變速器、傳動軸和操縱機構(gòu)設(shè)計-3
變速器、傳動軸和操縱機構(gòu)設(shè)計-3,變速器,傳動軸,以及,操縱,機構(gòu),設(shè)計
外文翻譯原文
INTERNAL COMBUSTION ENGINE
1.Engine Block and Cylinder Head
The engine block is the basic frame of the engine. All other engine parts either fit inside it or fasten to it. It holds the cylinders, water jackets, and oil galleries.The engine block also holds the crankshaft, which fastens to the bottom of the block. The camshaft also fits inside the block, except on overhead-cam engines (OHC). In most cars, this block is made of gray iron, or an alloy (mixture) of gray iron and other metals, such as nickel or chromium. Engine blocks are castings.
Some engine blocks, especially those in smaller cars, are made of cast aluminum. This metal is much lighter than iron. However, iron wears better than aluminum. Therefore, the cylinders in most aluminum engines are lined with iron or steel sleeves. These sleeves are called cylinder sleeves. Some engine blocks are made entirely of aluminum.
The cylinder head fastens to the top of the block, just as a roof fits over a house. The underside forms the combustion chamber with the top of the piston. The most common cylinder head types are the hemi, wedge, and semi-hemi.All three of these terms refer to the shape of the engine's combustion chamber. The cylinder head carries the valves, valve springs and the rockers on the rocker shaft, this part of the valve gear being worked by the push-rods. Sometimes the camshaft is fitted directly into the cylinder head and operates on the valves without rockers. This is called an overhead camshaft arrangement. Like the cylinder block, the head is made from either cast iron or aluminum alloy.
2.Gasket
The cylinder head is attached to the block with high-tensile steel studs. The joint between the block and the head must be gas-tight so that none of the burning mixture can escape. This is achieved by using cylinder head gasket. This is a sandwich gasket, i.e. a sheet of asbestos between two sheets of copper, both these materials being able to withstand the high temperature and pressures within the engine.
3.Oil Pan or Sump
The oil pan is usually formed of pressed steel. The oil pan and the lower part of the cylinder block together are called the crankcase; they enclose, or encase, the crankshaft. The oil pump in the lubricating system draws oil from the oil pan and sends it to all working parts in the engine. The oil drains off and runs down into the pan. Thus, there is constant circulation of oil between the pan and the working parts of the engine.
4.Cooling System
The purpose of the cooling system is to keep the engine at its most efficient operating temperature at all speeds under all driving conditions.As fule is burned in the engine, about one-third of the heat energy in the fuel is converted into power.Another third goes out through the exhaust pipe unused, and the remaining third must be handled by the cooling system.This means that the engine can work effectively only when the heat energy is equally handled so as to keep the engine temperature in balance.
So,the temperature is quite essential for an engine to produce power.No engines can work well without suitable operating temperatures.If the engine runs too hot, it may suffer from pre-ignition,while the air-fule charge is ignited prematurely from escessive combustion chamber temperature.Viscosity of the oil circulating in an over heating engine is reduced.Hot oil alvarnish and carbon depostis may be drawn into the combustion chamber where it increases HC emission.This also causes poor performance and premature wear, and may even result in engine damage.What's more, the begavior of the metals at excessively high temperature also differs from that at normal temperatures and can produce a condition in which the metal deforms slowly and continuously at a constant stress.If the engine runs too cold, the fuel will not vaporize properly. If liquid fuel reaches the cylinders, it will reduce lubrication by washing the oil from the cylinder walls and diluting the engine oil.This causes a loss of performance, an increase in HC emissions, and premature engine wear. For these reasons, a ooling system of some kind is necessary in any internal combustion ebgine.
5.Valve System
If the inlet valve opened at TDC of the intake stroke and closed at BDC of that stroke, it would have a duration of 180°.It would have remained open for half of a complete 360° revolution, or 180°. However, it takes some time for the valve to open to its full position. It also takes time for it to close tightly. Therefore the valve is opened before TDC (BTDC) and closed after BDC (ABDC).
If the exhaust valve opened at BDC at the beginning of the exhaust stroke and closed at TDC at the end of the exhaust stroke, it would have a duration of 180°. But like the inlet valve, the exhaust valve needs time to reach the full-open position, It also needs time to reach the full-closed position. So the exhaust valve opens before BDC and closes after TDC.
The intake opens at 17° BTDC and the exhaust closes at 17° ATDC. Thus, for a period of 34°, both of the valves are open: (17° + 17° =34°). This period of time is known as valve overlap. The closing of the exhaust valve laps over the opening of the intake valve. During this time, the first of the new mixture pushes the last of the burned gases out the exhaust valve. Valve overlap is held to a minimum on turbo-charged engines. This prevents the intake charge from being blown out the exhaust.
To coordinate the four-stroke cycle, a group of parts called the valve train opens and closes the valves (moves them down and up, respectively). These valve movements must take place at exactly the right moments. The opening of each valve is controlled by a camshaft.
The cam is an egg-shaped piece of metal on a shaft that rotates in coordination with the crankshaft. The metal shaft, called the camshaft, typically has individual cams for each valve in the engine. As the camshaft rotates, the lobe, or high spot of the cam, pushes against parts connected to the stem of the valve. This action forces the valve to move downward. This action could open an inlet valve for an intake stroke, or open an exhaust valve for an exhaust stroke.
As the camshaft continues to rotate, the high spot moves way from the valve mechanism. As this occurs, valve springs pull the valve tightly closed against its opening, called the valve seat.
Valves in modern car engines are located in the cylinder head at the top of the engine. This is known as an overhead valve (OHV) configuration. In addition, when the camshaft is located over the cylinder head, the arrangement is known as an overhead camshaft (OHC) design. Some high-performance engines have two separate camshafts, one for each set of inlet and exhaust valves. These engines are known as dual overhead camshaft (DOHC) engines.
The camshaft also can be located in the lower part of the engine, within the engine block. To transfer the motion of the cam upward to the valve, additional parts are needed.
In this arrangement, the cam lobes push against round metal cylinders called cam follower. As the lobe of the cam comes up under the cam follower, it pushes the cam follower upward (away from the camshaft). The cam follower rides against a push rod, which pushes against a rocker arm. The rocker arm pivots on a shaft through its center. As one side of the rocker arm moves up, the other side moves down, just like a seesaw. The downward-moving side of the rocker arm pushes on the valve stem to open the valve.
Because a push-rod valve train has additional parts, it is more difficult to run at high speeds. Push-rod engines typically run at slower speeds and, consequently, produce less horsepower than overhead-camshaft designs of equal size. (Remember, power is the rate at which work is done.)
When the engine runs in compression stroke and power stroke, the valves must close tightly on their seats to produce a gas-tight seal and thus prevent the gases escaping from the combustion chamber. If the valves do not close fully the engine will not develop full power. Also the valve heads will be liable to be burnt by the passing hot gases, and there is the likelihood of the piston crown touching an open valve, which can seriously damage the engine.
So that the valves can close fully some clearance is needed in the operating mechanism. This means that the operating mechanism must be able to move sufficiently far enough away from the valve to allow the valves to be fully closed against its seat by the valve spring. However, if the clearance is set too great this will cause a light metallic tapping noise.
Each cam must revolve once during the four-stroke cycle to open a valve. A cycle, remember, corresponds with two revolutions of the crankshaft. Therefore, the camshaft must revolve at exactly half the speed of the crankshaft. This is accomplished with a 2:1 great ratio. A gear connected to the camshaft has twice the number of teeth as a gear connected to the crankshaft. The gears are linked in one of three ways:
（1）Belt drive A cog-type belt can be used. Such belts are made of synthetic rubber and reinforced with internal steel or fiberglass strands. The belts have teeth, or slotted spaces to engage and drive teeth on gear wheels. A belt typically is used on engines with overhead-cam valve trains.
（2）Chain drive On some engines, a metal chain is used to connect the crankshaft and camshaft gears. Most push-rod engines and some OHC engines have chains. l
（3）Gear drive The camshaft and crankshaft gears can be connected directly, or meshed. This type of operating linkage commonly is used on older six-cylinder, inline engines.
A camshaft driven by a chain or belt turns in the same direction as the crankshaft. But a camshaft driven directly by the crankshaft gear turns in the opposite direction. Timing belts are used because they cost less than chains and operate more quietly. A typical timing belt is made of neoprene (synthetic rubber) reinforced with fiberglass.
6.Piston
The piston is an important part of a four-stroke cycle engine. Most pistons are made from cast aluminum. The piston , through the connecting rod, transfers to the crankshaft the force create by the burning fuel mixture. This force turns the crankshaft .Thin, circular , steel bands fit into grooves around the piston to seal the bottom of the combustion chamber. These bands are called piston rings. The grooves into which they fit are called ring grooves. A piston pin fits into a round hole in the piston . The piston pin joins the piston to the connecting rod . The thick part of the piston that holds the piston is the pin boss.
The piston itself , its rings and the piston pin are together called the piston assembly.
To withstand the heat of the combustion chamber, the piston must be strong. It also must be light, since it travels at high speeds as it moves up and down inside the cylinder. The piston is hollow. It is thick at the top where it take the brunt of the heat and the expansion force. It is thin at the bottom, where there is less heat. The top part of the piston is the head , or crown . The thin part is the skirt The sections between the ring grooves are called ring lands.
The piston crown may be flat , concave ,dome or recessed . In diesel engine , the combustion chamber may be formed totally or in part in the piston crown , depending on the method of injection . So they use pistons with different shapes.
7.Piston Rings
As Fig shows , piston rings fit into ring grooves near the of the piston. In simplest terms, piston rings are thin, circular pieces of metal that fit into grooves in the tops of the pistons.
In modern engines ,each piston has three rings. (Piston in older engines sometimes had four rings, or even five.) The ring’s outside surface presses against the cylinder walls. Rings provide the needed seal between the piston and the cylinder walls. That is, only the rings contact the cylinder walls. The top two rings are to keep the gases in the cylinder and are called compression rings. The lower one prevents the oil splashed onto the cylinder bore from entering the combustion chamber , and is called an oil ring. Chrome-face cast-iron compression rings are commonly used in automobile engines. The chrome face provide a very smooth , wear-resistant surface.
During the power stoke , combustion pressure on the combustion rings is very high. It causes them to untwist . Some of the high-pressure gas gets in back of the rings. This force the ring face into full contact with the cylinder wall. The combustion pressure also holds the bottom of the ring tightly against the bottom of the ring groove. Therefore , high combustion pressure causes a tighter seal between the ring face and the cylinder wall.
8. Piston Pin
The piston pin holds together the piston and the connecting rod . This pin fits into the piston pin holes and into a hole in the top end of the connecting rod. The top end of is much smaller than the end that fits on the crankshaft . This small end fits inside the bottom of the piston . The piston pin fits through one side of the piston , through the small end of the rod , and then through the other side of the piston . It holds the rod firmly in place in the center of the piston. Pins are made of high-strengh steel and have a hollow center . Many pins are chrome-plated to help them wear better.
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外文翻譯譯文
內(nèi)燃機
1.氣缸體和氣缸蓋
氣缸體是發(fā)動機的基本框架。發(fā)動機的其他零件都安裝在它里面或者固定在它上。缸體里有氣缸，水套和油道。曲軸也固定在氣缸體底部。除了頂置凸輪(OHC)發(fā)動機以外，凸輪軸都安裝在氣缸體里面。在大多數(shù)汽車?yán)铮瑲飧左w由灰鑄鐵或者一種灰鑄鐵和其他金屬的合金(混合物)做成，例如鎳或鉻。氣缸體是鑄件。
有些氣缸體，特別是在小汽車?yán)锏哪切际怯射X做成的。這種金屬比鑄鐵輕得多。但是，鑄鐵的耐磨性比鋁好。因此，在大多數(shù)鋁制發(fā)動機的氣缸內(nèi)鑲有鑄鐵或者鋼的軸套。這些軸套叫做氣缸套。而有些氣缸體完全由鋁做成。
氣缸蓋固定在氣缸體的頂上，正像屋頂套在一所房子上面一樣。氣缸蓋下面與活塞頂上的空間形成燃燒室。最常見的氣缸蓋類型是半球形，楔形和準(zhǔn)半球形。這三種說法都是指燃燒室的形狀。氣缸蓋攜帶閥門，氣門彈簧和在搖臂桿上的搖臂，這部分的氣門傳動機構(gòu)通過推桿工作。有時，凸輪軸直接安裝在氣缸蓋上并且不用搖臂控制閥門工作。這被叫為頂置凸輪軸裝置。像氣缸體一樣，氣缸蓋是由鑄鐵或者鋁合金制成。
2.襯墊
氣缸蓋與氣缸體用高強度的鋼螺栓縛連結(jié)。氣缸體和氣缸蓋之間的連接必須密封以便沒有燃燒的混合氣體泄漏。這通過使用氣缸蓋襯墊實現(xiàn)。這是一個夾層襯墊，即在兩片銅之間放一片石棉，這兩種材料都能禁得住在發(fā)動機內(nèi)的高溫和高壓。
3.油底殼
油底殼通常由鋼沖壓形成。油底殼和氣缸體的下半部分一同被叫做曲軸箱；他們把曲軸封閉起來。潤滑系統(tǒng)中的機油泵從油底殼抽取油并把油輸送到發(fā)動機內(nèi)全部正在工作的部分。機油流出后又流回油底殼。因而在油底殼和發(fā)動機工作零件之間有機油不斷流動循環(huán)。
4.冷卻系統(tǒng)
冷卻系統(tǒng)的作用是保證引擎在任何路況的任何車速下都在最高效的的運行溫度中。隨著燃油在引擎中燃燒，１／３的熱量轉(zhuǎn)化成動力。還有１／３隨排氣管排出而得不到有效利用，剩下的１／３熱量在冷卻系統(tǒng)的作用下散失掉了。這意味著只有當(dāng)熱量得到適當(dāng)?shù)奶幚硪鏈囟忍幱谄胶鉅顟B(tài)時引擎才能高效工作。
所以，溫度對引擎產(chǎn)生動力的意義是重大的。任何引擎在不好的運行溫度下都工作不好。如果引擎過熱，當(dāng)壓縮混合氣由于燃燒室溫度過高被過早點著，就會造成混合氣早燃。潤滑油潤滑循環(huán)在過熱的引擎中降低。灸熱的潤滑油氣和碳積物可能沉積在燃燒室中導(dǎo)致炭氫化物排放上升。這同樣會引起引擎性能欠佳和過早磨損，甚至導(dǎo)致引擎損壞。另外，在過高的溫度下金屬的反應(yīng)也不同于正常溫度，過高的溫度會引起金屬的緩慢變形和金屬承受持續(xù)的恒定壓力。如果引擎工作過冷，汽油蒸發(fā)就不好。如果氣缸有液態(tài)汽油，液態(tài)汽油會沖走氣壁的潤滑油稀釋引擎中的潤滑油導(dǎo)致潤滑油過少。這造成了引擎性能下降，ＨＣ排增加，和引擎過早磨損。由于這些原因，冷卻系統(tǒng)是內(nèi)燃機必不可少的。
5.配氣機構(gòu)
如果進口門在進氣行程的上止點打開并且在這次行程的下止點關(guān)閉，它將有180°的開度。氣門在180°轉(zhuǎn)角內(nèi)完全打開。然而氣門達(dá)到全開位置需要一定時間，完全關(guān)閉也需要一定時間。因此閥門在上止點(BTDC)之前被打開，在下止點(ABDC)之后關(guān)閉。
如果排氣門在排氣行程的下止點打開并且在這次行程的上止點關(guān)閉，它將有180°的持續(xù)。但是像進氣門一樣，排氣門需要時間到達(dá)充分打開和關(guān)閉的位置。因此排氣門在下止點之前打開，在上止點之后關(guān)閉。
進氣門在上止點前17°打開，排氣門在上止點后17°關(guān)閉。 因此，有34°的一段時期，兩個閥門都是開的：(17°+ 17°= 34°)。這時期被稱為氣門重疊。排氣門的關(guān)閉和進氣門的開啟重疊。在這個時候，新的混合氣推動燃燒后的廢氣從排氣門排出。在渦輪增壓發(fā)動機上氣門重疊角被保持在一個最小值。這就防止廢氣倒流入進氣管。
那些打開和關(guān)閉氣門的氣門傳動是為了協(xié)調(diào)四沖程的工作循環(huán)(使他們各自上下移動)。這些閥門運動必須正好在合適的時刻進行。每個閥門的開啟由凸輪軸控制。
凸輪是一在軸上的蛋形的金屬，通過曲軸協(xié)調(diào)旋轉(zhuǎn)。那金屬軸叫凸輪軸，在發(fā)動機里的每個氣門一般有各自的凸輪。當(dāng)凸輪軸旋轉(zhuǎn)時，凸輪凸起的或者高點的位置，推動氣門座。這行動強迫閥門向下移動。這過程能使進氣門在進氣行程打開，或者排氣門在排氣行程打開。
因為凸輪軸繼續(xù)旋轉(zhuǎn)，凸輪軸上的凸起部分離開氣門裝置。當(dāng)這發(fā)生時，氣門彈簧緊緊地關(guān)閉氣門口，叫做氣門座。
現(xiàn)代汽車發(fā)動機里的閥門位于發(fā)動機頂上的汽缸蓋。這被稱為頂置氣門(OHV)結(jié)構(gòu)。另外，當(dāng)凸輪軸位于汽缸蓋上面時，這種方式被稱為是頂置凸輪軸(OHC)結(jié)構(gòu)。一些高性能發(fā)動機有兩個單獨的凸輪軸，分別負(fù)責(zé)開關(guān)進氣門和排氣門。這些發(fā)動機被稱為雙頂置凸輪軸(DOHC)發(fā)動機。
凸輪軸也裝在發(fā)動機底部的氣缸體內(nèi)。為了將凸輪的運動傳給氣門需要一些附屬裝置。
在這種布置中，凸輪凸角推動凸輪挺桿。當(dāng)凸輪的凸角在凸輪挺桿下出現(xiàn)時，它推動凸輪挺桿向上運動(離開凸輪軸)。凸輪挺桿推動控制搖臂的推桿。搖臂以通過它的中心為軸而旋轉(zhuǎn)。當(dāng)搖臂的一側(cè)上升，其另一側(cè)下降，正如一塊蹺蹺板一樣。搖臂向下移動的那一邊推動氣門桿以打開氣門。
因為推桿氣閥傳動有另外的部分，所以很難以高速運轉(zhuǎn)。推桿發(fā)動機一般在低速運轉(zhuǎn)，從而產(chǎn)生比相同大小的頂置凸輪軸較少功率。(記住，功率反映了工作能力。)
當(dāng)發(fā)動機處于壓縮行程和做功行程時，閥門必須緊緊地關(guān)閉以產(chǎn)生一個不透氣的氣封，以防止氣體逃離燃燒室。如果閥門不完全關(guān)閉，發(fā)動機將不能發(fā)揮全部動力。此外氣門頭易于被通過的熱氣體燃燒，這有可能使活塞頻繁沖擊打開的氣門，使發(fā)動機嚴(yán)重?fù)p壞。
所以閥門能完全關(guān)閉，氣門間隙在操作機構(gòu)內(nèi)是必須的。這意味著操作機構(gòu)必須離閥門足夠遠(yuǎn)以允許閥門通過氣門彈簧使其完全關(guān)閉。但是，如果間隙太大，將引起金屬輕敲的噪音。
在四行程循環(huán)時，每凸輪必須旋轉(zhuǎn)打開一閥門。記住，一個循環(huán)相當(dāng)于曲軸旋轉(zhuǎn)兩次。因此，凸輪軸必須以曲軸正好一半的速度旋轉(zhuǎn)。這用2：1的傳動比完成。齒輪連接到凸輪軸的齒數(shù)是齒輪連接到曲軸的兩倍。齒輪連結(jié)有三種方式：
1.皮帶傳動 齒型帶能被使用。這樣的帶是由合成橡膠做成并且用內(nèi)部的鋼或者玻璃纖維絞合加強。皮帶上有齒，或者槽以嚙合并且驅(qū)動傳動齒輪上的齒。皮帶一般與頂置凸輪閥門傳動一起被用在發(fā)動機上。
2.鏈傳動 在一些發(fā)動機上，金屬鏈被用來連結(jié)曲軸和凸輪軸齒輪。大多數(shù)推桿發(fā)動機和一些頂置凸輪軸發(fā)動機都有鏈。
3.齒輪傳動 凸輪軸和曲軸齒輪可能被直接連結(jié)，或者相嚙合。這類操作聯(lián)動通常被用在更老的六氣缸，直列發(fā)動機上。
凸輪軸被鏈或者帶驅(qū)動，使其朝著曲軸相同的方向轉(zhuǎn)動。但是凸輪軸被曲軸齒輪直接驅(qū)動，其將在相反方向上轉(zhuǎn)動。正時皮帶被使用，因為他們花費少于鏈子，而且噪音少。一條典型的正時皮帶由用玻璃纖維加強的氯丁橡膠(合成橡膠)做成的。
6.活塞
活塞是四沖程發(fā)動機的一個重要組成部分。多數(shù)活塞是用鑄鋁制造的，活塞通過連桿將燃燒混合氣產(chǎn)生的動力傳遞到曲軸。這動力驅(qū)動曲軸轉(zhuǎn)動。圓形的稀薄的鋼圈卡進活塞凹槽處來密封活塞的燃燒室。這些鋼圈就是所謂的活塞環(huán)。與凹槽相適合的環(huán)就是所謂的環(huán)槽?；钊N與活塞上的孔是相適應(yīng)的?；钊N裝入活塞把連桿連在一起。在活塞上固定活塞的那厚的一部分是銷轂。
活塞本身，活塞環(huán)和活塞銷裝在一起就是活塞裝配。
為了經(jīng)受住燃燒室的熱，活塞必須耐熱 抗熱。它也必須輕，因為它在汽缸內(nèi)來回上下的高速度運轉(zhuǎn)?；钊强招牡摹Ｔ谒苿訜崃繘_擊和承受膨脹壓力的頂端是很厚的。底部相對較薄，那里承受較少的熱能壓力?；钊捻敹耸亲钪饕?。在環(huán)槽之間環(huán)繞著活塞部件的較薄的部分就是活塞環(huán)根部。
活塞頂部可能是平的，凹的，圓頂?shù)幕虬歼M去的。在柴油發(fā)動機中，在活塞頂處可形成完全或部分的燃燒室，這依靠噴射方法。因此，他們使用不同的形狀的活塞。
7.活塞環(huán)
正如圖顯示，活塞環(huán)裝入活塞附近的環(huán)槽。簡單的說，活塞環(huán)是很薄的圓形金屬片裝在活塞頂部的凹槽里。
在現(xiàn)代的發(fā)動機中，每個活塞通常有三個活塞環(huán)。（活塞在以前的發(fā)動機中，有時有四個活塞環(huán)，甚至五個。）活塞環(huán)外表面緊貼著汽缸壁。活塞環(huán)在活塞和汽缸壁間給了一定的密封。這就是，只有活塞環(huán)與汽缸壁相接觸。頂端兩只活塞環(huán)是保持氣體在氣缸被稱為壓縮環(huán)。較底那個環(huán)是防止燃燒室進入的油濺到氣套內(nèi)壁，是所謂的油環(huán)。在汽車發(fā)動機上普遍使用鉻合金活塞環(huán)，鉻合金表面非常光滑，耐磨。
在工作時，燃燒的壓力對環(huán)是非常高的。這能導(dǎo)致它張開，當(dāng)高氣壓作用在環(huán)上時，這壓力使環(huán)完全的和汽缸壁接觸。燃燒的壓力緊緊的壓著環(huán)根部，并反作用于槽環(huán)的根部。因此，高燃燒壓力在活塞環(huán)和汽缸壁之間形成了緊密的密封
8.活塞銷
活塞銷使活塞和連桿連接在一起。活塞銷穿過活塞銷孔穿到連桿的頂端。適合曲軸的連桿的頂端要比底端小一些，小頭伸入活塞的底部，活塞銷從活塞的一邊傳入，穿過連桿的小的一端，然后從活塞的另一端穿出。它把連桿合適的固定在活塞的中心。銷是用高強度鋼做成的并且是空心的。許多銷進行鍍鉻，使得幫助它有更好的耐磨性。
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