【正文】 .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 DrivesT。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。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。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。鏈條連接采用銷子連接平鋼板，平鋼板上通常是傾角為 60176。當(dāng)幾個平行軸一起驅(qū)動時，滾柱鏈條傳動尤為合適。當(dāng)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(zhuǎn)動，這樣鏈條可以在鏈輪上傳動。滾柱鏈條傳動的基本組成部分有側(cè)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。今天，隨著現(xiàn)代設(shè)計(jì)和制造方法的改進(jìn)，鏈傳動越來越比原來的傳動應(yīng)用得更有效和廣泛，已經(jīng)極大地提高了農(nóng)業(yè)機(jī)械、鉆探設(shè)備、礦業(yè)和建筑機(jī)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(shè)備上。帶輪運(yùn)行一定時間后槽的寬度可以調(diào)節(jié)，這樣帶輪的節(jié)距是變化的，因此需要進(jìn)行適當(dāng)?shù)恼{(diào)整以滿足速度比的要求。在帶輪槽的底部需要留有足夠的間隙，以保證V 形帶不接觸帶輪槽的底部，因?yàn)槟菢拥脑捜菀啄p。V 形帶在槽中的嵌入作用可以大大增加 V 形帶的牽引力。其次，帶輪槽的傾斜角度通常為 34176。帶輪可以是從上到下以一個任意角度傳動的。首先，V 形帶成本低，通過并排增加V 形帶的數(shù)量可以增加傳動的功率，傳動中的所有 V 形帶被拉伸相同的長度的目的是為了保持每條 V 形帶中載荷均勻。V 形帶一般做成兩個系列：標(biāo)準(zhǔn)V 形帶和重型V 形帶。蝸輪蝸桿是用一對齒輪就可以提供較大速度比的最簡單方法，但是蝸輪蝸桿的傳動總是比平行軸傳動的齒輪效率更低，因?yàn)檠刂X面方向存在滑動現(xiàn)象。為了得到線接觸和改進(jìn)螺旋齒輪的橫向軸向的傳動載荷能力，大齒輪可能被做成彎曲形狀以圍繞小齒輪，有時類似于螺帽套在螺釘上，這樣的結(jié)果就是圓柱形的蝸輪蝸桿。如果一個漸開線直齒小齒輪是用橡皮制成的，能均勻扭曲，從而一端會繞另一端為軸進(jìn)行旋轉(zhuǎn)，這樣小齒輪上的齒開始將是直的并行于傳動軸，最后會變成螺旋形。直齒輪和螺旋齒輪。這就意味著當(dāng)軸的排列布置形式?jīng)Q定后，齒輪的類型或多或少也就定下來了。非平行的齒輪，非交叉?zhèn)鲃拥妮S也有節(jié)圓，但是不存在純滾動節(jié)圓概念。這樣不管大齒輪的旋轉(zhuǎn)速度為多少，小齒輪的旋轉(zhuǎn)速度總是大