機(jī)械論文雙語(yǔ)翻譯(共8頁(yè))

1、1.手臂(shu b)可調(diào)式捆包打結(jié)器發(fā)明(fmng)背景這項(xiàng)捆繩打結(jié)器的發(fā)明(fmng)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

2、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)

3、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 teerein adjustably 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

4、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) 的 adjustmen,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

5、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.Bale twine knotter with adjustable wiperBackground of the inventionThis invention relates to twine knotters for hay or straw baling machines and more particularly to an improved wiper arm for such knotters. In

6、one conventional baler, the twine knotter includes a rotatably mounted billhook for forming a loop of twine thereabout. On one side of the billhook is a wiper arm which has a pair of finers defining a fork for receiving and guiding twine used to tie a bale. On one side of the billhook is a knife riv

7、eted to the fork for cutting the twine after a loop in the twine has been formed around the billhook. A wiper is formed integrally with the fork of the arm and strips or wipers the loop of twine form around the billhook as the severed end of the twine is held in the billhook jaw. Proper adjustment o

8、f the wiper arm relative to the billhook is critical to the operation of the nkotter as the wiper must strip or wipe the twine loop from the billhook to complete the formation of the knot. Wiper arm adjustment is performed initially at the point of manufacture and periodically thereafter when servic

9、ing the baler. It is accomplished by modeling or bending the arm in three areas with a special tool. By modeling, the wiper is centered with respect to the heel of the billhook and adjusted so theat it just clears the billhook jaw. For this reason, it is desirable that the wiper arm be relatively ri

10、gid and unyielding so that proper adjustment can be maintained and yet be sufficiently bendable to permit initial adjustmen. Also, in recent years , stronger twines are being used on such balers to tie bales of higher density. Such changes subject the wiper arm to higher forces during operation thus

11、 making it more difficult to maintain the arm in proper adjustmen, while at the same time, making the arm flexible enough to permit initial adjustment. Accordingly, it is an object of this invention to provide a knotter with an improved wiper arm having a strong and rigid construction tomaintain an

12、accurate adjustmen. Another object of this invention is to provide a knotter with a wiper arm which has a wiper which is easily and accurately adjustable with respect to the billhook of the knotter.SUMMARY OF THE INVENTIONThese and other objects of the invention are accomplished by knotter comprisin

13、g a rotatably mounted billhook for forming a loop of twine thereabout and a wiper arm with an improved adjustably mounted wiper for sliding a twine loop form the billhook while the twine end is retained in a jaw of the billhook to complete the formation of a weine knot. In one embodiment, the wiper

14、has slots formed teerein and is adjustably mounted on the arm and relative to the billhook by screws inserted through the slots and thereadably mounted in the arm. In a second embodiment, the wiper has first and second portions joined together at a right angle and is asjustably mounted relative to t

15、he arm and to the billhook of the knotter by the insertion and removal of shims between the second portion of the wiper and the arm.2.齒輪(chln)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(dwi)是不可動(dòng)搖的。齒輪和軸主要安裝(nzhung)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

16、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(kāi)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(kāi)這張紙，在血角刃邊上的每一個(gè)點(diǎn)就發(fā)生一漸開(kāi)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(kāi)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

17、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

18、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(hu y)速度最小。 然而(rn r)當(dāng)該齒的斜角不相等時(shí)， 如果兩個(gè)(lin )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)

19、圓柱上， 因此它們被稱(chēng)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

20、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，

21、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(chē)的各種不同用途中，有一個(gè)帶偏心軸的 類(lèi)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

22、輪(chln)，皮帶 輪，飛輪，曲柄，鏈輪和其他動(dòng)力傳遞(chund)零件。軸能夠承受彎曲，拉伸，壓縮或扭 轉(zhuǎn)載荷(zi h)， 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。 “軸”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(chēng)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?那么合應(yīng)力符合安全要求那是完全可能的。但決不意味著設(shè)

23、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?xún)?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

24、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(kāi)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(lèi) 型無(wú)關(guān)。

25、 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(lèi)：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(pán)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。 混合式離合器包括幾個(gè)類(lèi)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

26、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(tīng)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)

27、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(t men)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(rnhu)。電磁線圈被裝入磁路中的某處。借助激勵(lì)該 線圈(xinqun)， 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.GEAR AND SHAFT INTRODUCTIONAbstract:

28、 The important position of the wheel gear and shaft cant falterin traditional machine and modern machines.The wheel gear and shafts mainly install the direction that delivers the dint at the principal axis box.The passing to process to make them can is divided into many model numbers, useding for ma

29、ny situations respectively.So we must be the multilayers to the understanding of the wheel gear and shaft in many ways .Key words: Wheel gear;ShaftIn the force analysis of spur gears, the forces are assumed to act in a single plane. We shall study gears in which the forces have three dimensions. The

30、 reason for this, in the case of helical gears, is that the teeth are not parallel to the axis of rotation. And in the case of bevel gears, the rotational axes are not parallel to each other. There are also other reasons, as we shall learn. Helical gears are used to transmit motion between parallel

31、shafts. The helix angleis the same on each gear, but one gear must have a right-hand helix and the other a left-hand helix. The shape of the tooth is an involute helicoid. If a piece of paper cut in the shape of a parallelogram is wrapped around a cylinder, the angular edge of the paper becomes a he

32、lix. If we unwind this paper, each point on the angular edge generates an involute curve. The surface obtained when every point on theedge generates an involute is called an involute helicoid. The initial contact of spur-gear teeth is a line extending all the way across the face of the tooth. The in

33、itial contact of helical gear teeth is a point, which changes into a line as the teeth come into more engagement. In spur gears the line of contact is parallel to the axis of the rotation; in helical gears, the line is diagonal across the face of the tooth. It is this gradual of the teeth and the sm

34、ooth transfer of load from one tooth to another, which give helical gears the ability to transmit heavy loads at high speeds. Helical gears subject the shaft bearings to both radial and thrust loads. When the thrust loads become high or are objectionable for other reasons, it may be desirable to use

35、 double helical gears. A double helical gear (herringbone) is equivalent to two helical gears of opposite hand, mounted side by side on the same shaft. They develop opposite thrust reactions and thus cancel out the thrust load. When two or more single helical gears are mounted on the same shaft, the

36、 hand of the gears should be selected so as to produce the minimum thrust load. Crossed-helical, or spiral, gears are those in which the shaft centerlines are neither parallel nor intersecting. The teeth of crossed-helical fears have point contact with each other, which changes to line contact as th

37、e gears wear in. For this reason they will carry out very small loads and are mainly for instrumental applications, and are definitely not recommended for use in the transmission of power. There is on difference between a crossed helical gear and a helical gear until they are mounted in mesh with ea

38、ch other. They are manufactured in the same way. A pair of meshed crossed helical gears usually have the same hand; that is ,a right-hand driver goes with a right-hand driven. In the design of crossed-helical gears, the minimum sliding velocity is obtained when the helix angle are equal. However, wh

39、en the helix angle are not equal, the gear with the larger helix angle should be used as the driver if bothgears have the same hand. Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap around the pitch c

40、ylinder they are called threads. Its mating gear is called a worm gear, which is not a true helical gear. A worm and worm gear are used to provide a high angular-velocity reduction between nonintersecting shafts which are usually at right angle. The worm gear is not a helical gear because its face i

41、s made concave to fit the curvature of the worm in order to provide line contact instead of point contact. However, a disadvantage of worm gearing is the high sliding velocities across the teeth, the same as with crossed helical gears. Worm gearing are either single or double enveloping. Asingle-env

42、eloping gearing is one in which the gear wraps around or partially encloses the worm. A gearing in which each element partially encloses the other is, of course, a double-enveloping worm gearing. The important difference between the two is that area contact exists between the teeth of double-envelop

43、ing gears while only line contact between those of single-enveloping gears. The worm and worm gear of a set have the same hand of helix as for crossed helical gears, but the helix angles are usually quite different. The helix angle on the worm is generally quite large, and that on the gear very smal

44、l. Because of this, it is usual to specify the lead angle on the worm, which is the complement of the worm helix angle, and the helix angle on the gear; the two angles are equal for a 90-deg. Shaft angle. When gears are to be used to transmit motion between intersecting shaft, some of bevel gear is

45、required. Although bevel gear are usually made for a shaft angle of 90 deg. They may be produced for almost any shaft angle. The teeth may be cast, milled, or generated. Only the generated teeth may be classed as accurate. In a typical bevel gear mounting, one of the gearis often mounted outboard of

46、 the bearing. This means that shaft deflection can be more pronounced and have a greater effect on the contact of teeth. Another difficulty, which occurs in predicting the stress in bevel-gear teeth, is the fact the teeth are tapered. Straight bevel gears are easy to design and simple to manufacture

47、 and give very good results in service if they are mounted accurately and positively. As in the case of squr gears, however, they become noisy at higher values of the pitch-line velocity. In these cases it is often good design practice to go to the spiral bevel gear, which is the bevel counterpart o

48、f the helical gear. As in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, and hence are useful where high speed are encountered. It is frequently desirable, as in the case of automotive differential applications, to have gearing similar to b

49、evel gears but with the shaft offset. Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution. The tooth action between such gears is a combination of rolling and sliding along a straight line and has much in common with that of worm gears. A shaft is a rotatin

50、g or stationary member, usually of circular cross section, having mounted upon it such elementsas gears, pulleys, flywheels, cranks, sprockets, and other power-transmission elements. Shaft may be subjected to bending, tension, compression, or torsional loads, acting singly or in combination with one

51、 another. When they are combined, one may expect to find both static and fatigue strength to be important design considerations, since a single shaft may be subjected to static stresses, completely reversed, and repeated stresses, all acting at the same time. The word “shaft” covers numerous variati

52、ons, such as axles and spindles. Anaxle is a shaft, wither stationary or rotating, nor subjected to torsion load. A shirt rotating shaft is often called a spindle.When either the lateral or the torsional deflection of a shaft must be held to close limits, the shaft must be sized on the basis of defl

53、ection before analyzing the stresses. The reason for this is that, if the shaft is made stiff enough so that the deflection is not too large, it is probable that the resulting stresses will be safe. But by no means should the designer assume that they are safe; it is almost always necessary to calcu

54、late them so that he knows they are within acceptable limits. Whenever possible, the power-transmission elements, such as gears or pullets, should be located close to the supporting bearings, This reduces the bending moment, and hence the deflection and bending stress. Although the von Mises-Hencky-

55、Goodman method is difficult to use in design of shaft, it probably comes closest to predicting actual failure. Thus it is a good way of checking a shaft that has already been designed or of discovering why a particular shaft has failed in service. Furthermore, there are a considerable number of shaf

56、t-design problems in which the dimension are pretty well limited by other considerations, such as rigidity, and it is only necessary for the designer to discover something about the fillet sizes, heat-treatment, and surface finish and whether or not shot peening is necessary in order to achieve the

57、required life and reliability. Because of the similarity of their functions, clutches and brakes are treated together. In a simplified dynamic representation of a friction clutch, or brake, two inertias I1 and I2 traveling at the respective angular velocities W1 and W2, one of which may be zero in t

58、he case of brake, are to be brought to the same speed by engaging the clutch or brake. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in a temperature rise. In analyzing the performance of these devices we shall be intere

59、sted in the actuating force, the torque transmitted, the energy loss and thetemperature rise. The torque transmitted is related to the actuating force, the coefficient of friction, and the geometry of the clutch or brake. This is problem in static, which will have to be studied separately for eath g

60、eometric configuration. However, temperature rise is related to energy loss and can be studied without regard to the type of brake or clutch because the geometry of interest is the heat-dissipating surfaces. The various types of clutches and brakes may be classified as fllows: 1. Rim type with inter