缸。当负载缓慢上升时，有相当一部分流量从安全阀流失，造成很大的能量损失。假定泵流量的90%通过安全阀流失，损失的功率为：导致油液温度升高：由于这种情况只会偶尔发生，所以不必装冷却装置。设计一个好的油箱（如鳍状箱体）或鳍状回路管道有助于改善对流热量损失。请删除以下内容，o(_)o谢谢！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 because 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 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 its 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 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 and 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. 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, 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 world 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 emergency 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 of 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 individual 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 maximum 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 dividend 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 liquor 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, increased 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 individual 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 percent. 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, 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 pensions 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 individual 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). the 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 provide 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 deductions 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 exclusion 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 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 income 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 percent, 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 since 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 has 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