【正文】 ，因此需要進行適當?shù)恼{整以滿足速度比的要求。鏈傳動第一條鏈傳動或稱為“安全”自行車出現(xiàn)在 1874 年，那時，鏈用于驅動早期自行車的后輪。今天，隨著現(xiàn)代設計和制造方法的改進，鏈傳動越來越比原來的傳動應用得更有效和廣泛，已經(jīng)極大地提高了農(nóng)業(yè)機械、鉆探設備、礦業(yè)和建筑機械的效率，大約從 1930 年以來，鏈傳動已經(jīng)變得日益普遍，尤其是在動力鋸子、摩托車和自動扶梯等設備上。有至少 6 種類型的動力傳送的鏈，本文介紹其中的 3 種，分別命名為滾柱鏈條、齒型鏈條或低噪音鏈條和滾子鏈條。滾柱鏈條傳動的基本組成部分有側板、銷軸、套筒、滾柱、兩個或多個鏈輪，每個鏈輪上有類似齒輪形狀的齒。滾柱鏈條是用銷軸和滾柱等進行裝配而成的，用兩個銷軸插入兩個側板中的孔可以連接兩邊側板，銷軸緊緊地插入孔中，形成壓緊連接，滾柱是由兩個側板和兩個壓緊的套筒組成的，硬的鋼質滾柱可以自由地轉動。當全部裝配完成后，滾柱是一個組合件，可以相對于套筒輕松地轉動，這樣鏈條可以在鏈輪上傳動。 標準滾柱鏈條可以是單排的也可以是多排的，如果是多排的，那么兩條或多條鏈條一起連接在同一個銷軸上，這時要使?jié)L柱以一定的排列方式對齊，單個驅動的速度比一般控制在 10 ∶1 范圍內(nèi)，比較合適的軸中心距離一般為 30 到35 倍滾柱與滾柱之間的距離，鏈條速度一般不要超過每分鐘2500 英尺(每分鐘 800 米)。當幾個平行軸一起驅動時，滾柱鏈條傳動尤為合適。 齒型鏈條或低噪音鏈條基本上就是齒輪齒條的組合件，每個齒條有兩個齒，軸向連接形成一個封閉的、內(nèi)面有齒的鏈條，鏈輪上有共軛齒。鏈條連接采用銷子連接平鋼板，平鋼板上通常是傾角為 60176。的直齒，這是因為許多鏈條同時傳遞動力。相對于前面的滾柱鏈條來說，這種類型的鏈條噪音較低，能在較高速度下工作，同樣的寬度能傳遞更大的載荷。有時汽車就采用這種低噪音的凸輪軸驅動的鏈條。滾子鏈條提供了一種在傳動的速度和動力相對較低時，用于連接平行或非平行軸價格便宜且很靈活的方式。鏈輪含有球形或錐形凹槽的，滾子可以在凹槽內(nèi)活動，鏈條看上去像一串串鏈子一樣，用普通碳鋼、不銹鋼或實心的塑料滾子做在鏈條上，滾子鏈條用于計算機、空調、電視調諧器、百葉窗簾等場合，鏈輪可以是鋼、鍛壓或鑄造的鋅、或尼龍等。附錄B GearsGears are direct contact bodies，operating in pairs，that transmit motion and force from one rotating shaft to another, or from a shaft to a slide (rack)，by means of successively engaging projections called teeth ．Tooth profiles. The contacting surfaces of gear teeth must be aligned in such a way that the drive is positive；., the load transmitted must not depend on frictional contact．As shown in the treatment of direct contact bodies，this requires that the mon normal to the surfaces not to pass through the pivotal axis of either the driver or the follower.As it is known as direct contact bodies，cycloidal and involute profiles provide both a positive drive and a uniform velocity ratio ；i．e．，conjugate action．Basic relations．The smaller of a gear pair is called the pinion and the larger is the gear. When the pinion is on the driving shaft the pair acts as a speed reducer；When the gear drives，the pair is a speed increaser ．Gears are more frequently used to reduce speed than to increase it ．If a gear having N teeth rotates at n revolutions per minute，the product N*n has the dimension “teeth per minute”. This product must be the same for both members of a mating pair if each tooth acquires a partner from the mating gear as it passes through the region of tooth engagement．For conjugate gears of all types，the gear ratio and the speed ratio are both given by the ratio of the number of teeth on the gear to the number of teeth on the pinion．If a gear has 100 teeth and a mating pinion has 20，the ratio is l00/20=5． Thus the pinion rotates five times as fast as the gear，regardless of the speed of the gear．Their point of tangency is called the pitch point， and since it lies on the line of centers，it is the only point at which the tooth profiles have pure rolling contact ．Gears on nonparallel，nonintersecting shafts also have pitch circles，but the rollingpitchcircle concept is not valid ．Gear types are determined largely by the disposition of the shafts；in addition，certain types are better suited than others for large speed changes．This means that if a specific disposition of the shafts is required，the type of gear will more or less be fixed．On the other hand，if a required speed change demands a certain type，the shaft positions will also be fixed．Spur gears and helical gears．A gear having tooth elements that are straight and parallel to its axis is known as a spur gear．A spur pair can be used to connect parallel shafts only．If an involute spur pinion were made of rubber and twisted uniformly so that the ends rotated about the axis relative to one another，the elements of the teeth，initially straight and parallel to the axis，would bee helices．The pinion then in effect would bee a helical gear．Worm and bevel gears．In order to achieve line contact and improve the load carrying capacity of the crossed axis helical gears，the gear can be made to curve partially around the pinion，in somewhat the same way that a nut envelops a screw．The result would be a cylindrical worm and gear．Worms are also made in the shape of an hourglass, instead of cylindrical，so that they partially envelop the gear．This results in a further increase in loadcarrying capacity． Worm gears provide the simplest means of obtaining large ratios in a single pair． They are usually less efficient than parallelshaft gears ，however ，because of an additional sliding movement along the teeth ．VbeltThe rayon and rubber Vbelt are widely used for power transmission．Such belts are made in two series：the standard Vbelt and the high capacity Vbelt．The belts can be used with short center distances and are made endless so that difficulty with splicing devices is avoided．First，cost is low，and power output may be increased by operating several belts side by side．All belts in the drive should stretch at the same rate in order to keep the load equally divided among them. When one of the belts breaks, the group must usually be replaced. The drive may be inclined at any angle with tight side either top or bottom. Since belts can operate on relatively small pulleys, large reductions of speed in a single drive are possible.Second，the included angle for the belt groove is usually from 34176。to 38176。.The wedging action of the belt in the groove gives a large increase in the tractive force developed by the belt.Third，pulley may be made of cast iron, sheet steel, or diecast metal. [3]Sufficient clearance must be provided at the bottom of the groove to prevent the belt from bottoming as it bees narrower from wear. Sometimes the larger pulley is not grooved when it is possible to develop the required tractive force by running on the inner surface of the belt. The cost of cutting the grooves is thereby eliminated. Pulleys are on the market that permit an adjustment in the width of the groove. The effective pitch diameter of the pulley is thus varied, and moderate changes in the speed ratio can be secured.Chain Drives