【導(dǎo)讀】世界范圍內(nèi)大多數(shù)船舶都是采用柴油機(jī)作為動力。與蒸汽機(jī)、燃?xì)廨啓C(jī)等形式的動力裝置相比，無論是效率上的提高，還是設(shè)計上的進(jìn)步，柴油機(jī)都體現(xiàn)出了一定的優(yōu)勢。低速柴油機(jī)是體積較大、缸體較長、機(jī)身較重的二沖程柴油機(jī)。它們是已建造過的最大型的柴油機(jī)，它們的單機(jī)可用功率可達(dá)100000kw。還是被認(rèn)為是低速機(jī)。對于相同的功率輸出，相對于四沖程柴油機(jī)，二沖程柴油機(jī)的重量明顯輕很多。對于大功率需求場合這是一個最明顯的優(yōu)勢，二沖程柴油機(jī)能夠在相同的重量情況下，發(fā)出更大的功率。油機(jī)就能提供較大的功率。度較低，能夠直接和螺旋槳連接，不需要像離合器、齒輪箱等的中間傳動機(jī)構(gòu)。利用低速柴油機(jī)驅(qū)動的商船，通常。只有一臺直接連到定距槳上的大型主機(jī)。

　　

【正文】 nifold as an integrated part of the engine block while many water and oil channels are castin or machined as part of the engine structure. Such features make for easier maintenance, improved accessibility and a reduction in the number of engine parts. 在 20 實際 90 年代，柴油機(jī)設(shè)計開始運用整體鑄造結(jié)構(gòu)，把汽缸體和機(jī)座一起鑄造成一個鑄鐵構(gòu)件。由于設(shè)計和構(gòu)造上的整體性，使得球墨鑄鐵件非常的堅固。一些柴油機(jī)還利用長貫穿螺栓從主軸承的下表面通到構(gòu)件的上部為整個機(jī)體進(jìn)行額外加強(qiáng)。貫穿螺栓也用在汽缸頭的上表面和機(jī)架的下表面之間，以保證把燃 燒負(fù)荷從汽缸蓋傳到機(jī)架上。使用貫穿螺栓并不是意味著設(shè)計上存在缺陷，而是在需要的地方有效地利用加強(qiáng)機(jī)構(gòu)。一個剛性結(jié)構(gòu)應(yīng)該保證主機(jī)各部件，尤其是曲軸和凸輪軸的精確位置，將結(jié)構(gòu)的振動問題降到最低。一些機(jī)型（如： Wartsila Vasa 38）將進(jìn)氣總管與機(jī)體集成在一起，而水和油的通道則采用鑄造或車削后，做為機(jī)體結(jié)構(gòu)的部件。這樣設(shè)計特性簡化了維修保養(yǎng)，提高了可達(dá)性，降低了主機(jī)部件的數(shù)量。 With monoblock structures, a subframe is required to act as the engine sump. This subframe, which bolts directly to the lower face of the engine structure, takes no load and can be manufactured from welded plate. Lubricating oil suction pipes and strainers are arranged within the sump. 對于整體結(jié)構(gòu)來說，下部結(jié)構(gòu)被用作柴油機(jī)的油底殼。油底殼用螺栓 直接連接到主機(jī)整體結(jié)構(gòu)的下表面上，不承受負(fù)荷，可用金屬板焊接制成。潤滑油的吸入口和過濾器都安裝在油底殼中。 Main Bearings 主軸承 Main bearing support housings are cast as part of traditional bedplate arrangements, and these bine adequate rigidity for the crankshaft with relative ease of bearing adjustment. 主 軸承座作為傳統(tǒng)機(jī)座的一部分也是鑄鐵的，軸承座和機(jī)座具有足夠的剛度，這樣軸承的調(diào)整就相對容易 Bearing replacement requires lifting the bearing cap, which is held from above with studs and nuts. 軸承更換的時候需要卸下軸承蓋，軸承蓋是從上部用螺栓螺母固定的。 Although this type of arrangement can, in theory, be incorporated within a monoblock engine structure, it is not used. An underslung main bearing support system is preferred. Nodular castiron bearing caps are held from below by means of two hydraulically tensioned studs. 盡管理論上可把這種設(shè)計的軸承蓋與整體式機(jī)體結(jié)構(gòu)做成一體，但實際中并不這樣做。一般首選懸掛式的主軸承支撐系統(tǒng)，球墨鑄鐵軸 承蓋利用兩個液壓張緊螺栓從下面固定。 These bearing caps are guided laterally into the engine block at the top and bottom and the hydraulic jacks are often permanently fitted to allow for ease of maintenance. Hydraulically tensioned horizontal side studs support the main bearing caps and with the vertical studs and lateral guide arrangements provide a very rigid main bearing support for the crankshaft. 主軸承蓋可從上部和下部橫向?qū)霗C(jī)體結(jié)構(gòu)，為了方便維護(hù)保養(yǎng)經(jīng)常安裝固定式的液壓千斤頂。水平布置得液壓張緊螺栓支撐主軸承蓋，再加上垂直螺栓和側(cè)向楔形塊，就給曲軸的軸承提供了一個很大剛性的支撐。 Main bearings for medium speed engines currently in use are of the thin shell type. 中速機(jī)普遍使用薄瓦性的主軸承。 Similar bearing shells are employed for bottom end 承也利用相似的軸瓦 。 This type of bearing essentially consists of a thin steel backing shell with a layer, or layers, of bearing material cast, flashed or deposited on the rubbing surface. 這種類型的軸瓦基本上是在薄鋼襯殼內(nèi)部的粗糙的表面上澆注或沉淀一層或多層的軸承材料。 This type of bearing is prefinished and does not require scraping to fit。 indeed no scraping is possible due to the thin layer of bearing material present. 這種 類型的軸承只需要表面拋光，不需要過多處理，實際上由于軸承材料層很薄沒有必要進(jìn)行刮擦等處理。 Over the years bearing materials have changed to meet the operating conditions. 多年來為了滿足工作條件，軸承材料進(jìn)行了不斷地改進(jìn)。 Early arrangements simply had a layer of white metal on the steel backing shell but this gave way to the multilayer bearing with a layer of leadbronze or copper between the steel and white metal in order to improve adhesion. 早期的軸瓦只是簡單的在薄鋼襯殼內(nèi)部澆注一層白合金，但是這種制作方法為多層軸瓦提供了借鑒，多層軸瓦是在薄鋼襯殼和白合金之間又加了一層鉛青銅或者黃銅來提高金屬間的粘著力。 This layer also provided an emergency bearing surface. 添加的這一層也提供了一個應(yīng)急軸承面。 The use of overlay material provides a degree of protection against corrosion, while a thin layer of nickel prevents the lead in the overlay from migrating into the leadbronze layer 覆鍍材料能夠?qū)Ωg提供一定程度的保護(hù)，覆鍍一薄層的鎳就能夠防止鉛向青銅層的遷移。 The backs of the steel shells may have a soft layer which is designed to prevent corrosion. 鋼襯殼也可以加一層軟材料防止腐蝕。 During the 1990s a number of engine builders returned to bimetal bearings which employ a layer of aluminiumtin on the steel backing shell. 在 20 實際 90 年代，一些柴油機(jī)廠又從 新生產(chǎn)在鋼襯殼內(nèi)部加一層錫鋁合金的雙金屬軸承。 Others employ a multiple layer bearing with a tinantimony rubbing surface over a copperlead layer on the steel backing shell. 另外一些廠家利用在 鋼襯殼內(nèi)部的銅合金層之上又加了一層表面粗糙的錫銻合金生產(chǎn)多層軸瓦。 Bearing technology continues to change to meet the demands of higher loads but problems of lubricants contaminated by water and residual fuels must also be overe. 軸承技術(shù)不斷發(fā)展為滿足了更大負(fù)荷的需要，但是還需要克服由于水和殘油對潤滑油所造成的污染問題。 Crankshaft 曲軸 Crankshafts for medium speed engines are solid fings from a single alloy steel ingot. 中速 機(jī)的曲軸是用一塊合金鋼錠實鍛而成的。 Solid fing avoids stress problems, which would result from the presence of shrink fits, and ensures even stress transmission between journals, webs and pins. 實鍛避免了因收縮配合帶來的應(yīng)力問題，避免了軸頸、曲柄臂和曲柄銷上的應(yīng)力集中。 There are very rigorous Classification Society rules governing the dimensioning of crankshafts, based on a bination of theory and experience. 基于理論和實踐經(jīng)驗的結(jié)合，船級社規(guī)則對曲軸的尺寸有嚴(yán)格的要求。 Current designs make considerable use of puter finite element analysis which allows a wide range of loadings, dimensions and cylinder firing orders to be analysed before any manufacture takes 方法，在任何生產(chǎn)之前，都對大負(fù)荷范圍、不同尺寸和汽缸點火順序等進(jìn)行分析。 A crankshaft must be able to transmit the torque developed during operation. 曲軸必須能夠傳遞柴油機(jī)工作過程中所產(chǎn)生的扭矩。 This torque imposes stresses on the crankshaft journals. 扭矩在曲軸軸頸上產(chǎn)生扭轉(zhuǎn)力。 Pins are subject to direct stresses from the connecting rods, which impose bending and shear stresses. 曲柄銷承受從連桿傳來的力，這個力會在曲柄銷上彎曲力和剪切力。 Webs bend due to this loading but they also have a tendency to twist. 由于這 個負(fù)荷曲柄臂會產(chǎn)生彎曲，但是它們也有一個扭轉(zhuǎn)的趨勢。 Crankshafts will bend under load as each cylinder unit section acts like a simply supported beam, with the main bearings acting as the supports. 曲軸像一個被簡單支起來的梁，主軸承就像支撐體，這樣曲軸在每一個缸所產(chǎn)生負(fù)荷的作用下就會產(chǎn)生彎曲， Loadings vary with time making the analysis of stresses a plex matter, further plicated by the presence of oil holes through journals, webs and 間的變化使應(yīng)力的分析變得復(fù)雜，軸頸、曲柄臂和曲柄銷中鉆孔后使應(yīng)力的分析變得更加復(fù)雜 The firing order of an engine is primarily chosen to reduce engine torque fluctuations and minimize vibration. 對于降低扭矩的波動和降低振動，發(fā)動機(jī)點火順序的選擇很重要。 Any final solu