ZY1160貨車底盤總體及懸架設(shè)計(jì)【含CAD圖紙+文檔】

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機(jī)電工程學(xué)院 畢業(yè)設(shè)計(jì)外文資料翻譯 設(shè)計(jì)題目: ZY1160貨車底盤總體及懸架設(shè)計(jì) 譯文題目: 汽車工程學(xué)：汽車縱向動(dòng)力學(xué) 學(xué)生姓名： 學(xué) 號(hào)： 專業(yè)班級(jí)： 指導(dǎo)教師： 正文：外文資料譯文 附 件：外文資料原文 指導(dǎo)教師評(píng)語： 簽名： 年 月 日 正文：（選自《汽車工程學(xué)：汽車縱向動(dòng)力學(xué)》P123--132） 變速器 圖3-67顯示雙速行星齒輪作為后置組的二軸傳動(dòng)。 圖3-67 9速商用車變速器裝雙速行星齒輪的后部安裝組 在三軸傳動(dòng)中，16個(gè)不同的齒輪可以以相對(duì)較低的生產(chǎn)費(fèi)用從四級(jí)的變速器中獲得主傳動(dòng)。圖3-68是一個(gè)有16個(gè)齒輪的例子。圖3-69所描繪的是三軸變速器換檔圖。 分流部分 四齒輪零件與反向齒輪 范圍組 商用車的三組傳動(dòng) 齒輪 圖 3-69 三組傳動(dòng)的設(shè)計(jì)與功率 導(dǎo)閥位置 后置組 主要組 前置組 3.4.2機(jī)械無級(jí)變速器 在對(duì)比了目前使用的機(jī)械傳動(dòng)的汽車。機(jī)械無級(jí)變速器,也被稱為無級(jí)變速器，根據(jù)它們的原理，其具有一定的優(yōu)勢(shì)。功率特性如圖3- 70所示?；谶B續(xù)變量的轉(zhuǎn)矩轉(zhuǎn)換，達(dá)到的功率曲線（圖3-70b）代表轉(zhuǎn)換器的性能。其調(diào)整到不同的驅(qū)動(dòng)條件，可以達(dá)到傳動(dòng)區(qū)域（圖3-70c），該無級(jí)變速器只要求滿足發(fā)動(dòng)機(jī)特性曲線（圖3-70a）。除了起始區(qū)，這需要額外的離合器（要有足夠的傳動(dòng)比），其全部需求可以以 [3-33] 的方式所呈現(xiàn)。 轉(zhuǎn)換范圍 離合器范圍（起動(dòng)） 無級(jí)變速器轉(zhuǎn)換特性 變壓器輸出的曲線 變壓器特性曲線 發(fā)動(dòng)機(jī)特性曲線 變壓器輸出速度 變壓器輸出轉(zhuǎn)矩 速度比 發(fā)動(dòng)機(jī)轉(zhuǎn)速 轉(zhuǎn)矩比 發(fā)動(dòng)機(jī)扭矩 由于無級(jí)變速器允許自由選擇發(fā)動(dòng)機(jī)參數(shù)（扭矩和轉(zhuǎn)速），內(nèi)燃機(jī)的操作可以基于不同的標(biāo)準(zhǔn)來優(yōu)化。當(dāng)發(fā)動(dòng)機(jī)在圖象上顯示整個(gè)發(fā)動(dòng)機(jī)的性能的最佳點(diǎn)，這是曲線相對(duì)于功率的參數(shù)化，也叫“控制曲線”，圖3-71顯示的優(yōu)化準(zhǔn)則的“噪音”，“燃料消耗”和“駕駛動(dòng)態(tài)”的控制線。 噪聲 轉(zhuǎn)矩 駕駛動(dòng)態(tài) 速度 不同的優(yōu)化標(biāo)準(zhǔn)的控制線 控制曲線 燃料消耗 當(dāng)只有一條控制線，使用相對(duì)簡單的機(jī)械控制傳輸操作，繪制曲線是一個(gè)很好的辦法。在這種情況下，可以實(shí)現(xiàn)控制線對(duì)應(yīng)的需求以及需求的驅(qū)動(dòng)程序。這就意味著，無級(jí)變速器可以完全被實(shí)現(xiàn)為自動(dòng)變速器。 機(jī)械無級(jí)變速器，傳動(dòng)比的變化是通過改變應(yīng)用的力的半徑來實(shí)現(xiàn)。轉(zhuǎn)矩由摩擦傳遞?；谵D(zhuǎn)矩傳動(dòng)機(jī)械無級(jí)變速器的類型可分為： 1）帶式傳動(dòng) 2）間距傳動(dòng) 3.4.2.1帶式傳動(dòng) 在帶式傳動(dòng)中，使用皮帶、帶或鏈的強(qiáng)制傳輸來實(shí)現(xiàn)，這是一套適合于磁盤輪對(duì)之間的傳動(dòng)。通過改變不同的輪上的滾動(dòng)半徑，傳輸率可以是改變的。因此，磁盤輪對(duì)的調(diào)節(jié)機(jī)制也被稱為變速器。對(duì)于力傳遞，到目前為止，不同的皮帶，帶和鏈的概念已經(jīng)提出。圖3-72顯示目前使用的動(dòng)力傳動(dòng)系統(tǒng)。 現(xiàn)代皮帶傳動(dòng)中的動(dòng)力傳動(dòng) 橡膠帶用于皮帶式變速傳動(dòng)在50年代由Van doorne，荷蘭人所發(fā)明，通過改變扭矩（210 N?m）和效率，尤其是通過改變無級(jí)變速器鋼鏈連接電流，可以使傳輸顯著提高。傳動(dòng)元件，又稱推力連桿帶，包括約三百鋼段，在兩邊的鋼帶包（帶大小0.1mm）傳到遠(yuǎn)處。 相反的推力連接帶，由PIV-Antriebe Werner Reimers KG制造的變速器，一個(gè)鏈的拉載用于傳力。單鏈連接的封裝連接到彼此的壓縮部分。在壓縮部件和盤輪的接觸區(qū)域中發(fā)生摩擦。通過設(shè)計(jì)適當(dāng)?shù)腢形金屬卡子從外部鏈條導(dǎo)引，該卡子鉤環(huán)帶金屬夾，通常用于鏈傳動(dòng)，當(dāng)鏈路開始與磁盤車輪接觸，多多少少可以通過適當(dāng)設(shè)計(jì)的鏈避免。 為了保持離心載荷在U波段盡可能低。Gates Rubber，美國人，開發(fā)了由芳綸纖維增強(qiáng)的橡膠帶的動(dòng)力系統(tǒng)。為了提高橫向承載能力，橡膠帶具有一個(gè)集成的金屬結(jié)構(gòu)。在鋼-鋼摩擦副進(jìn)行油潤滑，是沒有必要的。這考慮到一個(gè)開放的傳輸設(shè)計(jì)與較低的重量。 Kumm Industries，美國人，提出的第四個(gè)傳輸系統(tǒng)對(duì)比前帶傳輸在圖3-72所示，其中傳力元件夾在兩錐盤對(duì)之間，Kumm的無級(jí)變速器包括橡膠帶這也是由凱夫拉（蓋茨開發(fā)）和運(yùn)行在每個(gè)磁盤端螺栓進(jìn)行加固。螺栓可在螺旋形槽內(nèi)移動(dòng)。這里不需要潤滑。 3.4.2.2間距傳動(dòng) 由于汽車的發(fā)展，一次又一次進(jìn)行間距變速器的設(shè)計(jì)、制造和測試，但是沒有成功。圖3-73描繪間距傳力的一些基本形式。 變速器上的力傳遞形式 通過改變力的作用點(diǎn)，即有效的間距半徑，可以使傳動(dòng)比發(fā)生變化。除摩擦系數(shù)外，傾斜的壓力也決定了可轉(zhuǎn)換的力。 間距傳輸?shù)陌l(fā)展可以歸因于新的高摩擦潤滑油，相比傳統(tǒng)的潤滑油有近兩倍大的間距，使機(jī)構(gòu)之間進(jìn)行力傳遞。 對(duì)于機(jī)動(dòng)車輛中的應(yīng)用，使輸入和輸出軸之間的位置牢固最合適的方法，這可以使用在旋轉(zhuǎn)對(duì)稱體形式的中間鏈路來實(shí)現(xiàn) 。 3.4.3液壓無級(jí)變速器 傳輸，在該系統(tǒng)中利用不可壓縮的流體轉(zhuǎn)移，可以根據(jù)功能的類型來分類： 1）液力傳動(dòng) 2）靜液壓傳動(dòng) 3.4.3.1液力傳動(dòng) 在液力傳動(dòng)，扭矩傳遞的發(fā)生根據(jù)佛廷格原理采用兩旋轉(zhuǎn)葉片、泵和渦輪盤。與液力離合器形成對(duì)比（3.3章），液力傳動(dòng)還包括定子轉(zhuǎn)矩支撐，支撐在殼體[ 3-34 ]。 結(jié)果： MTur = MPump + MSt （ 3-51 ） MTur------水輪機(jī)輪轉(zhuǎn)矩 MPump---泵輪轉(zhuǎn)矩； MSt--------定子轉(zhuǎn)矩。 圖3-74顯示了液力傳動(dòng)（特立勞格帝亞轉(zhuǎn)換器）的結(jié)構(gòu)細(xì)節(jié)，伴隨著葉片的原理和流動(dòng)條件下nA/ nE = 0.7，這在現(xiàn)在還被使用。 泵 自由輪 定子 圓周速度 定子 出口 渦輪 入口 泵 相對(duì)速度 絕對(duì)速度 特立勞格帝亞轉(zhuǎn)換器的原理 定子 渦輪 泵 流動(dòng)方向 渦輪 工作流體，通常是油，通過泵輪相連的發(fā)動(dòng)機(jī)，然后轉(zhuǎn)移到渦輪機(jī)輪，它在其中被減慢加速。在這樣做時(shí)，它將遠(yuǎn)處的能量到傳輸輸出。另外一個(gè)重定向， 或多或少的延遲，導(dǎo)致扭矩加強(qiáng)。如果在泵和渦輪之間的速度差大，這加強(qiáng)就大。當(dāng)v = 0時(shí)，這意味著一個(gè)牢牢制動(dòng)渦輪機(jī)，所述扭矩轉(zhuǎn)化率達(dá)到其最大值。隨著渦輪轉(zhuǎn)速增加，扭矩轉(zhuǎn)換降到幾乎線性的一個(gè)1:1的扭矩比（連接點(diǎn)）。 在這個(gè)例子中，在轉(zhuǎn)速比、最佳操作點(diǎn)出現(xiàn)在約nA/ nE = 0.7，無沖擊損失。如果速度比的進(jìn)一步增加，則流體從定子流向后面直到速比約nA/ nE = 0.9（連接點(diǎn)）和定子不產(chǎn)生任何變形了，這意味著它不吸收扭矩，為了避免這種轉(zhuǎn)矩惡化，再進(jìn)一步增加速度比，定子與單向離合器變速器殼體，它可以運(yùn)行，不傳遞扭矩，速度比為上面的連接點(diǎn)。在這個(gè)區(qū)域，特立勞格帝亞轉(zhuǎn)換器作為一個(gè)離合器。 圖3-75顯示，在一個(gè)理想的方式，轉(zhuǎn)矩和效率平均速度比。 摩擦損失 損失影響 轉(zhuǎn)矩比 效率 離合器 轉(zhuǎn)換器 特立勞格帝亞轉(zhuǎn)換器的特性 速度比 此外，圖片顯示效率的粗糙特征的影響損失（流量和葉片方向之間沒有聯(lián)系）和摩擦損失（流體和壁面之間的摩擦）。 特立勞格帝亞轉(zhuǎn)換器和發(fā)動(dòng)機(jī)之間進(jìn)行如下傳動(dòng)： 在連接點(diǎn)上，在泵輪輸入的流量比是獨(dú)立在傳輸?shù)妮敵?，因?yàn)樵摱ㄗ樱@是在靜止?fàn)顟B(tài)。重要的K值[式（3-18）]，因此泵的特性曲線是不變的。在這種情況下，泵特性曲線，如果可能的話，應(yīng)位于最佳的發(fā)動(dòng)機(jī)效率的區(qū)域內(nèi)。以上的耦合點(diǎn)，當(dāng)定子和渦輪機(jī)輪作為一個(gè)“共同的”渦輪輪旋轉(zhuǎn)，同樣的原理，在液力離合器，變得適用。在那里，泵特性曲線移動(dòng)的速度比nA/nE。從圖3-76，因此我們發(fā)現(xiàn)只有圖中的一部分可以通過發(fā)動(dòng)機(jī)的扭矩和特立勞格帝亞器特性的相互作用。輸出扭矩，這顯示在圖3-76，因此產(chǎn)生。 內(nèi)燃機(jī)和特立勞格帝亞變換器之間的相互作用（來源：米奇可，“車輛動(dòng)力學(xué)”） 傳輸輸出速度 不適用區(qū)域 發(fā)動(dòng)機(jī)轉(zhuǎn)矩 效率 滿負(fù)荷 部分負(fù)荷 效率 部分負(fù)荷 滿負(fù)荷 理想的牽引力曲線 適用 轉(zhuǎn)矩比 轉(zhuǎn)速比 發(fā)動(dòng)機(jī)轉(zhuǎn)速 泵的特性曲線 發(fā)動(dòng)機(jī)全負(fù)荷特性曲線 相比于理想的轉(zhuǎn)矩特性的轉(zhuǎn)矩要求和提供的轉(zhuǎn)矩之間仍然比較大的差異。這意味著可達(dá)到的轉(zhuǎn)換區(qū)（開始轉(zhuǎn)換約2.0-2.5），并在高扭矩比低效率不足以其唯一的工作如在機(jī)動(dòng)車輛的變矩器。特立勞格帝亞轉(zhuǎn)換器與這樣的傳輸加強(qiáng)聯(lián)合。除了對(duì)需求曲線的有利途徑，這可能是這里的特立勞格帝亞變換器的優(yōu)點(diǎn)成為明顯的只有采用組合臺(tái)階變速器。其優(yōu)點(diǎn)包括緊湊，良好的散熱性超過液壓流體，自由的磨損在很大程度上，在功能作為一個(gè)扭轉(zhuǎn)振動(dòng)阻尼器。 3.4.3.2靜液壓傳動(dòng) 泵或發(fā)動(dòng)機(jī)的雙排量機(jī)器的液壓傳動(dòng)系統(tǒng)使內(nèi)燃機(jī)的轉(zhuǎn)速與負(fù)荷無關(guān)。通過將液壓機(jī)、液壓機(jī)的軸向活塞泵或發(fā)動(dòng)機(jī)的速度移動(dòng)，在任一方向上的負(fù)速度可以設(shè)置為零和最大值之間。因此，在靜液傳動(dòng)裝置，既不啟動(dòng)離合器也沒有離合器齒輪集所需的向后駕駛。具有這種特性的變速器稱為IVT（無級(jí)變速器）。圖3-77顯示了這種傳動(dòng)的轉(zhuǎn)換特性。它基本上相當(dāng)于以前的機(jī)械式無級(jí)變速器[ 35 ]原理。 無級(jí)變速器轉(zhuǎn)換器特性 發(fā)動(dòng)機(jī)特性曲線 發(fā)動(dòng)機(jī)轉(zhuǎn)矩 變壓器輸出速度 變壓器輸出區(qū)域 變壓器特性曲線 轉(zhuǎn)換范圍 超壓閥限制 理論曲線 變壓器輸出轉(zhuǎn)矩 轉(zhuǎn)速比 轉(zhuǎn)矩比 發(fā)動(dòng)機(jī)轉(zhuǎn)速 這里的缺點(diǎn)是，每兩個(gè)液壓機(jī)需要傳送整個(gè)驅(qū)動(dòng)力，因此他們的尺寸必須相對(duì)較大。這有一個(gè)顯著效果的傳輸效率（負(fù)）。靜液壓傳輸?shù)娜秉c(diǎn)包括不利的特定輸出功率。它們的高生產(chǎn)成本和噪音，因此，這種傳輸將不再被使用了。這種變速器通常用于建筑和農(nóng)業(yè)機(jī)械，部分是高技術(shù)傳輸?shù)慕M件，其中一個(gè)機(jī)械部件負(fù)責(zé)提高效率。 3.4.4自動(dòng)變速器（AT） 存在不同的可能性，實(shí)現(xiàn)自動(dòng)變速器。在這樣做時(shí)，主要使用以下概念： 1）行星變速器與液力變矩器。 2）手自一體變速器。 3）機(jī)械式無級(jí)變速器。 3.4.4.1帶式纏繞式液力變矩器 最普遍的組合是一個(gè)由特立勞格帝亞轉(zhuǎn)換器轉(zhuǎn)移力矩傳動(dòng)，已經(jīng)證明，單獨(dú)特立勞格帝亞轉(zhuǎn)換器不能提供一個(gè)充分的傳遞圖（圖3-76）。圖3-78顯示轉(zhuǎn)矩特性可采用后置式階梯傳輸來實(shí)現(xiàn)。 傳輸輸出速度 傳輸輸出轉(zhuǎn)矩 自動(dòng)變速器傳送圖（來源：米奇克；“車輛動(dòng)力學(xué)”） 齒輪 常數(shù) 性能曲線 齒輪 齒輪 圖3-79顯示了轎車的三速自動(dòng)變速器。 轎車三速自動(dòng)變速器 附件：(Automotive Engineering Ⅰ:longitudinal dynamics of vehicles P123-132) Fig.3-67 Shows a two-group transmission with two-speed planetary train as a rearmounted gound . In a three-group transmission .up to 16 different gear levels can be obtained from a four-speed main transmission at a relatively low constructional expense. An example with 16 gears is shown in Fig.3-68. The shifting diagram of this three-group transmission is depicted in Fig.3-69. 3 .4 .2 Mechanical continuously variable transmissions In contrast to mechanical stepped transmissions so far used ire motor vehicles, mechanical continuous variable transmissions. Also called CVTs , have certain advantages based on their principle. The power characteristic is shown in Fig.3 -70. As a result of the continuous variable torque conversion. The achieved power curve (Fig.3-70b) represents the converter characteristic curare. In order to produce a delivery map (Fig.3-70c) which adjusts to different driving conditions，the CVT only requires a supply characteristic line (Fig.3-70a) from the engine. Except for the starting area , which requires an additional clutch (for a sufficient range of transmission ratios ), the entire demand map can be covered in this way [3-33]. Since the CVT allows .a free selection of the engine parameters (the torque and the speed)the operation of the combustion engine can be optimised based on different criteria. When the optimum points on the engine map are combined over the entire performance area of the engine，a curve which is parameterised with respect to power，also called the“control line”，results.Fig.3-71 shows the control lines for the optimisation criteria“noise”，“fuel consumption”，and“driving dynamics". When realising only one control line for transmission operation using a relatively simple mechanical control ,the drawn-in curve represents a good compromise. in this case，control lines that correspond to demand as well as the drivers needs , can be realized . This already implies that continuously variable transmissions can exclusively be realised as automatic transmissions. In mechanical CVTs，the variation of transmission ratio is achieved by varying the radius of the point of application forces. The torque is transferred by friction. Based on the type of torque transmission mechanical CVTs can be classified into: 1)Belt wrap transmission 2)Pitch transmission 3. 4. 2. 1 Belt wrap transmission In Belt wrap transmissions，force transmission is achieved using belts，bands or chains, which are farce-fit clamped between disk pairs. By varying the rolling radii on the disks，the transmission ratio can be varied infinitely. As a result, the disk pairs along with the accompanying adjusting mechanism are also called variators. For force transmission, so far different belt，band and chain concepts have been proposed. Fig .3-72 shows the currently used force transmission systems. In contrast to rubber belts used in variomatic transmissions in the 50s by Van Doorne，Holland，the transferable torque (up to 210 N·m) and efficiency，in particular，were significantly improved by changing over to steel-link bands in current CVTs，The transmission element，also called the thrust link band due to the kind of loading，consists of approx. three hundred steel segments that are held together on both sides by steel band packages(band size fl.1mm)piled onto each other. In contrast to the thrust link band，in transmissions manufactured by PIV-Antriebe Werner Reimers KG，a chain loaded by tension is used for force transmission. The single chain link packages are connected to each other by cradle compression parts. Force transmission takes place by friction in the contact areas of the cradle compression parts and the disk wheels. U-shaped metallic clips that enclose the shackle bandage from the outside take over chain guide，The whistle，otherwise typical for chain drives，which occurs when the link comes into contact with the disk wheels，can be more or less avoided by an appropriately designed chain. In order to keep the centrifugal load on a U-band as low as possible .Gates Rubber. USA, developed a rubber belt called power-trac which is reinforced by Kevlar fibers. In order to increase the transversal loading capacity, the rubber band is provided with an integrated metallic structure. Oil lubrication .as required in steel-steel friction pairings，is not necessary. This allows for an open transmission design associated with lower weight. Kumm Industries，USA，proposes the fourth transmission system shown in Fig.3-72.In contrast to former Belt wrap transmissions，in which the force transmission element is clamped between two conical disk pairs，the Kumm CVT includes a rubber band which is also reinforced by Kevlar (Gates-development)and runs at each disk end on studs. The studs can be shifted in spirally-shaped grooves. No lubrication is required here as well. 3.4.2. 2 Pitch transmission Since the development of automobiles，pitch transmissions have been designed, manufactured and tested over and over again，however with no lasting success. Fig.3-73 depicts some basic forms of pitch body force transmission. The continuous variable change of the transmission ratio takes place under load by varying the point of action of the force，i.e. the effective pitch body radius. Apart from friction coefficient，the pressure force of the pitch bodies also determines the transferable force. A renewed interest in pitch transmissions can be attributed to the development of new high-friction lubricants which enable nearly twice as large the force transmission between pitch bodies when compared to conventional lubricants. For application in motor vehicles，only concepts which enable a firm position between the input and the output shafts can be used. This can be achieved using an intermediate link in the form of a rotationally symmetrical body. 3.4.3 Hydraulic continuously variable transmissions Transmissions，in which power is transferred by an incompressible fluid，can be classified, according to the type of function，into: 1) Hydrodynamic transmission 2) Hydrostatic transmission 3.4.3.1 Hydrodynamic transmission In hydrodynamic transmissions，the transmission of torque takes place according to Foettinger principle using two rotating blade wheels，the pump and the turbine wheel. In contrast to hydrodynamic clutches(Chapter 3.3)，the hydrodynamic transmission additionally includes a stator as torque support，that props up at the housing[3-34]. As a result: MTur = MPump + MSt ( 3 -51) Where MTur -turbine wheel torque MPump - pump wheel torque; MSt - stator torque. Fig.3-74 shows the constructional details of a hydrodynamic transmission( Trilok converter )which is exclusively used today，with the accompanying blade principle and flow conditions for nA/nE=0. 7. The working fluid，which is generally oil，is accelerated by the pump wheel linked to the engine and then transferred to the turbine wheel where it is slowed down. While doing so，it gives away its energy to the transmission output. An additional redirection， more or less without delay，leads to torque reinforcement. This reinforcement is high if the speed difference between the pump and the turbine is high. With v=0，implying a firmly braked turbine，the torque conversion reaches its maximum value. With increasing turbine speeds，the torque conversion drops almost linearly to a torque ratio of 1:1 (coupling point) . In this example，at the indicated speed ratio，an optimal operation point appears at approx. nA/nE=0.7，without impact loss. If the speed ratio increases further，then the stator is increasingly streamed from behind until at a speed ratio of approx. nA/nE=0.9 (coupling point)and the stator does not produce any deflection anymore，meaning that it does not absorb a reaction torque，In order to avoid this torque deterioration at a further increased speed ratio，the stator is connected with the transmission housing by a one-way clutch so that it can run along，without torque transmission，at speed ratios above the coupling point. In this region，the trilok converter operates as a clutch. Fig.3-75 shows，in an idealised way，the torque-and efficiency course aver the speed ratio. Moreover the picture shows the rough characterisitcs of efficiency，the impact losses(no correspondence between flow and blade direction)and the friction losses(friction between fluid and walls)。 The interaction between a trilok converter and the combustion engine proceeds as follows: Up to the coupling point，the flow ratios at the pump wheel input are independent of the ones at the transmission output because of the stator，which is at standstill. The important k-factor [Eq. (3-18)] and thus the pump characteristic curve are constant. in this case，the pump characteristic curve，if possible，should be located within the area of optimum engine efficiency. Above the coupling point，when the stator- and the turbine wheels rotate as a“common”turbine wheel，the same principle，as in the hydrodynamic clutch，becomes applicable. There, the pump characteristic curve moves in relation to the speed ratio nA/nE. From Fig.3-76，we thus notice that only a part of the engine map can be used through the interaction of the engine torque and the trilok converter characteristic. The output torque which is indicated in Fig.3-76，thus results. Compared to the ideal torque characteristic there are still relatively large differences between the torque demanded and the torque supplied. This means that the attainable conversion area (starting conversion approx. 2.0-2.5) and the poor efficiency at high torque ratios are not sufficient for its exclusive employment as a torque converter in the motor vehicle. Trilok converters are thus combined with stepped transmissions. Apart from the favourable approach towards the demand characteristic curve, which is possible here, the advantages of the trilok converter thus become obvious only when used combination with stepped transmissions. The advantages include compactness，good heat dissipation over the hydraulic fluid，the fact that it is free of wear to a large extent and also in its function as a torsional vibration damper。 3.4.3.2 Hydrostatic transmission Hydrostatic transmissions with two displacement machines working as a pump or as an engine enable a variation of the combustion engine speed independent of load. By shifting the hydraulic machines，e .g. axial piston pump or engine，the negative velocity of flow can be set between zero and the maximum value in either direction. Thus，in hydrostatic transmissions，neither starting clutches nor gear clusters are required for backwards driving. Transmissions having such characteristics are called IVT’s (Infinitely Variable Transmissions).Fig.3-77 shows the conversion characteristic of such a transmission. It essentially corresponds to the principle of the previously mechanical CVT [ 3-35]. The disadvantage here is that each of the two hydraulic machines has to transfer the entire driving power and thus they have to be dimensioned correspondingly large. This has a significant effect (negative) on the transmission efficiency. Further disadvantages of hydrostatic transmissions include the unfavorable specific power output，their high production costs and the noise development. Therefore such transmissions shall not be dealt with anymore. Such transmissions are often used in construction and agricultural machinery，partly as components of hi-tech transmissions in which a mechanical component is responsible for improving the efficiency. 3 .4 .4 Automatic transmissions(AT) There exist different possibilities to realise automatic transmissions. In doing so，the following concepts are mostly used: 1) Planetary transmission with a hydrodynamic converter. 2) Automated manual transmission. 3) Mechanical CVT. 3.4.4. 1 Belt wrap transmission with a hydrodynamic converter The most widespread combination is the one consisting of a trilok converter arid a power-shifted planetary transmission，It has already been explained that the trilok converter alone doesn’t provide a sufficient delivery map(Fig.3-76). Fig.3-78 shows the torque characteristic which can be achieved using a rear-mounted stepped transmission. Fig .3-79 shows the example of a passenger car three-speed automatic transmission.