轎車變速器設(shè)計(jì)【機(jī)械式變速器】

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中文題目：轎車變速器設(shè)計(jì) 外文題目：THE DESIGN OF PASSENGER VEHICLE TRANSSION GEARBOX 畢業(yè)設(shè)計(jì)（論文）共 40 頁(yè)（其中：外文文獻(xiàn)及譯文10頁(yè)） 圖紙共4張 完成日期 2006年6月 答辯日期 2006年6月 遼寧工程技術(shù)大學(xué)畢業(yè)設(shè)計(jì)(論文) 附錄A 含有碳氮化合物的高壓力鋼應(yīng)用于自動(dòng)傳動(dòng)齒輪的發(fā)展 Youichi Watanabe Nissan Motor Co.， Ltd.，6-1，Daikoku-cho，Tsurumi-ku，Yokohama，Japan 摘要：為了縮小和減輕自動(dòng)傳輸機(jī)構(gòu)的構(gòu)成，被安裝的齒輪必須被加強(qiáng)，以防止腐蝕斑或者/及磨損抗力。最重要的冶金學(xué)因素我們已經(jīng)知道，當(dāng)鋼鐵的溫度大約到達(dá)573K時(shí)，它的阻抗就會(huì)變小。高氮化合物是一個(gè)非常有效的措施，因?yàn)榈黾恿嘶鼗饡r(shí)的阻抗。然而，當(dāng)表面出現(xiàn)不規(guī)則形狀時(shí)，氮的含量大于0.6%的鉻鋼就會(huì)經(jīng)常被使用。為了解決這種情況，我們已經(jīng)發(fā)明了一種新的壓力鉻鋼，這種鉻鋼具有最優(yōu)的化學(xué)成分，這種成分能夠有效的抑制當(dāng)碳氮化合物的成分大于0.6%時(shí)出現(xiàn)的不規(guī)則表面。在一個(gè)設(shè)計(jì)有極好接觸疲勞沖擊力的自動(dòng)傳輸裝置中，我們完成了一次動(dòng)力傳輸系統(tǒng)的耐力測(cè)試。我們發(fā)現(xiàn)，在已經(jīng)發(fā)展的碳氮化合物的質(zhì)量達(dá)到0.9%的鋼按照慣例具有4.5個(gè)周期。 關(guān)鍵詞：碳氮化合物；氮；接觸疲勞壓力；腐蝕斑；齒輪 根據(jù)全球環(huán)境問(wèn)題和石油產(chǎn)量下降的問(wèn)題，改善汽車燃油消耗量已經(jīng)變的非常重要。因此，科學(xué)技術(shù)應(yīng)該被應(yīng)用到汽車的主要部分上。對(duì)于小型運(yùn)貨汽車，已安裝的齒輪傳動(dòng)裝置必須根據(jù)忍耐力和反抗力而被加強(qiáng)以便減少它們的尺寸和重量。最重要的冶金學(xué)良好的影響因素已經(jīng)被我們所了解去減少當(dāng)鋼鐵在573K時(shí)的軟化問(wèn)題。帶有高數(shù)量氮的碳氮化合物是一個(gè)非常有效的產(chǎn)品，因?yàn)榈脑黾涌梢栽黾踊鼗饡r(shí)的阻抗。然后，當(dāng)?shù)暮康陀?.6%時(shí)，鉻鋼就會(huì)被用于出現(xiàn)不規(guī)則的表面上。 這篇文章描述了氮的含量大大超過(guò)0.6%的碳氮高壓力鋼，以及連接有硬沖擊錘的碳氮科技產(chǎn)品。 1.影響輪齒表面壓力的因素 重要的表面因素，例如腐蝕斑和磨損，常常出現(xiàn)在自動(dòng)傳輸裝置的輪齒側(cè)表面。看上去都不能繼續(xù)保持原有的硬度和強(qiáng)度，因?yàn)樵谶\(yùn)轉(zhuǎn)過(guò)程中，輪齒的側(cè)表面的溫度會(huì)升高到大約573K。 2.碳氮化合物 美國(guó)最高的碳氮化合物的專利是在1883年申請(qǐng)的，但是直到1935年，這些產(chǎn)品才被廣泛的應(yīng)用。出現(xiàn)這種情況的原因是氮在微觀結(jié)構(gòu)和機(jī)械道具上的作用沒(méi)有被闡述清楚。這種高溫處理最初只能被應(yīng)用于廉價(jià)的鋼鐵，因?yàn)榇阈詢H僅可以通過(guò)提高氮的含量超過(guò)0.2%時(shí)提高。然而，當(dāng)加溫時(shí)氮也可以增加阻抗，這種結(jié)果可以改良表面耐久力。 機(jī)構(gòu)是形成許多機(jī)械裝置的基本幾何結(jié)構(gòu)單元，這些機(jī)械裝置包括自動(dòng)包裝機(jī)，打印機(jī)，機(jī)械玩具，紡織機(jī)械和其他機(jī)械等。典型的機(jī)構(gòu)要設(shè)計(jì)成使剛體構(gòu)件相對(duì)基準(zhǔn)構(gòu)件產(chǎn)生所希望的運(yùn)動(dòng)，機(jī)構(gòu)的運(yùn)動(dòng)設(shè)計(jì)即運(yùn)動(dòng)的綜合，把第一步常常是先設(shè)計(jì)整部機(jī)器。當(dāng)考慮受力時(shí)，要提出動(dòng)力學(xué)方面的問(wèn)題，軸承的載荷，應(yīng)力，潤(rùn)滑等類似的問(wèn)題，而較大的問(wèn)題是機(jī)器結(jié)構(gòu)問(wèn)題。 齒輪是借助于輪齒成功嚙合來(lái)傳遞運(yùn)動(dòng)的機(jī)器零件，齒輪從一根回轉(zhuǎn)軸到另一回轉(zhuǎn)軸傳遞運(yùn)動(dòng)或傳遞運(yùn)動(dòng)到一傳動(dòng)齒條。多數(shù)應(yīng)用中都以恒定角速比（或常定扭矩比）而存在。恒定角速比應(yīng)用中必定是軸向傳動(dòng)。在各種各樣有用的齒輪類型基礎(chǔ)上，輸入軸和輸出軸需要在一直線上或需要互相平行都不受什么限制。由于使用非圓齒輪，非線性角度比也是很有用的。為了保持恒定的角速度，各個(gè)齒輪齒廓必須服從齒輪嚙合的基本規(guī)律：為了一對(duì)齒能傳遞恒定角速比，他們接觸齒廓的形狀必須是要這樣：公法線通過(guò)兩齒輪中心連線上的固定點(diǎn)。 滿足嚙合基本規(guī)律的兩嚙合齒廓被稱為共軛齒廓。盡管有著許多滿足相嚙合齒的可能齒形 能被設(shè)計(jì)出來(lái)，以滿足基本嚙合規(guī)律。但一般僅有兩種在使用：擺線齒廓和漸開(kāi)線齒廓。漸開(kāi)線具有若干重要的優(yōu)點(diǎn)：它易于加工制造和一對(duì)漸開(kāi)線齒輪之間的中心距可以變化而不改變速比，當(dāng)使用漸開(kāi)線齒廓時(shí)，可不要求精度的軸間公差。 有幾種標(biāo)準(zhǔn)齒輪可供選用。為了在平行軸條件下應(yīng)用，通常使用直齒圓柱齒輪，平行軸斜齒輪或人字齒齒輪。在相交軸的情況下使用直齒錐齒輪或螺旋齒輪。對(duì)于非相交軸和非平行軸齒輪傳動(dòng)，交錯(cuò)軸螺旋齒輪，蝸桿蝸輪，端面齒輪，斜齒圓錐齒輪或準(zhǔn)雙曲面齒輪將被選用。對(duì)于直齒圓柱齒輪，相嚙合齒輪的節(jié)圓是彼此相切的。他們互相滾動(dòng)而無(wú)滑動(dòng)，齒頂高是輪齒伸出超過(guò)節(jié)圓的高度（也是節(jié)圓和齒頂圓之間在徑向的距離）。頂隙是一個(gè)給定齒的齒根高（在節(jié)圓以下的齒高）大于與它相嚙合的齒輪的齒頂高的量（差值）。齒厚是沿著節(jié)圓圓弧上跨齒的距離，而齒間距（齒槽S）是沿著節(jié)圓圓弧上相鄰兩齒間的空間距離。而齒側(cè)間隙是在節(jié)圓上的齒槽寬度大于其相嚙合齒輪在節(jié)圓上的齒厚的差值。 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)必須是右旋斜齒，而另一個(gè)必須是是左旋斜齒，齒的形狀是一漸開(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，紙上印粗齒的角刃邊就變成斜線，如果我展開(kāi)這張紙，在斜角刃邊上的每一個(gè)點(diǎn)微發(fā)生一漸開(kāi)曲線。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。在斜齒輪中，該線是跨過(guò)齒面的對(duì)角線。它是輪齒逐漸進(jìn)行嚙合并平穩(wěn)地從一個(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)軸向推力變得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)或更多的單向齒斜齒輪被裝在同一軸上時(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，他們的軸中心線既不相交也不平行，交錯(cuò)軸斜齒輪的辭彼此之間發(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嚙合之前是沒(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)軸卸齒輪設(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)齒輪具有相同的齒向的話，大斜角齒輪應(yīng)該用作主動(dòng)齒輪。 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，通常設(shè)計(jì)使用螺旋錐齒輪，實(shí)踐證明是切實(shí)可行的，那是和配對(duì)斜齒輪很相似的配對(duì)錐齒輪，當(dāng)在斜齒輪情況下，螺旋錐齒輪比直齒輪能產(chǎn)生平穩(wěn)得多的嚙合作用，因此碰到高速運(yùn)轉(zhuǎn)的場(chǎng)合那時(shí)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)樗麄兊墓?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)相組合的運(yùn)動(dòng)并和蝸輪蝸桿的輪齒作用有著更多的共同之處。 軸是一轉(zhuǎn)動(dòng)或靜止桿件。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可以承受靜應(yīng)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。 短的轉(zhuǎn)動(dòng)軸常常被稱為主軸。當(dāng)軸的彎曲或扭轉(zhuǎn)變形必須被限制于很小范圍內(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，如果軸做得有足夠的剛度以致?lián)锨惶?，那么合?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)置在靠近支撐軸承附近，這就減低了彎矩，因而減小變形和彎曲應(yīng)力。 3.結(jié)束語(yǔ) 我們已經(jīng)發(fā)展了高壓力鋼，這種鋼在碳氮化合物的作用下，已經(jīng)得到了很大程度的提高。這種技術(shù)在改良表面壓力上有了很大的改善。至此以后，例如環(huán)形恒壓變壓器的新的傳輸系統(tǒng)就可以通過(guò)增加自身的重量和大小而增加它們的容量。為了適應(yīng)這種需求，它們的滑輪和動(dòng)力滾筒必須被改善，以適應(yīng)接觸疲勞強(qiáng)度、磨損和腐蝕。 我們相信，使用了新的碳氮加工方法和發(fā)展高壓力鋼最優(yōu)過(guò)程，將有助于改善機(jī)械自動(dòng)傳輸，最終驅(qū)動(dòng)系統(tǒng)和CVT系統(tǒng)的可靠性，減少它們的重量，大小和制造成本。 參考 [1] T.B. Massalski. Et al.， Binary Alloy Phase Diagrams， second ed.， 2. ASM International， p. 1792. [2] M. Yoshida， et al.， A study on the pitting Fatigue Strength of Carburized Gears (in Japanese with English summary)， JSAE， Vol. 27， No. 2， pp. 125-130 (1996). [3] Y. Watanabe， et al.， Effect of Nitrogen Content on Microstructure and Resistance to Softening during Tempering of Carbonitrided Chromium Alloy Steels (in Japanese with English summary)， NETSU SHORI， Vol. 40， No. l，pp. 18-24(2000). [4] D.P. Koistinen and R.E. Marburger， A General Equation Prescribing the Extent of the Austenite-Martensite Transformation in Pure Iron-Carbon Alloys and Plain Carbon Steels， Acta Met.， Vol. 7， pp. 59-60 (1959). [5] Y. Watanabe， et al.， Effects of Shot Peening on Resistance to Softening during Tempering and Contact Fatigue Strength of Carburized and Carbonitrided JIS SQ420H Steels (in Japanese with English summary)， TETSU-TO-HAGANE， Vol. 84， No. 12， pp. 66-73 (1998). 附錄B Development of High Strength Steel Designed for Carbonitriding with High Nitrogen Content to Be Used for Automatic Transmission Gears Youichi Watanabe Nissan Motor Co.， Ltd.， 6-1， Dalkoku-cho， Tsurumi-ku， Yokohama， Japan Abstract： To downsize and lighten automatic transmission components， the gears installed must be strengthened in terms of pitting endurance and/or wear resistance. The most important metallurgical factor affecting fractures is well known to be resistance to softening when steel is tempered at approximately 573 K. Carbonitriding with a high amount of nitrogen is a very effective production technique because nitrogen increases the resistance during tempering. However， structural anomalies begin to appear in the surface layer when the nitrogen content exceeds 0.6 mass% in the chromium steel generally used. To address this， we have developed new high-strength chromium steel with an optimized chemical composition that effectively inhibits anomalies even when Carbonitriding with a nitrogen content of more than 0.6 mass%. We performed a drivetrain durability test on an automatic transmission component designed to have excellent contact fatigue strength and a tooth root bending impact and fatigue strength. We found that the developed steel that was carbonitrided with a content of about 0.9 mass%， and then shot peened hard， has a pitting life of roughly 4.5 times that of conventionally manufactured steel. Key words： Carbonitriding， Nitrogen， Shot peening， Contact fatigue strength， Pitting， Gear IMPROVING the fuel consumption of automobiles is becoming ever more important in response to global environmental problems and declining oil production. Therefore， technical work needs to be performed to lighten automobile bodies. To downsize and lighten automatic transmission components， the gears installed must be strengthened in terms of pitting endurance and/or wear resistance so as to reduce their size and weight. The most important metallurgical factor affecting fractures is well known to be resistance to softening when steel is tempered at approximately 573 K. Carbonitriding with a high amount of nitrogen is a very effective production technique because nitrogen increases the resistance during tempering. However， when the nitrogen content exceeds 0.6 mass%， structural anomalies begin to appear in the surface layer of the chromium steel generally used. This paper describes high strength steel designed for Carbonitriding with high nitrogen content greater than 0.6 mass%， and a new Carbonitriding production technology combined with hard shot peening. 1. Factors Affecting the Surface Strength of Gear Teeth Significant surface fractures， such as pitting and wear， occur frequently on the flank surface of gear teeth in automatic transmissions. Whether it has been shot peened or not， the surface layer of a conventional carburized gear seems unable to maintain virgin high surface hardness and strength because the tooth flank surface temperature rises to approximately 573 K during operation. 2. Carbonitriding The U.S. patents on Carbonitriding were initially applied for in 1883， but it is only since 1935 that these production technologies began to be put to practical use. The reason for this was that the effects of nitrogen on microstructures and mechanical properties had not yet been clarified. This heat treatment was originally applied only to low-cost steels， that is， steels with low hardenability such as plain carbon steel， because the hardenability could only be improved by using a small amount of nitrogen up to about 0.2 %. However， nitrogen also has the effect of increasing the resistance to softening during tempering， which results in improved durability to pitting. Mechanisms form thee basic geometrical element of many mechanical devices including automatic machinery，typewriters，mechanical toys，textile machinery，and others.A mechanism typically is designed to create a desied motion of a rigid body relative to a reference member.Kinematic design，or kinematic syntheses，of mechaaanisms often is the first step in the design of a complete machine.When forces are considered，the additional problems of dynamics，bearing loads，stresses，lubrication，and the like are introduced，aad the larger problem become one of machine design. Gear are machine elements that transmit motion by means of successively engaging teeth，Gears transmit motion from one ratating shaft to another，or to a rack that translates.Numerous applications exist in which a constant angular velocity ratio(or constant torque ratio)must be transmitted between shafts，Based on the variety of gear types available，there is no restriction that the input and the output shafts need be either in-line or parallel.Nonlinear angular velocity tratios are also available by using noncircccuar gear，In order to maintain a constant angular velocity，the individual tooth prifle must obey the fundamental law of gearing：for a pair of gears to transmit a constant angular velocity ratio，the shape of their contacting profiles must be such that the common normal passes through a fixed point on the lineof the centers. Any two mating tooth profiles that satisfy the fundamental law of gearinig are called conjugate profiles，Although there re may tooth sshapes possible in which a maring tooth could be designed to satisfy the fundamental law，only two are in genetal use;the cycloidal and involute profiles.The involute has important advantages;it is easy to manufacture and the center distance berween a pair o involute gears can be varied without changing the velocity ratio，Thus close tolerances between shafts are not required when utilizing the involute profile. There are several standard gear types.For applications with parallel shafts，straight spur gear，parallel helical，or herringbone gears are usually ued，In the case of intersecting shafts，straight bevel or spiral bevel gears are employed.For nonintersecting and nonparallel shafts，crossed helical，worm，face，skew bevel or hypoid gears would be acceptable choices.For spur gears，the pirch circles of mating gears are tangent to wach other.They roll on one another without sliding.The addendum is the height by which a tooth projects beyond the pitch circle(also the tadial distance between the pitch circle and the addendum circle).The clearance is the amount by which the dedendum (tooth height below the pitch circle)in a given gear exceeds the addendum of its mating gear，The tooth thickness is the distance across the tooth along the are of the pitch circle while the tooth space is the distance between adjacent teeth along the are of the pitch circle.The backlash is the amount by which the width of the tooth space exceeds the thickness of the engaging tooth at the pitchi circle. Helical gears are used to transmit motion between parallel shafts.The helix angle I 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 the angular edge of the paper becomes a helix.If we unwind this paper，eachpoint on the angular edge genetares an involute curve，The surface obtained when every point on the edge generates an involute is called an involute helicoids.in helical gears，the line is diagonal across the face of the tooth，It is this gradual engagement of the teeth and the smooth transfer of load from one tooth to another，which give helical gears the ability to transmit heavy loads at high soeeds，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 double helical gears.A double helical gear(herringbone)is equivalent to two helical gears of opposite hand，mounted side by side on he same shaft.They develop opposite thrust reactions and thus cancel at the thrust load.when two or more single helcal gears are mounted on the same shaft，the 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 not interecting.The teeth of crossed-helical gears have point contact with each other，which changs to line contact as the 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 thee transimission of power.There is no difference between a crossed helical gear and a helical gear until the are mounted in mesh with each other.They are manufactured in the same way.A pair of meshed crossed helical gears usually have the ame hand;that is ，a right-hand driver goes with a right-hand driven.In the desin of crossed-helical gears，the minimum sliding velocity is obtained when the helix angle are equal.However，when the helix angle are not equal，the gear with the lrger helix angle should be used a the driver if both gears 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 cylinder they are called threads.Its mating gear is called a worm gear，which is not a true helical gear.Aworm and worm gear are used to provide a high angular-velocity reduction berween nonintertsecting shafts which are usually at tight angle.The worm gear is not a helical gear because its face is made concave to fit the curvarure of the worm in order to provide line contact instead of point contact.However，a disadvangtage of worm gearing I the high sliding velocities across the teeth，the same as with crossed hlical gears.Worm gearing are either single-or double-enveloping.A single-enveloping geating is one in which the gear wtaps a found to 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-enveloping gears while only line contact between those of single-enveloping gears.The worm and worm gear a set have the same hand of helix as for crossed helical gears，but the helix angles are usually quete different，The helx angle on the worm is generally quite large，and that on the gear very small.Because of this ，it is usual to specify the lead angle on the worm.which is the compliment of the worm helix angle，and the helix angle on the gear;the two angles are equal for a 90-deg.shaft angle. A shaft is a rotating or stationary member.usually of circular cross section，having mounted upon it such elementsa gears，pilleys，flywheels，cranks，sprockets，and other power-transmissionlements.Shafmay subjected to bending，tension，compression，or torsional loads，acting singly or in combination with one 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 too static stresses，completely reversed，and repeated stresses，aii acting at the same time. The word”shaft”cover numerous variationgs，such as axles and spindles.An axle is a shaft，either stationary or rotating，not subjected to torsion load.A short rotating shaft is often called a spindle. 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 calculate them so that he knows they are within acceptable limits.Whenever possible，the power-transmission elements，such as gears or pulleys ，should be located close to the supporting bearings.This reduces the bending moment，and hence the deflection and bending stress. 3. Concluding Remarks We have developed high-strength steel that further enhances the effect of a new production technique， carbonitriding with high nitrogen content. This technique makes the best use of nitrogen following hard shot peening. Henceforth， new transmission systems such as belt- or toroidal-CVTs (continuously variable transmissions) will also need to have their capacity increased and/or weight and size minimized. To accommodate these needs， their pulleys， output discs and power rollers should have improved contact fatigue strength in terms of resisting pitting， wear， and flaking. We are confident that using the new carbonitriding process， and the developed high strength steel optimized for that process， will contribute to further improving automatic transmissions， final drive systems， and CVTs by improving their reliability and reducing their weight， size， and manufacturing costs. References： [1] T.B. Massalski. Et al.， Binary Alloy Phase Diagrams， second ed.， 2. ASM International， p. 1792. [2] M. Yoshida， et al.， A study on the pitting Fatigue Strength of Carburized Gears (in Japanese with English summary)， JSAE， Vol. 27， No. 2， pp. 125-130 (1996). [3] Y. Watanabe， et al.， Effect of Nitrogen Content on Microstructure and Resistance to Softening during Tempering of Carbonitrided Chromium Alloy Steels (in Japanese with English summary)， NETSU SHORI， Vol. 40， No. l，pp. 18-24(2000). [4] D.P. Koistinen and R.E. Marburger， A General Equation Prescribing the Extent of the Austenite-Martensite Transformation in Pure Iron-Carbon Alloys and Plain Carbon Steels， Acta Met.， Vol. 7， pp. 59-60 (1959). [5] Y. Watanabe， et al.， Effects of Shot Peening on Resistance to Softening during Tempering and Contact Fatigue Strength of Carburized and Carbonitrided JIS SQ420H Steels (in Japanese with English summary)， TETSU-TO-HAGANE， Vol. 84， No. 12， pp. 66-73 (1998). 10