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1、 畢業(yè)設(shè)計說明書（論文） Engine Servive and Maintenance (I) This section and the following two describe various engine services and explain how various troubles in the engine are corrected. Later sections discuss servicing of the fuel, lubricating, cooling, and ignition systems. You will notice, in the disc

2、ussions of various engine-servicing jobs, that the time to do the job is often given. These figures are included to give you some idea of the size of the job and must not be considered accurate enough for cost-estimating jobs. The procedures discussed in the three engine-sections are aimed at correc

3、tion specific troubles. The major enemy of good work is dirt. A trace of dirt left on a bearing or cylinder wall would ruin an otherwise good job. Thus, you must be absolutely sure that you do not leave dirt or abrasive in the engine or on engine parts when you finish a job. Before any major job

4、, the block should be cleaned. Electrical units should be removed or covered if the engine is steam-cleaned so that moisture does not get into them. Connecting rods and rod bearings service On many engines, the connection-rod and main bearings (crankshaft bearings) can be checked for wear with an

5、 oil-leak detector before the engine is torn down. To use the detector, the oil pan is removed, and the detector hose is connected to the pressure side of the engine lubricating system (at the oil filter, for example). Then, with the detector filled with oil, an air pressure of 175 kPa is applied to

6、 the detector tank. This pressure forces oil through the engine lubricating system. If bearings are worn, considerable oil will leak from them. Worn bearings greatly increase engine oil consumption because they pass more oil. The detector manufacturer states that a normal bearing will leak between 2

7、0 and 150 drops of oil a minute. If it leaks more, the bearing is worn. If it leaks less than 20 drops per minute, then either the bearing clearance is too small or else the oil line to the bearing is stopped up. Connecting rods and pistons are removed as assembly from the engine. Removing, servici

8、ng, and replacing connecting rod requires about 5 to 8 hours, according to the type of engine. About 3 additional hours are required to install new piston rings. Additional time is needed for such services as piston-pin or bushing replacement. Pistons and rings service After the piston-and-connect

9、ing-rod assemblies have been removed from the engine and the pistons and rods separated, the rings should be removed from the piston. A special ring tool is required for ring removal. The tool has two small claws that catch under the ends of the ring. Then, when pressure is applied to the tool handl

10、es, the ring is sprung enough that it can be lifted out of the ring groove and off the piston. (1) Piston cleaning. Remove carbon and varnish from piston surfaces. Do not use a caustic cleaning solution or a wire brush! These could damage the piston-skirt finish. Use solvent to remove deposits. Cle

11、an out ring grooves with a clean-out tool. Oil ring slots, or holes, must be clean; a drill of the proper size is handy for this job. Be sure that you do not remove metal when cleaning ring grooves or oil slots. (2) Piston inspection. Examine the pistons carefully for worn, scuffed, or scored skirt

12、s and for cracks at the ring lands, skirts, ring bosses, and heads. Check the piston with a micrometer. Compare the sizing-point reading with the measurement of the cylinder diameter taken with an inside micrometer, an outside micrometer and a dial indicator, or a telescope gauge and a micrometer. I

13、f the cylinder wall is excessively worn, it will require refinishing. Cylinder wall refinishing means that an oversize piston will be required. (3) New pistons. New pistons are supplied either finished or semifinished. The finished type, ready for installation, is available in a number of sizes. Wh

14、en these are used, the cylinders must be finished to fit the pistons, as a rule, engine manufacturers supply oversize pistons of the same weight as the standard pistons. Thus, it is not necessary to replace all pistons when only part of the cylinders require service. There is no problem of balance i

15、f all pistons are of the same weight, even if some are oversize. Semifinished pistons are oversize and must be finished down to size to fit the cylinders. If an engine is torn down for overhaul after considerable mileage, the chances are that the rings will require replacement. Sometimes, all that

16、is required is to free up the rings in the ring grooves by cleaning out carbon. In examining rings to determine whether or not they should bereused, several conditions may be found. Conditions requiring ring replacement include loss of tension, irregular lightand dark areas (showing uneven wear caus

17、ed by warped or worn rings), and scores or scratches. Engine Service and Maintenance (Ⅱ) This section describes the servicing of crankshafts, main bearings, and engine blocks and cylinders. Crankshaft and main bearings service Most modern automotive engines have precision-insert-type main bearin

18、gs which can be replaced without removing the crankshaft. Many bearing difficulties can be taken care of by this method of bearing replacement. However, if the bearing problem has been caused by such conditions as a warped engine block, stopped-up oil passages, a worn crankshaft journal, or a bent c

19、rankshaft, then simply replacing the bearings will not correct the condition. Such conditions as these will cause uneven bearing wear, with some bearings wearing faster (and more unevenly) than others. If the bearings seem to have worn fairly uniformly, then the chances are that only crankshaft-jou

20、rnal checks and bearing replacement will be required. Use of the bearing oil-leak detector will determine whether or not bearing wear has been uneven. If bearing wear is uneven, then the safest procedure is to remove the crankshaft from the engine block and check both separately for alignment and f

21、or clogged oil passages. Replacing precision-insert main bearings without removing the crankshaft requires about 5 hours. Removing and replacing the crankshaft requires several additional hours. Semifinished main bearings require finishing and fitting after installation, so that the crankshaft mus

22、t be taken out. To perform the complete replacement job on semifinished main bearings requires about 19 to 22 hours. Cylinder and cylinder blocks service and maintenance Before any service operations are performed, the cylinder block should be cleaned and inspected. There are several methods of cl

23、eaning. One method uses steam directed by a nozzle onto the block to wash away oil, sludge and dirt. A good solvent applied with a brush will also clean the block. After the block is cleaned, inspect it for cracks, especially in the cylinder walls, top, water jackets, and main-bearing webs. The pis

24、ton and ring movement, the high temperatures and pressures of combustion, the washing action of gasoline entering the cylinder -- all these tend to cause cylinder-wall wear. There are certain limits to which cylinders may wear tapered or out of round before they require refinishing. Special drastic

25、 replacement rings will control compression and oil in cylinders with some taper and out-of-round wear. But when wear goes beyond a certain point, even the severest rings cannot hold compression and control oil; loss of compression, high oil consumption, poor performance, and heavy carbon accumulati

26、ons in the cylinders will result. In such a case, the only way to get the engine back into good operation condition is to refinish the cylinders and fit new pistons and new rings to them. If wear, taper, or eccentricity is not too great, only honing will be required. In operation, the hone revolves

27、 in the cylinder, and the abrasive stones in the hone remove material from the cylinder wall. If wear is too great to be taken care of by honing alone, cylinders must be bored first and them boned. Cylinders must be cleaned thoroughly after the honing or boring operation. Even slight traces of gri

28、t or dust left on the cylinder walls may cause rapid ring and wall wear and early engine failure. Refinishing cylinders requires 12 to 20 hours (according to the type of engine). This includes fitting and installing new pistons, rings, piston pins, and connection rods. When new bearings are fitted,

29、 about 10 additional hours is required. Grinding valves would require several more hours. These various times are mentioned because an engine that requires cylinder refinishing is usually in need of a general overhaul and these other services will also be required. Engine Service and Maintenance (

30、III) Valves and valve mechanisms service Valves must be properly timed. They must seat tightly and operate without lag. Valve-tappet clearance, as well as the clearance between the valve stems and guides, must be correct. Failure to meet any of these requirements means valve and engine trouble. T

31、ypes of valve troubles include sticking, burning, breakage, wear, and deposits. Valve sticking. Gum or carbon deposits on the valve stem will cause valve sticking. Excessive valve-stem clearance speeds up valve deposits. Another cause of valve sticking is warped stems. This could result from overhe

32、ating, an eccentric seat (which throws side pressure on the valve), or from a cocked spring or retainer (which tends to bend the stem). Insufficient oil would also cause valve sticking. Sometimes valves will stick when cold but will work free as the engine warms up. Valve burning. This is usually

33、an exhaust-valve problem. Any condition that prevents normal exhaust-valve seating may lead to valve burning. Valve breakage. Any condition that causes the valve to overheat or to be subjected to heavy pounding (as from excessive tappet clearance or from detonation) may cause valves to break. Valv

34、e-face wear. In addition to the conditions discussed above, excessive tappet clearance or dirt on the valve face or seat could cause valve-face wear. Dirt may cause valve-face wear if the engine operates in dusty conditions or if the car-burettor air cleaner is not functioning properly. The dust ent

35、ers the engine with the air-fuel mixture, and some of it settles on the valve seat. The dust will also cause bearing, cylinder-wall, and piston and ring wear. Valve deposits. If the fuel has excessive amounts of gum in it, some of this gum may be deposited on the intake valve as the air-fuel mixtur

36、e passes the valve on the way to the engine cylinder. Carbon deposits may form because of an excessively rich mixture or because of oil passing a worn valve guide (in the intake valve). Improper combustion, due to a rich mixture, defective ignition system, loss of compression in the engine, a cold e

37、ngine, and so forth, will result in carbon deposits on the exhaust valves. Dirty or improper oil will cause deposits to form on the valves. Valve Service and Maintenance includes adjusting valve-tappet clearances (also called adjusting valve lash), grinding valves and valve seats, installing new se

38、at inserts, cleaning or replacing valve guides, servicing the camshaft and camshaft bearings, and timing the valves. A complete valve Service and Maintenance job, including grinding valves and seats, checking springs, cleaning guides, and tuning the engine, requires from about five hours (for an ove

39、rhead-valve six-cylinder engine) to about eight hours (for an eight-cylinder L-head engine). Replacing the camshaft requires about eight hours; four additional hours are required for replacing camshaft bearings. 譯文： 發(fā)動機維修(I) 本節(jié)和下面兩節(jié)的內(nèi)容是介紹各種發(fā)動機的維修，并討論如何正確處理發(fā)動機的各種故障。再后的幾節(jié)討論燃料供給系、潤滑系、冷卻系和點火系的維

40、修。你會注意到在講述發(fā)動機的各種維修工作時，都提供了完成各項工作所需的時間。這些數(shù)據(jù)會使你了解維修工作的規(guī)模，但并非精確到可以作為維修價格的參考。這三節(jié)有關(guān)發(fā)動機維修工作的內(nèi)容，其目的在于介紹排除發(fā)動機具體故障的方法。 高質(zhì)量維修工作的最主要問題是油污。殘留在軸承或是氣缸壁上的油污會影響維修工作的質(zhì)量。當維修工作完成時，必須保證不能把油污或磨料殘留在發(fā)動機內(nèi)部或發(fā)動機機件上。 在進行重要維修工作之前，氣缸體應加以清洗。如果發(fā)動機進行高壓清洗，電氣部件必須拆卸或遮蓋。這樣，水分才不會滲入。 連桿和連桿軸承的維修 許多發(fā)動機在拆卸之前，可以用漏油檢測裝置檢查連桿和主軸承(曲軸軸承)的磨損情

41、況。使用這種裝置時，拆掉油底殼，并把該裝置的油管連接到發(fā)動機潤滑系統(tǒng)加壓的一側(cè)(如濾清器上)。這時，檢查器充滿油，提供給檢查器油槽l 75千帕的壓力，這一壓力使油流過發(fā)動機的潤滑系統(tǒng)。如果軸承磨損，從軸承中漏出的油會較多。磨損的軸承大量增加了發(fā)動機油的消耗，因為更多的油是漏掉的。這種裝置的制造廠商指出，標準軸承每分鐘應漏油20～1 50滴。如果油漏的過多，軸承即以磨損；如果每分鐘漏油少于20滴，那么或是軸承的配合間隙太小，或是油道堵塞。 把連桿和活塞做為整體組件從發(fā)動機上拆卸下來。不同類型的發(fā)動機，拆卸、維修和更換連桿的時間從5小時到8小時不等，安裝新活塞環(huán)需要另外增加3小時；像更換活塞銷或

42、襯套之類的維修項目，也需要另外增加時間。 活塞和活塞環(huán)的維修 先將活塞及連桿組件從發(fā)動機上拆下再把活塞與連桿分開之后，即可將活塞環(huán)從活塞上取下。活塞環(huán)的拆卸要求使用專用工具進行。這種工具有兩個小爪，可以伸到活塞環(huán)下端將其卡住。然后用力壓住工具手柄，使活塞環(huán)足以彈起，即可使之從環(huán)槽中脫出，而將其從活塞上取下。 (1)清潔活塞環(huán)：絕不能使用苛性溶液或金屬刷清除活塞表面的積碳和漆膜。因為這樣會損壞活塞裙部的粗糙度?？墒褂萌軇┣宄e垢；使用清除工具清潔活塞環(huán)槽；油環(huán)開縫或孔隙必須清理干凈，用適當尺寸的鉆機進行這項工作較為便利。清潔活塞環(huán)槽或油環(huán)開縫，絕對不能損傷金屬部分。 (2)活塞探傷：仔細

43、檢查活塞，找出裙部的磨損，劃傷或劃痕，以及環(huán)槽岸、裙部、軸套和頂部的裂痕?？墒褂们Х殖邫z查活塞，用內(nèi)徑千分尺、外徑千分尺和千分表或用內(nèi)徑規(guī)和干分尺測量出氣缸直徑，并與原尺寸標準進行對照。如果氣缸壁磨損過大，就需要修整表面，這意味著需要更換較大尺寸的活塞。 (3)更換新活塞：新活塞或者是精加工的；或者是半精加工的?？芍苯友b配的精加工的活塞有若干種尺寸可供選擇。更換時，氣缸必須與活塞具有裝配精度。通常情況下，發(fā)動機制造廠商提供具有相同重量的，與標準活塞相比尺寸較大的活塞。這樣，當氣缸僅需要部分維修時，就不必更換全部活塞。所有的活塞，包括加大尺寸的活塞，重量都相同，也就不存在平衡問題了。半精加工的

44、活塞是加大尺寸的，必須進行修整以便與氣缸相配合。 在行駛了一定的里程后，發(fā)動機被拆下檢修，這正是維修更換活塞環(huán)的機會。有時，所要做的僅僅是清除積碳，使活塞環(huán)在活塞環(huán)槽中活動自如。檢查活塞環(huán)，判斷是否還可以繼續(xù)使用。張力下降，有的部位凹凸不平(由翹曲或磨損的活塞環(huán)所引起的不平整)，有裂痕或劃痕的活塞環(huán)需要更換。 發(fā)動機維修(II) 本節(jié)介紹曲軸、主軸承、發(fā)動機機體和氣缸的維修。 曲軸和主軸承的維修 大多數(shù)現(xiàn)代汽車發(fā)動機的主軸承是精密嵌入型，不必拆下曲軸即可更換。許多軸承故障能夠通過更換主軸承或軸承來解決。如果軸承問題是由缸體翹曲、油道堵塞、曲軸軸頸磨損或是曲軸彎曲變形所引起，那么僅

45、更換軸承就不能解決問題。類似這樣的情況會造成軸承不均勻磨損，而且一些軸承會比另一些磨損得更快。 如果軸承看上去似乎已磨損的相當均勻，那么只需要檢查曲軸軸頸并更換軸承。使用漏油檢測裝置即可判定軸承磨損是否均勻。 如果軸承磨損不均勻，那么較為保險的作法是從發(fā)動機機體上卸下曲軸，然后分別進行調(diào)校，并檢查油道是否堵塞。 不拆曲軸更換精密嵌入型主軸承，大約需要5小時，拆卸和更換軸承要額外增加幾小時。 半精加工的主軸承安裝后需要修整和調(diào)配，這樣曲軸就必須拆下。完成更換半精加工主軸承的工作需要1 9～20小時。 氣缸和氣缸體的維修 在進行任何維修工作之前，應對氣缸體進行清潔處理和探傷檢查。有幾種

46、清潔方式可供選擇。一種是直接用噴管噴出的蒸汽沖洗氣缸體，從中清洗出油、金屬碎屑和污垢。當然，也可使用刷子和優(yōu)質(zhì)清潔劑清洗氣缸體。 氣缸體清潔之后，檢查有無裂痕，尤其是氣缸壁、頂部、冷卻水套和主軸承腹板。 活塞和活塞環(huán)的運動，燃燒產(chǎn)生的高溫、高壓，以及汽油進入氣缸時的沖刷作用，均是造成氣缸壁磨損的原因。 氣缸磨損形成錐度或不圓，在達到一定的限度前，不必整修表面。在這種情況下，特別精選的油環(huán)有助于控制氣缸的壓力和油耗。但是，一旦磨損超過某一限度，即使是嚴格挑選的活塞環(huán)也無法保持壓力和控制油耗，而且產(chǎn)生壓力不足、油耗高、效率低、積炭嚴重等情況。在這樣的情況下，要使發(fā)動機保持良好的工作狀態(tài)，只有

47、整修氣缸表面，并配裝新的活塞和活塞環(huán)。 如果磨損造成錐度或偏心度不是很嚴重，僅需要進行衍磨即可解決問題。操作時，衍磨頭在氣缸中旋轉(zhuǎn)，衍磨頭上的磨石從氣缸壁上磨去余量。 如果磨損嚴重，僅靠衍磨不能解決問題，那么氣缸必須先進行鏜削，然后再衍磨。 鏜削和衍磨加工之后，氣缸必須徹底清潔。殘留在氣缸壁上的砂礫或塵埃所造成的劃痕，均能引起活塞環(huán)和氣缸壁的迅速磨損以及發(fā)動機的早期損壞。 整修氣缸需要1 2～20小時(時間長短取決于發(fā)動機的類型)，這包括調(diào)配和安裝新活塞、活塞環(huán)、活塞銷和連桿。新軸承的配裝大約需增加1 O小時。磨削氣門則需要更多的時間。這里之所以提供幾種不同的時間，是因為需要整修氣缸的

48、發(fā)動機通常必須進行大修，那么這些維修工作也就必不可少。 發(fā)動機維修(III) 氣門和氣門機構(gòu)的維修 氣門必須嚴格定時，落座嚴密并且開啟無滯怠。不僅氣門桿與氣門導管之間的間隙，氣門推桿間隙也必須適當。不能滿足這些要求意味著氣門和發(fā)動機發(fā)生了故障。 氣門故障包括沾著、燒傷、破裂、磨損和積炭。 氣門沾著：氣門桿上的膠質(zhì)或積炭是造成沾著的原因。氣門桿間隙過大會加速氣門的積炭。氣門沾著的另一個原因是氣門桿變形，產(chǎn)生的原因是過熱、氣門落座不正常(使氣門受到側(cè)壓)以及氣門彈簧或鎖銷上翹(使氣門桿彎曲)。潤滑不良也是沾著的原因。有時，發(fā)動機冷態(tài)時，氣門也會粘?。话l(fā)動機預熱后，氣門工作就正常了。

49、 氣門燒傷：這種情況通常發(fā)生在排氣門。任何妨礙排氣門密封面貼合的情況都會導致氣門燒傷。 氣門破裂：氣門過熱或遭受重載(氣門桿間隙過大或爆裂)均可造成氣門破裂。 氣門表面磨損：除上述介紹的情況外，氣門間隙過大或氣門表面與氣門座的污垢均會使氣門表面磨損。如果發(fā)動機在高塵條件下工作，或者化油器凈化空氣的效果較差，灰塵會造成氣門表面磨損?；覊m會隨混合油氣進入發(fā)動機，其中一些會沉積在氣門表面?；覊m同樣也會導致軸承、氣缸壁、活塞和活塞環(huán)的磨損。 氣門積垢：如果燃油中含有過量的膠粘劑，當混合油氣通過氣門進入氣缸時，就會沉積在進氣門上?；旌蠚膺^濃或潤滑油流到磨損的氣門導管中(進氣門)，都可形成積炭。因混合氣過濃、點火系統(tǒng)有故障、發(fā)動機內(nèi)壓力損失、冷機等導致的不正常燃燒都會形成氣門積炭。含有灰塵或不合格的油也會在氣門上形成積炭。 氣門維修包括調(diào)校氣門間隙(也稱氣門余隙)，研磨氣門和氣門座，鑲配氣門座，清潔或更換氣門導管，保養(yǎng)凸輪軸和凸輪軸軸承，氣門的正時調(diào)整。全部氣門維修工作，包括研磨氣門和氣門座，檢查氣門彈簧，清潔氣門導管，調(diào)整發(fā)動機，大約需要5小時(頂置氣門六缸發(fā)動機)到8小時(側(cè)置氣門八缸發(fā)動機)。更換凸輪軸需要8小時左右；更換凸輪軸軸承需要額外增加4小時。