2015年电大液压气动技术基础期末复习题及答案参考小抄【电大考试必备】

电大 液压气动技术基础期末 复习题及答案 参考小抄 一、填空 1液压系统中的两个重要参数是 (流量 )和 (压力 )，液压传动是以液体的 (压力 )能传递动力的。 2根据度量基准的不同，液体的压力分为 (相对压力 )和 ( 绝对压力 )两种，大多数表测得的压力是 (相对压力 )。 3调速阀是由 (定差减压 )阀和节流阀 ( 串联 )连接而组成。 4容积调速基本回路有三种，它们是 (变量泵 -定量马达 )、 (变量泵 -变量马达 )及 (复合调速 )。 5 差动回路可以实现油缸的 ( 快速 )运动 ， 但差动连接时 ， 油缸的推力却明显的 ( 降低 )。 二、选择题 1运动速度（ B ）时宜采用粘度较低的液压油减少摩擦损失：工作压力 （ ）时宜采用粘度较高的液压油以减少泄漏。 A. 高 低 B. 高 高 C. 低 高 D. 低 低 2. 在用一个泵驱动一个执行元件的液压系统中，采用三位四通换向阀使泵卸荷，应选用（ D ）型中位机能 A. “ P”型 B. “O”型 C. “ Y”型 D. “H”型 3 限 制齿轮泵工作压力提高的主要因素是 ( C )。 (A)存在困油现象 (B)流量脉动 (C)泄漏 (D)径向力不平衡 4 溢流阀的控制油压来自阀的 ( A )。 (A)进口端 (B)出口端 (C)设有单独的泄油油路 (D)没有单独的泄油油路 5 调速阀是用（ B）而成的 A. 节流阀和顺序阀串联 B. 节流阀和定差减压阀串联 C. 节流阀和顺序阀并联 D. 节流阀和定差减压阀并联 三、简答 题 1.液压传动系统由哪几部分组成部分 ?各组成部分的作用是什么 ? （ 答：液压传动系统主要有以下 五 部分组成： 动力元件：液压泵，其功能是将原动机输入的机械能转换成液体的压力能，为系统提供动力。 执行元件：液压缸、液压马达，它们的功能是将流体的压力能转换成机械能，输出力和速度（或转矩和转速），以带动负载进行直线运动或旋转运动。 控制元件：压力 、 流量和方向控制阀，它们的作用是控制和调节系统中液体的压力、流量和流动方向，以保证执行元件达到所要求的输出力（或力矩）、运动速度和运动方向。 辅助元件：保证系统正常工作所 需要的辅助装置，包括管道、管接头、油箱、过滤器和压力计等。 工作介质：用以传递动力并起润滑作用。 2简述液压冲击产生的原因。 在液压系统中，由于某种原因，液体压力在一瞬间会突然升高，产生很高的压力峰值，这种现象称为液压冲击 。 液压冲击产生的原因：（ 1）液流通道迅速关闭或液流迅速换向使液流速度的大小或方向突然变化时，由于液流的惯力引起的液压冲击。（ 2）运动着的工作部件突然制动或换向时，因工作部件的惯性引起的液压冲击。（ 3）某些液压元件动作失灵或不灵敏，使系统压力升高而引起的液压冲击。 3何谓气穴现象？它有 哪些危害？通常采取哪些措施防止气穴及气蚀？ 在液压系统中（或液压元件中）因局部压力降低而有气泡形成的现象称为气穴现象。 危害：引起气蚀，产生振动噪声；形成气塞破坏系统正常工作。 措施：尽力减少油液中空气的含量，防止气体混入系统；防止系统局部压力过低；在易发生气穴部位采用耐蚀材料及保护镀层。 4.说明下图所示双泵双速回路的工作原理，并分析确定阀 3、 4 的调定压力关系 ？ （ 1） 快速时：低压大流量泵 2、高压小流量泵 1 同时向系统供油； 慢速时：高压小流量 1 向系统供油，低压大流量泵 2 卸荷 （ 2） 阀 3 的调定压力大于 阀 4 的调定压力 四、分析题 1.若把先导式溢流阀的远控制口当成泄漏口接油箱， 试分析 液压系统会产生什么问题 产生卸荷现象，系统压力近乎零。 2夹紧回路如下图所示，若溢流阀的调整压力 p1 3Mpa、减压阀的调整压力 p2 2Mpa。 （ 1）试分析活塞空载运动时 A、 B 两点的压力各为多少？减压阀的阀芯处于什么状态？ （ 2）工件夹紧，活塞停止运动后， A、 B 两点的压力又各为多少？此时，减压阀芯又处于什么状态？ 答： （ 1）活塞空载运动，由于没有负载力作用，系统工作压力为 0，不考虑沿程阻力损失， A、B 两点压力相等，都是 0MPa，此时减压阀处在非工作状态，阀口常开 （ 2）工件夹紧后，溢流阀工作，此时 A 点压力为溢流阀调定压力， 3MPa，减压阀也开始工作， B 点压力为 2MPa，减压阀阀芯处于半开状态，保证出口压力恒定在 2MPa。 五、计算题 1 图示的简化回路中，溢流阀的调定压力是 2.5106Pa,系统工作时溢流阀始终有油流回油箱，活塞有效工作面积为 0 .1m2,求当负载分别为： F=2104N； F=0； F=-5103N 时，油缸出口压力 P2各为多少？ 解：由于溢流阀始终有油流回油箱，油缸进油腔压力等于溢流阀 的调定压力，为 2.5106Pa。油缸两腔的作用力相等，则有： P20.1+F=2.51060.1 即有： P2 2.5106+ F/0.1 当 F 2104N 时， P2 2.7106Pa 当 F 0 时， P2 2.5106Pa 当 F 5104N 时， P2 2.55106Pa 2已知液压泵转速为 1000r/min， 排量为 160ml/r，额定压力为 30Mpa，实际输出流量为 150L/min，泵的总效率为 0.87，求： 泵的理论流量； 泵的容积效率和机械效率； 驱动液压泵所需 的电动机功率。 解： 1)泵的理论流量： q=nV=1000160=160000ml/min=160(L/min) 2)泵的容积效率： v=q/qt=150/160=0.9375=93.75 机械效率 ： m=/v=0.87/0.9375=0.928=92.8% 3) 驱动液压泵所需的电动机功率等于液压泵的输入功率： P=pqt=3010616010-3=80103(W)=80(kW) 六、综合题 下图所示回路可实行“快进 工进快退原位停止和液压泵卸荷”的工作循环 ， 完成电磁铁 动作顺序表（通电“”，断电“”） 七、综合题 某机床进给回 路如图所示，它可以实现快进工进快退的工作循环。根据此回路 工作原理，填写电磁铁动作表。（电磁铁通 电时，在空格中记“” 号；反之，断电记“”号） 电磁铁 工作环节 1YA 2YA 3YA 快进 + - + 1YA 2YA 3YA 4YA 快 进 + - - + 工 进 + - + + 快 退 - + - + 原位停止，泵卸荷 - - _ _ 工进 + - - 快退 - + - 请您删除一下内容， O( _ )O 谢谢！ 2015 年中央电大期末复习考试小抄大全，电大期末考试必备小抄，电大考试必过小抄 After earning his spurs in the kitchens of The Westin, The Sheraton, Sens on the Bund, and a sprinkling of other top-notch venues, Simpson Lu fi nally got the chance to become his own boss in November 2010. Sort of. The Shanghai-born chef might not actually own California Pizza Kitchen (CPK) but he is in sole charge of both kitchen and frontof- house at this Sinan Mansionsstalwart. Its certainly a responsibility to be the head chef, and then to have to manage the rest of the restaurant as well, the 31-year-old tells Enjoy Shanghai. In hotels, for example, these jobs are strictly demarcated, so its a great opportunity to learn how a business operates across the board. It was a task that management back in sunny California evidently felt he was ready for, and a vote of confi dence from a company that, to date, has opened 250 outlets in 11 countries. And for added pressure, the Shanghai branch was also CPKs China debut. For sure it was a big step, and unlike all their other Asia operations that are franchises, they decided to manage it directly to begin with, says Simpson. Two years ago a private franchisee took over the lease, but the links to CPK headquarters are still strong, with a mainland-based brand ambassador on hand to ensure the business adheres to its ethos of creating innovative, hearth-baked pizzas, a slice of PR blurb that Simpson insists lives up to the hype. They are very innovative, he says. The problem with most fast food places is that they use the same sauce on every pizza and just change the toppings. Every one of our 16 pizza sauces is a unique recipe that has been formulated to complement the toppings perfectly. The largely local customer base evidently agrees and on Saturday and Sunday, at least, the place is teeming. The kids-eat-for-free policy at weekends is undoubtedly a big draw, as well as is the spacious second-fl oor layout overlooked by a canopy of green from Fuxing Park over the road. The company is also focusing on increasing brand recognition and in recent years has taken part in outside events such as the regular California Week. Still, the sta are honest enough to admit that business could be better； as good, in fact, as in CPKs second outlet in the popular Kerry Parkside shopping mall in Pudong. Sinan Mansions has really struggled to get the number of visitors that were envisaged when it first opened, and it hasnt been easy for any of the tenants here, adds Simpson. Were planning a third outlet in the city in 2015, and we will probably choose a shopping mall again because of the better foot traffic. The tearooms once frequented by Coco Chanel and Marcel Proust are upping sticks and coming to Shanghai, Xu Junqian visits the Parisian outpost with sweet treats. One thing the century-old Parisian tearoom Angelina has shown is that legendary fashion designer Coco Chanel not only had style and glamor but also boasted great taste in food, pastries in particular. One of the most popular tearooms in Paris, Angelina is famous for having once been frequented by celebrities such as Chanel and writer Marcel Proust. Now Angelina has packed up its French ambience, efficient service, and beautiful, comforting desserts and flown them to Shanghai. At the flagship dine-in and take-out space in Shanghai, everything mimics the original tearoom designed from the beginning of the 20th century, in Paris, the height of Belle Epoque. The paintings on the wall, for example, are exactly the same as the one that depicts the landscape of southern France, the hometown of the owner； and the small tables are intentional imitations of the ones that Coco Chanel once sat at every afternoon for hot chocolate. The famous hot chocolate, known as LAfricain, is a luxurious mixture of four types of cocoa beans imported from Africa, blended in Paris and then shipped to Shanghai. Its sinfully sweet, rich and thick as if putting a bar of melting chocolate directly on the tongue and the fresh whipped cream on the side makes a light, but equally gratifying contrast. It is also sold in glass bottles as takeaway. The signature Mont-Blanc chestnut cake consists of three parts: the pureed chestnut on top, the vanilla cream like stuffing, and the meringue as base. Get all three layers in one scoop, not only for the different textures but also various flavors of sweetness. The dessert has maintained its popularity for a century, even in a country like France, perhaps the worlds most competitive place for desserts. A much overlooked pairing, is the Paris-New York choux pastry and N226 chocolate flavored tea. The choux pastry is a mouthful of airy pecan-flavored whipped cream, while the tea, a blend of black teas from China and Ceylon, cocoa and rose petals, offers a more subtle fragrance of flowers and chocolate. Ordering these two items, featuring a muted sweetness, makes it easier for you to fit into your little black dress. Breakfast, brunch, lunch and light supper are also served at the tearoom, a hub of many cultures and takes in a mix of different styles of French cuisines, according to the management team. The semi-cooked foie gras terrine, is seductive and deceptive. Its generously served at the size and shape of a toast, while the actual brioche toast is baked into a curved slice dipped with fig chutney. The flavor, however, is honest: strong, smooth and sublime. And you dont actually need the toast for crunchiness. This is the season for high teas, with dainty cups of fine china and little pastries that appeal to both visual and physical appetites. But there is one high tea with a difference, and Pauline D. Loh finds out just exactly why it is special. Earl Grey tea and macarons are all very well for the crucial recuperative break in-between intensive bouts of holiday season shopping. And for those who prefer savory to sweet, there is still the selection of classic Chinese snacks called dim sum to satisfy and satiate. High tea is a meal to eat with eye and mouth, an in-between indulgence that should be light enough not to spoil dinner, but sufficiently robust to take the edge off the hunger that strikes hours after lunch. The afternoon tea special at Shang-Xi at the Four Seasons Hotel Pudong has just the right elements. It is a pampering meal, with touches of luxury that make the high tea session a treat in itself. Whole baby abalones are braised and then topped on a shortcrust pastry shell, a sort of Chinese version of the Western vol-au-vent, but classier. Even classier is the dim sum staple shrimp dumpling or hargow, upgraded with the addition of slivers of midnight dark truffles. This is a master touch, and chef Simon Choi, who presides unchallenged at Shang-Xi, has scored a winner again. Sweet prawns and aromatic truffles whats not to love? His masterful craftsmanship is exhibited in yet another pastry a sweet pastry that is shaped to look like a walnut, but which you can put straight into the mouth. It crumbles immediately, and the slightly sweet, nutty morsel is so easy to eat youll probably reach straight for another. My favorite is the dessert that goes by the name yangzhi ganlu, or ambrosia from the gods. The hotel calls it chilled mango cream with sago, pomelo and birds nest made with ingredients that resonate with every female soul. It does taste like ambrosia, with the sweet-sour fragrance of the mango forming the first layer of taste and sensation, and the pomelo sacs and sago pearls providing the tactile contrast. The birds