機(jī)械論文雙語(yǔ)翻譯

1.手臂可調(diào)式捆包打結(jié)器發(fā)明背景這項(xiàng)捆繩打結(jié)器的發(fā)明和割草機(jī)有關(guān)，更特別的是為打結(jié)機(jī)器改良了手臂裝置。傳統(tǒng)的打包機(jī)、捆繩打結(jié)器包括一個(gè)可旋轉(zhuǎn)地已安裝好的鉤鐮，用來(lái)形成一個(gè)纏繞線圈。鉤鐮的一邊是一個(gè)手柄臂，這個(gè)手柄臂有一對(duì)靈敏的叉子用來(lái)接放繩子捆包。在鉤鐮的另一邊是一個(gè)和叉子固定在一起的執(zhí)長(zhǎng)刀，用來(lái)剪斷捆綁后在鉤鐮里面的線圈。一個(gè)手臂完整的形成是叉子臂和手臂線圈在鉤鐮外形成纏繞，最終放置在鉤鐮鉗口里。適當(dāng)調(diào)整和鉤鐮相關(guān)的手柄臂來(lái)實(shí)現(xiàn)打包，手柄臂必須從鉤鐮里退掉打包線圈來(lái)完成一個(gè)打包循環(huán)。手柄臂的調(diào)節(jié)主要表現(xiàn)在最初的加工制造和打包后周期性的定時(shí)維修。它的完成是通過(guò)建?；蛘哂靡环N特殊的工具進(jìn)行三個(gè)區(qū)域的手臂彎曲。通過(guò)建模，手柄臂被置于鉤鐮的跟部的中心，調(diào)整后就會(huì)出現(xiàn)清晰的鉤鐮鉗口。正式因?yàn)檫@個(gè)原因，手柄臂被定為相對(duì)嚴(yán)格不能彎曲為了可以適當(dāng)?shù)恼{(diào)整并且保持，然而適當(dāng)?shù)膹澢诳烧{(diào)節(jié)范圍內(nèi)是允許的。在近幾年來(lái)，更粗的打包繩子應(yīng)用于這種打包機(jī)來(lái)捆綁高強(qiáng)度的大包。這種改變以手柄臂在運(yùn)行過(guò)程中提供更高的強(qiáng)度為條件的，因此適當(dāng)調(diào)節(jié)來(lái)保持手柄臂就變得更難了，然而，使手柄臂的撓性更高就可以完成主要的調(diào)節(jié)。照此，這項(xiàng)發(fā)明的目標(biāo)就是提供一種打包機(jī)能夠提高手柄臂的強(qiáng)度并且可以保持手柄臂調(diào)節(jié)的精確度。這項(xiàng)發(fā)明的另一個(gè)目標(biāo)是提供一個(gè)容易并且精確調(diào)節(jié)的手柄臂給打結(jié)機(jī)。總結(jié)的發(fā)明這些和其他物體的發(fā)明是由knotter包括安裝執(zhí)長(zhǎng)刀(rotatably形成回路及雨刮器臂纏繞在其附近adjustably刮了滑動(dòng)一個(gè)麻繩安裝時(shí)形成的執(zhí)長(zhǎng)刀(回路中保留最終麻繩下顎執(zhí)長(zhǎng)刀(形成一套完整的weine打結(jié)。在一個(gè)化身,鋁槽,形成具有teereinadjustably安裝到機(jī)架和相對(duì)的執(zhí)長(zhǎng)刀(用螺絲插入通過(guò)槽和thereadably安裝的手臂。在第二個(gè)表現(xiàn)、刮雨器第一和第二部分有一起參加直角,asjustably安裝相對(duì)的手臂和對(duì)執(zhí)長(zhǎng)刀(由插入的knotter之間的shims第二部分雨刮器、手臂。想的手臂較嚴(yán)格的刮不屈以便適當(dāng)調(diào)整,還能維持足夠bendable允許初始adjustmen。同樣,最近幾年,強(qiáng)大的纏繞正被用于等5個(gè)系包密度高。這種變化的手臂,更高的力量在刮操作從而使它更難以保持手臂在適當(dāng)?shù)腶djustmen,同時(shí),使手臂足夠的靈活性,允許初始的調(diào)整。對(duì)發(fā)明的總結(jié)這項(xiàng)發(fā)明是通過(guò)打結(jié)器包括已放置好的執(zhí)長(zhǎng)刀和用來(lái)形成打包線圈的鉤鐮來(lái)完成的，一個(gè)手柄臂有一個(gè)改良后可調(diào)節(jié)的手柄，用來(lái)滑行在鉤鐮里形成線圈，當(dāng)線圈末端停留在鉤鐮鉗口里時(shí)就完成了一個(gè)打包循環(huán)。具體的一點(diǎn)是，手柄跟蹤形成纏繞，已放置的一個(gè)手柄臂的調(diào)節(jié)和鉤鐮是相關(guān)的通過(guò)在槽內(nèi)放置螺絲釘和在手柄里形成纏繞。具體額第二點(diǎn)是，手柄有主次兩部分在一個(gè)正確的角度內(nèi)結(jié)合在一起，這種調(diào)節(jié)相對(duì)于手柄和鉤鐮是通過(guò)嵌入和移動(dòng)兩部分手柄和手臂之間的薄墊片來(lái)實(shí)現(xiàn)的。1.BaletwineknotterwithadjustablewiperBackgroundoftheinventionThisinventionrelatestotwineknottersforhayorstrawbalingmachinesandmoreparticularlytoanimprovedwiperarmforsuchknotters.Inoneconventionalbaler,thetwineknotterincludesarotatablymountedbillhookforformingaloopoftwinethereabout.Ononesideofthebillhookisawiperarmwhichhasapairoffinersdefiningaforkforreceivingandguidingtwineusedtotieabale.Ononesideofthebillhookisakniferivetedtotheforkforcuttingthetwineafteraloopinthetwinehasbeenformedaroundthebillhook.Awiperisformedintegrallywiththeforkofthearmandstripsorwiperstheloopoftwineformaroundthebillhookastheseveredendofthetwineisheldinthebillhookjaw.Properadjustmentofthewiperarmrelativetothebillhookiscriticaltotheoperationofthenkotterasthewipermuststriporwipethetwineloopfromthebillhooktocompletetheformationoftheknot.Wiperarmadjustmentisperformedinitiallyatthepointofmanufactureandperiodicallythereafterwhenservicingthebaler.Itisaccomplishedbymodelingorbendingthearminthreeareaswithaspecialtool.Bymodeling,thewiperiscenteredwithrespecttotheheelofthebillhookandadjustedsotheatitjustclearsthebillhookjaw.Forthisreason,itisdesirablethatthewiperarmberelativelyrigidandunyieldingsothatproperadjustmentcanbemaintainedandyetbesufficientlybendabletopermitinitialadjustmen.Also,inrecentyears,strongertwinesarebeingusedonsuchbalerstotiebalesofhigherdensity.Suchchangessubjectthewiperarmtohigherforcesduringoperationthusmakingitmoredifficulttomaintainthearminproperadjustmen,whileatthesametime,makingthearmflexibleenoughtopermitinitialadjustment.Accordingly,itisanobjectofthisinventiontoprovideaknotterwithanimprovedwiperarmhavingastrongandrigidconstructiontomaintainanaccurateadjustmen.Anotherobjectofthisinventionistoprovideaknotterwithawiperarmwhichhasawiperwhichiseasilyandaccuratelyadjustablewithrespecttothebillhookoftheknotter.SUMMARYOFTHEINVENTIONTheseandotherobjectsoftheinventionareaccomplishedbyknottercomprisingarotatablymountedbillhookforformingaloopoftwinethereaboutandawiperarmwithanimprovedadjustablymountedwiperforslidingatwineloopformthebillhookwhilethetwineendisretainedinajawofthebillhooktocompletetheformationofaweineknot.Inoneembodiment,thewiperhasslotsformedteereinandisadjustablymountedonthearmandrelativetothebillhookbyscrewsinsertedthroughtheslotsandthereadablymountedinthearm.Inasecondembodiment,thewiperhasfirstandsecondportionsjoinedtogetheratarightangleandisasjustablymountedrelativetothearmandtothebillhookoftheknotterbytheinsertionandremovalofshimsbetweenthesecondportionofthewiperandthearm.2.齒輪和軸的介紹摘要:在傳統(tǒng)機(jī)械和現(xiàn)代機(jī)械中齒輪和軸的重要地位是不可動(dòng)搖的。齒輪和軸主要安裝在主軸箱來(lái)傳遞力的方向。通過(guò)加工制造它們可以分為許多的型號(hào)，分別用于許多的場(chǎng)合。所以我們對(duì)齒輪和軸的了解和認(rèn)識(shí)必須是多層次多方位的。關(guān)鍵詞:齒輪；軸在直齒圓柱齒輪的受力分析中，是假定各力作用在單一平面的。我們將研究作用力具有三維坐標(biāo)的齒輪。因此，在斜齒輪的情況下，其齒向是不平行于回轉(zhuǎn)軸線的。而在錐齒輪的情況中各回轉(zhuǎn)軸線互相不平行。像我們要討論的那樣，尚有其他道理需要學(xué)習(xí)，掌握。斜齒輪用于傳遞平行軸之間的運(yùn)動(dòng)。傾斜角度每個(gè)齒輪都一樣，但一個(gè)必須右旋斜齒，而另一個(gè)必須是左旋斜齒。齒的形狀是一濺開線螺旋面。如果一張被剪成平行四邊形（矩形）的紙張包圍在齒輪圓柱體上，紙上印出齒的角刃邊就變成斜線。如果我展開這張紙，在血角刃邊上的每一個(gè)點(diǎn)就發(fā)生一漸開線曲線。直齒圓柱齒輪輪齒的初始接觸處是跨過(guò)整個(gè)齒面而伸展開來(lái)的線。斜齒輪輪齒的初始接觸是一點(diǎn)，當(dāng)齒進(jìn)入更多的嚙合時(shí)，它就變成線。在直齒圓柱齒輪中，接觸是平行于回轉(zhuǎn)軸線的。在斜齒輪中，該先是跨過(guò)齒面的對(duì)角線。它是齒輪逐漸進(jìn)行嚙合并平穩(wěn)的從一個(gè)齒到另一個(gè)齒傳遞運(yùn)動(dòng)，那樣就使斜齒輪具有高速重載下平穩(wěn)傳遞運(yùn)動(dòng)的能力。斜齒輪使軸的軸承承受徑向和軸向力。當(dāng)軸向推力變的大了或由于別的原因而產(chǎn)生某些影響時(shí)，那就可以使用人字齒輪。雙斜齒輪（人字齒輪）是與反向的并排地裝在同一軸上的兩個(gè)斜齒輪等效。他們產(chǎn)生相反的軸向推力作用，這樣就消除了軸向推力。當(dāng)兩個(gè)或更多個(gè)單向齒斜齒輪被在同一軸上時(shí)，齒輪的齒向應(yīng)作選擇，以便產(chǎn)生最小的軸向推力。交錯(cuò)軸斜齒輪或螺旋齒輪，他們是軸中心線既不相交也不平行。交錯(cuò)軸斜齒輪的齒彼此之間發(fā)生點(diǎn)接觸，它隨著齒輪的磨合而變成線接觸。因此他們只能傳遞小的載荷和主要用于儀器設(shè)備中，而且肯定不能推薦在動(dòng)力傳動(dòng)中使用。交錯(cuò)軸斜齒輪與斜齒輪之間在被安裝后互相捏合之前是沒(méi)有任何區(qū)別的。它們是以同樣的方法進(jìn)行制造。一對(duì)相嚙合的交錯(cuò)軸斜齒輪通常具有同樣的齒向，即左旋主動(dòng)齒輪跟右旋從動(dòng)齒輪相嚙合。在交錯(cuò)軸斜齒設(shè)計(jì)中，當(dāng)該齒的斜角相等時(shí)所產(chǎn)生滑移速度最小。然而當(dāng)該齒的斜角不相等時(shí)，如果兩個(gè)齒輪具有相同齒向的話，大斜角齒輪應(yīng)用作主動(dòng)齒輪。蝸輪與交錯(cuò)軸斜齒輪相似。小齒輪即蝸桿具有較小的齒數(shù)，通常是一到四齒，由于它們完全纏繞在節(jié)圓柱上，因此它們被稱為螺紋齒。與其相配的齒輪叫做蝸輪，蝸輪不是真正的斜齒輪。蝸桿和蝸輪通常是用于向垂直相交軸之間的傳動(dòng)提供大的角速度減速比。蝸輪不是斜齒輪，因?yàn)槠潺X頂面做成中凹形狀以適配蝸桿曲率，目的是要形成線接觸而不是點(diǎn)接觸。然而蝸桿蝸輪傳動(dòng)機(jī)構(gòu)中存在齒間有較大滑移速度的缺點(diǎn)，正像交錯(cuò)軸斜齒輪那樣。蝸桿蝸輪機(jī)構(gòu)有單包圍和雙包圍機(jī)構(gòu)。單包圍機(jī)構(gòu)就是蝸輪包裹著蝸桿的一種機(jī)構(gòu)。當(dāng)然，如果每個(gè)構(gòu)件各自局部地包圍著對(duì)方的蝸輪機(jī)構(gòu)就是雙包圍蝸輪蝸桿機(jī)構(gòu)。著兩者之間的重要區(qū)別是，在雙包圍蝸輪組的輪齒間有面接觸，而在單包圍的蝸輪組的輪齒間有線接觸。一個(gè)裝置中的蝸桿和蝸輪正像交錯(cuò)軸斜齒輪那樣具有相同的齒向，但是其斜齒齒角的角度是極不相同的。蝸桿上的齒斜角度通常很大，而蝸輪上的則極小，因此習(xí)慣常規(guī)定蝸桿的導(dǎo)角，那就是蝸桿齒斜角的余角；也規(guī)定了蝸輪上的齒斜角，該兩角之和就等于90度的軸線交角。當(dāng)齒輪要用來(lái)傳遞相交軸之間的運(yùn)動(dòng)時(shí)，就需要某種形式的錐齒輪。雖然錐齒輪通常制造成能構(gòu)成90度軸交角，但它們也可產(chǎn)生任何角度的軸交角。輪齒可以鑄出，銑制或滾切加工。僅就滾齒而言就可達(dá)一級(jí)精度。在典型的錐齒輪安裝中，其中一個(gè)錐齒輪常常裝于支承的外側(cè)。這意味著軸的撓曲情況更加明顯而使在輪齒接觸上具有更大的影響。另外一個(gè)難題，發(fā)生在難于預(yù)示錐齒輪輪齒上的應(yīng)力，實(shí)際上是由于齒輪被加工成錐狀造成的。直齒錐齒輪易于設(shè)計(jì)且制造簡(jiǎn)單，如果他們安裝的精密而確定，在運(yùn)轉(zhuǎn)中會(huì)產(chǎn)生良好效果。然而在直齒圓柱齒輪情況下，在節(jié)線速度較高時(shí)，他們將發(fā)出噪音。在這些情況下，螺旋錐齒輪比直齒輪能產(chǎn)生平穩(wěn)的多的嚙合作用，因此碰到高速運(yùn)轉(zhuǎn)的場(chǎng)合那是很有用的。當(dāng)在汽車的各種不同用途中，有一個(gè)帶偏心軸的類似錐齒輪的機(jī)構(gòu)，那是常常所希望的。這樣的齒輪機(jī)構(gòu)叫做準(zhǔn)雙曲面齒輪機(jī)構(gòu)，因?yàn)樗鼈兊墓?jié)面是雙曲回轉(zhuǎn)面。這種齒輪之間的輪齒作用是沿著一根直線上產(chǎn)生滾動(dòng)與滑動(dòng)相結(jié)合的運(yùn)動(dòng)并和蝸輪蝸桿的輪齒作用有著更多的共同之處。軸是一種轉(zhuǎn)動(dòng)或靜止的桿件。通常有圓形橫截面。在軸上安裝像齒輪，皮帶輪，飛輪，曲柄，鏈輪和其他動(dòng)力傳遞零件。軸能夠承受彎曲，拉伸，壓縮或扭轉(zhuǎn)載荷，這些力相結(jié)合時(shí)，人們期望找到靜強(qiáng)度和疲勞強(qiáng)度作為設(shè)計(jì)的重要依據(jù)。因?yàn)閱胃S可以承受靜壓力，變應(yīng)力和交變應(yīng)力，所有的應(yīng)力作用都是同時(shí)發(fā)生的?！拜S”這個(gè)詞包含著多種含義，例如心軸和主軸。心軸也是軸，既可以旋轉(zhuǎn)也可以靜止的軸，但不承受扭轉(zhuǎn)載荷。短的轉(zhuǎn)動(dòng)軸常常被稱為主軸。當(dāng)軸的彎曲或扭轉(zhuǎn)變形必需被限制于很小的范圍內(nèi)時(shí)，其尺寸應(yīng)根據(jù)變形來(lái)確定，然后進(jìn)行應(yīng)力分析。因此，如若軸要做得有足夠的剛度以致?lián)锨惶螅敲春蠎?yīng)力符合安全要求那是完全可能的。但決不意味著設(shè)計(jì)者要保證；它們是安全的，軸幾乎總是要進(jìn)行計(jì)算的，知道它們是處在可以接受的允許的極限以內(nèi)。因之，設(shè)計(jì)者無(wú)論何時(shí)，動(dòng)力傳遞零件，如齒輪或皮帶輪都應(yīng)該設(shè)置在靠近支持軸承附近。這就減低了彎矩，因而減小變形和彎曲應(yīng)力。雖然來(lái)自M.H.G方法在設(shè)計(jì)軸中難于應(yīng)用，但它可能用來(lái)準(zhǔn)確預(yù)示實(shí)際失效。這樣，它是一個(gè)檢驗(yàn)已經(jīng)設(shè)計(jì)好了的軸的或者發(fā)現(xiàn)具體軸在運(yùn)轉(zhuǎn)中發(fā)生損壞原因的好方法。進(jìn)而有著大量的關(guān)于設(shè)計(jì)的問(wèn)題，其中由于別的考慮例如剛度考慮，尺寸已得到較好的限制。設(shè)計(jì)者去查找關(guān)于圓角尺寸、熱處理、表面光潔度和是否要進(jìn)行噴丸處理等資料，那真正的唯一的需要是實(shí)現(xiàn)所要求的壽命和可靠性。由于他們的功能相似，將離合器和制動(dòng)器一起處理。簡(jiǎn)化摩擦離合器或制動(dòng)器的動(dòng)力學(xué)表達(dá)式中，各自以角速度w1和w2運(yùn)動(dòng)的兩個(gè)轉(zhuǎn)動(dòng)慣量I1和I2，在制動(dòng)器情況下其中之一可能是零，由于接上離合器或制動(dòng)器而最終要導(dǎo)致同樣的速度。因?yàn)閮蓚€(gè)構(gòu)件開始以不同速度運(yùn)轉(zhuǎn)而使打滑發(fā)生了，并且在作用過(guò)程中能量散失，結(jié)果導(dǎo)致溫升。在分析這些裝置的性能時(shí)，我們應(yīng)注意到作用力，傳遞的扭矩，散失的能量和溫升。所傳遞的扭矩關(guān)系到作用力，摩擦系數(shù)和離合器或制動(dòng)器的幾何狀況。這是一個(gè)靜力學(xué)問(wèn)題。這個(gè)問(wèn)題將必須對(duì)每個(gè)幾何機(jī)構(gòu)形狀分別進(jìn)行研究。然而溫升與能量損失有關(guān)，研究溫升可能與制動(dòng)器或離合器的類型無(wú)關(guān)。因?yàn)閹缀涡螤畹闹匾允巧岜砻?。各種各樣的離合器和制動(dòng)器可作如下分類：1．輪緣式內(nèi)膨脹制凍塊；2．輪緣式外接觸制動(dòng)塊；3．條帶式；4．盤型或軸向式；5．圓錐型；6．混合式。分析摩擦離合器和制動(dòng)器的各種形式都應(yīng)用一般的同樣的程序，下面的步驟是必需的：1．假定或確定摩擦表面上壓力分布；2．找出最大壓力和任一點(diǎn)處壓力之間的關(guān)系；3．應(yīng)用靜平衡條件去找尋（a）作用力；（b）扭矩；(c)支反力?；旌鲜诫x合器包括幾個(gè)類型，例如強(qiáng)制接觸離合器、超載釋放保護(hù)離合器、超越離合器、磁液離合器等等。強(qiáng)制接觸離合器由一個(gè)變位桿和兩個(gè)夾爪組成。各種強(qiáng)制接觸離合器之間最大的區(qū)別與夾爪的設(shè)計(jì)有關(guān)。為了在結(jié)合過(guò)程中給變換作用予較長(zhǎng)時(shí)間周期，夾爪可以是棘輪式的，螺旋型或齒型的。有時(shí)使用許多齒或夾爪。他們可能在圓周面上加工齒，以便他們以圓柱周向配合來(lái)結(jié)合或者在配合元件的端面上加工齒來(lái)結(jié)合。雖然強(qiáng)制離合器不像摩擦接觸離合器用的那么廣泛，但它們確實(shí)有很重要的運(yùn)用。離合器需要同步操作。有些裝置例如線性驅(qū)動(dòng)裝置或電機(jī)操作螺桿驅(qū)動(dòng)器必須運(yùn)行到一定的限度然后停頓下來(lái)。為著這些用途就需要超載釋放保護(hù)離合器。這些離合器通常用彈簧加載，以使得在達(dá)到預(yù)定的力矩時(shí)釋放。當(dāng)?shù)竭_(dá)超載點(diǎn)時(shí)聽到的“喀嚓”聲就被認(rèn)定為是所希望的信號(hào)聲。超越離合器或連軸器允許機(jī)器的被動(dòng)構(gòu)件“空轉(zhuǎn)”或“超越”，因?yàn)橹鲃?dòng)驅(qū)動(dòng)件停頓了或者因?yàn)榱硪粋€(gè)動(dòng)力源使被動(dòng)構(gòu)件增加了速度。這種離合器通常使用裝在外套筒和內(nèi)軸件之間的滾子或滾珠。該內(nèi)軸件，在它的周邊加工了數(shù)個(gè)平面。驅(qū)動(dòng)作用是靠在套筒和平面之間契入的滾子來(lái)獲得。因此該離合器與具有一定數(shù)量齒的棘輪棘爪機(jī)構(gòu)等效。磁液離合器或制動(dòng)器相對(duì)來(lái)說(shuō)是一個(gè)新的發(fā)展，它們具有兩平行的磁極板。這些磁極板之間有磁粉混合物潤(rùn)滑。電磁線圈被裝入磁路中的某處。借助激勵(lì)該線圈，磁液混合物的剪切強(qiáng)度可被精確的控制。這樣從充分滑移到完全鎖住的任何狀態(tài)都可以獲得。2.GEARANDSHAFTINTRODUCTIONAbstract:Theimportantpositionofthewheelgearandshaftcan'tfalterintraditionalmachineandmodernmachines.Thewheelgearandshaftsmainlyinstallthedirectionthatdeliversthedintattheprincipalaxisbox.Thepassingtoprocesstomakethemcanisdividedintomanymodelnumbers,usedingformanysituationsrespectively.Sowemustbethemultilayerstotheunderstandingofthewheelgearandshaftinmanyways.Keywords:Wheelgear;ShaftIntheforceanalysisofspurgears,theforcesareassumedtoactinasingleplane.Weshallstudygearsinwhichtheforceshavethreedimensions.Thereasonforthis,inthecaseofhelicalgears,isthattheteetharenotparalleltotheaxisofrotation.Andinthecaseofbevelgears,therotationalaxesarenotparalleltoeachother.Therearealsootherreasons,asweshalllearn.Helicalgearsareusedtotransmitmotionbetweenparallelshafts.Thehelixangleisthesameoneachgear,butonegearmusthavearight-handhelixandtheotheraleft-handhelix.Theshapeofthetoothisaninvolutehelicoid.Ifapieceofpapercutintheshapeofaparallelogramiswrappedaroundacylinder,theangularedgeofthepaperbecomesahelix.Ifweunwindthispaper,eachpointontheangularedgegeneratesaninvolutecurve.Thesurfaceobtainedwheneverypointontheedgegeneratesaninvoluteiscalledaninvolutehelicoid.Theinitialcontactofspur-gearteethisalineextendingallthewayacrossthefaceofthetooth.Theinitialcontactofhelicalgearteethisapoint,whichchangesintoalineastheteethcomeintomoreengagement.Inspurgearsthelineofcontactisparalleltotheaxisoftherotation;inhelicalgears,thelineisdiagonalacrossthefaceofthetooth.Itisthisgradualoftheteethandthesmoothtransferofloadfromonetoothtoanother,whichgivehelicalgearstheabilitytotransmitheavyloadsathighspeeds.Helicalgearssubjecttheshaftbearingstobothradialandthrustloads.Whenthethrustloadsbecomehighorareobjectionableforotherreasons,itmaybedesirabletousedoublehelicalgears.Adoublehelicalgear(herringbone)isequivalenttotwohelicalgearsofoppositehand,mountedsidebysideonthesameshaft.Theydevelopoppositethrustreactionsandthuscanceloutthethrustload.Whentwoormoresinglehelicalgearsaremountedonthesameshaft,thehandofthegearsshouldbeselectedsoastoproducetheminimumthrustload.Crossed-helical,orspiral,gearsarethoseinwhichtheshaftcenterlinesareneitherparallelnorintersecting.Theteethofcrossed-helicalfearshavepointcontactwitheachother,whichchangestolinecontactasthegearswearin.Forthisreasontheywillcarryoutverysmallloadsandaremainlyforinstrumentalapplications,andaredefinitelynotrecommendedforuseinthetransmissionofpower.Thereisondifferencebetweenacrossedhelicalgearandahelicalgearuntiltheyaremountedinmeshwitheachother.Theyaremanufacturedinthesameway.Apairofmeshedcrossedhelicalgearsusuallyhavethesamehand;thatis,aright-handdrivergoeswitharight-handdriven.Inthedesignofcrossed-helicalgears,theminimumslidingvelocityisobtainedwhenthehelixangleareequal.However,whenthehelixanglearenotequal,thegearwiththelargerhelixangleshouldbeusedasthedriverifbothgearshavethesamehand.Wormgearsaresimilartocrossedhelicalgears.Thepinionorwormhasasmallnumberofteeth,usuallyonetofour,andsincetheycompletelywraparoundthepitchcylindertheyarecalledthreads.Itsmatinggeariscalledawormgear,whichisnotatruehelicalgear.Awormandwormgearareusedtoprovideahighangular-velocityreductionbetweennonintersectingshaftswhichareusuallyatrightangle.Thewormgearisnotahelicalgearbecauseitsfaceismadeconcavetofitthecurvatureoftheworminordertoprovidelinecontactinsteadofpointcontact.However,adisadvantageofwormgearingisthehighslidingvelocitiesacrosstheteeth,thesameaswithcrossedhelicalgears.Wormgearingareeithersingleordoubleenveloping.Asingle-envelopinggearingisoneinwhichthegearwrapsaroundorpartiallyenclosestheworm..Agearinginwhicheachelementpartiallyenclosestheotheris,ofcourse,adouble-envelopingwormgearing.Theimportantdifferencebetweenthetwoisthatareacontactexistsbetweentheteethofdouble-envelopinggearswhileonlylinecontactbetweenthoseofsingle-envelopinggears.Thewormandwormgearofasethavethesamehandofhelixasforcrossedhelicalgears,butthehelixanglesareusuallyquitedifferent.Thehelixangleonthewormisgenerallyquitelarge,andthatonthegearverysmall.Becauseofthis,itisusualtospecifytheleadangleontheworm,whichisthecomplementofthewormhelixangle,andthehelixangleonthegear;thetwoanglesareequalfora90-deg.Shaftangle.Whengearsaretobeusedtotransmitmotionbetweenintersectingshaft,someofbevelgearisrequired.Althoughbevelgearareusuallymadeforashaftangleof90deg.Theymaybeproducedforalmostanyshaftangle.Theteethmaybecast,milled,orgenerated.Onlythegeneratedteethmaybeclassedasaccurate.Inatypicalbevelgearmounting,oneofthegearisoftenmountedoutboardofthebearing.Thismeansthatshaftdeflectioncanbemorepronouncedandhaveagreatereffectonthecontactofteeth.Anotherdifficulty,whichoccursinpredictingthestressinbevel-gearteeth,isthefacttheteetharetapered.Straightbevelgearsareeasytodesignandsimpletomanufactureandgiveverygoodresultsinserviceiftheyaremountedaccuratelyandpositively.Asinthecaseofsqurgears,however,theybecomenoisyathighervaluesofthepitch-linevelocity.Inthesecasesitisoftengooddesignpracticetogotothespiralbevelgear,whichisthebevelcounterpartofthehelicalgear.Asinthecaseofhelicalgears,spiralbevelgearsgiveamuchsmoothertoothactionthanstraightbevelgears,andhenceareusefulwherehighspeedareencountered.Itisfrequentlydesirable,asinthecaseofautomotivedifferentialapplications,tohavegearingsimilartobevelgearsbutwiththeshaftoffset.Suchgearsarecalledhypoidgearsbecausetheirpitchsurfacesarehyperboloidsofrevolution.Thetoothactionbetweensuchgearsisacombinationofrollingandslidingalongastraightlineandhasmuchincommonwiththatofwormgears.Ashaftisarotatingorstationarymember,usuallyofcircularcrosssection,havingmounteduponitsuchelementsasgears,pulleys,flywheels,cranks,sprockets,andotherpower-transmissionelements.Shaftmaybesubjectedtobending,tension,compression,ortorsionalloads,actingsinglyorincombinationwithoneanother.Whentheyarecombined,onemayexpecttofindbothstaticandfatiguestrengthtobeimportantdesignconsiderations,sinceasingleshaftmaybesubjectedtostaticstresses,completelyreversed,andrepeatedstresses,allactingatthesametime.Theword“shaft”coversnumerousvariations,suchasaxlesandspindles.Anaxleisashaft,witherstationaryorrotating,norsubjectedtotorsionload.Ashirtrotatingshaftisoftencalledaspindle.Wheneitherthelateralorthetorsionaldeflectionofashaftmustbeheldtocloselimits,theshaftmustbesizedonthebasisofdeflectionbeforeanalyzingthestresses.Thereasonforthisisthat,iftheshaftismadestiffenoughsothatthedeflectionisnottoolarge,itisprobablethattheresultingstresseswillbesafe.Butbynomeansshouldthedesignerassumethattheyaresafe;itisalmostalwaysnecessarytocalculatethemsothatheknowstheyarewithinacceptablelimits.Wheneverpossible,thepower-transmissionelements,suchasgearsorpullets,shouldbelocatedclosetothesupportingbearings,Thisreducesthebendingmoment,andhencethedeflectionandbendingstress.AlthoughthevonMises-Hencky-Goodmanmethodisdifficulttouseindesignofshaft,itprobablycomesclosesttopredictingactualfailure.Thusitisagoodwayofcheckingashaftthathasalreadybeendesignedorofdiscoveringwhyaparticularshafthasfailedinservice.Furthermore,thereareaconsiderablenumberofshaft-designproblemsinwhichthedimensionareprettywelllimitedbyotherconsiderations,suchasrigidity,anditisonlynecessaryforthedesignertodiscoversomethingaboutthefilletsizes,heat-treatment,andsurfacefinishandwhetherornotshotpeeningisnecessaryinordertoachievetherequiredlifeandreliability.Becauseofthesimilarityoftheirfunctions,clutchesandbrakesaretreatedtogether.Inasimplifieddynamicrepresentationofafrictionclutch,orbrake,twoinertiasI1andI2travelingattherespectiveangularvelocitiesW1andW2,oneofwhichmaybezerointhecaseofbrake,aretobebroughttothesamespeedbyengagingtheclutchorbrake.Slippageoccursbecausethetwoelementsarerunningatdifferentspeedsandenergyisdissipatedduringactuation,resultinginatemperaturerise.Inanalyzingtheperformanceofthesedevicesweshallbeinterestedintheactuatingforce,thetorquetransmitted,theenergylossandthetemperaturerise.Thetorquetransmittedisrelatedtotheactuatingforce,thecoefficientoffriction,andthegeometryoftheclutchorbrake.Thisisprobleminstatic,whichwillhavetobestudiedseparatelyforeathgeometricconfiguration.However,temperatureriseisrelatedtoenergylossandcanbestudiedwithoutregardtothetypeofbrakeorclutchbecausethegeometryofinterestistheheat-dissipatingsurfaces.Thevarioustypesofclutchesandbrakesmaybeclassifiedasfllows:1.Rimtypewithinternallyexpandingshoes2.Rimtypewithexternallycontractingshoes3.Bandtype4.Diskoraxialtype5.Conetype6.MiscellaneoustypeTheanalysisofalltypeoffrictionclutchesandbrakesusethesamegeneralprocedure.Thefollowingsteparenecessary:1.Assumeordeterminethedistributionofpressureonthefrictionalsurfaces.2.Findarelationbetweenthemaximumpressureandthepressureatanypoint3.Applytheconditionofstaticalequilibriumtofind(a)theactuatingforce,(b)thetorque,and(c)thesupportreactions.Miscellaneouspositive-contactclutchesclutches,includeseveraltypes,sucha